Caprock breakthrough pressure for geological CO2 sequestration: advances in characterization and controlling mechanisms

: Breakthrough pressure is a critical parameter for evaluating the sealing capacity of caprocks in geological CO 2 sequestration and shale gas extraction. This review synthesizes recent progress in experimental methods, mathematical models, and multi-factor controlling mechanisms. Experimental comparisons indicate that while rapid techniques such as mercury intrusion porosimetry and residual capillary pressure methods are prone to significant error, the step-by-step method remains the most reliable approach for obtaining representative in-situ breakthrough pressure, despite being time-consuming. Furthermore, empirical models generally provide more accurate predictions of breakthrough pressure than theoretical models alone, with the inverse power-law relationship between breakthrough pressure and permeability being the most widely validated. Pore structure, mineral composition (particularly clay content), absolute permeability, and wetting-phase saturation primarily govern breakthrough pressure by controlling the effective hydraulic radius of connected flow pathways. In contrast, non-wetting phase properties, temperature, and pressure exert an indirect influence by modifying interfacial tension and wettability. This study provides practical information for further studies of the breakthrough pressure and is expected to provide theoretical support for geological CO 2 sequestration and evaluation of shale gas resource potential.