Enhancing Recovery Efficiency in Ultra-Low Permeability Reservoirs Using Multistage Flow-Controlled Complex Displacement

The Changqing Oilfield contains abundant ultra-low permeability reservoirs, contributing substantially to production. However, after years of water displacement development, injection and extraction conflicts have become more pronounced. The fracture network is highly complex, further intensifying water displacement challenges. Under strong heterogeneity reservoir conditions, nanogel particles were developed to dynamically regulate fluid flow direction in a graded manner, effectively expanding the wave volume. To address the evolving needs of weakly oleophilic reservoirs, improved oil repellent enhance surface wettability, optimizing fluid movement efficiency. This approach facilitates the establishment of a multistage flow-controlled complex displacement system—ensuring deep injection, compatibility with complex heterogeneity, and effective oil washing with precise regulation. Experimental results suggest that the interfacial tension of the multistage flow-controlled complex displacement system remains within the range of 10−2–10−3 mN/m. Compared to water displacement, the system improves oil displacement efficiency in cores by 21.43%, highlighting its promising potential for widespread application and technological advancement.