Abstract: Aiming at the problems of low recovery of water flooding, high cost and high carbon emission of thermal recovery in conventional heavy oil reservoirs, anionic viscosity reducer and salt-resistant polymers were preferred based on the low-temperature and high-salt properties of reservoirs in Chunguang Oilfield. The water cut reduction and oil production increase mechanisms of hot-water flooding, single viscosity reducer flooding, and composite flooding were clarified based on indoor physical simulation experiments. The kinetic equations of the reaction of viscosity-reducing composite flooding were established. The numerical simulation method of viscosity-reducing composite flooding was developed in CMG-STARS software. Well-pattern spacing and injection-production strategy of viscosity-reducing composite flooding were optimized for conventional heavy oil reservoirs in Chun 2 unit. The results show that the viscosity-reducing composite flooding could give full play to the synergistic effect of viscosity enhancement of the displacing phase and viscosity reduction of the displaced phase, and it has the advantages of low system dosage, low carbon emission, and significant recovery enhancement; the viscosity-reducing composite flooding is suitable for five-spot pattern, the injector-producer distance should be less than 200 m; the optimal injection slug volume is 0.5 times of the pore volume and the injection to production ratio is 1.05 with the mass fraction of the viscosity-reducing agent at 0.25%. Practice shows that the water cut in wells was reduced by more than 30%, and the daily oil production was increased by 5 t/d after the viscosity-reducing composite flooding was implemented in extra-high water cut (water cut of 96%) reservoir at the late stage. This study confirms the feasibility of this technology applied in the field. It provides a reference to improve the effect of the development of conventional heavy oil reservoirs and realize the reduction of industrial emissions.

Key words: conventional heavy oil, composite flooding, numerical simulation, enhanced oil recovery, Chunguang Oilfield