J.E.deiongh.

J.E.deiongh.
AES/PE/09-28
Acidic flow experiments to seal highly
permeable thief zones in chalk formations
23-10-2009
Joris E. de Iongh
Confidential until June 2010
Title
:
Acid flow experiments to seal highly permeable thief
zones in chalk formations
Author(s)
:
Joris E. de Iongh
Date
:
23 October 2009
Professor(s)
:
Dr. Karl-Heinz Wolf
Supervisor(s)
:
Dr. Karl-Heinz Wolf
TA Report number
:
AES/PE/09-28
Postal Address
:
Section for Petroleum Engineering
Department of Applied Earth Sciences
Delft University of Technology
P.O. Box 5028
The Netherlands
Telephone
:
(31) 15 2781328 (secretary)
Telefax
:
(31) 15 2781189
Copyright ©2008
Section for Petroleum Engineering
All rights reserved.
No parts of this publication may be reproduced,
Stored in a retrieval system, or transmitted,
In any form or by any means, electronic,
Mechanical, photocopying, recording, or otherwise,
Without the prior written permission of the
Section for Petroleum Engineering
ii
Acknowledgements
This report would not have been possible without the help of a lot of people. Firstly I
would like to thank Maersk Oil and M. Jensen for their interest in this research. Also I
would like to thank all my personal supervisors Prof. Dr. J. Bruining and Dr. S. Rudolph
for all help with the mass balances. One who can not be forgotten is Dr. K.H.A.A. Wolf
for all help and support during the whole scope of the thesis work. Without the help of R.
Ephraim and J. van Meel I would never had been able to do all modeling work. I would
like to thank all lab assistants for all the help in the lab and at the CT-scanner, especially
H. van Asten. This brings me to the thanking of the Department of Geo Technology and
the Dietz lab for providing the research facilities.
Abstract
This work is based on the idea that an acid mixture of hydrochloride and sulpheric acid
react with the calcite in a chalk oilfield to create anhydrite which has a larger molecular
size. The anhydrite will clog the present fractures and prevents that these fractures offer a
shortcut for the injected water from the injector well to the producing oil well. This
would result in artificial thieve zones.
In this work mass balance calculations and experimental lab work has been done to see
how the acidic reaction works. It is concluded that during the conversion of calcite to
anhydrite 60% of the formed CO2 is dissolved in the present liquid; the rest is in the
gaseous phase.
The core samples of fractured chalk are approximately 30 cm long and have a diameter of
10 cm. The fracture is situated in the flow direction. The samples are tested under
reservoir conditions with an acid flow rate of 2 ml/min. The determined permeability
indicates that the fracture is sealed after half an hour of acid injection, but this seal in the
fracture is only a pasty substance clogging the flow. After approximately six hours of
acid injection the first wormholes appear and the fracture is totally sealed. The change in
mass is calculated based on the amount of anhydrite created during acid injection. The
mass changes are equivalent to the mass change determined during the experiment.
CT-scans are made before, during and after the acid injection of many experiments. Each
CT-scan consists of approximately 300 images. These images are used to determine the
contribution of the fracture, calcite, anhydrite, wormholes and fossils to the core samples
and to compute their volume percentages which coincide with the calculated weight
percentages.
Fracture experiments under reservoir temperature and pressure conditions and Brazilian
tests under atmospheric are done on the sealed samples to see if the fractures can be
reopened. The samples were tested with an annular pressure of 310 bar, 80oC and
injection pressure of 270 bar. The production pressure was released, even with a pressure
iv
difference over the core of 160 bar and did not fracture. The tensile strength of the sealed
samples proved to be as strong as original chalk samples without fractures.
v
Table of Contents
1
Introduction................................................................................................................. 9
2
Geology..................................................................................................................... 10
2.1
3
4
5
6
7
8
Chalk petrography............................................................................................. 12
Theory ....................................................................................................................... 13
3.1
Overview of chemical aspects .......................................................................... 13
3.2
Applied reaction scheme................................................................................... 16
3.3
Overall mass balance in the core ...................................................................... 19
3.4
Carbon dioxide calculations.............................................................................. 21
3.5
pH calculations.................................................................................................. 24
3.6
Fracture permeability theory............................................................................. 26
Flow experiment ....................................................................................................... 28
4.1
Introduction....................................................................................................... 28
4.2
Procedure .......................................................................................................... 29
Data acquisition results ............................................................................................. 30
5.1
Introduction....................................................................................................... 30
5.2
Permeability calculations and discussion of the results.................................... 32
5.3
pH and hplc ....................................................................................................... 36
5.4
Hplc/mass balance equations and some results ................................................ 39
Images CT-Scan........................................................................................................ 42
6.1
CT-scans introduction....................................................................................... 43
6.2
Images results.................................................................................................... 45
Image analysis........................................................................................................... 50
7.1
Description of the image analysis scripts.......................................................... 51
7.2
Image analysis difficulties ................................................................................ 54
7.3
Modeling Results .............................................................................................. 55
Fracture experiments................................................................................................. 61
8.1
Introduction....................................................................................................... 61
8.2
Theory hydraulic fracturing .............................................................................. 62
8.3
Brazilian test ..................................................................................................... 64
8.3.1
Theory ....................................................................................................... 64
6
8.3.2
Brazilian test results.................................................................................. 66
8.4
Hydraulic fracture experiments under confining stress .................................... 69
8.5
Experimental results.......................................................................................... 70
9
Conclusions............................................................................................................... 73
9.1
Conclusions of the flow experiments................................................................ 73
9.2
Conclusions on the fracturing experiments and Brazilian test.......................... 74
10
Recommendations................................................................................................. 75
11
References............................................................................................................. 76
Appendix A: Porosity Permeability measurements .......................................................... 79
A.1 Dry Porosity ........................................................................................................... 79
A.2 Wet Porosity........................................................................................................... 79
A.3 Dry Permeability .................................................................................................... 80
A.4 Wet Permeability.................................................................................................... 80
A.5 XRD measurement on pure chalk .......................................................................... 81
Appendix B: Stream results Electrolyte-NRTL model..................................................... 82
B.1 Brine flow through the sample ............................................................................... 82
B.2 Acid flow through the sample ................................................................................ 84
Appendix C: Fracture experiment Frac43......................................................................... 86
Appendix D: CT-scan filter comparison........................................................................... 96
Appendix E: Leica Qwin Scripts .................................................................................... 108
E.1 Script 1.................................................................................................................. 108
E.2 script 2 .................................................................................................................. 109
E.3 Script 3.................................................................................................................. 115
Appendix F: Volume percentages according to mass balance equations and Modelling117
Appendix G: Experimental results of all core flooding experiments compared............. 123
7
Nomenclature
L
Length
[m]
Q
Flow rate
[ml/min]
K
Equilibrium constant
[-]
T
Temperature
[oC]
a
Concentration
[mol/l]
pH
Acidity
[-]
P
Pressure
[bar]
ΔGo
Standard molar Gibbs energy
[J/mol]
R
Gas constante
[J/molK]
ΔH
Standard molar reaction enthalpy
[J/mol]
t
Time
[sec]
V
Volume
[ml]
mol
Amount of substance
[mol]
kh
Henry’s constant
[mol/lAtm]
m
Mass
[kg]
μ
Viscosity
[Pas]
A
Area
[m2]
k
Permeability
[mD]
τ
Turtuosity
[-]
σt
Tensile strength
[Mpa]
F
Load
[N]
D
Diameter
[m]
o
8
1 Introduction
It is necessary to use secondary oil recovery in highly porous low permeable chalk oil
reservoirs in order to produce oil. This is usually done with horizontal water injectors
parallel to the horizontal producers with a spacing of hundred to two hundred meters. The
water is injected to push out all the oil in the pores towards the producer well.
A chalk reservoir is by definition easy to fracture. These fractures are due to; (1) natural
in-situ pressures; (2) EOR treatment or; (3) the pressure of the injected water. Usually
fractures will contribute to the flow of the oil to the production well, because it resembles
a highway which will connect several layers through the reservoir.
In some cases the produced oil in a chalk reservoir can contain high amounts of water. It
is assumed that this is because of porous fracture (zones) created by any of the three
above mentioned mechanisms. This will result in a short cut between the two wells, so
that the injected water will flow directly from the injection well to the production well,
thereby bypassing a considerable amount of oil in the reservoir.
Injection of gel-forming solutions to close these fractures will also clog the open hole part
of the reservoir resulting in a poorly performing well.
Schuiling et al. (1990) proposed to increase the total volume of a carbonate reservoir by
changing the matrix from calcite to gypsum, with a higher volume, to compensate for
subsidence by using acids. The research at hand focuses on the possibility to close the
fracture system by ‘swelling of the matrix’. When the fractures are closed the injected
water will be diverted into the matrix and thus the sweep efficiency will be improved.
9
2 Geology
The chalk cores used in for this thesis research are taken from the Rørdal quarry from the
Danish Basin, an analogue for the Danish offshore oil fields. All chalks in Denmark and
offshore Denmark are part of the Danish Basin. The Danish Basin is bordered in the West
by the North Sea Graben, in the South by the Ringkøbing-Fyn High and in the North and
East by the Sorgenfrei-Tornquist Zone.
The Danish basin, (Figure 1) has its origin initiated by the rifting in the Late
Carboniferous- Early Permian, when the super continent Pangaea drifted apart (180 Ma.).
Because of this the Danish basin was an extensional rift zone. Most regional subsidence
took place during the Cretaceous, sometimes interrupted by a relative uplift of the
Sorgenfrei-Tornquist Zone.
This relative shalow basin was the perfect zone of deposition for the carbonates which
became increasingly common during the early Cretaceous (Surlyk, 2006). During the
Late Cretaceous the carbonate deposits became dominant. This is the CampanianMaastrichtian succession and is composed of almost pure chalk sediments, and reaches
thicknesses of more then two kilometers. This was possible because of subsidence and
sea level rise, the high temperatures and the abundance of carbonates.
10
Figure 1 Palaeogeographical map of NW Europe in the Late Cretaceous (F. Surlyk, 2007)
The climate was warm so the global sea level appears to have reached one of its highest
sea level stands. Huge cratonic areas were flooded and this situation remained relatively
stable for 25 million years, resulting in thick successions of monotonous white chalk
deposits in the sea covering North West Europe. This chalk is composed mainly of
minute skeletal fragments of one cell organisms, such as Globigerinida, etc.
The basin got tilted because of the strong uplift in the North East during the late Cenozoic
(Figure 2). This is the reason of the exposure of the chalk and limestone in the East of
Denmark. This part of the basin is much richer in benthic fossils, probably because of
shallower water depths, but still too deep to be in the photic zone.
11
The basin had a steep slope along the North East margin, which was formed due to the
Sorgenfrei-Tornquist Zone. A gentler slope was formed on the South East of the basin by
the Ringkøbing-Fyn High. This resulted in the West to be the deepest part of the basin.
Figure 2 Block diagram of the Danish Basin (DB), Sorgenfrei-Tornquist
Zone (STZ) and Ringkøbing-Fyn High (RFH) in the Late Cretaceous (F.
Surlyk, 2007)
2.1 Chalk petrography
General characteristic data of the chalk of the Rørdal quarry is obtained to give insight
for this research. The fossils present are belonites and shells. Lab porosity and
permeability tests on chalk samples from the Rørdal quarry are done. The effective
porosity of the chalk proved to be between 47 % and 52 % and the permeability proved to
be between 3 mD and 5 mD (Appendix A). XRD experiments are done on the chalk,
which proved to be pure CaCO3 (Appendix A).The cores used in these experiments are
20 to 30 cm long and have a diameter of 10 cm. The fractures induced in these cores are
always 3 mm wide and in the flow direction of the core.
12
3
Theory
3.1 Overview of chemical aspects
Acids are widely used in the oil and gas industry to open up pore spaces around the
borehole, to enhance porosity and permeability and to improve the skin factor of an oil
well. In this thesis project the acids will be used to clog or close the high permeable
fractures, which are the macro pore spaces in the low permeable matrix. This is the
inverse of the normal use of acids in the oil and gas industry.
Research of Hoefner and Fogler (1988) describes the treatment in chalk cores with
hydrochloric acid. They observed a random tortuous tube system in chalk cores, known
as wormholing. The acidic reaction only takes place on an interface between the liquid
and the matrix, in this case the fracture wall. The matrix of the chalk core is a
heterogeneous medium with a varying permeability. The main flow will be between the
highest pressure differences in the reservoir. This can be a result of a near fracture with
high permeability or a higher permeable zone. Because the flow of the acid solution will
mainly go through these higher permeable portions of the reservoir; consequently,
typically the above described reactions will take place in these high permeable zones.
Resulting in wormholes towards the highest pressure difference (fracture). Due to the
acidic reactions these zones will become even more permeable, and consequently more
fresh acidic solution will flow there to enhance further reaction. This will result in highly
tortuous tubes depending of micro permeability distribution. In a reservoir with flow
from the injector to the producer, this means that channels connecting the injector and
producer will be formed.
As discussed above injecting HCl in chalks will result in dissolution of the matrix. For
this reason Singurindy and Berkowitz (2003) studied the effect of injecting mixtures of
sulfuric and hydrochloric acids into a chalk core under room conditions.
13
Singurindy and Berkowitz concluded in their study that at low H + / SO42− ratios
precipitation of CaCO3 occurs, which will plug the core.
At high H + / SO42− ratios
dissolution of CaCO3 prevails and wormholes will be created. However, also the rates of
reaction should be considered, which cause a flow rate dependence. Figure 3 shows that
high flow rates and high H + / SO42− ratios will lead to dissolution of the chalk, while low
H + / SO42− ratios cause precipitation and hence plugging in the core.
Figure 3 Plot of flow experiments over a range of injected [ H + / SO42 − ] ratios and flow rates Q,
(Singurindy et al., 2003)
Considering that the reaction with HCl is much faster than the reaction with H2SO4 we
observe maily dissolution at high flow rates. In their experiments they observed a region
in which the hydraulic conductivity oscillated strongly. This oscillating hydraulic
conductivity can be explained by the competitive process of pore clogging due to the
precipitating process and the channel forming due to the dissolution process. The domain
in Figure 3 where oscillations occurs is of particular interest for our research.
14
In a consecutive research Singurindy et al. (2005) injected acid mixtures of 0.1 M
HCl/0.1 M H2SO4 and 0.1 M HCl/0,.3 M H2SO4 in fractured chalk cores. Thereby, the
ratios of H + / SO42− with a value of 3/1 and 7/3 could be identified to be in the region of
competition. They found that the orientation of the fracture to the flow direction of the
fluid is crucial. If the (natural occurring) fracture is orientated perpendicular to the flow
direction clogging is favored. Fractures orientated in the flow direction results in favoring
of the dissolution process. Additionally, they found that the fracture as seed for
precipitation.
15
3.2 Applied reaction scheme
Considering the above, the injected sulfuric acids ( H 2 SO4 ) react with the calcite to
anhydrite at the typical reservoir pressures and temperatures.
The formed anhydrite molecule ( CaSO4 ) is slightly larger then a calcite molecule
( CaCO3 ) and seals the fracture due to size exclusion. If enough calcite molecules react
with the sulfuric acid into anhydrite the fracture closes.
In theory the general sequence of reaction is:
HCl → H + + Cl −
Eqn 3-1
H 2 SO4 → H + + HSO4−
Eqn 3-2
HSO4− R H + + SO42−
Eqn 3-3
CaCO3 + H + → Ca 2+ + HCO3−
Eqn 3-4
SO42− + Ca 2+ → CaSO4
Eqn 3-5
H + + HCO3− → H 2O + CO2
Eqn 3-6
During the flow experiments the H 2O and CO2 flows continuously out of the reactor,
while fresh acid is injected. In this way the reaction is kept on running which then results
in the clogging of the core due to the anhydrite formation.
The reaction of calcium carbonate with sulfuric acid as described above can form three
morphologies of calcium sulphate ,namely Gypsum, Basanite and Anhydrite (Figure 4).
Which structure is formed depends on the pressure and temperature.
16
Figure 4 Stability regions for the three different forms of calcium sulphate (Yamamoto et al., 1969)
Since reservoir conditions in the North sea do not exceed 250 bar (25 MPa), we can
exclude the possibility of basanite formation. Additionally, the reservoir temperature is
above 80oC, thus according to Figure 4, anhydrite will be the most abundant compound.
To get representative results, the temperature and pressure conditions in the lab were
chosen such that only anhydrite was formed.
17
The plugging of the pores by anhydrite is due to precipitation of the anhydrite.
Precipitation of the anhydrite can be described by the solubility product of anhydrite. The
solubility product gives the maximum solubility of an electrolyte. If the concentrations of
the ions of the dissociated anhydrite are higher that the maximum solubility anhydrite
will precipitate. The solubility product of anhydrite is described by:
K s = aCa2+ aSO2−
4
Eqn 3-7
Thereby it was assumed that the activity of the nondissociated anhydrite (solid) is 1.
The equilibrium of dissociation constant, Ks, is a function of the standard molar reaction
Gibbs energy ( ΔG o );
ΔG o = − RT ln K s
Eqn 3-8
From this dependence the temperature dependence of the solubility product Ks can be
deduced:
ln ( K s ) = ∫
ΔH o
dT
RT 2
Eqn 3-9
R is the gas constant and ΔH o is the known standard molar reaction enthalpy. If the
temperature dependence of the molar reaction enthalpy is known or if it can be assumed
that the molar reaction enthalpy does not very with temperature, the solubility product of
the anhydrite can be computed at every temperature.
By the Petri experiments (van Lier et al. 2007) it was investigated which H + / SO42− ratios
are most favorable for these flow experiments. It was found that this should be 0.3 mol/l
HCl and 0.9 mol/l H2SO4, this is a 5/2 H + / SO42− ratio.
18
3.3 Overall mass balance in the core
In general a mass balance of relevant components over a relevant balance space can be
written as:
d
Cα = Qαin − Qαout + Rα
dt
Eqn 3-10
Accumulation = Flow in – flow out + reaction
The accumulation describes the change of the mass with the time (dm/dt). The inflow and
outflow is described by (dm/dx) and describes the convective contribution of the mass
balance. For the study at hand the reference space is defined as the whole reactor, the
inflow, the outflow with their components and the change in overall weight of the core
are known.
The time required for a flowing particle passing through the reference space (dm/dt) is
the retention time. The retention time can be estimated by the flow rate and accessible
pore volume. The flow rate of the fluid is 2 ml/min for all samples. The accessible pore
volume is equal to 1100 ml determined from the total volume of the sample, which is
approximately 2200 ml and the initial porosity of 50 %. This means that the average
retention time, ignoring diffusion is 33000 sec. Indeed diffusion can be neglected,
because diffusion in liquids and solids is very slow.
To determine the source and sink term the above described chemical reactions need to be
combined with the maximum solubility of CO2. In particular to close the mass balance it
is important to know which part of the produced CO2 flows out as gas phase and which
part is dissolved in the water. Additionally, the presence of the different ions in the water
gives insight whether dissociation takes place. It is assumed that the equilibrium of the
above given dissociation and reaction equations are completely on the side of the
products. Eqn 3-1 to Eqn 3-6 show how the different chemical reactions are coupled.
19
Therefore, the number of moles H2SO4 injected should be the same as the number of
moles SO42− ions in the water flowing out of the sample combined with the number of
moles forming CaSO4. From Eqn 3-4 and 3-5 we observe that the amount of CaSO4
formed is equal to the amount of Ca2+ ions formed by dissolving CaCO3.
According to the reaction equation describing the dissociation of CaCO3 the amount of
formed Ca2+ ions is equal to the amount of formed CO3− . The CO3− is consumed in the
reaction forming CO2. Furthermore the amount of H+ ions in the core, created from the
HCl and H2SO4 is twice the amount of CO2 (see Eqn 3-6)
The amount of dissolved Cl- ions in the water at the outflow together with the formed and
retained amount of CaCl2 in the sample can be balanced with the inflow of HCl and NaCl
(brine).
Therefore, from this analysis it can be seen that by analyzing (see, chapter hplc/ mass
balance equation) the composition of the outflowing water shows how much CaCl2 and
CaSO4 are formed and retained in the sample. Additionally, it is necessary to determine
the flow rate of the outflowing gas assuming that the gas phase consists completely of
CO2. Unfortunately, it was not possible to determine the flow rate of the gas in such a
manner that the amount of gas flowing out of the experiment could be determined.
During the experiments test tubes are filled with the production fluid; using hplc
measurements, the concentrations of the various ions was measured. Since the hplc
measurements are not done continuously a linear approximation between hplc
measurements is done to show the amount of Cl- ions in the outflow, in the whole time
span.
20
3.4 Carbon dioxide calculations
As mentioned above it is important to know how much of the CO2 has been dissolved in
the water and how much will stay in the gas phase. The total amount of formed CO2 can
be estimated if the amount of HCl and H2SO4 injected into the sample is known. It is
assumed that all reactants dissociate completely.
Thus according to the reaction scheme in combination with the mass balance injecting
0.3 mol/l HCl and 0.9 mol/l H2SO4, results in 2.1 mol/l H+ . For the production of 1 mol
CO2 two moles H+ ions are required. Thus, with the available amount of H+ ions a
maximum of 1.05 mol/l CO2 is formed.
The amount of soluble CO2 can be calculated following Henry’s law:
P = kx ,
Eqn 3-11
where p is the pressure in Pascal, x is the mole fractions
and k is Henry’s constant with,
xCO2 =
nCO2
nCO2 + nH 2O
,
Eqn 3-12
which can be written in terms of concentration as:
xCO2 =
CCO2
CCO2 +
,
ρH O
2
Eqn 3-13
nH 2O
where ρ H 2O the density of water and nH 2O the molecular weight of water. Commonly, the
concentration of CO2 dissolved in water is much smaller than
ρH O
2
nH 2O
and can therefore
be neglected.
For CO2 the Henry’s constant at atmospheric conditions khΘ is 0.034 M/Atm
(Sander,1999). But kh is also temperature dependent following the formula:
21
⎛ −d ln kh ⎛ 1 1 ⎞ ⎞
kh = khΘ exp ⎜⎜
⎜ + Θ ⎟ ⎟⎟
d
1/
T
(
)
⎝ T T ⎠⎠
⎝
With T Θ is 298,15K and
Eqn 3-14
−d ln kh
is 2400K (Sander,1999).
d (1/ T )
In the approach from Sander it is assumed that the gas behaves as an ideal gas.
The concentrations are calculated for several temperatures and pressures and the
solubility’s of CO2 in water for conditions of interest for this research are given by Figure
5 and Figure 6.
10
10
1
1
10
20
30
40
50
60
70
80
90 100
0
20 T[C]
0,1
80 T[C]
0,01
Molarity[mol/kg]
Molarity[mol/kg]
1
10
20
30
40
60
70
80
90
10
1 P[bar]
0,1
60 P[bar]
0,01
0,001
0,001
P[bar]
Figure
50
5
Carbon
T[C]
dioxide
concentration
(logarithmic) versus pressure at two different
Temperatures
Figure
6
Carbon
dioxide
concentration
(logarithmic) versus Temperature at two different
pressures
Therefore, if a full reaction occurs at a temperature of 200C and 1.05 mol/l CO2 is formed,
a gaseous phase of CO2 is formed already at a pressure of 30 bar.
For the experiments a fluid pressure of approximately 60 bars was used and a temperature
of 800C, the solubility of CO2 gas in water is 0.60 mol/kg, which is approximately 0.60
mol/l. This is almost half of the 1.05 mol/l CO2 that was formed. Therefore it can be
assumed that unless the reaction is by far not complete the gas phase of CO2 is formed
22
during the experiments. Following the phase Diagram 1 of CO2 (Diamond,2003), under
reservoir conditions the CO2 is supercritical. This means that two phase flow will occur;
water with some solved CO2 and the super critical CO2 with some water vapor. These
experiments are done with 60 bar fluid pressure and 80oC (see Diagram 1).
Diagram 1 P–xCO2(aq) diagram showing selected solubility isotherms between 0 and 100 ◦C,
CO2 is supercritical for all temperatures below the critical point (Diamond,2003),.
23
3.5 pH calculations
During the experiments the pH in the outflow was experimentally determined every 13
minutes. The pH change gives an indication of the reaction taking place in the sample.
With the help of the simulator Aspen Plus 12.0 using the Electrolyte-NRTL model the pH
in the outflow can be computed. This models workflow is based on Figure 7.
Figure 7 Electrolyte-NRTL model
For this model it is needed to specify all inflowing fluids (brine and acid); it is based on
the fact that there is enough solid CaCO3 to complete all reactions under a pore pressure
of 60 bar and 80oC (reservoir conditions). The model predicts with flash calculations the
amount that flows out under reservoir conditions, this is called Vap. and Liq. Then it is
calculated in the second part under atmospheric conditions, illustrated as Vap2 and Liq;,
so it is comparable with the pH measured (appendix B). This check has been done for
brine only flowing through the sample to calculate what the resulting pH should be. It has
been done for the brine present in the pores with acid injection. All resulting pH’s, solids,
liquids and gaseous phases are calculated by this model as shown in Appendix B.
For brine flowing through the sample the pH of the injected brine is 6.3. The pH of the
production fluid under reservoir conditions is 9.0, while the pH under atmospheric
24
conditions is 10.1. This is also the one which in theory is the highest pH measured in the
system.
This model also predicts that when the acid is flowing through the system there should be
gaseous CO2 in the reactor, the model predicts a pH of 4.75 under reservoir conditions
and a pH of 5.75 under atmospheric conditions
The model describes the situation to be a perfect reaction, so all reactions go to the right.
If the pH measured is the same as the pH calculated in the model this would mean that
the reaction is also complete in the reactor.
25
3.6 Fracture permeability theory
Darcy’s equation for a cylindrical sample in the horizontal direction is used to calculate
the average permeability of a sample. This average permeability is the permeability of the
matrix together with the present permeabilities of the fracture and/or wormholes:
k=
qμ L
AΔP
with k in m2, q in m/s and P in Pa.
