- Email: [email protected]
Predicting the Interactions of H2S-CO2 Mixtures with Aquifer Rock, based on Experiments and Geochemical Modeling
Available online at www.sciencedirect.com
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 288 – 291
15th Water-Rock Interaction International Symposium, WRI-15
Predicting the interactions of H2S-CO2mixtures with aquifer rock, based on experiments and geochemical modeling Krzysztof Labusa, , Katarzyna Suchodolskaa a
Silesian University of Technology, 2 Akademicka St., Gliwice 44- 100, Poland
Abstract Greenhouse effect prevention, oil and gas stimulation, and other recent technologies require a recognition of the acid gas interactions with geologic formations. The experimental study coupled with hydrogeochemical modeling was focused on the impact of CO2, H2S and their mixtures on the formations of the Upper Silesian Coal Basin. Significant changes in structure and composition of rock samples influenced by acid gas were identified in autoclave experiments. Skeletal grains dissolution was most intense in carbonates and chlorite, and caused an increase of porosity. In the case of geological storage of H2S, a release of significant amounts of CO2, from dissolution of primary carbonates should be expected, as demonstrated the results of modeling. Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2017 2017The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15. Peer-review under responsibility of the organizing committee of WRI-15 Keywords: acid gas sequestration, carbon dioxide, hydrogen sulfide, hydrogeochemical modeling
1. Introduction Interactions of acid gases with rocks is a subject of intensive research in recent decades. The interest in this subject is associated with the need to reduce global warming 1,2, with stimulation of oil and gas fields by carbon dioxide injection, and also with the use of energized fracturing fluids3. Despite numerous works there are still many doubts about the behavior of hydrogeochemical systems rocks impacted by injection of the acid gas. Knowledge of that issue requires deepening especially on the basis of experimental studies. In order to partially identify these phenomena laboratory experiments and modeling were performed to determine the impact of CO2 and H2S or their mixtures on the rocks typical for the Upper Silesian Coal Basin – USCB (Poland).
* Corresponding author. Tel.: +48-32-2372942; fax: +48-32-2372290. E-mail address: [email protected]
1878-5220 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.059
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
2. Materials and methods Core samples were selected to represent cap rock (mudstone) and aquifer (sandstone) typical of the Upper Silesian Coal Basin. Mineralogical composition of mineral assemblages was determined by XRD (Table 1). Porosity was measured by means of mercury porosimetry. Identification of mineral phases in the samples before and after the experimental tests was performed with scanning electron microscope with EDX analyzer. In the experiments the samples were placed in an autoclave filled with the brine that reproduced original composition of pore water (Table 2). The autoclave was pressurised with CO2 and/or H2S gases to 75-120 bar; temperature was kept at 30-50 ° C. The experiments lasted for 75 days and allowed for simulation of gas-rock-water interactions after the gas injection into system. Composition of pore waters for hydrogeochemical simulations was calculated based on equilibration of the formation water (Table 2) with mineral assemblages typical for the modeled rocks. The pore waters were characterized by TDS ranging from 135.0 to 140.0 g/l and pH between 6.0 and 7.0. Hydrostatic formation pressures were assumed in modeling studies, carried out with the use of Geochemist's Workbench software4. The temperatures were estimated according to measurements and archival data. The simplified equation kinetics of dissolution/crystallization5 was applied