Active polymer flooding for strongly heterogeneous reservoir associate with foam combination technology

After prolonged water flooding development, reservoir heterogeneity has become a serious issue. Polymer f looding, though the most mature and widely applied technique, faces adaptability challenges and struggles to achieve ideal oil displacement results. In response to strong heterogeneity in reservoirs, this paper adopts a “profile control before displacement” strategy, proposing an enhanced foam-active polymer profile control and displacement technology. Initially, a polymer-enhanced foam (AOS-DYG) is used to plug dominant flow channels, increasing the startup pressure in high-permeability layers and improving the sweep efficiency of subsequent fluids. Subsequently, an active polymer AM/AMPS/DMCA, capable of both enhancing sweep efficiency and displacement efficiency, is injected into secondary pore regions, ultimately forming an efficient chemical f looding system. Experimental results show that the optimal slug combination for the AOS-DYG + AM/AMPS/ DMCA chemical flooding system is 0.2 PV AOS-DYG+0.4 PV AM/AMPS/DMCA. In cores with a gas permeability of 1200 mD, this system enhanced oil recovery by 44.3%; in heterogeneous cores with a permeability contrast of 5–30, the EOR value ranged from 18.36% to 36.79%. This chemical system demonstrated an excellent oil displacement ability in strongly heterogeneous cores. The displacement mechanism in strongly heterogeneous reservoirs is investigated using a micro-etching visualization model and core nuclear magnetic resonance in-line displacement experiments. The AOS-DYG enhanced foam preferentially entered high-permeability layers, effectively plugging them and increasing the flow resistance in these areas, thereby expanding the sweep volume. This allows the subsequent active polymer AM/AMPS/DMCA to enter the lower permeability layers of the core, mobilizing the residual oil in low-permeability layers not reached during the water flooding stage, further confirming the feasibility of this chemical flooding system in EOR in strongly heterogeneous reservoirs