Nanoscale Pore Structure Characteristics of Deep Coalbed Methane Reservoirs and Its Influence on CH4 Adsorption in the Linxing Area, Eastern Ordos Basin, China.

The high gas content of deep coal seams is a driving force for the exploration and development of deep coalbed methane (CBM). The nanoscale pores, which are the main spaces for adsorption and storage of CBM, are closely related to the burial depth. Based on integrated approaches of vitrinite reflectance (Ro), maceral composition, scanning electron microscope (SEM), proximate analysis, fluid inclusion test, low-temperature N2 adsorption-desorption, and CH4 isothermal adsorption, the nanoscale pore structure of coals recovered at depths from 650 to 2078 m was determined, and its influence on the CH4 adsorption capacity was discussed. The results show that the coal rank has a good linear relationship with the current burial depth of the coal seams; that is, the influences of the burial depth on the coals can be reflected by the influences of the coal rank on the coals. With the increase in the coal rank, the moisture and volatile content decrease, and the fixed carbon content increases. The variation in the pore volume and specific surface area with the increase in the coal rank can be divided into two stages: the rapid decline stage (when 0.75% 1.0%, the FD of the micropores is close to 2. This indicates that with the increase in the degree of coalification, the surface of the micropores is simpler. The above results show that the gas adsorption capacity of coal first slightly decreases (when 0.75% < Ro < 1.0%) and then increases (when 1.0% < Ro < 1.35%), and the coincident results are shown in the Langmuir volume (VL) test results.