Enhanced oil recovery in limestone. Chemical effects of seawater injection on the rock surface at different temperatures

Abstract

The fluid location, flow and distribution in a reservoir rock are to a large extent governed by the wetting condition of the rock. These factors influence oil and gas production, water flood recovery and the performance of enhanced oil recovery processes. The wetting condition of carbonates is influenced by the surface chemistry of the rock. The impact of potential determining ions (Mg2+, Ca2+ and SO4 2-) on the rock surface at various temperatures (ambient, 80°C, 100°C and 130°C) on limestone cores from the Thamama field were carried out by slowly (1 PV/day) flooding the cores with synthetic seawater, SSW . Chromatographic tests and spontaneous imbibition tests were also carried out. In the chromatographic tests different brine solution (SW-½M and SW-¼M) were flooded to detect the active surface area by the adsorption of SO4 2-. Spontaneous imbibition were carried out on several cores, both limestone and chalk, with increasing the temperature during the experimental time (ambient, 50°C and 70°C). Both the spontaneous imbibition tests and chromatographic tests gave indication of the wettability. From the experimental results obtained, major observations were: − The cleaned limestone cores from the Thamama field behaved oil-wet during spontaneous imbibition tests. − The water-wet surface area detected by the chromatographic test in the limestone cores was dependent on rate and concentration of SO4 2-. − Chromatographic test could be used on the limestone from Thamama field as identification on the wettability/fraction of water-wet surface area. − The impact of potential determining ions in seawater was dependent on the temperature.