Analysis on pore structure characteristics and influencing factors of coal reservoir in Yushe-Wuxiang Block

To study the reasons for controlling high productivity of coalbed methane wells in low porosity and low permeability coal reservoirs,the coal reservoirs of Shanxi and Taiyuan Formations in Yushe - Wuxiang Block located in the central and eastern Qinshui Basin were studied. The pore structure characteristics and influencing factors of coal reservoirs were studied and analyzed by scanning electron microscopy (SEM) electronic imaging technology and the cryogenic liquid nitrogen adsorption experiment. The results show that the nano-scale pores of coal reservoirs mostly developed in the vitrinite group while a few of them developed in the inverting group. Among them, the metamorphic pore is the most widely encountered. The protogenetic pores and mineral pores also developed. The pore morphology is mainly ink-bottle holes and slit holes. The average specific surface area of coal reservoir is 1.342 9 m2/g, and the average pore volume is 0.005 0 cm3/g. Additionally, the average pore diameter is 15.744 2 nm. The influent capacity of pore system is poor. The contribution of specific surface area is dominated by micropores. The specific surface area shows a simple increasing trend as the metamorphism deepened and the percentage content of the vitrinite increased. However, the coal structure is the most important factor in influencing the pore volume and pore diameter. The pore volume and pore diameter of fractured coal are apparently higher than that of the protogenetic coal.