Influence of tectonic evolution on pore structure and fractal characteristics of coal by low pressure gas adsorption

In the process of tectonic evolution, a comprehensive understanding of pore structure and fractal characteristics of coals with different tectonic degrees is critical. For this paper, the tectonic evolution process of coal is divided into two stages (Stage 1 and Stage 2) and N-2 (77 K)/CO2 (273 K) adsorption methods were conducted. The results show that the original coal-bearing strata underwent multiple periods of stress action, the original stratified stripband structure of the coal was destroyed gradually and formed pulverized coal in the Stage 1. In Stage 2, the original structure of pulverized coal disappeared, fractures in the coal body developed intensively and the internal structure changed greatly, forming tectonic coal with low strength and weak cohesion. The mesopore, macropore volumes and BET specific surface area of coal increase gradually during the tectonic evolution due to the closed and open pores that are connected by constricted pore openings may be destroyed in the Stage 1, and some chemical changes may have occurred in Stage 2, resulting in relatively developed pore structure. However, the micropore structure characteristics of coals first suffered from the closed pores being opened and then collapsed in the Stage 1, and the changes of micropore were not significant in Stage 2. Moreover, the fractal dimension D-1 of coal samples shows a general trend of increasing (from 2.075 to 2.359) and D-2 decreases from 2.683 to 2.469 during the Stage 1 of tectonic evolution, illustrating the pore surface becomes rougher and the irregularity of pore structure gradually decreases. The Stage 2 of tectonic evolution shows the same results. The variations of pore structure characteristics of coal are of great significance for understanding desorption and diffusion characteristics of coal in the process of tectonic evolution.

Automated summary

In the process of tectonic evolution, coal undergoes changes in pore structure and fractal characteristics, with the original stratified stripband structure gradually destroyed and transformed into tectonic coal. The evolution leads to an increase in mesopore, macropore volumes, and BET specific surface area, while the micropore structure experiences opening and collapsing changes. The variations in the coal's pore structure characteristics are crucial for understanding desorption and diffusion behavior during tectonic evolution.