Investigation of Wettability Alteration by Low Salinity Water in Sandstone Rock

Abstract

Abstract Optimization of any oil recovery process is based on understanding of recovery mechanisms, though the underlying mechanisms of improving oil recovery by low salinity water injection are still debated. Wettability alteration is one of the dominant mechanisms of any IOR/EOR process. In this paper, wettability alteration by low salinity water in sandstone reservoirs is examined by using contact angle measurements. Moreover, the impact of changing ionic strength on the electrokinetic charge at oil/brine interface is investigated using zeta potential technique to explain the causes of wettability alteration by low salinity water. The behavior of wettability with pressure and temperature was studied by running contact angle measurements different ranges of pressure and temperature (500-1000 psi, and 140-250°F). Sandstone rock was represented by mica sheets to eliminate the influence of rock heterogeneity and hysteresis on the contact angle measurements. Effect of salinity on wettability alteration was studied by utilizing synthetic water at a wide range of salinity (from 0 to 174,000 mg/l). In addition, two different crude oils with different compositions were used to evaluate the effect of oil characteristics on low salinity water efficiency. Zeta potential test were conducted to measure the oil/brine interface electrokinetic charge for combinations between the two crude oils, and different brines. The contact angle increased with the increase of temperature, and pressure. High salinity water showed high contact angles, while low salinity water decreased the contact angles significantly for the two types of crude oil. This proves that low salinity water could alter the wettability to more water-wet. In addition, the electrokinetic charges at oil/brine interfaces were sensitive to the change of ionic strength. Oil/brine charges were highly negative with low salinity water, which resulted in repulsion forces between oil/brine and brine/rock surfaces and altered the wettability towards water-wet. This paper demonstrates the efficiency of low salinity water in improving oil recovery by altering rock wettability, and it contributes to the understandings of the main mechanism of low salinity water.