Fine Fractionation Of Chemical Composition Of Whole-Process Desorption CBM From Bituminous Coal In Well Zhong 2

Based on the theories and methods of coal petrology,coalbed methane geology and organic geochemistry,the whole process of fine desorption of bituminous coal in Dahebian syncline Zhong2 well was sampled by using the extended grinding process and method established by the subject group.The gas geochemical characteristics of three series of gas samples with different coal body structures,especially the carbon,hydrogen and oxygen isotope compositions of hydrocarbon gas and carbon dioxide monomer,were systematically tested.The fine fractionation process of gasification chemical components and isotope compositions of bituminous coal with different coal body structures was revealed.The control effect of pore structure on fractionation process was discussed through different characterization of pore structure of solid samples.It is found that the desorption gas showed a three-stage change in the natural desorption stage of the primary structured coal and structured coal,which is related to the pore structure of coal samples.Molecular sieve effect of ink bottle pore inhibits the release of hydrocarbon gas with large dynamic diameter in coal bed gas.The chemical composition of residual gasification of coal samples has significant difference in different degassing stages.The smaller the particle size of coal sample,the higher the propane concentration of residual gas,indicating that heavy hydrocarbon gas mainly exists in closed pores.It is found that the micropore volume and total pore volume of coal samples increase with the crushing process,which proves that the crushing process opens the isolated closed pore in coal samples and releases excessive coal bed gas.Comprehensive analysis shows that the methane in the open pore of coals in the study area is mainly caused by pyrolysis of organic matter.There is inorganic methane in the closed pore,and the carbon dioxide in the open pore and the closed pore is mainly organic thermal,which does not exclude the possibility of mixing some inorganic carbon dioxide.