- Email: [email protected]
Cap Rock CO2 Breakthrough Pressure Measurement Apparatus and Application in Shenhua CCS Project
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 63 (2014) 4766 – 4772
GHGT-12
Cap rock CO2 breakthrough pressure measurement apparatus and application in Shenhua CCS project Shuai Gao, Ning Wei*, Xiaochun Li, Yan Wang, Qian Wang State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
Abstract
CO2 breakthrough pressure is a very important factor for cap rock integrity evaluation. It is mainly acquired by laboratory experiments. We developed a set of apparatus to measure CO2 breakthrough pressure, which was based on pulse decay method (residual capillary pressure approach). Breakthrough pressure measurement experiments were conducted on the mudstone samples derived from four important seal formations in Shenhua CO2 aquifer storage project located in Ordos basin in China. The main conclusions are listed below based on experiment results and site characterization: 1) the breakthrough pressure of mudstone samples have sufficient capillary pressure to keep the stored CO2 underground. 2) the mudstones at a deeper burial depth, which may be better consolidated and better diagenetic, tend to have a higher breakthrough pressure. However, mudstones that are too diagenetic may be more likely to generate fractures, which will enhance the permeability and reduce the breakthrough pressure. 3) Breakthrough pressure is just a core scale parameter and site characterization about cap rock thickness, integrity is necessary before a specific formation is selected as a cap rock in CO 2 geological storage. 4) Intercalated sand layers will greatly influence the sealing ability of mudstone formations. © Published by Elsevier Ltd. This © 2014 2013The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of GHGT. Peer-review under responsibility of the Organizing Committee of GHGT-12 Keywords: CO2 breakthrough pressure, measurement, cap rock, sealing ability
* Corresponding author. Tel.: +86-13995659295; fax: 027-87197135. E-mail address: [email protected]
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of GHGT-12 doi:10.1016/j.egypro.2014.11.507
4767
Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772
1. Introduction Carbon dioxide capture and geological storage (CCS) is considered as an important option to mitigate CO2 emission [1]. CO2 breakthrough pressure (threshold pressure) is an important property of cap rock sealing ability in long-term CO2 geological storage. In 1949, Purcell used mercury intrusion porosimetry to acquire the breakthrough pressure of cap rock in underground natural gas storage [2]. Since then, many different technologies and methods have been developed to measure breakthrough pressure cap rock both in underground natural gas storage and CO2 geological storage. CO2 breakthrough pressure is mainly acquired by laboratory experiments, including indirect methods and direct methods. The indirect methods mainly consist of mercury intrusion porosimetry, which is used widely around world. Mercury intrusion porosimetry can obtain breakthrough pressure quickly, however, it needs conversion from mercury-air condition into CO2-brine condition, including interfacial tension, contact angle, stress condition and temperature. The direct methods consist of step-by-step method, continuous injection method, displacement method and pulse decay method (or residual capillary pressure approach). Step-by-step approach is based on the definition of breakthrough pressure with high accuracy, but it is really time-consuming [3]. Experiment period always ranges from several weeks to several months. Continuous injection approach also has a good accuracy, but it could over-estimate the CO2 breakthrough pressure due to the high pressure gradient in the water phase which cannot be neglected. Pulse decay method (residual capillary pressure approach), which stems from step-by-step approach, can acquire CO2 breakthrough pressure in several days with certain resolution [4, 5]. The objective of this study is to develop a set of apparatus, which can be used to conduct CO 2 breakthrough pressure measurement with pulse decay method. And then, we measure the CO2 breakthrough pressure of mudstone samples from Shenhua CO2 aquifer storage project in Ordos basin and evaluate the sealing ability of cap rock at core-scale. 2. Experimental equipment 2.1. Experiment setup
+2 3D[LDO
3FRQILQLQJ
3D[LDO &2 Fig. 1 Schematic maps of our CO2 breakthrough pressure measurement apparatus.
Fig. 2 Simplified schematic map of the core holder.
