Quantitative Evaluation of the Influence of Injected Water on Methane Desorption Behaviors of Coal in the Ordos Basin

Hydraulic fracturing technology is widely utilized to enhance gas drainage efficiency in underground coal mines. Water plays a crucial role in gas migration within coal after water is injected into the coal seams. In this study, methane desorption behaviors of coal were quantitatively evaluated under the influence of the injected water content. X-ray photoelectron spectroscopy (XPS), mercury intrusion porosimetry (MIP), and methane desorption experiments were combined to reveal the influencing mechanism. XPS results show that sample DLT also has the greatest content of the total oxygen-containing groups, which is 99.67% and 176.55% higher than those of samples HJH and BJG, respectively. MIP results indicate that sample DLT has the smallest pore volume (0.0315 cm(3)/g) and pore surface area (2.79 m(2)/g), while sample BJG shows the largest pore parameters. It is confirmed that the pore structures of anthracite are more complex than those of bituminous coals. Methane desorption characteristics of anthracite and bituminous coal are affected by injected water to varying degrees. Gas desorption in bituminous B is the most sensitive to the injected water content, and only 6% of the water content triggers a 46.83% reduction of the methane desorption capacity, which is attributed to the less accessible pore space and more hydrophilic oxygen-containing groups. Due to the highly developed pore networks and less oxygen-containing groups, CH4 molecules are replaced by H2O molecules in anthracite at the lower injected water content (<6%), resulting in the increase of the desorption capacity. The higher water content (>6%) accounts for the pore-blocking effect, resulting in the abrupt reduction of the gas desorption capacity.