in the calculations. Kinetic rate constants (K – Table 1) in modeled reactions were taken from6. Water-rock-gas interactions were modeled in two stages according to7.The first stage was aimed at simulating the immediate changes in the aquifer and insulating rocks impacted by the beginning of gas injection. The second stage enabled assessment of long-term effects of sequestration. The reactions quality and progress were monitored and their effects on formation porosity and mineral sequestration capacity of carbon and/or sulfur were calculated. Table 1. Mineral composition of rock samplesand kinetic parameters applied in modeling Sample Porosity
Cap-rock Aquifer 0,034 0,251 Participation Specific surface Participation Specific surface Minerals log K [mol/m2/s] [% vol.] [cm2/g] [% vol.] [cm2/g] Quartz 47 227 31 23 -13.99 Muscovite 14 212 28 106 -11.85 Microcline 8 235 5 23 -10.06 Albite 22 229 8 23 -10.16 Chlorite IIb 9 1120 7 1120 -11.11 Calcite 9 22 -0.03 Ankerite Fe 0,55 10 21 -3.19 Phlogopite 2 1080 -12.40 Tab. 2. Pore water composition applied in experiments and modeling Parameter pH ClSO42HCO3Ca2+ Mg2+ Na+ K+
Unit mol/kg mol/kg mol/kg mol/kg mol/kg mol/kg mol/kg
Value 7.8 2.831 7.8·10-4 0.002 0.939 0.053 0.842 0.005
3. Experimental results The SEM analysis revealed that skeletal grains dissolution occurred in all reacted samples, and was the most advanced in the case of carbonates and chlorite. Numerous aggregates, as well as scattered, single, small crystals of pyrite were identified amongst the secondary minerals produced during the experiment (Fig. 1A, B). Cavities situated along the cleavage planes in microcline were also observed. Cavities probably developed as a result of preferential dissolution of the potassic lamellae relative to the sodic ones, as reported in7. On the surface of quartz grains small cavities were found, which record the initial stage of dissolution in aggressive environment. The
289
290
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
precipitation of secondary minerals can lead to partial formation damage (closure of the pore space), as observed for dawsonite (few crystals were identified only in the reacted samples) formed mainly in the intergranular spaces. Degradation of chlorite was accompanied by the formation of dispersed pyrite and aggregates of fine magnesite crystals. Small pyrite crystals were frequent in areas of iron carbonate dissolution – Fig. 1A. The SEM/EDX analysis of mudstones, reacted with H2S-CO2 mixture injected, showed elemental sulfur surrounded by fine crystals of FeS2– Fig. 1B.
Fig. 1. A – pyrite aggregates – Py on Ankerite – An; B – native Sulphur – S, and small pyrite grains (white) on clay mineral mass.
4. Modeling results During the first stage of simulation, 100 days injection of acid gas resulted in an increase of gas fugacity and elevation of CO2(aq) and/or H2S(aq) concentrations (Fig.2). Simultaneously a sharp drop of pH in pore waters occurred, except for the injection process of H 2S into carbonate-free, cap rock sample. In the next stage, in all the cases pH values grew above the initial level, and practically achieved stabilization. In the model for the cap rock sample, a growth of porosity was observed during the 100 days injection, and in the early period of storage. After 1000 years the values reached stabilization. For the Aquifer sample (rich in carbonates: ankerite, calcite) initially there was a fast rise of porosity during the injection (and increase of the formation permeability). During the storage porosity was nearly stable. Aquifer
Cap rock
8
8
7
6
CO2
pH
pH
7
CO2+H2S
5
6
CO2 CO2+H2S
5
H2S
H2S
4
4
0
100d
100y
1000y
10000y
0
100d
Time
1000y
10000y
Time
Aquifer
Cap rock
0,29
0,046
0,28
0,042
0,27 CO2
0,26
CO2+H2S
0,25
Porosity
Porosity
100y
0,038
CO2 CO2+H2S
0,034
H2S
H2S 0,03
0,24 0
100d
100y
Time
1000y
10000y
0
100d
100y
1000y
10000y
Time
Fig. 2. Changes in pH and porosity of aquifer and cap rock, based on numerical modeling.