The matrix permeability is given as 3-5 mD (chapter chalk petrography)
The fracture permeability can be calculated with (Bird, 2002):
k *f =
φf d2
12τ
with k *f the permeability of the fracture, d the fracture width in m, φ f the porosity of the
fracture and τ the tortuosity. In theory we can taken φ f as 1, d is 3*10-3 m at the start of
the experiment, but because of the confining pressure or annulus pressure, d is probably
1*10-3 m. And τ is taken 1. k *f is 8*10-8 m2. Since k f = k *f * d , k f (the fracture
permeability) will be 8*10-11 m2 (which is 80 D).
Wormhole permeability can be calculated with (Bird, 2002):
k w* =
φw r 2
8τ
with k w* the permeability of the wormhole, r the wormhole radius, φw the wormhole
porosity and τ is the tortuosity. In theory we can take φw as 1, r has an average of
0.5*10-3 m and τ is around 2. And k w = k w* * 2r , kw (the wormhole permeability) will be
1.5*10-11 m2 (which is 15 D).
If the permeability of the fracture and its area is averaged with the permeability of the
matrix and its area, a new average permeability is obtained (Table 1). The same is done
for the wormhole permeability (for this calculation a presence of 5 wormholes in the core
is used).
26
It can be concluded that high permeabilities induced by the fractures should be found
during the experiments. If not the fracture is already partly closed by the annular pressure.
And wormhole permeability can influence the average core permeability slightly, but
only if a large wormhole appears.
Table 1 Average permeability of the whole core, concerning fractures and wormholes
Fracture
Wormholes
d [m]
r [m]
0.001
8.33333E-08
8.33333E-11
A core
0.031
# fractures
1
A matrix
A fracture
0.031
0.0001
0.997 0.003183099
P core
P matrix
P fracture
2.68E-13 3.00E-15 8.33333E-11
0.0005
1.5625E-08
1.5625E-11
A core
# wormholes
5
A matrix
0.031
0.031
1.000
A wormhole
2.13048E-10
6.78154E-09
P core
P matrix
P wormhole
3.00E-15
3.00E-15
1.5625E-11
27
4 Flow experiment
4.1 Introduction
Dynamic flow experiments were performed on cylindrical chalk samples with a diameter
of 10 cm and a length varying between 20 and 35 cm. The samples were sawed and dust
from sawing has been removed. Thereafter, the samples were measured, photographed
and weighted (dry).
Two different experiment setups are used, the principle is the same. The only difference
is that with the second setup (all FEN experiments) the reactor is mobile, so the sample
can be scanned during the experiments. The mobile experiment is shown in Figure 8 and
is described below. The only difference in the workflow is that with the immobile setup,
the sample is scanned dry before the experiment and wet after the experiment.
Figure 8 Experimental setup for the Flow experiments
28
4.2 Procedure
1) The sample is put into the rubber sleeve, with the upper and lower injection
and production heads are connected on both ends. The whole system is put
inside the reaction chamber and closed with the injection head fixed on the
reactor chamber. The production head is free to move in the flow direction, so
extension of the sample core can be measured.
2) The sample is now connected to all tube systems of the reactor, CO2 is
injected for a couple of hours. Thereafter it is connected to a vacuum pump
and the whole system is vacuumed for 48 hours. In this time oil flows in the
annulus chamber of the reactor around the sample and sleeve.
3) A vessel of brine is connected instead of the vacuum pump and the vacuum
inside the reactor will suck in the brine. This takes several hours. The amount
of brine injected, gives an approximation of the connecting pore volume.
4) The brine/acid pump is connected. The annulus pressure is pressured up to 80
bar while the injection and production pressure is pressured up to 50 bar and
the temperature goes up to 90oC. The brine flows through the reactor for
several hours.
5) After that, the reactor is closed in (flow is stopped), so all pressures will be
contained and the reactor is brought to the CT-scanner and is scanned.
6) The reactor is reconnected to the system and pressures are checked. Now acid
injection starts at 2 ml/min. Intermediate CT-scans are taken every few hours.
Continuously all pressures and flows are checked and stored by the computer.
The acid will flow for two to three days untill the production tube is plugged.
The acid consisted out of 0.3 M HCl and 0.9 M H2SO4.
29
5 Data acquisition results
5.1 Introduction
During the experiment several types of direct information is gathered. This information
was directly used to check if the experiment was going according to plan and-if-not to
clean out the clogged parts of the setup or repair parts. Everything done to the setup and
experiment is noted down in the lab report with corresponding time and date. In this
chapter data from experiments Fe38 to Fe51 is discussed by examples out of experiment
Fe51, all other experiments can be seen in Appendix G. These experiments are all done
with the standard fracture distance between the two matrix blocks of 3mm.
The data acquisition system (DAS) gathers the temperature in the sample, injection
pressure, production pressure, annulus pressure and the pressure difference between
injector and producer every 10 seconds Figure 9. The information of the lab records are
compared to give more insight in what happened at which time.
All images in this chapter are based on ‘example’ experiment number Fe51.
Back pressure failed
120
Pressure [bars]
100
Production
100
tube plugged
80
Press1
Press2
80
60
60
40
Dp40Bar
40
20
Temp1
20
0
Temp2
130000
140000
150000
160000
170000
180000
190000
200000
210000
220000
230000
240000
30000
40000
50000
60000
70000
80000
90000
100000
110000
120000
-20
0
10000
20000
0
Press3
Tem p [deg C]
Time [seconds]
Figure 9 Fe51 Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
30
In Figure 9 it can be observed from the outliers at which times during the experiment the
results show unstable moments while the rest of the graph is very stable. This means that
the experiment has gone according to plan. Interesting is that the beginning (0 to 10000
sec) of the graph is unstable. After that the graph is stable until 55000 sec and then it
keeps on being unstable. From this point on, some gases escape out of the production
tube. These have been tested and proven to be CO2. It is assumed that the irregularities in
the graph from 55000 sec are caused by burps of gas. This is also the moment of acid
breakthrough. This is better observed in a permeability plot (Figure 10) in the chapter
Permeability calculations.
31
5.2 Permeability calculations and discussion of the results
For permeability calculations the pressure difference between injector and producer is
calculated every ten seconds. In the beginning brine is the only fluid in the sample. The
brine consists of 35 gram of NaCl per liter. And at reservoir temperature and pressure the
viscosity of the brine is approximately 1.007·10-3 Pas. The acid has a viscosity of
approximately 1.092·10-3 Pas (Lide,2009). For the permeability calculations the viscosity
has been taken linear between these two viscosities with respect to the start of the acid
injection until acid production. Since the difference between these two viscosities is ca
10%, any errors with respect to flow patterns are ignored.
The flow rate is kept at 2 ml/min and the other parameters (area perpendicular to the flow
direction and length) are known for every sample. Darcy’s equation for a cylindrical
sample in the horizontal direction is used:
k=
qμ L
AΔP
k51
Gas burps
1E-14
Start acid inj
9E-15
Wormholes
closing and
opening?
Acid
breakthrough
8E-15
7E-15
Production tube
is getting
clogged
k[m^2]
6E-15
5E-15
4E-15
3E-15
2E-15
1E-15
0
0
50000
100000
150000
200000
250000
t(sec)Time[sec]
Figure 10 Fe51 Permeability k, versus Time
32
All information from the lab journal is put in Figure 10, so incomplete information for
conclusions to irregularities are not assumed. It can be concluded that there are no big
permeability differences created by the fracture as discussed in chapter Fracture
permeability theory, thus the fracture has been closed by the annular pressure to a
fracture width of 1 mm or less. After some initial irregularities the permeability is stable
and stays around 5 mD, after 50000 sec the graph starts fluctuating, this is mainly
because gas escapes the production tube. In the theory was stated that during the reaction
CO2 gas should be partly dissolved in the fluids and partly in the super critical phase and
that this super critical phase resembles the gaseous behavior of the CO2 gas. Hence, this
gas will be formed in the pore spaces and it will flow to the production tube where it
creates plug flow with the fluid. When the liquid passes the backpressure valve the
pressure drops to atmospheric conditions and the CO2 bubbles out of the liquid.
In the Figure 10 some permeability drops can also be seen and after that the permeability
rises again. This happens from 75000 sec to 120000 sec and from 140000 sec to 180000
sec. This is probably due to plugged wormholes and formation of new wormholes. At
220000 sec the production tube gets plugged, which means the end of the experiment.
The permeability graph also shows that the permeability fluctuates highly in the first
10000 sec (Figure 11).
33
K51
1.2E-14
1E-14
Start acid injection
Fracture
closing
K[m^2]
8E-15
6E-15
4E-15
2E-15
0
0
1000
2000
3000
4000
5000
6000
Time[sec]
Figure 11 Fe51 Permeability k, versus Time in the first stage of injection
Because of the pressurizing of the reactor the fracture closes from the initial 3 mm to less
than 1 mm. In Figure 11, experiment Fe51 can be seen that the acid injection starts at
approximately 3300 sec. The first interval where the permeability drops and pressure
rises is at approximately 5100 sec. Here we assume that the fracture starts to close. So,
the fracture is possibly already closed within 1800sec after acid injection. This
phenomenon was tested in the experiments FEN04 and FEN05 (Figure 12) which were
done inside the CT-scanner with scans every ten minutes. Due to the fact that the cores
had several natural fractures and vug holes the samples collapsed partly and the sleeves
started leaking oil from the annulus. This collapsing was in both experiments after 900
sec and 1500 sec of acid injection; on the CT-scans the fracture looks closed. When the
samples were taken out of the reactor, the closed fractures came apart with a pasty
substance in an early stage. This means that the fractures were already closing and started
clogging, dropping the overall permeability of the core. However they were not closed by
solid cement.
34
kFEN05
1E-12
0
1000
2000
3000
4000
5000
6000
8000
9000
Fracture
closing
1E-13
k[m^2]
7000
1E-14
kFEN05
Start acid
injection
1E-15
1E-16
Time[sec]
Figure 12 FeN05 Permeability, k versus Time in the first stage of injection
35
5.3 pH and hplc
In general, during the experiment test tubes are filled with the production fluid every 13
minutes. The produced fluid comes out of the reactor and flows into the test tubes under
atmospheric pressure. The pH is measured of every tube and put into a pH versus time
graph, on average 300 tubes are filled during an experiment. Ca 20 Hplc measurements
are done of every experiment of the most interesting tubes. With hplc measurements, the
amount of the containing ions in the produced fluid is measured. The results are obtained
under room conditions. This means that the solubility of the CO2 is lowered, see Figure 5.
And that an additional amount of the other ions in the fluid precipitate as solids.
The hplc combined with the pH versus time graph (Figure 13) is divided into four
different stages. This is typical for all experiments. Every 13 minutes a pH measurement
was done, indicated by a continuous line. And on 20 of these tubes a hplc measurement
has been doen, indicated by the points on the dotted lines.
1) Time from zero too ca 12000 sec. Initially a high amount of SO42− ions is
shown in the hplc measurements. an increase in pH is seen. This is the first
measurement and is done on the pure acids. So this is the hplc measurement
on the injected fluid. All other hplc measurements are done on the production
fluid.
After this a increase in pH, Cl- and Na+ ions is seen this is caused because
initially the brine is injected, resulting in a high pH. This pH is later calculated
in the Thermodynamic model chapter.
2) Ca 12000-23500 sec. Acid is injected resulting in a lowering of the pH. All
ions in the production fluid are stable. So production fluid is mainly brine.
During this time the acid still reacts in the pasty sealed fractures, and it is
assumed that after this peak the fracture is totally closed.
3) 23500-55000 sec. pH is stable. Here the first wormhole is developed.
4) 55000-110000 sec (15 hours-30hours). Acid breakthrough and removal of the
brine. pH is lowered, Na+ ions are totally flushed out, the remaining Cl- ions
are all from the injected HCl. Ca+ ions from the matrix are in the fluid.
36
5) 110000 sec to end. Continuous transition from calcite matrix to anhydrite
matrix.
In general the acid breakthrough is based on these graphs, because it is the indicator for
the total removal of NaCl out of the sample. The pH line exactly follows the NaCl line
and stabilizes when all Na+ ions are out of the core.
The high pH peak in the beginning of the graph (6500-25000 sec) is caused by all Ca+,
Na+, Cl- and Co32− ions in suspensions, this is lowered fast by the acid injection. Since
there is a negligible amount of SO42− ions in the production fluid during the whole
experiment, it can be said that all is reacted to anhydrite and the reaction theory is upheld.
All this is also observed in the other experiments (appendix G). In Chapter 4,2
(Permeability calculations and discussion of the results) it was concluded that the fracture
has a pasty seal after 1800 sec, and now it is concluded that the fracture is totally closed
after ca 23500 sec.
80,0
10
70,0
9
Acid breakthrough
8
60,0
7
6
40,0
5
30,0
4
20,0
3
10,0
2
0,0
-10,0
Stage 1
pH
g/L
50,0
0
50000
Stage 2 Stage 3
100000
150000
T(sec)
Stage 4
200000
Stage 5
1
250000
0
g/L Na
g/L Ca
g/L Cl
g/L SO4
pH
Figure 13 Fe51 hplc measurements, g/l (left y-axis) and pH (right y-axis) versus time (x-axis)
This indicates that during this fast lowering of the pH peak the acid still flows through the
pasty seal in the fracture and that when this high peak is over the fracture is totally closed.
This indicates that the fracture was totally closed directly after this high peak and
37
indicating the start of the first wormhole, which breaks through the sample at the
indicated acid breakthrough in Figure 13.
This is also observed in other experiments. These facts can be concluded in that the
fractures are closed for flow after 1800sec (see chapter permeability calculations), but the
anhydrite has not had time to strengthen the fracture enough. This is most probably after
23500sec, which is 6,5 hours.
So the acid reacts with the area of the fracture first, making it pasty. This pasty area
makes it possible for the confining annulus pressure to press the two halves of the core to
each other, thus closing the fracture. Now the reaction will solidify this thin area further,
closing the fracture solid.
As discussed (chapter pH calculations) if brine is injected in the sample the pH calculated
in the thermodynamic model is 10.1 at its maximum. In Figure 13 the maximum pH
measured is 9, the difference can be explained because the pH is already influenced by
the injected acid.
The model (chapter pH calculations) also predicts that reaction stabilizes at a pH of 4.75
under reservoir conditions and a pH of 5.75 under atmospheric conditions. The pH
measured in the experiments is also under atmospheric conditions and as can be seen in
Figure 13 stabilizes at a pH of 5.6 which is approximately the same.
The model (chapter pH calculations) describes the situation to be a perfect reaction, so all
reactions go to the right. The pH measured is the same as the pH calculated in the model
this means that the reaction is also complete in the reactor. This means that the mass
calculations can be done according to all reactions going to the right.
38
5.4 Hplc/mass balance equations and some results
In this chapter the results are discussed from experiments Fe38 to Fe51, where possible,
and the conclusions are valid for all.
1) Since the amount of mol injected acid is known, and the amount of lost acid
due to experimental failure is known, the net amount of injected acid can be
calculated.
2) Assuming that the complete core 100% calcite, it can be calculated how much
mol CaCO3 is initially present, based weight. As is stated in the chemical
reaction formulas in chapter 3.1 Chemical reactions and in chapter 3.2 Mass
Balance, based on the amount of mol H2SO4 injected it is now calculated how
much CaCO3 is converted to CaSO4, in amounts of mol.
3) With the amount of unconverted mol calcite and the converted amount of
anhydrite in moles a new weight can be calculated, based on mol mass. The
new weight is supposed to be slightly heavier then the weight before the
acidizing treatment.
4) This is compared to the measured weight before acid injection (Table 2). For
example, for experiment Fe51 the measured weight before and after the
experiment are respectively 3.21 kg and 3.54 kg. The weight calculated after
the experiment, based on the amount of injected acid, is 3.50 kg.
5) The difference between the calculated weight based on the amount of injected
acid and the measured weight after the experiment are small enough to be
negligible.
Table 2 Fe36-Fe51 measured weight and calculated weight compared
Fe38
Measured Weight (before)
Measured Weight (after)
Calculated Weight(total)
Fe39
2.025
?
2.096
Fe44
Measured Weight (before)
Measured Weight (after)
Calculated Weight(total)
Fe40
2.138
2.171
2.189
Fe45
3.352
3.540
3.549
Fe42
2.154
2.174
2.185
Fe48
3.027
3.120
3.216
2.580
2.634
2.610
Fe43
3.233 [kg]
3.401 [kg]
3.337 [kg]
3.331
3.564
3.527
Fe50
Fe51
3.031
3.188
3.238
Fe49
3.329
3.688
3.625
3.199 [kg]
3.539 [kg]
3.505 [kg]
39
Note: the results can also be compared with the volume percentage calculated with the
image analyses (chapter Modeling results).
CO2 is the only gas that has been detected during the experiments. Values could not be
measured, since the production fluid samples works with open tubes so excess gas can
escape.
1) As stated above the amount of mol acid injected is known.
2) As is stated in the chemical reaction formulas in chapter 3.1 Chemical
reactions and in chapter 3.2 Mass Balance, the amount of created CO2 can be
calculated based on the amount of injected acid.
3) The amount of solved and gaseous CO2 in the sample can also be calculated,
based on the solubility (Figure 6).
Table 3 Fe38-Fe51 Amount of CO2 in gaseous phase and solved in the liquid
Fe38
Solubility CO2
CO2 Total
CO2 in water
CO2 gas
CO2 gas Atm
Fe39
0.600
2.311
1.387
0.924
20.697
Fe42
Solubility CO2
CO2 Total
CO2 in water
CO2 gas
CO2 gas Atm
Fe43
0.600
0.957
0.574
0.382
8.566
Fe48
Solubility CO2
CO2 Total
CO2 in water
CO2 gas
CO2 gas Atm
0.600
9.603
5.765
3.839
85.990
Fe40
0.600
1.641
0.985
0.656
14.693
0.600
3.373
2.024
1.348
30.199
Fe49
0.600
6.337
3.804
2.533
56.739
0.600
0.990
0.594
0.396
8.862
Fe44
0.600
6.397
3.840
2.557
57.277
Fe50
0.600
6.697
4.020
2.677
59.968
mol/l
mol
mol
mol
l
Fe45
0.600
6.120
3.674
2.447
54.802
mol/l
mol
mol
mol
l
Fe51
0.600
9.909
5.948
3.961
88.729
mol/l
mol
mol
mol
l
In Table 3 shows that under reservoir conditions the solubility is 0.63 mol/l, this was
calculated in chapter 3.3 Carbon dioxide calculations. The total amount of CO2 which is
40
created by the reaction is also in Table 3 for these four experiments. With the solubility
of CO2 in water it can be calculated how much CO2 is dissolved in the liquid and how
much will escape as a gaseous phase.
The hplc measurements give the amount of Cl- ions in g/l in the test tubes. This is used to
calculate the total amount of Cl- ions in the outflow for these experiments. The inflow is
calculated with the amount of brine flown in the reactor together with the amount of HCl
flown in the reactor, these are both recorded. Following these calculations for experiment
Fe48 and Fe49 more Cl- ions were produced than injected, while for experiments Fe50
and Fe51 more Cl- ions were injected than produced. Since there is no presence of any
kind of chlorides in the samples the following options can lead to this discrepancy:
1) The hplc measurements are only done on 15 to 20 test tubes of the total of 300
test tubes. So, the amount of Cl- ions are a linear interpretation between the
different intervals of hplc measurements.
2) When the backpressure valve fails on the production side, the pressure is
lowered to atmospheric pressure and core fluid escapes uncontrolled. The test
tube in use overflow, hence fluid will be spilled and lost.
3) The pressure in the test tube is atmospheric pressure so some solid
components come out of solution, resulting in the absence of some ions in
solution.
The amount of Cl- ions missing in the calculations is given in Table 4; it is less then 0,5
mol for experiments of 6 days acid injection, so it is assumed negligible. Since no further
conclusions can be done on the amount of Cl- ions the calculations have not been done
for all other experiments. This also is shown more elaborately in Appendix F.
Table 4 Cl- ions calculations
Fe48
Fe49
Fe50
Fe51
L Acid inj mol Cl- in
mol/l Cl- out
difference [mol]
difference[%]
8.790
3.022
3.447
-0.424
-14.0
5.800
2.108
2.282
-0.174
-8.3
6.130
2.331
2.184
0.147
6.3
9.070
3.080
2.965
0.115
3.7
41
6 Images CT-Scan
During the research the CT-scanner in the laboratory has been used, because it is a vital
element in observing the change of the cores induced by the acid treatment. All cores are
scanned before the acid treatment and most cores are scanned after treatment. During the
last sequence of experiments multiple scans have been made during the acid treatment
under reservoir conditions.
During each scan approximately 300-350 photos are taken from the core.
In every photo macro pore space, calcite, wormholes (when present), anhydrite (when
present), fossils (when present), fractures (when present) and surrounding objects (rubber
sleeve etc.) can be identified.
The identification process is performed best when the photos are as sharp as possible for
obvious reasons.
42
6.1 CT-scans introduction
Computed tomography is a (medical) imaging method in which digital geometry
processing is used. With this digital processing a three-dimensional image of the inside of
an object is generated from large series of two-dimensional X-ray images. These X-ray
images are taken around a single axis of rotation. The volume of data produced by CT
can be manipulated through a windowing process. This windowing is to optimize various
structures on the ability to block X-ray beams. This again is based on the process of using
the calculated Hounsfield units (HU), which represents the degree of attenuation. These
Hounsfield units are 4096 possible grey values arranged on a scale from -1024 HU to
+3071 HU. -1024 HU is the attenuation produced by air and 0 HU is the attenuation
produced by water (Brenner, D. J. et al., 2007). These again are used in the Leica Qwin
modeling and converted to grey images with 256 shades of grey.
With experiments Fe38 to Fe51 CT-scans are made before and after every experiment.
Both scans are under atmospheric pressure and temperature. Before the experiment the
core is scanned dry, while the scan after the experiment is done as soon as the wet core is
out of the reactor. The remaining fluid in the pore spaces does not visibly influence the
images; textures are clearly visible. A pure chalk core with the same diameter and 5 cm
long is always scanned together with all experiments, this is to provide a reference
between the acidized cores and the original chalk.
The experiments FeN01 to FeN05 are scanned during the flow experiment, always under
reservoir P,T-conditions. During a CT-scan image slices were made every 1 mm. Since
the cores were between 20 cm and 35 cm this means that for every scan between 300 and
350 images were taken. When density of the measured material in the grey images
becomes higher, the resulting pixel will be whiter. The pixels precision of the
reconstructed CT-images is higher than 0,5 mm, so only macro pore space is visible.
When the CT-beams go from a low density to a higher density, the CT-image will show
some resulting beam hardening effects. For this reason all CT-images will show a lighter
43
ring on every new interface. This makes the anhydrite-calcite interpretation useless on
air-core interface. And the outer ring of the core is subtracted in the Leica-Qwin script.
44
6.2 Images results
For this research different filters of the CT-scan have been tried and evaluated on their
sharpness of the resulting images, the filters are visualized in Appendix D. Filter Genoux
b60 gave the best results and was used for all further CT-scans. The algorithm of this
filter is unknown.
In every image before the acidizing treatment the following materials, and image
properties can be observed (Figure 14):
•
Calcite matrix mainly consisting of calcite
•
Fracture (i.e. pore space)
•
Rubber sleeve
•
Black surroundings
•
Some images contain fossils
•
Beam hardening effects along the air-core interface
In the black surrounding some lighter back scatter can be seen and when looked closely
the macro pore space in the calcite can be spotted. The grey bow underneath the whole
core is part of the CT-scan table.
45
Beam
hardening
Figure 14 Fe51 before treatment CT-scan image 108
In the images, after acidizing, the following materials or image properties can be
observed (Figure 15):
•
Calcite matrix consisting of calcite and anhydrite
•
Anhydrite
•
Fracture ends (Pore space)
•
Rubber sleeve (rubber composite)
•
Black surroundings with back scatter
•
Wormholes (Pore space)
•
Some images contain fossils
•
And the beam hardening effects on the border of the image
The fracture ends are the remainders of the fracture after acidizing. Usually the fractures
were fully closed and only the ends, where the rubber sleeve was pushed into the fracture
46
because of the annulus pressure, were visible (Figure 15). In some experiments the
fractures were only partly closed. Some macro pore space can also be observed.
Beam
Hardening
Figure 15 Fe51 after treatment CT-scan image 105
If the pixel values of an image are gathered in a frequency distribution plot, then each
material group shows its specific distribution (Figure 16). This graph shows three
different pictures of the same scan series. Certain intervals can be observed:
•
Air: the black surrounding (including wormholes and fractures)
•
Rubber sleeve
•
Calcite and anhydrite
•
Fossils
The green line is based on a picture made of the control block placed at the end of the
acidized scan, where no anhydrite is present. The red line is based on a picture of the
same scan where a little amount of anhydrite is present. The graph shows that the
distribution of the calcite and anhydrite are overlapping. The blue line is based on a
picture from the same scan, but with even more anhydrite present (estimated at 40%). In
this picture can be observed that the further the acidizing treatment is done the flatter and
47
brighter this calcite/anhydrite interval is placed. Hence, it can be stated that the calcite
with micro pores and anhydrite have overlap in grey values. However in the curve often a
slight kink is visible at the right side, which is taken as the transition between calcite and
anhydrite.
Pixels/greyscale
6000
4000
pixels
No anhydrite content
Black
surrounding
5000
High anhydrite content
Low anhydrite content
Calcite
More and more
anhydrite
3000
Fossils
Rubber
sleeve
2000
1000
0
0
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
greyscale
Figure 16 Fe51 after treatment, amount of pixels per grayscale for three different images from
the same scan series, low, high and no anhydrite content
The areas of interest of calcite and anhydrite in Figure 17 are based on the greyscales
from Figure 16. For calcite these values are between 130 and 170, and for anhydrite
between 150 and 200. The corners of the areas of interest fall on the porosity line; these
intersections give representative values for porosity. This shows that discrimination
between calcite and anhydrite is difficult. Since the slight kink in the curve can be spotted
with a high anhydrite content, while this is difficult to do in a low anhydrite content
(Figure 16). This is because the grey value area of interest for calcite and anhydrite
overlap (Figure 17). So for the discrimination of anhydrite and calcite a representative
image with a high amount of anhydrite content should be chosen from a scan series. The
kink in the line (such as in the high anhydrite content, Figure 16) is taken for every scan
series as the discrimination between calcite and anhydrite.
