Carbonate reservoir

1. See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/332594750
Static dissolution-induced 3D pore network modification and its impact on
critical pore attributes of carbonate rocks
Article in Petroleum Exploration and Development · April 2019
DOI: 10.1016/S1876-3804(19)60017-0
CITATIONS
0
READS
69
4 authors, including:
Some of the authors of this publication are also working on these related projects:
A HYBRID ARIMA POLYNOMIAL HARMONIC GMDH MODEL TO FORECAST CRUDE OIL PRICE View project
Joel Ben-Awuah
Laurentian University
30 PUBLICATIONS 56 CITATIONS
SEE PROFILE
Rajalingam Sokkalingam
Universiti Teknologi PETRONAS
10 PUBLICATIONS 3 CITATIONS
SEE PROFILE
All content following this page was uploaded by Joel Ben-Awuah on 30 April 2019.
The user has requested enhancement of the downloaded file.

2. RESEARCH PAPER
PETROLEUM EXPLORATION AND DEVELOPMENT
Volume 46, Issue 2, April 2019
Online English edition of the Chinese language journal
Cite this article as: PETROL. EXPLOR. DEVELOP., 2019, 46(2): 374–383.
Received date: 11 Aug. 2018; Revised date: 04 Jan. 2019.
* Corresponding author. E-mail: spariharijaona.andr@petronas.com.my
https://doi.org/10.1016/S1876-3804(19)60017-0
Copyright © 2019, Research Institute of Petroleum Exploration & Development, PetroChina. Publishing Services provided by Elsevier B.V. on behalf of KeAi Com-
munications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Static dissolution-induced 3D pore network modification
and its impact on critical pore attributes of carbonate
rocks
ANDRIAMIHAJA Spariharijaona1, 2,
*, PADMANABHAN Eswaran2
, BEN-AWUAH Joel3
,
SOKKALINGAM Rajalingam4
1. Hydrocarbon Recovery and Technology, Group Research and Technology, PETRONAS Research Sdn. Bhd., Jalan Ayer Itam, Kawasan
Institusi Bangi, 43000 Bandar Baru Bangi, Selangor, Malaysia;
2. Department of Geosciences, Faculty of Petroleum Engineering and Geosciences, Universiti Teknologi PETRONAS, 32610 Seri Iskandar,
Perak, Malaysia;
3. Department of Applied Geology, Faculty of Engineering and Science, Curtin University, CDT250, Miri 98009, Sarawak, Malaysia;
4. Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia
Abstract: To determine the effect of dissolution on pore network development in carbonate rocks, dissolution experiments, X-Ray mi-
crotomography, and thin section analysis were conducted on argillaceous limestone and grain limestone samples at different temperatures and
constant pH, HCl concentration. The relationship between Ca2+
concentration and time was revealed through the experiments; pore size
distribution before and after dissolution indicate that there is no correlation between the temperature and pore size variation, but pore size
variation in grain limestone is more significant, indicating that the variation is mainly controlled by the heterogeneity of the rock itself
(initial porosity and permeability) and the abundance of unstable minerals (related to crystal shape, size and mineral type). At different
temperatures, the two kinds of carbonate rocks had very small variation in pore throat radius from 0.003 mm to 0.040 mm, which is 1.3 to
3.5 times more, 1.7 on average of the original pore throat radius. Their pore throat length varied from 0.05 mm to 0.35 mm. The minor
changes in the pore throat radius, length and connectivity brought big changes to permeability of up to 1 000×103
μm2
.
Key words: 3D pore networks; carbonate rocks; pore structure; mudstone; grainstone; acidizing; dissolution, X-Ray micro tomography
Introduction
Fluid flowing in the rock mainly depends on the pore sys-
tem. The presence of highly soluble carbonate minerals would
result in changes of pore geometry and petrophysical proper-
ties in carbonate reservoirs under fluid-rock interactions[12]
.
These interactions at pore scale can be used to improve the
performance of carbonate reservoirs[37]
and to evaluate the
reservoir integrity for long-term Carbon Capture and Storage
(CCS)[811]
. Knox et al.[3]
considered that the performance of
acidizing was affected by multiple factors, including acid
penetration, acid density, fracture flow capacity, temperature,
acid concentration, fluid density and viscosity. Mcleod et al.[4]
attributed the success of acidizing to the evaluation of produc-
tion history, as well as the design for acid damaged perfora-
tions such as selection of solvents and acid components.
McDuff et al.[5]
used a new 3D visualization method to evalu-
ate the performance of acidizing on carbonate reservoirs.
