Comparative Experimental Investigations of Multiple P–T Effects on CO ₂ /N ₂ Breakthrough Pressures in an Unsaturated Sandstone of Low Permeability

ABSTRACT Gas breakthrough pressure is a pivotal parameter for assessing the sealing integrity of cap rocks, which is vital for the safety of CO 2 geo‐sequestration and underground gas storage. This study presents a systematic evaluation of the breakthrough pressures of CO 2 and N 2 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 CO 2 and N 2 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 CO 2 and N 2 with temperature and pressure, respectively. Notably, the breakthrough pressure for N 2 is higher than that for CO 2 under identical conditions. Furthermore, N 2 breakthrough pressure is more sensitive to changes in temperature or pressure compared to CO 2 . There is an inverse correlation between CO 2 /N 2 breakthrough pressure and effective permeability. CO 2 demonstrates a greater ability to migrate through the rock core, facilitating easier breakthrough compared to N 2 . Our analysis indicates that the viscosity ratio is the primary factor influencing CO 2 and N 2 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.