A MODEL FOR CAPILLARY PRESSURE INTERMEDIATED LIQUID-GAS TWO-PHASE FLOW IN SINGLE FRACTURES

Abstract

The liquid-gas two-phase flow in rock fractures is of great significance in the community of civil engineering. The flow velocity of a fluid through a rock fracture depends on both the hydraulic conductivity of the fracture and the applied pressure drop along the fracture. The capillary pressure intermediates the liquid-gas two-phase flow in fractures by altering the "effective" pressure drop acting on both gas and liquid phases flowing in fractures. This paper presents a liquid-gas two-phase flow model, into which the influence of capillary pressure was introduced to quantify the interaction between the liquid phase and the gas phase. The liquid-gas two-phase flow was found to exhibit different patterns at different flow rates, i.e., bubble flow, slug flow, annular flow, and droplet flow. The contact angle, capillary pressure, and relative permeability at different liquid-gas flow rates were calculated. Numerical simulation data and experimental data were used to compare the predictions using the capillary pressure model with those using the existing liquid-gas two-phase flow models. It is found that the capillary pressure model prevails over the existing models in describing the characteristics of complex flow patterns. The effect of capillary pressure on relative permeability was discussed as well.