Several researchers reported that pore structure changes
caused by dissolution was controlled by multiple factors such
as fluid temperature, pressure, pH, porosity, permeability and
crystal size[1220]
. However, there are few studies on the
change of pore network attribute induced by dissolution re-
ported.
The X-ray micro tomography (X-Ray micro CT) technique
is now commonly used to study pore systems in reservoir[2123]
.
The 3D pore network information extracted via several ap-
proaches such as segmentation binarization or skeletonization
can give us an understanding on fluid flowing within complex
porous media, through working out attributes such as porosity
distribution, pore radius, pore throat radius, pore throat length
and coordination number[2430]
.
X-ray micro CT can be also used to evaluate dissolution
induced pore changes at various conditions (different tem-

3. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 375 
peratures and pressures). Luquot et al.[1]
analyzed the impact
of CO2-rich brine on limestone reservoir properties and con-
cluded that porosity and permeability changes were controlled
by inlet fluid disequilibrium and the initial reaction rate.
Noiriel et al.[31]
evaluated the 3D changes of fractures in lime-
stone at room temperature and noticed that there was no pref-
erential flow pathways formed and the presence of any sili-
cates in carbonate rocks led to heterogeneous dissolution at
micro-scale. Menke et al.[11]
investigated the dynamic evolu-
tion of pores in carbonate rocks saturated with CO2 brine at
50 °C and 10 MPa and concluded that the ratio of surface area
to volume and porosity increased. Rötting et al.[32]
found that
significant dissolution only occurred in certain pore diameter
at specific conditions. Even though, these researches have
given important knowledge on pore system modifications at
different pressure and temperature conditions, the impact of
dissolution on carbonate pore systems still needs further
study[3337]
. Therefore, the objective of this study is to find out
the effect of dissolution on pore network in carbonate rocks at
various well conditions and temperatures.
1. Materials and methods
1.1. Dissolution experiment
The dissolution experiments of two types of carbonate
rocks, mudstone (type 1 rock) and grainstone (type 2 rock),
were performed in a closed bath reactor system[3839]
. The pH,
concentration of HCl and rotation rate of stirrer were main-
tained constant at 1.2, 0.1 mol/L, 12.56 rad/s respectively
during the experiments. The dissolution experiment was con-
ducted at 25 °C, 50 °C and 75 °C for 100 min. Aliquots of
samples were collected every 10 min and the calcium concen-
tration in each aliquot was tested using Plasma-Optical Emis-
sion Spectrometry (Perkinelmer, Optima 8300 ICP-EOS
Spectrometer) to figure out the Ca2+
concentration released by
the carbonate rock sample. Variation of Ca2+
concentration
with time was analyzed to find out the dissolution rate law
and characteristics of dissolution kinetic.
1.2. X-Ray Micro CT imaging
Each sample was scanned with X-Ray CT System (inspeXio
SMX-255CT) at 160 kV and 100 µA. After scanning, the im-
ages were processed and then pore networks were extracted
using VGStudio Max 2.1, ProAnalyzer, Fiji ImageJ and Avizo
Fire software. In order to evaluate the impact of dissolution on
fluid flow properties of the samples, Avizo Fire software was
used to simulate the permeability before and after dissolution.
These simulations were performed following Darcy’s law,
under the following conditions: inlet and outlet pressures of
2.75106
Pa and 0.10106
Pa respectively, and the viscosity of
1.96105
Pa·s (helium viscosity at room temperature).
1.3. Petrophysical analysis
Thin section observation of both rock types shows that they
differ widely in pore characteristics. Type 1 rock has pores
that are restricted and isolated within the general fabric of the
rock (Fig. 1a). Type 2 rock has pores that are interconnected
and distributed throughout the rock fabric (Fig. 1b).
Comparing the two types of rock shows type 1 rock has a
porosity of 20% and permeability of 1.39103
μm2
; type 2
rock has a porosity of 36% and permeability of 1 063.38103
μm2
. From XRD analysis, type 2 rock is composed of 96.88%
of calcite and 3.12% of dolomite whereas type 1 rock is com-
posed of 87% of calcite and 13% of dolomite. In terms of the
mineralogical composition, type 1 rock contains more stable
minerals than type 2 rock. This implies that type 2 rock would
dissolve faster than type 1 rock.
According to the different dissolution temperatures (25, 50
and 75 C), each rock type was divided in three portions. The
type 1 rock portions were coded as M1, M2, M3 and the type
2 rock portions were B1, B2 and B3.
