Pore Pressure-Stress Coupling Controls on Fault Reactivation and Fracture Evolution: Insights from Analytical Modeling and Case Studies

Session: Faults, Fractures, and Geomechanics for the Energy Transition

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Pore pressure-stress coupling (PSC) governs stress redistribution during fluid injection and depletion in subsurface reservoirs, with significant implications for fault stability and fracture development. This study presents a quantitative analytical framework to assess how PSC influences fault slip tendency and fracture mode transitions across typical stress regimes. Closed-form expressions linking PSC magnitude to both slip tendency and critical pore pressure thresholds were derived and validated using a case study from the Dunkirk Shale in the Appalachian Basin. Results show that the effect of PSC on fault slip is directionally dependent: vertical PSC promotes fault reactivation in normal regimes but suppresses it in reverse regimes, while horizontal PSC exhibits the opposite behavior. Additionally, PSC raises the critical pressure required for fault reactivation, enhancing fault sealing capacity under certain conditions.

Fracture evolution is likewise sensitive to PSC magnitude. When PSC < 0.4, high differential stress promotes shear fractures; PSC > 0.4 favors tensile and hybrid fractures, with associated shifts in fracture orientation from vertical to bedding-parallel. These findings help explain the occurrence of horizontal microcracks and fibrous veins in overpressured mudrocks, and offer predictive insight into fracture network geometry under evolving pore pressure. This work highlights PSC as a key control on geomechanical behavior in reservoirs targeted for hydrocarbon production, CO₂ storage, and geothermal development, and underscores its role in supporting risk assessment and optimization efforts during the energy transition.