A fully coupled model for caprock sealing efficiency

The sealing integrity of a suitable low permeability caprock is one of the most important issues to the safety of long-term CO₂ sequestration in a saline aquifer over long geological time periods. From the microscopic viewpoint, caprocks contain microcracks which make caprocks anisotropic in mechanical and hydraulic properties. Additionally, the growth of microcracks could lead to permeability increasing exponentially, which extremely harms caprock sealing efficiency. To assess caprock sealing efficiency accurately, a fully coupled model should include caprock deformation, two-phase flow, CO₂ sorption and damage evolution of caprocks. The purpose of this paper is to present such a model for investigating caprock sealing efficiency. Firstly, a conceptual model is proposed for the CO₂/water flow in a caprocks with microcracks. In this model CO₂/water flow is described by two-phase flow equation with variable porosity and permeability. This provides a solid basis to the further development of numerical simulations for the caprock sealing efficiency assessment. Finally, this fully coupled mathematical model is applied to a caprock layer to investigate the combined effect of fully coupling processes on the caprock sealing efficiency. Model results demonstrate that the damage effects on the caprock sealing efficiency are significant.