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
For the pure CO2injection porosity remained almost unchanged. In general, for the pure CO 2injection model, the changes in porosity were the least intense at both stages for all the samples. Results of the second stage of modeling allowed to evaluate the long-term effects of water-gas-rock interactions in the simulated repository. As a result of gas sequestration lasting 10,000 years, in the case of the model of Paralic series mudstones (cap-rock), the porosity of the rocks increased by 25%, 31%, and 29 % for CO 2, H2S, and the mixture, respectively. This porosity growth was caused by dissolution of significant amounts of K-feldspar, chlorite and albite, which was not compensated by precipitation of secondary muscovite, saponite-Na, annite and minnesotaite (Fe3Si4O10(OH)2). In the case of the aquifer formation model, the changes in porosity were minor, reaching 10% for pure H2S and the mixture while for CO2 there was almost no change. This phenomenon is associated with the balanced volumes of decomposed ankerite, calcite, feldspars and chlorites, and newly precipitated dolomite, muscovite, minesotaite, Saponite-Na, calcite and phengite, depending on the gas was injected. 4. Conclusions The experimental studies and modeling allowed evaluation of the impact of CO2 and H2S or their mixtures on the mineralogical composition and porosity of the rock matrix of the rocks typical for the Upper Silesian Coal Basin. On the basis of SEM analysis of reacted samples it was found that at injection step the dominant process is the dissolution of rock matrix (most evident in the case of carbonates and chlorite). This phenomenon was also reflected in modeling. The calculated increase in porosity resulted from the decomposition of those minerals in a volume higher than secondary, precipitating minerals such as: pyrite, magnesite or dawsonite. In the model for the cap rock sample, initially a slow increase in porosity was observed at the stage of injection and the first phase of the sequestration; at later time the values reached stabilization. For the aquifer sample there was an initial rise of porosity at the injection stage; during the phase of storage the porosity was nearly constant. For the pure CO2 experiment the porosity remained almost unchanged. The results of modeling showed that, in the case of two analyzed rock types, geological sequestration of pure H2S and mixtures thereof with CO2 should cause the release of significant amounts of CO2 as a result of the decomposition of primary carbonate minerals. Acknowledgements This work was funded by the National Science Centre – Polish executive agency - set up to fund basic research according to the decision DEC-2012/05/B/ST10/00416. References 1. Holloway S. Underground sequestration of carbon dioxide e a viable greenhouse gas mitigation option. Energy 2005; 30: 2318-33. 2. Xu T, Apps JA, Pruess K. Reactive geochemical transport simulation to study mineral trapping for CO2 disposal in deep arenaceous formations. J Geophys Res 2007;108: 2071– 84. 3. Wilk K, Kasza P, Labus K. Analysis of the applicability of foamed fracturing fluids. Nafta-Gaz 2015; LXXI: 425-433. 4. Bethke CM. Geochemical and biogeochemical reaction modeling. Cambridge Cambridge Univ. Press; 2008. 5. Lasaga AC. Chemical kinetics of water-rock interactions. J Geophys Res 1984; 89: 4009-25. 6. Palandri JL, Kharaka,YK. A compilation of rate parameters of water-mineral interaction kinetics for application to geochemical modeling. US Geological Survey, 2004; Open File Report 2004 -1068:1-64. 7. Labus K, Bujok P. CO2 mineral sequestration mechanisms and capacity of saline aquifers of the Upper Silesian Coal Basin (Central Europe) Modeling and experimental verification. Energy 2011; 36: 4974-4982.
291
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 288 – 291
15th Water-Rock Interaction International Symposium, WRI-15
Predicting the interactions of H2S-CO2mixtures with aquifer rock, based on experiments and geochemical modeling Krzysztof Labusa, , Katarzyna Suchodolskaa a
Silesian University of Technology, 2 Akademicka St., Gliwice 44- 100, Poland
Abstract Greenhouse effect prevention, oil and gas stimulation, and other recent technologies require a recognition of the acid gas interactions with geologic formations. The experimental study coupled with hydrogeochemical modeling was focused on the impact of CO2, H2S and their mixtures on the formations of the Upper Silesian Coal Basin. Significant changes in structure and composition of rock samples influenced by acid gas were identified in autoclave experiments. Skeletal grains dissolution was most intense in carbonates and chlorite, and caused an increase of porosity. In the case of geological storage of H2S, a release of significant amounts of CO2, from dissolution of primary carbonates should be expected, as demonstrated the results of modeling. Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2017 2017The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15. Peer-review under responsibility of the organizing committee of WRI-15 Keywords: acid gas sequestration, carbon dioxide, hydrogen sulfide, hydrogeochemical modeling
1. Introduction Interactions of acid gases with rocks is a subject of intensive research in recent decades. The interest in this subject is associated with the need to reduce global warming 1,2, with stimulation of oil and gas fields by carbon dioxide injection, and also with the use of energized fracturing fluids3. Despite numerous works there are still many doubts about the behavior of hydrogeochemical systems rocks impacted by injection of the acid gas. Knowledge of that issue requires deepening especially on the basis of experimental studies. In order to partially identify these phenomena laboratory experiments and modeling were performed to determine the impact of CO2 and H2S or their mixtures on the rocks typical for the Upper Silesian Coal Basin – USCB (Poland).