Pulse decay method (residual capillary pressure approach) has been proved to be a more time-saving and more accurate method of measuring breakthrough pressure. In order to further improve the accuracy and efficiency of breakthrough pressure measurement, we developed a set of apparatus based on pulse decay method (residual capillary pressure approach). The schematic maps of our CO2 breakthrough pressure measurement apparatus are shown in Fig. 1. Teledyne ISCO pumps were adopted to control the pressure or flow rate, which can meet the
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Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772
demands of different measurement methods. At the downstream of the experimental system, there is a back pressure regulator used to keep the downstream fluid pressure constant if necessary. The simplified schematic map of the core holder is shown in Fig. 2. In order to avoid surface flow between the rock sample and FKM (fluorine rubber) sleeve, a thin layer of silicone is needed on the surface of rock samples. 2.2. Experimental procedure The CO2 breakthrough experiments were performed with pulse decay method (residual capillary pressure approach) [4, 5]. The mudstone samples were completely saturated with distilled water before the experiments as a defined initial condition. A dead volume of the downstream side was set by the needle valve and a constant CO2 pressure at upstream side was maintained by ISCO 100D pump with 0.1% pressure resolution. At the beginning of the experiments, the pressure of upstream side (P1) was set much higher than the pressure of downstream side (P 2). The differential pressure between upstream side and downstream side (P1-P2) would exceed the expected CO2 breakthrough pressure, which was needed to generate water or CO2-water flux across the mudstone sample [4]. Then the pressure of downstream side would increase continuously due to water compression. At last, the differential pressure between upstream side and downstream side would reach a steady state. The steady differential pressure was regarded as the measured CO2 breakthrough pressure of the sample. In order to minimize the risk of hydrofracturing and surface flow between the fragile rock sample and FKM (fluorine rubber) sleeve, the confining pressure was set 5 MPa higher than the upstream pressure. The experimental procedure used is shown schematically in Fig. 3.
3UHVVXUH3
3
3
7LPHW
Fig. 3 The experimental procedure of pulse decay method (residual capillary pressure approach)[4]
2.3. Equipment reliability The resolution will largely depend on the leakage of experiment system. Very small amount of CO 2 leaked out of experiment system and into of core holder system can cause very high deviation from its true property, especially for these low permeable rock samples, such as, mudstone, shale, dolomite and other cap rocks. The current experiment system cannot prevent CO2 dissolving into the seal materials, such as, Viton, Teflon, FKM, Buna-N rubber, and other rubber sleeves; reacting with rock minerals and materials of experiment system; and leaking from the connection and moving parts of experiment system. The CO2 loss, caused by this phenomena during the experiments, certainly causes the deviation or error of measurement results. Some tests have been conducted in this study on the equipment about the resolution of pressure and flow rate added by ISCO pump, the resolution of pressure sensors and temperature sensors and the leakage rate of the whole system. The main parameters of this equipment are shown in Table 1. Table 1 Main parameters of the breakthrough pressure measurement apparatus Device parameter Detail Proof pressure of the system is 40MPa. Temperature ranges from room temperature to 99ć. Proof pressure & leakage The leakage rate of whole system without pump is less than 0.01μlMPa-1s-1 (measured by rate water at 32MPa and 25ć).
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Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772 Fluid pressure & flow rate Sensor accuracy
Repeatability
Pressure range is 0~51.7MPa (or 0~7500 psi) and pressure accuracy is about ±0.5%FS. The flow rate ranges from 1μl/min to 107ml/min, with a resolution of ±0.5%. The range of pressure sensors is 0~50MPa and their accuracy is about ±0.5%FS. The temperature sensors have a range between 0 and 100 ć with ±0.1ćresolution. The Validyne-DP360 can use different diaphragm to measure the differential pressure ranging from 550KPa to 86500KPa. The accuracy is about ±0.5%FS. Less than 5% measured by 0606D01-B15M1 porous ceramic plate produced by Soilmoisture.
Core holder
Diameter of rock samples is 25.4mm and the length can range from 10.0 to 50.0 mm.
Corrosion resistance
Resistant to conventional acid alkali corrosion and has a good resistance to CO2.
Fluid composition analysis
Chromatographic analysis on gas phase and liquid phase.
Data acquisition
NI USB6008 data acquisition system (14-bit).
