关键词: 低渗透油藏, 水力压裂, 渗流模型, 动态预测, 有限元方法

Abstract: Microscopic residual oil in reservoir after water flooding can be classified into three types:oil droplets,oil films and oil clusters.Former research work shows that in order to overcome the capillary forces trapping the residual oil after water flooding,the driving viscous forces must increase by one thousand to ten thousands times than before.In fact,the viscous forces in the reservoir can not increase to such a magnitude.Though polyacrylamide(PAM) solution has little effect on the tension of oil-water interface,the lab test and field data show that all types of residual oils in pores are reduced after PAM flooding.The magnitude of reduction is related to the elasticity of the solution.The higher the elasticity is,the lower the saturation of residual oil will be.Research results of flooding visualization cores show that viscous-elastic fluid flooding can decrease the residual oil saturation of cores with all types of wettabilities.The driving force of viscous-elastic fluid is different from that of Newtonian fluid.The viscous-elastic fluid not only has a viscous driving force perpendicular to the oil-water interface for overcoming the capillary trapping force,but also has a strong viscous dragging force parallel to the oil-water interface for pulling all types of residual oils after water flooding.

Key words: polymer solution, viscous-elastic behavior, oil-water interface, parallel force, residual oil, flooding