48
Grey values specified for acidized matrix
250
Calcite
Anhydrite
200
Grey values
Area of interest
150
100
50
0
0
20
40
60
80
100
Porosity [% ]
Figure 17 Grey values for calcite and anhydrite versus different porosity percentages, with the area
of interest in this research
49
7 Image analysis
Image analysis with CT-scanner images is done to provide comparison with the volume
percentages, from the hplc/mass balance equations. If both give comparable results for
different volume components results are confirmed. Quantification is done in the image
analysis program Leica Qwin. This program is used to recognize certain reoccurring
features in a picture; here we choose the rubber ring for its consistent grey range. The
same procedure has to be repeated for every picture and one scan contains 250 to 300
pictures. So, the script was written in a program loop. The modeling is done to get a
quantified image of what happened with the fracture during the experiments. The script
separates binary pictures of the image components of which image volume percentages
can be calculated. The script has been written to recognize all relevant volume
components of every original image (Appendix E, script 2). Binary files are produced
from the calcite matrix, anhydrite matrix, fractures, wormholes, fossils and the envelop of
the sample.
50
7.1 Description of the image analysis scripts
Three different scripts are written for the image analysis. The second script is the most
important, because here the actual discrimination between image components takes place.
Therefore the second script is discussed more elaborately in this chapter.
•
The first (Appendix E, script 1) was written because the program Osiris which
visualizes the CT-data has an auto contrast feature which could not be switched
off. The auto contrast averaged the grey values over all pictures. Since there are
always some pictures taken without the core these images are totally black and
grey values over the interesting pictures are therefore influenced. Because of this
the pictures fluctuated a lot in average grey values, making discrimination based
on the grey values of calcite and the anhydrite impossible. Since all CT-scans are
made with the core inside the sleeve, the sleeve is always present and its grey
scale is measured for every picture. Based on the sleeve all pictures in the CTscan were then darkened or lightened to a picture taken as a reference, reversing
the auto contrast of Osiris. Later the program k-pacs is used instead of Osiris, here
the auto contrast was an option bypassing the use of this script.
•
The second script (Appendix E, script 2) in use is to do the actual discrimination
between the different components. First a representative image has to be taken to
discriminate between all different components. This discrimination is done in the
first part, before the loop. The circle obtained on the end part one is needed to
subtract all the area around the area of interest, the inner core. The description is
visualized in the flow diagram (Figure 18).
1) Read a selected image.
2) Detect the worm holes in the core. To do this detect the black around the core
and in the core.
3) Detect all parts in the core (anhydrite, calcite, fractures, fossils) and set a
pause at every detect, so this can be checked and changed for every run. Here
the discrimination between the different components is done for all images in
the loop.
51
4) Fill the holes (wormholes) of the core.
5) Add up the binary image of the core and the binary image of the black with a
logical operation, this will give the binary image of the wormholes.
6) Add up all these binary images to get a smooth circled core by setting a
sequence of close.
7) Find the centre of this image.
8) Find the diameter of the core.
9) Make a circle of this diameter.
Start the loop (flow diagram in Figure 19)
1) Read the first image.
2) Repeat step 2 to 7.
3) Clean the (inevitable) loose point (single pixels) surrounding the core with a
Measure area and accept sequence.
4) Use the selected diameter on this core centre.
5) Fill the circle.
6) Now the entire core is covered by the circle created with the first image.
7) Erode this circle a few steps. This is to clean the core of the whiter outer
circles, which are results of beam hardening. This zone would be falsely
detected as being anhydrite if not done.
8) Ad up all found binary images in step 2 with the eroded circle, by using a
logical operation so that only where both binary images have a surface the
object will exist.
9) Save the binaries, i.e. Calcite, Anhydrite, Macro pore space (including
Wormholes), Fractures, fossils and.
10) Loop to read second image.
•
The third script (Appendix E, script 3) in use is to detect the amount of pixels in
every binary image and write this to excel.
52
Insert
Representative
image
A=Detect core
Make a circle
with
Diameter and
centre
Detect core
components
Use circle for loop
Find diameter of C
B=Fill holes
(fractures and
Wormholes)
Add
C=A and B
Find centre of C
Figure 18 Flow diagram to find the representative circle diameter and grey values for all components
Insert
Next
image
A=Detect core
Save all binaries
Detect core
components
Discriminate
Components
in different
binaries
B=Fill holes
(fractures and
Wormholes)
Add
C=A and B
Erode circle
Fill circle
Set circle
(flow chart1)
over the centre
Find centre of C
Figure 19 Flow diagram of the loop to discriminate and save all binary files of all images
53
7.2 Image analysis difficulties
During the development of the procedures certain problems had to be solved.
The biggest problem was that the cores where not placed parallel to the scan line in the
CT-scanner, and further, the diameters of every sample changed. This made a simple loop
for picture place based recognition impossible. The problems have been solved by first
recognizing the sample, and then an enveloping circle by using the outer diameter of the
representative image. This diameter is remembered for every picture of the sample and
calculated from the centre in the sample of every new picture in the loop. Fill this circle
and now every important aspect is taken. If the sample is out of line the centre of the
circle will always jump to the centre of the sample in the next picture.
The second problem is separating the black wormholes from the black fractures and the
black surroundings. This problem has also been solved with the circle principle. Since the
circle is filled in for every sample and a detection of the matrix without wormholes and
fractures was done; subtract the two and the open spaces within the core are left. From
this subtraction the division between macro pore space and fractures is done by the
principle that the open space attached to the sides of the sample are fractures and the rest
are the wormholes and macro pore space.
Third problem was that the rim of the sample is lighter then it should be due to beam
hardening effects of the CT-scanner. By eroding the outer cm of the core only the correct
part of the core was used for calculations.
54
7.3 Modeling Results
From this model every original image is now divided in six different pictures, see Figures
below:
•
A picture of the original image (Figure 20)
•
A picture of the whole sample image (Figure 21)
•
A picture of the calcite in the image (Figure 22)
•
A picture of the anhydrite in the image (Figure 23)
•
A picture of the wormhole/macro pore space in the picture (Figure 24)
•
A picture of the fossils in the image (Figure 25)
•
A picture of the fracture in the image (Figure 26)
Because there are 250- 300 original images throughout a scan, there are now on 15001800 pictures.
55
Figure 20 original image
Figure 21 whole core detected
Figure 22 calcite matrix
Figure 23 anhydrite matrix
Figure 24 macro pore space
Figure 25 fossils
Figure 26 fracture
These pictures are now used in a new Leica Qwin loop to count the amount of pixels in
every picture. With these spatial characteristics such as volume percentages can be
calculated.
Now all binary pictures of the same subject are rendered to a 3D image in Avizo, a 3D
visualization program. The different 3D models of the same scan can be combined so that
a complete image is created (Figure 27 to Figure 34). Because the recognition is done in
56
Qwin the different 3D models can be switched on and off to get a better idea of the
different components. The samples can be orientated with respect to the fossils, and the
wormhole propagation is visualized in detail.
Figure 27 Fe51 before treatment 3D model of the
Figure 28 Fe51 before treatment 3D model of the fossils
fracture (green)
(red)
Figure 29 Fe51 before treatment 3D model of the
Figure 30 Fe51 before treatment 3D model of the
macro pore space (blue)
fracture (green), fossils (red) and macro pore space
(blue) together
57
Figure 31 Fe51 after treatment 3D model of the macro
Figure 32 Fe51 after treatment 3D model of the macro
pore space/wormholes (blue), fracture (green), fossils
pore space/wormholes (blue), fossils(red), fractures
(red) and anhydrite (purple)
(green) and calcite (yellow)
Figure 33 Fe51 after treatment 3D model of the macro pore
space/wormholes (blue) and fossils (red)
Figure 34 Fe51 after treatment 3D model of the macro pore
space/wormholes (blue), fractures (green) and fossils (red)
Now volumes of every component can be calculated with the help of the obtained
pictures from the Leica Qwin loop, and volume percentages are calculated and shown for
experiments Fe38 to Fe51 in the Table 5. Although many fossils have been observed
(Figure 34) their volume does not add up to more then 0. 1 %. Experiment Fe50 and Fe51
are fractured in the direction perpendicular to the flow direction because force had to be
58
used to get these samples out of the sleeve. These fractures are also the reason why the
calculated fracture volume adds up to more then 1 %.
Table 5 Image analysis volume percentages for all components of experiment Fe38-Fe51
Image Analyses
Fe38
Fe39
Fe40
Fe42
Fe43
Fe44
Fe45
Fe48
Fe49
Fe50
Fe51
Anh[%]
Cal[%]
10.363
1.196
5.406
5.731
15.638
20.030
23.912
28.847
24.124
24.016
30.580
87.647
98.068
93.287
92.371
81.779
76.812
71.763
67.568
72.812
71.174
64.385
Fos[%]
Frac[%]
Pore[%]
0.013
0.004
0.796
0.015
0.014
0.618
0.050
0.032
0.654
0.014
0.186
0.992
0.012
0.126
0.969
0.009
0.030
0.000
0.027
0.497
2.366
0.020
0.067
1.208
0.007
0.039
1.179
0.107
1.686
2.426
0.042
1.032
1.491
To compare these results with the weight percentages obtained in the hplc/mass balance
equations chapter, the volumes obtained by the image analysis have to be corrected by
the pore volumes. After this these volume percentages are corrected with the densities of
calcite and anhydrite to obtain mass percentages (Table 6). When correcting for the
densities, the difference in porosity between the calcite and anhydrite is neglected. These
mass percentages obtained by the image analyses differ less than 4% from those obtained
by the hplc/mass balance equations (Table 6 and Figure 35). The first is from the
hplc/mass balance equations and the second from image analysis. The results are
extensively explained in Appendix F.
59
Table 6 Calculated mass percentages and Image analysis volume percentages for experiment Fe38Fe51
Calculated mass
Cal[%]
Anh[%]
Fe38
Fe39
Fe40
Fe42
Fe43
87.147
91.260
94.719
85.352
88.219
12.853
8.740
5.281
14.648
11.781
Mass Image Analysis
Cal[%]
Anh[%]
Fe38
Fe39
Fe40
Fe42
Fe43
88.529
98.681
94.029
89.115
82.674
11.471
1.319
5.971
10.885
17.326
Calculated mass
Cal[%]
Anh[%]
Fe44
Fe45
Fe48
Fe49
Fe50
Fe51
78.991 77.81427
69.121
79.054
75.887
67.040
21.009 22.18573
30.879
20.946
24.113
32.960
Mass Image Analysis
Cal[%]
Anh[%]
Fe44
Fe45
Fe48
Fe49
Fe50
Fe51
77.774
73.2503
68.125
73.362
73.003
65.767
22.226
26.7497
31.875
26.638
26.997
34.233
Calculated versus Image analysis
100
90
[%]
80
70
Calculated calcite mass
percentage
60
Image analysis Calcite mass
percentage
50
40
Calculated anhydrite mass
percentage
30
Image analysis anhydrite mass
percentage
20
10
Fe
38
Fe
39
Fe
40
Fe
42
Fe
43
Fe
44
Fe
45
Fe
48
Fe
49
Fe
50
Fe
51
0
Experiment number
Figure 35 Calculated mass percentages and Image analysis volume percentages for experiment Fe38Fe51
60
8 Fracture experiments
8.1 Introduction
These tests were done to recognize if after the acid treatment the fractures would not
reopen again. Fracture experiments were conducted to see if the acidized fracture samples
would reopen on the same fracture under tensile strength. If this happens the conclusion
will be that the anhydrite fractures are weaker then the rest of the matrix. If so, the
probability would be higher that this would happen after acidizing the reservoir. If the
sample does not fracture over the old acidized fracture the conclusion is that the sealed
fracture is stronger then the matrix. For these tests a confining pressure of 30 bars higher
then the injection pressure was used. And injection and producer pressure differences
between 5 and 200 bars are used. The cores FE43 and Fe44 were used.
Additionally Brazilian tests have been done to prove tensile strength differences between
the original chalk samples and acidized samples with stronger anhydrite contents.
61
8.2 Theory hydraulic fracturing
Figure 36 Schematic drawing illustrating the three fundamental mode of fracture
(Atkinson B.K., 1987)
There are three types of fundamental modes of fractures, see Figure 36.
Mode I shows the way the rock will fracture due to hydraulic fracturing. This is due to
the failing of the tensile strength of the rock. Hydraulic fracturing uses hydraulic pressure
in a fluid to break up open fractures away from the wellbore, which results in a ‘path’ that
has a much higher permeability than the surrounding formation (see Figure 37).
Figure 37 Flow area increase due to fracturing (Economides and Nolte, 2000)
62
To create a hydraulic fracture high enough injection pressures are used to cause tensile
failure of the rock. The rock opens at the fraction initiation pressure (also known as
breakdown pressure) and propagates as additional fluids are injected and the opening is
extended. In low permeability reservoirs, the fracture length is the priority and in high
permeability reservoirs high conductivity is more important than length, so this results in
a wide fracture (Economides et al, 1994). Hydraulic fractures form perpendicular to the
least principal stress, because there is the least resistance. In the majority of the reservoirs
which are tectonically relaxed, this is usually the horizontal stress and the fracture will be
vertical. (Hubbert and Willis, 1957)
Figure 38 Brittle behavior of the same rock
under different conditions, (Atkinson B.K.,
Figure 39 Ductile behavior of the same rock under
different conditions, (Atkinson B.K., 1987)
1987)
The hydraulic fracture tests are performed under high confining pressure and temperature
which is expected to induce ductile behavior (Figure 39). However when the pressure
difference between injector, producer and annular pressure are very high, the sample is
expected to return to its brittler (Figure 38) behavior and fractures.
The Brazilian tests are done under room temperature without confining pressure so
brittler behavior is expected.
63
8.3 Brazilian test
As earlier described these tests are done to compare the tensile strength difference
between the original chalk and the acidized samples. The acidized samples contain
anhydrite, less porosity and by that a denser matrix composition. So, higher tensile
strength is expected. Hubbert and Willis (1957) already stated that fracturing will first
occur at a point of the boundary of the wellbore where the effective stress is equal or
greater than the tensile strength of the rock. With measuring the tensile strength, fracture
behavior of the reservoir can be estimated.
8.3.1 Theory
By definition, the tensile strength has to be found using a direct uniaxial test, difficult to
perform with our samples. The splitting tensile or Brazilian Test offers a good alternative
(ASTM, 1995). A circular disk of rock with a thickness to diameter ratio (t/d) between
0.2 and 0.75 (ASTM, 1995) is placed on its radial side between a compression machine
and is loaded. As seen in Figure 40 a load in the vertical direction (red arrows) and
induces a parallel fracture. The tensile strength (Figure 41) is perpendicular to the load
(see arrows).
64
Figure 40 Chalk sample in the Brazilian test,
Figure 41 Chalk sample after Brazilian test, tensile
pressure load is in the vertical direction
strength in the horizontal direction failed because of
the vertical load
In this situation the following equation for the Brazilian tensile strength can be applied
(Goodman, 1989):
σt =
2F
π LD
Eqn 8-1
In which,
σ t = the splitting tensile strength [MPa],
F = maximum applied load indicated by the testing machine [N],
L = thickness of the specimen [mm],
D = Diameter of the specimen [mm]
65
8.3.2 Brazilian test results
Seven cores were drilled from a block of chalk and six from the treated cores of
experiment Fe49 and Fe50, It has been made sure that the original sealed fractures are in
the treated cores. The cores all have a diameter of approximately 50 mm. It was
calculated with the acid injection calculations and the image analysis calculations that
Fe49 has an anhydrite content of approximately 22% and Fe50 an approximate anhydrite
content of 24 %. These cores are sawed in blocks of approximately 20 mm in length. Of
both experiments only 3 of these cores could be obtained. Normally more tests are done
to give valid results of the tensile strength.
During these experiments the core length, diameter and maximum loading pressure were
measured, in order to calculate the tensile strength (Figure 42 and Figure 43).
Tensile Strength
0.7
Tensile strenght [MPa]
0.6
0.5
Chalk
0.4
Fe50
0.3
Fe49
0.2
0.1
0
0
5
10
15
Experiment nr
Figure 42 Tensile strength, sigma versus experiment number
66
Figure 43 Tensile strength difference between the original chalk and acidized chalks shown in a
boxplot
•
In Figure 42 it can be seen that the tensile strength of the chalk differs between
0.15 MPa and 0.65 MPa. All samples of the acidized cores vary in the same range.
•
Hence, the tensile strength is not different compared to of the original chalk. In
other words the tensile strength is not improved due to the increase of matrix
density and the presence of the anhydrite.
•
Two acidized samples were placed with their sealed fracture in the vertical
pressure direction. And the others were placed with their sealed fracture under
small angles of the vertical pressure difference. This was done to see if the old
fracture is a preferential path for the new fracture.
•
All acidized samples had a new fracture in the vertical direction as seen in Figure
41, the fracture path was not influenced by the old sealed fracture.
•
Some of the fractures in the chalk samples had deviated fractures over a visible
fossil.
67
•
This was even closer examined with experiment number six (on the original
chalk), where the fossil was put into the vertical pressure direction, the tensile
strength proved very low.
•
Experiment number seven where the fossil was put in the horizontal direction,
perpendicular to the pressure load, the tensile strength proved to be very high.
•
Concluded is that a fossil does influence the tensile strength of the samples and
the fracture path.
•
Furthermore, the old sealed fractures are not preferential new fracture paths.
68
8.4 Hydraulic fracture experiments under confining stress
Three experiments have been performed, of which two were successful and one gives
adequate results. The three experiments were done on sealed fractures in the resulting
cores of FE44 and FE43. The fracture tests were performed under reservoir conditions,
where the annular/confining pressure is 320 bar, the pore/injection pressure 270 bar and
temperature 80oC . The pore pressure was created with fresh water. The content of the
produced water is analyzed with XRD measurements. The experimental setup is very
similar to the flood tests equipment. However, here measured much higher pressure
differences, so the experiments had to be performed in the high pressure lab. The core is
put inside a rubber sleeve in the reactor, the annulus pressure is brought up to 30 bars
while flooding the core with water. The injection pressure and production pressure is
brought to 270 bar while the annulus pressure is brought up to 320 bar. At time is zero
the back pressure valve on the production side is released to 200 bar unto 0 bar in steps of
60 bar, while pumping water hard in the core on the production side to keep the inlet
pressure at 270 bar. In this way high pressure differences are created over the sample.
Every single fracture test with a pressure difference could only be performed for several
minutes due to the fact that the pressure pump used for injecting the water has a reservoir
of 50 ml. During the Fe43 experiment this is procedure is followed 9 times (Figure 44).
69
8.5 Experimental results
The first experiment with FE44 failed, since the end piece of the reactor was squeezed
out of the sleeve and annulus oil penetrated the sample. The repeat experiment with the
same sample was successful; a nice pressure built up, and no fracture development in the
core. However, the data-acquisition system failed during pressure built-up. A successful
third experiment with FE43 showed the pressure built up (Figure 44), a minor axial
compaction (about 3.5 mm or ca. 1.3 vol. %). After the experiment the core was cut in
order to recognize new fractures.
4
test 4
test 5
350
3,5
test 7
300
250
dP[bar]
test 6
test 3
3
2,5
test 8
200
2
test 1 try 2
150
test 9
test 2
100
1,5
1
test 1
50
0,5
0
Displ[mm]
400
Pinj-Pprod [bar]
Pann[bar]
Disp [mm]
0
0
400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 6800
-50
-0,5
Time[sec]
Figure 44 Fracture test on Fe 43 Pressure difference, annular pressure and displacement versus time
Figure 44 shows the confining pressure, pressure difference steps and the compaction.
•
The annulus pressure or confining pressure is maintained at 320 bar during the
test.
•
During each pore pressure step until a pressure difference of 110 bar the sample
gets longer, due to ductile behavior of the sample.
•
During these pressure steps it was difficult to keep up the injection pressure; the
pump rate was insufficient.
•
After the pressure difference of 110 bar was reached; compaction reduced the
porosity and permeability sufficiently to a level that the injection pump was able
to keep the pressure at 270 bars injection pressure.
70
•
After the experiments no fractures were found in the sample.
•
However, the axial strain was 0.013. When considering ∆V=3∆L, the volume
reduction is about 4 vol. %. We consider the ductile behavior. It is assumed that
the original chalk is less ductile, which would result in an earlier failure of a chalk
sample tested in the same way.
The composition of the produced water shows that dissolution of the core was minimal
(Table 7) The mineral content of the substrate consisted at the start of calcite and at a
later stage (when higher differential pressures were used) of mostly calcite and some
secondary gypsum.
Table 7 Hplc fracture test results
Resultaten HPLC analyse project Maersk
sample
Frac 43-1
Frac 43-2
Frac 44
kation analyse
g/L Na
g/L Ca
2.50
1.84
1.74
2.04
2.57
1.76
anion analyse
g/L Cl
g/L SO4
<0,1
2.36
<0,1
1.92
<0,1
2.38
The photographs (Figure 45) of the slices of the core after cutting show no signs of new
fractures, newly cemented fractures or compaction effects (multi-cracks, pressure
solution, etc.). Only an old cemented fracture became visible.
Following the theory, the difference in brittle behavior of the Brazilian tests and the
ductile behavior of the hydraulic fracture tests could be explained by the fact that;
1) The Brazilian tests are done with dried samples resulting in britller behavior.
2) And the hydraulic fracture tests had high over pressured annular pressure
which could hold the sample in tact.
So this condition of the Brazilian test with the same strength of the treated samples
compared to the chalk samples could be very different under reservoir pressure.
71
Fracture cemented
during acid
experiments
Figure 45 Fe43 after fracture experiment cut through the centre to check if the new
fractures are visible
72
9 Conclusions
9.1 Conclusions of the flow experiments
•
The calculated resulting pH under atmospheric conditions is the same as the
experimental resulting pH. This indicates full reaction from both the acids.
•
A large amount of gaseous CO2 is formed of which approximately 60% dissolves
in the water.
•
Mass balance calculation based on the injection of acid which forms anhydrite
comes very close to the measured change in mass, and can be called accurate.
•
Concluding from the permeability graph, the fractures in the samples will clog
within 40 minutes time. CT-scans made clear that the film between the two parts
of the sample is still pasty and not solid yet.
•
The anhydrite formation in the fracture is finished within a time span of six hours.
Then the first wormholes have reached the opposite site of the sample and no
more flow through the fractures is needed.
•
The worm holing process and anhydrite formation in the sample continues till the
production tube clogs or till all calcite has been transformed to anhydrite.
•
So the process during the flow experiments is:
1) The acid reacts with the area of the fracture first, making a pasty film.
2) This pasty area makes it possible for the confining annulus pressure to press
the two halves of the core to each other, thus closing the fracture.
3) Wormhole development and low permeable flow through the fracture.
4) ‘Solid ‘ fracture closing and further wormhole development.
•
Recognition of all different volume components in the samples is possible with
the image analysis scripts on the CT-scans.
•
Mass percentages calculated with the CT-scans the Leica Qwin program are
within 4% difference of the mass percentages calculated with the mass balance
calculations based on the acid injected.
73
9.2 Conclusions on the fracturing experiments and Brazilian test
•
From the experimental results of the Brazilian test it was concluded that the
acidized samples have comparable strengths to the original chalk samples.
•
Hence, it was proven that the tensile strength is not changed by the increase in
matrix density and the presence of the anhydrite.
•
In the Brazilian ductile behavior was not observed. This is mostly based on the
fact that the sealed fracture samples have more anhydrite and will behave more
ductile under reservoir conditions.
•
All acidized samples had a new fracture in the vertical direction, the new fracture
was not influenced by the fracture path of the old sealed fracture.
•
The fracture path and tensile strength is influenced by the presence and
orientation of fossils.
•
As was explained in the experimental results of the fracture experiments, the
sealed fracture could withstand high pressure differences between the injector and
producer, without failure of the tensile strength.
•
The changing of the axial length in the fracturing test indicates ductile behavior,
mainly because there was no new fracture present.
•
The fractures have not been reopened by high pressure differences.
The difference in brittle behavior of the Brazilian tests and the ductile behavior of the
hydraulic fracture tests could be explained by the fact that;
1) The Brazilian tests are done with dried samples under atmospheric conditions
resulting in britller behavior.
2) And the hydraulic fracture tests had high over pressured annular pressure
which could hold the sample in tact.
The main conclusion of both experiments is that the old sealed fracture is not a
preferential fracture path for a new fracture. So when the fractures are sealed, they will
have no bigger chance to failing then the rest of the reservoir.
74
10 Recommendations
•
Make an exact core set up in the CT-scanner to be sure that all cores are always
scanned perfectly straight, this will make modeling work easier.
•
Fracture tests on original chalk cores will give more insight in the difference in
tensile strength between the chalk samples and acidized samples.
•
More fracture tests on the acidized samples will give more insight in the tensile
strength and its ductile behavior of the cores.
•
More Brazilian tests will give more accurate insight on the tensile strength
difference between the original chalk cores and the acidized core and it will give
more insight on brittle behavior of the two different rock types.
•
More dynamic flow experiments in the CT-scanner to give more exact insight on
the closing time of the fracture.
75
11 References
Schuiling, R.D., Geochemical engineering: some thoughts on a new research field,
Applied Geochemistry, Vol.5 (1990), pp. 251-262.
Surlyk, F., Contourite drifts, moats and channels in the Upper Cretaceous chalk of the
Danish Basin, (2007), pp 405-422
Yamamoto, H., Kennedy, G.C., Am. J. Sci., 267A, (1969), pp. 550-557.
