Balanced displacement methods and effect evaluation of heterogeneous combination flooding in different reservoirs

The synergistic oil production of heterogeneous combination flooding and field adjustment measures has achieved good effects of oil production increase and water cut decrease in the Ng3 block of the Gudao Oilfield. However, due to the complex heterogeneity of the actual formation, differences in the deployment of interlayer well networks, and different injection volume of chemical agents in different layers, the extraction of planar and vertical remaining oil by heterogeneous combination flooding will be affected. It is difficult to clarify the contribution of different balanced displacement methods, and to elucidate the mechanism of extracting different types of remaining oil. Therefore, this paper establishes five different types of remaining oil reservoir mechanism models based on the actual formation parameters of the target block through reservoir numerical simulation. The remaining oil, extracted remaining oil, oil displacement efficiency, sweep coefficient, planar water saturation variation coefficient, and vertical water absorption imbalanced coefficient were used to evaluate the balanced displacement effects of heterogeneous combination flooding. On this basis, the mechanism of remaining oil extraction was elucidated. The numerical simulation results show that field adjustment measures such as well network adjustment or layered injection allocation for heterogeneous combination flooding can maximize the balanced displacement effect. For different types of remaining oil reservoirs, the priority of implementing balanced displacement methods has been clarified. In practical application, suitable balanced displacement methods should be selected based on the type of reservoir and the conditions of the field implementation. In reservoirs with developed high permeability zones, heterogeneous combination flooding can effectively advantageous channels of water flow; Well network infilling can enlarge the sweep volume of heterogeneous combination flooding in low-permeability areas and enhance the displacement efficiency of enriched remaining oil. The balanced displacement effect of heterogeneous combination flooding is better than that of well network adjustment. In reservoirs with imperfect injection production well networks, improvement of the well network can increase the sweep range of streamlines, and synergistic heterogeneous combination flooding can dynamically regulate and strengthen the extraction of remaining oil. The balanced displacement effect of well network adjustment is better than that of heterogeneous combination flooding. In unconnected reservoirs, the enriched remaining oil blocked by faults is difficult to connect with production wells. So well network adjustment can effectively overcome the blocking effect of faults and extract unconnected remaining oil. The balanced displacement effect of well network adjustment is better than heterogeneous combination flooding. In rhythmic reservoirs, injected fluids are prone to flow along high permeability water flooded intervals. Heterogeneous combination flooding can effectively plug them, thereby increasing the water absorption of weak water flooded low permeability intervals and extracting high saturation remaining oil. In interbed reservoirs, layered water injection can significantly improve the vertical water absorption imbalance degree. Heterogeneous combination flooding further plays a role in conformance control and oil displacement at different layers, enhancing sweep effect and improving oil displacement efficiency, effectively extracting the remaining oil controlled by interbeds. The effect of heterogeneous combination flooding on improving balanced displacement is better than that of layered water injection, and layered allocation of heterogeneous combination flooding can achieve vertical balanced displacement to the maximum extent. This study provides a reasonable explanation for extracting different types of remaining oil and achieving balanced displacement for heterogeneous combination flooding, and affords reference significance for the future promotion and field application in different reservoirs.