Many previous researches have proved that foam can increase the sweep efficiency and control gas mobility, and thus increase oil recovery. However, research on the effects of reservoir conditions such as the permeability, reservoir heterogeneity, formation rhythm and the viscosity of prude oil remains incomplete. Therefore, it is significant to study the foam efficiency in different reservoir conditions for large scale application of foam flooding.

The foaming agent was evaluated in laboratory and flooding experiments were conducted upon two groups of long real formation cores from Shengli oilfield to study foam flooding efficiencies. The effects of core permeability and gas liquid ratio on foam resistance factor were discussed. And then operating parameters including gas liquid injection ratio, injection rate and foam injection time were optimized and the influence of reservoir heterogeneity, the viscosity of crude oil and formation rhythm on nitrogen foam flooding efficiency were investigated at length by means of numerical simulation in the light of Shengli specific reservoir conditions.

The results show that, nitrogen foam flooding has excellent blocking ability and the optimum ratio of gas to liquid is 1.5:1; and the optimum foam rate is0.2 pore volume; the best foam flooding time is when the water cut of production well is 85%~ 90%. Nitrogen foam flooding is more effective for heterogeneous formations rather than for homogeneous ones. Furthermore, the efficiency of the flooding system decreases with the increasing viscosity of crude oil and is better in regular rhythm formation than that in negative rhythm formation. Finally, some easy-to-use and practical charts are drawn to analyze the economic benefits of nitrogen foam flooding for the given reservoir.

The study results provide a set of reservoir criteria that can be used as guidelines to choose potential reservoir candidates for nitrogen foam flooding.

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