CONTROL EFFECT OF COAL METAMORPHIC DEGREE ON PHYSICAL PROPERTIES OF COAL RESERVOIRS

Through analyzing the results of mercury injection experiments and static cryogenic nitrogen adsorption experiments,this paper discusses the control effect of coal metamorphic degree on the physical properties of coal reservoirs. The following understandings are obtained. a. the porosity values of coal samples obtained from mercury injection experiments show a trend of high-low-high variation along with the rising of coal rank; b. pores with an average diameter of throat smaller than 1 μm are extensively distributed in coal samples of various coal ranks,while that with an average diameter of throat larger than 1 μm are extensively distributed only in coal samples of medium and low coal ranks,and are rare in anthracite. c. for coals of medium and low ranks,their specific surface area measured through cryogenic nitrogen test lowers progressively along with the increase of metamorphic degree,while for anthracite,their specific surface area increases. It is concluded that the porosity of coal,pore structure and specific surface area are all controlled by metamorphic degree and they change abruptly on the border between bituminite and anthracite.