3. Breakthrough pressure measurements 3.1. Mudstone samples The mudstone samples are derived from Ordos basin in Shenhua CO2 aquifer storage project, the first 10 Mt/a fullchain CO2 capture and geological storage (CCS) project in China [6, 7]. The Ordos Basin is located in North China and lies entirely within the North China Block. The Ordos Basin is the oldest still-utilized source of hydrocarbons in central China and remains an important one. It is a typical cratonic basin that developed on the Archean granulites and lower Proterozoic green schists of the North China block [8]. The Ordos Basin is presently a topographic plateau; however, after the Permian, this basin became a site of continental sedimentation with repeated deformation along the margins. It is a typical example of the continental, oil-generating sedimentary basins in China. The region developed into a large, stable basin during Paleozoic, shaped predominantly by tectonic movements dominated by regional uplift and subsidence. Table 2 Overview of the mudstone samples used in this study
Middle Triassic mudstone
Burial depth / [m] 1248
Sample thickness / [mm] 10
Early Triassic mudstone
1300
15
Shiqianfeng Fm
Late Permian mudstone
1828
15
Taiyuan Fm
Late carboniferous mudstone
2100
10
Sample name
Sample type
Zhifang Fm Liujiagou Fm
The set comprises two Triassic mudstone samples (Zhifang FM, Liujiagou FM), one Permian mudstone sample (Shiqianfeng FM) and one Carboniferous mudstone sample (Taiyuan FM). The mudstone samples cover a burial depth range from 1200 to 2100 m. An overview of the mudstone samples investigated in this study is given in Table 2. 3.2. CO2 breakthrough experiments CO2 breakthrough pressure measurement was performed on each mudstone sample. Pressure and temperature conditions for each experiment were determined based on the in-situ condition of the potential reservoir for CO2 geological storage. The results of CO2 breakthrough experiments on four different samples are given in Fig. 4. Shown on left are the recorded upstream and downstream pressures as a function of experimental time. The figures on the right show the pore size distribution calculated based on mercury intrusion curve. Residual differential pressures are in the range of 6.9 to 15.7 MPa, with the lowest CO2 breakthrough pressure for Taiyuan Fm sample, and the highest value found for Liujiagou Fm sample.
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Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772 Zhifang Fm
0.020 dv/d(log d) [cc/g]
30
Pressure [MPa]
25
P_residual=10.1MPa
20 15
P_CO2 P_H2O
0.010 0.005 0.000
10 0
2
4 Time [h]
6
1
8
10
100
1000
Pore radius [nm]
Liujiagou Fm
Te
0.015
5.000
40
dv/d(log d) [cc/g]
Pressure [MPa]
4.000 30
P_residual=15.7MPa 20 P_CO2 P_H2O 1
2
Time [h]
3
4
10
10000
0.030 dv/d(log d) [cc/g]
P_residual=10.6MPa
30 25
P_CO2 P_H2O
20 0
2
0.020 0.010 0.000
4
1
6
Time [h]
0.016
29
0.012
P_residual=6.9MPa
23 P_CO2 P_H2O
20 0
0.3
0.6 Time [h]
0.9
1.2
dv/d(log d) [cc/g]
32
26
10
100
1000
Pore radius [nm]
Taiyuan Fm
Pressure [MPa]
1000
0.040
35
Liq
100
Pore radius [nm]
40
Pressure [MPa]
1.000
5
Shiqianfeng Fm
Bal
2.000
0.000
10 0
3.000
0.008
0.004
0.000 1
10
100
Pore radius [nm]
Fig. 4 Results of CO2 breakthrough experiments on four different samples
4. Discussion According to the Washburn equation [9], the breakthrough pressure is connected with interfacial tension, wetting angle and the radius of pore throat. So the breakthrough pressure has something to do with mineral components of the rock and the degree of consolidation. As a result, the depth and the diagenetic grade, which are related to the mineral components and consolidation degree of the rock, will influence the breakthrough pressure of the cap rocks. However, just as the experiment results, the breakthrough pressures of the four rock samples from different burial depth did not present the monotonicity. For the first reason, rocks with deeper burial depth tend to be better
Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772
4771
