Performance and enhanced oil recovery efficiency of an acid-resistant polymer microspheres of anti-CO₂ channeling in low-permeability reservoirs

CO₂ flooding is a vital development method for enhanced oil recovery in low-permeability reservoirs. However, micro-fractures are developed in low-permeability reservoirs, which are essential oil flow channels but can also cause severe CO₂ gas channeling problems. Therefore, anti-gas channeling is a necessary measure to improve the effect of CO₂ flooding. The kind of anti-gas channeling refers to the plugging of fractures in the deep formation to prevent CO₂ gas channeling, which is different from the wellbore leakage. Polymer microspheres have the characteristics of controllable deep plugging, which can achieve the profile control of low-permeability fractured reservoirs. In acidic environments with supercritical CO₂, traditional polymer microspheres have poor expandability and plugging properties. Based on previous work, a systematic evaluation of the expansion performance, dispersion rheological properties, stability, deep migration, anti-CO₂ channeling and enhanced oil recovery ability of a novel acid-resistant polymer microsphere (DCNPM-A) was carried out under CQ oilfield conditions (salinity of 85,000 mg/L, 80 ℃, pH = 3). The results show that the DCNPM-A microsphere had a better expansion performance than the traditional microsphere, with a swelling rate of 13.5. The microsphere dispersion with a concentration of 0.1%–0.5% had the advantages of low viscosity, high dispersion and good injectability in the low permeability fractured core. In the acidic environment of supercritical CO₂, DCNPM-A microspheres showed excellent stability and could maintain strength for over 60 d with less loss. In core experiments, DCNPM-A microspheres exhibited delayed swelling characteristics and could effectively plug deep formations. With a plugging rate of 95%, the subsequent enhanced oil recovery of CO₂ flooding could reach 21.03%. The experimental results can provide a theoretical basis for anti-CO₂ channeling and enhanced oil recovery in low-permeability fractured reservoirs.