Experiment on the Gas Permeability and Gas–Water Relative Permeability in High-Rank Coal with a Self-Developed Device

Abstract

Water saturation, displacement pressure, and gas type are essential factors affecting the seepage characteristic of fluid in coal due to the swelling induced by gas adsorption. However, the understanding of the seepage behavior of water, CH 4 , and CO 2 in coal seams is still poor owing to the lack of research. In this work, a series of gas permeability and gas−water relative permeability experiments were conducted by our self-developed device. The results can be summarized as follows: (1) with the increase in water saturation, the gas permeability decreased rapidly at first and then reduced sharply again after a period of slow decline; (2) the two-phase flow span showed no significant difference for He−water and CH 4 −water systems under different displacement pressures, but it increased for CO 2 -water system. The different behaviors of the two-phase flow span suggested that the effect of displacement pressure on relative permeability properties is dependent on the gas type. (3) The CO 2 −water relative permeability showed a sizeable two-phase flow span compared to the He−water or CH 4 −water system under the same displacement pressure, and the gas relative permeability decreased obviously in the following sequence: He > CH 4 > CO 2 . The concept of relative permeability surface was proposed based on the experimental results. A parametric interpolation method was applied to determine the relative permeability surface, which could be used to accurately describe the flow characteristics of fluids in a mixed gas−water system.

Hydraulic Fracturing and Enhanced Recovery in Shale Reservoirs: Theoretical Analysis to Engineering Applications

“…Fang et al 209 established a permeability model under the influence of thermal−hydraulic− mechanical fields and considered matrix and crack effects separately. Shen et al 210 extended a multiphase and multicomponent permeability model, which quantifies the effect of different gas components by introducing a concentration interpolation function.…”

The development and application of novel apparatus for relative permeability measurement

“…Water production was determined by the DPT, while gas production was recorded by a gas flow meter. The relative permeability of gas and water was calculated based on the recorded data, using the calculation method described in our previous study [26]. By investigating the gaswater flow characteristics in coal under different gas types and pressures, this study aims to provide insights into the behavior of coal reservoirs and enhance our understanding of gas and water migration in such porous media.…”

“…The results of carbon dioxide-water relative permeability under different displacement pressures are listed in Table 4. The irreducible water saturation in the carbon dioxide-water system ranged from 25.7% to 78.7% as the displacement Reprinted (adapted) with permission from reference [26]. Copyright 2023 American Chemical Society.…”

“…It was observed that the gas type significantly affected the relative permeability of anthracite coal. For the helium- Reprinted (adapted) with permission from reference [26]. Copyright 2023 American Chemical Society.…”

“…(a) the relative permeability of water; and (b) the relative permeability of gas. Reprinted (adapted) with permission from reference [26]. Copyright 2023 American Chemical Society.…”