Reactivation of critically-stressed basement faults and related induced seismicity in the southeastern Sichuan basin

The southeastern Sichuan basin possesses abundant gas shale resources that are currently being recovered. The basement strata are seismically active making it important to understand the effect of fluid injection during geo-energy extraction and storage. We recovered outcropping basement rocks and conducted friction experiments on simulated rock gouge to assess the potential for frictional stability. Meanwhile, we also calculated the poroelastic Coulomb stresses resulting from fluid injection to define the impact of stress perturbations on fault stability. These results are combined with the seismic reflection images to analyze the seismic potential. Results indicate the basement rocks include clay-lean granites and sandstones and clay-rich slates; gouge frictional strength and stability are controlled by the clay contents. The gouge frictional strength monotonically decreases and fault stability is enhanced with increasing clay content. Poroelastic stresses induced by fluid injection can reactivate critically-stressed faults within 2 km of the injection site, but decay rapidly with increasing distance. The experimental-modelling results combined with seismic reflection profiles indicate that basement fault stability is controlled by various factors, including fault aseismic slip in the pressurized zones, poroelastic stress transfer from fluid injection and gouge mineralogy. These results have important implications for understanding instability of basement faults induced by fluid injection during energy extraction and storage and contribute to reducing seismic hazard in the southeastern Sichuan basin.