A multiphysical-geochemical coupling model for caprock sealing efficiency in CO2 geosequestration

Abstract

Precipitation or dissolution due to geochemical reactions has been observed in the caprocks for CO₂ geosequestration. Geochemical reactions modify the caprock sealing efficiency with self-limiting or self-enhancement. However, the effect of this modification on the caprock sealing efficiency has not been fully investigated through multiphysical-geochemical coupling analysis. In this study, a multiphysical-geochemical coupling model was proposed to analyze caprock sealing efficiency. This coupling model considered the full couplings of caprock deformation, two-phase flow, CO₂ concentration diffusion, geochemical reaction, and CO₂ sorption. The two-phase flow only occurs in the fracture network and the CO₂ may partially dissolve into water and diffuse through the concentration difference. The dissolved CO₂ has geochemical reactions with some critical minerals, thus altering flow channels. The CO₂ in the fracture network diffuses into matrix, causing the matrix swelling. This fully coupling model was validated with a penetration experiment on a cement cube and compared with two other models for CO₂ storage plumes. Finally, the effects of geochemical reactions on penetration depth and pore pressure were studied through parametric study. The numerical simulations reveal that the coupling of geochemical reactions and matrix diffusion significantly affect the caprock sealing efficiency. Geochemical reactions occur at a short time after the arrival of CO₂ concentration and modify the fracture porosity. The CO₂ diffusion into the matrix requires a much longer time and mainly induces matrix swelling. These effects may produce self-enhancement or self-limiting depending on the flow rate in the fracture network, thus significantly modifying caprock sealing efficiency.