Laboratory investigation of wettability and hysteresis effects on resistivity index and capillary pressure characteristics

This paper focuses on the experimental aspects of resistivity index and water/oil capillary pressure measurements. A novel experimental procedure using water-wet and oil-wet membranes has been developed. Six potential electrodes and two current electrodes are used to provide resistivity readings across the sample and for seven adjacent intervals along the length of the core plug. The resistivity profile along the core length enables assessment of saturation distribution and end effects. The desaturation tests mimic different displacement processes that could occur during the history of the reservoir, for example, the displacement of water by oil during the initial hydrocarbon migration; the displacement of oil by mud filtrate around the wellbore during drilling and the displacement processes during the formation of transition zones under gravity/capillary forces and during waterflooding. Results from our studies indicate that both the phase-dependent and cycle-dependent hysteresis should be taken into consideration for resistivity index and capillary pressure measurements. The hysteresis effects also depend on the wettability of the rock samples.