Tracer Responses in Gas-liquid, Two-phase Flow through Porous Media

Tracer responses in gas-liquid, two-phase flow through a fractured layer are discussed. Experiments were carried out using a glass bead bed in a cylinder. In the results, over a wide range of flow conditions of particle size, fluids-flow velocity, and water saturation (Sw), one of three types of liquidand gas-flow pattern was obtained: a single-phase (water) flow with entrapped gases, a bubble flow, and a channel flow. Tracer tests were performed for each flow type in the bed to obtain breakthrough curves for the water phase, which determined the hydrodynamic dispersion coefficient (Dh) being compared with the numerical model described by a one-dimensional advection-dispersion equation. In a relationship between the dispersion coefficient and water saturation, critical water saturation was observed, which depended on whether or not the gas phase in the bed is mobile. Above the critical saturation, there was a single-phase (water) flow with entrapped gases, and the dispersion coefficient linearly increased as Sw decreased. Below the critical saturation, waterand gas-phase flow (channel flow) appeared. The relationship was characterized by a steep increase in Dh as Sw decreases. In the bubble flow, gases flow unsteadily in porous media as bubbles, so flow paths of water become more complex. However, the dispersion coefficients obtained by tracer experiments show that the bubble flow and unsteady fluids paths do not have serious effects on hydrodynamic dispersion.