The Experimental Study on Relative Permeability Hysteresis in CO2‑Enhanced Oil Recovery and Sequestration Processes.

In the process of CO2-enhanced oil recovery and sequestration, understanding fluid flow characteristics is crucial for developing effective injection and production strategies. The phenomenon of relative permeability hysteresis, particularly during multiple injection and production cycles, has garnered significant attention. Existing studies have shown that factors such as reservoir pressure, core permeability, displacement cycles, and saturation paths all have a substantial impact on relative permeability hysteresis. A comprehensive consideration of these factors will contribute to a more thorough understanding and resolution of hysteresis-related issues. However, current research on hysteresis tends to focus on individual factors, and a systematic research methodology with integrated analysis is still lacking. To address this gap, this study conducted CO2-water two-phase and CO2-oil-water three-phase relative permeability experiments, taking into account multiple factors including temperature, pressure, core permeability, displacement cycles, and saturation history. By considering these variables, this research aims to explore the complex mechanisms of relative permeability hysteresis in depth, providing more comprehensive and effective solutions for the CO2 sequestration and enhanced oil recovery. The results indicate that in the CO2-water two-phase relative permeability experiments, both permeability and pressure reductions lead to a decrease in the coflow interval and endpoint permeability, as well as an increase in trapped gas saturation. In high-permeability samples, pressure had a smaller impact; however, in low-permeability samples, trapped gas saturation increased with decreasing pressure. Regarding irreducible water saturation, under the same pressure, high-permeability cores exhibited lower values compared to low-permeability ones and lower pressure resulted in higher irreducible water saturation. In the CO2-oil-water three-phase experiments, reductions in permeability and pressure both led to a decrease in the coflow interval, endpoint permeability, and oil recovery. The findings of this study are expected to provide valuable insights and guidance for theoretical research and engineering practices in CCUS applications.