An Research On The Physical Properties Of Different Rank Coal Reservoirs

Coalbed methane (CBM) is an unconventional gas resource which is self--generation and self-bearing, and CBM is priority occurrenced with adsorption state in the rock’ pore—fissure system of coal bed. When there is CBM in the coal seam, it can be called the coal reservoir. Coal reservoir has many physical properties, such as coal and rock features、hole crack characteristics、permeability and adsorption, ect. In the numerous influencing factors of coal reservoir physical property, coal rank (coal metamorphic degree) is the main controlling factors.The dissertation based on sampling different rank coal samples under regional metamorphism and magmatic thermal metamorphism in North China permo--carboniferous coal-bearing area, and they had been done the same experiment testing in laboratory, including:coal rock maceral test, the coal industrial analysis, fluorescence microscope fracture observation, mercury injection experiment, adsorption of nitrogen in low temperature、low temperature nitrogen isothermal adsorption experiment. On the basis of careful analysis for the experimental datas, Increased along with the coal rank, the changing rule of coal reservoir physical properties are discussed. Through research, come to the following conclusions:(1) Mercury injection experiment datas show that increased along with the coal rank, changing rule of coal reservoir porosity is "high—low—high"; Pore throat diameter decreases; Expulsion pressure increasing; The tendency of the sorting coefficient is "little·big—little".(2) Low temperature nitrogen adsorption test datas show that increased along with the coal rank, BET specific surface area, and BJH cumulative increase specific surface area are decreased at the first, then increase. According to adsorption/desorption curve shape, it can be divided into four categories.(3) Low temperature nitrogen isothermal adsorption test data show that the adsorption ability of different ranks coal under regional metamorphism is overall weaker than he coal sample under magmatic thermal metamorphism.The factors that affect adsorption ability include:coal rank,water,ash, carbon content and coal maceral.