Coupling mechanism between microscopic pore network architecture and interfacial properties for gas occurrence within coal reservoirs: Model deduction and theoretical formulation

The efficient development of coalbed methane (CBM) requires a systematic understanding of gas occurrence in coal reservoirs, and of how gas adsorption influences the pore network architecture and interfacial properties. In this study, the characteristics of CH 4 occurrence in coal and the response of microscopic pore network architecture and interfacial properties parameters before and after CH 4 adsorption are obtained through experimental methods. The parameter response model of “roughness-wettability- surface charge density” is innovatively constructed, and the coupling mechanism of “Organic fractions - Fluid particles - pore network architecture” is revealed. It is found that: (a) Gas occurrence space dynamically adjusts with pressure variations during adsorption in coal reservoirs; (b) Significant variations exist in pore network architecture and interfacial properties among coals with different metamorphic grades; (c) Gas occurrence modifies the pore network architecture and interfacial properties of coal reservoirs through coalification processes, chemical structure evolution, stress-temperature coupling effects, and intermolecular interactions; (d) The CH 4 adsorption capacity of coal shows a “stepwise” change characteristic, which decrease first and then increase. Strong correlations exist between interfacial properties and gas adsorption capacity of coal. Adsorption/ desorption kinetic parameters are primarily governed by surface chemical activity and molecular mobility, whereas the maximum CH 4 adsorption capacity is determined by the coupling between pore structure evolution and adsorption potential field intensity. • Quantitative characterization of microstructural alteration patterns of coal reservoir interfaces induced by gas occurrence. • Establishment of an interfacial properties parameter response model of gas occurrence integrating surface roughness, wettability, and surface charge density. • Systematic elucidation of the tripartite coupling interaction mechanisms involving organic fractions, fluid particles, and pore network architecture. • The “stepwise” change characteristic of the CH 4 adsorption capacity of coal with different metamorphism degrees, which shows a decrease first and then an increase, has been analyzed in detail.