Quantitative assessment of fault reactivation risk based on pore pressure diffusion and poroelastic effects: Application to the Luzhou shale gas field, Sichuan, China

Abstract

Quantitative fault reactivation risk assessment is essential for managing induced seismicity and ensuring safe subsurface energy development. Although both pore pressure diffusion and poroelastic effects govern stress evolution during fluid injection and extraction, most existing risk assessment methods consider only pore pressure changes, thereby limiting predictive accuracy. In this study, we propose a novel Pore pressure Diffusion - Poroelastic Effects Fault Reactivation (PDPE-FR) method that couples pore pressure diffusion and poroelastic stress responses, incorporates both in-situ stress field and injection-induced stress perturbations, and accounts for parameter uncertainties related to fault orientation and stress conditions. We apply this method to the Luzhou shale gas field in China by: (1) collecting and interpolating in-situ stress measurements; (2) constructing fully coupled poroelastic finite element models to simulate injection-induced stress perturbations; and (3) integrating Coulomb stress change and normalized fault slip tendency with parameter uncertainty to evaluate fault reactivation probabilities. The results indicate high reactivation probabilities (50–80 %) for NNE-striking faults in the Fuji Syncline in Luzhou shale gas field under far-field injection, and elevated probabilities (50–90 %) for faults of all orientations under near-field conditions. Strong spatiotemporal correlations between predicted fault reactivation risks and observed seismicity, along with fracturing timelines, validate the robustness of the proposed method. In addition to assessing fault reactivation risk, the method also demonstrates broad applicability in optimizing injection-production strategies and guiding well placement.