Efficiency of Oil Recovery by Low Salinity Water Flooding in Sandstone Reservoirs

Abstract

Abstract Low salinity water is a promising technique for improving oil recovery in sandstone reservoirs. However, the optimum conditions that improve oil recovery by low salinity flooding are uncertain due to the lack of understanding of fluid-rock interaction mechanisms. In this study, several coreflood experiments were conducted to explain the mechanisms involved when recovering oil with low salinity water. Core flood experiments were run to determine the effect of water salinity on oil recovery in the secondary and tertiary modes. Deionized water and three different brines (from 5,000 to 174,000 mg/l) were tested; these brines represent a Middle East field case. Two different types of crude oils were used to investigate the effect of oil composition on the applicability of low salinity water flooding. All experiments were conducted on 5 to 6 in. long outcrop Berea sandstone cores. Core flood effluent was sampled regularly to follow rock-fluid interactions, and it was achieved by measuring the concentration of different cations. Core flood tests indicated that injection of deionized water in the secondary mode resulted in a significant improvement in oil recovery, up to 22%, compared to seawater. However, no additional oil was recovered in the tertiary mode. This paper contributes to the understanding of cation exchange caused by low salinity water injection, and how this exchange alters the wettability of the rock and reduces the electrostatic attraction forces between oil and rock. Likewise, we discuss formation damage that might occur during low salinity waterflooding in Berea sandstone, and investigate the contribution of formation damage to oil recovery improvement.