The dynamic effect in capillary pressure during the displacement process in ultra-low permeability sandstone reservoirs

The relationship between the capillary pressure and saturation is a primary factor to describe and simulate the multiphase flow. This relationship is also fundamental to understand the characteristics of oil and gas reservoirs and make the reservoir development plan. Traditionally, the capillary pressure is measured under the equilibrium process; however, this equilibrium is hard to establish when the multiphase flow is expected in low to tight permeability porous media, and the capillary pressure is dynamic. This laboratory study conducts specially designed dynamic displacement experiments to examine the dynamic effect in capillary pressure in ultra-low permeability sandstone oil reservoirs. The dynamic capillary pressure, the dynamic relative permeabilities, the dynamic coefficient and the change rate of water saturation are obtained. Results show that the dynamic coefficient is relatively larger in ultra-low permeability reservoirs compared with that in high to low permeability reservoirs. Difference between the dynamic and the steady capillary pressures becomes more significant for less permeable porous media, with a higher dynamic coefficient and a stronger dynamic effect. Wettability advancement has been triggered during the dynamic displacement process, which is responsible for the water-wet rock before the displacement to be oil-wet during the displacement process. The difference between the dynamic and the steady relative permeabilities becomes obvious, and the dynamic effect in capillary pressure cannot be neglected when the permeability reaches ultra-low. The dynamic coefficient can reveal the shape of the displacement front. Cited as : Li, Y., Li, H., Cai, J., Ma, Q., Zhang, J. The dynamic effect in capillary pressure during the displacement process in ultra-low permeability sandstone reservoirs. Capillarity, 2018, 1(2): 11-18, doi: 10.26804/capi.2018.02.01.