consolidated and better diagenetic. Meanwhile, they are more likely to generate more fractures through the rocks, which will enhance the permeability and reduce the breakthrough pressure of the rocks. Besides, breakthrough pressure is just a core scale parameter that high breakthrough pressure means high sealing ability for the core. For the cap rock scale, the sealing ability of the cap rock also is connected with its thickness, integrity and intercalated sand layers. For example, Liujiagou Fm mudstone sample has a CO2 breakthrough pressure value of 15.7 MPa, which is much higher than that of Shiqianfeng Fm mudstone sample. But a higher intercalated sand layers’ proportion is found in Liujiagou Fm. In addition, the thickness of Liujiagou Fm mudstone only is 5~15 m, while the thickness of Shiqianfeng Fm mudstone is in the range of 30~140 m. Therefore, the Shiqianfeng Fm mudstone is more appropriate to act as a cap rock in CO2 geological storage than the Liujiagou Fm mudstone. Breakthrough pressure is still an important core scale parameter to evaluate the potential sealing ability of the expected cap rocks. In addition, some other monitoring measures, like 4D seismic survey, wireline logging and aqueous geochemistry analysis and so on, should be taken to estimate the sealing ability of cap rocks more precisely. 5. Conclusions In order to further improve the accuracy and efficiency of breakthrough pressure measurement, we developed a set of CO2 breakthrough pressure measurement apparatus based on pulse decay method (residual capillary pressure approach). Four breakthrough pressure measurements were conducted using this apparatus. Main conclusions of this work are listed below based on experiment results and site characterization. 1. The breakthrough pressure of the mudstone samples in this study have sufficient capillary pressure to keep the stored CO2 underground. 2. The mudstones at a deeper burial depth, which may be better consolidated and better diagenetic, tend to have a higher breakthrough pressure. However, mudstones that are too diagenetic may be more likely to generate fractures, which will enhance the permeability and reduce the breakthrough pressure. 3. Breakthrough pressure in this experiment can only give the sealing ability at core scale. Large-scale site characterization on cap rock is necessary before large-scale deployment of CCS preoject. 4. Intercalated sand layers will greatly influence the sealing ability of mudstone formations. Acknowledgements The authors gratefully acknowledge the financial support of the Chinese Academy of Sciences, Strategic Priority Research Program—Demonstration of Key Technologies for Clean and Efficient Utilization of Low-Rank Coal, CO2 geological storage, and Demonstration project (Grant no. XDA07040300) and the financial support of National Key Technologies R&D Program of the Ministry of Science and Technology of China, (Grant no. 2011BAC08B00). References [1] Metz, B., O. Davidson, H.d. Coninck, M. Loos, and L. Meyer, IPCC special report on carbon dioxide capture and storage. Other Information: IEACR LIB 700. 2005. Medium: X; Size: 440; 23.3 MB pages. [2] Purcell, W.R., Capillary Pressures - Their Measurement Using Mercury and the Calculation of Permeability Therefrom. Transactions of the American Institute of Mining and Metallurgical Engineers, 1949. 186(2): p. 39-48. [3] Egermann, P., J.M. Lombard, and P. Bretonnier. A fast and accurate method to measure threshold capillary pressure of caprocks under representative conditions. in International Symposium of the Society of Core Analysts, Trondheim, Norway. 2006. 2006. [4] Hildenbrand, A., S. Schlomer, and B.M. Krooss, Gas breakthrough experiments on fine-grained sedimentary rocks. Geofluids, 2002. 2(1): p. 3-23. [5] Hildenbrand, A., S. Schlomer, B.M. Krooss, and R. Littke, Gas breakthrough experiments on pelitic rocks: comparative study with N2, CO2 and CH4. Geofluids, 2004. 4(1): p. 61-80. [6] Wang, Y., D. Crandall, K. Bruner, N. Wei, M. Gill, X. Li, and B. Grant, Core and Pore Scale
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Characterization of Liujiagou Outcrop Sandstone, Ordos basin, China for CO 2 Aquifer Storage. Energy Procedia, 2013. 37: p. 5055-5062. [7] Wei, N., M. Gill, D. Crandall, D. McIntyre, Y. Wang, K. Bruner, X. Li, and G. Bromhal, CO 2 flooding properties of Liujiagou sandstone: Influence of sub-core scale structure heterogeneity. Greenhouse Gases: Science and Technology, 2014. 4: p. 1-19. [8] Yang, Y.T., W. Li, and L. Ma, Tectonic and stratigraphic controls of hydrocarbon systems in the Ordos basin: A multicycle cratonic basin in central China. Aapg Bulletin, 2005. 89(2): p. 255-269. [9] Washburn, E., Note on a method of determing the distribution of pore size in a porous material. Proceedings of the National Acadamy of science, 1921. 7(4): p. 115-116.