2. Results and discussions
2.1. Dissolution analysis
2.1.1. Relationship of calcium ion concentration and time
As can be seen from Fig. 2, the released Ca2+
increases
Fig. 1. Pore characteristics of two types of carbonate rocks.

4. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 376 
Fig. 2. Relationship between Ca2+
concentration released from two types of carbonate rocks and time at different temperatures.
rapidly in the first 20 min at the initial stage of dissolution,
and the increase of Ca2+
concentration gradually slows down
with time. The second phase of dissolution is stable, which is
related to the gradual decrease of released Ca2+
. The temporal
variation of released Ca2+
is described by the following gen-
eral equation (Eq. 1) and obtained from the best fit model of
Ca2+
concentration and time curve at 25, 50 and 75 °C.
ca ca 0 ca 0
ln ln lg ln
C C k t C kx
   
， ， (1)
where lg
x t

The generated model follows the first-order reaction char-
acteristics and can be expressed by linear equation. The new
model is defined by two constants, the rate constant k and the
initial Ca2+
concentration Cca,0. The time and Ca2+
concentra-
tion show good correlation, with R2
of 0.9. The dissolution
experiments show carbonate dissolution is stronger at higher
temperature (Fig. 2).
The fast increase of Ca2+
concentration initially can be at-
tributed to the presence of highly soluble, fine and unconsoli-
dated carbonate crystals or grains and unstable and highly
reactive minerals at the rock surface (Fig. 3). Scanning elec-
tron microscopic image of Fig. 3a shows calcite mineral on
type 1 rock surface before dissolution. Fig. 3b shows type 1
rock after dissolution, in which most of the fine and soluble
particles have been dissolved, leaving a more porous and
smoother rock surface. Once these unstable carbonate com-
ponents are dissolved, the release of Ca2+
generally decreases
and the dissolution remains constant. This could possibly be
due to the gradual saturation of the aqueous solution, or re-
duction of highly reactive surface minerals as the experimen-
tal conditions remain unchanged (pH remains constant).
2.1.2. Dissolution kinetic models
The instantaneous dissolution rate model is a function of
rate constant and the released Ca2+
concentration, and can be
written as the following equation (2).
ca
ca,0 ca
d
e
d
kx
C
r C k kC
x
   (2)
The dissolution kinetic model has characteristic of first or-
der reaction. Based on this model, dissolution rate depends on
initial concentration of Ca2+
, the rate constant and laboratory
conditions (Table 1). Type 1 sample dissolved slowest at 25 °C
and type 2 sample dissolved fastest at 75 °C. The comparison
of dissolution rates of the 2 types of carbonate rock shows that
type 1 dissolves slower than the type 2 at any given tempera-
ture. This is attributed to the type 1 (13% of dolomite) con-
tains more stable carbonate minerals than type 2 (3% of
dolomite). As the experimental conditions of dissolution were
identical, the variation of rate constant between the samples is
attributed to the heterogeneities of rocks. These heterogenei-
ties include chemical element composition and petrophysical
Fig. 3. SEM images before and after dissolution of type 1 rock.

5. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 377 
Table 1. Dissolution kinetics parameters of 2 kinds of carbonate rocks at 25, 50 and 75 °C.
Type 1 rock Type 2 rock
Tempera-
ture/C Cca,0/106
k/(106
·min1
) DR*
mean/(106
·min1
) Cca,0/106
k/(106
·min1
) DR*
mean/(106
·min1
)
25 1.711 0.163 0.198 2.085 0.122 0.202
50 1.417 0.212 0.206 2.201 0.131 0.244
75 3.095 0.041 0.211 2.503 0.122 0.312
Table 2. Pore network model variation induced by dissolution at various temperatures.
Rock
type
Sample and
temperature
Experimental
condition
Measured
porosity/%
Pore
number
Pore
size/mm
Pore throat
number
Average
pore throat
radius/mm
Average
pore throat
length/mm
Coordina-
tion number
Absolute per-
meability/
103
μm2
Before dissolution 1.70 801 0.18 411 0.022 0.27 4.2 13.04
M1, 25 C
After dissolution 5.20 564 0.24 291 0.030 0.37 5.3 50.00
Before dissolution 0.11 25 0.21 9 0.049 0.53 1.0 4.16
M2, 50 C
After dissolution 0.43 13 0.32 6 0.065 0.65 2.9 17.75
Before dissolution 0.23 794 0.24 313 0.035 0.38 1.2 2.50
Type
1 rock
M3, 75 C
After dissolution 1.06 274 0.26 88 0.050 0.52 2.2 9.45
Before dissolution 8.07 4 139 0.10 792 0.026 0.23 3.0 751.53
B1, 25 C
After dissolution 12.70 1 637 0.18 515 0.036 0.33 4.4 950.00
Before dissolution 6.80 1 604 0.19 348 0.052 0.51 2.7 843.40
B2, 50 C
After dissolution 10.80 875 0.30 195 0.055 0.56 4.0 2 358.30
Before dissolution 8.01 1 588 0.12 691 0.015 0.18 4.9 1 638.50
Type
2 rock
B3, 75 C
After dissolution 22.34 1 035 0.23 321 0.053 0.53 7.9 5 556.50
characteristics (porosity and permeability).
