A New Unsteady-State Method for the Determination of Oil-Water Relative Permeabilities in Tight Sandstone Reservoir

Abstract

The experiment on the determination of pseudo-threshold pressure gradient of two-phase seepage in condition of different properties and different water saturation, is conducted with the tight sandstone cores from the north of Songliao Basin. Moreover, mathematics characterization method for two-phase pseudo-threshold pressure gradient is established, which takes rock properties and water saturation into consideration. Based on non-Darcy seepage theory, a mathematics model of oil-water relative permeability with unsteady-steady waterflood method is deduced and established taking varietal threshold pressure gradients into account. And the mathematics model is combined with the mathematics characterization method for pseudo-threshold pressure gradient to create a new calculation method for oil-water relative permeability in tight sandstone reservoir. Afterward, we make a comparative analysis on the results of the new calculation method and JBN method. The analysis shows that the two-phase threshold pressure gradient in tight sandstone reservoir rises then declines with the increase of water saturation. There exists close correlation between maximum pseudo-threshold pressure gradient and Kleinberg permeability. It can be seen from the curve of oil-water relative permeability in tight sandstone reservoir from the north of Songliao Basin that the simultaneous seepage zone for two phases is narrow. The water phase permeability is low and so is the oil-displacement efficiency of waterflood. Therefore, it is difficult to develop such reservoir by waterflooding.