Influencing factors of caprock sealing performance for multi-layer CO₂ injection

Due to the heterogeneity and low permeability of most CO₂ reservoirs in China, CO₂ storage within a single reservoir is difficult to meet the demand for emission reduction. To achieve large-scale CO₂ geological storage, multi-formation injection technology has been proposed to increase the amount of CO₂ geological storage. To explore the main influencing factors on the caprock sealing performance under the condition of multi-formation CO₂ injection, the seepage-stress coupling simulation analysis was carried out. Pore pressure, displacement, and incremental Coulomb failure stress (ΔCFS) are used as the basis for evaluating the caprock sealing performance. The tornado analysis method was used for sensitivity analysis to select the factors that have a significant impact on the caprock sealing performance. The research results indicate that the more injection layers, the smaller the displacement, pore pressure, and ΔCFS of the caprock, and the better the caprock sealing performance. However, if the number of layers exceeds 3, the efficiency increase brought by the number of layers will no longer be significant; The main controlling factors for the sealing performance of the caprock include the Poisson’s ratio and Young’s modulus of the caprock, thickness and permeability coefficient of the reservoir, and injection rate; When the thickest caprock is located at the topmost part of the entire formation, the caprock sealing performance is the best, producing the smallest vertical displacement, pore pressure, and ΔCFS.