An Experimental Study of the Characteristics of Oxidation Displacement via Air Injection in a Deep, Medium–High-Pressure Reservoir

A high-temperature and high-pressure experimental device was upgraded to accommodate a maximum pressure of 40 MPa and a maximum temperature of 800 °C. Using this experimental device, one-dimensional oxidation displacement experiments were carried out via air injection in the Hudson original reservoir to change the pressure from low pressure (5 MPa) to high pressure (30 MPa) and via air injection after water injection under 30 MPa high-pressure conditions. A stable medium–high-temperature thermal oxidation front and displacement state could be formed in the experiments under different pressure measurements of 5 MPa, 15 MPa, and 30 MPa and in the air injection experiment after water injection under high pressure, at 30 MPa, which was similar to the oxidation front and displacement characteristics of heavy oil air injection in situ combustion. However, as the pressure increased, the air consumption and fuel consumption became smaller, and the temperature of the oxidation front became lower. And compared with the original reservoir, the air consumption and fuel consumption of air injection after water injection increased, and the temperature of the oxidation front became higher. This was completely different from the law of heavy oil in situ combustion. With the increase in pressure, the pore volume number (PV) of the injected air was smaller, the gas production/injection ratio was smaller, and the oil displacement efficiency was higher. Therefore, the stability of the 30 MPa high-pressure air injection displacement was better. The gas/oil ratio (GOR) produced by 30 MPa air injection after water injection in the experiment was stable, and air injection after water injection could reduce the water cut and greatly improve oil displacement efficiency. Therefore, air-injection-enhanced oil recovery technology was still feasible in the reservoir after water injection.