ROCK-FLUID AND FLUID-FLUID INTERACTIONS DURING LOW SALINITY WATER INJECTION IN SILICICLASTIC OIL RESERVOIRS
Oil recovery. Low salinity water injection. pH-Dependent charge. Ionic exchange. Recôncavo basin.
Low salinity water injection (LSWI) is a current, cost-effective, and environmentally friendly method to enhance oil recovery by changing the salinity and/or composition of the injected water. However, the synergistic effect of chemical composition, concentration, and the pH of the injected brine in oil recovery during LSWI remains not well understood. This fact is due to the complexity of the interactions among the crude oil, the formation and injected brine solutions, and the rock surface, for both sandstone and carbonate reservoirs, particularly when they contain a diversity of clay minerals. In addition, there is a lack of low salinity studies in Brazilian sandstone rocks and light paraffinic crude oils to date. This research investigates the oil recovery performance and mechanisms in high and low salinity brine solutions using samples from a siliciclastic reservoir in Recôncavo basin, northeastern Brazil. Zeta potential measurements, oil adsorption analysis in silica, core flooding experiments, and interfacial tension and contact angle measurements are among the main experiments performed in this study. Furthermore, a commercial numerical simulator was used to create a representative model of the coreflooding. The experimental results showed a simultaneous increase in oil recovery and pH of the effluent in the coreflooding during IABS. Zeta potential measurements confirmed a thicker water film was formed on the rock and oil surface with brine dilution. The experimental observations also indicate that when the reservoir pH changes towards the alkaline conditions driven by ionic exchanges during LSWI, it may approximate the isoelectric point (IEP) of pH-dependent surface charges in oil and rock minerals, weakening the electrostatic attraction between their surfaces, and consequently contributing to release of oil in the porous media and increase in oil recovery. Optimization and sensitivity analysis showed that the concentration of Na+ and Ca++, and the water injection rate were the most important parameters in LSWI. Finally, interfacial tension and contact angle measurements in systems containing samples that mimic Recôncavo basin rock, high and low salinity brine solutions, crude oil, and CO2 indicate that low salinity brine favors CO2 solubility, may lead the increase in oil recovery in hybrid applications of LSWI-CO2. The findings of this research contribute substantially to the understanding of oil recovery mechanisms during LSWI. This study also provides useful data for oil
companies that have acquired mature fields and exploration blocks in the Recôncavo basin, supporting them in operational and investment decisions.