2.2. Pore network system induced by dissolution
Table 2 summarizes the pore network system variations at
different temperatures. The pore networks are characterized
by several attributes, including porosity, pore size distribution,
number of pores, pore throat radius, and pore throat length
and coordination number. The permeability is also affected by
dissolution as a consequence of pore network variation.
2.2.1. Porosity variations
Porosity extracted from X-ray microCT analysis is defined
as ratio of mapped pore volume and bulk volume of rock
sample. It comprises isolated and connected pores. As ex-
pected, dissolution of carbonate rock enhances the overall poro-
sity (Fig. 4). The porosity profiles before and after dissolution
exhibit similar distribution characteristics in some sections
along the samples, which is interpreted as enhancement of the
initial pore due to dissolution (Fig. 4a). However, in some part
of the porosity profile, porosity after dissolution greatly in-
creases compared to the initial porosity profile. This important
increase of porosity suggests a significant expansion of initial
pore system. Dissolution of calcite results in dense pore wall
where the diluted HCl solution can easily percolate because of
the presence of unstable calcite minerals and large initial pore
size. This dissolution can lead to very large cavities and new
pore system (Fig. 4c), improving considerably the total poros-
ity. Before dissolution, these newly formed pores were filled
by fine and unstable calcite minerals. After dissolution, these
materials have been dissolved and formed new pores.
Fig. 4. Porosity distribution of carbonate sample before and
after dissolution.
Fig. 5 shows the porosity changes of type 1 rock of samples
M1, M2 and M3 and type 2 rock of samples B1, B2 and B3 at
25, 50, 75 °C respectively. Because of the heterogeneity of
rock samples, different samples of type 1 rock and samples of
type 2 rock are slightly different in initial porosity (before
dissolution). During dissolution, porosity increases as ex-
pected. The porosity change is significant at the top of sample
where there is continuous reacts with HCl solution by the
stirrer, leading to faster dissolution than the other part of the
rock. Porosity change occurs throughout the sample which
implies that sample is dissolved in 3 directions along x-axis,
y-axis and z-axis. However, the uniform porosity change
throughout the sample indicates that the change is mainly

6. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 378 
Fig. 5. Porosity variation induced by dissolution of two types of carbonate rocks at different temperatures.
dominated by pore enlargement rather than creation of new
pore system.
It can be seen from Fig. 6, porosity distribution is charac-
terized by positive skewness. After dissolution at different
temperatures, porosity distribution is still characterized by
positive skewness but is slightly left skewed. After dissolution,
kurtosis value decreases, implying that porosity distribution
peak is flatter than before dissolution. Porosity range after
dissolution also increases as compared to the porosity range
before dissolution. In the type1 rock, porosity increases by 3.0,
4.0 and 4.5 times from the initial porosity at 25, 50, 75 °C
respectively. However, these increment factors only corre-
spond to 3.50%, 0.32% and 0.83% increase of porosity at 25,
50, and 75 °C respectively. In the type 2 rock, porosity only
increases by 1.6, 1.6, and 2.8 times from the initial porosity,
but these increment factors correspond to a significant in-
crease of porosity of 4.7%, 4% and 14.3% at 25, 50, 75 °C
respectively. At 25 °C and 50 °C, the porosity variations are
similar whereas, at 75°C, the change is much more significant.
From these results, it can be inferred that the porosity in-
crement factor increases as the temperature increases. More-
over, having a significant increment factor does not necessary
mean high porosity variation. In this case, the initial porosity
of carbonate rock contributes to the porosity enhancement by
dissolution. Therefore, during dissolution, in porous carbon-
ates such as grainstones, small increment factor can result in a
Fig. 6. Histogram of porosity distribution before and after dis-
solution.
significant porosity variation, whereas in less porous carbon-
ate rocks such as mudstone, important increment factor can
lead to small porosity variation. Therefore, the most signifi-
cant porosity variation is obtained from the dissolution at the
highest temperature of carbonate rock with high initial poros-
ity.
