136-2 Molecular mechanism of water-bearing effect of deep coal-rock gas on methane adsorption

Session: Micro-Nano Scale Pore-Fracture Architecture and Fluid Dynamics in Shale and Coal Reservoirs

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To investigate the micro-mechanism of moisture and salinity on the methane adsorption capacity of coal, this study uses the Suide coal sample from the Ordos Basin as a case study. Scanning electron microscopy (SEM), CO₂/N₂ adsorption experiments, and methane isothermal adsorption experiments with varying moisture content levels were conducted to elucidate pore characteristics and moisture’s impact on methane adsorption in high-rank coal. Molecular simulations were employed to construct a molecular pore structure model of high-rank coal, exploring the formation of water films/water bridges and the effects of varying water contents and salinities on methane adsorption from a microscopic perspective. Experimental results indicate that Suide coal pores are predominantly elliptical, circular, and slit-shaped, with poor connectivity and most pores existing in isolation. Pores smaller than 0.9 nm significantly contribute to pore volume and specific surface area. Methane adsorption capacity decreases as coal moisture content increases. Molecular simulations reveal that water molecules in pore models form water films and water bridges. In small pores with limited adsorption space and overlapping adsorption forces on pore walls, water molecules primarily form water films on both walls. As pore size increases and water molecule numbers grow, both water films and water bridges emerge, leading to a gradual decline in methane adsorption capacity. Increasing inorganic salt ion concentrations (e.g., CaCl₂) result in a slow reduction in methane adsorption. Furthermore, methane adsorption capacity decreases with rising temperature across varying moisture contents and salt concentrations. Compared to moisture content, inorganic salt ion concentration has a weaker influence on methane adsorption. This study elucidates the formation mechanisms of water films and water bridges in coal matrix pores and analyzes pore size, moisture, and salinity effects on methane adsorption. The findings provide novel insights into moisture’s role in methane adsorption and strategies to enhance deep coal-rock gas extraction efficiency.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8663

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