Abstract: In response to the problems of low recovery rate of water flooding and steam injection difficulty in steam stimulation in the strongly water-sensitive conventional heavy oil reservoirs in Block Jin8, the chemical viscosity reduction, mine pilot test were conducted in two well groups, and the feasibility of this technology was verified by laboratory research and mine practice. The study shows that the interaction among crude oil, viscosity reducer and solid-phase model in porous media resulted in three effects: crude oil emulsification and dispersion, rock wettability change, and droplet deformation, bridging and blocking, thus reducing the apparent viscosity of crude oil, stripping the crude oil and expanding the swept volume. After water flooding, the remaining oil was dispersed and emulsified by injecting 0.3 times pore volume of viscosity reducer solution, and the immovable oil was changed into movable oil and flowed again, which decreased the water cut and improved the recovery efficiency by 7.29 percentage points. The test well clusters were designed with reservrir simulation technology. In the current inverted nine-spot water flooding well pattern, a single chemical viscosity-reducing solution was injected first; when the water content exceeded 75%, foam was added for viscosity-reducing compound flooding, and the volume of chemical agent injected into the slug should be 0.4 times the pore volume. Comparing the indicators of the test well cluster with water injection and chemical viscosity reduction for 1 year, chemical viscosity reduction has five advantages: slowing down the rise of water content, improving oil recovery rate, increasing the effective period of displacement, enhancing the water absorption capacity of the reservoir, and promoting the economic benefits of development. There is much for reference of the achievement of the study to similar reservoirs.

Key words: enhanced oilrecovery, chemical viscosity reduction, conventional heavy oil, high water sensitivity, effect evaluation