95 / 2023-06-14 23:41:38

Study on variation characteristics of coal pore and fractures affected by carbon disulfide

carbon disulfide; pore and fracture; experimental measurement

    China's coal mining is gradually moving to the deep. The characteristics of high ground stress, high gas pressure and low permeability in deep coal seams make gas extraction more difficult and the extraction efficiency lower. Chemical modification of coal is one of the effective methods to improve the efficiency of gas extraction and eliminate the risk of coal and gas outbursts. In this paper, the variation law of pore and fracture structure characteristics of coal under chemical modification is studied by means of laboratory experiments and theoretical analysis. The experimental platform of chemical reagent-modified coal was built, and carbon disulfide was selected as the main experimental solvent. Based on the nuclear magnetic resonance test technology, the quantitative analysis of pore structure change of coal after solvent treatment was realized. Based on the ultrasonic testing technology, the relationship between different solvent treatments and the longitudinal wave velocity of coal was analyzed, and the variation characteristics of coal fractures under solvent treatment were obtained. Based on scanning electron microscopy, the changes in pore fractures in coal samples before and after chemical reagent treatment were observed intuitively by the image method. The main conclusions are as follows :

1. In terms of the effect of chemical solvent treatment on the pore structure characteristics of coal, the effect of carbon disulfide solvent on the erosion of different coals is different, but it can promote the development of pores of all sizes in coal. The results of nuclear magnetic resonance experiments show that carbon disulfide treatment has the best effect on promoting the pore development of lignite, and T2 spectrum corresponding to the medium and large pores increases significantly. After 12 h of solvent treatment, the degree of porosity increase of coal samples from large to small is lignite > bituminous coal > anthracite. It shows that solvent treatment can effectively improve the pore structure of coal.

2. In terms of coal fracture changes, after solvent treatment, the longitudinal wave velocity of three kinds of coal has different degrees of attenuation, while the ultrasonic attenuation coefficient ( α value ) and the ultrasonic attenuation ratio ( β value ) have different degrees of increase. It shows that carbon disulfide solvent treatment promotes fracture development of three coal samples to varying degrees.

3. By observing the different magnification images presented by the scanning electron microscope, the evolution law of microscopic pores and fractures of three coal samples were obtained. The results show that the surface of lignite coal sample is mostly uplifted to form a convex surface, and the surface is attached to many coal particles and rough, with the most developed pores and fractures. The surface of bituminous coal sample develops small and simple pore fractures, and the development degree of pore fractures of anthracite coal sample is the smallest. The characteristics of pore fractures on the surface of three kinds of coal samples are quite different.

   The above experimental results are consistent with each other, which indicates that the effect of carbon disulfide erosion on lignite coal is the best, followed by bituminous coal, and anthracite is the weakest. The relevant research results are helpful to grasp the influence of chemical solvent treatment on the characteristics of coal pores and fractures and reveal the mechanism of coal permeability enhancement, which has important guiding significance for the application of solvent erosion coal permeability enhancement technology. This study can provide a theoretical reference for industrial test analysis, improve the efficiency of coalbed methane mining, and ensure the safety of coal mine production.