Study on mechanical modeling and sealing property of caprock during carbon dioxide geological storage: A case study of S229 block of CCUS test area in Liaohe Oilfield

Carbon capture, utilization, and storage (CCUS) is of great significance in addressing global climate change and reducing greenhouse gas emissions. Carbon dioxide (CO₂) geological storage is a dynamic process, and it can easily trigger changes in the stress field of the geological body, induce mechanical failure of the caprock, and lead to CO₂ leakage. Therefore, the study on the sealing property of caprock is one of the key contents in the implementation of CCUS projects. The S229 block of the CCUS test area in Liaohe Oilfield was studied. In response to the evaluation requirements for the sealing property of the caprock during the geological storage process of CO₂, geological, logging, and core experimental data were utilized, and three-dimensional (3D) geomechanical modeling technology was adopted. Based on the capillary pressure theory and Mohr-Coulomb failure criterion, the maximum height of the CO₂ plume column of the caprock was calculated, and the tensile failure and shear failure pressure of the caprock were analyzed. The threshold value of the failure pressure at the injection well point was innovatively extracted for point-to-point and quantitative evaluation, which could clearly determine the limit pressure of the CO₂ injection wells in the study area. The analysis shows that the capillary sealing capacity of the caprock mudstone in the study area is good, and the maximum height of the CO₂ plume column that it can seal is 379.08 m. The tensile failure pressure range of the caprock is 58.3–62.1 MPa, and the shear failure pressure range is 54.8–60.9 MPa. The shear failure risk of the caprock near Well 36-70 is the highest, with an upper limit pressure of 54.8 MPa. The conclusion shows that the caprock in the S229 block has good sealing properties, but the CO₂ injection pressure should be strictly controlled to avoid mechanical failure. The research results provide direct guidance for injection parameter optimization and safe implementation of CCUS projects.