Abstract: In order to solve the problem of decreasing viscosity and oil displacement effect of the oil displacement system due to polymer aging of the chemical displacement in a certain block in Dongying, Hejian, Huabei Oilfield, the microscopic oil displacement mechanism of branched pre-crosslinked gel particles (B-PPGs) as well as the oil displacement effect of parallel cores were clarified based on a variety of experimental means such as viscosity and viscoelasticity tests, particle size distribution measurements, nuclear magnetic resonance (NMR) tests, and parallel core displacement. The results show that the branched structure of B-PPG molecules has better water solubility, which can improve the apparent viscosity of the solution; the B-PPG reticulated molecular structure enters into the formation in a crushed or deformed manner, which improves the mobility ratio and increases the sweep efficiency of the non-homogeneous reservoirs; when the permeability gradient of the main reservoir is 7.4, the recovery enhancement of the B-PPG system with a mass concentration of 2000 mg/L is 20% higher than that of the water displacement. The study shows that: The B-PPG system has good viscoelasticity, strong deformation ability, and ideal salt resistance, which can form an effective seal in the highly permeable layer and substantially increase the recovery rate. This study provides a reference for improving the profile of high-temperature and high-salt reservoirs, sealing the preferential channels of high permeability, and substantially increasing the reservoir sweep efficiency and recovery rate.

Key words: branched pre-crosslinked gel particles, viscoelasticity test, performance test, enhanced recovery, sealing experiment, sweep efficiency