Capillary pressure has a great influence on the percolation of oil-water two-phase. We find that the seepage resistance of oil-water two-phase in ultra-low permeability reservoir is complex and the capillary pressure presents dynamic variation features through water flooding experiment. In this paper, first, we study the variation features of seepage resistance by mercury injection experiment. Second, we establish a percolation numerical model of oil-water twophase which considers the dynamic capillary pressure in ultra-low permeability reservoir. Finally, we analyze the sensitive factors of dynamic capillary pressure and the effects of dynamic capillary pressure on oil-water two-phase seepage.

The results show that the capillary pressure and the dynamic effect of capillary pressure are obvious in ultra-low permeability reservoir. When the coefficient τ of dynamic capillary pressure or the injection rate is larger, the dynamic capillary pressure will be bigger. The existence of dynamic capillary pressure hinders the fltting speed of waterflood front and reduces the oil production. The dynamic capillary pressure makes the moisture content rise faster for water wetting ultra-low permeability reservoirs while it reduces the rising velocity of moisture content for oil wetting ultra-low permeability reservoirs. This study is of great benefit to finding out the percolation law of ultra-low permeability reservoir and the subsequent work of development.