Coupled Thermo-Hydro-Mechanical Modelling of Carbon Dioxide Sequestration in Saline Aquifers Considering Phase Change

Carbon dioxide (CO₂) sequestration in saline aquifers is considered to be one of the most viable measures to control its emissions. During the process of CO₂ injection, phase changes of gas, liquid and supercritical CO₂ will lead to changes in the density, dynamic viscosity, specific heat capacity and CO₂ heat conductivity and solubility in water, which will influence the injection pressure and spatial distribution of CO₂. To study the characteristics of injection pressure and spatial distribution of CO₂ in saline aquifers, equations of state such as Peng–Robinson equation were used to realize the continuous calculation of the physical property parameters of gas, liquid and supercritical CO₂. Based on the continuous physical property parameters, a fully thermo-hydro-mechanical (THM) coupled model was developed and then solved and verified using COMSOL Multiphysics software. It has been shown in this study that: (i) the predicted CO₂ injection pressure by the THM coupled model is higher than that obtained from the uncoupled model; (ii) at the top boundary of the reservoir, the spatial distribution of CO₂ can be divided into a rapid increase region, a slow decrease region, a rapid decrease region and an initial saturation region along the direction of CO₂ migration and (iii) larger the reservoir geothermal gradient, more obvious is the gravity override effect.