Abstract: The Shanshan Block in the Tuha Oilfield has entered a high-water-cut development stage, limiting additional oil recovery by waterflooding, it is imperative to explore novel EOR technologies. Although CO₂ flooding is proven effective by reseaches home and abord, but it is highly costly for Shanshan Block due to the lack of CO₂ resources. This study examines mixing hydrocarbon-associated gas with CO₂ to reduce injection expenses. Minimum miscibility pressures were tested using crude oil, cores, and associated gas in Shanshan Block. Under high temperature and pressure, cores were waterflooded and then displaced with gas mixtures at varying CO₂ concentrations, tracked by nuclear magnetic resonance and computed tomography. Results show that miscibility occurs above 43% CO₂ content. At approximately 50% CO₂, displacement performance is comparable to pure CO₂ flooding and surpasses pure associated gas, Microscopic analysis reveals that the hybrid CO₂-associated gas flooding effectively mobilizes remaining oil at the pore scale, demonstrating economic feasibility and technical efficacy. Hence, it offers a promising method for Shanshan Block.

Key words: high water-cut, associated gas, CO₂ flooding, NMR, CT scanning