Network modelling of mixed-wettability on electrical resistivity, capillary pressure and wettability indices

This paper presents a network model that examines the effects of a physical development of pore-scale wettability on various petrophysical characteristics (in particular, electrical resistivity and capillary pressure) for a full-flooding cycle. The model incorporates pore-scale displacement mechanisms that are physically based. Models with different wettability type (correlated and uncorrelated to pore size), various fractions of mixed-wet pores and water advancing contact angles have been investigated. In each case, Amott–Harvey and USBM wettability indices have also been calculated and compared. A detailed description of wettability at the pore-scale was simulated to allow both water- and oil-wet regions existing within a single pore. Crevices of the pore space play a crucial role in simulating observed experimental electrical resistivity trends. This is because water in the crevices maintains continuity through the tube and conducts electrically. Our results suggest resistivity curves for non-uniform wettability samples show hysteresis and trends similar to experimental observations. Different wettability types can give a variety of electrical resistivity behaviour. This has important implications in determining the water saturation, from electric logs, of hydrocarbon reservoirs.