Recovery of light oil by air injection at medium temperature: Experiments

•Medium pressure air injection into light oil reservoir is a potentially attractive method.•Laboratory experiments indicate oil recoveries between 75 and 90%.•Oxygen adsorption step takes place in the initial stage before the combustion reactions occur.•Oxygen dissolution in hydrocarbon plays an important role together with the formation of oxygenated hydrocarbon.

Volatile oil recovery through air injection is a promising method for highly heterogeneous low permeability reservoirs. Thermal effects due to oxidation reaction, vaporization/condensation and flue gas drive are the most important mechanisms for light oil recovery by medium pressure air injection. To gather evidence for this claim, we performed ramped temperature experiments with consolidated cores filled with hexadecane injecting either air or nitrogen at different injection rates at medium pressures. The experiments show that oxygen is removed from the injected air through physical and chemical sorption by the hydrocarbon at low temperatures. Most of the bonded oxygen is released later at higher temperatures and reacts to form carbon oxides. The amount of oil burned in the air injection process relative to the amount of oil recovered increased from 2% at 10 bar to 18% at 30 bar, and again decreased to 5% at 45 bar and 3% at 70 bar. This trend was predicted theoretically in an earlier study of the medium temperature oxidation process.