Study on the evolution of solid-liquid-gas in multi-scale pore methane in tectonic coal

The rich accumulation of methane (CH4) in tectonic coal layers poses a significant obstacle to the safe and efficient extraction of coal seams and coalbed methane. Tectonic coal samples from three geologically complex regions were selected, and the main results obtained by using a variety of research tools, such as physical tests, theoretical analyses and numerical simulations, are as follows: 22.4–62.5 nm is the joint segment of pore volume, and 26.7–100.7 nm is the joint segment of pore specific surface area. In the dynamic gas production process of tectonic coal pore structure, the adsorption method of methane molecules is "solid-liquid adsorption is the mainstay, solid-gas adsorption coexists". Methane stored in micropores with a pore size smaller than the jointed range is defined as solid-state pores. Pores within the jointed range, which transition from micropore filling to surface adsorption, are defined as gaseous pores. Pores outside the jointed range, where solid-liquid adsorption occurs, are defined as liquid pores. The evolution of pore structure affects the methane adsorption mode, which provides basic theoretical guidance for the development of coal seam resources.