ScienceDirect Energy Procedia 63 (2014) 4766 – 4772
GHGT-12
Cap rock CO2 breakthrough pressure measurement apparatus and application in Shenhua CCS project Shuai Gao, Ning Wei*, Xiaochun Li, Yan Wang, Qian Wang State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
Abstract
CO2 breakthrough pressure is a very important factor for cap rock integrity evaluation. It is mainly acquired by laboratory experiments. We developed a set of apparatus to measure CO2 breakthrough pressure, which was based on pulse decay method (residual capillary pressure approach). Breakthrough pressure measurement experiments were conducted on the mudstone samples derived from four important seal formations in Shenhua CO2 aquifer storage project located in Ordos basin in China. The main conclusions are listed below based on experiment results and site characterization: 1) the breakthrough pressure of mudstone samples have sufficient capillary pressure to keep the stored CO2 underground. 2) the mudstones at a deeper burial depth, which may be better consolidated and better diagenetic, tend to have a higher breakthrough pressure. However, mudstones that are too diagenetic may be more likely to generate fractures, which will enhance the permeability and reduce the breakthrough pressure. 3) Breakthrough pressure is just a core scale parameter and site characterization about cap rock thickness, integrity is necessary before a specific formation is selected as a cap rock in CO 2 geological storage. 4) Intercalated sand layers will greatly influence the sealing ability of mudstone formations. © Published by Elsevier Ltd. This © 2014 2013The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of GHGT. Peer-review under responsibility of the Organizing Committee of GHGT-12 Keywords: CO2 breakthrough pressure, measurement, cap rock, sealing ability
* Corresponding author. Tel.: +86-13995659295; fax: 027-87197135. E-mail address: [email protected]
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of GHGT-12 doi:10.1016/j.egypro.2014.11.507
4767
Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772
1. Introduction Carbon dioxide capture and geological storage (CCS) is considered as an important option to mitigate CO2 emission [1]. CO2 breakthrough pressure (threshold pressure) is an important property of cap rock sealing ability in long-term CO2 geological storage. In 1949, Purcell used mercury intrusion porosimetry to acquire the breakthrough pressure of cap rock in underground natural gas storage [2]. Since then, many different technologies and methods have been developed to measure breakthrough pressure cap rock both in underground natural gas storage and CO2 geological storage. CO2 breakthrough pressure is mainly acquired by laboratory experiments, including indirect methods and direct methods. The indirect methods mainly consist of mercury intrusion porosimetry, which is used widely around world. Mercury intrusion porosimetry can obtain breakthrough pressure quickly, however, it needs conversion from mercury-air condition into CO2-brine condition, including interfacial tension, contact angle, stress condition and temperature. The direct methods consist of step-by-step method, continuous injection method, displacement method and pulse decay method (or residual capillary pressure approach). Step-by-step approach is based on the definition of breakthrough pressure with high accuracy, but it is really time-consuming [3]. Experiment period always ranges from several weeks to several months. Continuous injection approach also has a good accuracy, but it could over-estimate the CO2 breakthrough pressure due to the high pressure gradient in the water phase which cannot be neglected. Pulse decay method (residual capillary pressure approach), which stems from step-by-step approach, can acquire CO2 breakthrough pressure in several days with certain resolution [4, 5]. The objective of this study is to develop a set of apparatus, which can be used to conduct CO 2 breakthrough pressure measurement with pulse decay method. And then, we measure the CO2 breakthrough pressure of mudstone samples from Shenhua CO2 aquifer storage project in Ordos basin and evaluate the sealing ability of cap rock at core-scale. 2. Experimental equipment 2.1. Experiment setup
+2 3D[LDO
3FRQILQLQJ
3D[LDO &2 Fig. 1 Schematic maps of our CO2 breakthrough pressure measurement apparatus.
