China is rich in shale gas resources,however,wellbores in shale gas reservoirs are frequently unstable.This has a serious impact on the shale gas drilling cycle.Polyamine,a common additive in water-based shale drillin...China is rich in shale gas resources,however,wellbores in shale gas reservoirs are frequently unstable.This has a serious impact on the shale gas drilling cycle.Polyamine,a common additive in water-based shale drilling fluids,can effectively inhibit shale hydration.However,there is a lack of quantitative research on the effect of polyamine inhibitors on the microstructure and macromechanical properties of shale.Therefore,this study investigated those issues via a systematic hydration experiment carried out on shale from the Longmaxi Formation.The results show that microfractures are created and expand during shale hydration,that they also connect to form a complex microfracture network,and that 3%polyamine inhibitors(polyamine solution with volume fraction of 3%)can effectively inhibit their evolution.The ultrasonic velocities and UCS of the Longmaxi shale are significantly anisotropic;the former first increases and then decreases with the laminae angle,reaching its maximum when the laminae angle is 30°.The UCS of the shale is highest and lowest,respectively,when the laminae angles are 0°or 90°and 30°.In general,these UCS appear as a"U"pattern,high on two sides with a dip in the center.Polyamines can effectively inhibit both the expansion of shale and the reduction of P-wave and S-wave velocities,the UCS,and elastic modulus.The UCS of a shale sample was reduced by 28%e40%after immersion for 96 h in water,compared to 2%e20%after immersion in a 3%polyamine inhibitor for the same amount of time.The inhibiting effect of the polyamine was remarkable.展开更多
基金We gratefully acknowledge the financial support from the National Natural Science Foundation of China(Grant No.51774248,U20A20266)the International Science&Technology Cooperation and Exchange Program of Sichuan(Grant No.2019YFH0166)。
文摘China is rich in shale gas resources,however,wellbores in shale gas reservoirs are frequently unstable.This has a serious impact on the shale gas drilling cycle.Polyamine,a common additive in water-based shale drilling fluids,can effectively inhibit shale hydration.However,there is a lack of quantitative research on the effect of polyamine inhibitors on the microstructure and macromechanical properties of shale.Therefore,this study investigated those issues via a systematic hydration experiment carried out on shale from the Longmaxi Formation.The results show that microfractures are created and expand during shale hydration,that they also connect to form a complex microfracture network,and that 3%polyamine inhibitors(polyamine solution with volume fraction of 3%)can effectively inhibit their evolution.The ultrasonic velocities and UCS of the Longmaxi shale are significantly anisotropic;the former first increases and then decreases with the laminae angle,reaching its maximum when the laminae angle is 30°.The UCS of the shale is highest and lowest,respectively,when the laminae angles are 0°or 90°and 30°.In general,these UCS appear as a"U"pattern,high on two sides with a dip in the center.Polyamines can effectively inhibit both the expansion of shale and the reduction of P-wave and S-wave velocities,the UCS,and elastic modulus.The UCS of a shale sample was reduced by 28%e40%after immersion for 96 h in water,compared to 2%e20%after immersion in a 3%polyamine inhibitor for the same amount of time.The inhibiting effect of the polyamine was remarkable.
