Abstract:

Breakthrough pressure serves as a critical parameter for characterizing the capillary sealing capacity of caprock formations. The injection of CO₂ into subsurface reservoirs triggers complex interactions among CO₂, formation brine and rock. These interactions have been shown to significantly affect the rock’s transport properties and sealing performance. However, the mechanisms by which CO₂-brine-caprock interactions affect caprock breakthrough pressure remain poorly understood. To elucidate the response mechanism of caprock breakthrough pressure to CO₂–brine–rock interactions, breakthrough pressure experiments were performed over different durations of CO₂–brine–rock interaction, utilizing two distinct types of caprock cores obtained from the Junggar Basin. A suite of complementary analytical methods, including nuclear magnetic resonance, scanning electron microscopy, liquid chromatography, and contact angle measurements, was employed to characterize the evolution of pore structure and wettability within the cores. The results show that CO₂-brine-rock interactions reduce the breakthrough pressure of the caprock samples. This reduction is attributed to the combined effects of increased pore volume, enhanced permeability, and diminished wettability. Further kinetic analysis of mineral dissolution suggests that the decline in breakthrough pressure slows over time and may eventually reach a steady state. This behavior is likely attributable to the inhibitory effect of secondary mineral precipitation. These finding underscore the critical importance of accounting for CO₂-brine-rock-induced degradation of caprock sealing capacity when defining pressure thresholds for the safe operation of CO₂ geological storage projects, thereby helping to ensure long-term stability and safety.

Key words: CO₂ geological storage, caprock, breakthrough pressure, CO₂-brine-rock interactions