Experimental Investigation of the Effect of Salinity and Type of Ion on the Stability of Water in Oil Emulsion

Water injection especially low-salinity water injection has provided a low-cost EOR method for more oil recovery. In recent years, most of the studies on low-salinity waterflooding have been focused on the investigation of the effect of water injection on rock/oil/water interaction. The purpose of this study is to investigate the fluid/fluid interaction which has received less attention in comparison with the rock/fluids interaction. In this experimental work, a series of bottle tests have been performed with 20 percent of crude oil and 80 percent of saline water (for five different common salts in the seawater) with different salinities from 6,000 to 40,000 ppm. By sampling the emulsified portion at the oil/water interface, the size distribution of the water droplets in oil has been obtained. Moreover, the size of water droplets have varied from 0.02 to 1.65 mm, and relative frequency of categories was 0.73 at its maximum. The size of water droplets decreases with a decease in the salinity. Among the salts, calcium chloride is more effective in comparison with others as the water droplet size is the lowest among three other salts, and consequently it could attract more natural surface active materials from oil to water-oil interface. The sorting of salts from highest to lowest stable emulsion is calcium chloride, magnesium chloride, sodium sulfate and sodium chloride. Ultimately, this is due to the interactions of ions in saline water with oil, charge density of ions and their surface activity.