A numerical study of CO2 flow through geopolymer under down-hole stress conditions: Application for CO2 sequestration wells

The well cement used in injection/production wells plays a major role in the success of a carbon capture and storage project. Ordinary Portland cement (OPC)-based well cement has been used in injection/production wells and it has been found to be unstable in CO₂-rich environments. In recent times, geopolymers have been tested as an alternative to OPC, and it has been found that geopolymers perform better than OPC under CO₂-rich down-hole conditions. In this research work, a numerical study was performed to model CO₂ flow through geopolymer under down-hole stress conditions using COMSOL multiphysics. First, the model was validated using experimental flow results under drained triaxial conditions for various injection and confining pressures. The model was then extended to predict the flow characteristics such as permeability, Darcy’s velocity, CO₂ pressure and CO₂ concentration distributions in geopolymer under high injection and confining pressures. The CO₂ permeability values predicted by the model were in good agreement with the experimental permeability values for various injection (3–13 MPa) and confining pressures (10–25 MPa). The CO₂ permeability of geopolymer varies between 0.008 and 0.014 μD for injection pressures of 15–40 MPa and confining pressures of 30–45 MPa. The flow parameters including Darcy’s velocity, CO₂ pressure and CO₂ concentration in geopolymer reduces with increase in confining pressures due to the reduction of pore volume with increase in confinement. Pressure-driven advection is the dominant CO₂ transport mechanism during the injection period compared to concentration-driven diffusion. CO₂ transport through geopolymer can be modelled using COMSOL multiphysics.