Wetting characteristics of coal and water interface under gas atmosphere and its influencing mechanism

Abstract

Coal seam water injection is widely used for coal seam gas control, and the key to its effectiveness in controlling gas lies in the wetting effect of water on coal body. However, the gas in coal seriously interferes with the wetting effect of water on coal. This paper uses a self-developed coal and water contact angle testing equipment under gas atmosphere and a self-developed water’s surface tension testing software under gas atmosphere to study the wetting parameters of coal and water interface under gas atmosphere, elucidating the wetting characteristics of coal and water interface under gas atmosphere and revealing its influencing mechanism. The results show that the surface tension of water, surface energy of coal, and adhesion work gradually decrease with the increase of gas pressure in a gas atmosphere. However, the coal and water contact angle and coal and water interface energy gradually increase with the increase of gas pressure, which implies a decrease in the wetting effect of water on coal. A molecular structure model of anthracite coal has been established based on the industrial analysis, elemental analysis, and micro spectral analysis of coal. The molecular formula of coal can be described by C99H54N2O3S. The bridge carbon ratio of the coal molecular model is 0.61, which is consistent with the bridge carbon ratio in the 13C-NMR spectrum. In the micro wetting system of coal water under gas atmosphere, with the increase of gas pressure, the adsorption degree of water molecules weakens, the degree of gas displacement in coal decreases, the diffusion coefficient of methane molecules decreases, the dispersion degree of water molecules increases, the aggregation degree of water molecules weakens, and the diffusion coefficient of water molecules increases. The research results lay a theoretical foundation for revealing the mechanism of wetting coal containing gas by coal seam water injection.

Keywords

• gas pressure
• coal seam water injection
• wetting
• surface tension
• coal and water contact angle