The Physical Characteristics Of Deep Coal Reservoir In Daning-Jixian Area

There is about 55.3 x 10¹² m³ resources of Coalbed methane in China,the Coalbed methane resources of buried depth more than 1000 m is about 41 x 10¹² m³,which accounts for 74.1%of the total CBM resources.there is rich deep CBM resources in China,the exploration&development breakthrough of which should be an important approach to improve the CBM production in our country.At present,the existing mature development of CBM wells are in shallow depth of 1000m,however,for the coal seam depth deeper than 1000m,the CBM geology theory has not yet mature.In this paper,deep CBM of Daning-jixian area is serve as the research object,based on basic geological data,combined with scanning electron microscopy,nuclear magnetic resonance,X-ray imaging techniques,high temperature and pressure adsorption,and pressure permeability test,the physical properties of deep coal seam reservoirs in the Daning-Jixian region are as follows:?1?Scanning electron microscopy,nuclear magnetic resonance,and X-ray imaging experiments showed that the fracture types of coal and rock are radial,fluvial,and network-like.Under the microscope,some fractures can be observed to be filled with minerals.The pore types mainly include intracavity pores and crumbs.Interstitial pores,pores,dissolved pores,and intercrystalline pores;their pore structures are mainly macropores and fissures,followed by mesopores and micropores.When the confining pressure increases,the porosity of coal samples decreases,and the pressure decreases.The effect of percolation pores is dominant,and the change of micropores is small;fractures of coal and rock are not developed,most of the fractures are filled with minerals,and the main development is mainly axial fractures,and the fracture distribution of coal samples is not uniform,and the fracture is three-dimensionally heavy.The structure shows that the crack content is less,but the fracture connectivity is better.?2?The high-temperature and high-pressure adsorption experiments show that the adsorption capacity increases with the increase of pressure,and the adsorption capacity tends to be stable under high pressure conditions.With the increase of temperature,the adsorption capacity decreases as a whole,but at 35°C and 45°C,There is a turning pressure for methane adsorption.When the pressure is less than 7MPa,the adsorption capacity at 35°C is greater than 45°C.When the pressure is greater than 7MPa,the adsorption capacity at 45°C is greater than that at35°C.?3?The gas content of No.5 coal seam in the study area is3.81²0.87m³/t,and the gas content of No.8 coal seam is 1.12²0.84m³/t.The gas content of No.5 coal seam in the same area is higher than that of No.8 coal seam,including the gas volume is controlled comprehensively by geological factors such as burial depth,structural conditions,groundwater conditions,coal seam thickness,roof and floor cover,etc.The gas content has a?critical depth?with the increase of burial depth,and the critical depth of No.5 coal seam is approximately 1000m,The critical depth of No.8 coal seam is about 1200m.The critical depth is shallow,and the gas content increases with the increase of burial depth.The critical depth is deep,and the gas content decreases with the increase of buried depth.?4?The permeability of coal reservoirs in the study area is relatively small.The permeability of No.5 coal seam ranges from 0.0065to 42.86mD.The permeability of No.8 coal seam ranges from 0.005 to3.01mD.With the increase of buried depth,the permeability decreases.In the range of 800¹100m,the permeability decreases by an order of magnitude for each additional 100m of depth.Through the permeability test of the pressure,it can be seen that with the increase of effective stress,the permeability decreases in a negative exponential manner;as the temperature increases,the permeability shows a decrease small trend.