Hoefner, M.L., Fogler, H.S., Pore evolution and channel formation during flow and
reaction in porous media, AIChE Journal, Vol. 34 (1988), pp. 45-54.
Singurindy, O., Berkowitz, B., Evolution of hydraulic conductivity by precipitation and
dissolution in carbonate rock, Water resources research, Vol. 39, (2003), pp. 1-14.
Singurindy, O., Berkowitz, B., The role of fractures on coupled dissolution and
precipitation patterns in carbonate rock, Advances in Water Resources, Vol. 28
(2005) pp. 507-521.
van Lier et al., Sealing of thieve zones in chalk reservoirs, (2007)
Sander, R., Compilation of Henry’s Law Constants for Inorganic and Organic Species of
Potential Importance in Environmental Chemistry, (1999)
Lide, D.R., Handbook of Chemistry & Physics, (2009)
Diamond, L.W., Solubility of CO2 in water from −1.5 to 100 ◦C and from 0.1 to 100
MPa, (2003)
Bird, R.B. et al., Transport Phenomena, second edition, (2002)
76
Brenner, D.J. et al., Computed Tomography - An Increasing Source of Radiation
Exposure, (2007)
Atkinson B.K., Fracture mechanics of rock, (1987)
Economides, M.J. and Nolte, K.G. Reservoir Simulation, 3rd edition, John Wiley and
Sons, (2000)
Goodman, R.E. Introduction to Rock Mechanics, 2nd edition, John Wiley and Sons (1989)
77
78
Appendix A: Porosity Permeability measurements
A.1 Dry Porosity
Sample nr
D[cm]
L[cm]
Vbulk[cc]
M dry[g]
A[cm2]
Gas visc[cp]
Vmatrix[cc]
Por
expected error[%]
1
2,48
2,975
14,371
20,6
4,84
0,0175
7,208
0,498434
5,43
2
2,477
2,98
14,36
20,07
4,82
0,0175
7,0306
0,51
8,3
3
2,468
2,975
14,675
2
2,475
2,97
14,4
20,19
4,81
1
0,985
3
2,481
2,97
19,99
4,837
0,0998
0,982
26,6
0,555
4,612
26,81
0,4757
7,55
7,286
0,5
7,012
4
2,47
3,07
14,7
20,88
4,81
0,01781
7,377
0,498
14,06
5
2,47
2,95
4,78
0,0179
6,95
0,51
1,65
6
2,47
2,99
14,38
20,26
4,8
7,1202
0,505
1,103
7
2,48
3
4,83
0,0179
6,9507
0,511
1,9
8
2,463
14,4
4,765
9
2,471
2,98
14,289
4,792
0,001751
7,2443
7,1868
0,4979
0,497
5,2
2,75
A.2 Wet Porosity
Sample nr
D[cm]
L[cm]
Vbulk[cc]
M dry[g]
A[cm2]
RhoFluid[g/cc]
Fluid visc[cp]
Rhobulk[g/cc]
M wet[g]
Por
expected error[%]
1
2,475
2,97
14,289
19,933
4,81
1
1,395
26,6
0,47
1,95
4
2,47
2,98
14,279
20,4
4,792
0,96
1,629
0,45
0,98
5
2,467
2,99
20,22
4,78
0,9983
1,3
0,46
2,2
6
2,48
2,933
14,2
19,7
1
26,75
0,49
2,2
7
2,486
2,965
14,38
19,96
4,85
1
0,985
26,52
0,523
4,07
8
2,47
2,995
9
2,48
2,98
20,22
4,778
0,998
4,861
0,01751
0,46
2,2
0,549
0,94
79
A.3 Dry Permeability
experiment #
1
2
P[bar]
K[D]
K[D]
K[D]
0.5
0.0045
0.00454
0.75
0.005
0.00473
1
0.0047
0.0046
3
4
5
6
7
8
K[D]
K[D]
K[D]
K[D]
0.0081
0.00464
0.00503
0.0046
0.0081
0.00473
0.0051
0.0047
0.0085
0.00461
0.00492
0.0046
K[D]
0.005034
0.004596
0.004815
A.4 Wet Permeability
experiment #
1
2
3
4
5
6
7
8
P[bar]
K[D]
K[D]
K[D]
K[D]
K[D]
K[D]
K[D]
K[D]
2
0.00274
0.00271 0.003513
0.00049
0.0029
0.00292
0.0029
0.0067
2
0.0027
0.00338
0.00038
0.00292
0.0064
2
0.00273 0.003387
0.00293
0.0062
80
A.5 XRD measurement on pure chalk
81
Appendix B: Stream results Electrolyte-NRTL model
B.1 Brine flow through the sample
ACID
Temperature C
Pressure bar
Vapor Frac
Solid Frac
Mole Flow kmol/hr
Mass Flow kg/hr
Volume Flow cum/hr
Enthalpy Gcal/hr
Mass Flow kg/hr
H2O
CO2
CACO3
NACL
CA++
CAOH+
NA+
H3O+
HCL
CALCI(S)
CACL2(S)
CACO3(S)
SODIU(S)
WEGSC(S)
TRONA(S)
NAOH:(S)
NAOH(S)
NACL(S)
CLHCO3OHCO3-Mass Frac
H2O
CO2
CACO3
NACL
CA++
CAOH+
NA+
H3O+
HCL
CALCI(S)
CACL2(S)
CACO3(S)
SODIU(S)
WEGSC(S)
TRONA(S)
NAOH:(S)
NAOH(S)
NACL(S)
CL-
LIQ
LIQ2
80
60
0
0
0.057
1.035
0.001
-0.004
80
60
0
0.946
1.056
101.035
0.038
-0.291
25
1.013
0
0.946
1.056
101.035
0.038
-0.292
1
0
0
0
0
0
0.014
0
0
0
0
0
0
0
0
0
0
0
0.021
0
0
0
1
0
0
0
0
0
0.014
0
0
0
0
100
0
0
0
0
0
0
0.021
0
0
0
1
0
0
0
0
0
0.014
0
0
0
0
100
0
0
0
0
0
0
0.021
0
0
0
0.966
0
0
0
0
0
0.013
0
0
0
0
0
0
0
0
0
0
0
0.021
0.01
0
0
0
0
0
0
0
0
0
0
0.99
0
0
0
0
0
0
0
0.01
0
0
0
0
0
0
0
0
0
0
0.99
0
0
0
0
0
0
0
82
ACID
HCO3OHCO3-Mole Flow kmol/hr
H2O
CO2
CACO3
NACL
CA++
CAOH+
NA+
H3O+
HCL
CALCI(S)
CACL2(S)
CACO3(S)
SODIU(S)
WEGSC(S)
TRONA(S)
NAOH:(S)
NAOH(S)
NACL(S)
CLHCO3OHCO3-Mole Frac
H2O
CO2
CACO3
NACL
CA++
CAOH+
NA+
H3O+
HCL
CALCI(S)
CACL2(S)
CACO3(S)
SODIU(S)
WEGSC(S)
TRONA(S)
NAOH:(S)
NAOH(S)
NACL(S)
CLHCO3OHCO3-*** LIQUID PHASE ***
pH
LIQ
LIQ2
0
0
0
0
0
0
0
0
0
0.056
0
0
0
0
0
0.001
0
0
0
0
0
0
0
0
0
0
0
0.001
0
0
0
0.056
0
0
0
0
0
0.001
0
0
0
0
0.999
0
0
0
0
0
0
0.001
0
0
0
0.056
0
0
0
0
0
0.001
0
0
0
0
0.999
0
0
0
0
0
0
0.001
0
0
0
0.979
0
0
0
0
0
0.011
0
0
0
0
0
0
0
0
0
0
0
0.011
0
0
0
0.053
0
0
0
0
0
0.001
0
0
0
0
0.946
0
0
0
0
0
0
0.001
0
0
0
0.053
0
0
0
0
0
0.001
0
0
0
0
0.946
0
0
0
0
0
0
0.001
0
0
0
6.392
9.088
10.125
83
B.2 Acid flow through the sample
LIQ2
Temperature C
Pressure bar
Vapor Frac
Solid Frac
Mole Flow kmol/hr
Mass Flow kg/hr
Volume Flow cum/hr
Enthalpy Gcal/hr
Mass Flow kg/hr
H2O
CO2
H2SO4
HCL
CASO4
CACO3
CA++
CAOH+
H3O+
CACO3(S)
CASO4(S)
CACL2(S)
CLHSO4HCO3OHSO4-CO3-Mass Frac
H2O
CO2
H2SO4
HCL
CASO4
CACO3
CA++
CAOH+
H3O+
CACO3(S)
CASO4(S)
CACL2(S)
CL-
LIQ
ACID
SOLID
VAP
VAP2
25
1.013
0
0.946
1.056
101.056
0.038
-0.292
80
60
0
0.945
1.057
101.08
0.038
-0.291
80
60
0
0
0.057
1.101
0.001
-0.004
80
60
0
0
0.999
100
80
60
1
0
0
0.021
0
0
25
1.013
1
0
0.001
0.024
0.014
0
1.02
0.001
0
0
0
0
0.007
0
0
99.894
0.119
0
0.011
0
0.001
0
0.002
0
1.02
0.025
0
0
0
0
0.007
0
0
99.894
0.122
0
0.011
0
0.002
0
0.001
0
0.98
0
0
0
0
0
0
0
0.023
0
0
0
0.011
0.085
0
0
0.003
0
0
0
0
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0.021
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.024
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.01
0
0
0
0
0
0
0
0
0.989
0.001
0
0
0.01
0
0
0
0
0
0
0
0
0.988
0.001
0
0
0.89
0
0
0
0
0
0
0
0.021
0
0
0
0.01
0
0
0
0
0
1
0
0
0
0
0
0
0
0.005
0.995
0
0
0
0
0
0
0
0
0
0
0
0.013
0.987
0
0
0
0
0
0
0
0
0
0
0
84
LIQ2
HSO4HCO3OHSO4-CO3-Mole Flow kmol/hr
H2O
CO2
H2SO4
HCL
CASO4
CACO3
CA++
CAOH+
H3O+
CACO3(S)
CASO4(S)
CACL2(S)
CLHSO4HCO3OHSO4-CO3-Mole Frac
H2O
CO2
H2SO4
HCL
CASO4
CACO3
CA++
CAOH+
H3O+
CACO3(S)
CASO4(S)
CACL2(S)
CLHSO4HCO3OHSO4-CO3-*** LIQUID PHASE ***
pH
LIQ
ACID
SOLID
VAP
VAP2
0
0
0
0
0
0
0
0
0
0
0.077
0
0
0.002
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.057
0
0
0
0
0
0
0
0
0.998
0.001
0
0
0
0
0
0
0
0.057
0.001
0
0
0
0
0
0
0
0.998
0.001
0
0
0
0
0
0
0
0.054
0
0
0
0
0
0
0
0.001
0
0
0
0
0.001
0
0
0
0
0
0
0
0
0
0.999
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.001
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.054
0
0
0
0
0
0
0
0
0.945
0.001
0
0
0
0
0
0
0
0.054
0.001
0
0
0
0
0
0
0
0.945
0.001
0
0
0
0
0
0
0
0.957
0
0
0
0
0
0
0
0.022
0
0
0
0.005
0.015
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0.013
0.987
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.032
0.968
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5.75
4.749
0.441
85
Appendix C: Fracture experiment Frac43
Summary and Conclusions of the Fracking Experiments.
Introduction
Three experiments have been performed, of which two were successful and one has adequate
measurements. The three experiments were done on cemented fracs in the resulting cores of FE44 and
FE43. The fracs were performed under reservoir conditions. The pore pressure was created with fresh water.
After the experiment, the water composition was analyzed on Ca, Na, Cl and SO4
(
Frac43.1). The fines in the produced water were analyzed by XRD.
The first experiment (with FE44) failed, since the end piece of the reactor was squeezed out of the sleeve.
Annulus oil penetrated the sample.
The second experiment (with FE44), ran well. Nice pressure built up, and no fracture development in the
core. However, the data-acquisition system failed during pressure built-up.
The third experiment (with FE43) also ran well. Nice pressure built up (see Fig.Frac43.1 and
Fig.Frac43.2)and a minor axial compaction (about 3.5 mm or ca. 1.3 %, see Fig.Frac43.1) After the
experiment the core was cut in order to recognize any traces of a new frac.
The experimental procedure was executed as discussed with Maersk in November 2008 and described in
the section “workflow”.
Findings and conclusions
No fracs were created in any of the cores used.
The axial length reduced with 1.3 %. When considering ∆V=3∆L, the volume reduction is about 4 vol.%.
Chalks are much weaker and already are crumble with the differential pressures used on these (partly)
remineralized calcite/anhydrite cores. The stiffness is created of the Anhydrite filling the pores in the
calcite texture. (Perhaps an electron microprobe analysis should be suggested.)
The composition of the produced water showed that dissolution of the core was minimal (HPLC-results,
Fig.Frac43.4 and Fig.Frac43.5) The mineral content of the substrate consisted at the start of only calcite
and at a later stage (when higher differential pressures were used) of mostly calcite and some secondary
gypsum. Note that here calcite fines and SO4 at low temperatures created gypsum in the solution.
The photographs (Fig.Frac43.9)of the slices of the core after cutting show no signs of new fracs, newly
cemented fracs or compaction effects (multi-cracks, pressure solution, etc.). Only an old cemented frac
became visible (see also fig. 44.7).
Work flow
Building the setup
Core in sleeve
Injector and producer caps in the sleeves on both sides of the core
Twinge iron cables around the sleeves and caps to secure them
But the total in the reactor and connect it
Fill the annulus with oil (no extra pressure)
Attach the vacuum pump and vacuum the whole system for (at least) 24 hours
Heat the reactor
Close the valve on the injector side
Uncouple the vacuum pump
Put the valve in the filled water bottle and open valve
Measure the water capacity sucked into the system
86
Calculate the amount of water in the reservoir and the system
Pressure build up
Raise the annulus pressure and its back pressure valve to 20 bar
Start injecting water (10ml/min), there is production
Turn back pressure valve of the production side up a few bars
This will raise injection, production and annulus pressure a few bars
Keep on raising the pressures this way (by stopping the production flow of the experiment)
Always keep the annulus pressure 20 bars above the other two
Do this until annulus pressure is approximately 260 bars and injection and production pressure is
approximately 240 bars
Inject water at 2 ml/min
Turn down the production back pressure valve till water is produced and pressure is 240 bars at the injector
and producer side
Raise annulus pressure with back pressure valve and the oil flow in to 330 bars
Refill ISCO-pump and write down its start up volume
Set ISCO-pump on a constant pressure of 240 bars
Measurements
Before experiment
Length
= 0282
Diameter
= 0099
Weight
= 3401
Water cap.
= 0915
After experiment
Length
Diameter
mm
mm
gr
ml
= 0278.6 mm
= 0099 mm
Start Experiment write Logbook
ET: 500 sec
When raising all three pressures to 260 and 240 bar the back pressure valve of the producer malfunctioned.
Calcite of the last experiment had to be cleaned out.
ET: 1450 sec
Displacer might have gotten a slight accidental bump when the back pressure valve was put back, so any
change is due to this.
ET: 1500 sec
Proceed with the pressure build up.
Annulus pressure is 260 bar and injector and producer pressure is 240 bar, displacement is 1,34. When
raising the annulus pressure to 350 bars the displacer moves to 1,54.
If the displacer becomes more positive the core gets shorter.
ET: 0:31:24
Annulus pressure is 350 bar, injection and production pressure are 250 bar. Total production is 130 gram.
Refill ISCO-pump from 150 ml to 266 ml.
Set ISCO-pump on constant pressure of 240 bar to flow water in the reservoir.
Test 1
Pann
Pinj
Pprod
Displ
Prod
= 335 bar
= 240 bar
= 240 bar
= 1,555
= 157,8 gr
87
ETstart = 00:49:40
Aim
= 70 bar Pprod drop, to get a Pinj - Pprod = 20-30 bar
First try fails; production valve was still closed because of refilling ISCO-pump
2e try Test 1
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 2
= 335 bar
= 240 bar
= 240 bar
= 1,719
= 182,25 gr
= 263 ml
= 00:52:00
= 170 bar Pprod , to get a Pinj - Pprod = 20-30 bar
> 100 ml/min
= 00:53:50
= 1,719 to 1,84
= 350,01 gr
= 93 ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 3
= 335 bar
= 240 bar
= 240 bar
= 1,736
= 351,80 gr
= 263,45 ml
= 01:00:28
= 100 bar Pprod , to get a Pinj - Pprod = 70 bar
> 100 ml/min
= 01:03:50
= 1,736 to 2,683
= 628,0 gr
= 33 ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 4
= 335 bar
= 240 bar
= 240 bar
= 2,505
= 630,7 gr
= 263,6 ml
= 01:10:00
= 50 bar Pprod, to get a Pinj - Pprod = 100 bar
> 100 ml/min
= 01:12:30
= 2,505 to 3,174
= 911,0 gr
= 22 ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
= 336 bar
= 240 bar
= 240 bar
= 3,191 moved by hand to 1,807, because the max could be reached
= 912+4 gr
= 254,9 ml
= 01:23:00
= 0 bar Pprod, to get a Pinj - Pprod = 150 bar
88
q
ETstop
Displm
Prod
ISCO
> 100 ml/min
= 01:25:25
= 1,807 to 1,848
= 912 + 260,6 gr
= 20 ml
Test 5
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 6
= 335 bar
= 240 bar
= 240 bar
= 1,897
= 912 +267,8 gr
= 250,9 ml
= 01:31:30
= 0 bar Pprod, to get a Pinj - Pprod = 180 bar
= 99 ml/min
= 01:33:40
= 1,897 to 2,002
= 912 + 483,7 gr
= 39 ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 7
= 335 bar
= 240 bar
= 240 bar
= 1,943
= 912 + 486,36 gr
= 261,9 ml
= 01:10:00
= 50 bar Pprod, to get a Pinj - Pprod = 175 bar
= 98 ml/min
= 01:40:35
= 1,943 to 1,943
= 912 + 637,5 gr
= ? ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 8
= 335 bar
= 240 bar
= 240 bar
= 1,938
= 912 + 640,8 gr
= 259,8 ml
= 01:45:00
= 100 bar Pprod, to get a Pinj - Pprod = 140 bar, Pinj stays 240 bar!
= 93 ml/min
= 01:40:35
= 1,938 to 1,94
= 912 + 758,4 gr
= ? ml
Pann
Pinj
Pprod
Displ
Prod
= 335 bar
= 240 bar
= 240 bar
= 1,931
= 912 + 760,7 gr
89
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
Test 8
= 252,3 ml
= 01:53:00
= 170 bar Pprod, to get a Pinj - Pprod = 90 bar, Pinj stays 240 bar!
= 50 ml/min
= 01:54:25
= 1,931 to 1,934
= 912 + 829,6 gr
= 192,2 ml
Pann
Pinj
Pprod
Displ
Prod
ISCO
ETstart
Aim
q
ETstop
Displm
Prod
ISCO
= 335 bar
= 240 bar
= 240 bar
= 1,931
= 912 + 831,2 gr
= 189,8 ml
= 01:56:30
= 0 bar Pprod, to get a Pinj - Pprod = 180 bar, Pinj is 184 bar
> 100 ml/min
= 01:57:34
= 1,931 to 2,031
= 912 + 954,4 gr
= 88,2 ml
250
4
test 4
test 5
test 6
200
3,5
test 7
3
2,5
test 3
test 8
2
100
test 1 try 2
test 2
1,5
Displ[mm]
dP[bar]
150
test 9
Pinj-Pprod [bar]
Disp [mm]
1
50
test 1
0,5
-50
7072
6800
6528
6256
5984
5712
5440
5168
4896
4624
4352
4080
3808
3536
3264
2992
2720
2448
2176
1904
1632
1360
816
1088
544
0
272
0
0
-0,5
Time[sec]
Fig.Frac43.1: dP versus Time
90
400
4
350
3,5
3
300
2,5
2
200
1,5
150
Pann [bar]
Disp[mm]
P[bar]
250
Pinj [bar]
Pprod [bar]
Disp [mm]
1
100
0,5
50
0
6950
6672
6394
6116
5838
5560
5282
5004
4726
4448
4170
3892
3614
3336
3058
2780
2502
2224
1946
1668
1390
834
1112
556
0
-0,5
278
0
Time[sec]
Fig.Frac43.2: P and Displacement versus Time
Axial displacement
ratio
dP
0,014
250
0,012
0,01
150
0,008
0,006
100
dP[bar]
Axial displacement ratio
200
0,004
50
0,002
0
7092
6698
6304
5910
5516
5122
4728
4334
3940
3546
3152
2758
2364
1970
1576
788
1182
-0,002
394
0
0
-50
Time[sec]
Fig.Frac43.3: Axial displacement and dP versus Time
91
Resultaten HPLC analyse project Maersk
sample
Frac 43-1
Frac 43-2
Frac 44
kation analyse
g/L Na
g/L Ca
2.50
1.84
1.74
2.04
2.57
1.76
anion analyse
g/L Cl
g/L SO4
<0,1
2.36
<0,1
1.92
<0,1
2.38
Table Frac43.1: HPLC-results
Fig.Frac43.4: XRD-results of the first half of the test
92
Fig.Frac43.5: XRD-results of the second half of the test
Fig.Frac43.6: Photo of the core after frac-test
93
Fig.Frac43.7: Photo of the production side of the core after frac-test
94
Fig.Frac43.8: Photo of the injection side of the core after frac-test
Fracture
cemented by acid
Figure
46
hplc
95
Appendix D: CT-scan filter comparison
In this appendix the filter qualities of the CT-scanner are compared based on the picture
quality and their grayscale histograms. Greyscales are on the X-axis and the amount that
they are present in the picture is on the y-axis. The numbers above the histograms are the
filter names.
2B30
Pixels
12000
10000
8000
6000
Pixels
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
96
2b60
Pixels
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
97
2b70
Pixels
16000
14000
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
98
3b30
Pixels
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
99
3b60
Pixels
9000
8000
7000
6000
5000
Pixels
4000
3000
2000
1000
0
1
20 39 58 77 96 115 134 153 172 191 210 229 248
100
3b70
Pixels
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
101
LungCT2
Pixels
10000
9000
8000
7000
6000
5000
Pixels
4000
3000
2000
1000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
102
LungCT3
Pixels
9000
8000
7000
6000
5000
Pixels
4000
3000
2000
1000
0
1
20 39 58 77 96 115 134 153 172 191 210 229 248
103
LungCT4
Pixels
14000
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
104
LungCT5
Pixels
9000
8000
7000
6000
5000
Pixels
4000
3000
2000
1000
0
1
20 39 58 77 96 115 134 153 172 191 210 229 248
105
LungCT6
Pixels
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
106
LungCT7
Pixels
12000
10000
8000
Pixels
6000
4000
2000
0
1
21 41 61 81 101 121 141 161 181 201 221 241
107
Appendix E: Leica Qwin Scripts
E.1 Script 1
Dialog Box NEXTFILE, in D:\@Quips Rudy\QDG\NEXTFILE.QDG, at x 1028, y 305
On Command3 Call BROWSE
Read image [PAUSE] ( from file ACQFILE$ into ACQOUTPUT )
Colour Transform ( Mono Mode )
Measure frame ( x 4, y 25, Width 496, Height 459 )
Calibrate ( CALVALUE CALUNITS$ per pixel )
ring detection
Detect [PAUSE] ( from grey level 0 to 50, from Image0 into Binary1 )
Measure feature ( plane Binary1, 64 ferets, minimum area: 0, grey image: Image0 )
Selected parameters: Area, X FCP, Y FCP, Roundness, Int.Grey,
MeanGrey, GreyVarianc
Copy Accepted Features ( from Binary1 into Binary2 )
Binary Logical ( C = A XOR B : C Binary3, A Binary1, inverted, B Binary2, inverted )
Binary Amend ( Dilate from Binary3 to Binary4, cycles 13, operator Disc, edge erode on )
Binary Logical ( C = A XOR B : C Binary5, A Binary3, inverted, B Binary4, inverted )
MFEATINPUT = 5
FERETS = 64
MINAREA = 1000
FTRGREY.IMAGE = 0
SYMBOLIC !!!
Measure feature ( plane MFEATINPUT, FERETS ferets, minimum area: MINAREA, grey image: FTRGREY.IMAGE
feature counts into FTRCOUNT(2), results into FTRRESULTS(count,4), statistics into FTRSTATS(8,4) )
Selected parameters: X FCP, Y FCP, MeanGrey, GreyVarianc
Display Feature Results ( x 65, y 426, w 829, h 136 )
GREYRING = FTRRESULTS(1,3)
Display ( GREYRING, 4 digits after '.', tab follows )
eerste meting = referentiewaarde ring
REFRING = GREYRING
Common ( REFRING )
laadt bestanden achtereenvolgens op grond van teller voor de extensie
TELLER MOET VOOR EERSTE PUNT STAAN, zonder leading zero: xxxxxxxxx1.yyyy.zzz
Colour Transform ( Mono Mode )
PATH$ = "D:\test\"
FIRST = VAL(DLG.EDIT1$)
COUNTSTEP = VAL(DLG.EDIT2$)
LAST = VAL(DLG.EDIT3$)
make new directory for corrected images
EXTDLL$ = "D:\naringcorrectie\"
Call Utilities ( MakeDirectory (EXTDLL$ = next subdirectory) )
For ( FILETELLER = FIRST to LAST, step COUNTSTEP )
bereken volgende filenaam
Gosub NEXTFILE
ACQOUTPUT = 0
Read image ( from file ACQFILE$ into ACQOUTPUT, import calibration )
ring detection
Detect ( from grey level 0 to 50, from Image0 into Binary1 )
Measure feature ( plane Binary1, 64 ferets, minimum area: 0, grey image: Image0 )
Selected parameters: Area, X FCP, Y FCP, Roundness, Int.Grey,
MeanGrey, GreyVarianc
Copy Accepted Features ( from Binary1 into Binary2 )
Binary Logical ( C = A XOR B : C Binary3, A Binary1, inverted, B Binary2, inverted )
Binary Amend ( Dilate from Binary3 to Binary4, cycles 13, operator Disc, edge erode on )
Binary Logical ( C = A XOR B : C Binary5, A Binary3, inverted, B Binary4, inverted )
MFEATINPUT = 5
FERETS = 64
MINAREA = 1000
FTRGREY.IMAGE = 0
SYMBOLIC !!!
