Investigating the Performance of Generalized Fick and Maxwell-Stefan Molecular Diffusion Models for Simulation of Oil Recovery from Fractured Reservoirs during CO2 and Methane Gas Injection Processes

Molecular diffusion is the controlling mechanism for oil recovery from fractured reservoirs with low permeable and low height matrixes during gas injection process. However, the application of conventional models for simulation of molecular diffusion process faces with some limitations. The main purpose of this study is to investigate the performance of different diffusion molecular models for oil recovery from fractured reservoirs during gas injection process and compare the results with a commercial simulator. Therefore, the models are introduced and implemented as a simulator, then the prepared simulator is validated by experimental data. Lastly, the developed simulator is applied for evaluation of CO2 and methane injection in one matrix block. The difference among the results of different models is based on using irreversible thermodynamic for calculating component concentration in gas-oil interface, using matrix form of molecular diffusion coefficients and using chemical potential gradient as the driving force in generalized Fick and Maxwell-Stefan verse classical Fick. In addition, the results of commercial simulator are near classical Fick model results because of same formulation. Also, mole fraction of methane and CO2 and oil viscosity verse time are compared for gas injection. Finally, the result of this work demonstrates that using classical Fick’s law or the commercial simulator for forecasting oil recovery from fractured reservoirs when the molecular diffusion is the main mechanism is not accurate, so generalized Fick and Maxwell-Stefan are more efficient models.