Effects of Heterogeneity and Wetting on Relative Permeability Using Pore Level Modeling

We present a three-dimensional, capillary equilibrium based, pore level network model that computes relative permeability and capillary pressure for drainage and imbibition cycles. The model accounts for wetting layers in crevices of the pore space, cooperative pore filling and different contact angles. Arbitrary distributions of pore size with different spatial correlations are studied. We show that relative permeabilities for unconsolidated media can be represented in the model using spatially uncorrelated distributions of pore size, but that curves typical of consolidated rock can only be explained by allowing spatial correlation in the pore structure. We also study the effects of flow in wetting layers and different types of cooperative pore filling. This represents changes in contact angle from a completely water-wet system to a neutrally-wet rock. Relative permeability can be extremely sensitive to small changes in contact angle. In general, the residual non-wetting phase saturation decreases as the system becomes less strongly water-wet.