* Corresponding author. Tel.: +48-32-2372942; fax: +48-32-2372290. E-mail address: [email protected]
1878-5220 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.059
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
2. Materials and methods Core samples were selected to represent cap rock (mudstone) and aquifer (sandstone) typical of the Upper Silesian Coal Basin. Mineralogical composition of mineral assemblages was determined by XRD (Table 1). Porosity was measured by means of mercury porosimetry. Identification of mineral phases in the samples before and after the experimental tests was performed with scanning electron microscope with EDX analyzer. In the experiments the samples were placed in an autoclave filled with the brine that reproduced original composition of pore water (Table 2). The autoclave was pressurised with CO2 and/or H2S gases to 75-120 bar; temperature was kept at 30-50 ° C. The experiments lasted for 75 days and allowed for simulation of gas-rock-water interactions after the gas injection into system. Composition of pore waters for hydrogeochemical simulations was calculated based on equilibration of the formation water (Table 2) with mineral assemblages typical for the modeled rocks. The pore waters were characterized by TDS ranging from 135.0 to 140.0 g/l and pH between 6.0 and 7.0. Hydrostatic formation pressures were assumed in modeling studies, carried out with the use of Geochemist's Workbench software4. The temperatures were estimated according to measurements and archival data. The simplified equation kinetics of dissolution/crystallization5 was applied in the calculations. Kinetic rate constants (K – Table 1) in modeled reactions were taken from6. Water-rock-gas interactions were modeled in two stages according to7.The first stage was aimed at simulating the immediate changes in the aquifer and insulating rocks impacted by the beginning of gas injection. The second stage enabled assessment of long-term effects of sequestration. The reactions quality and progress were monitored and their effects on formation porosity and mineral sequestration capacity of carbon and/or sulfur were calculated. Table 1. Mineral composition of rock samplesand kinetic parameters applied in modeling Sample Porosity
Cap-rock Aquifer 0,034 0,251 Participation Specific surface Participation Specific surface Minerals log K [mol/m2/s] [% vol.] [cm2/g] [% vol.] [cm2/g] Quartz 47 227 31 23 -13.99 Muscovite 14 212 28 106 -11.85 Microcline 8 235 5 23 -10.06 Albite 22 229 8 23 -10.16 Chlorite IIb 9 1120 7 1120 -11.11 Calcite 9 22 -0.03 Ankerite Fe 0,55 10 21 -3.19 Phlogopite 2 1080 -12.40 Tab. 2. Pore water composition applied in experiments and modeling Parameter pH ClSO42HCO3Ca2+ Mg2+ Na+ K+
Unit mol/kg mol/kg mol/kg mol/kg mol/kg mol/kg mol/kg
Value 7.8 2.831 7.8·10-4 0.002 0.939 0.053 0.842 0.005
3. Experimental results The SEM analysis revealed that skeletal grains dissolution occurred in all reacted samples, and was the most advanced in the case of carbonates and chlorite. Numerous aggregates, as well as scattered, single, small crystals of pyrite were identified amongst the secondary minerals produced during the experiment (Fig. 1A, B). Cavities situated along the cleavage planes in microcline were also observed. Cavities probably developed as a result of preferential dissolution of the potassic lamellae relative to the sodic ones, as reported in7. On the surface of quartz grains small cavities were found, which record the initial stage of dissolution in aggressive environment. The
289
290
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
precipitation of secondary minerals can lead to partial formation damage (closure of the pore space), as observed for dawsonite (few crystals were identified only in the reacted samples) formed mainly in the intergranular spaces. Degradation of chlorite was accompanied by the formation of dispersed pyrite and aggregates of fine magnesite crystals. Small pyrite crystals were frequent in areas of iron carbonate dissolution – Fig. 1A. The SEM/EDX analysis of mudstones, reacted with H2S-CO2 mixture injected, showed elemental sulfur surrounded by fine crystals of FeS2– Fig. 1B.
Fig. 1. A – pyrite aggregates – Py on Ankerite – An; B – native Sulphur – S, and small pyrite grains (white) on clay mineral mass.
