Does miscibility of in situ generated flue gases with light crude oils contribute to oil recovery under high pressure air injection?

The improvement in recovery of light oil by high pressure air injection (HPAI) involves a combination of complex processes, each contributing to the overall recovery. One of such processes is the spontaneous oil ignition of the air-oil mixture with complete oxygen utilization. This process generates flue gases, which are in contact with the reservoir oil at the displacement front. An experimental study was carried out to investigate the mechanism and contribution of miscible displacement, by in situ generated flue gases, to the recovery of light oil in reservoirs undergoing HPAI. The flue gas displacements were carried out on recombined reservoir oil in a slim-tube apparatus at reservoir temperature of 116°C and pressures ranging from 4028 psi (27.77 MPa) to 6680 psi (46.06 MPa). Results show that miscibility could not be achieved between the test oil and flue gases under the test conditions. Experiments conducted between 5987 psi (41.28 MPa) and 6532 psi (45.04 MPa), however, gave an indication of near-miscible displacement of the test oil. The flue gases displaced the oil in a forward contacting extraction process, resembling a multi-contact vapourizing gas drive mechanism. The relatively high recovery, high extraction of oil components, and the pattern of flow behind the displacement front, exhibited at high pressures, demonstrate that near-miscible displacement by in situ generated flue gases could significantly contribute to oil recovery in light oil reservoirs undergoing HPAI.