Capillary Sealing Capability Alteration of Shale Caprock Induced by CO2-brine-rock Interaction: Implication for CO2 Geological Storage

The capillary sealing mechanism plays a pivotal role in the sealing capability of caprock in CO2 geological storage. The interactions between CO2, brine, and rock induced by CO2 injection may potentially impact the capillary sealing capability of the caprock. To characterize the capillary sealing capability of Yanchang shale, breakthrough pressure (Pb) tests were conducted before and after CO2-brine-rock interaction while analyzing the contributions of pore structure and wettability to Pb alteration. The results revealed that Pb of Yanchang shale samples decreased by 7.14% to 22.22% after CO2-brine-rock interaction, indicating a deterioration in their capillary sealing capability. This degradation can be attributed to changes in pore structure and wettability, as they collectively influence the capillary sealing capability of shale caprock. The increase of small-pore (< 200 nm) porosity and contact angle promoted the reduction of Pb. The alteration of shale caprock’s capillary sealing capability due to CO2-brine-rock interaction significantly impacts CO2 storage potential and long-term safety, which should be considered prior to large-scale CO2 injection.