Pore-scale connectivity evolution during oil–water redistribution induced by pressure release in fractured porous media

Following stimulation and shut-in, production progressively depletes the pressure stored in a fractured formation, yet the accompanying changes in oil–water connectivity remain poorly quantified. Here, volume-of-fluid simulations are performed in a pore model comprising a sandstone matrix derived from micro-computed tomography and a prescribed fracture network. A finite oil-filled buffer, coupled to the pore domain through an oil-phase mass balance, represents the surrounding pressure-storage region. A constant-pressure outlet represents the production side. The effects of initial pressure differential and wettability are examined. The normalized pressure histories exhibit approximately exponential relaxation. The relaxation times are nearly identical for Δp0 = 0.20–0.50 MPa, whereas the 0.10 MPa case relaxes more slowly. This domain-scale behavior coexists with pressure-dependent connectivity evolution at the pore scale. As the buffer pressure decreases, oil-phase connectivity develops through selective pore-throat activation, interface rearrangement, and reconnection of previously separated oil regions. This evolution is quantified using the buffer–fracture oil-connectivity index, Ibf, and the largest connected oil-cluster fraction, Fo,max. Higher initial pressure differentials accelerate the growth of both metrics and expand the connected oil region. Wettability also influences the amount and distribution of matrix water. Water-wet conditions retain more water in fine pore bodies, whereas oil-wet conditions leave a greater fraction of the remaining water in large pore bodies. These results clarify how pressure depletion, phase connectivity, and water localization evolve together during post-shut-in production.