Visualized experimental investigation on the hydraulic characteristics of two-phase flow in a single smooth and single rough rock fractures

Abstract

In present engineering applications, calculations of hydraulic properties in two-phase flow are still highly dependent on empirical or semi-empirical equations obtained from experiments. However, the empirical equations that can reproduce the experiment data on a certain fracture specimen may have errors on other specimens. Researchers have obtained results that show quite different evolution forms of hydraulic characteristics of two-phase flow, which is induced by the variety of the influencing factors in two-phase flow. This paper aims at expanding the experimental results on the hydraulic characteristics of two-phase flow in rock fractures. With a newly developed experiment system, visualized two-phase flow experiments were introduced. The difference in the surface morphology of the fractures leads to totally different flow structures, which indicates the role of capillary pressure differs due to different fracture surfaces. The relative permeability in the rough specimen approximately follows the Corey model, which confirmed that the pressure drop is in this rough fracture is dominated by the capillary pressure, but the relative permeability is not only the function of saturation, but also the function of water flow velocities. However, the relative permeability is not perfect for evaluating the difference of two-phase hydraulic characteristics induced by the fracture surface morphology. On the contrary, the Lockhart-Martinelli model is appropriate for evaluating the difference in the two-phase hydraulic characteristics between the smooth fracture and the rough fracture, which indicates that the two-phase flow turbulence is obviously increased by the fracture roughness.