ANALYSIS AND PROSPECTS OF CASING DEFORMATION INDUCED BY FAULT SLIP IN DEEP SHALE RESERVOIRS OF SOUTHERN SICHUAN BASIN

The development of deep shale gas reservoirs in the Southern Sichuan Basin faces significant challenges due to severe casing deformation,primarily caused by fault slip triggered by engineering activities. However,a subset of such deformation events lacks clear microseismic precursors,leaving their underlying mechanisms poorly understood. This study investigates the intrinsic relationship and governing mechanisms between fault slip and casing deformation in deep,high-temperature,and high-pressure shale reservoirs in Southern Sichuan. A systematic analysis was conducted to evaluate the combined effects of shale mineral composition,formation temperature,and high pore pressure on the frictional stability of faults. The results indicate that the fault slip behavior is jointly controlled by clay mineral content and formation temperature,which exhibit competing influences. An increase in clay mineral content significantly reduces the friction coefficient of the fault while raising the rate-strengthening parameter(a-b),promoting stable aseismic creep. In contrast,the high-temperature conditions prevalent in deep reservoirs tend to lower the(a-b)value,increasing the potential for unstable fault slip with tremor-like characteristics. It is proposed that in clay-rich shale intervals,hydraulic fracturing can induce large-scale shear creep with minimal microseismic response,representing a critical mechanism for casing deformation that is difficult to predict using conventional monitoring methods. Therefore,the safe development of deep shale gas requires not only consideration of the in-situ stress state but also the establishment of a fault activity risk assessment system based on mineral composition. Accordingly,fracturing design and deformation monitoring strategies should be optimized for clay-rich intervals to effectively mitigate casing deformation risks.