Pore Structure And Adsorption Characteristics Of Coal Reservoir In Southeastern Qinshui Basin

The pore characteristics and adsorption capacity of coal is limited by coal quality,which also has an affect on coalbed methane enrichment.The macro observation,microscopic component analysis and vitrinite reflectivity measurement,scanning electron microscope,low tempreture nitrogen adsorption analysis and the isotherm adsorption experiments of coal samples from southeastern Qinshui Basin were carried out to analyze the pore structure and adsorption characteristics of coal reservoir.Based on these researches and previous study,the relationship between coal quality and pore structure and adsorption characteristics was discussed.The following conclusions were as follows:Bright coal,semi-bright coal is as a focus in the study area,the rest is dark coal.Various industrial indicators,the ash content of coal is between 8.4% and 13.49%,the average value is 10.41%,which belongs a low gray partition.The moisture content of the coal is moderate(1.86),volatile content is low(8.66).Vitrinite content is high(93.85%),The vitrinite reflectance is between 2.44% and 3.07%,the average value is 2.67%,with a higher degree of metamorphism.The coal pore in the study area is developed well,the great majority is micropores and transition hole.Pore volume distribution is wide from 0.00052cm3/g to0.0095cm3/g,the average value is 0.0028cm3/g.The specific surface area distribution is between 0.22m2/g and 16.95m2/g,the average value is 3.42m2/g.The specific surface area is determined by the pore volume.Coal samples in the study area has a significant pore fractal feature,the integrated fractal dimension ranges from 2.47 to 2.97,the average value is 2.72.The pore volume and the specific surface area first decreases and then increases with coal rank increasing.There is a positive correlation between fractal dimension and vitrinite reflectance.Coal industry index and Maceral is not the decisive factor in coal porosity characteristics.The coal samples in the study area has a strong adsorption capacity.Langmuir volume is between 28.17cm3/g and 36.5cm3/g,the average value is 33.6cm3/g,Langmuir pressure is between 2.01 MPa and 3.12 MPa,the average value is 2.66 MPa.The adsorption capacity increases with the increase of vitrinite reflectivity.There is anegative correlation between adsorption capacity and moisture and ash content of coal.besides,the adsorption capacity increased with the increase of vitrinite content.There is a positive correlation between fractal dimension and Langmuir volume and Langmuir pressure.The total fractal dimension not only reflects the situation of coalbed methane enrichment,but also the degree of difficulty of coalbed methane desorption.The total fractal dimension play an important role in the development of coalbed methane of high rank coal.The higher the total fractal dimension of high rank coal,the more beneficial to coalbed methane development.The coal samples in the study area has a suitable coal indicators and a high degree of thermal evolution,which is a typical anthracite and very favorable for the formation of coalbed methane reservoirs.The developed pore system and the presence of a large number of micropores and transitional are beneficial to coalbed methane adsorption.The strong adsorption ability has laid a good foundation for the enrichment of CBM coalbed methane.The high Langmuir pressure is good for methane desorption of coal reservoir.