Temperature-resistant and salt-tolerant mixed surfactant system for EOR in the Tahe Oilfield

Abstract

A new temperature-resistant and salt-tolerant mixed surfactant system (referred to as the SS system) for enhancing oil recovery at the Tahe Oilfield (Xinjiang, China) was evaluated. Based on the analysis of the crude oil, the formation water and rock components in the Tahe Oilfield, the long-term thermal stability, salt tolerance and the ability to change the wettability, interfacial activity and oil washing efficiency of the mixed surfactant system were studied. The system contains the anionic surfactant SDB and another cationic surfactant SDY. When the total mass concentration of the SS solution is 0.15 wt%, m(SDB)/m(SDY) ratio is 1 to 1, and excellent efficiencies are achieved for oil washing for five kinds of Tahe Oilfield crude oils (more than 60%). In addition, after adding cationic surfactant, the adsorption capacity of the surfactant is further reduced, reaching 0.261 mg/g. The oil displacement experiments indicate that under a temperature of 150 °C and a salinity of 24.6 × 10⁴ mg/L, the SS system enhances the oil recovery by over 10% after water flooding. The SS anionic–cationic surfactant system is first presented in the open literature that can be successfully applied to obtain predictions of Tahe Oilfield carbonate reservoirs with a high temperature and high salinity.