Study On Pore Structure Characteristics Of Deep-seated Coal Seal No.13-1 From Panji Huainan Area

Coal reservoir pores is used as storage and transport sites for coalbed methane,its structural characteristics determine coal adsorption and gas bearing.The study on the characteristics of coal seam pore structure is beneficial to the exploration and development of coalbed methane.In this paper,deep-seated No.13-1 coal seam from Panji Huainan was taken for the study object.Based on many deep exploration data and gas geological data,the coal lithotypes and the coal quality have were analyzed by microscopic observation,coal quality analysis and vitrinite reflectance.The characteristics of pore structure of coal seam have were analyzed by scanning electron microscopy,mercury intrusion test and low temperature nitrogen adsorption test.The influencing factors of the pore structure characteristics of the coal seam are also analyzed and studied.The maceral composition of 13-1 coal seam in the study area is dominated by vitrinite.The vitrinite reflectance is between 0.70%and 0.95%,which belonging to low-grade bituminous coal to medium-quality bituminous coal stage,generally bottle coal and gas-fat coal.Scanning electron microscopy showed that the plant tissue pores,intergranular pores,inter-chain pores,blowholes,dissolution pores,intergranular pores and mold holes,etc.Blowholes and the original holes are more obvious and poor connectivity.For the exogenous pores which developed in the damaged coal have better connectivity.While using pressure mercury test it shows that the porosity of the coal seam is between 3.07%and 24.24%.The pore distribution basically shows a bipolar distribution that is transition pores and micropores possession of advantages,macropores are slightly less,mesopores are the least.Semi-closed pores with poor connectivity dominates the pore form.In the structural fault there are open holes,macropores possession of advantages,mesopores are slightly less,the pore connectivity is better.Low temperature liquid nitrogen test BET pore specific surface area of 0.05-4.01 m2/g,the total pore volume of BJH is in the range of 0.0014-0.0163 cm3/g.The adsorption curves can be divided into semi-closed pore,"ink bottle" type pore and coal matrix loose of semi-closed pore.There is a certain relationship between the characteristics of coal pores structure and the degree of coal metamorphism,tectonic action and coal seam burial depth,coal metamorphic degree is the main controlling factors of the pore structure characteristics.In addition,the pore structure characteristics of differential development has a certain influence on the adsorption of coal seam and the gas-bearing.Under the same conditions,the same aperture within the period of BET surface area is larger,the stronger its adsorption.Total gas-bearing mainly comes from the transition pores and micropores.