Fig. 2 Simplified schematic map of the core holder.
Pulse decay method (residual capillary pressure approach) has been proved to be a more time-saving and more accurate method of measuring breakthrough pressure. In order to further improve the accuracy and efficiency of breakthrough pressure measurement, we developed a set of apparatus based on pulse decay method (residual capillary pressure approach). The schematic maps of our CO2 breakthrough pressure measurement apparatus are shown in Fig. 1. Teledyne ISCO pumps were adopted to control the pressure or flow rate, which can meet the
4768
Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772
demands of different measurement methods. At the downstream of the experimental system, there is a back pressure regulator used to keep the downstream fluid pressure constant if necessary. The simplified schematic map of the core holder is shown in Fig. 2. In order to avoid surface flow between the rock sample and FKM (fluorine rubber) sleeve, a thin layer of silicone is needed on the surface of rock samples. 2.2. Experimental procedure The CO2 breakthrough experiments were performed with pulse decay method (residual capillary pressure approach) [4, 5]. The mudstone samples were completely saturated with distilled water before the experiments as a defined initial condition. A dead volume of the downstream side was set by the needle valve and a constant CO2 pressure at upstream side was maintained by ISCO 100D pump with 0.1% pressure resolution. At the beginning of the experiments, the pressure of upstream side (P1) was set much higher than the pressure of downstream side (P 2). The differential pressure between upstream side and downstream side (P1-P2) would exceed the expected CO2 breakthrough pressure, which was needed to generate water or CO2-water flux across the mudstone sample [4]. Then the pressure of downstream side would increase continuously due to water compression. At last, the differential pressure between upstream side and downstream side would reach a steady state. The steady differential pressure was regarded as the measured CO2 breakthrough pressure of the sample. In order to minimize the risk of hydrofracturing and surface flow between the fragile rock sample and FKM (fluorine rubber) sleeve, the confining pressure was set 5 MPa higher than the upstream pressure. The experimental procedure used is shown schematically in Fig. 3.
3UHVVXUH3
3
3
7LPHW
Fig. 3 The experimental procedure of pulse decay method (residual capillary pressure approach)[4]
2.3. Equipment reliability The resolution will largely depend on the leakage of experiment system. Very small amount of CO 2 leaked out of experiment system and into of core holder system can cause very high deviation from its true property, especially for these low permeable rock samples, such as, mudstone, shale, dolomite and other cap rocks. The current experiment system cannot prevent CO2 dissolving into the seal materials, such as, Viton, Teflon, FKM, Buna-N rubber, and other rubber sleeves; reacting with rock minerals and materials of experiment system; and leaking from the connection and moving parts of experiment system. The CO2 loss, caused by this phenomena during the experiments, certainly causes the deviation or error of measurement results. Some tests have been conducted in this study on the equipment about the resolution of pressure and flow rate added by ISCO pump, the resolution of pressure sensors and temperature sensors and the leakage rate of the whole system. The main parameters of this equipment are shown in Table 1. Table 1 Main parameters of the breakthrough pressure measurement apparatus Device parameter Detail Proof pressure of the system is 40MPa. Temperature ranges from room temperature to 99ć. Proof pressure & leakage The leakage rate of whole system without pump is less than 0.01μlMPa-1s-1 (measured by rate water at 32MPa and 25ć).
4769
Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772 Fluid pressure & flow rate Sensor accuracy
Repeatability
Pressure range is 0~51.7MPa (or 0~7500 psi) and pressure accuracy is about ±0.5%FS. The flow rate ranges from 1μl/min to 107ml/min, with a resolution of ±0.5%. The range of pressure sensors is 0~50MPa and their accuracy is about ±0.5%FS. The temperature sensors have a range between 0 and 100 ć with ±0.1ćresolution. The Validyne-DP360 can use different diaphragm to measure the differential pressure ranging from 550KPa to 86500KPa. The accuracy is about ±0.5%FS. Less than 5% measured by 0606D01-B15M1 porous ceramic plate produced by Soilmoisture.
Core holder
Diameter of rock samples is 25.4mm and the length can range from 10.0 to 50.0 mm.
