Frictional stability of Longmaxi shale gouges and its implication for deep seismic potential in the southeastern Sichuan Basin

Abstract

Microearthquakes accompanying shale gas recovery highlight the importance of exploring the frictional and stability properties of shale gouges. Aiming to reveal the influencing factors on fault stability, this paper explores the impact of mineral compositions, effective stress and temperature on the frictional stability of Longmaxi shale gouges in deep reservoirs located in the Luzhou area, southeastern Sichuan Basin. Eleven shear experiments were conducted to define the frictional strength and stability of five shale gouges. The specific experimental conditions were as follows: temperatures: 90–270°C; a confining stress: 95 MPa; and pore fluid pressures: 25–55 MPa. The results show that all five shale gouges generally display high frictional strength with friction coefficients ranging from 0.60 to 0.70 at the aforementioned experiment condition of pressures, and temperatures. Frictional stability is significantly affected by temperature and mineral compositions, but is insensitive to variation in pore fluid pressures. Fault instability is enhanced at higher temperatures (especially at >200°C) and with higher tectosilicate/carbonate contents. The results demonstrate that the combined effect of mineral composition and temperature is particularly important for induced seismicity during hydraulic fracturing in deep shale reservoirs.