An experimental evaluation of low salinity water mechanisms in a typical Brazilian sandstone and light crude oil with low acid/basic number

Low salinity water injection (LSWI) is a current and cost-effective method to enhance oil recovery by changing the salinity and composition of the injected water. However, the synergistic effect of chemical composition, concentration and in particular the pH of the brine in oil recovery during LSWI remains not well understood. In addition, there is a lack of low salinity studies in Brazilian sandstone rocks and light paraffinic crude oils of low acid/basic number to date. This paper investigates oil recovery mechanisms and the pH effect in high and low salinity brine solutions using samples from a clastic reservoir in Reconcavo basin, northeastern Brazil. Zeta potential and interfacial tension measurements, oil adsorption analysis using a quartz crystal microbalance with dissipation monitoring, and core flooding experiments were performed using different concentrations and pH values of synthetic formation water (SFW), NaCl and CaCl2 brine solutions. The results 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 increased oil recovery. The findings of this study can help understand oil recovery mechanisms during LSWI according to the type and content of pH-dependent surface charges in sandstone rocks and crude oils. This study also shows how to preselect potential field candidates in the Reconcavo basin and similar formations for stand-alone and hybrid LSWI applications.