Experimental study on EOR potential of water-in-oil emulsion via CO<inf>2</inf>/N<inf>2</inf> triggered wormlike micelle solution

Abstract

Oil in water (O/W) emulsion flooding appears to be an effective method to boost oil production of mature oilfields, while few works have been done to investigate the enhanced oil recovery (EOR) potential of water in oil (W/O) emulsion, especially in in-situ W/O emulsion. In the present work, a CO2/N2 triggered wormlike micelle solution (CO2-TWMS) for forming in-situ W/O emulsion was prepared firstly. Then, its CO2/N2 responsiveness was characterized through the change in viscosity and microstructure. Subsequently, the emulsifying ability of CO2-TWMS and the effect of CO2/N2 responsiveness on emulsion stability were investigated, followed by the study of oil displacement efficiency. Experimental results manifested that CO2 bubbling triggered the formation of wormlike micelles, which induced the formation of W/O or O/W/O emulsion under stirring condition. While N2 bubbling destroyed wormlike micelles and accelerated the breaking of emulsion. 0.5 pore volume (PV) CO2-TWMS flooding and sequent water flooding could significantly improve oil recovery of 20.7–31.9% in three-floor heterogeneous cores, which was mainly contributed to the enlargement in sweeping efficiency that caused by mobility ratio improvement of emulsion and Jamin effect of water droplets. The results from this study demonstrated that the CO2-TWMS has great potential for EOR in waterflooded heterogeneous reservoirs, which provides valuable insights for novel EOR technology that combined chemical flooding with CO2 capture.