Measure feature ( plane MFEATINPUT, FERETS ferets, minimum area: MINAREA, grey image: FTRGREY.IMAGE
feature counts into FTRCOUNT(2), results into FTRRESULTS(count,4), statistics into FTRSTATS(8,4) )
Selected parameters: X FCP, Y FCP, MeanGrey, GreyVarianc
Display Feature Results ( x 65, y 426, w 829, h 136 )
GREYRING = FTRRESULTS(1,3)
108
Display ( GREYRING, 4 digits after '.', tab follows )
If ( REFRING>=GREYRING )
GREYDIF = REFRING-GREYRING
GREYUTILOUT = 1
CLRTO = GREYDIF
Grey Util ( Clear GREYUTILOUT to CLRTO )
Grey Arithmetic ( C = A+B : C Image2, A Image0, B Image1 )
Else
GREYDIF = GREYRING-REFRING
GREYUTILOUT = 1
CLRTO = GREYDIF
Grey Util ( Clear GREYUTILOUT to CLRTO )
Grey Arithmetic ( C = B-A : C Image2, A Image1, B Image0 )
Endif
save corrected image2
TEMPACQFILE$ = ACQFILE$
ACQOUTPUT = 2
ACQFILE$ = EXTDLL$+"corr"+STR$(FILETELLER)+EXTENSIE$
Write image ( from ACQOUTPUT into file ACQFILE$, export calibration )
ACQFILE$ = TEMPACQFILE$
Next ( FILETELLER )
============================SUBROUTINE NEXTFILE
Subroutine NEXTFILE
NAAM$ = ACQFILE$
zoek het volgnummer
J = MATCH(".",NAAM$,1)
EXTENSIE$ = RIGHT$(NAAM$,LEN(NAAM$)-J+1)
If ( FILETELLER<10 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-2)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<100 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-3)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<1000 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-4)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
FILENAAMSTAM$ = LEFT$(NAAM$,J-5)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Endif
Endif
Endif
ACQFILE$ = NEXTFILE$
HEBBES:
Return
============================
============================SUBROUTINE BROWSE
Subroutine BROWSE
OPENFILE$ = "D:\a.tif"
FILESPEC$ = "*.tif"
File Open Dialog ( FILESPEC$, FILEEXT$, OPENFILE$, at FILEX, FILEY )
NIEUWEFILE$ = OPENFILE$
Return
E.2 script 2
instruction window
Setup Output Window ( "Core diameter", Close )
Setup Output Window ( "Core diameter", Move to x 37, y -2, w 542, h 202 )
Display ( "Core diameter in memory:", tab follows )
Display ( COREDIAM, 4 digits after '.', no tab follows )
Display Line
Display ( "If this value is correct: fill it in", no tab follows )
Display Line
Display ( "otherwise leave it open, an image for measurement can be choosen", tab follows )
ACQFILE$ = ""
109
asking for core diameter
Input ( COREDIAM )
check on value for initial core diameter
If ( COREDIAM=0 )
if core diameter has no start value, choose an image for measurement
Read image [PAUSE] ( from file ACQFILE$ into ACQOUTPUT, import calibration )
measurement routine of core diameter ......
Binary Logical ( C = Clear : C Binary20, A Binary16, B Binary13 )
Binary Logical ( C = Clear : C Binary21, A Binary16, B Binary13 )
Colour Transform ( Mono Mode )
Measure frame ( x 5, y 9, Width 472, Height 485 )
Image frame ( x 2, y 6, Width 479, Height 494 )
Calibrate ( CALVALUE CALUNITS$ per pixel )
lucht+ring :
Detect [PAUSE] ( from grey level 0 to 130, from Image0 into Binary1 )
Measure feature ( plane Binary1, 64 ferets, minimum area: 0, grey image: Image0 )
Selected parameters: Area, X FCP, Y FCP, Roundness, Int.Grey,
MeanGrey, GreyVarianc
lucht binnen kern geaccepteerd..
Copy Accepted Features ( from Binary1 into Binary2 )
bin3: NOT kern
Binary Logical ( C = A XOR B : C Binary3, A Binary1, inverted, B Binary2, inverted )
Detect [PAUSE] ( from grey level 0 to 115, from Image0 into Binary6 )
bin7: kern min lucht
Binary Logical ( C = A AND B : C Binary7, A Binary2, inverted, B Binary6, inverted )
bin8: hele kern
Binary Identify ( FillHoles from Binary7 to Binary8 )
Binary Amend ( Erode from Binary8 to Binary9, cycles 10, operator Disc, edge erode on )
Detect [PAUSE] ( from grey level 131 to 166, from Image0 into Binary4 )
Detect [PAUSE] ( from grey level 167 to 255, from Image0 into Binary5 )
Detect [PAUSE] ( from grey level 190 to 255, from Image0 into Binary30 )
Detect [PAUSE] ( from grey level 167 to 190, from Image0 into Binary31 )
Binary Logical ( C = A XOR B : C Binary10, A Binary8, B Binary7 )
bin11: calciet
Binary Logical ( C = A AND B : C Binary11, A Binary4, B Binary9 )
bin12: anhydriet
Binary Logical ( C = A AND B : C Binary12, A Binary5, B Binary9 )
bin13: wormholes
Binary Logical ( C = A AND B : C Binary13, A Binary2, B Binary10 )
Binary Logical ( C = A OR B : C Binary14, A Binary11, B Binary12 )
bin15: calciet+anhydriet+wormholes
Binary Logical ( C = A OR B : C Binary15, A Binary13, B Binary14 )
Binary Logical ( C = A XOR B : C Binary16, A Binary4, B Binary5 )
bin17: hele kern schoon, ongelijkmatige buitenrand
Binary Logical ( C = A XOR B : C Binary17, A Binary16, B Binary13 )
Binary Amend ( Close from Binary17 to Binary18, cycles 30, operator Disc, edge erode on )
Clear Accepts
MFEATINPUT = 18
FERETS = 64
MINAREA = 20
FTRGREY.IMAGE = 0
SYMBOLIC !!!
Measure feature ( plane MFEATINPUT, FERETS ferets, minimum area: MINAREA, grey image: FTRGREY.IMAGE
feature counts into FTRCOUNT(2), results into FTRRESULTS(count,7), statistics into FTRSTATS(8,7) )
Selected parameters: X FCP, Y FCP, Length, Breadth, XCentroid,
YCentroid, EquivDiam
Display Feature Results ( x 31, y 785, w 815, h 144 )
omgezet in COMMENT: DDE Read ( CALVALUE, from channel #3, item name "X,Ycoordinaten", no timeout )
berekening kerncirkel...
KERNRANDKRIMP = 5
GRAPHNX = 2
GRAPHWID = FTRRESULTS(1,3)-KERNRANDKRIMP
COREDIAM = GRAPHWID
GRAPHORGX = FTRRESULTS(1,5)
GRAPHORGY = FTRRESULTS(1,6)
GRAPHTHIK = 2
GRAPHOUT = 20
tonen kerncirkel...
SYMBOLIC !!!
Graphics ( Rings, Number GRAPHNX, Diameter GRAPHWID, Origin GRAPHORGX x GRAPHORGY,
110
Thickness GRAPHTHIK, to GRAPHOUT Cleared )
GRAPHORNT = 0
GRAPHSPAC = 90
Graphics ( Spokes, Number GRAPHNX, Diameter GRAPHWID, Origin GRAPHORGX x GRAPHORGY,
Thickness GRAPHTHIK, Orientation GRAPHORNT, Angle GRAPHSPAC, to GRAPHOUT )
LOGINPUTA = GRAPHOUT
LOGOUTPUT = GRAPHOUT+1
Binary Logical ( copy LOGINPUTA to LOGOUTPUT )
Display ( Image0 (on), frames (on,on), planes (off,off,off,off,off,21), lut 0, x 0, y 0, z 1, Reduction off )
example of possible output to screen:
Display Line
Setup Output Window ( "Core diameter", Close )
Setup Output Window ( "Core diameter", Move to x 37, y -2, w 542, h 202 )
Display ( "Core diameter in memory:", tab follows )
Display ( COREDIAM, 4 digits after '.', no tab follows )
Display Line
If ( ACQFILE$<>"" )
Display Line
Display ( "used image for diameter measurement:", no tab follows )
Display Line
Display ( ACQFILE$, no tab follows )
Endif
Endif
=======================================================================
laadt bestanden achtereenvolgens op grond van teller voor de extensie
TELLER MOET VOOR EERSTE PUNT STAAN, zonder leading zero: xxxxxxxxx1.yyyy.zzz
Colour Transform ( Mono Mode )
>>>>>>>>>>>>>>>>>>>>>>
PATH$ = "G:\Qwinuitkosten\"
<<<<<<<<<<<<<<<<<<<<
>>>>>>>>>>>>> locatie van Nextfile.QDG aanpassen !
Dialog Box NEXTFILE, in G:\EindQuipsen\NEXTFILE.QDG, at x 1028, y 305
On Command3 Call BROWSE
FIRST = VAL(DLG.EDIT1$)
COUNTSTEP = VAL(DLG.EDIT2$)
LAST = VAL(DLG.EDIT3$)
Read image [PAUSE] ( from file ACQFILE$ into ACQOUTPUT, import calibration )
For ( FILETELLER = FIRST to LAST, step COUNTSTEP )
voer opdrachten uit
=======================================================================
now that the core diameter has a value, start with the analysis ....
here follows the original code which uses COREDIAM as reference circle diameter and calculates its centre for each slice
remark: the CLOSE command uses now 31 cycles
You can also integrate NEXTFILE (or TEST) to make a loop
Binary Logical ( C = Clear : C Binary20, A Binary16, B Binary13 )
Binary Logical ( C = Clear : C Binary21, A Binary16, B Binary13 )
Image frame ( x 2, y 2, Width 479, Height 494 )
Read image ( from file ACQFILE$ into ACQOUTPUT )
Colour Transform ( Mono Mode )
Calibrate ( CALVALUE CALUNITS$ per pixel )
lucht+ring :
Detect ( from grey level 0 to 115, from Image0 into Binary1 )
Measure feature ( plane Binary1, 64 ferets, minimum area: 0, grey image: Image0 )
Selected parameters: Area, X FCP, Y FCP, Roundness, Int.Grey,
MeanGrey, GreyVarianc
lucht binnen kern geaccepteerd..
Copy Accepted Features ( from Binary1 into Binary2 )
bin3: NOT kern
Binary Logical ( C = A XOR B : C Binary3, A Binary1, inverted, B Binary2, inverted )
Detect ( from grey level 0 to 130, from Image0 into Binary6 )
bin7: kern min lucht
Binary Logical ( C = A AND B : C Binary7, A Binary2, inverted, B Binary6, inverted )
bin8: hele kern
Binary Identify ( FillHoles from Binary7 to Binary8 )
Binary Amend ( Erode from Binary8 to Binary9, cycles 10, operator Disc, edge erode on )
============================insert detect waardes van eerste meting!!!!!!
Calcite waarde
Detect ( from grey level 116 to 174, from Image0 into Binary4 )
anhydrite en fossielen waarde
Detect ( from grey level 175 to 255, from Image0 into Binary5 )
111
fossielen waarde
Detect ( from grey level 175 to 255, from Image0 into Binary30 )
============================insert detect waardes van eerste meting!!!!!!
Binary Logical ( C = A XOR B : C Binary10, A Binary8, B Binary7 )
bin11: calciet
Binary Logical ( C = A AND B : C Binary11, A Binary4, B Binary9 )
bin12: anhydriet
Binary Logical ( C = A AND B : C Binary12, A Binary5, B Binary9 )
bin13: wormholes
Binary Logical ( C = A AND B : C Binary13, A Binary2, B Binary10 )
Binary Logical ( C = A OR B : C Binary14, A Binary11, B Binary12 )
bin15: calciet+anhydriet+wormholes
Binary Logical ( C = A OR B : C Binary15, A Binary13, B Binary14 )
Binary Logical ( C = A XOR B : C Binary16, A Binary4, B Binary5 )
bin17: hele kern schoon, ongelijkmatige buitenrand
Binary Logical ( C = A XOR B : C Binary17, A Binary16, B Binary13 )
-----------------------------------------------------------------------------------------------------------------------------------------------------------------Clear Accepts
FACCLOWLIM1 = 150
>>>>>>>> jij had: FACCLOWLIM2 = 200000
>>>>>>>> maar het moet zijn
FACCUPLIM1 = 200000
SYMBOLIC!!!
Feature Accept :
Area from FACCLOWLIM1 to FACCUPLIM1
feature counts into FTRCOUNT(2)
MFEATINPUT = 17
FERETS = 64
MINAREA = 20
FTRGREY.IMAGE = 0
SYMBOLIC!!!
Measure feature ( plane MFEATINPUT, FERETS ferets, minimum area: MINAREA, grey image: FTRGREY.IMAGE
feature counts into FTRCOUNT(2), results into FTRRESULTS(count,3), statistics into FTRSTATS(8,3) )
Selected parameters: Area, X FCP, Y FCP
>>>>>>>> jij had: Display Field Results ( x 64, y 716, w 832, h 281 )
>>>>>>>> maar het moet zijn
Display Feature Results ( x 31, y 785, w 815, h 144 )
MFEATINPUT = 17
FACCOUTPUT = 18
Copy Accepted Features ( from MFEATINPUT into FACCOUTPUT )
Binary Amend ( Close from Binary18 to Binary19, cycles 31, operator Disc, edge erode on )
-----------------------------------------------------------------------------------------------------------------------------------------------------------------Clear Accepts
>>>>>>>> jij had: MFEATINPUT = 18
>>>>>>>> maar het moet zijn
MFEATINPUT = 19
FERETS = 64
MINAREA = 20
FTRGREY.IMAGE = 0
SYMBOLIC !!!
Measure feature ( plane MFEATINPUT, FERETS ferets, minimum area: MINAREA, grey image: FTRGREY.IMAGE
feature counts into FTRCOUNT(2), results into FTRRESULTS(count,7), statistics into FTRSTATS(8,7) )
Selected parameters: X FCP, Y FCP, Length, Breadth, XCentroid,
YCentroid, EquivDiam
Display Feature Results ( x 31, y 785, w 815, h 144 )
omgezet in COMMENT: DDE Read ( CALVALUE, from channel #3, item name "X,Ycoordinaten", no timeout )
berekening kerncirkel...
KERNRANDKRIMP = 5
GRAPHNX = 2
GRAPHWID = COREDIAM
GRAPHORGX = FTRRESULTS(1,5)
GRAPHORGY = FTRRESULTS(1,6)
GRAPHTHIK = 2
GRAPHOUT = 20
tonen kerncirkel...
SYMBOLIC !!!
Graphics ( Rings, Number GRAPHNX, Diameter GRAPHWID, Origin GRAPHORGX x GRAPHORGY,
112
Thickness GRAPHTHIK, to GRAPHOUT Cleared )
GRAPHORNT = 0
GRAPHSPAC = 90
Graphics ( Spokes, Number GRAPHNX, Diameter GRAPHWID, Origin GRAPHORGX x GRAPHORGY,
Thickness GRAPHTHIK, Orientation GRAPHORNT, Angle GRAPHSPAC, to GRAPHOUT )
LOGINPUTA = GRAPHOUT
LOGOUTPUT = GRAPHOUT+1
Binary Logical ( copy LOGINPUTA to LOGOUTPUT )
Display ( Image0 (on), frames (on,on), planes (off,off,off,off,off,21), lut 0, x 0, y 0, z 1, Reduction off )
Setup Output Window ( "Core diameter", Close )
Setup Output Window ( "results", Restore )
Display ( "analysed image:", tab follows )
Display Line
Display ( ACQFILE$, tab follows )
Binary Identify ( FillHoles from Binary21 to Binary22 )
Binary Amend ( Erode from Binary22 to Binary23, cycles 15, operator Disc, edge erode on )
bin24: calciet
Binary Logical ( C = A AND B : C Binary24, A Binary4, B Binary23 )
bin31: anhydriet
Binary Logical ( C = A AND B : C Binary25, A Binary5, B Binary23 )
Binary Logical ( C = A AND B : C Binary31, A Binary25, B Binary30, inverted )
bin26: wormholes
Binary Logical ( C = A AND B : C Binary26, A Binary2, B Binary23 )
Binary Logical ( C = A OR B : C Binary27, A Binary24, B Binary25 )
bin28: calciet+anhydriet+wormholes
Binary Logical ( C = A OR B : C Binary28, A Binary26, B Binary27 )
bin29: Fracture
Binary Logical ( C = A XOR B : C Binary29, A Binary23, B Binary28 )
bin32: Fossils
Binary Logical ( C = A AND B : C Binary32, A Binary30, B Binary23 )
and here, within the loop, the measured data can be saved
>>>>>>>>>>>>>>>>>>>>>>>>> opslaan toegevoegd
Binary Identify ( FillHoles from Binary21 to Binary22 )
Binary Amend ( Erode from Binary22 to Binary23, cycles 15, operator Disc, edge erode on )
bin24: calciet
Binary Logical ( C = A AND B : C Binary24, A Binary4, B Binary23 )
OUTPUT
LOGOUTPUT = 24
COMPONENT$ = "calcite"
Gosub WRITEBINARY
bin31: anhydriet
Binary Logical ( C = A AND B : C Binary25, A Binary5, B Binary23 )
OUTPUT
LOGOUTPUT = 31
COMPONENT$ = "anhydrite"
Gosub WRITEBINARY
bin26: wormholes
Binary Logical ( C = A AND B : C Binary26, A Binary2, B Binary23 )
Binary Logical ( C = A OR B : C Binary27, A Binary24, B Binary25 )
OUTPUT
LOGOUTPUT = 26
COMPONENT$ = "wormholes"
Gosub WRITEBINARY
bin28: calciet+anhydriet+wormholes
Binary Logical ( C = A OR B : C Binary28, A Binary26, B Binary27 )
OUTPUT
LOGOUTPUT = 28
COMPONENT$ = "calc+anhydr+wormh+fos"
Gosub WRITEBINARY
bin29: Fracture
Binary Logical ( C = A XOR B : C Binary29, A Binary23, B Binary28 )
OUTPUT
LOGOUTPUT = 29
COMPONENT$ = "fracture"
Gosub WRITEBINARY
bin29: Fossils
Binary Logical ( C = A XOR B : C Binary29, A Binary23, B Binary28 )
OUTPUT
LOGOUTPUT = 32
COMPONENT$ = "fossils"
113
Gosub WRITEBINARY
<<<<<<<<<<<<<<<<<<<<
bereken volgende filenaam
Gosub NEXTFILE
Read image ( from file ACQFILE$ into ACQOUTPUT, import calibration )
Next ( FILETELLER )
============================ SUBROUTINES ===============================
============================SUBROUTINE WRITEBINARY
Subroutine WRITEBINARY
SYMBOLIC!!!
LOGFILE$ = PATH$+COMPONENT$+STR$(FILETELLER)+".TIF"
Write binary image ( from LOGOUTPUT into file LOGFILE$ )
Setup Output Window ( "Routine Output", Move to x 156, y 688, w 464, h 197 )
Display ( LOGFILE$, tab follows )
Display Line
<<<<<<<<<<<<<<<<<<<<<<<
============================SUBROUTINE NEXTFILE
Subroutine NEXTFILE
NAAM$ = ACQFILE$
zoek het volgnummer
J = MATCH(".",NAAM$,1)
EXTENSIE$ = RIGHT$(NAAM$,LEN(NAAM$)-J+1)
If ( FILETELLER<10 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-2)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<100 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-3)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<1000 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-4)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
FILENAAMSTAM$ = LEFT$(NAAM$,J-5)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Endif
Endif
Endif
ACQFILE$ = NEXTFILE$
HEBBES:
Return
============================
============================SUBROUTINE BROWSE
Subroutine BROWSE
OPENFILE$ = "D:\a.tif"
FILESPEC$ = "*.tif"
File Open Dialog ( FILESPEC$, FILEEXT$, OPENFILE$, at FILEX, FILEY )
NIEUWEFILE$ = OPENFILE$
Return
114
E.3 Script 3
laadt bestanden achtereenvolgens op grond van teller voor de extensie
TELLER MOET VOOR EERSTE PUNT STAAN, zonder leading zero: xxxxxxxxx1.yyyy.zzz
Colour Transform ( Mono Mode )
PATH$ = "D:\test\"
Wegschrijven naar file
Open File ( G:\DDE.Q5D, channel #1 )
Wegschrijven naar Excel
DDE.APP$ = "Excel"
DDE.NAME$ = "G:\concentration.xls"
DDE.CHAN = 2
DDE.ROWCHAR$ = "R"
DDE.COLCHAR$ = "C"
DDE Initiate ( DDE.APP$, DDE.NAME$ on channel #DDE.CHAN, row char DDE.ROWCHAR$, column char DDE.COLCHAR$ )
Dialog Box NEXTFILE, in G:\EindQuipsen\NEXTFILE.QDG, at x 1028, y 305
On Command3 Call BROWSE
FIRST = VAL(DLG.EDIT1$)
COUNTSTEP = VAL(DLG.EDIT2$)
LAST = VAL(DLG.EDIT3$)
Read image [PAUSE] ( from file ACQFILE$ into ACQOUTPUT, import calibration )
For ( FILETELLER = FIRST to LAST, step COUNTSTEP )
voer opdrachten uit
LOGFILE$ = PATH$+"bin"+STR$(FILETELLER)+".TIF"
Detect ( from grey level 1 to 1, from Image0 into Binary0 )
Measure field ( plane Binary0 )
Selected parameters: Area, Area Fract, Area%
Display Field Results ( x 64, y 716, w 832, h 281 )
Wegschrijven naar File
File Field Results ( channel #1 )
Wegschrijven naar Excel
DDE Send Field Results ( channel #2, row 1, column 1 )
SYMBOLIC!!!
Write binary image ( from LOGOUTPUT into file LOGFILE$ )
Setup Output Window ( "Routine Output", Move to x 156, y 688, w 464, h 197 )
Display ( LOGFILE$, tab follows )
Display Line
bereken volgende filenaam
Gosub NEXTFILE
Read image ( from file ACQFILE$ into ACQOUTPUT, import calibration )
Next ( FILETELLER )
============================SUBROUTINE NEXTFILE
Subroutine NEXTFILE
NAAM$ = ACQFILE$
zoek het volgnummer
J = MATCH(".",NAAM$,1)
EXTENSIE$ = RIGHT$(NAAM$,LEN(NAAM$)-J+1)
If ( FILETELLER<10 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-2)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<100 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-3)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
If ( FILETELLER<1000 )
FILENAAMSTAM$ = LEFT$(NAAM$,J-4)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Else
FILENAAMSTAM$ = LEFT$(NAAM$,J-5)
NEXTFILE$ = FILENAAMSTAM$+STR$(FILETELLER+COUNTSTEP)+EXTENSIE$
Endif
Endif
Endif
ACQFILE$ = NEXTFILE$
HEBBES:
Return
============================SUBROUTINE BROWSE
115
Subroutine BROWSE
OPENFILE$ = "D:\a.tif"
FILESPEC$ = "*.tif"
File Open Dialog ( FILESPEC$, FILEEXT$, OPENFILE$, at FILEX, FILEY )
NIEUWEFILE$ = OPENFILE$
Return
116
Appendix F: Volume percentages according to mass balance equations and Modelling
Fe38
nr of empties
5
All[%]
Average[%]
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 10,36302 87,64702 0,012872
0,00411 0,796249
Measured
Weigt(before)
2,025 [kg]
SO4 injected
0,190198 [kg]
Weight(after) ?
[kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
1,826877
0,269447
0
2,096324
Fe39
nr of empties
2
All[%]
Average[%]
[kg]
[kg]
[kg]
[kg]
20,25 mol
1,981228 mol
Percentage
87,14669
12,85331
0
100
SO4
CaCO3
CaSO4
CaCl2
18,26877 mol
1,981228 mol
mol
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 1,196339 98,06773 0,014623 0,013712 0,617788
Measured
Weigt(before)
SO4 injected
Weight(after)
2,138 [kg]
0,135022 [kg]
2,171 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
1,997353
0,191281
0
2,188633
[kg]
[kg]
[kg]
[kg]
21,38 mol
1,406475 mol
Percentage
91,26027
8,739729
0
100
Fos[%]
0,012872
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
87,64702 %
CaSO4
10,36302 %
Macropores 0,796249 %
Volumepercentages of the images(IA)
89,42658 %
10,57342 %
0%
Density
CaCO3
2,71
2,33
CaSO4.2H2
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Fos[%]
0,014624
SO4
CaCO3
CaSO4
CaCl2
19,97353 mol
1,406475 mol
mol
molmass
96
100
136
110,978
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
98,06773 %
CaSO4
1,196339 %
Macropores 0,617788 %
Volumepercentages of the images(IA)
98,79479 %
1,205209 %
0%
117
Fe40
nr of empties
6
All[%]
Average[%]
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 5,405649 93,28712 0,049687 0,031926 0,653547
Measured
Weigt(before)
SO4 injected
Weight(after)
2,154 [kg]
0,081442 [kg]
2,174 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,069165
0,115376
0
2,184541
Fe42
nr of empties
5
All[%]
Average[%]
[kg]
[kg]
[kg]
[kg]
21,54 mol
0,84835 mol
Percentage
94,71854
5,281458
0
100
SO4
CaCO3
CaSO4
CaCl2
20,69165 mol
0,84835 mol
mol
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 9,797516 87,90424 0,014477 0,185672 0,992258
Measured
Weigt(before)
SO4 injected
Weight(after)
2,58 [kg]
0,277521 [kg]
2,634 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,290915
0,393155
0
2,68407
[kg]
[kg]
[kg]
[kg]
25,8 mol
2,890847 mol
Percentage
85,35228
14,64772
0
100
Fos[%]
0,049695
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
93,28712 %
CaSO4
5,405649 %
Macropores 0,653547 %
Volumepercentages of the images(IA)
94,52275 %
5,477249 %
0%
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Fos[%]
0,014502
SO4
CaCO3
CaSO4
CaCl2
22,90915 mol
2,890847 mol
mol
molmass
96
100
136
110,978
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
87,90424 %
CaSO4
9,797516 %
Macropores 0,992258 %
Volumepercentages of the images(IA)
89,97202 %
10,02798 %
0%
118
Fe43
nr of empties
5
All[%]
Average[%]
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 15,63777 81,77949 0,011944 0,126001 0,969445
Measured
Weigt(before)
SO4 injected
Weight(after)
3,233 [kg]
0,277521 [kg]
3,401 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,943915
0,393155
0
3,33707
Fe44
nr of empties
6
All[%]
Average[%]
100
[kg]
[kg]
[kg]
[kg]
32,33 mol
2,890847 mol
Percentage
88,21855
11,78145
0
100
SO4
CaCO3
CaSO4
CaCl2
29,43915 mol
2,890847 mol
mol
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
2870,58
10349,8 1,211896 2,292818
0,00017
Measured
Weigt(before)
SO4 injected
Weight(after)
3,352 [kg]
0,526365 [kg]
3,54 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,803704
0,745683
0
3,549387
[kg]
[kg]
[kg]
[kg]
33,52 mol
5,482964 mol
Percentage
78,99121
21,00879
0
100
Fos[%]
0,011946
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
81,77949 %
CaSO4
15,63777 %
Macropores 0,969445 %
Volumepercentages of the images(IA)
83,94763 %
16,05237 %
0%
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Fos[%]
1,227748
SO4
CaCO3
CaSO4
CaCl2
28,03704 mol
5,482964 mol
mol
molmass
96
100
136
110,978
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
10349,8 %
CaSO4
2870,58 %
Macropores 0,00017 %
Volumepercentages of the images(IA)
78,28671 %
21,71329 %
0%
119
Fe45
nr of empties
7
All[%]
Average[%]
Measured
Weigt(before)
SO4 injected
Weight(after)
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 23,91224 71,76252 0,027092 0,490965 1,817604
3,027 [kg]
0,503 [kg]
3,12 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,502396
0,713461
0
3,215857
Fe48
nr of empties
23
All[%]
Average[%]
[kg]
[kg]
[kg]
[kg]
Percentage
77,81427
22,18573
0
100
SO4
CaCO3
CaSO4
CaCl2
25,02396 mol
5,24604 mol
mol
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 28,84657 67,56838 0,019918 0,067383 1,208485
Measured
Weigt(before)
3,329 [kg]
SO4 injected
0,790221 [kg]
Weight(after)
3,688 [kg]
Weight(directly
3,922 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
30,27 mol
5,24604 mol
2,505853
1,11948
0
3,625333
[kg]
[kg]
[kg]
[kg]
33,29 mol
8,231469 mol
Percentage
69,12064
30,87936
0
100
Fos[%]
0,027166
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
71,76252 %
CaSO4
23,91224 %
Macropores 1,817604 %
Volumepercentages of the images(IA)
75,00674 %
24,99326 %
0%
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Density
CaCO3
2,71
CaSO4.2H2
2,33
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Fos[%]
0,01993
\
SO4
CaCO3
CaSO4
CaCl2
25,05853 mol
8,231469 mol
0 mol
molmass
96
100
136
110,978
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
67,56838 %
CaSO4
28,84657 %
Macropores 1,208485 %
Volumepercentages of the images(IA)
70,08082 %
29,91918 %
0%
120
Fe49
nr of empties
14
All[%]
Average[%]
Measured
Weigt(before)
SO4 injected
Weight(after)
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 24,12368 72,81211 0,007391 0,038516 1,179038
3,331 [kg]
0,52142 [kg]
3,564 [kg]
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
2,787854
0,738678
0
3,526533
Fe50
nr of empties
20
All[%]
Average[%]
Measured
Weigt(before)
SO4 injected
Weight(after)
Weight(directly
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
100
[kg]
[kg]
[kg]
[kg]
Percentage
79,05369
20,94631
0
100
SO4
CaCO3
CaSO4
CaCl2
27,87854 mol
5,431458 mol
0 mol
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
72,81211 %
CaSO4
24,12368 %
Macropores 1,179038 %
Volumepercentages of the images(IA)
75,11375 %
24,88625 %
0%
Density
CaCO3
2,71
2,33
CaSO4.2H2
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Density
CaCO3
2,71
2,33
CaSO4.2H2
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
24,0163 71,17384 0,107291 1,685679 2,425608
3,031 [kg]
551,087 [kg]
3,188 [kg]
3,713
2,456951
0,780707
0
3,237658
33,31 mol
5,431458 mol
Fos[%]
0,007391
[kg]
[kg]
[kg]
[kg]
30,31 mol
5,74049 mol
Percentage
75,88668
24,11332
0
100
SO4
CaCO3
CaSO4
CaCl2
24,56951 mol
5,74049 mol
0 mol
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
71,17384 %
CaSO4
24,0163 %
Macropores 2,425608 %
Volumepercentages of the images(IA)
74,77018 %
25,22982 %
0%
121
Fe51
nr of empties
5
All[%]
Average[%]
Measured
Weigt(before)
SO4 injected
Weight(after)
Calculated
CaCO3(after)
CaSO4(after)
CaCl2(after)
Weight(total)
Anh[%]
Cal[%]
Fos[%]
Frac[%]
Pore[%]
100 30,57975 64,38549 0,042423 1,031798 1,490882
3,199 [kg]
0,8154 [kg]
3,539 [kg]
2,3496
1,155184
0
3,504784
[kg]
[kg]
[kg]
[kg]
31,99 mol
8,494 mol
Percentage
67,03979
32,96021
0
100
Fos[%]
0,042432
SO4
CaCO3
CaSO4
CaCl2
23,496 mol
8,494 mol
0 mol
molmass
96
100
136
110,978
g/mol
g/mol
g/mol
g/mol
Image Analysis
CaCO3
64,38549 %
CaSO4
30,57975 %
Macropores 1,490882 %
Volumepercentages of the images(IA)
67,79901 %
32,20099 %
0%
Density
CaCO3
2,71
2,33
CaSO4.2H2
CaSO4
2,95
CaCl2
2,159
NaCl
2,179
g/cm3
g/cm3
g/cm3
g/cm3
g/cm3
122
Appendix G: Experimental results of all core flooding
experiments compared
Experimental results of all core flooding experiments compared
FE-34
FE-35
FE-36
FE-37
Chalk original
y
y
y
y
After experiment
y
Chalk &
Chalk &
Chalk &
anhydrite
anhydrite
anhydrite
0,5
0,5
1
2
Injection rate [ml/min]
None
10
5
2
Duration
None
5:44:20
24:16:00
22:17:00
669
610
695
610
45
43
47
42
Brine only
34 PV
60 PV
14 PV
No
24 PV
No
9.5 PV
Fracture width [mm]
of
acid
injection
Pore Volume (based
on brine inj.) [cc]
Porosity
(based
on
brine inj.) [%]
Pore Volume (based
on density) [cc]
Porosity
(based
on
density) [%]
Total
PV
of
acid
injection
Acid breakthrough
breakthrough
Fracture cemented
Almost fully
Partly
Almost fully
Almost fully
No
Multiple
Single
Multiple
Fully, partly, none
Matrix conversion
Low, med, high
Wormholes
Single or multiple
123
Cemented wormholes
No
Yes
No
Yes
Micro porosity at the
No
Yes
Yes
Yes
No
No
Yes
Yes
Parallel
Perpendicular
production side.
Hydraulic
related
fractures
to
Z-axis
direction
Scans
Average permeability
[m^2]
Permeability
change[m^2]
Acids
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
124
Experimental results of all core flooding experiments compared
FE-38
FE-39
FE-40
FE-41
y
y
y
y
Chalk &
Chalk &
Chalk &
Chalk &
anhydrite
anhydrite
anhydrite
anhydrite
Fracture width [mm]
1
1
2
2
Injection rate [ml/min]
2
5
5
2
22:40:20
4:58:20
3:06:23
10:54:30
520
515
495
540
on
38
34
34
30
Pore Volume (based
622
707
795
825
45
47
46
46
2721
1512
912
1309
No acid
6100
N.N.
No acid
Chalk original
After experiment
Duration
of
acid
injection
Pore Volume (based
on brine inj.) [ml]
Porosity
(based
brine inj.) [%]
on density) [ml]
Porosity
(based
on
density) [%]
Acid injected[ml]
Acid
breakthrough
(sec)
Fracture cemented
breakthrough
breakthrough
Fully
Fully
Partly
Partly
High
High
Low
No scans after
Fully, partly, none
Matrix conversion
Low, med, high
Wormholes
experiment
Multiple
Multiple
Single
Single
Yes
Yes
Yes
No scans after
Single or multiple
Cemented wormholes
experiment
Micro porosity at the
125
production side.
Hydraulic
related
fractures
to
No
No
No
Yes
Before & after
After
Before & after
Before
4E-15
3E-15
2E-15
5E-15
No
No
Yes
No
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
Z-axis
direction
Scans
Average permeability
[m^2]
Permeability
change[m^2]
Acids
126
Experimental results of all core flooding experiments compared
FE-42
Chalk original
FE-43
FE-44
FE-45
y
y
y
y
Chalk &
Chalk &
Chalk &
Chalk &
anhydrite
anhydrite
anhydrite
anhydrite
Fracture width [mm]
2
2
3
2
Injection rate [ml/min]
2
2
2
2
7:15:20
27:05:00
48:00:30
45:17:00
585
975
600
810
on
33
45
26
39
Pore Volume (based
816
977
1071
981
46
45
46
47
Acid injected [ml]
871
3087
5855
5434
Acid
780
36000
41100
41750
Partly
Fully
Fully
Partly
Low
High
High
High
Single
Multiple
Multiple
Multiple
Partly
Yes
Partly
Yes
After experiment
Duration
of
acid
injection
Pore Volume (based
on brine inj.) [cc]
Porosity
(based
brine inj.) [%]
on density) [cc]
Porosity
(based
on
density) [%]
breakthrough
[sec]
Fracture cemented
Fully, partly, none
Matrix conversion
Low, med, high
Wormholes
Single or multiple
Cemented wormholes
Micro porosity at the
production side.
127
Hydraulic
related
fractures
to
No
No
No
Yes
Before & after
After
After
After
5E-15
4E-15
6E-15
4E-15
No
Yes
Yes
No
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
Z-axis
direction
Scans
Average permeability
[m^2]
Permeability
change[m^2]
Acids
128
Experimental results of all core flooding experiments compared
FE-48
Chalk original
FE-49
FE-50
FE-51
y
y
y
y
Chalk &
Chalk &
Chalk &
Chalk &
anhydrite
anhydrite
anhydrite
anhydrite
Fracture width [mm]
3
3
3
3
Injection rate [ml/min]
2
2
2
2
73:30:00
48:00:00
51:05:00
66:35:00
395
505
600
510
on
18
22
29
24
Pore Volume (based
989
1036
945
975
45
46
46
46
Acid injected [ml]
8165
5800
Leak
6500
Acid
29500
29250
83960
51580
Fully
?
Fully
Fully
High
?
High
High
Multiple
?
Single
Multiple
Partly
?
Partly
Yes
After experiment
Duration
of
acid
injection
Pore Volume (based
on brine inj.) [cc]
Porosity
(based
brine inj.) [%]
on density) [cc]
Porosity
(based
on
density) [%]
breakthrough
[sec]
Fracture cemented
Fully, partly, none
Matrix conversion
Low, med, high
Wormholes
Single or multiple
Cemented wormholes
Micro porosity at the
production side.
129
Hydraulic
related
fractures
to
No
?
Yes
Yes
Before & after
Before
Before
Before & After
4E-15
4E-15
4E-15
4E-15
No
Yes
Yes
Yes
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.3 M HCl &
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
0.9 M H2SO4
Z-axis
direction
Scans
Average permeability
[m^2]
Permeability
change[m^2]
Acids
130
131
Appendices Part 2: Experimental results compared
Sample ID: FE 38
Weight
Before: 2025 [g], After: 2472 [g]
Length
178 [mm]
Diameter
99.8 [mm]
Goal Experiment
Core flooding experiment
Fracture width
1 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 520 [ml], 0.38, Wet weight porosity = 0.45
2721 [ml]
Not measured
1.98 [mol]
Yes HPLC only
Yes; before and after
Experimental history
Pore fluid: brine
16 June: Brine injection and reparation of the back pressure gauge, the leakage of the
production line.
17 June: started with the injection of acid. Minor technical problems.
18 June: End of the experiment.
Observation and comments
Any technical problem during the experiment.
Visual analysis and conclusive remarks.
During the acid injection, the differential pressure over the system was kept at about 2-4
bars. The fluctuations as found in all pressures (i.e. pressure drops and recline) are
probably due to escape of CO2 and associated lowering of the pore pressure (Figure
38.1,2). The fluid analysis shows that after ca. 4 hrs acid breaks through and after
another 3 hrs the brine was replaced by acid (Na+ goes to 0) . Chemical analysis of the
produced fluid showed that anhydrite precipitation still happens after the pressure
FE38
1
dropped. The concentration of SO4 in original acid is 70 g/l in the produced fluid less
than 5 g/l. Up to 31 hrs no significant change in acid composition was recognized, which
means that continuously replacement of carbonate by anhydrite took place.
The CT-scans show that the fractures closed by anhydrite formation during this
experiment. The question of the influence of the used pore fluid brine and the annular
pressure remains open. As for the experiment FE35 it was anhydrite which has cemented
the fracture and NOT fines of the original calcite. Furthermore, it has been disseminated
to different zones in the core, which means that the main flow path was not through the
original fracture system.
The CT-scans (figures 38.9-11) also show that the fracture is closed, and anhydrite has
been produced during this experiment in the fracture and around the wormholes.
Conclusion
• Precipitation of anhydrite occurs in the core and recrystalization took place
around the wormholes.
• The high permeable 1 mm fracture has been cemented.
• The wormholes reached half way the core and permeability remained high.
Since the SO42—concentration remained low in the production fluid, it is
concluded that recrystalization continued till the end of the experiment.
Conclusion on permeability (Fig. 38.4).
Up to ca. 110.000 s, permeability remained more or less constant at about 5*10-15- m2.
After repair of the back pressure, the permeability lowered to 1*10-15- m2. No flow
apparently induces minor deposition of anhydrite?
FE38
2
Experimental results
120
pressures increase to P max
Pressures Fluctuation
Pressure [bars]
100
100
80
80
60
P_product
P_annular
60
40
Dp
20
T_Reservoir
40
20
0
0
-20
0:00
P_injection
Decrease of pressure difference
Start acid injection
6:00
12:00
-20
18:00
24:00
30:00
36:00
42:00
48:00
Tem p [deg C]
Time [hours]
Fig.38.1. : Pressures and temperature versus time. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore
pressure P(1,2) and T_reservoir: temperature in the sample (°C).
FE38 Qinject=2ml/min
100
80
Pressure [Bar]
60
P1
DP
40
P2
P3
20
0
0.000
1.000
2.000
3.000
4.000
5.000
6.000
-20
Cum_injection/Volume_pores
Fig.38.2. : Pressures versus Pore volumes. 0.00 is start of acid injection. P1: Injection
pressure, P2: production pressure, P3: annular pressure, Dp: differential pore pressure
P(1,2)
FE38
3
HPLC
16.00
Concentration gram/litter
14.00
12.00
10.00
Na
Ca
8.00
Cl
No acid breakthrough.
6.00
SO4
4.00
2.00
30:40:23
29:59:53
29:19:23
28:38:53
27:58:23
27:17:53
26:37:23
25:56:53
25:16:23
24:35:53
23:55:23
23:14:53
22:34:23
21:53:53
21:13:23
20:32:53
19:52:23
19:11:53
18:31:23
17:50:53
0.00
Time
Fig. 38.3.: HPCL-results when starting acid injection. The graph shows a decrease of
the Cl- and Na+, increase of Ca2+ and a reduced production of SO42-.up to 25.16 hrs.
Thereafter, calcium and SO4 concentration became constant. No real acid break
trough (Original acid composition).
k38
1E-14
dP is zero
9E-15
8E-15
7E-15
k[m^2]
Start acid
6E-15
injection
5E-15
k[m^2]
4E-15
3E-15
Stop experiment
Pinj & Pprod=0
2E-15
1E-15
141693
137443
133193
128943
124693
120443
116193
111943
107693
103443
99193
94943
90693
86443
82193
77943
73693
69443
65193
0
Time[sec]
Fig 38.4.: Stop experiment because of failure of back pressure valve at the production
side. But the production tube was already plugged by anhydrite. The pressure
difference has risen, this explains the permeability drop.
FE38
4
CT_Scan
Fracture and plastic
material to maintain
the width
Fig. 38.5: CT-slice before experiment scan No:181
Fracture
Fig. 38.6: CT-slice before experiment scan No:13
FE38
5
Anhydrite
Fracture
Wormholes
Fig. 38.7: CT-slice after experiment scan No:51
Anhydrite
Fracture
Wormholes
Fig. 38.8: CT-slice after experiment scan No:212
FE38
6
Fracture affected by
flow of acid
Wormhole
Fig. 38.9: Sample after experiment. Injection side
Fracture
Plastic material
kept the width,
anhydrite
around it.
Fig. 38.10: Sample after experiment. Production side
FE38
7
Wormhole
Fractures
Fig. 38.11: Sample after experiment. All fractures cemented.
Fig. 38.12: Sample after experiment. 3D scan.
FE38
8
Sample ID: FE 39
Weight
2138 [g] , after exp: 2472 [g]
Length
191 [mm]
Diameter
99,9 [mm], Volume: 1462 [cc]
Goal Experiment
Core flooding experiment
Fracture width
1 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
5 [ml/min]
Pore Volume
Ml acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 515 [ml], 0.34, Wet weight porosity = 0.47
1512 [ml]
Not measured
1.406 [mol]
Yes HPLC only
yes
Experimental history
Pore fluid: brine
24 June:
• Brine injection.
• Acid injection. No problems
• End of the experiment.
Observation and comments
At time 2260 s (PV = 0), start of the acid injection (Fig. 39.1, 39.2). The pressure build
up of acid took 280 s. The pressures and pressure difference remained constant from
2542 s to 6872 s (0.675 PV). The differential pressure was in between 2 to 3 bars.
In between 6702 s and 6872 s the differential pressure dropped, which means high
permeabilities. With irregular annular pressure built-ups, no differential pressures could
be reached up to 20600 s. In this period of constant pore pressure, the HPCL results
shows mostly SO42- , i.e. production of the original acid. Hence, no reactions with the
chalk took place. After production of 2.8 PV of fluids, we decided to end the experiment.
Visual analysis and conclusive remarks.
The CT images after the experiments (fig. 39.5,6 and 7) show that the original fractures
are all almost completely closed. Locally anhydrite is visible as replacement.
Furthermore, the development of a few wormholes, with surrounding transformation of
FE39
9
chalk to anhydrite, is clearly present. However, only a limited amount of anhydrite
patches are present. The 3D-compilation (figure 39.8) shows that one single “major”
wormhole is present. The eventual smaller ones are not recognized. One fossil remnant
has been recognized, but no association with wormholes has been found.
Conclusion
The early acid break through after ca. 6100 s., the first acid already is produced. After ca.
7000 s. the almost original SO42- concentration coincides with the differential pressure
drop which means that after creation of wormholes and a fixed route, hardly any reaction
to anhydrite occur.
Conclusion on permeability
In all, the permeability is about 4*10-15 m2 up to acid break trough. Thereafter the
pressure difference goes to zero.
Recommendation
More continuous monitoring of acid composition and pH-measurements.
FE39
10
.
120
80
100
70
Pressure[bars]
CO2-production
50
60
20
brine
injection
40
40
Decrease of
differential pressure
30
Temperature(°C)
60
80
20
0
10
-20
P_injection
P_production
P_annular
DP
T_reservoir
0
0
5000
10000
Acid injection
15000
20000
Time [second]
Fig.39.1. : Pressures and temperature versus time. Press1: Injection pressure, Press2:
production pressure, Press3: annular pressure, Dp: differential pore pressure (P1,2) and
Temp1: temperature in the sample (°C).
FE40 Qinject=5ml/min
100
90
80
Pressure [Bar]
70
60
50
40
P_injection
30
Decrease of differential
pressure and acid break
through
Start
20
10
DP
P_production
P_annular
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
0
PV [-], Cum _Qinjection/Volum e_pores
Fig.39.2.: Pressures and temperature versus pore volumes (-). Press1: Injection pressure,
Press2: production pressure, P-annular: annular pressure, DP: differential pore pressure over
P1 and P2.
FE39
11
HPLC
100.00
80.00
Acid
production
Concentration gram/litter
90.00
70.00
60.00
Na
Ca
50.00
Start acid
injection
40.00
Cl
SO4
30.00
20.00
10.00
20500
16900
13300
9700
6100
2500
0.00
Time [Second]
Fig.39.3.: HPCL-results when starting acid injection. The graph shows a decrease of the Cland Na+ and increase of Ca2+ and SO42- . After 6100 S, acid production starts.
k39
1E-14
9E-15
dP is zero
8E-15
dP is zero
7E-15
Start acid
injection
k[m^2
6E-15
Acid
Production
5E-15
k
4E-15
3E-15
2E-15
1E-15
6452
6112
5772
5432
5092
4752
4412
4072
3732
3392
3052
2712
2380
2040
1700
1360
1020
680
340
0
0
Time[sec]
Fig.39.4.: After 6600 seconds in the experiment the dP=Pinj- Pprod is zero.
FE39
12
CT-scans before experiments: not available.
39.5 CT Scan: CT-scan slice no.8: injection side: part of the original frac visible. Irregular
wormhole development with transformation to anhydrite.
39.6 CT-scan: slice 73: the original frac has been filled with anhydrite. One side frac is partly
open and present. The wormholes are all surrounded by minor amounts of anhydrite
formation.
FE39
13
Fig.39.7. slice 178, towards the production side. Most of the frac cannot be recognized, minor
anhydrite patches and lines are visible as former fracs. Further wormholes and fossils can be
recognized.
Fig.39.8.: 3D rendering of CT-scans, visualizing the open holes. I.e., the larger wormholes
from injection to the sleeve are visualized. Pores < 300 µm are below the detection limit.
FE39
14
Sample ID: FE 40
Weight
Before:2154 [gr], After:2532 [gr]
Length
190 [mm]
Diameter
99 [mm], Volume: 1462 [cc]
Goal Experiment
Core flooding experiment
Fracture width
2 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
5 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 495 [ml], 0.34, Wet weight porosity = 0.46
912 [ml]
Not measured
0.85 [mol]
No
yes
Experimental history
Pore fluid: brine
1 July:
• Injection of brine.
• Acid injection. Problem with the pneumatic and hydraulic high pressure system.
• End of the experiment.
Observation and comments
1. At time 0 (PV = 0) Start of the acid injection (Fig. 40.1, 40.2). A pressure build
up with acid took 2720 s. which is around 0.45PV.
2. From 2750 s. (0.47PV) to 3890 s. (0.65PV) the pressures remained constant and
the differential pressure was kept around 3 bars.
3. At 3890 sec a power failure caused a pressures drop in the entire system.
4. From 4173 s. (0.66PV) to 5633 s (0.89PV): new pressure build up (1460 s).
5. The build up was followed by a period of constant pressures which ended at 7530
s. by a fall of the differential pressure to zero.
6. After 3600 s. of acid production. At 11185 sec. (1.84PV) ends the experiment.
Visual analysis and conclusive remarks.
• A small amount of CaSO4 has been created but a large part of the fracture has
remained open. Due to pressure problems occurred during the experiment the new
formed material could be gypsum of basanite.
• CT scans pictures show the development of several wormholes of which one
transverses the length of the sample from the injection to the production sides.
FE40
15
Note:
No acid analysis have been performed.
Visualization:
The figures 40.5 and 40.9 show that the fracture is still partly open at the injection and
production sides. However partly through the frac but also through the matrix wormholes
developed and cemented again with anhydrite. One wormhole goes from the injection to
the production side.
Conclusion and Recommendation
• The fracs are mostly cemented.
• The wormhole is evolved from previous wormholes and one of the many bypasses.
• From about 5000 s, all small pore pressure drops are attributed to evacuation of
gas when wormhole systems reach the production side.
Conclusion on permeability
• In the beginning of the experiment there was almost no annular pressure, this
resulted in high permeability and a different scale then the usual permeabilities
seen in other experiments.
• When the annular pressure was increased, the permeability stayed in the same
range (4*10-15) as found in the previous experiments.
FE40
16
Pressure [bars]
120
100
100
80
Flow trough
wormholes
Problems with: pneumatic and
pressure regulation systems
80
40
40
20
Decrease of the
Pressure difference
-20
1800
3600
Start acid injection
5400
7200
9000
P_annular
DP
T_reservoir
0
0
0
P_product
60
60
20
P_injection
10800
Te m p [de g C]
End of the experiment
Time [Second]
Fig.40.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
FE41 Qinject= 5 ml/min
100
90
80
Problems with:
pneumatic and pressure Preferential
flow: wormholes
regulation systems
Pressure [Bar]
70
60
T_reservoir
DP
50
P_production
40
P_annular
P_injection
30
Restart of the Exp
Decrease of Differential
Pressure
20
10
0
0.0
Start of acid
injection
0.5
1.0
1.5
2.0
Cum_injection/Volume_pores
Fig.40.2. : Pressures and temperature versus Pore volumes. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore pressure
P(1,2) and T_reservoir: temperature in the sample (°C).
