Monotonic fluid injection induces fault instability and slip: A laboratory study

This study investigates the instability and slip behavior of Longmaxi shale faults with specific surface morphologies under monotonic fluid injection. The results indicate that the slip process can be categorized into dynamic and quasi-dynamic slip stages, with both the injection rate and surface morphology significantly influencing fault slip characteristics and stability. An increase in the injection rate and a decrease in surface roughness lead to a notable rise in dynamic slip displacement and released energy Es, causing the overall slip mode to transition from slow slip to seismic slip. Furthermore, the seismic injection efficiency observed in this study (5.4 × 10−3% ∼ 7.9 × 10−1%) aligns well with results from other experiments, numerical simulations, and field observations. The relationships among seismic injection efficiency, seismic moment magnitude Mw, seismic moment M0, and released energy Es are also strongly affected by fault surface morphology. When fluid pressure exhibits heterogeneity along the fault, the rapid increase in driving shear stress τd in the unpressurized zone may not only mitigate fluid overpressure but also enhance the fault's sensitivity to fluid injection, leading to higher Mw and M0. This work provides critical theoretical insights and technical guidance for assessing and mitigating seismic risks associated with shale gas extraction. © 2025 Elsevier B.V.