Modeling investigation of low salinity water injection in sandstones and carbonates: Effect of Na+ and SO^sub 4^^sup 2-

Low salinity water injection (LSWI) has gained great attention as a promising enhanced oil recovery (EOR) method with numerous advantages (e.g., economic and environmental aspects), compared to other conventional chemical EOR methods. For the past two decades, a number of laboratory studies have been performed by researchers to understand the main pore-scale mechanisms of oil displacement during LSWI; however, further experimental and modeling research works are required to comprehend the LSWI governing mechanisms. The focus of this paper is to investigate important aspects such as oil recovery mechanisms, wettability alteration, changes in pH of formation water, and mineral reactions (dissolution/precipitation) which occur during LSWI in sandstones and carbonates. To explore the effect of ion-exchange, a compositional model is developed with the aid of laboratory data provided by Computer Modeling Group (CMG), where Na+ and SO42− are used as interpolants to model LSWI in sandstone and carbonate cores, respectively. In this study, it is concluded that wettability change from preferentially oil-wet to more water-wet is the dominant mechanism for a considerable increase in the oil recovery in carbonate rocks. Based on the simulation runs, the amount of calcite precipitation and dissolution is found to be small in the carbonate case studied in this research work; exhibiting an insignificant impact. However, the calcite precipitation and dolomite dissolution are the central factors, affecting oil recovery during LSWI if there is a high bicarbonate content (HCO3-), in the presence of other catalytic ions.