Methane

Adsorption

Mathematics education

Engineering

Ecology

Biology

Materials science

Coalbed methane

Petroleum engineering

Coal mining

Mass transfer

Geology

Homogenization (climate)

Multiscale modeling

Coal

Porosity

Waste management

Thermodynamics

Physics

Organic chemistry

Mathematics

Flow (mathematics)

Environmental science

Computational chemistry

Porous medium

Composite material

Microscale chemistry

Chemistry

Darcy's law

Mechanics

Biodiversity

Enhanced coal bed methane recovery

Advances in Water Resources

In this work we develop a multiscale model for flow and transport problem in CO2-enhanced coalbed methane recovery. The coalbed methane reservoir is characterized by two levels of porosity associated with nanopores in the matrix and cleat network. Mass conservation equations for fluid mixture (CH4 and CO2) in the matrix at the microscale are rigorously derived by using the formal homogenization technique taking into account the gas mixture adsorption in the nanopores. The Density Functional Theory (DFT) is used to compute the gas adsorption isotherms and the solvation force acting on the nanopore wall, showing a much more pronounced adsorption capacity of CO2 compared to CH4. The average transport equations in the matrix together with the multiphase flow problem in fracture network (gas mixture and water) are homogenized giving rise to a macroscopic model ruled by the effective conductivities, partition and transfer coefficients. The cleat permeability evolution due to deformation is taken into account through a three-scale poromechanical model reported in a previous work. Computational simulations illustrate the macroscopic laws underlying the gas pressure distributions, cleat closure phenomena and CH4 production curve enhanced by CO2 injection.

Multiscale model for flow and transport in CO2-enhanced coalbed methane recovery incorporating gas mixture adsorption effects