Design and Optimization of Low-Salinity Alkali–Surfactant Flooding for Chemical Enhanced Oil Recovery in Carbonate Reservoirs

Abstract

Oil-wet carbonate reservoirs may also have low recovery efficiency in the Middle East where the reservoir temperature is high and there exists capillary trapping in addition to poor wettability. In this paper, I have estimated the performance of a hybrid low salinity waterflooding (LSWF) and alkaline-surfactant (AS) injection enhanced oil recovery (EOR) method. Laboratory coreflood experiments and numerical simulation were conducted on a representative carbonate reservoir from the Kurdistan Region of Iraq with a reservoir temperature of ˜100°C, and high-salinity formation brine. An anionic surfactant formulation that is thermally stable was mixed with sodium carbonate alkali and the salinity of the injection-brine optimized. The results demonstrate that low-salinity smart water can move the rock towards more water-wet conditions and the alkali-surfactant mixture can reduce the interfacial tension (IFT) by four to five orders of magnitude. The hybrid process was able to reduce the residual oil saturation from 0.32 ± 0.01 to 0.15 ± 0.01 during the coreflood experiments at 100°C. Hybrid LS + AS water flooding incrementals were 20.4% ± 1.0% OOIP in the tertiary mode, compared to 5.5% ± 0.7% OOIP and 9.0% ± 0.8% OOIP for low-salinity water flooding and high-salinity surfactant flooding, respectively. The total oil recovery after baseline waterflooding was 47.3% ± 1.1% OOIP, and 67.7% ± 1.3% OOIP after the treatment. Optimum concentrations of chemicals and water salinity are plotted against predicted recovery gains on the design charts. The study provides a mechanistic insight into the chemical EOR synergy in the carbonate reservoirs and provides useful guidelines for designing hybrid EOR pilots in the high temperature oil fields. Other issues such as scaling, corrosion, chemical cost, produced-water treatment and high pH fluid handling are also considered.