2.2.2. Pore size distribution changes
In the 2 types of carbonate rocks, the total numbers of pores
vary from 25 (in the less porous mudstone) to 4139 (in the
porous grainstone). After dissolution, these numbers decrease
to 131637, which is in agreement with results provided in
Reference [11]. The reduction in pore numbers suggest that
pores are merged together forming larger pores. Fig. 7 shows
the pore size distribution (PSD) of all samples before and after
dissolution at 25, 50 and 75 °C. Pore size distributions of two
types of carbonates are lognormal distribution with normal
skewness. After dissolution, regardless of the temperature
variations, pore size distributions still show positive skewness
but are slightly skewed left, and the pore size distribution
curve is flatter than the one before dissolution. The skewness
of PSD after dissolution toward the higher value confirms that
the increase of overall pore size. The decrease of kurtosis of
PSD after dissolution suggests that the PSD is more spread
around the median than the one before dissolution.
For type 1 rock, the dissolution at 25, 50 and 75 °C made
pore size increase by 1.3, 1.5 and 1.1 times from the initial
pore size, and made the pore diameter increase by 0.06, 0.11,
0.02 mm respectively (Fig. 8a). Dissolution has more signifi-
cant effect on pore diameter of the type 2 rock than type 1
rock. At 25, 50 and 75 °C, pore diameter of type 2 rock in-
creased by 1.80, 1.60 and 1.92 times, corresponding to 0.08,
0.11 and 0.11 mm respectively (Fig. 8b).
No correlation is observed between the temperature and
pore size variation for the two rock types. On the other hand,
the pore size variation of type 2 rock is larger than that of type
1, which indicates that the heterogeneity of the rock and exis-
tence of unstable carbonate minerals are the key factors af-
fecting pore size enlargement.

7. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 379 
Fig. 7. Pore size distribution variation of 2 types of carbonate rock at different temperatures.
Fig. 8. Pore size variation of 2 types of carbonate rock at different temperatures.
Fig. 9. Pore throat radius distribution variation of 2 types of carbonate rock at different temperatures.
2.2.3. Variation of pore throat radius
Pore throat of carbonate rock is characterized by its radius
and its length. Similar to pore size distribution, the best dis-
tribution fit for the pore throat radius distribution (PTRD) is
lognormal distribution (Fig. 9). Both pore throat radius distri-
bution before and after dissolution show positive skewness.
However, after dissolution, the pore throat radius distribution
is slightly left skewed, indicating an overall increase of pore
throat size.
For type 1 rock, the average pore throat radius increased by
0.01 mm at 25 °C and 0.02 mm at 50 and 75 °C (Fig. 10a).
The pore throat radius increased by 1.3 times at 50 °C, 1.4
times at 25 and 75 °C after dissolution. For type 2 rock, dis-
solution at 25, 50 and 75 °C make pore throat radius enlarge
by 0.010, 0.003 and 0.040 mm respectively (Fig. 10b).

8. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 380 
Fig. 10. Pore throat radius variation of two types of 2 types of carbonate rock at different temperatures (using independent standard
deviation to calculate the interval).
2.2.4. Variation in pore throat length
Similar to PTRD, the pore throat length also shows log-
normal distribution, and both distributions are characterized
by positive skewness before and after dissolution at different
temperatures. The pore throat length distribution after dissolu-
tion skewed left than before dissolution, indicating the pore
throat length increased. In addition, the peak of pore throat
length after dissolution is slightly flatter and has more data in
the tail than that before dissolution, and is characterized by a
decrease of kurtosis value (Fig. 11).
For the type 1 rock, the average pore length increased by
0.1 mm at 25 °C, 0.12 mm at 50 °C and 0.14 mm at 75 °C
(Fig. 12a). For type 2 rock, this pore throat length increased
by 0.10 mm at 25 °C, 0.05 mm at 50 °C and 0.35 mm at 75 °C
(Fig. 12b). On the whole, pore throat length increased by 1.1
to 3.5 times after dissolution. These results suggest that tem-
perature and heterogeneity of the samples are major factors
controlling pore throat variation due to dissolution.
From analysis of pore throat attributes before and after dis-
solution, the variation of pore throat radius is proportional to
the variation of pore throat length (Fig. 13), suggesting
Fig. 11. Pore throat length distribution variation of 2 types of carbonate rock at different temperatures.
Fig. 12. Variation of pore throat length of 2 types of carbonate rock at different temperatures.

9. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 381 
Fig. 13. The relationship of variation of pore throat radius and
variation of pore throat length.
uniform development of the pore throat in 3 directions.
2.2.5. Changes in coordination number
The coordination number is related to connectivity of pores.
It defines the number of throats connected to each pore.
Therefore, the higher the coordination number, the better the
pore connectivity is. Before dissolution, for type 1 rock, the
average coordination number of the 3 samples were 4.2 (M1),
1.0 (M2) and 1.2 (M3) at 25, 50 and 75 °C respectively. After
dissolution, the coordination number changed to 5.3 (M1), 2.9
(M2) and 2.2 (M3) respectively. For type 2 rock, the coordi-
nation number of the 3 samples were 3.0 (B1), 2.7 (B2) and
4.2 (B3) at 25, 50 and 75 °C respectively, the coordination
number after dissolution increased to 4.4 for B1 at 25 °C, 4.0
for B2 at 50 °C and 7.9 for B3 at 75 °C. The observation re-
sults show that the carbonate rock sample with highly con-
nected initial pores would have the best connectivity after
dissolution at the highest temperature.
2.3. Simulation of permeability before and after dissolution
In order to evaluate the effect of dissolution on fluid flow
ability of the carbonate rocks, permeability before and after
dissolution were simulated. For type 2 rock, the simulated
permeability changed significantly. For B1 after dissolution at
25 °C, the simulated permeability increased by 1.3 times,
from 751.5×103
μm2
to 950.0×103
μm2
(increase of 198.5×
103
μm2
). For B2 after dissolution at 50 °C, the permeability
increased from 843.3×103
μm2
to 2358.3×103
μm2
(increase
of 1514.9×103
μm2
) by 2.8 times. For B3 after dissolution at
75 °C, the permeability increased by 3.4 times than the initial
permeability, from 1639×103
μm2
to 5566.5×103
μm2
(in-
crease of 3928×103
μm2
). For type 1 rock, After dissolution
at 25, 50 and 75 °C, the permeability increased from 13.04×
103
, 4.80×103
, 2.50×103
μm2
to 50.00×103
, 17.75×103
,
9.45×103
(that is an increment of 36.96×103
, 12.95×103
,
6.95×103
μm2
) respectively. Simulated permeability of the
two types of carbonate rocks both increased significantly after
dissolution. But the variation of permeability induced by dis-
solution is more significant in type 2 rock with higher initial
permeability than type 1, suggesting that the permeability
increase caused by dissolution is relatively selective. There-
fore, dissolution is more effective in permeable carbonate rock
than in less permeable carbonate rock due to connectivity of
pore networks. Moreover, the analysis of pore throat attributes
changes, coordination number and the variation of simulated
permeability (Table 2) suggests that small changes of pore
attributes like the variation of 0.01 mm in pore radius, 0.1 mm
in pore length and slight variation in coordination number
(one unit) can lead to very significant permeability changes of
an order of 1 000×103
μm2
in porous carbonate reservoir rock
and 10×103
μm2
in less porous reservoir.
3. Conclusions
In this study, the change of released Ca2+
concentration was
described by the dissolution kinetics model of carbonate rock.
The average dissolution rate is directly related to temperature
for all samples tested. The study shows that the dissolution
process that modifies pore systems differently and complicat-
edly for each sample, and the more porous carbonate rock
dissolved at the high temperature has the most significant
porosity variation. The comparison between pore size distri-
bution before and after dissolution at different temperatures
indicates that there is no correlation between the temperature
and pore size variation. However, pore size variation in type 2
rock is larger than the variation in the Type 1, indicating that
the pore size variation is mainly controlled by the physical
property (initial porosity and permeability) of the rock itself
and the abundance of unstable minerals (function of crystal
shape, size and mineral type) at the pore wall. Pore throat
attributes (radius and length) are also affected by dissolution.
However, the pore throat radius variation at different tem-
peratures are very small, ranging from 0.003 mm to 0.040 mm
and with an average increment factor of 1.7 for the studied
rock types. Pore throat length also had small variations, rang-
ing from 0.05 to 0.35 mm. The pore throat attributes generally
increase as the temperature of dissolution increases. After
dissolution, coordination number representing the connec-
tivity of pore networks increased. The carbonate rocks with
higher initial coordination number would have better pore
connectivity after dissolution at high temperature. Permeabil-
ity increases as the temperature increases from the analysis of
permeability simulation before and after dissolution at differ-
ent temperatures. Variation of permeability is more significant
in porous carbonate rocks than in less porous carbonate rock.
