Coalbed methane diffusion and water blocking effects investigated by mesoscale all-atom molecular dynamic simulations

Area of Science:

• Geochemistry
• Petroleum Engineering
• Materials Science

Background:

• Water blocking effect (WBE) is a significant challenge in coalbed methane (CBM) extraction, limiting recovery efficiency.
• Understanding WBE at the molecular level requires realistic models of coal's porous structure and fluid interactions.

Purpose of the Study:

• To investigate the molecular mechanisms of WBE in coal using advanced computational modeling.
• To simulate the adsorption and diffusion dynamics of methane and water within coal's mesopores and macropores.

Main Methods:

• Development of a massive, scalable all-atom coal tube model.
• Molecular dynamics simulations to analyze methane and liquid water behavior in coal pores.
• Investigation of methane adsorption layers and diffusion coefficients under varying conditions.

Main Results:

• Methane exhibits multilayer adsorption on the coal surface.
• Methane diffusivity is significantly influenced by pore size and the presence of water.
• Liquid water acts as a substantial barrier, impeding methane diffusion within the coal matrix.

Conclusions:

• The study elucidates the molecular mechanism behind WBE, where liquid water blocks methane migration.
• Findings provide critical insights for developing effective strategies to mitigate WBE and enhance CBM extraction.