Formulation development and visualized investigation of temperature-resistant and salt-tolerant surfactant-polymer flooding to enhance oil recovery

Abstract

As a tertiary oil recovery technique with broad application prospects, surfactant-polymer flooding can significantly improve sweep efficiency and enhance oil recovery, while eliminate the negative effects of alkali thoroughly. However, for most oil reservoirs abroad, belonging to marine carbonate reservoirs with high temperature and high salt content, SP flooding is largely limited. In this paper, the surface (interface) chemical properties of different types of surfactants were evaluated to select a mixed surfactant system with better performance and synergistic effect. And experiments on the physicochemical properties evaluation of polymers were performed to select a more suitable polymer. On this basis, the formulation of the surfactant-polymer binary composite system was optimized and the performance was evaluated. A visualized model was adopted to study the process of SP flooding, which vividly reflected the interaction of chemical agents with crude oil and the migration of chemical agents in porous media, as well as macroscopic and microscopic EOR mechanisms of SP Flooding. The results showed that Hexadecyl dimethyl carboxybetaine (C16HSB), heavy alkyl the linear alkylated diphenylmethane sulfonate (C14-DSDM) and the hydrophobically modified polyacrylamide-based novel functional polymer GT-1 were selected. The optimized formulation of the SP flooding system was selected for 2000 mg/L GT-1 + 3000 mg/L C14-DSDM + 1000 mg/L C16HSB, which showed higher apparent viscosity and lower interfacial tension (7.2 × 10−3 mN/m) under the condition of 70 °C and 9780.5 mg/L formation water salinity. The system showed a certain resistance to temperature and salt, and stability under the conditions of temperature below 80 °C and salinity below 40000 mg/L and an EOR value of 31.2% in the visualized displacement experiment. Surfactants in the SP flooding system can emulsify the residual oil into spherical and flocculent emulsions, which are then stripped, drawn into filaments, and easily motivated. The retention of more polymer molecules in the throat causes the intermolecular association of polymer molecules to form a denser network structure, which plays an important role in increasing flow resistance and changing the direction of liquid flow, and its viscoelasticity contributes to the discharge of residual oil. Under the synergistic effect of surfactants and polymer, hydrodynamic residual oil, membrane residual oil, and residual oil droplets can be mobilized, thus beneficial to enhance oil recovery.