La-sa-xing oilfield of Daqing in China, which accomplished polymer flooding in quick succession, had now entered into subsequent water flooding stage with yearly increase reserves, so various development contradiction were serious, the effect of conventional measures by water flooding were poor, the potential oil-bearing areas became complicate and were increasingly difficult to be produced.

The paper proposed redevelopment trends after polymer flooding for La-sa-xing oilfield, on the basis of analysis of residual oil distribution and present technologies of EOR after polymer flooding, includes subdivision of layer series of development, well pattern reconstruction, application of horizontal well to producing residual oil in the top of thick layer, using high concentration polymer, comprehensive implementation of various optimization measures and accelerating tertiary oil recovery technique etc.

The paper took the typical block of North 1 Area in Sazhong oilfield as a case study, established detailed reservoir geological model and carried out reservoir numerical simulation, made clear residual oil characteristics and residual oil distribution law after polymer flooding and calculated residual oil potential after polymer flooding. The paper provided a technical strategy and ideology for recombination of layer series of development and combined well spacing of horizontal and vertical wells, and formed a set of post-polymer-flooding's optimization and adjustment technology of vertical well infilling, combination of horizontal and vertical wells and re-polymer-flooding. The paper developed EOR mechanism simulation research for further enhanced recovery optimization. Numerical simulation results of optimization plan indicated that recombination of layer series of development and combined production by using horizontal-vertical wells is a feasible and effective way to improve further development effectiveness and the incremental recovery rate can reach to 5%.

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