Corrosion resistance
Resistant to conventional acid alkali corrosion and has a good resistance to CO2.
Fluid composition analysis
Chromatographic analysis on gas phase and liquid phase.
Data acquisition
NI USB6008 data acquisition system (14-bit).
3. Breakthrough pressure measurements 3.1. Mudstone samples The mudstone samples are derived from Ordos basin in Shenhua CO2 aquifer storage project, the first 10 Mt/a fullchain CO2 capture and geological storage (CCS) project in China [6, 7]. The Ordos Basin is located in North China and lies entirely within the North China Block. The Ordos Basin is the oldest still-utilized source of hydrocarbons in central China and remains an important one. It is a typical cratonic basin that developed on the Archean granulites and lower Proterozoic green schists of the North China block [8]. The Ordos Basin is presently a topographic plateau; however, after the Permian, this basin became a site of continental sedimentation with repeated deformation along the margins. It is a typical example of the continental, oil-generating sedimentary basins in China. The region developed into a large, stable basin during Paleozoic, shaped predominantly by tectonic movements dominated by regional uplift and subsidence. Table 2 Overview of the mudstone samples used in this study
Middle Triassic mudstone
Burial depth / [m] 1248
Sample thickness / [mm] 10
Early Triassic mudstone
1300
15
Shiqianfeng Fm
Late Permian mudstone
1828
15
Taiyuan Fm
Late carboniferous mudstone
2100
10
Sample name
Sample type
Zhifang Fm Liujiagou Fm
The set comprises two Triassic mudstone samples (Zhifang FM, Liujiagou FM), one Permian mudstone sample (Shiqianfeng FM) and one Carboniferous mudstone sample (Taiyuan FM). The mudstone samples cover a burial depth range from 1200 to 2100 m. An overview of the mudstone samples investigated in this study is given in Table 2. 3.2. CO2 breakthrough experiments CO2 breakthrough pressure measurement was performed on each mudstone sample. Pressure and temperature conditions for each experiment were determined based on the in-situ condition of the potential reservoir for CO2 geological storage. The results of CO2 breakthrough experiments on four different samples are given in Fig. 4. Shown on left are the recorded upstream and downstream pressures as a function of experimental time. The figures on the right show the pore size distribution calculated based on mercury intrusion curve. Residual differential pressures are in the range of 6.9 to 15.7 MPa, with the lowest CO2 breakthrough pressure for Taiyuan Fm sample, and the highest value found for Liujiagou Fm sample.
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Shuai Gao et al. / Energy Procedia 63 (2014) 4766 – 4772 Zhifang Fm
0.020 dv/d(log d) [cc/g]
30
Pressure [MPa]
25
P_residual=10.1MPa
20 15
P_CO2 P_H2O
0.010 0.005 0.000
10 0
2
4 Time [h]
6
1
8
10
100
1000
Pore radius [nm]
Liujiagou Fm
Te
0.015
5.000
40
dv/d(log d) [cc/g]
Pressure [MPa]
4.000 30
P_residual=15.7MPa 20 P_CO2 P_H2O 1
2
Time [h]
3
4
10
10000
0.030 dv/d(log d) [cc/g]
P_residual=10.6MPa
30 25
P_CO2 P_H2O
20 0
2
0.020 0.010 0.000
4
1
6
Time [h]
0.016
29
0.012
P_residual=6.9MPa
23 P_CO2 P_H2O
20 0
0.3
0.6 Time [h]
0.9
1.2
dv/d(log d) [cc/g]
32
26
10
100
1000
Pore radius [nm]
Taiyuan Fm
Pressure [MPa]
1000
0.040
35
Liq
100
Pore radius [nm]
40
Pressure [MPa]
1.000
5
Shiqianfeng Fm
Bal
2.000
0.000
10 0
3.000
0.008
0.004
0.000 1
10
100
Pore radius [nm]
Fig. 4 Results of CO2 breakthrough experiments on four different samples
4. Discussion According to the Washburn equation [9], the breakthrough pressure is connected with interfacial tension, wetting angle and the radius of pore throat. So the breakthrough pressure has something to do with mineral components of the rock and the degree of consolidation. As a result, the depth and the diagenetic grade, which are related to the mineral components and consolidation degree of the rock, will influence the breakthrough pressure of the cap rocks. However, just as the experiment results, the breakthrough pressures of the four rock samples from different burial depth did not present the monotonicity. For the first reason, rocks with deeper burial depth tend to be better
