LNMR Study on Microstructure Characteristics and Pore Size Distribution of High‐Rank Coals with Different Bedding

Abstract

In order to study the pore structure characteristics of high-rank coals with different bedding, NMR experiments were carried out for high-rank coals with different bedding angles (0°, 30°, 45°, 60°, and 90°). The results show that the distribution of T2 map of high-rank coal with different bedding is similar to some extent, showing a double peak or triple peak distribution, and the first peak accounts for more than 97% of the total, indicating that small holes are developed in high-rank coal with different bedding, while macropores are not developed. The influence of bedding angle on the fracture proportion is less than 0.3%. Compared with the fracture proportion, the effect of bedding angle on the proportion of microhole, medium hole, and large hole is greater and presents a certain rule. There are certain differences in T2 cutoff value (T2C) of high-rank coal with different bedding. The relationship between bedding angle and T2C conforms to exponential function, and the correlation degree R2 is 0.839. The research results provide a theoretical basis for gas extraction and utilization and prevention of gas disaster in coal mines in China.

Evolution Characteristics of Coal Microstructure before and after Supercritical CO2 Treatment Based on the L-Weighing-LNMR Method

“…Since this experiment uses a uniform magnetic field, the effects of free relaxation and diffusion relaxation can be disregarded, and the transverse relaxation time is equal to the surface relaxation time Equations and were combined to give the following expression 1 / T 2 = ρ 2 ( S / V ) …”

“…Since this experiment uses a uniform magnetic field, the effects of free relaxation and diffusion relaxation can be disregarded, and the transverse relaxation time is equal to the surface relaxation time. 30 Equations 1 and 2 were combined to give the following expression (3) Assuming that the pore structures inside the coal all have simple shapes, 31 eq 4 is applied (4) where F S is the pore shape factor and r is the pore radius. Equations 3 and 4 can be combined to get (5) Given that C = ρ 2 F S , eq 6 is expressed as (6) where C is the conversion coefficient, C > 0.…”

Dynamic Tensile Mechanical Properties of Outburst Coal Considering Bedding Effect and Evolution Characteristics of Strain Energy Density

“…Li et al [16][17][18] investigated the effect of circumferential pressure and bedding angle on the mechanical properties of coal. Liu et al [19,20] carried out LNMR and NMR studies of the microstructural characteristics and pore size distribution of high-grade coals with different bedding structures. Influence of bedding on the fracture pattern of the coal mass during blasting was investigated Zhao et al [21].…”