Effects of Low Salinity Water Ion Composition on Wettability Alteration in Sandstone Reservoir Rock: A Laboratory Investigation

Abstract

For various decades, water-flooding mechanisms have been playing important role for improving oil recovery. It was not until recently that researchers discovered that the ionic strength of the brine was substantial. With regard to this, many studies started being published which focused more on the comparison of effects of having high ionic strength and low ionic strength for brine during flooding processes. Low salinity water comprises brine concentration below 5000ppm. At optimum concentration, low salinity water (LSW) when injected into the reservoir enhances the oil recovery considerably. This is attributed to the change of reservoir rock wettability. The process governing these changes are not well understood thus requiring a scrupulous investigation. Moreover there is no a certain fixed salinity range. This study investigates wettability alteration of Berea sandstone rock with brine of different ion composition (NaCl, KCl, MgCl₂, CaCl_2, and formation water-mostly Mg²⁺ and Ca²⁺ ions) and strength (500ppm-6500ppm with exception of formation water which consisted of 13000ppm). For the study, (31) core slabs were extracted from the core plug then saturated with formation water (FW). Next, the slabs underwent aging process in crude oil at ambient pressure and a temperature of 80⁰c. Later, the slabs were removed and immersed in containers with low salinity water at different ionic composition and strength, which is mentioned. The wettability was measured by applying the sessile drop method in certain range of time. According to the results, there have been significantly great change of wettability at Low salinity water in case of KCl was observed.

Keywords: ionic strength, wettability, low salinity water, saturation, brine composition