Nanoconfined Methane Storage Mechanism in Deep Coal Seams: A Wettability-Coupled Simplified Local Density Model

Area of Science:

• Geochemistry
• Petroleum Engineering
• Materials Science

Background:

• Nanopores dominate deep coal seams, influencing methane storage.
• Wettability effects on molecule-wall interactions are critical but poorly understood.
• Accurate modeling of nanoconfined methane behavior is essential for resource assessment.

Purpose of the Study:

• To develop a theoretical framework coupling the Simplified Local Density (SLD) model with wettability effects.
• To systematically describe nanoconfined methane behavior in deep coal seams.
• To bridge the knowledge gap between nanoconfined behavior, pore size, and wettability.

Main Methods:

• Modification of the equation of state (EoS) by incorporating a molecule-wall interaction term.
• Correlation of nanopore wall energy parameter and adsorption layer thickness with interaction strength.
• Derivation of wettability-dependent shifted critical properties.

Main Results:

• Bulk-like gas proportion in deep seams exceeds 35%, indicating high development potential.
• Adsorption amount decreases by up to 46% as contact angle increases from 0° to 80°.
• Modified EoS reduces bulk-like gas by ~8% in 3 nm pores due to weakened interactions.

Conclusions:

• Wettability is a crucial factor for accurately predicting nanoconfined fluid behavior in coal seams.
• Integrating wettability into models enhances the understanding of methane storage and recovery potential.
• This framework provides a novel approach for evaluating deep coal seam gas resources.