Coal Bed Methane Physical Properties Of Reservoir Strata,Concentration Law And Evaluation For Exploration And Development Of Tiefa Coal Field

Coal bed methane is a new type of clean energy and high quality chemical raw material.The development and utilization of coal bed methane can not only alleviate the contradiction between supply and demand of natural gas in China,but also improve the conditions of mine safety production and help to protect the environment.Therefore,it is of great significance to study the control factors of CBM enrichment and the optimal selection of development blocks.Based on geology,seepage mechanics and experimental mechanics,this paper analyzes the geological characteristics of Tiefa coal field and coal bed by combining theory research,numerical simulation analysis and field production data.Through experiments to reveal the law of coal bed methane occurrence and migration,identify the selection evaluation index,establish a mathematical evaluation model for selecting exploration and development blocks,and predict the production capacity for coal bed methane,which provide basis for coal bed methane ground mining.Through a lot of investigation and in-depth analysis,it is clarified that the geological characteristics of coal bed methane in the study area are:(1)The Daxing Coal Mine,located in the southwest of the basin,is the central subsidence area of the basin.It is also the developing area of the rich coal belt and the distribution area of gas coal.(2)The coal bed thickness in the study area is large,there are many seam layers,the gas content of coal bed is stable,and the minable amount of resources is large.(3)The magmatic intrusion has important contribution to the formation and storage of coal bed methane,mainly in increasing the coal rank,increasing the amount of coal bed formation,increasing the storage space and gas content of coal bed methane,and improving the permeability of coal reservoir.(4)According to the regional tectonic stress field,the faults are all positive faults,the fault mud is developed,the sealing property is good;At the axial part of the fold,the fracture zone shows obvious directionality,and the main fissure in the NW direction perpendicular to the axial development of the primary fold in the area is the dominant position of permeability.(5)Coal bed cleat development,connectivity and permeability is better.(6)The buried depth of coal bed is moderate and has better cover shield.The above geological conditions provide an important guarantee for the feasibility of CBM development in the study area.By domestic and foreign investigation and SEM micro-test,permeability test,adsorption and desorption experiment,it is revealed that the pores and intergranular pores in the coal of the study area are distributed in large quantities and connected with each other;the pore types are mainly mesopores,small pores and micropores,which are the main occurrence space for methane adsorption.The adsorption,desorption and migration of coal bed methane in the reservoir are as follows: the adsorption capacity of coal to gas is positively correlated with the pressure and negatively correlated with the temperature;when the desorption temperature of coal is fixed,the higher the adsorption equilibrium pressure is,the greater the total amount of gas desorption with the increase of temperature,the amount of gas adsorption decreases and the amount of desorption increases;As the confining pressure increases,the permeability of the coal sample shows an exponential decreasing trend;the seepage of gas in the coal body has a significant Klinkenberg effect.When the ratio of pore pressure to volume stress is small,the permeability of the coal sample decreases with the increase of gas pressure;as the gas pressure increases,the influence of temperature on the permeability of the coal sample decreases gradually.On the basis of analyzing the favorable conditions of coal bed methane development in each mine in the study area,it is determined that the gas potential,reservoir physical properties and preservation conditions are the first grade indexes of coal bed methane selection evaluation,and the coal bed thickness,coal metamorphism degree,gas content,porosity,coal bed permeability,buried depth,roof lithology,tectonism,hydrogeology and so on are the second grade indexes,and the quantitative criteria of evaluation indexes are determined.A hierarchical analysis-entropy weight-fuzzy mathematical comprehensive evaluation model is established,and the prospect of coal bed methane resource development in each mine is evaluated.The top three priority areas for exploration and development are Daxing,Dalong and Xiaonan Mines.The paper has 65 pictures,57 tables and 145 references.