Analysis Of The Main Controlling Geological Factors Of Deep Coal Seam Gas

Based on more than 200 coal samples from more than 20 coal mines and 10 boreholes of 4 mining area in southern Qinshui Basin,this thesis taking the coal of No.3 and No.15 in the study area as the research object,the basic research work has been carried out to study the influence of sedimentary,diagenesis and tectonism processes on the thickness of coal seam,the depth of the coal seam,the physical properties of the coal seam,the type of coal and rock and the micro component,the experiments were carried out with mercury injection,low temperature nitrogen adsorption,isothermal adsorption,nuclear magnetic resonance,microscope and scanning electron microscope,compared with the geological conditions of different depth of the two coal seams and the characteristics of the gas content in the two coal seams,the characteristics of reservoir physical properties and the geological conditions of the physical properties of coal reservoirs in the two coal seam are analyzed,and the main controlling factors of the gas production in the deep coal seams are revealed.The main understanding is as follows:Permeability is the main factor affecting the production of coal-bed methane,No.15 coal seam in the study area has been compared with the No.3 coal seam which has been industrialized,gas content had little difference,compound syncline structure and hydrodynamic effects are conducive to the preservation of coal bed gas and other geological conditions were the same or similar,but gas production disparity,permeability is main control factors affecting coal seam gas production.Sedimentary environment,in-situ stress,thermal evolution and coal structure have a controlling effect on coal seam permeability.The ash yield of No.3 coal seam is 9.04% ? 19.19%,with an average of 13.13%.The ash yield of 15 coal seam is12.52% to 23.37%,with an average of 16.38%.Sedimentary environment affect ash content,ash control cracks and development degree of the circumcision,and controls the reservoir porosity and permeability,considering the negative correlation between ash content and physical property of reservoir,No.15 coal reservoir is worse than No.3 coal seam.When the depth of the coal seam is greater than 1000 m,the average permeability of the coal is 0.17 md;when the depth of the coal seam is less than 1000 m,the permeability with a large change range.Therefore,the range of permeability of the deep coal seam is not large.The buried depth of coal seam is positively correlated with the minimum principal stress,while the minimum principal stress is negatively correlated with the permeability of coal reservoir.The influence of thermal evolution on coal and gas production is mainly through the influence of the percentage content of the coal and rock organic hole and then affects the permeability of coal seam.With the increase of buried depth,the thermal evolution degree increases.However,the contribution of thermal evolution to coal reservoir permeability increases first and then decreases.Therefore,the permeability of coal reservoir increases at first and then decreases with the increase of buried depth.Effect of coal body structure on coal seam gas production can be understood as:due to the extremely low permeability of coal powder,and almost impossible to artificially increase the permeability and therefore the development of pulverized coal in the coal seam has great influence on the exploitation of the coal bed methane;The tectonic coal in No.15 coal seam is more than that in No.3 coal seam and in the deep coal seam is more than that in the shallow coal seam.