FE40
17
Scale
difference
k40
Start acid
injection
8E-14
7E-14
6E-14
dP is zero
Pressure buid up
k[m^2]
5E-14
Problems with:
air, record and
pressure
regulation
systems
4E-14
3E-14
2E-14
k
End
experiment
1E-14
11033
9953
10493
9413
8873
8333
7793
7253
6713
6173
5633
5093
4553
3780
3240
2700
2160
1620
1080
540
0
0
Time[sec]
Fig40.3.: At ET = 3900 sec back pressure valve on the production side failed, so there was no
pressure on the experiment, after this there was a new pressure build up.
The high flow in the beginning is due to the fact that the annular pressure was not build up
yet, so the acid could flow much easier , which is why the scale of the graph is different.
Fracture
Fig.40.4. CT scan original sample Slice no: 110
FE40
18
Open fracture
Wormholes
Fig.40.5.: After experiment; CT-SCAN, slice No:51.
Wormholes and
remained open frac.
Closed with CaSO4 fracture
Fig.40.6.: After experiment; CT-SCAN, slice No:166.
FE40
19
Fig.40.7.: 3D rendering of CT-scans, visualizing the open holes. I.e., the larger wormholes
from injection to the sleeve are visualized. Pores < 300 µm are below the detection limit.
Wormhole
Open fracture
Fig.40.8.: Sample after experiment. Production side. Showed the open fracture and the end of
the high permeable wormhole.
FE40
20
Fracture
Wormhole
Fig.40.9. Sample after experiment. Injection side. Showed the open fracture and a begin point
of the high permeable wormhole.
FE40
21
Sample ID: FE 41
Weight
2617[gr]
Length
230[mm]
Diameter
99.6[mm], Volume: 1791 [cc]
Goal Experiment
Core flooding experiment
Fracture width
2 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 540 [ml], 0.30, Wet weight porosity = 0.45
1309 [ml]
Not measured
1.23 [mol]
Yes HPLC only
Yes, Before
Experimental history
Pore fluid: brine.
7 July:
• Brine injection.
• Start with acid injection.
• End of the experiment, due to problems with the security valve.
Experimental observation and comments
• Saturation of the sample by vacuuming of the sample and filling with brine;
determination of the pore space (1PV).
• The pressure build up with acid from 0 s.(0 PV) to 8220 s.(0.511 PV); see
fig 41.1 and 2.
• A steeply decrease of the pressure occurred at 8570 s.(49 bars) to 10390 s
probably due to “gas burst”; CO2-formation and sudden escape through the
production line caused a pressure drop. (35 Bars). This drop was followed by a
moderate normalisation of the pressure of about 2800 s. At 13610 s (0.844PV)
the pore pressure was stabilised around 50 bars.
• A differential pressure of about 2 bars is created based on a stable pore pressures
of around 50 bars, any small decrease of the pore pressures at the injection side
was immediately followed by a decrease at the production side. In other words,
permeability remained constant (see fig. 41.1, around 18000 s.).
• After 24840 s. (1.537 PV) a fluctuation of the production and injection pressure
started, continuing up to the slow loss of the differential pressure up to 36780 s.
(2.274 PV). Thereafter an increase of the both injection and production pressure
FE41
22
•
•
to 70 bars at 38360 s. (2.372PV).
The HPLC results showed that concentration of SO42- in the produced fluid is
lower than its concentration in the injected fluid, or, formation of anhydrite is
continuously creating wormholes and remineralized matrix (Fig. 41.3).
After 38000 s the experiment was stopped due to fast increase of the pore
pressure caused by clogging of the back pressure valve and failure of the safety
valve.
Visual analysis and conclusive remarks.
Observations:
• High injection and production pore pressures at the end of the experiment created
“hydraulic” fractures parallel to the confining stress (Fig.41.9). The sample
showed 8 major fractures.
• At the injection side the fracture was closed and a high permeable wormhole was
created (Fig. 41.7).
• Figure 41.8 shows that at he centre of the core the fracture was cemented.
• At the end of the experiment, the sample was severely damaged and a CT-scan
was not performed on this fragmented core.
Conclusion and Recommendation
•
•
•
At the flow rate of 2 ml/min anhydrite precipitations occurs in the reservoir
sample.
The differential pressure over the sample remains more or less the same, which
means that the permeability of the entire system doesn’t change very much.
Further experiments over larger time spans, with the same flow rate, have to be
done to recognize wormhole development associated with changes in differential
pore pressure.
Conclusion on permeability
• Permeability remains in the same range, 5*10-15. Fig. 41.3 shows that after 25000
s. a big Na drop took place, while more Ca is produced. This indicates that the
first amounts of injected acid are produced. At the same time the permeability
starts fluctuating.
FE41
23
Start Fluid
productions
120
Loss of the
pressures
100
80
Pressures irregulatity
60
40
Increase of
pressures
Pressure [bars]
100
80
P_injection
60
P_product
40
P_annular
Dp40Bar
20
20
Temp1
pressures stability
0
0
-20
40000
36000
32000
24000
20000
16000
12000
8000
4000
0
Pressure
Build Up
28000
decrease of diff-pressure
-20
Tem p [deg C]
Time [seconds]
Fig.41.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
Treservoir: temperature in the sample (°C).
FE41 Pressure/Pore Volumes
90
80
Start Fluid
productions
Increase of pressures
70
Pressure in Bars
60
50
40
30
20
Temp1
P_injection
P_product
DP
P_annular
Loss of the pressures
10
0
0,000
-10
0,500
start acid injection
1,000
1,500
Cum injection / Volume pore
2,000
2,500
decrease of diff-pressure
Fig.41.2. : Pressures and temperature versus Pore volumes. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore pressure
P(1,2) and T_reservoir: temperature in the sample (°C).
FE41
24
HPLC Results
No fluid production
Concentration in gram/litter
20
15
10
Ca
Cl
SO4
5
Na
0
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
Start of fluid production
-5
Time in seconds
Fig. 41.3.: HPCL-results when starting acid injection. The graph shows a decrease of the Cland Na+, increase of Ca2+ and a reduced production of SO42- .
k41
1E-13
gas burps
9E-14
Pressure build
up
Bp fail
8E-14
k[m^2]
7E-14
6E-14
5E-14
k
4E-14
3E-14
2E-14
1E-14
38800
36860
34920
32980
31040
29100
27160
25220
23280
21340
19400
17460
15520
13580
11640
9700
7760
5820
3880
1940
0
0
Time[sec]
Fig.41.4.: Permeability-results, in the graph it can be seen that when acid has broken through
at T=25000 sec (as can be seen in the HPLC graph), permeability starts to fluctuate which
indicates gas burps and CO2 production.
FE41
25
Frac
Fossil or chert
Fig. 41.5: CT-scan slice 60 before the experiment. Note the slightly heterogeneity in density
by the minor variations in grey values.
Frac
Fossil or chert
Fig. 41.6: CT-scan slice before the experiment. Note the slightly heterogeneity in density by
the minor variations in grey values. The white patches are fossils or chert.
Note: No CT-scans from the acid treated sample.
FE41
26
Wormholes
Closed
fracture
Fig.41.7. Sample after experiment. Injection side. Showed the closed fracture and a high
permeable wormhole.
Open fracture
Fig.41.8.: Sample after experiment. Production side. Showed the original partly open fracture
FE41
27
Original
fracture
Cemented part of the
original frac.
Hydraulic
fractures
Fig.41.9. Sample after experiment. Axial view. Hydraulic fracturing of the sample
perpendicular to the length axis.
FE41
28
Sample ID: FE 42
Weight
2579[gr]
Length
227 [mm]
Diameter
99.6[mm], Volume: [cc]
Goal Experiment
Core flooding experiment
Fracture width
2 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 585 [ml], 0.33, Wet weight porosity = 0.46
871 [ml]
Not measured
0.82 [mol]
Yes HPLC only
Yes, before and after
Experimental history
Pore fluid: brine
14 July.
• Brine injection by sample evacuation.
• Start with acid injection
• End of the experiment after ca. 13 hrs; only acid is produced.
Observation and comments
• Saturation of the sample by evacuation of air and filling with brine; determination
of the pore space (1PV).
• The pressures build up with acid from 0 s. (0 PV) to 7810 s. (0.45 PV).
Fig.42.1.and Fig. 42.2. During the pressure build up a slight differential pore
pressure was created and reduced at the end of this stage.
• From 7810 s (0.45 PV) to 13590 s (0.77 PV), at stable pressures of ca. 50 bars, a
differential pressure of about 2.2 bars was created.
• At 0.77 PV or 12560 s, a pressure drop was caused by break trough and since
then the differential pressure remained zero.
• After ca. 25200 s, or 12560 s (= 0.71 PV) of acid production, the experiment was
stopped.
• HPLC analyses already show at the start of the experiment, after 1000 s, an early
high concentration of SO42- in the produced fluid Fig.42.3. It means that limited
reaction/anhydrite formation occurred.
FE42
29
Visual analysis and conclusive remarks.
• From 780 s. (0.45 PV) the concentration of SO42- in the produced fluid was 83 g/l
and the concentration in the injected mixture of acid is of 90 g/l.
• Less than 10 percents of the injected SO42- is precipitated into CaSO4. Hence,
porosity remains high.
• CT scan rendering shows that the fracture is only partly cemented. In addition,
one high permeable wormhole has been created, which may certainly be a direct
bypass for the SO42--. In total, the differential pore pressure was very low or zero.
• Note that the pore pressures build up with acid, in the previous experiment in time
and pore volumes, corresponds to this experiment.
EXP
FE41
FE42
Time Pressure Build Up
8220 s.
7810 s.
PV Pressure Build Up
0.47 PV.
0.45 PV.
Conclusion and Recommendation
The early SO42- break through due to the open fracture and formation of the high
permeable wormhole, have reduced the contact of the injected fluid with limestone.
To solve this problem:
1. Pressure build up with brine, before any acid injection.
2. A second filter at the injection side to disseminate injected sample fluid.
Conclusion on permeability
• Permeability remains in the same range during the experiment.
• It can be concluded that permeability is not affected by the acid
treatment and sealing of the fracture.
FE42
30
Start Fluid Production
120
P1-P2 = 0
100
End of the experiment
Pressure [bars]
100
80
60
40
20
0
P_Injection
60
P_Product
40
P_Annular
20
25200
21600
18000
14400
10800
7200
3600
Start Acid Injection
Dp
T_Reservoir
0
-20
0
-20
80
Te m p [de g C]
Time [seconds]
Fig.42.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
FE42 Qinject=2ml/min
90
70
P1 - P2 = 0
60
T_Reservoir
End of the experiment
Cum_Injection/Pore_Volume
80
50
40
30
20
10
P_Injection
DP
P_Production
P_Annular
Start Acid Injection
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
-10
0.0
0
Pressure [Bar]
Fig.42.2. : Pressures and temperature versus PV; pore volumes. P_injection: Injection
pressure, P_product: production pressure, P_annular: annular pressure, Dp: differential pore
pressure P(1,2) and T_reservoir: temperature in the sample (°C).
FE42
31
HPLC
90.0
80.0
Concentration gram/Litter
70.0
60.0
Na
50.0
Ca
40.0
Cl
30.0
SO4
20.0
10.0
0.0
-10.0
0
5000
10000
15000
20000
25000
30000
Time in Seconds
HPLC
90.0
SO4 Concentration ≈ Original acid
concentration
80.0
Concentration gram/Litter
70.0
60.0
Na
50.0
Ca
40.0
Cl
30.0
SO4
20.0
10.0
0.0
-10.0
0
200
400
600
800
1000
Time in Seconds
Fig. 42.3.: Top: HPLC results of the entire experiment. Bottom: HPCL-results when starting
acid injection in the first 1000 seconds. The graph shows that the concentration of SO42- in
the produced fluid corresponds to its concentration in the injected fluid and only at the start of
the experiment reaction took place.
FE42
32
k42
1E-14
Reparation
Back
Pressure
dP is zero
9E-15
8E-15
dP is
zero
Pressure build up
k[m^2]
7E-15
6E-15
5E-15
k
start acid
inj
4E-15
3E-15
2E-15
1E-15
13600
12920
12240
11560
10880
10200
9520
8840
8160
7480
6800
6120
5440
4760
4080
3400
2720
2040
1360
680
0
0
Time[sec]
Fig. 42.4.: Permeability-results
FE42
33
Chert
Belemnite
Frac
Fig.42.5.: Before experiment; CT-SCAN, slice No:52. Note the slight change in grey tone of
the matrix, which represents a variation in density, i.e. porosity heterogeneity. The bright
parts are chert and/or fossils.
Frac
Matrix heterogeneity
Fig.42.6.: before experiment; CT-SCAN, slice No:208. Note the grey variation of the matrix
heterogeneity. Note also the overall difference in brightness of the two images. This is due to
fluctuation of the electron beam energy.
FE42
34
Partly open fracture
Wormhole
Fig.42.7.: After experiment; CT-SCAN, slice No:051.
Partly closed fracture and
wormhole
Wormhole
Fig.42.8.: After experiment; CT-SCAN, slice No:198.
FE42
35
(Early) creation of a high permeable wormhole
Fig.42.9. 3D rendering of CT-scans, visualizing the open holes. I.e., the larger wormhole
from injection to the sleeve is visualized. Pores < 300 µm are below the detection limit.
Fig.42.10. 3D rendering of CT-scans, to demonstrate the difference in the models, visualizing
the open holes. I.e., the larger wormhole from injection to the sleeve is visualized. Pores <
300 µm are below the detection limit. Here the original fracture is not totally sealed as can be
seen because of the flat area.
FE42
36
Remained open fracture
Fig.42.11. Sample after experiment. Axial view. The fracture remained open since the
injected acid bypassed the fracture or the fracture plane sealed the matrix, so no more SO4/Careactions took place.
Wormholes and a by acid
affected surface at the
injection side
Remained open fracture
Fig. FE42.12. Sample after experiment. Injection side. Showed the remained open fracture
and high permeable wormholes.
FE42
37
Partly open fracture after
experiment
Fig.42.13.: Sample after experiment. Production side. Showed the open fracture
FE42
38
Sample ID: FE 43
Weight
3233 [gr]
Length
282 [mm]
Diameter
99 [mm], 3233 Volume: [cc]
Goal Experiment
Core flooding experiment with extra sample length!
Fracture width
2 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Brine injected
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
975 [ml], 0.45 Porosity:
3087 [ml]
Not measured
2.89 [mol]
Yes HPLC only
Yes
Experimental history
Pore fluid: brine
29 July: Pore saturation with brine and start of the acid injection.
End of the experiment after 97000 seconds.
Observation and comments
• Saturation of the sample by evacuation of the air and filling with brine; determination
of the pore space (1 PV).
• The pressure build up with brine took about one hour (Fig 43.1).
• Acid injection started at 4260 s (0 PV); Fig 43.1; Fig 43.2.
• From 8160 s. (0.13 PV) to 12060 s. (0.27 PV) a period of instable pressures was
observed in the pore pressure, followed by the annular pressure. This is due to
clogging. After cleaning of the production pipes and a repair of the back pressure
gauge, a stable pressures period started at 11400 and ended at 34240 s.
• A second instable pressures period followed during the night, starting 60320 s (1.93
PV). From ca. 36000 s, the Ca content in the production fluid increased and by that
the production of CO2, which means that CO2 gas burst could be the cause. Note: the
differential pore pressure remains relatively high but irregular in this period.
• At 72680 s. (2.35 PV) a normalisation of the pressures was reached.
• At 96860 s. (3.09 PV) end of the experiment.
FE43
39
Visual analysis and conclusive remarks.
•
•
•
•
•
Fig 43.5. Core sample shows the presence of anhydrite in the fracture zone, which
closed the fracture.
From the CT scan anhydrite (white) appears in the slides. Fig 43.8-10.
High permeable wormholes have been created; the diameter, number and length
differ along the core sample. Fig 43. 8-10, Fig 43. 11.
HPLC results show that the produced fluid contains les than 2 g/l SO42-,
compared with the concentration of 90 g/l in the injected fluid; we can conclude
that the most of the sulphate ions are precipitated into CaSO4.
Figures 43.10 show that in the two different parts of the sample different types of
wormholes developed.
Conclusion and Recommendation
•
•
One of the most successful experiments. With a good visualisation of anhydrite in
the fracture. Fig 43.7.
The new porosity is estimated at 0.39, which gives a difference of 0.06 from the
initial porosity.
Conclusion on permeability
• During the whole experiment the permeability remains in the same range.
• After acid breakthrough, the permeability starts fluctuating due to gas production.
• When the experiment is not producing for example because of the break down of
the back pressure, the production line will get clogged because of precipitation of
solids. This will influence the permeability.
• The presence of an (artificial) axial fracture creates a new “starting point” for
wormhole development.
NOTE: The complete different cementation behaviour of this experiment compared to
experiment exp.42. Reason: yet unknown.
FE43
40
120
80
Loss of the pressures
Pressure [bars]
100
100
Instable Pressure
Start Acid Injection
Instable pressures
60
40
20
0
80
P_product
40
P_annular
20
90000
80000
70000
60000
50000
40000
30000
20000
10000
-20
0
Dp
T_reservoir
0
-20
Repair of the Back
Pressure gauge
P_injection
60
Te m p [de g C]
Time [seconds]
Fig.43.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
90
Instable Pressures
80
Loss of the pressures
Pressure in Bars
70
60
50
40
30
20
T_Reservoir
P_Injection
DP
P_Product
P_annular
10
0
-10 0
Start Acid
Injection
1
2
3
4
Cum injection/ Volume Pore
Fig.43.2. : Pressures and temperature versus Pore volumes. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore pressure
P(1,2) and T_reservoir: temperature in the sample (°C).
FE43
41
HPLC Results
25
20
15
No production
Concentration in gram/litter
Breakthrough of injected fluid
Ca
Cl
SO4
10
Na
5
0
0
20000
40000
60000
80000
100000
120000
Time in Seconds
start acid injection
Fig. 43.3.: HPCL-results when starting acid injection. The graph shows a decrease of the Cland Na+, increase of Ca2+ and a reduced production of SO42- .
k43
Acid
breakthrough
1E-14
Start acid
9E-15
i j
8E-15
Gas burps
Back
pressure
failure
Pressure Loss
because of
Back Pressure
Failure
k[m^2]
7E-15
6E-15
5E-15
k
4E-15
3E-15
2E-15
1E-15
95200
90440
85680
80920
76160
71400
66640
61880
57120
52360
47600
42840
38080
33320
28560
23800
19040
9520
14280
4760
0
0
Time[sec]
Fig.43.4.: Permeability-results, during the whole experiment the permeability stays
approximately the same. When the back pressure valve failed, which is usually due to
precipitation of calcite inside the valve, the production valve is closed and the injector is shut
off, this means that the calcite has time to precipitate in the production tube, usually after such
a reparation the experiment can be stopped.
FE43
42
Fig.43.5. Sample after experiment. Injection side. Showed the fracture, a high permeable
wormhole, and anhydrite.
Fig.43.6. Sample after experiment. Production side. Showed the open fracture.
FE43
43
Fig.43.7. Sample after experiment. Axial view. Anhydrite in the fracture.
FE43
44
Closed fracture
Anhydrite = white
Wormholes
Fig.43.8.: After experiment; CT-SCAN, slice No:45. The closed frac,, open and cemented
wormholes, and anhydrite.
Anhydrite = White
Wormholes
Fig.43.9.: After experiment; CT-SCAN, slice No:79. Closed frac, wormholes, and anhydrite.
FE43
45
Wormhole
Anhydrite = White
Open Fracture
Fig.43.10.: After experiment; CT-SCAN, slice No:279. The partly open frac, wormholes,
and anhydrite.
FE43
46
Fig.43.11: 3D rendering of CT-scans. Top, visualizing the open holes (blue). I.e., the larger
wormholes from injection to production side are visualized. Pores < 300 µm are below the
detection limit. Also visible are the fossils (red). Note the flat blue area on the right, this is the
non sealed area of the fracture.
FE43
47
Figure 43.12 The original core: note the fractured end part and compare wit the worm hole
behaviour of the previous two images.
FE43
48
Sample ID: FE 44
Weight
3352 [gr]
Length
297 [mm]
Diameter
99.5 [mm], 2308 Volume: [cc]
Goal Experiment
Core flooding experiment: (Extra long sample)
Fracture width
3 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 600 [ml], 0.26, Wet weight porosity = 0.45
5855 [ml]
Not measured
5.5 [mol]
Yes HPLC only
Yes, after acid injection only
Experimental history
Pore fluid: brine
4 August: Pore saturation with brine and start of the acid injection.
5 August: After 175000 seconds, end of the experiment.
Observation and comments
• Saturation of the sample by evacuation of the air and filling with brine;
determination of the pore space (1 PV).
• The pressure build up with brine took about one hour (Fig 44.1)
• Acid injection started at 11150 s. (0 PV) (Fig 44.1,2).
• From 8160 s. (0.22 PV) to 12060 s (0.34 PV) during pressure build up and
initial acid injection a period of instable pressures was observed. This due to
either creation of new flow paths (i.e. new pore regions available) or CO2 gas
burps.
• From 12060 s (0.34 PV) to 29100 s (0.88 PV), a differential pressure of 2 bars
was created and maintained in a period of stable pressure.
• A new period of slightly instable pressures followed and ends at 41100 s (1.26
PV) by a loss of the differential pressure due to (acid) break through, followed
by anhydrite clogging, and by that an increase of the pore pressure up to the
maximum (safety) pressure (Fig. 44.1,2,3).
• At 47500 s. (1.46 PV) probably a clogging of the flow path in the core led to
an increase of the differential pressure, a decrease of the production rate and
of the concentration of SO42- in the produced fluid. Up to 80000 s, the period
was used to restore the pressures under controlled conditions, i.e. slow
pressure build up combined with cleaning of the tubing and controller systems
FE44
49
•
•
(ca. 80000-88000 s).
From 88000 s, with constant injection rate, up to the end of this experiment,
the pore pressure slowly raised (Fig. 44.1,2). The core permeability was
seriously reduced. To keep the pore pressure below the safety pressure, the
injection rate was slowly reduced (Fig. 44.5)
After 170.000 s the system became less stable and it was decided to cease the
experiment.
Visual analysis and conclusive remarks.
No CT-images were made of the original core.
•
•
•
The fracture is closed and anhydrite formation has been created in the sample
(Fig 44.5,6,7,9).
Several generations of highly permeable wormholes have been created (Fig.44.6,
7, 10). All wormholes are ending in a small branches in a “micro” pore zone.
As a contradiction, a reduction of the production rate is associated to a
permeability reduction, caused by the precipitation of anhydrite. Fig.44.5.
Conclusion and Recommendation
•
•
At this flow rate of 2 ml/min and fracture width of 3 mm was completely closed.
Cementation induced permeability reduction. Secondary permeability is available
through the wormholes.
Conclusion on permeability
• NOTE: In contrast to experiment 43, here permeability reduction was created.
• This permeability reduction is just after a no flow time. With this experiment the
no flow time was longer then in experiment 43, so solids have more time to
precipitate in the production line.
FE44
50
Clogging of the
production system
120
P_inj= P_annular
100
Pressure [bars]
100
80
60
P_inj >> P_prod.
40
80
P_Injection
60
P_Product
40
P_Annular
DP
20
20
Cleaning of the back
pressure gauge
0
T_Reservoir
0
Stable pressures
180000
170000
160000
150000
140000
130000
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
10000
Start Acid
injection
20000
-20
0
-20
Tem p [deg C]
Time [seconds]
Fig.44.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
T_Reservoir
FE44 Qinject=2 ml/min
Clogging of the production
system.
P Inj = P_secur = P_ production.
100
90
P_Injection
DP
P_inj = P_annular
P_Product
P_Annular
80
Pressure [Bar]
70
Stable
Pressures
60
P_Inj >> P_product
50
40
30
20
10
0
Start -1
Acid
Injectin
0
1
2
3
4
5
6
7
8
9
10
Cum_Qinjection/Volume_Pores
Fig.44.2. : Pressures and temperature versus Pore volumes (PV). P_injection: Injection
pressure, P_product: production pressure, P_annular: annular pressure, Dp: differential pore
pressure P(1,2) and T_reservoir: temperature in the sample (°C).
FE44
51
HPLC FE44
Acid
Breakthrough
60
Concentration in gram/litter
50
40
Na
30
Ca
Cl
20
SO4
10
200000
180000
160000
140000
120000
100000
80000
60000
-10
Start Acid
Production
40000
20000
0
0
Time in seconds
Fig. 44.3.: HPCL-results when starting acid injection. The graph shows a decrease of the Cland Na+, increase of Ca2+ and a breakthrough of SO42-, followed by a reduced production of
SO42Gas burps
k44
1E-14
9E-15
Acid
breakthrough
Back
pressure
Production and Perm low
probably production
tubing plugged
k[m^2]
8E-15
Start acid inj
7E-15
6E-15
5E-15
k
4E-15
3E-15
2E-15
1E-15
172400
163780
155160
146540
137920
129300
120680
112060
103440
94820
86200
77580
68960
60340
51720
43100
34480
25860
17240
8620
0
0
Time[sec]
Fig.44.4.: Permeability-results, again the experiment should have been stopped after the back
pressure valve failed, due to precipitation in the production tube and back pressure valve. This
is the reason why at T=43000sec the permeability decreases and the Dp rises.
FE44
52
Production Rate
3,000
Production Rate ml/min
2,500
2,000
1,500
1,000
0,500
200000
180000
160000
140000
120000
100000
80000
60000
40000
-0,500
20000
0
0,000
Time in Seconds
Production Rate
Fig.44.5. Average production rates versus time (4000s per bin). The production rate decreases
due to the cementation of the flow paths by anhydrite.
FE44
53
White = Anhydrite.
Wormholes
Fig.44.6. CT scan original sample Slice no: 266
Plastic used to
maintain the
fracture width
Fig.44.7.: CT scan original sample Slice no: 11
FE44
54
Several wormholes
Fig.44.8. Sample after experiment. Injection side.
