Caprock sealing for geologic CO2 storage: Research advances, challenges and prospects
Bowen Chen, Qi Li, Yongsheng Tan
Abstract
The sealing capacity of caprock is critical for preventing CO 2 migration and ensuring the safety of geological storage. However, existing research lacks a comprehensive overview of its sealing mechanisms and failure risks. Here, recent findings on caprock sealing mechanisms, its influencing factors, failure risks, and evaluation methods are summarized. The main results include the following: (i) Caprock sealing mechanisms include capillary, hydraulic, hydrocarbon concentration, and hydrate sealing. (ii) Capillary and hydrate sealing block fluid-phase CO 2 , hydrocarbon concentration sealing prevents diffusive CO 2 , and hydraulic sealing prevents fluid and water-soluble phases. (iii) The sealing capacity is influenced by the storage site, stratigraphic environment, and caprock properties, with breakthrough pressure ranked as follows: gypsum rock > salt rock > mudstone/shale > limestone > silty mudstone. (iv) Diffusion leakage occurs when the diffusion coefficients is less than 10 −12 m 2 /s, the seepage leakage ranges between 10 −8 m 2 /s and 10 −12 m 2 /s, and the fracture leakage is greater than 10 −8 m 2 /s. (v) Hydro-mechanical (HM) coupling mechanisms, including CO 2 diffusion, breakthrough migration, uplift deformation, and fracture flow, are essential for leakage risk simulations. Future research should address sealing mechanisms under complex conditions, define leakage risk thresholds, optimize multiphysical coupling computations, and implement effective engineering solutions to mitigate leakage risk.