Development Characteristics Of Pores In Coal From Peigou Mine,Xinmi Coalfield

The coal pores/fractures play an important role in the coalbed gas adsorption,desorption,diffusion and migration process as a main part of the coal reservoir.Different history of sedimentary burial,tectonic evolution,coalification,fluid activity and organic gas lead to the different distribution of the internal pore/fracture system,especially the tectonic coal structure which is related to the gas outburst closely are more complex.Taking the No.2-1 coalseam that were collected from the Peigou Coal Mine of Henan Xinmi coalfield as objects,the change characteristics and distribution rules of the pore volume and specific surface area were systematic analysis.The results show that:(1)The pore volume of coal samples range from 0.0175 to 0.0415 ml/g and with an average of 0.0295 ml/g;the distribution chart shows a shock level of "W" shape from the bottom to top,most of the samples show multi peak distribution in different aperture distribution;The specific surface area range from 0.3010 to 1.3756 m2/g and with an average of 0.7305 m2/g;the overall trend is a downward shock of "W" shape from the bottom to top,and the distribution of different aperture section show unimodal or double peak;the average aperture range from 77.72 to 284.47 nm and with an average of 184.36 nm,the distribution chart shows a tendency of increasing shock;the pore shape are mainly open shaped or semi closed pore.(2)Compared to coal samples,the pore volume and BET specific surface area of the direct roof/floor are large,while the average aperture is smalle significantly;in addition,the pore shape are mainly ink bottle structure;the fractal dimensions of small aperture section are small,but the large pore size section are large.(3)Compraed to these coal samples which have low ash content,the pore volume and the average pore size of the gangue layer are small,while the BET surface area are large;the difference of the pore shape are not obvious;in addition,the fractal dimensions of the gangue layer in small aperture section are small,whle the fractal dimensions in small aperture section are in contrast.(4)The MIP can measure the pore/fracture range from 5.5 nm to 400 um,while the low temperature nitrogen adsorption can measure the pore that below 500 nm,what's more,the assumed condition,analytical model and other multiple factors that result in the obvious difference of the pore volume,specific surface area and average pore.Combined the analysis of the fractal theory and BJH model method,the lower limit of the accurate measured pore of different coal types by MIP are different and range from 80 to 200 nm mainly,the upper limit aperture of low temperature nitrogen adsorption that can be measured are about 100 nm.(5)The tectonism is the major geological factor that controlls the pore development in the same coalmine,but the effect of ash can not be ignored,too,such as the kaolinite,illite and other inorganic minerals,especially under various factors,the effect of coal ash may be complicated;and the related influence of different mineral on coal pore also need more experiments to investigate.