Pore Structure Characteristics Of Low-rank Coal And Its Influence Of Methane Adsorption In The Southeastern Margin Of Junggar Basin

My country has abundant coal-bed methane resources,with the development of science and technology and the improvement of coal-bed methane exploition conditions in recent years,the theory of scale production and commercial development and technical foundation have been completed in coal-bed methane industry.With the perfect end of the fourth round of national coalbed methane resource evaluation,my country's shallow coalbed methane resources are 2.98×10¹³ m³,and the recoverable resources are 1.25×10¹³m³(an increase of 1.64×10¹² m³ compared to 2009),so the coal-bed methane industry has broad prospects.Xinjiang is mainly rich in low-rank coal and has abundant resource reserbes.However,the current development and research work for different coal fields in Xinjiang started late,and there is a lack of research on the complexity of coal itself and the factors affecting methane adsorption.Low-rank coal has a complex pore structure,which has an important impact on methane adsorption.Based on physical experiments,this paper systematically analyzes the pore structure characteristics of low-rank coal through high-pressure mercury intrusion experiment and low-temperature nitrogen adsorption experiment,combined with different fractal models,and discusses the adsorption law of low-rank coal methane in combination with the fractal dimensions.And further analyzed the influence of pore structure characteristics on methane adsorption.It provides a theoretical basis for the development and utilization of low-rank coal and the implementation of CO₂-ECBM technology.With the help of high-pressure mercury injection experiment and low-temperature nitrogen adsorption experiment,the pore morphology and pore size distribution characteristics of different samples were studied.The results show that the samples have developed many kinds of pores,mainly macropores and mesopores.The pores have good connectivity,and the types are mostly open pores such as slit-shaped pores and cylindrical pores,and contain a certain amount of semi-open pores such as wedge-shaped pores.With the help of fractal theory,combined with pore scale characteristics,the applicability of each fractal model is analyzed and optimized,aiming to discuss the influence of different components on the fractal dimension value.The results show that the Menger sponge model,the capillary model and the Sierpinski model have segmented characteristics for the fitting results.Through correlation analysis and interpretation of the fitting results,the Sierpinski model is used as a pore model with a characterization scale>50 nm;the FHH model reflects The fractal characteristics of pores with a scale of<50 nm in the low-pressure section(P/P₀<0.5)and high-pressure section(P/P₀>0.5)are extracted,and the FHH model is used as a pore model with a characterization scale of<50 nm.Combining the advantages of the high-pressure mercury intrusion test and the low-temperature liquid nitrogen test,through the selection of the optimal model,the comprehensive fractal dimension of the coal sample is obtained,and the correlation between each component and the fractal dimension is discussed,and it is found that fixed carbon and volatile The correlation between vitrinite and vitrinite reflectance and chitinite is obvious,which is the main factor affecting the complexity of coal.With the help of isotherm adsorption test,the adsorption characteristics of different samples to methane and its control mechanism are discussed.The results show that the adsorption capacity of coal samples under different pressures is different,and the adsorption rise rate in the low pressure section is higher than that in the high pressure section;both the langmuir model can play a good role in data fitting.The parameters reflect different characteristics.By comparing the popularity and applicability of the equation,the langmuir model has obvious adsoption characteristics and a high degree of fit,and is easy to quantify,so it is used as a gas adsorption characteristic expression model;gas adsorption is not only affected by pore volume and pore specific surface area,but also restricted by other factors.