Study On Desorption And Seepage Mechanism Of Coalbed Methane In Double Porosity Media

CBM is not only one of the main disaster to threaten the security of coal main in the coalexploitation but also a high-quality, clean and efficient energy. It is an unconventional naturalgas that has the features of self-generation and self-storage, during the process ofcarbonization, which mainly generates methane and absorbs in the coal bed by physicaladsorption, it is different from conventional oil and gas in accumulation、occurrence andseepage, the production method also has obvious difference. The process of CBM exploitationis consist of the gas desorption from coal matrix and seepage from fracture to the bottom.Therefore, further researches on the desorption and Seepage Mechanism of CBM in coal seamhave an important meaning for the exploitation of CBM. According to the characteristics ofcoal seam.This paper firstly simplifies coal seam into the double porosity media of pore-fissure tobe studied, and analyzes the mechanism of accumulate、migration、occurrence of CBM on thebasis of it, by this the theoretical basis has been established for the CBM seepage mathematicmodel; the process of the desorption of coal seam gas has been discussed in detail, theinfluential factors of CBM desorption has been analyzed, and the essence of CBM desorptionhas been revealed; And the influential factors of permeability dynamic changes were analyzed,establishing the dynamic changing permeability model that considers effective stress、shrinkage、Klinkenberg. Then based on dual-porous medium theory and by considering theinfluence of the actuating pressure gradient in the low permeability coal bed and analyzing theflow rules of gas and water in pore-fissure of coal, the fluid-solid coupling model of thetwo-phase flow of gas and water has been established under the conditions of non-equilibriumabsorption and quasi-steady state. The coupling equation is solved with the finite differencemethod and the finite element method, the program has been compiled to have the analogcalculation and it is found that pressure drop is more smooth in condition of consideringcoupling. The pressure is the main governing factor of reservoir characteristic parameters, theporosity、permeability and other parameters are affected by it. Therefore, the fluid-solidcoupling effect should be considered when seepage mechanism research of CBM.