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consolidated and better diagenetic. Meanwhile, they are more likely to generate more fractures through the rocks, which will enhance the permeability and reduce the breakthrough pressure of the rocks. Besides, breakthrough pressure is just a core scale parameter that high breakthrough pressure means high sealing ability for the core. For the cap rock scale, the sealing ability of the cap rock also is connected with its thickness, integrity and intercalated sand layers. For example, Liujiagou Fm mudstone sample has a CO2 breakthrough pressure value of 15.7 MPa, which is much higher than that of Shiqianfeng Fm mudstone sample. But a higher intercalated sand layers’ proportion is found in Liujiagou Fm. In addition, the thickness of Liujiagou Fm mudstone only is 5~15 m, while the thickness of Shiqianfeng Fm mudstone is in the range of 30~140 m. Therefore, the Shiqianfeng Fm mudstone is more appropriate to act as a cap rock in CO2 geological storage than the Liujiagou Fm mudstone. Breakthrough pressure is still an important core scale parameter to evaluate the potential sealing ability of the expected cap rocks. In addition, some other monitoring measures, like 4D seismic survey, wireline logging and aqueous geochemistry analysis and so on, should be taken to estimate the sealing ability of cap rocks more precisely. 5. Conclusions In order to further improve the accuracy and efficiency of breakthrough pressure measurement, we developed a set of CO2 breakthrough pressure measurement apparatus based on pulse decay method (residual capillary pressure approach). Four breakthrough pressure measurements were conducted using this apparatus. Main conclusions of this work are listed below based on experiment results and site characterization. 1. The breakthrough pressure of the mudstone samples in this study have sufficient capillary pressure to keep the stored CO2 underground. 2. The mudstones at a deeper burial depth, which may be better consolidated and better diagenetic, tend to have a higher breakthrough pressure. However, mudstones that are too diagenetic may be more likely to generate fractures, which will enhance the permeability and reduce the breakthrough pressure. 3. Breakthrough pressure in this experiment can only give the sealing ability at core scale. Large-scale site characterization on cap rock is necessary before large-scale deployment of CCS preoject. 4. Intercalated sand layers will greatly influence the sealing ability of mudstone formations. Acknowledgements The authors gratefully acknowledge the financial support of the Chinese Academy of Sciences, Strategic Priority Research Program—Demonstration of Key Technologies for Clean and Efficient Utilization of Low-Rank Coal, CO2 geological storage, and Demonstration project (Grant no. XDA07040300) and the financial support of National Key Technologies R&D Program of the Ministry of Science and Technology of China, (Grant no. 2011BAC08B00). References [1] Metz, B., O. Davidson, H.d. Coninck, M. Loos, and L. Meyer, IPCC special report on carbon dioxide capture and storage. Other Information: IEACR LIB 700. 2005. Medium: X; Size: 440; 23.3 MB pages. [2] Purcell, W.R., Capillary Pressures - Their Measurement Using Mercury and the Calculation of Permeability Therefrom. Transactions of the American Institute of Mining and Metallurgical Engineers, 1949. 186(2): p. 39-48. [3] Egermann, P., J.M. Lombard, and P. Bretonnier. A fast and accurate method to measure threshold capillary pressure of caprocks under representative conditions. in International Symposium of the Society of Core Analysts, Trondheim, Norway. 2006. 2006. [4] Hildenbrand, A., S. Schlomer, and B.M. Krooss, Gas breakthrough experiments on fine-grained sedimentary rocks. Geofluids, 2002. 2(1): p. 3-23. [5] Hildenbrand, A., S. Schlomer, B.M. Krooss, and R. Littke, Gas breakthrough experiments on pelitic rocks: comparative study with N2, CO2 and CH4. Geofluids, 2004. 4(1): p. 61-80. [6] Wang, Y., D. Crandall, K. Bruner, N. Wei, M. Gill, X. Li, and B. Grant, Core and Pore Scale
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