Ding Nan, Si Leilei, Wei Jianping, Jiang Wan, Zhang Jian, Liu Yong
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
ACS Omega. 2023 Jun 7;8(24):22211-22222. doi: 10.1021/acsomega.3c02645. eCollection 2023 Jun 20.
Coal seam water injection is a kind of comprehensive prevention and control measure to avoid gas outburst and coal dust disasters. However, the gas adsorbed in the coal seriously influence the coal-water wetting effect. With the deepening of coal seam mining, the gas pressure also gradually increases, but there is still a lack of in-depth understanding of the coal-water wetting characteristics under the high-pressure adsorbed gas environment. Therefore, the mechanism of coal-water contact angle under different gas environments was experimentally investigated. The coal-water adsorption mechanism in pre-absorbed gas environment was analyzed by molecular dynamics simulation combined with FTIR, XRD, and C NMR. The results showed that the contact angle in the CO environment increased most significantly, with the contact angle increasing by 17.62° from 63.29° to 80.91°, followed by the contact angle increasing by 10.21° in the N environment. The increase of coal-water contact angle in the He environment is the smallest, which is 8.89°. At the same time, the adsorption capacity of water molecules decreases gradually with increasing gas pressure, and the total system energy decreases after the coal adsorbs gas molecules, leading to a decrease in the coal surface free energy. Therefore, the coal surface structure tends to be stable with rising gas pressure. With the increase in environmental pressure, the interaction between coal and gas molecules enhances. In addition, the adsorptive gas will be adsorbed in the pores of coal in advance, occupying the primary adsorption sites and thus competing with the subsequent water molecules, resulting in a decline of coal wettability. Moreover, the stronger the adsorption capacity of gas, the more obvious the competitive adsorption of gas and liquid, which further weakens the wetting capacity of coal. The research results can provide a theoretical support for improving the wetting effect in coal seam water injection.
煤层注水是一种避免瓦斯突出和煤尘灾害的综合防治措施。然而，煤中吸附的瓦斯严重影响煤与水的润湿效果。随着煤层开采深度的增加，瓦斯压力也逐渐增大，但目前对于高压吸附瓦斯环境下煤与水的润湿特性仍缺乏深入认识。因此，通过实验研究了不同瓦斯环境下煤与水接触角的机理。结合傅里叶变换红外光谱（FTIR）、X射线衍射（XRD）和碳核磁共振（C NMR），利用分子动力学模拟分析了预吸附瓦斯环境下的煤与水吸附机理。结果表明，在CO环境中接触角增大最为显著，接触角从63.29°增大到80.91°，增大了17.62°，其次是在N环境中接触角增大了10.21°。He环境中煤与水接触角增大最小，为8.89°。同时，随着瓦斯压力的增加，水分子的吸附量逐渐减小，煤吸附瓦斯分子后体系总能量降低，导致煤表面自由能减小。因此，随着瓦斯压力升高，煤表面结构趋于稳定。随着环境压力的增加，煤与瓦斯分子间的相互作用增强。此外，吸附瓦斯会预先吸附在煤的孔隙中，占据主要吸附位点，从而与后续水分子竞争，导致煤的润湿性下降。而且，瓦斯的吸附能力越强，气液竞争吸附越明显，进一步削弱了煤的润湿能力。研究结果可为提高煤层注水的润湿效果提供理论支撑。
