Molecular Dynamics Simulation of the Gas Hydrate Nucleation Process in a Coal Matrix

Area of Science:

• Geochemistry
• Materials Science
• Chemical Engineering

Background:

• Gas hydrates are ice-like structures formed from water and gas molecules.
• Coal and gas outbursts are a significant hazard in underground mining.
• Understanding hydrate nucleation in coal is crucial for outburst prevention.

Purpose of the Study:

• To investigate the nucleation mechanism of gas hydrates within a coal matrix.
• To compare hydrate formation in a coal matrix model versus pure water.
• To provide molecular-level insights for preventing coal and gas outbursts.

Main Methods:

• Utilized molecular dynamics simulations with a graphene slit model representing the coal matrix.
• Simulated gas hydrate formation under varying temperature and pressure conditions.
• Analyzed density distribution, self-diffusion coefficients, and structural parameters (RDF, F4 order parameter).

Main Results:

• The coal matrix model formed fewer clathrate cage structures compared to pure water.
• Methane exhibited a competitive migration mechanism within the coal matrix, moving from wall adsorption to hydrate cage trapping.
• Water and methane molecules showed higher self-diffusion coefficients in the coal system, indicating less mass transfer hindrance.
• Hydrate formation was observed at 250-260 K in coal systems, inhibited above 270 K.
• Temperature significantly influenced hydrate formation, while pressure (40-60 MPa) had minimal effect.

Conclusions:

• Coal matrices influence gas hydrate nucleation by altering methane migration and water/methane mobility.
• The findings suggest a molecular-level mechanism for hydrate formation inhibition in coal, relevant to outburst prevention strategies.