Numerical study on the injection of heated CO₂ to enhance CH₄ recovery in water-bearing coal reservoirs

ABSTRACT

A hydraulic-mechanical-thermal coupled numerical model for enhanced CBM recovery by injecting heated CO₂ (CO₂-ECBM) is established, which fully couples the gas-water two-phase flow, competitive adsorption, and temperature change as well as coal deformation. Through the finite element simulation software COMSOL Multiphysics, the model is used to investigate the effects of initial water saturation, CO₂ injection temperature and pressure on the CO₂-ECBM process from the perspectives of CO₂ storage, CH₄ production and the evolution of reservoir permeability. The coalbed water hinders the migration of gases in the reservoir. The CO₂ migration distance is always negatively correlated with the initial water saturation in the reservoir, even after the coalbed water is discharged. Interestingly, in the early stage of drainage and recovery, the rapid decrease of pore water pressure facilitates the desorption of adsorbed CH₄, especially near the producing well. The increase of CO₂ injection temperature and pressure is conducive to the transport of CO₂ in the reservoir, allowing more opportunities for CO₂ to come into contact with coal, which promotes CO₂ sequestration and thus enhances CH₄ recovery. The coalbed water can delay the decline of permeability induced by CO₂ adsorption by impeding CO₂ migration. The increase of CO₂ injection temperature and pressure can exacerbate the reduction of absolute permeability by inducing more CO₂ to be adsorbed.

KEYWORDS:

• Numerical study
• multiphysics
• CO₂-ECBM
• heat injection
• two-phase flow
• coal permeability

Disclosure Statement

The authors have nothing to disclose.

Additional information

Funding

The work was funded by National Natural Science Foundation of China [U1810206].

Notes on contributors

Yongliang Mu

Yongliang Mu is a doctoral candidate at Liaoning Technical University, specializing in coalbed methane recovery.

Yongpeng Fan

Yongpeng Fan is a postdoctoral fellow at Liaoning Technical University, specializing in coalbed methane recovery.

Jiren Wang

Jiren Wang is professor at Liaoning Technical University and academician of the Russian Academy of Natural Sciences, dedicated to the teaching and research in the fields of mining engineering and safety science and engineering.

Nan Fan

Nan Fan is a doctoral candidate at Liaoning Technical University, specializing in coalbed methane recovery.