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

• CO2 flow through geopolymer was modelled under triaxial stress conditions.
• Model predicted permeability values are consistent with the experimental values.
• The CO2 pressure and concentration in geopolymer reduces with increase in confinement.
• Pressure driven advection is the dominant CO2 transport mechanism through geopolymer.

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.