Effect of Brine Salinity on Wettability Behavior of Crude Oil/Reservoir Rock/Reservoir Brine/Supercritical CO2 System

Wettability affects fluid distribution and fluid flow in a porous medium. The main purpose of this paper is to investigate the effect of brine salinity on the wetting behavior of the crude oil/brine/rock/CO2 system at reservoir conditions to explore the effect of brine salinity on miscible CO2 flooding and water alternating gas (WAG) injection scheme. Synthetic reservoir brines are prepared by dissolving NaCl in doubly distilled water with different salinities varying between 5000-25000 ppm (mg/L). In the experiments, a rock slab at residual oil saturation is mounted into a high pressure cell. A shape analysis of a bubble captured on the rock surface is then applied to obtain dynamic and equilibrium contact angles. The electron microprobe analysis (EMPA) and micro-computed x-ray tomography (Micro-CT) are used to evaluate compositional changes that occur both at and within the rock surface. According to the results, salinity increases the contact angle which shows that the rock surface becomes intermediate wet. The contact angle never exceeds 90° even at high pressures and elevated temperatures. In the range of pressure and salinity examined in this work, the system changes from strongly water-wet to intermediate gas wet. The system dose not become completely gas wet.