19 / 2025-11-17 20:10:27

Pressure-Driven Pore Evolution in Coal of Different Maturity Stages and Its Implications for Gas Sequestration

Low-field NMR experiments; Pore structure; Pore size distribution; Pressure pores; Gas storage

A thorough understanding of gas storage and transport mechanisms in coal seams requires a precise characterization of pore structure evolution under dynamic conditions. In this study, we used low-field nuclear magnetic resonance to analyze five highly metamorphosed coal samples from distinct mining regions. Their pore structure, fractal dimensions, and pressure-dependent pore reorganization were systematically investigated. Our results demonstrated that pore development in the samples was dominated by micropores and small pores, with fractal dimensions below 2 revealing low structural heterogeneity. Increasing the pressure from 1 to 6.7 MPa induced a 2%–7% reduction in porosity, accompanied by a redistribution of pore sizes: small pores were proliferated, while the proportion of medium and large pores diminished. Pressure-driven pore restructuring in highly metamorphosed coal is a double-edged sword. While it enhances storage security through “enhanced adsorption,” it simultaneously challenges storage capacity and injection efficiency by “compressing pores” and “degrading flow.” These pressure-driven structural transformations provide critical insights into gas storage capacity and transport dynamics, with direct implications for optimizing coalbed methane extraction and CO₂ sequestration strategies.