Comprehensive investigation of low-salinity waterflooding in sandstone reservoirs

Abstract

AbstractWaterflooding has been applied for many years as secondary recovery method with no or little regard to the effect of the injected water salinity on oil recovery. However, in the last decade, there has been an increasing interest in understanding the effects of changing injected water salinity on reservoir performance. The potential of low-salinity waterflooding (LSWF) has been studied in sandstone reservoirs by numerous core-flooding experiments. These experiments have shown diverse results. This paper aims to investigate the effects of changing water salinity on oil recovery. A comprehensive review and analysis of the results of more than 500 core-flood experiments from published work were investigated to study the effects of several parameters such as clay content, clay type, and temperature on oil recovery. The relation between incremental oil recovery and sodium adsorption ratio SAR, and exchangeable sodium percentage (ESP) parameters which control clay swelling was illustrated. The analysis of the results revealed that there is an optimum composition and optimum salinity for waterflooding in secondary flooding stage. However, for tertiary flooding stage, the results showed that the controlling factor may be not decreasing the salinity but rather changing the salinity (e.g., either increasing or decreasing) with minor improvement in oil recovery. It was clear also that applying the optimum salinity in the secondary recovery stage is more effective than applying it in the tertiary recovery stage. This study aims to develop important guidelines for screening and designing optimum salinity for waterflooding projects in sandstone reservoirs.