CO₂ Breakthrough Characteristics in Argillaceous Sandstone for Geological Storage

Breakthrough characteristics under varying reservoir conditions is critical for evaluating the sealing capacity of caprocks in geological CO2 storage. Due to the absence of reliable in situ methods to estimate key parameters influencing its variability, laboratory testing remains essential. This study employs a stepwise experimental approach to investigate the effects of CO2 pressure–temperature (P–T) conditions, water saturation, and effective stress on the breakthrough pressure in argillaceous sandstone, with mechanistic analysis. The results demonstrate that CO2 breakthrough pressure, ranging from 1.18 to 2.26 MPa, increases with temperature but decreases with pressure. Analysis of interfacial tension, wettability, and viscosity reveals that the viscosity ratio dominates the breakthrough mechanism. CO2 breakthrough pressure exhibits exponential relationships with water saturation and effective stress. Elevated water saturation severely degrades gas pathway connectivity, while clay swelling further reduces effective pore-throat dimensions. Increased effective stress induces pore contraction, enhancing the confinement capability of water films and requiring CO2 to overcome greater disjoining pressure. These findings provide critical guidance for selecting target caprocks in CO2 storage projects.