Coal Reservoir Characteristics And Main Controlling Factors In Kubai Coalfield

The fine characterization of coal reservoir physical properties can provide basic prerequisite geological conditions and basic parameter information for the selection of coalbed methane development technology.It is an important geological guarantee technology in the process of coalbed methane exploration and development.In order to describe the coal reservoir characteristics and its primary controlling factors in the Taliqike coal seam,Kubai coalfield,this paper analyzed the coal quality characteristics,morphology and distribution of pores-fissure,absorption and resolution capabilities on the basis of the previous studies combined with multiple experiments including coal properties,high pressure mercury injection,low-temperature N₂ desorption,NMR,CH₄ isothermal adsorption,and SEM.What's more,the fractal theory is used to compare the heterogeneity of coal reservoir physical properties.On this basis,the three-dimensional spatial distribution and connectivity of the pore-fissure,as well as the association relationship between the pore-fissure system and minerals were visualized by using X-ray CT technology.According to different curves of capillary pressure,pore structures can be divided into 3 types,?,?and?,and the structure has a“double-peak”,mainly micropores and macropores,especially micropores.The different characteristics of low temperature liquid nitrogen adsorption curves reveral the pore morphology in coal,which are flat plate pores and wedge-shaped pores with one end closed,and open plate pores or cylindrical pores.Micropores have the largest contribution to the specific surface area,and there is a positive correlation between specific surface area and total pore volume.Different pore size ratios and effective porosity sizes are obtained according to NMR T2 spectrum curve.The comparison of the pore size distribution characteristics of high-pressure mercury injection proves that the coal is mainly composed of adsorption pores,followed by seepage pores.Based on X-ray CT scanning experiments,the fracture system and connectivity characterization models of coal reservoirs in the study area were established.Simultaneously,the development characteristics,spatial morphology and distribution of pores were explored in detail.The results of experiment show that the distribution of pores is generally more scattered,with continuous fractures formed locally.The fractures are filled with minerals on different scales,and the axial distribution of porosity is generally heterogeneous.The Langmuir volume of the coal samples in the study area is relatively high.The vitrinite and fixed carbon content play a positive role in the increase of the Langmuir volume,while the increase of ash and moisture reduces the adsorption ability of the coal.The density of microfractures is consistent with the distribution of vitrinite reflectance,and vitrinite content controls the expansion of microfractures in coal.With the increase of Ro,max,the coal seam porosity presents a trend of first increasing and then decreasing.Meanwhile,the coal seam porosity in Baicheng mining area is higher than that of Kuche;the coal quality characteristics affect the development of pores,in which the contents of vitrinite and fixed carbon are positively correlated with the BET specific surface and BJH pore volume.On the contrary,the inertinite content is negatively correlated with the BET specific surface and BJH pore volume,indicating that vitrinite is beneficial to the development of adsorption pores.