Comparative study on fire flooding development characteristics of heterogeneous heavy oil reservoirs

The complex heterogeneity inside heavy oil reservoirs makes obtaining excellent development results difficult through conventional fire flooding technology. In view of this issue， this paper proposed that chemical ignition could be carried out by adding catalysts in heterogeneous reservoirs and compared the development characteristics with that of fire flooding in homogeneous reservoirs to reveal the improvement of fire flooding development effect by this technology. The fire flooding experiments with or without physical barriers were carried out through the three-dimensional （3D） physical model， and the development of the temperature field， as well as the formation and expansion law of coke zones were explored. The development characteristics of fire flooding under two reservoir conditions were further revealed through the analysis of the production effect and the distribution of remaining oil after fire flooding. The results showed that reservoir heterogeneity affects the advance of the combustion front， and local high temperatures appear due to shielding action， especially at physical barriers. Relay ignition can break through physical barriers in cooperation with the combustion front after adding catalysts， and the temperature cavity continues to expand， with the highest temperature reaching 583.2 °C. Different from homogeneous reservoirs， the coke zones formed in heterogeneous reservoirs are discontinuous. However， stress fracture occurs in physical barriers after relay ignition， and the combustion front continues to advance to the production well through the fracture zones. Then， combustion chambers expand rapidly. In the process of fire flooding in homogeneous reservoirs， high oil production is maintained in the stable combustion stage， and the ultimate recovery is 53.27%. After relay ignition in heterogeneous reservoirs， stable oil production begins and enters the main oil production period. A large amount of crude oil is displaced， and only a small amount of crude oil exists in the non-flow field， with the ultimate recovery being 51.46%. The distribution of remaining oil in the two reservoirs tends to zero in the high-temperature area. The oil saturation in the area affected by physical barriers is higher in heterogeneous reservoirs before relay ignition， but the oil saturation in the whole area is significantly reduced after relay ignition. The oil saturation in the lower part of the two reservoirs is the lowest because of the most intense combustion.