Tectonically Deformed Coal Properties and Methane Behavior

Tectonic stresses profoundly alter the internal structure of coal, affecting its micro- and nanoporosity, mechanical properties and capacity to adsorb and desorb methane. Under varying regimes of brittle or ductile deformation, coal undergoes metamorphic transformations: aromatic structures grow at the expense of aliphatic side chains, pore networks evolve in size and connectivity, and interlayer spacing narrows. These changes govern gas storage within super-micropores (<2 nm) and mesopores (2–50 nm), control adsorption–desorption hysteresis and determine the rate and extent of methane release. A detailed understanding of these processes underpins safer coal extraction, more efficient coalbed-methane recovery and improved prediction of gas outburst hazards.

Research from Nature Portfolio

Recent studies have employed a combination of low-temperature nitrogen adsorption, mercury intrusion porosimetry and methane isothermal adsorption to characterise tectonically deformed coals from a major coal-bed-methane province. By subdividing pore systems into critical size ranges (2 nm, 4 nm and 10 nm), researchers have mapped the transition of methane between solid, liquid and gas-like phases as a function of pore diameter and adsorption energetics. Molecular simulation reveals how heat of adsorption varies with pore spacing, leading to a three-phase endowment model that links pore evolution under tectonic stress to methane storage and liberation. The findings offer a new conceptual framework for assessing gas content in structurally complex coal reservoirs.

Tectonically Deformed Coal Properties and Methane Behavior publication trend

The graph below shows the total number of articles in tectonically deformed coal properties and methane behavior across all publications each year (not limited to Nature Index journals).

Technical terms

Tectonically Deformed Coal (TDC): Coal whose macromolecular and pore structures have been modified by geological stress, exhibiting brittle or ductile deformation features.

Coalbed Methane (CBM): Methane gas stored within coal seams, adsorbed onto internal surfaces of micro- and nanopores.

Pore Structure: The network of voids within coal, classified by size into micropores (<2 nm), mesopores (2–50 nm) and macropores (>50 nm).

Adsorption–Desorption Hysteresis: The phenomenon whereby gas uptake and release follow different paths due to pore shape, connectivity and capillary effects.

Ink-Bottle Pores: Pore geometries characterised by narrow necks and wider bodies, leading to trapping of adsorbate and delayed desorption.

References

1. Study on the mechanism of methane “solid–liquid–gas” conversion controlled by the evolution of coal micro- and nanopore structure. Scientific Reports (2024).
2. The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis. Frontiers in Earth Science (2022).
3. The characteristics of methane adsorption capacity and behavior of tectonic coal. Frontiers in Earth Science (2023).