Geological CO2 sequestration has been proposed to mitigate greenhouse gas emissions. Massive CO2 injection into subsurface formation involves interactions among pressure and temperature change, chemical reactions, solute transport, and the mechanical response of the rock; this is a coupled thermalโhydraulicโmechanicalโchemical (THMC) process. Numerical modeling of CO2 injection around the wellbore area can provide information such as changes in rock properties as well as stress and pressure changes, and this helps better predict injectivity evolution and leakage risk. In this paper, a fully coupled THMC model based on finite element methods is presented to analyze the transient stress, pressure, temperature and chemical solute concentration changes simultaneously around an injection well. To overcome these numerical oscillations in solving the transient advectionโdiffusion equations involved in the heat transfer and solute transport processes, we employ a stabilized finite element approach, the subgrid scale/gradient subgrid scale method (SGS/GSGS). A hypothetical numerical experiment on CO2 saturated water injection into a carbonate aquifer is conducted and preliminary results show that the fully coupled model can successfully analyze stress and pressure changes in the rock around a wellbore subjected to thermal and chemical effects.