Effects of discontinuous fluid interfaces on pressure drops and relative permeabilities for gas-liquid two-phase flow in porous media

Abstract

After gas is injected into the Earth's crust, it gradually transitions from continuous flow to discontinuous flow as the flow distance increases. This study aims to investigate the relationship between pressure drop and fluid interface properties in gas-liquid two-phase discontinuous flow. Based on the capillary bundle model, a simple equation is proposed to separate the capillary pressure drop caused by the fluid interfaces from the viscous pressure drop within the total pressure drop of gas-liquid two-phase flow. The viscous pressure drop is linearly related to both the flow rate and the effective viscosity of the gas and liquid, while the capillary pressure drop is indirectly derived from the viscous pressure drop. Through steady-state gas-liquid two-phase flow experiments in micromodels, we further determined that the capillary pressure drop is linearly related to the specific interfacial area of the moving fluid. Moreover, the slope of this linear relationship decreases as the flow rate increases, showing a negative exponential power function relationship. By regression analysis, we established the functional relationship between the specific interfacial area and variables such as gas volume fraction, flow rate, viscosity, and pore structure. Based on this, we empirically derived a calculation formula for two-phase relative permeability as a function of the specific interfacial area. This study quantifies the significant influence of fluid interface on both pressure drop and relative permeability in discontinuous flow.