Abstract: The CO2 breakthrough pressure (threshold pressure) is one of key indicators for the caprock sealing ability and safety of CO2 geological storage. Different breakthrough pressures experiments have been carried out for different caprock examples around world, and set up a fundamental database for caprock sealing ability evaluation; however, very few researches has been carried out on CO2 breakthrough pressure experiment under different pressures and temperatures. Based on the characteristics and range of breakthrough pressure equipment, the CO2 breakthrough pressure measurement apparatus is developed. The apparatus integrates several methods, such as, step method, continuous method, pulse decay method, and dynamic method. It covers the ordinary range of breakthrough pressure in cap-rocks. Experimental studies of CO2 breakthrough pressure in water saturated argillaceous siltstone sample from Xujiahe formation are carried out; for the Xujiahe formation is an important target formation and seal formation for CO2 aquifer storage in Sichuan Basin. The CO2 breakthrough pressures of core samples under different temperatures and pressures are studied in the experiment. The experiment results show that the breakthrough pressure increases with temperature increasing and CO2 pressure decreasing within the studied pressure and temperature range. The experiment results have the same tendency as the theoretical results deduced by theoretical method; however, there is a discrepancy between experiment results and theoretical results. The discrepancy might be caused by the variation of contact angle, pore-geometry heterogeneity, and experiment method; and this need further study.

Key words: caprock, sealing ability, breakthrough pressure, pulse decay method, CO2 saline aquifer storage