Wettability and Its Effects on Oil Recovery in Fractured and Conventional Reservoirs

Wettability, as the tendency of a reservoir rock surface to preferentially contact a particular fluid in a multiphase fluid system (Agbalaka et al., 2008), is determined by complex interface boundary conditions acting within the pore scale of porous media. Capillary pressure and relative permeability can be changed quite substantially from a wetting to a non-wetting phase, with subsequent influences on transition zone height, water-oil contacts, and residual oil saturation (Cockcroft et al., 1989). Wettability has a dominant effect on interface movement and associated displacement of different phases within porous media. For example, during tertiary miscible injection for a water-invaded oil column (double displacement process), gas and oil direct contact can be prevented by water surrounding residual oil due to wettability effects (water shielding phenomenon). Therefore, understanding formation wettability and its management is crucial for optimizing oil recovery. The wettability concept and its effect on multiphase flow within conventional and naturally fractured reservoirs (NFRs) is discussed here with some case studies.