Furthermore, it is found that minor changes of the pore throat
radius, length and connectivity have great impact on perme-
ability. The results of this study give us a better understanding
on carbonate reservoir behavior at pore-scale caused by
fluid-solid interactions. This information can be useful when
implementing EOR such as acidizing at specific zones of the
reservoir, although the experiment condition is static acidizing.
Acknowledgment
This study is sponsored by PETRONAS and YUTP
(Yayasan Universiti Teknologi PETRONAS).

10. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 382 
Nomenclature
Cca—Ca2+
concentration, 106
;
Cca,0—Ca2+
concentration at t=1 min, 106
;
DR*
mean—average dissolution velocity, 106
/min;
k—rate constant, 106
/min;
r—instantaneous dissolution velocity, 106
/min;
t—time, range from 0 to100, min.
References
[1] LUQUOT L, GOUZE P. Experimental determination of po-
rosity and permeability changes induced by injection of CO2
into carbonate rocks. Chemical Geology, 2009, 265(1/2):
148–159.
[2] YASUDA E Y, SANTOS R G D, VIDAO T O. Kinetics of
carbonate dissolution and its effects on the porosity and per-
meability of consolidated porous media. Journal of Petroleum
Science and Engineering, 2013, 112: 284–289.
[3] KNOX J A, RIPLEY E H. Fracture acidizing in carbonate
rock. Journal of Canadian Petroleum Technology, 1979, 18(4):
77–90.
[4] MCLEOD H O. Significant factors for successful matrix
acidizing. SPE 20155, 1989.
[5] MCDUFF D R, JACKSON S K, SHUCHART C E, et al. Un-
derstanding wormholes in carbonates: Unprecedented experi-
mental scale and 3D visualization. SPE 129329, 2010.
[6] TANSEY J. Pore-network modeling of carbonate acidization.
SPE 173471, 2014.
[7] LIU N, LIU M. Simulation and analysis of wormhole propa-
gation by VES acid in carbonate acidizing. Journal of Petro-
leum Science and Engineering, 2016, 138: 57–65.
[8] MARLAND G, FRUIT K, SEDJO R. Accounting for seques-
tered carbon: The question of permanence. Environmental
Science & Policy, 2001, 4(6): 259–268.
[9] HERZOG H, CALDEIRA K, REILLY J. An issue of perma-
nence: Assessing the effectiveness of temporary carbon stor-
age. Climatic Change, 2003, 59(3): 293–310.
[10] METZ B, DAVIDSON O, CONINCK D H, et al. Carbon di-
oxide capture and storage. UK: Cambridge University Press,
2005.
[11] MENKE H P, BIJELJIC B, ANDREW M G, et al. Dynamic
three-dimensional pore-scale imaging of reaction in a carbon-
ate at reservoir conditions. Environmental Science and Tech-
nology, 2015, 49(7): 4407–4414.
[12] LETTERMAN R D. Calcium carbonate dissolution rate in
limestone contactors. Ohio: US Environmental Protection
Agency, 1995.
[13] ALKATTAN M, OELKERS E H, DANDURAND J, et al. An
experimental study of calcite and limestone dissolution rates
as a function of pH from -1 to 3 and temperature from 25 C
to 80 C. Chemical Geology, 1998, 151(1/2/3/4): 199–214.
[14] DOLGALEVA I V, GORICHEV I G, IZOTOV A D, et al.
Modeling of the effect of pH on the calcite dissolution kinet-
ics. Theoretical Foundations of Chemical Engineering. 2005,
39(6): 614–621.
[15] ADHAM A K M, KOBAYASHI A. Effect of intensity and pH
of rain on the dissolution of limestone: The Nineteenth Inter-
national Offshore and Polar Engineering Conference. Japan:
International Society of Offshore and Polar Engineers, 2009:
1196–1201.
[16] CROCKFORD P, TELMER K, BEST M. Dissolution kinetics
of Devonian carbonates at circum-neutral pH, 50 bar pCO2,
105 C, and 0.4 M: The importance of complex brine chemistry
on reaction rates. Applied Geochemistry, 2014, 41: 128–134.
[17] KIRSTEIN J, HELLEVANG H, HAILE B G, et al. Experi-
mental determination of natural carbonate rock dissolution
rates with a focus on temperature dependency. Geomorphol-
ogy, 2016, 261: 30–40.
[18] COHEN C E, DING D, QUINTARD M, et al. From pore scale
to wellbore scale: Impact of geometry on wormhole growth
in carbonate acidization. Chemical Engineering Science, 2008,
63(12): 3088–3099.
