Non-equilibrium 3-D simulator applied to air injection EOR in light oil reservoirs

Abstract

In this paper, a 3-D simulator based on the assumption of both chemical and thermal non-equilibrium is presented for a more realistic view of non-equilibrium process for simulating air injection EOR (enhanced oil recovery). The mathematical model is based on a non-equilibrium stage with dynamic mass transfer process between different fluid phases and energy transfer process between fluid and matrix (solid). The light crude oil oxidation and air injection process are both simulated by this simulator, through which the pore blocking, gas breakthrough and gas override process are presented through the visualization of oil, gas saturation distributions. The crude oil oxidation is refined as in-phase and interphase reactions to investigate the effect of reactant dispersion caused by the gas-liquid mass transfer. The oxygen dissolution and the evaporation of light components in crude oil are considered in the non-equilibrium process. The results without mass transfer, with dynamic mass transfer and with instantaneous mass transfer between gas and liquid phases are compared through multiplying the gas-liquid interface area 0, 1 and 100 times respectively, and the influence of these different mass transfer conditions on the migration of temperature peak front and oil recovery is revealed. In addition, the effect of local chemical and thermal non-equilibrium in different matrix permeability as well as porosity scenarios is also investigated to obtain non-equilibrium behavior in different reservoir conditions when implementing air injection EOR. In the last section, we investigated the result with different simulation timescale to see if the non-equilibrium behavior can be captured in the simulator used in this paper. This study suggests that the non-equilibrium behavior would show obvious influence on oil recovery for air injection in the lower permeability reservoir. The non-equilibrium behavior is desirable to be considered for simulating air injection EOR in light oil reservoirs. The developed 3-D simulator is robust that can better reflect the mechanism of air injection EOR in light oil reservoirs. We hope this work encouraging more investigations for the simulation side of non-equilibrium phase behavior and energy transfer in the air injection process.