4. Modeling results During the first stage of simulation, 100 days injection of acid gas resulted in an increase of gas fugacity and elevation of CO2(aq) and/or H2S(aq) concentrations (Fig.2). Simultaneously a sharp drop of pH in pore waters occurred, except for the injection process of H 2S into carbonate-free, cap rock sample. In the next stage, in all the cases pH values grew above the initial level, and practically achieved stabilization. In the model for the cap rock sample, a growth of porosity was observed during the 100 days injection, and in the early period of storage. After 1000 years the values reached stabilization. For the Aquifer sample (rich in carbonates: ankerite, calcite) initially there was a fast rise of porosity during the injection (and increase of the formation permeability). During the storage porosity was nearly stable. Aquifer
Cap rock
8
8
7
6
CO2
pH
pH
7
CO2+H2S
5
6
CO2 CO2+H2S
5
H2S
H2S
4
4
0
100d
100y
1000y
10000y
0
100d
Time
1000y
10000y
Time
Aquifer
Cap rock
0,29
0,046
0,28
0,042
0,27 CO2
0,26
CO2+H2S
0,25
Porosity
Porosity
100y
0,038
CO2 CO2+H2S
0,034
H2S
H2S 0,03
0,24 0
100d
100y
Time
1000y
10000y
0
100d
100y
1000y
10000y
Time
Fig. 2. Changes in pH and porosity of aquifer and cap rock, based on numerical modeling.
Krzysztof Labus and Katarzyna Suchodolska / Procedia Earth and Planetary Science 17 (2017) 288 – 291
For the pure CO2injection porosity remained almost unchanged. In general, for the pure CO 2injection model, the changes in porosity were the least intense at both stages for all the samples. Results of the second stage of modeling allowed to evaluate the long-term effects of water-gas-rock interactions in the simulated repository. As a result of gas sequestration lasting 10,000 years, in the case of the model of Paralic series mudstones (cap-rock), the porosity of the rocks increased by 25%, 31%, and 29 % for CO 2, H2S, and the mixture, respectively. This porosity growth was caused by dissolution of significant amounts of K-feldspar, chlorite and albite, which was not compensated by precipitation of secondary muscovite, saponite-Na, annite and minnesotaite (Fe3Si4O10(OH)2). In the case of the aquifer formation model, the changes in porosity were minor, reaching 10% for pure H2S and the mixture while for CO2 there was almost no change. This phenomenon is associated with the balanced volumes of decomposed ankerite, calcite, feldspars and chlorites, and newly precipitated dolomite, muscovite, minesotaite, Saponite-Na, calcite and phengite, depending on the gas was injected. 4. Conclusions The experimental studies and modeling allowed evaluation of the impact of CO2 and H2S or their mixtures on the mineralogical composition and porosity of the rock matrix of the rocks typical for the Upper Silesian Coal Basin. On the basis of SEM analysis of reacted samples it was found that at injection step the dominant process is the dissolution of rock matrix (most evident in the case of carbonates and chlorite). This phenomenon was also reflected in modeling. The calculated increase in porosity resulted from the decomposition of those minerals in a volume higher than secondary, precipitating minerals such as: pyrite, magnesite or dawsonite. In the model for the cap rock sample, initially a slow increase in porosity was observed at the stage of injection and the first phase of the sequestration; at later time the values reached stabilization. For the aquifer sample there was an initial rise of porosity at the injection stage; during the phase of storage the porosity was nearly constant. For the pure CO2 experiment the porosity remained almost unchanged. The results of modeling showed that, in the case of two analyzed rock types, geological sequestration of pure H2S and mixtures thereof with CO2 should cause the release of significant amounts of CO2 as a result of the decomposition of primary carbonate minerals. Acknowledgements This work was funded by the National Science Centre – Polish executive agency - set up to fund basic research according to the decision DEC-2012/05/B/ST10/00416. References 1. Holloway S. Underground sequestration of carbon dioxide e a viable greenhouse gas mitigation option. Energy 2005; 30: 2318-33. 2. Xu T, Apps JA, Pruess K. Reactive geochemical transport simulation to study mineral trapping for CO2 disposal in deep arenaceous formations. J Geophys Res 2007;108: 2071– 84. 3. Wilk K, Kasza P, Labus K. Analysis of the applicability of foamed fracturing fluids. Nafta-Gaz 2015; LXXI: 425-433. 4. Bethke CM. Geochemical and biogeochemical reaction modeling. Cambridge Cambridge Univ. Press; 2008. 5. Lasaga AC. Chemical kinetics of water-rock interactions. J Geophys Res 1984; 89: 4009-25. 6. Palandri JL, Kharaka,YK. A compilation of rate parameters of water-mineral interaction kinetics for application to geochemical modeling. US Geological Survey, 2004; Open File Report 2004 -1068:1-64. 7. Labus K, Bujok P. CO2 mineral sequestration mechanisms and capacity of saline aquifers of the Upper Silesian Coal Basin (Central Europe) Modeling and experimental verification. Energy 2011; 36: 4974-4982.
291