Reservoir wetting in sandstone reservoirs, adsorption of polar basic oil components onto quartz and feldspar minerals.

Abstract

For more than a decade the mechanism behind flooding with low salinity water have been studied and well documented as increased oil recovery method (EOR) in sandstone reservoirs. Recently Austad et. al. proposed a new chemical wettability alteration mechanism showing increases in pH as the high saline water is displaced by low saline water is a key factor. Proposed mechanism discusses desorption of cations, Ca2+ from clay surface during flooding with water of low salt concentration. Local pH increase occurs near clay surface and saltwater since active cations (Ca2+) are replaced by protons (H+) from water. Desorption of the organic material is a result of quick reaction between OH- and adsorbed basic and acidic material. Reservoir rocks becomes more water –wet and more oil is displaced toward the production well resulting in increased recovery. This study attempts to evaluate adsorption of polar basic components onto sandstone minerals, and to understand the potential of each mineral in a wettability alteration process. Experimets are performed to determine adsorption amount of quinoline onto feldspar minerals and quartz. Experiments conducted under ambient temperature with three types of brines. Low salinity brine (1015 ppm), high salinity brine (30 000 ppm) and NaCl brine (36 000). End result shows adsorption is highly dependent on mineral size distribution in samples and pH. Increased adsorption is noted for low salinity compared to high salinity brine in feldspar mineral anorthite. The amount of adsorption of organic material in anorthite is comparable with clay mineral kaoliniteii. While for quartz adsorption was reduced with increased pH in low salinity brine.