Can low salinity water injection be an efficient option for the Recôncavo Basin? An experimental and simulation case study

Abstract

Low salinity water injection (LSWI) has been studied by several researchers as an enhanced oil recovery (EOR) method in laboratory experiments, numerical simulations, and field applications. However, its effects on oil recovery remain uncertain due to the complexity of the interactions among crude oil, brine, and the rock surface, for both sandstone and carbonate reservoirs, particularly when they contain a diversity of clay minerals. This paper investigates LSWI performance and mechanisms in sandstone rock, brine, and light crude oil with low polar compounds from a reservoir in Brazil. Core flooding experiments and reservoir simulations were carried out to understand the influence of key parameters on oil recovery. Zeta potential measurements were performed to investigate the influence of the formation water and NaCl and CaCl2 brine solutions on rock and oil surface charges. Increased oil recovery, Ca++ desorption from the rock surface, and a substantial pH increase in the effluent were noticed during LSWI. Based on the zeta potential measurement, a thicker water film was also formed on the rock and oil surface with brine dilution. A recovery factor of 64% was reached by testing LSWI from the beginning of the waterflooding (secondary mode) and this was the highest recovery of all the scenarios evaluated. Ten parameters were successfully history matched to core flood data, and optimization and sensitivity analysis showed that the concentration of Na+ and Ca++, and the water injection rate were the most important parameters in the LSWI process. Overall, this study sheds light on the LSWI mechanisms for the Brazilian oil field investigated and provides useful operational parameters for designing and achieving better LSWI performance.