Numerical modeling on air injection in a light oil reservoir: Recovery mechanism and scheme optimization

Air injection in light oil reservoirs is a promising enhanced oil recovery (EOR) method because of its wide availability, low cost, and ability to stimulate subterranean oil combustion. However, oil recovery mechanisms and physical processes for air injection in conventional light oil reservoirs are still not well understood. An improved understanding of air injection mechanism in conventional light oil reservoirs is provided in this paper. We use the reservoir simulation approach to study air injection in a light oil reservoir. Effects of O₂ mole concentration, activation energy, intake air temperature, geological structure and development scheme on the well performance of air injection are examined. The driving mechanism of thermal effect is revealed through the observation of oil rate fluctuating and dynamic temperature distribution. We present the evidence of the "bulldozing effect (or pore blocking)" for air injection in a light oil reservoir which shows the sudden decrease of gas relative permeability. The effect has the potential of re-directing gas flow to improve sweep efficiency. Analysis of influence factors from this work indicates that the oil recovery factor is sensitive to O₂ content in air and geological structure of the reservoir. The performance with gas injected updip is better than that downdip. It is insensitive to intake air temperature or activation energy in the reaction scheme favoring a generation of more H₂O, insoluble CO and CH₄.