Abstract: To address the severe areal and interlayer contradictions, rapid water cut increase, complex remaining oil distribution, and difficult oil stabilization and water control in the high-water-cut development stage of Chang 6 ultra-low permeability reservoirs in Jing'an Oilfield, polymer microsphere flooding experiments with macroscopic and microscopic visualization were conducted via laboratory and field tests. The flooding mechanism was analyzed, and the field application performance was evaluated.Results show that after polymer microsphere flooding,permeability decreases by 39.5%~68.7%,and the residual resistance factor reaches 1.65~3.19.The crossover point of relative-permeability curves shifts significantly to the right,residual-oil saturation decreases,water-phase relative permeability decreases,and oil-phase relative permeability increases.Under uniform polymer microsphere displacement,residual oil shows spotty or locally scattered distribution patterns;under non-uniform displacement,residual oil shows locally contiguous enrichment or enrichment along the flanks of preferential flow channels. After polymer microsphere flooding in the target blocks,the water injectivity of injection wells decreases,water-injection utilization and reservoir displacement conditions improve,the waterflood swept volume expands,and the reservoir recovery factor increases by 2.0~2.9 percentage points.These results provide important guidance and reference value for stabilizing oil production,controlling water,enhancing residual-oil tapping,and improving recovery in ultra-low-permeability reservoirs during middle-to-high water-cut stages.

Key words: ultra-low-permeability reservoir, microsphere flooding, displacement experiment, mechanism, performance evaluation, Jing'an Oilfield