Investigation of Dynamic Effect of Capillary Pressure in Ultra-Low Permeability Sandstones

Abstract

Generally, an empirical relationship between capillary pressure and saturation obtained by means of laboratory experiments is used to describe capillary pressure. However, this relationship assumes equilibrium in the distribution of the phases in the porous medium. This assumption is valid in cases where saturation varies slowly, however it may not be appropriate for application in faster processes. In such cases, dynamic effects may have an influence on the system. In this study, an extended relationship of capillary pressure that includes the dynamic effect is chosen to be implemented into the percolation model of two-phase flow in ultra-low permeability (K is less than 1 × 10−3 μm2) sandstones. This model is used for the numerical simulation. The purpose of this study is to examine the influence of the inclusion of the extended relationship on two-phase flow. Firstly, the dynamic effect was investigated through laboratory tests and then the factors influencing on the dynamic capillary pressure were analyzed. Secondly, the percolation model of two-phase flow considering the dynamic effect was established. Finally, the influences of dynamic capillary pressure on two-phase flow were investigated. The results reveal that the dynamic effect of capillary pressure is obvious in ultra-low permeability reservoir. The inclusion of the dynamic capillary pressure relationship has a different influence compared to the cases without capillary pressure. The existence of dynamic effect has a significant influence on the water saturation distribution and oil production. The moisture content rises faster for water-wetting sandstones but the rising velocity is reduced for oil-wetting sandstones considering the dynamic effect.