Enhancing Tight Oil Recovery in Aqueous-Affected Reservoirs: Experimental Investigation of Triphilic Surfactant Synergy with CO2 Huff-and-Puff Stimulation

Abstract

CO₂ huff-and-puff demonstrates excellent injectivity and gas channeling resistance in tight reservoirs, yet aqueous phase invasion significantly diminishes its oil recovery efficiency. To investigate the mechanisms of aqueous phase impacts, CO₂ huff-and-puff experiments were conducted under varying water saturation levels, complemented by extended core displacement tests with different injection patterns. A triphilic surfactant, C₈EO₃PO₂COOCH₃ (CEPC), was introduced to mitigate aqueous phase interference. Its performance in reducing interfacial tension (IFT) and enhancing CO₂ dissolution/diffusion was systematically evaluated. Optimal injection parameters were determined through 1D core experiments, followed by 2D planar flooding experiments to assess recovery enhancement mechanisms. Results reveal that aqueous phases impair CO₂ diffusion and sweep efficiency, weakening solution gas drive effects. Compared to anhydrous conditions, oil recovery decreased by 10.25%, 19.12%, and 26.03% at 5%, 10%, and 20% water saturation, respectively. CEPC reduced the CO₂–water and CO₂–oil IFT by 89.4% and 76.8%, respectively, while accelerating the CO₂ dissolution kinetics by 2.1–3.4 times at 50% water saturation. At 20% water saturation, the optimal concentration of CEPC is 0.5 wt %, while the optimal soaking pressure and soaking time for the CO₂ huff-and-puff are 20 MPa and 12 h, respectively. In 2D experiments, CEPC-assisted CO₂ huff-and-puff achieved 25.36% oil recovery, representing a 9.56% enhancement over conventional CO₂ injection. The synergy arises through two mechanisms: CEPC facilitates CO₂ breakthrough across aqueous phases to amplify dissolved gas drive by increasing CO₂–oil contact and dissolution capacity, while simultaneously reducing capillary confinement of aqueous phases in micronano pores to alleviate water blockage and enhance sweep efficiency. These findings provide critical insights for optimizing the recovery of CO₂-enhanced nanoparticles in water-bearing tight reservoirs.