Fracture
SO4 acidized
chalk parts
Fig.44.9. Sample after experiment. Production side.
FE44
55
Closed
fractures
Fig.44.10. Sample after experiment. Axial view. Closed fractures.
FE44
56
Fig. 44.11.: 3D rendering of CT-scans, visualizing the open holes (blue). I.e., the larger
wormholes from injection to the sleeve are visualized. Pores < 300 µm are below the
detection limit. And the fossils are visible (red)
FE44
57
Sample ID: FE 45
Weight
3027 [gr]
Length
270 [mm]
Diameter
99.5 [mm], Volume: 2098 [cc]
Goal Experiment
Core flooding experiment
Fracture width
2 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 810 [ml], 0.39, Wet weight porosity = 0.47
5434 [ml]
Not measured
5.1 [mol]
Yes HPLC only
Yes, after
Experimental history
Pore fluid: brine
11 August:
• Brine injection by sample evacuation.
• Start with acid injection, and repair of the back pressure regulator.
12 August:
• Repair of the heat element of the production line, cleaning of the back pressure
valve and production pipe.
13 August:
• 171500 seconds, end of the experiment.
Observation and comments
• Saturation of the sample by evacuation of the sample and filling with brine;
determination of the pore space (1PV).
• Acid injection started at 2750 s (0 PV): A differential pressure of about 3 bar has
been created (Fig.45.1-2).
• At 20150 s (0.72 PV) repair of the back pressure gauge.
• A decrease of the differential pressure, which corresponded to a breakthrough of
SO42- occurred at 41750 s (1.62 PV), and led to the blockage of the backpressure
gauge and the production line. As result of this blockage, the production and
injection pressure increased to the value of the secure valve (70 bars).
• From 83120 s to 115280 s the production line and the back pressure valve were
cleaned different times. This finally led to the reduction of the production
pressure and the increase of the differential pressure to about 40 bars.
• Between 83120 s. and 115280 s, the production rate remained low (Figure 45.5),
FE45
58
•
•
and the choice for rates depends on the (fully open) back pressure valve. Hence,
clogging occurred in the line between the sample and the production valve.
To keep the experiment running it was decided, from 115280 s on, to use the
injection rate for keeping the maximum differential pore pressure under control (<
40 bar). Therefore, the production pressure remained low and the pressure
declines are probably caused by changing wormhole volumes and CO2 gas
belching.
After 170000 the experiment was stopped.
Visual analysis and conclusive remarks
•
•
•
The fracture was mostly cemented with anhydrite (Fig 45.6 -12).
A clogging of the flow path led to the reduction of the flow rate, which normally
is related to the permeability reduction in the sample (see FE44).
Multiple wormholes have been created.
Conclusion and Recommendation
•
A low-pressure experiment can give an idea of the evolution of the injection
pressure. Keeping the flow rate constant and the injection pressure related to the
resistance of the flow it would be possible to observe the increase of the
resistance of the flow with changing wormhole configuration (and thus
permeability).
Conclusion on permeability
• After acid breakthrough, the permeability starts fluctuating due to gas production.
• When the experiment is not producing for example because of malfunctioning of
the back pressure, the production line gets clogged because of precipitation of
solids. This will influence the permeability.
FE45
59
Start Acid injection
120
Repair of the heat element , cleaning of the
production tubing and back pressure valve 100
Increase pressures
Pressure [bars]
100
80
60
40
80
P_Injection
60
P_Product
40
P_Annular
20
20
Dp
T_Reservoir
0
0
180000
170000
160000
150000
140000
130000
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
-20
0
-20
Repair of the
Back-Pressure
valve
Different Pressure is 0
Tem p [deg C]
Low production pressure due
to low production rate.
Time [seconds]
Fig.45.1. : Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
100
Pressures in Bars
80
60
T_Reservoir
P_Injection
DP
P_Product
P_annular
40
20
0
P_injection = P_Production
-20
-1
0
Repair of the back
pressure valve
1
2
3
4
5
6
Cum_injection/ Volume_pores
Fig.45.2. : Pressures and temperature versus Pore volumes. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore pressure
P(1,2) and T_reservoir: temperature in the sample (°C).
FE45
60
FE 45 HPLC Results
Breakthrough of SO4
90
Concentration in gram/litter
80
70
60
Na
50
Ca
40
Cl
30
SO4
20
10
0
180000
170000
160000
150000
140000
130000
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
0
-10
Time in Seconds
Fig. 45.3.: HPCL-results when starting acid injection. The graph shows a decrease of the Cland Na+, increase of Ca2+ and a reduced production of SO42- .
Start acid
inj
1E-14
k45
A lot back pressure
problems
Acid
breakthrough
9E-15
8E-15
dP zero
gas burps
k[m^2]
7E-15
6E-15
k
5E-15
4E-15
3E-15
2E-15
1E-15
168800
160360
151920
143480
135040
126600
118160
109720
101280
92840
84400
75960
67520
59080
50640
42200
33760
25320
16880
8440
0
0
Time[sec]
Fig.45.4.: Permeability-results.
FE45
61
Production Rate FE45 [ml/min]
Pick of the production rate
3
Increase of the
pressures
Rate in ml/min
2,5
2
1,5
1
0,5
180000
170000
160000
150000
140000
130000
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
0
0
Tim e in Se conds
Fig.45.5. Evolution of the production rate (per bin 1600 s). Reduction of the production rate
became very low after a breakthrough of SO42-.
FE45
62
Fracture
perpendicular to
fl
Cemented fracture parallel to
flow
Fig.45.6. Sample after experiment. Axial view shows the closed axial fracture and open
perpendicular fracture.
Partially
closed
fracture and
Fig.45.7. Sample after experiment. Production side. Showed the partially closed fracture and
new material formed into the fracture.
Wormhole
Open
Closed fracture
Fig.45.8. Sample after experiment. Injection side. Showed a partially closed fracture and
wormholes.
FE45
63
Wormhole
Cemented frac
Anhydrite patches
Fig. 45.9: CT-scan slice 25 After experiment.
Wormhole
Cemented frac
Anhydrite patches
Fig. 45.10: CT-scan slice 122 After experiment.
FE45
64
Wormhole
Cemented frac
Anhydrite patches
Fig. 45.11: CT-scan slice 122 After experiment.
Fig.45.12: 3D rendering of CT-scans, visualizing the open holes. I.e., the larger wormholes
and the fossils from injection to the sleeve are visualized. Pores < 300 µm are below the
detection limit.
FE45
65
Sample ID: FE 48
Weight
3329 [gr]
Length
288 [mm]
Diameter
99 [mm], Volume: 2217 [cc]
Goal Experiment
Core flooding experiment
Fracture width
3 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2 [ml/min]
Pore Volume
Acid injected
Fluid produced
Moles SO42- injected
pH analysis
CT scan
Wet porosity: 395 [ml], 0.18, Wet weight porosity = 0.45
8165 [ml]
Not measured
8.2 [mol]
Yes HPLC only
Yes, Before & after
Experimental history
Pore fluid: brine
23 September 2008:
• Brine injection by sample evacuation (09:15h), start 1000ml. End 605 ml,there
was a leak of the vacuüm.
• Brine injection with pump 2 ml/min, (10:50h).
• Start with acid injection ET 02:15h (13:06h ).
• Temperature too high, and leak of the back pressure valve (ET 2:15h).
25 September 2008:
• Leakage of back pressure valve <12 ml/h (ET 46:47).
• 3-way valve and parts of the injection tube replaced because they were leaking
(ET 52:45), <3.5 ml/h
26 September 2008:
• Seal in back pressure valve replaced.
• Stop experiment (ET 75:30)
Observation and comments
The experiment runs rather smoothly as shown in the figures 48.1, 48.2 and 48.3. From
ca. 40000 s to 85000 s, the experiment shows fast and small differential pressures due to
gas production; i.e. wormholing. At 58000 s., most of the brine has been produced and a
FE48
66
sudden increase of acidity AND SO4-concentration implies temporary complete acid
break trough. This happens again at ca. 86000 s. Thereafter, SO4 concentrations are very
low, which means complete reaction with the chalk to anhydrite.
Permeability:
From the start of the acid injection (ca. 5000 s) till the acid breaktrough, the permeability
rises from 4*10-15 m2 to 7*10-15 m2. In the meantime the pH decreases slightly and the Ca
concentration in the product fluid increases. After the major wormholing activities, i.e. in
between 40000 s and 85000 s, the permeability fluctuates and slow decreases. After ca.
120000 s, clogging of the production line brings the permeability almost to zero.
Visual analysis and conclusive remarks
• The Ct-scans after prove that many small wormholes and SO4/Ca reactions have
taken place through the entire sample.
• The frac is partly open at the injection side and completely closed at the
production side.
• The wormholes are not directly associated to the frac and the fracture orientation.
Comparing the original slices scan and the slices after the experiment, they show
that no association is visible of any influence of the original sedimentation pattern
and the anhydrite reaction patterns (compare figures 48.11 and 48.12)
FE48
67
120
Pressure [bars]
100
80
Press1
60
Press2
40
Press3
20
Dp40Bar
0
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
110000
120000
130000
140000
150000
160000
170000
180000
190000
200000
210000
220000
230000
240000
250000
260000
270000
-20
Time [seconds]
Fig.48.1: Pressures and temperature versus time. P_injection: Injection pressure,
P_product: production pressure, P_annular: annular pressure, Dp: differential pore
pressure P(1,2) and T_reservoir: temperature in the sample (°C).
120
120,0
100
100,0
Acid
breakthrough
80
Gas burps
Production tube
plugged
Start acid
80,0
inj
60
g/L Na
20
60,0
0
40,0
dP(bar)
g/L
40
g/L Ca
g/L Cl
g/L SO4
dP(press1-2)
-20
-40
20,0
-60
0,0
0,0
-80
50000,0 100000,0 150000,0 200000,0 250000,0 300000,0
T(sec)
Fig.48.2: HPLC and Pressure difference versus time.
FE48
68
120
8
Gas burps
100
7
80
6
60
40
dP(bar)
pH
5
20
4
pH
dP(press1-2)
0
3
-20
2
-40
1
-60
0
0
50000
100000
150000
200000
250000
-80
300000
T(sec)
Fig.48.3: pH and Pressure difference versus time.
k48
1E-14
gas burps
Acid
breakthrough
9E-15
Start
acid
8E-15
inj
7E-15
Production tube is
plugged
k[m^2]
6E-15
5E-15
4E-15
3E-15
2E-15
1E-15
0
0
50000
100000
150000
200000
250000
300000
Time[sec]
Fig.48.4: Permeability versus time.
FE48
69
Brine flowing
out of the core
Back pressure valve
failure, acid flows
directly through core
Fig.48.5: Photo of all test tubes collected during the experiment. The brown matter is
suspended anhydrite with “dirt” from the chalk.
Both axial and normal
fracture are cemented by
the anhydrite
Fig.48.6: Photo of the sample after the experiment.
FE48
70
Closed frac.
Fig.48.7: Photo of the production side of the sample after the experiment.
Fracture
partly closed
Anhydrite
Wormholes
Fig.48.8: Photo of the injection side of the sample.
FE48
71
Partly closed
frac.
Wormholes
Fig.48.9: CT image of the injection side of the sample, lighter parts are anhydrite and the
greyer parts calcite. The fracture is partly open, although it is mostly closed by the
anhydrite.
Fig.48.10: CT image of the production side of the sample, Frac is totally closed, a lot of
small wormholes can be seen and there is a lot of anhydrite visible.
FE48
72
Fig.48.11: 3D rendering of the CT scan. Frac and some fossils are visible.
Fig.48.12: 3D rendering of the CT scan. Wormhole branching into multiple wormholes.
Note the location of the fossils.
FE48
73
Sample ID: FE 49
Weight
3331.4 [g] , after exp: 3564[g]
Length
289[mm]
Diameter
99,9[mm], Volume: [cc]
Goal Experiment
Core flooding experiment
Fracture width
2265mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2[ml/min]
Pore Volume
Ml acid injected
505 [ml], Porosity: 0,22, Wet weight porosity = 0.45
5800 [ml]
Moles SO42- injected
CT scan
5,4 [mol]
Yes, Before and after
Experimental history
Pore fluid: brine
7 October 2008:
• Brine injection by vacuum 505ml (09:52).
• Start brine pump (13:40).
• Acid injection (14:45, ET=1:05)
• Heating problem and back pressure valve reparation(ET=1:25-1:35)
• Pump reparation (ET=2:25-2:36)
8 October 2008:
• Back pressure reparation, during the night 670ml of production fluid to spillage
container.
9 October 2008:
• No production, dP is rising, (most) precipitated solids are removed in production
tube, still no flow (ET=49:20).
• End of the experiment(ET=49:25)
• After deconstructing the reactor a plug has been found just behind the core and
filter in the beginning of the production tube.
Observation and comments
This experiment looks from the start on very smoothly!
At ca. 65000 s, a temporary minor pressure reduction (T-drop from 100°C to 80°C)
didn’t produce much fluid; i.e. no pH measurements. Up to 110000 s, the dP shows fast
minor pressure changes which are assumed to be gas burps (production of CO2 during
the formation of wormholes.). At 110000 s, the pH drops from 5.5. to 1.5. This is
probably a temporary breaktrough through a wormhole running from the injection to the
FE49
74
production side. For sure it was a short cut where thee original acid could flow from the
injector to the production side.
Permeability:
During the regular parts of the experiment, the permeability varies around 4*10-15 m2. At
the end it slowly reduces to 1*10-15 m2 due to clogging at the production side.
Visual analysis and conclusive remarks.
The CT-scans before the experiment show the presence of fossils, majorly Belemnite
relics. The CT’s after show that all fracs are partly cemented and the branching of
wormholes is partly influenced by the presence of fossils. The photos show that the
original fracs have been cemented. Both injection and production side show wormholes.
FE49
75
Shift in raw data; no acquisition error
120
Pressure [bars]
100
80
60
40
100
80
Press1
60
Press2
40
Press3
20
20
Dp40Bar
Temp1
0
0
180000
170000
160000
150000
140000
130000
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
-20
0
-20
Tem p [deg C]
Time [seconds]
Fig.49.1: Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
90
8
80
7
70
6
60
5
g/L Na
g/L Ca
4
Acid production
40
pH
g/L
50
g/L Cl
g/L SO4
3
pH
30
2
20
1
10
0
0
50000
100000
150000
0
200000
T(sec)
Fig.49.2: HPLC and Pressure difference versus time.
FE49
76
8
80
7
60
6
40
pH
20
4
0
dP(bar)
5
pH
dP(press1-2)
3
-20
2
-40
1
0
0
50000
100000
150000
-60
200000
T(sec)
Fig.49.3: pH and Pressure difference versus time.
k49
Start acid inj
1E-14
dP is zero
9E-15
Gas burps
Production tube is
getting clogged
8E-15
dP is
zero
7E-15
Acid
brakethrough
k[m^2]
6E-15
5E-15
4E-15
3E-15
2E-15
1E-15
0
0
20000
40000
60000
80000 100000 120000 140000 160000 180000 200000
Time[sec]
Fig.49.4: Permeability versus time.
FE49
77
Fig.49.5: Photo of the injection side of the sample after the experiment.
. Fig.49.6: Photo of the production side of the sample.
FE49
78
Fig.49.7: Photo of the sample after the experiment.
Fig.49.9: Snapshot of the sample rendering of the CT-scan after the experiment. The red
matter represents some fossil artefacts. Visible are multiple wormholes converging into one
major wormhole which branches into multiple wormholes. The circles are the Teflon pieces
for maintaining the original frac aperture.
FE49
79
Sample ID: FE50
Weight
3031[g] , after exp: 3713[g]
Length
268[mm]
Diameter
99[mm], Volume: 2026[cc]
Goal Experiment
Core flooding experiment
Fracture width
3mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2[ml/min]
Pore Volume
Ml acid injected
600[ml], Porosity: 0,29, Wet weight porosity = 0.46
6310[ml]
Moles SO42- injected
CT scan
5,7[mol]
Yes, Before
Experimental history
The core consist of 3 fitting parts. The sample was broken in the radial plane during
preparation.
Pore fluid: brine
13 October 2008:
• Brine injection by vacuum 600ml (09:10).
• Start brine pump.
• Acid injection (ET=02:05 ET)
• Pump repaired (ET=03:45-4:00).
14 October 2008
• Heating and back pressure valve repaired (ET=22:05)
• Pump repaired (ET= ±27:25).
15 October 2008
• Pinj =70bar, dP high, acid flows out through the injector back pressure, amount of
acid lost is unknown, Pprod = 50 bar (ET=± 46:00 ET)
• dP problem unsolvable, stop experiment (ET=53:10)
Observation and comments
A complex experiment, it had some heating and production problems (Fig. 50.1). Figures
50.1 and 50.2 show that reduction of the annular pressure induces faster transport of
acids. This is recognized by the sudden decrease in Ph and increase of SO4-concentration
in the production fluid. It is also recognized in the permeability, since the dP drastically
reduces (goes to zero).
FE50
80
Visual analysis and conclusive remarks.
• The frac is closed on both sides at the end of the experiment.
• No evidence for large wormholes at both the injection and production side.
• The CT-rendering shows one major wormhole with some branches near the radial
fracture planes. These planes are cemented.
• During the experiment the Ph remains the same, independent of the P,T effects.
Conclusion
Now it becomes clear that if the Ph of the production fluid is 5 – 6, then a stable
equilibrium is reached. Further, P,T-problems often start after working hours. The
anhydrite precipitates in the back pressure valve, causing clogging and it can’t close.
Permeability
Despite the sudden alterations of differential pressures, the permeability remains in the
same order of magnitude; 3*10-15-4*10-15. The permeability decreases due to clogging of
the production line at the end of the experiment.
Recommendation
Heating ribbons around the back pressure valve and production have already been tried.
Try it again with more and at higher temperatures.
FE50
81
100
Pressure [bars]
Pinj has gone up
Heating and
back pressure
repared
120
100
80
80
60
60
40
20
0
Press3
Dp40Bar
20
Temp1
0
Temp2
190000
180000
170000
160000
150000
140000
130000
120000
110000
90000
100000
80000
70000
60000
50000
40000
30000
20000
10000
Press2
40
-20
0
-20
Press1
Tem p [deg C]
Time [seconds]
Fig.50.1: Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
80,0
8
Heating and back
pressure down, acid flows More back
rapidly through core
pressure
problems
70,0
7
60,0
6
50,0
5
40,0
4
g/L Na
pH
g/L
g/L Ca
g/L Cl
g/L SO4
30,0
3
20,0
2
10,0
1
0,0
0
50000
100000
150000
pH
0
200000
T(sec)
Fig.50.2: HPLC and Pressure difference versus time.
FE50
82
120
8
Pressure difference
is rising, calcite
precipitation in
production tube
7
6
100
80
60
pH
40
4
20
dP(bar)
5
pH
dP(press1-2)
3
0
2
-20
1
-40
0
0
50000
100000
150000
-60
200000
T(sec)
Fig.50.3: pH and Pressure difference versus time.
k50
1E-14
Acid
breakthrough
9E-15
dP is zero
Gas burps
8E-15
Start acid inj
7E-15
Production
tube is getting
clogged
k[m^2]
6E-15
5E-15
4E-15
3E-15
2E-15
1E-15
0
0
20000
40000
60000
80000 100000 120000 140000 160000 180000 200000
Time[sec]
Fig.50.4: Permeability versus time.
FE50
83
Fig.50.5: Photo of the production side of the sample after the experiment. Frac completely
closed.
Fig.50.6: Photo of the injection side of the sample, frac completely closed.
FE50
84
Fig.50.7: 3D rendering of results after the experiment: CT scan, all fossils red. The
wormholes reaches through the sample, till the end.
FE50
85
Sample ID: FE51
Weight
3199[g] , after exp: [g]
Length
280 [mm]
Diameter
99[mm], Volume: 2155[cc]
Goal Experiment
Core flooding experiment
Fracture width
3 mm
Acid used
HCl
H2SO4
H+/SO42- ratio
0.3 M
0.9 M
2.33
Flow Rate
2[ml/min]
Pore Volume
Ml acid injected
510 [ml], Porosity: 0,24, Wet weight porosity = 0.45
9070[ml]
Moles SO42- injected
CT scan
8,5 [mol]
Yes, Before & After
Experimental history
The core consist of 3 fitting parts. The sample was broken in the radial plane during
preparation.
Pore fluid: brine
27 October 2008:
• Brine injection by vacuum 505ml (13:30).
• Start brine pump.
• Acid injection (ET=0:55)
28 October 2008:
• Heater repaired
• Back pressure on the injector and heater failed during the night, 900ml acids to
the waste container (ET= 18:00).
• Back pressure on the injector side and heater repaired (ET= 18:57)
• Same back pressure is still leaking, repaired at (ET= 23:57)
• Thermometer on the injection side stopped working, can not be replaced while
running experiment(ET=24:15)
29 October 2008:
• Pressure has dropped due to calcite precipitation in the back pressure on the
production side. Repaired, pressure to normal(ET=42:59)
30 October 2009:
• Pinj low, 600ml to waste container. When corrected there was no more
production (ET=66:05).
• Last 24000sec no fluid production, only gas production.
• Experiment stopped (ET=67:30)
• Production tube was proven to be pugged when reactor was opened.
FE51
86
Permeability
The permeability remains around 4*10-15 - 5*10-15 m2. The slight drop around 100000 s
is due to a temperature drop. The drop around 145000 s – 165000 s is due to a
malfunction of the back pressure valve. Thereafter the permeability slowly recovers to
4*10-15 m2. Over the entire experiment, the SO4-concentration remains low, i.e.
anhydrite production and wormhole development.
Visual analysis and conclusive remarks.
• All fracs are closed and at some places not recognizable anymore.
• Wormholes visible at the injection side.
• CT-scans show fossils, but no preferential association between wormhole
formation and the presence of fossil vacuoles.
• The wormholes majorly develops branches between the injection side and the first
radial fracture plane.
Conclusion
Immediately after acid breakthrough, the “gas burps” start.
The permeability remains stable and more or less the same: about 5*10-15 m2.
Based on FE50 and FE51, it is concluded that there is a relation between branching of
wormholes and the presence of radial fracture planes.
FE51
87
Back pressure failed
120
Production
100
tube plugged
80
Pressure [bars]
100
80
60
60
40
20
0
Press3
Dp40Bar
20
Temp1
0
Temp2
240000
220000
230000
190000
200000
210000
170000
180000
130000
140000
150000
160000
110000
120000
90000
100000
70000
80000
50000
60000
30000
40000
0
Press2
40
-20
10000
20000
-20
Press1
Tem p [deg C]
Time [seconds]
Fig.51.1: Pressures and temperature versus time. P_injection: Injection pressure, P_product:
production pressure, P_annular: annular pressure, Dp: differential pore pressure P(1,2) and
T_reservoir: temperature in the sample (°C).
10
80,0
70,0
9
Acid breakthrough
8
60,0
7
50,0
5
pH
g/L
6
40,0
30,0
4
20,0
3
10,0
2
0,0
0
50000
100000
150000
-10,0
T(sec)
200000
1
250000
0
g/L Na
g/L Ca
g/L Cl
g/L SO4
pH
Fig.51.2: HPLC and Pressure difference versus time.
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Acid braek through,
and directly gas
burps
10
9
60
40
8
7
20
0
5
dP(bar)
pH
6
pH
dP(press 1-2)
4
-20
3
2
-40
1
0
0
50000
100000
150000
200000
250000
-60
300000
T(sec)
Fig.51.3: pH and Pressure difference versus time.
k51
Gas burps
1E-14
Start acid inj
9E-15
Acid
breakthrough
Back pressure
fail
8E-15
7E-15
Production tube
is getting
clogged
k[m^2]
6E-15
5E-15
4E-15
3E-15
2E-15
1E-15
0
0
T-drop
50000 effect
100000
150000
200000
250000
t(sec)Time[sec]
Fig.51.4: Permeability versus time.
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Fig.51.5: Photo of the sample after the experiment, multiple fractures are cemented.
Fig.51.6: Photo of the production side of the sample after the experiment, no fracture visible.
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Fig.51.7: Photo of the injection side of the sample, no fracture visible. Visible are big
wormholes, anhydrite and calcite.
Fig.51.8: CT image on the injection side, frac is gone, large amounts of anhydrite and big
wormholes are visible.
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Fossil
Fig.51.9: CT image on the injection side behind the perpendicular fracture. Again large
amount of anhydrite and big wormholes are visible. A fossil is also visible.
Fig.51.10: CT image on the Production side, large amount of anhydrite and small wormholes
are visible. Frac is totally cemented.
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Fig.51.11: 3D rendering of the CT images before acidizing, visible are the fossils (red).
Fig.51.12: 3D rendering of the CT images before acidizing, visible is the macro pore volume
(blue).
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Fig.51.13: 3D rendering of the CT images before acidizing, visible is the macro pore volume
(blue) and the fossils (red)
Fig.51.14: 3D rendering of the CT images before acidizing, visible is the fracture (green)
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Fig.51.15: 3D rendering of the CT images before acidizing, visible is the macro pore volume
(blue), fracture (green) and the fossils (red)
Fig.51.16: 3D rendering of the CT images after acidizing, visible are the fossils (red).
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Fig.51.17:3D rendering of the Ct images after acidizing, visible are the fossils (red) and the
wormholes (blue)
Fig.51.18:3D rendering of the Ct images after acidizing, visible are the fossils (red),t the
fractures perpendicular to the flow (green) and the wormholes (blue)
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Fig.51.19:3D rendering of the Ct images after acidizing, visible is the anhydrite (purple)
Fig.51.20:3D rendering of the Ct images after acidizing, visible are the fossils (red), anhydrite
(purple, the fractures perpendicular to the flow (green) and the wormholes (blue), so only the
anhydrite is missing in this picture.
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Fig.51.20:3D rendering smoothed of the Ct images after acidizing, visible are the fossils (red),
anhydrite (purple, the fractures perpendicular to the flow (green) and the wormholes (blue), so
only the anhydrite is missing in this picture.
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