Quantitative Characterization of Coal Shale Pores and Fractures Based on Combined High-Pressure Mercury Pressure and Low-Temperature N2/CO2 Adsorption Methods

Coal shale gas is an important type of shale gas. The microscopic pore size distribution and pore structure characteristics of coal shale determine the macroscopic storage and transportation of coal shale gas. In order to quantitatively characterize the microscopic pore size distribution and pore structure properties of coal shale from a multiscale perspective, the pore size distribution and pore structure of coal shale specimens with different grain sizes were quantitatively characterized using low-temperature N-2/CO2 adsorption and high-pressure mercuric pressure methods, taking the coal shale of high-gas mines of the Dongbaowei Mine in the Shuangyashan Basin as the object of study. The pore size distribution fractal pattern and pore structure characteristics of coal shale were quantitatively analyzed by the joint characterization method of the coal shale pore fractal theory and pore size distribution. Relevant experimental studies found the following: (1) The specific surface area and volume of coal shale pores and fractures decrease gradually with the increase in coal shale grain size. (2) The pore size distribution of coal shale has obvious fractal characteristics at the stages of high and low mercury pressures, and the demarcation point of medium and large pores is 55 nm. (3) The difference in pore and fracture structural parameters between coal shale with different grain sizes and the original rock specimens is relatively small, and it is feasible to study the general rules of gas adsorption, desorption, diffusion, and seepage in the pores and fractures of coal shale by using coal shale shapes instead of the original rock specimens.