The critical role of fracture flow on two-phase matrix-fracture transfer mechanisms

We analyze the dynamics of imbibition in a fractured medium using the Direct Numerical Simulation of the Navier-Stokes equations. Pore geometries with homogeneous and heterogeneous pore distributions at the matrix and fracture interface are considered in this study. We evaluate the role of critical factors such as wettability, viscosity ratio, injection rate, and the magnitude of the interfacial tension on the porescale dynamic of mass exchange between matrix and fracture for 2D geometries consisting of a complex pore-geometry and a single fracture. Two different regimes are identified during the injection of wetting fluid through the fracture into the domain saturated with a non-wetting fluid: (1) co-operative (co-current) imbibition before the wetting phase breakthrough and, (2) counter-current imbibition follows afterwards. For the studied 2D geometries, the displacement efficiency is higher in the co-operative imbibition, while the counter-current imbibition occurs at a slow pace. Lower injection rates in the fracture are in favor of improving displacement efficiency in the porous matrix. Higher wettability and interfacial tension help the wetting fluid to penetrate further into the matrix and improve the displacement rate for both co-operative and counter-current modes of displacement.