Abstract: To investigate the use of hot water flooding to reduce water injection pressure and increase injection capacity in tight sandstone reservoirs, laboratory-based physical models were used to study the effects of hot water flooding on clay minerals from the target block in terms of hydration-induced expansion, rock pore structure, oil-water viscosity, crude oil thermal expansion, oil-water interfacial tension, oil and water phase starting pressures, and oil-water relative permeability curve. The mechanisms by which hot water flooding reduced water injection pressure and increased injection capacity in tight sandstone reservoirs were analyzed, and the effectiveness of hot water flooding at achieving these processes was assessed for a range of hot-water temperatures. Our experimental results showed that hot water flooding was highly effective at reducing water injection pressure and increasing injection capacity. Increase in the temperature of the water flood decreased the starting pressure of water injection and weakened the impact of the peak effect, thus improving the ability of the water flood at reducing water injection pressure and increasing injection capacity. The effectiveness of hot water flooding differed with the permeabilities of the rock cores and generally improved with decreases in the permeability coefficients of the rock cores. Finally, it was found that the optimal temperature for hot water flooding in the targeted tight sandstone reservoir block was approximately 100℃.

Key words: tight oil reservoir, hot water flooding, decreasing water injection pressure and increasing injection capacity, start-up pressure, pore structure