Mathematical modelling of carbonated water injection including mass transfer kinetics

Carbonated water injection (CWI) process is an improved water flooding technique in which CO2 is used efficiently. As CO2 remains dissolved in CWI, it can also be deployed as a safe CO2 storage technique. During CWI in an oil reservoir, due to higher CO2 solubility in the oil phase, dynamic transfer of CO2 from carbonated water to oil takes place. This leads to enhanced oil recovery by a number of mechanisms including improving oil mobility due to oil viscosity reduction and swelling. Compositional simulations of CWI using commercially available reservoir simulators pose a number of challenges. Such a modelling approach is based on instantaneous equilibrium while core flooding experiments show that this assumption is not valid. That is, CO2 transfer and distribution between water and oil is a gradual process and thermodynamic equilibrium is not achieved. Under such conditions, the use of existing compositional simulators leads to the wrong performance prediction for this promising enhanced oil recovery process. In this work, a new one dimensional compositional simulator has been developed that is based on non-equilibrium conditions including a mass transfer term describing the kinetics of the CO2 transfer between phases. The simulator results were validated using our core flood experimental data. In a step-wise history matching process, first, the water flood relative permeability (kr) data were obtained by history matching the corresponding core flood production history. Then, the early time production data of the CWI experiment was used to fine-tune the water flood kr data and obtain the corresponding CWI-kr data. Finally, the late time production data that are affected by mass transfer between the two phases are history matched to estimate a proper mass transfer coefficient. The results lead to better understanding of the CWI process and an improved tool for simulation and prediction of the performance of CWI.