Mechanical alterations in shale formations due to exposure to water-based fracturing fluids and supercritical carbon dioxide(ScCO_(2))significantly affect the performance of shale gas exploration and CO_(2) geo-seques...Mechanical alterations in shale formations due to exposure to water-based fracturing fluids and supercritical carbon dioxide(ScCO_(2))significantly affect the performance of shale gas exploration and CO_(2) geo-sequestration.In this study,a hydrothermal(HT)reaction system was set up to treat Longmaxi shale samples of varying mineralogies(carbonate-,clay-,and quartz-rich)with different fluids,i.e.deionized(DI)water,2%potassium chloride(KCl)solution,and ScCO_(2) under HT conditions expected in shale formation.Statistical micro-indentation was conducted to characterize the mechanical property alterations caused by the shale-fluid interactions.An in situ morphological and mineralogical identification technique that combines scanning electron microscopy(SEM)and backscattered electron(BSE)imaging with energy-dispersive X-ray spectroscopy(EDS)was used to analyze the microstructural and mineralogical changes of the treated shale samples.Results show no apparent changes in the Young's modulus,E,and hardness,H,after treatment with DI water under room temperature(20℃)and atmospheric pressure for 7 d.In contrast,E and H were decreased by 31.2%and 37.5%at elevated temperature(80℃)and pressure(8 MPa),respectively.The addition of 2%KCl into DI water mitigated degradation of the mechanical properties.Quartz-rich shale specimens are the least sensitive to the water-based fracturing fluids,followed by the clay-rich and carbonate-rich shale formations.Based on in situ morphological and mineralogical identification,the primary factors for the mechanical degradation induced by water-based fluids include carbonate dissolution,clay swelling,and pyrite oxidation.Slight increases in the measured E and H and compression of porous clay aggregates were observed after treatment with ScCO_(2).The major factor contributing to the mechanical changes resulting from the exposure to scCO_(2) appears to be the competition between swelling caused by adsorption and compression of shale matrix.展开更多
基金funded by the Open Research Fund Programof State Key Laboratory of Hydroscience and Engineering(Project Number:sklhse-2023-D-04)the National Natural Science Foundation of China(Grant Nos.51979144,51661165015,and 51323014).
文摘Mechanical alterations in shale formations due to exposure to water-based fracturing fluids and supercritical carbon dioxide(ScCO_(2))significantly affect the performance of shale gas exploration and CO_(2) geo-sequestration.In this study,a hydrothermal(HT)reaction system was set up to treat Longmaxi shale samples of varying mineralogies(carbonate-,clay-,and quartz-rich)with different fluids,i.e.deionized(DI)water,2%potassium chloride(KCl)solution,and ScCO_(2) under HT conditions expected in shale formation.Statistical micro-indentation was conducted to characterize the mechanical property alterations caused by the shale-fluid interactions.An in situ morphological and mineralogical identification technique that combines scanning electron microscopy(SEM)and backscattered electron(BSE)imaging with energy-dispersive X-ray spectroscopy(EDS)was used to analyze the microstructural and mineralogical changes of the treated shale samples.Results show no apparent changes in the Young's modulus,E,and hardness,H,after treatment with DI water under room temperature(20℃)and atmospheric pressure for 7 d.In contrast,E and H were decreased by 31.2%and 37.5%at elevated temperature(80℃)and pressure(8 MPa),respectively.The addition of 2%KCl into DI water mitigated degradation of the mechanical properties.Quartz-rich shale specimens are the least sensitive to the water-based fracturing fluids,followed by the clay-rich and carbonate-rich shale formations.Based on in situ morphological and mineralogical identification,the primary factors for the mechanical degradation induced by water-based fluids include carbonate dissolution,clay swelling,and pyrite oxidation.Slight increases in the measured E and H and compression of porous clay aggregates were observed after treatment with ScCO_(2).The major factor contributing to the mechanical changes resulting from the exposure to scCO_(2) appears to be the competition between swelling caused by adsorption and compression of shale matrix.
