# Research on the evolution mechanism of main control factors for coalbed methane extraction

## TL;DR

This study investigates how gas adsorbs and desorbs in anthracite, revealing that adsorption and desorption processes are not reversible and affect gas extraction efficiency.

## Contribution

The study introduces a dual-pore model for simulating gas migration in coal seams and clarifies the non-reversibility of adsorption and desorption processes.

## Key findings

- The DR equation best fits gas adsorption in anthracite, with an R² of 0.9986.
- Gas desorption is less than adsorption due to pore throat blocking after coal matrix expansion.
- Adsorption and desorption processes differ fundamentally, with adsorption under constant volume and desorption under constant pressure.

## Abstract

To study the isothermal adsorption and desorption diffusion processes of anthracite, isothermal adsorption and desorption experiments of coal powder were conducted, and numerical simulations were carried out using COMSOL Multiphysics. The results showed that the DR equation had the best fitting effect on the gas adsorption curve, followed by the Langmuir equation, and the BET equation had the worst fitting effect, with R2 values of 0.9986, 0.9976, and 0.9765, respectively. The potential reason for this is the development of micropores in anthracite, with a relatively large proportion of gas molecules are primarily adsorbed in micropores; The single-pore model is suitable for fitting the gas adsorption process, but not for fitting the gas desorption process. Taking into account the spatial and temporal evolution characteristics of the gas diffusion coefficient, the dual-pore model is more suitable for simulating gas migration at the coal seam scale; Gas adsorption can cause expansion and deformation of the coal matrix, and some molecular scale pore throats have smaller pore throats than gas molecules after adsorption and expansion, resulting in a blocking effect on gas molecules in the pores. Therefore, the amount of gas desorption is usually smaller than the adsorption amount; There are specific differences between gas adsorption and desorption processes. Gas adsorption is a constant volume condition, while desorption is a constant pressure condition. Therefore, adsorption and desorption cannot be simply regarded as reversible processes. The research results provide theoretical support for a deeper understanding of the processes and mechanisms of gas adsorption-diffusion and desorption-diffusion.