Effects Of Microscopic Composition And Pore Structure Of Coal Rock In Shaqu No.1 Mine On Methane Adsorption Characteristics

The development and utilization of coal-measure gas can effectively alleviate the contradiction between energy supply and demand,ensure the safety of coal-measure formation construction,and improve the environment.At present,the level of development and utilization of coal-measure gas in my country is relatively low,and the methane gas in coal-measure rocks has not been paid enough attention.In the field of mine gas control,the gas content in the surrounding rock of the coal seam is also generally ignored,which has led to rock gas dynamic disasters in some mines,as well as records of gas injuries in the construction of coal-measure strata tunnels.Therefore,it is imperative to pay attention to the methane gas content in coal-measure rocks.With the mining depth of the coal seam going down year by year,the methane content of the coal-measure strata as a whole is also gradually increasing,and the utilization prospect is very broad.How to effectively predict the gas content in coal and surrounding rocks to achieve the goal of"safe-efficient-clean"energy utilization,is an important guide for relevant researchers.Studying the adsorption characteristics of coal and rock on methane is the premise of predicting the gas content of coal-rock system,and the adsorption characteristics depends on the microscopic composition and pore structure.It provides a basic theory for rationally evaluating the methane content in coal-measure strata in the field of coalbed methane exploitation.The coal seam of Shaqu No.1 Mine of Huajin Coking Coal Group has the characteristics of low permeability and strong adsorption,while the surrounding rocks are mostly composite rock layers with certain adsorption properties.The gas content in the coal-rock system is high and the treatment is difficult.Aiming at this problem,this paper studies the 3+4#coal and its roof and floor,5#coal and its roof and floor of the mine.The microscopic components of the six groups of samples was studied by industrial analysis,XRD analysis and SEM-EDS analysis.The pore characteristics of each sample were studied by means of scanning electron microscopy,low temperature nitrogen adsorption and CT scanning,and the methane adsorption law of each sample was studied by high pressure volumetric method.The in-depth study of the effect of the microscopic composition and pore characteristics of coal and rock mass on the adsorption characteristics has revealed the difference in methane adsorption characteristics between the coal seam and the roof and floor rock layers.The research results are summarized as follows:（1）The content of organic components in 3+4#coal and 5#coal is 79.07%and 84.18%,respectively,while the inorganic component content of rock samples are all greater than 90%.Therefore,the affinity of coal to CH₄molecules is greater than that of rock.The inorganic components of the samples are mainly quartz and clay minerals.（2）The BET specific surface area and adsorption pore volume of the rock samples are larger than the coal samples,which can create favorable conditions for the adsorption of more CH₄molecules.In addition,surface roughness and structure complexity of pore of the rock samples are slightly larger than the coal samples,which is related to the high content of clay minerals.（3）The pore size distribution and coordination number distribution of some macropores and fracture grade pores in each samples are similar,showing a single peak distribution;the average pore throat ratio and average tortuosity of each sample have little difference;the three-dimensional shape factor of 3+4#coal is larger than that of the other five groups of samples,and there are many fracture structures;the absolute permeability of coal and rock is little difference.By comprehensive comparison,there is no significant difference in the connectivity of macropores and fracture pores in each samples.（4）The adsorption curves of methane of each samples are all in line with the Langmuir model,and the adsorption law can be described by the limit adsorption capacity V_Land Langmuir pressure P_L.At the same adsorption temperature,the adsorption capacity of 5#coal is the largest,and that of 3+4#coal is slightly smaller,which is much larger than that of the rock samples.With the increase of the adsorption ambient temperature,the adsorption curve of each sample decreased slightly,which had little effect on the order of adsorption amount.（5）The influences of micro-components and pore structure parameters on V_Land P_Lwere studied by linear analysis method one by one,and it was found that the content of organic components,clay mineral content,surface fractal dimension,specific surface area and adsorption pore volume had a significant effect on the methane adsorption process.This is consistent with the grey correlation analysis results.Based on multiple linear regression analysis,the influence relationship of five factors on the methane adsorption law was obtained,namely V_L=1.03×organic component content-0.30×clay mineral content+0.27×fractal dimension D1+2.00×specific surface area-1.85×adsorption pore volume;P_L=-0.89×organic component content+2.92×clay mineral content+1.15×fractal dimension D1+21.32×specific surface area-25.62×adsorption pore volume.