Coal Reservoir Physical Properties And Its Control Mechanism Of Coal Petrography In Hancheng Area

Reservoir study is an important part of the exploration and development of coalbed methane.Coal petrography controlling mechanism is a key scientific problem in coalbed methane exploitation geology.Based on a variety of new research and test methods,taking coalbed methane exploration and development demonstration area of Hancheng as the research target zone,this paper studied the physical properties of coal reservoir and the control mechanism of coal petrography.Sophisticated,quantitative,systematic and scientific description of the coal reservoir was carried out,and the physical properties controlled by coal petrography were analysed.Combined with lithotypes predicted by logging data,the physical characteristics of 3#,5#,11#coal seams were compared,and the porosity-permeability model was established.1.On the basis of microscopy and scanning electron microscopy observation of coal samples,through the low temperature of liquid nitrogen test,according to the adsorption-desorption curve,pore geometric models were divided and the pore size of the coal samples were mainly micro pores;Based on the morphological characteristics of the NMR T₂ spectrum,this paper distinguished the difference pore scale and its ratio.The connectivity between pores and fractures was evaluated,and the proportion of bound fluid and free fluid was calculated,which could be other evidence that there adsorption pores mainly and the seepage hole is less in the coal.2.BET and D-R adsorption models were selected to calculate the surface area of coal,compared with the Langmuir volume which was obtained by adsorption isothermal experiment,the adsorption capacity of coal was evaluated by specific surface area.The specific surface area was much smaller than the real specific surface area under the BET model,while the carbon dioxide adsorption data can characterize the pore surface area of 1.5nm or less,the D-R model has good correlation with Langmuir volume.3.Using a variety of emerging technologies and mathematical methods,based on microscope and scanning electron microscope observation,the length,width,density and other parameters of fractures were statisticed;the fractal characteristics of fractures were got by fractal theory;Using X-ray CT tomographic scanning analysis,the slices of coal samples were reconstructed three-dimensionally,which the spatial distribution,contact characteristics and mineral filling condition of pores and fractures could be revealed intuitively4.Analysing the pore and fracture characteristics caused by anthracology,the control of macrolithotype of coal,maceral,coal quality and other factors on the pore and fracture characteristics and adsorption characteristics of coal reservoir was discussed.From bright coal,semibright coal to semidull coal and dull coal,the development of fracture and the connectivity between seepage pore and absorbed pore weakened gradually.Micro pore was well developed in light and semibright coal,with higher specific surface area.With higher density,better extensibility and connectivity of microcracks,light and semibright coal has better adsorption and filtration performance.5.There are quite different logging response on different macrolithotype of coal,so the macrolithotype of coal could be predicted by acoustic logging,density logging,neutron logging and hole diameter logging,and the porosity-permeability model could be built.With statistics of 3#,5#and 11#coal seam,the poroperm characteristics were analysed.Bright coal and semibright coal are in the majority in the 3#coal seam,the 5#coal develops dull coal mostly,and there are more semibright coal and semidull coal in 11#coal.