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

Microearthquakes accompanying shale gas recovery highlight the importance of exploring the frictional and stability properties of shale gouges. Aiming to reveal the in fl uencing 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 de fi ne the frictional strength and stability of fi ve shale gouges. The speci fi c experimental conditions were as follows: temperatures: 90 – 270°C; a con fi ning stress: 95 MPa; and pore fl uid pressures: 25 – 55 MPa. The results show that all fi ve shale gouges generally display high frictional strength with friction coef fi cients ranging from 0.60 to 0.70 at the aforementioned experiment condition of pressures, and temperatures. Frictional stability is signi fi cantly affected by temperature and mineral compositions, but is insensitive to variation in pore fl uid 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.