Comparative Experimental Investigations of Multiple P–T Effects on CO2/N2 Breakthrough Pressures in an Unsaturated Sandstone of Low Permeability

Gas breakthrough pressure is a pivotal parameter for assessing the sealing integrity of cap rocks, which is vital for the safety of CO2 geo‐sequestration and underground gas storage. This study presents a systematic evaluation of the breakthrough pressures of CO2 and N2 in an unsaturated sandstone of low permeability at various temperature and pressure conditions. The focus of this research is on the variations in breakthrough pressures for CO2 and N2 under different experimental conditions, as well as a comparative analysis between the two gases. Meanwhile, the research examines the impact of two‐phase fluid properties, including interfacial tension (IFT), viscosity ratio, and wettability, on breakthrough pressure. The findings demonstrate a positive correlation between the breakthrough pressures of CO2 and N2 with temperature and pressure, respectively. Notably, the breakthrough pressure for N2 is higher than that for CO2 under identical conditions. Furthermore, N2 breakthrough pressure is more sensitive to changes in temperature or pressure compared to CO2. There is an inverse correlation between CO2/N2 breakthrough pressure and effective permeability. CO2 demonstrates a greater ability to migrate through the rock core, facilitating easier breakthrough compared to N2. Our analysis indicates that the viscosity ratio is the primary factor influencing CO2 and N2 breakthrough pressures, whereas the effects of IFT and wettability are relatively minor. This study provides valuable insights into the factors that influence breakthrough pressure and aids in assessing the sealing ability of cap rock.