CO₂-ECBM simulation study considering Klinkenberg factor state

In order to explore the role of Klinkenberg effect and Klinkenberg factor in different states in the process of CO₂-Enhanced Coal Bed Methane (CO₂-ECBM), the effects of Klinkenberg factor of zero, fixed Klinkenberg factor and dynamic Klinkenberg factor on CO₂-ECBM were simulated and analyzed by COMSOL finite element software. The dynamic changes of CH₄ and CO₂ pressure with this factor were studied, and the CH₄ gas production was compared with the engineering practice. The results show that the effective permeability of CH₄ and CO₂ increases slowly at first, then decreases rapidly and gradually tends to be gentle. Compared with the fixed Klinkenberg factor or Klinkenberg factor of zero, the effective permeability of CH₄ and CO₂ under the influence of dynamic Klinkenberg factor is larger. When the Klinkenberg factor is a dynamic variable, the effective permeability of CO₂ is less than that of CH₄ due to the influence of molar mass and dynamic viscosity of different gases. The CH₄ pressure in the coal seam decreases faster and the CO₂ pressure rises faster. When the Klinkenberg factor is fixed or zero, the CH₄ pressure in the coal seam will be overestimated, and the influence range of CH₄ extraction and CO₂ pressure injection will be underestimated, and the valuation will increase with time. The research results are helpful to analyze the variation trend of effective permeability of CH₄ and CO₂, estimate the influence range of CH₄ extraction and CO₂ injection and the gas production of CH₄, and have theoretical guiding significance in exploring coal seam permeability, optimizing well pattern layout and quantitatively evaluating gas production of coalfield.