[19] KALIA N, BALAKOTAIAH V. Effect of medium heteroge-
neities on reactive dissolution of carbonates. Chemical Engi-
neering Science, 2009, 64(2): 376–390.
[20] ANDRIAMIHAJA S, PADMANABHAN E, BEN-AWUAH J.
Characterization of pore systems in carbonate using 3D X-ray
computed tomography. Petroleum and Coal, 2016, 63(4):
507–516.
[21] BERG S, OTT H, KLAPP S A, et al. Real-time 3D imaging of
Haines jumps in porous media flow. Proceedings of the Na-
tional Academy of Sciences of the United States of America,
2013, 110(10): 3755–3759.
[22] WILDENSCHILD D, SHEPPARD A P. X-ray imaging and
analysis techniques for quantifying pore-scale structure and
processes in subsurface porous medium systems. Advances in
Water Resources, 2013, 51: 217–246.
[23] BLUNT M J, BIJELJIC B, DONG H, et al. Pore-scale imag-
ing and modelling. Advances in Water Resources, 2013, 51:
197–216.
[24] GARING C, LUQUOT L, PEZARD P A, et al. Electrical and
flow properties of highly heterogeneous carbonate rocks.
AAPG Bulletin, 2014, 98(1): 49–66.
[25] BIRD M B, BUTLER S L, HAWKES C D, et al. Numerical
modeling of fluid and electrical currents through geometries
based on synchrotron X-ray tomographic images of reservoir
rocks using Avizo and COMSOL. Computers & Geosciences,
2014, 73: 6–16.
[26] BULTREYS T, HOOREBEKE L V, CNUDDE V. Multi-scale,
micro-computed tomography-based pore network models to
simulate drainage in heterogeneous rocks. Advances in Water
Resources, 2015, 78: 36–49.
[27] BECKINGHAM L E, PETERS C A, UM W, et al. 2D and 3D
imaging resolution trade-offs in quantifying pore throats for
prediction of permeability. Advances in Water Resources,
2013, 62(A): 1–12.
[28] RABBANI A, AYATOLLAHI S, KHARRAT R, et al. Estima-

11. ANDRIAMIHAJA Spariharijaona et al. / Petroleum Exploration and Development, 2019, 46(2): 374–383
 383 
tion of 3-D pore network coordination number of rocks from
watershed segmentation of a single 2D image. Advances in
Water Resources, 2016, 94: 264–277.
[29] DONG H, TOUATI M, BLUNT M J. Pore network modeling:
Analysis of pore size distribution of Arabian core samples.
SPE 105156, 2007.
[30] FREIRE-GORMALY M, ELLIS J S, MACLEAN H L, et al.
Pore structure characterization of Indiana limestone and pink
dolomite from pore network reconstructions. Oil & Gas Sci-
ence and Technology, 2016, 71(3) : 1–14.
[31] NOIRIEL C, GOUZE P, MADÉ B. 3D analysis of geometry
and flow changes in a limestone fracture during dissolution.
Journal of Hydrology, 2013, 486: 211–223.
[32] RÖTTING T S, LUQUOT L, CARRERA J, et al. Changes in
porosity, permeability, water retention curve and reactive sur-
face area during carbonate rock dissolution. Chemical Geol-
ogy, 2015, 403: 86–98.
[33] FREDD C N, FOGGLER H S. Influence of transport and re-
action on wormhole formation in porous media. AICHE Jour-
nal, 1998, 44(9): 1933–1949.
[34] FREDD C N, FOGGLER H S. Alternative stimulation fluids
and their impact on carbonate acidizing. SPE 31074, 1998.
[35] FREDD C N, FOGGLER H S. Optimum conditions for
wormhole formation in carbonate porous media: Influence of
transport and reaction. SPE 56995, 1999.
[36] GOLFIER F, BAZIN B, ZARCONE C, et al. Acidizing car-
bonate reservoirs: Numerical modelling of wormhole propa-
garion and comparison to experments. SPE 68922, 2001.
[37] TANSEY J, BALHOFF T. Pore network modelling of reactive
transport and dissolution in porous media. Transport in Porous
Media, 2016, 113(2): 303–327.
[38] AMACHER M C. Methods of obtaining and analyzing kinetic
data. USA: Soil Science Society of America, 1991.
[39] LIU Z, WOLFGANG D. Kinetics and rate-limiting mecha-
nisms of dolomite dissolution at various CO2 partial pressures.
Science in China, Series B, 2001, 44(5): 500–509.
View publication stats
View publication stats