Low Nuclear Magnetic Resonance Experimental Study on Gas Adsorption of High-Rank Coals with Different Beddings

Abstract

In order to deeply study the influence of the coal bedding structure on coal gas adsorption, low nuclear magnetic resonance (LNMR) and a confining pressure loading system were used to carry out the LNMR experiment of gas adsorption of high-rank coals with different beddings under different confining pressures. The results showed that the amount of gas adsorption of high-rank coals with different beddings increases with time and decreases with the increase of confining pressure. In the process from low confining pressure to high confining pressure, the coal sample with oblique bedding (bedding angles 30°, 45°, and 60°) has the largest average increment of gas adsorption, followed by the coal sample with vertical bedding (bedding angle 90°), and the coal sample with parallel bedding has the smallest increment of gas adsorption (bedding angle 0°). The linear function relation between the different-bedding high-rank coal gas adsorption state and the confining pressure is y = a – bx . The relation between the free peak area and the confining pressure conforms to the exponential function y = a + b exp( cx ). Different-bedding high-rank coal adsorption peaks and the peak area decrease with the increase of confining pressure, and the free peak continues to move to the left; that is, the large pores gradually shrink. With the increase of angle and bedding, the area of the adsorption peak increases first and then decreases, presenting an “inverted V” shape on the whole. The area of the free peak decreases first and then increases, presenting a “V” shape on the whole.

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

“…The experimental methods used for testing the microstructural changes in coal include high-pressure mercury intrusion, − low-temperature liquid nitrogen adsorption, − low-pressure CO 2 adsorption, − and low-field nuclear magnetic resonance (LNMR). − Among these, the high-pressure mercury intrusion, low-temperature liquid nitrogen adsorption, and low-pressure CO 2 adsorption methods cause secondary damage to the coal, which affects the accuracy of the experimental results, while the LNMR method is nondestructive, continuous, and quantifiable, and it better reflects the pore size distribution of the coal. − In this study, coal was soaked with supercritical CO 2 , and LNMR was used to characterize the microstructural changes of coal. The LNMR experiment determines the T 2 distribution of dry, water-saturated, and centrifugal coal samples.…”

Experimental Study on the Variation Mechanism of Permeability and Seepage Characteristics of High-Rank Coal with Different Bedding

“…Nowadays, the experiments on the seepage characteristics of coal are mainly carried out from different stress loading conditions, different types of coals, different seepage media, etc. − Among them, most of the experiments that study the relationship between coal permeability and stress. − Such as triaxial seepage tests can be carried out to reveal the seepage characteristics of coal under triaxial stress; − It can also study the evolution mechanism of coal permeability by controlling the cyclic load; − different loading conditions can also be designed to study the seepage characteristics of coal under different stress environments. , In addition to the stress experimental study, there are experimental studies that analyze the relationship between the water saturation of coal and the effective stress coefficient and stress sensitivity by controlling the different water saturation of coal and comparative seepage experimental studies that control different seepage media. , These experimental studies can reveal the seepage characteristics of coal. However, it can be seen that these experiments are all based on the external environment of coal.…”

Anisotropic Flow-Solid Coupling Model for Gas Extraction from Cis-Layer Boreholes and Its Application

“…In terms of numerical simulation, the influence of ground stress factors on permeability is very significant, and a multistage pore fluid–solid coupling model considering the influence of ground stress factors on gas seepage is established; , flow-solid coupling mathematical models of coal and gas protrusion considering moisture, stress damage, and permeability coefficient factors are established; − flow-solid coupling models of multiphysical field coupling considering different physical field factors are established; , experimental study of coal permeability was carried out under consideration of effective stress, matrix expansion/contraction, and gas slip factors, , and then, matrix expansion/contraction factors were provided to the coal seam gas transport flow-solid coupling model. , In terms of gas extraction from boreholes, the extraction radius of underground gas extraction boreholes is deduced by numerical simulation method and verified on site; , gas migration characteristics of coal seam considering high-stress factors are studied, and the mechanism of gas extraction efficiency improved by pressure relief mining technology is further elaborated; considering the influence of the number of boreholes on gas extraction, the pressure sensor was used to monitor the change of gas pressure under a different number of boreholes; the theoretical equation of the plastic zone radius considering the plastic deformation factor was established, and the effective radius of gas extraction in the plastic zone was determined; considering the factor of water content, different water content factors are provided to study the change of gas pressure in coal seam gas extraction . In terms of laboratory experimental research, different physical and chemical factors of the coal body are considered to carry out experimental studies on the seepage characteristics of different coal steps, and the gas transport characteristics of the coal body under different fracture scales are studied. − Based on the self-developed coal triaxial seepage instrument and low-field NMR instrument, the adsorption characteristics and pore size distribution characteristics of different coal ranks were studied, and the seepage characteristics of different bedding coal bodies were obtained. − From microscopic and macroscopic perspectives, it can reveal the coal pore size distribution and gas transport characteristics comprehensively from microscopic and macroscopic perspectives, which is of guiding significance for coal seam gas extraction.…”