| In order to more accurate study CH4 adsorption characteristics and the pore structure characteristics of deep coalbed,to understand the influence factors and mechanism of deep coal reservoir CH4 adsorption.The microstructure of coal samples was characterized by proximate and elemental analysis,coal petrology,true density,13C NMR(13C-NMR),Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?,and the macromolecular structure models of HLG and HMG were constructed.Based on the macromolecular structure model,the pore structure was simulated.Combined with low-pressure CO2 adsorption experiment,low-temperature N2 adsorption and desorption experiment and pore structure simulation,the pore structure characteristics of coal samples were analyzed from the perspectives of ultrapore,micropore,mesopore and macropore.The adsorption characteristics of CH4were analyzed by isothermal adsorption simulation.Main research results include:1.The coal samples were characterized by 13C-NMR,FTIR and XPS.The research results show that:?1?The process of coalification is also the process of increasing the degree of condensation of aromatic compounds in the molecular structure of coal.?2?In the low-rank stage,aromatic rings are highly substituted.With the increase of coal rank,the degree of substitution of aromatic rings decreases and tends to be stable.The content of methylene in the macromolecular structure of coal is higher than that of methyl,and hydrogen bonds mostly exist in the form of self-associating hydroxyl hydrogen bonds.When the degree of metamorphism is similar,the aromaticity and condensation degree of inertinite-rich coal are slightly higher than vitrinite-rich coal.High volatile bituminous coal has excellent hydrocarbon generating potential,and the second coalification jump will also lead to the jump of hydrocarbon generating potential.?3?The main forms of nitrogen and sulfur in HLG and HMG coal samples are pyrrole and thiophene sulfur.2.The plane structure model and three-dimensional structure models of HLG and HMG coal samples were constructed by 13C-NMR,FTIR and XPS parameters.The density of structural model of HLG and HMG coal samples is1.45g/cm3.3.The pore structure characteristics of HLG and HMG coal samples were studied by means of adsorption and desorption experiments of low temperature N2 and low pressure CO2 and simulation of ultra-micro pore structure.The results show that:?1?Compared with HMG coal sample,HLG coal sample has more complex pore structure and larger pore volume and specific surface area.?2?The traditional volumetric isothermal adsorption experiment underestimated the amount of CH4 adsorption;the underestimated amount of CH4 adsorption increases with the increase of burial depth,so the underestimated amount of CH4adsorption for deep coal reservoirs is very large and can not be ignored.4.The adsorption characteristics and influencing mechanism of CH4 in deep coal seam were analyzed by isothermal adsorption simulation.The results show that:?1?Pressure has a positive effect on CH4 adsorption,while temperature and water content have a negative effect on CH4 adsorption and the higher the pressure,the more sensitive the adsorption capacity is to temperature change.At the same temperature and pressure range,the adsorption capacity of HLG coal sample is greater than HMG.?2?From the point of view of adsorption heat,CH4 adsorption belongs to exothermic reaction,which results in the negative effect of CH4 adsorption with inceasing temperature.The interaction between H2O and coal molecule is stronger than that between CH4 and coal molecule,which results in water disadvantageous to CH4 adsorption.From the point of view of pore structure,H2O molecule occupies many advantageous adsorption pore sites,which leads to the inability of these advantageous adsorption pore sites to adsorb CH4,Moreover,the presence of H2O will also hinder the diffusion of CH4 and other fluid molecules,resulting in the decrease of CH4 adsorption. |
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