Structural and fractal characterization of adsorption pores of middle–high rank coal reservoirs in western Yunnan and eastern Guizhou: An experimental study of coals from the Panguan syncline and Laochang anticline

Abstract

To better understand the structural characteristic of adsorption pores (pore diameter < 100 nm) of coal reservoirs around the coalbed methane production areas of western Yunnan and eastern Guizhou, we analyzed the structural and fractal characteristics of pore size range of 0.40-2.0 nm and 2-100 nm in middle-high rank coals (R o,max ¼ 0.93-3.20%) by combining low-temperature N 2 /CO 2 adsorption tests and surface/volume fractal theory. The results show that the coal reservoirs can be divided into three categories: type A (R o,max < 2.15%), type B (2.15% < R o,max <2.50%), and type C (R o,max > 2.15%). The structural parameters of pores in the range from 2 to 100 nm are influenced by the degree of coal metamorphism and the compositional parameters (e.g., ash and volatile matter). The dominant diameters of the specific surface areas are 10-50 nm, 2-50 nm, and 2-10 nm, respectively. The pores in the range from <2 nm provide the largest proportion of total specific surface area (97.22%-99.96%) of the coal reservoir, and

Volume and Surface Distribution Heterogeneity of Nano‐pore in Coal Samples by CO2 and N2 Adsorption Experiments

“…3. Compared with adsorption pore size distribution of coal samples in the same study area calculated by the DFT model (Zhang et al, 2018), the pore size distribution interval calculated by the BJH model is larger, which is related to the different calculation principle.…”

“…The sampling area, the Western Guizhou and the eastern Yunan Province, is an important coal production base and has abundant CBM resources (Yang et al, 2018;Xu et al, 2019;Zhang et al, 2018). The Tucheng and the Laochang coal mining areas are located in the Southwest and Northeast of the region, respectively (Fig.…”

“…The LPN 2 and CO 2 GA were simultaneously conducted on the nine solid samples using a Quanta Chrome Autosorb-1 physical adsorption instrument. Data processing process can be found in Zhao et al 2016 andZhang et al 2018. It is noted that Barrett-Joyner-Halenda (BJH) model is adopted to analyze the pore volume and specific surface area distribution of pore with diameters within 2~100nm.…”

“…However, there are relatively few studies on the fractal characteristics of pore surface areas. and Zhang et al (2018) studied the structure and fractal characteristic of micro-and meso-pores in low, middle and high rank tectonically deformed and primary coals based on the theory of surface and volume fractal analysis. However, the study on the relationship between surface fractal and volume fractal is not sufficient.…”

“…However, the study on the relationship between surface fractal and volume fractal is not sufficient. Zhang et al (2018) systematically studied adsorption pore structure and volume distribution heterogeneity of middle and high rank coal samples collected from Western Guizhou and eastern Yunnan. This paper focuses on the detailed description of the distribution heterogeneity of adsorption pore volume and specific surface area of typical coal samples collected from same study area.…”