Effects of Interfacial Tension, Emulsification, and Surfactant Concentration on Oil Recovery in Surfactant Flooding Process for High Temperature and High Salinity Reservoirs

Surfactant flooding as a potential enhanced oil recovery technology in depleted reservoirs after water flooding has attracted extensive attention. In this study, 12 surfactants belonging to five different types of surfactants and their compounded formulations were investigated for surfactant flooding under 90–120 °C and 20 × 104 mg/L salinity. Two surfactant formulations obtained a stable ultralow interfacial tension (IFT) level (≤10–3 mN/m) with crude oil after aging for 125 days. The surfactant formulations were used to further investigate the effects of the initial IFT values, the dynamic reduction rate of IFT, and the surfactant concentration and emulsification on oil recovery through core flooding experiments. The results indicated that oil recovery increased with the decrease of the initial IFT values and the increase of the dynamic reduction rate of IFT. The 10–3 mN/m IFT level yielded an additional oil recovery of approximately 7% compared with the 10–1 mN/m IFT level. However, under the same IFT level (10–4 mN/m), it was not the bigger the surfactant concentration that resulted in a higher additional oil recovery. In four surfactant concentrations (0.2%, 0.5%, 1%, and 3%), the 0.5% surfactant formulation obtained the highest oil recovery of 36.65%. Further study manifested that emulsification has important effects on oil recovery. When surfactant concentrations were increased to 1% and 3%, the emulsification was too strong, which makes it more difficult to displace oil. The two selected surfactant formulations could successfully yield additional oil recovery of 20–26%, which indicates these two formulations have great potential for improving oil recovery in high temperature and high salinity oil reservoirs.