Reservoir Ductility Effects on Hydrofracturing-Induced Seismicity: Mechanisms, Evaluation, and Perspectives

Deep and ultra-deep hydrocarbon resources are of strategic importance for energy security. The pronounced ductility of deep reservoirs and faults makes hydraulic fracture propagation and induced seismicity mechanisms fundamentally different from those in conventional brittle reservoirs. This review systematically synthesizes recent theoretical, experimental, and numerical advances in hydraulic-fracturing-induced seismicity, covering triggering mechanisms, fault reactivation risk evaluation, and perspectives. A core distinction is identified: brittle faults exhibit instantaneous stick-slip rupture with high seismic frequency and significant magnitude, whereas ductile faults undergo stable aseismic creep and progressive slip, with long-term deformation prone to delayed large earthquakes—their nucleation shows unique mechanical responses including high stress drop, low rupture velocity, and low seismic radiation efficiency. Subsequently, four major challenges are distilled for risk evaluation systems: insufficient dynamic characterization of mechanical parameters in ductile reservoirs, lack of fracturing-control strategies adapted to ductile behavior, poor understanding of multi-scale slip transition mechanisms, and inadequacy of multi-field coupling models in capturing long-term delayed evolution. Traditional brittle-based risk frameworks cannot characterize the time-dependent slip and progressive reactivation of ductile faults, limiting their applicability to deep reservoirs. Future works are proposed, including refined characterization of mechanical parameters under high temperature and pressure, intelligent full-cycle hydrofracturing control, quantitative criteria for slip activation, and optimization of long-term multi-field coupling models. This study elucidates recent progress in hydrofracturing-induced seismicity mechanisms and quantitative risk assessment in ductile reservoirs, filling a gap in the conventional brittle-dominant research. It also provides theoretical support for seismic risk evaluation and early warning in deep fracturing operations, with significant implications for improving induced seismicity management and ensuring safe, efficient, and sustainable deep-resource development.