Study on the material composition and pore structure characteristics of coal seams after magma intrusion

In order to study the changes in the material composition and pore structure of the coal seam after magma intrusion, the influence characteristics of magma thickness and distance from the coal seam on the coal seam were studied based on FTIR, XRD and LF-NMR, and we also simulated the temperature change process of the coal seam using COMSOL. The results show that magma intrusion decreases the volatile content in coal and increases its ash content and mineral types. The heating of coal seam leads to a decrease in carboxyl content and a slight increase in ester content. V1, H1 and H2 were pyrolyzed, shortening the length of fat chains but not significantly changing the aromatic structure. The thermal environment promotes the pore development in coal, increasing effective porosity and enhancing pore connectivity. With the infiltration of hydrothermal fluid into coal, inorganic minerals change the composition of coal and fill the pores in coal, resulting in the decrease of saturated T2 spectrum area of H1 and V1 samples and weakening pore connectivity, which is unfavorable for the gas migration in coal seams. The samples with simulated temperature below 300 ℃ did not undergo pyrolysis or only slightly pyrolyzed, and the maximum temperature of all samples during the invasion was lower than 600 ℃, and the polymerization degree of aromatic structure in the corresponding samples had no significant change. The greater the magma thickness and the smaller its distance from the coal seam, the greater the degree of thermal evolution of the coal seam, which corresponds to the extension of higher temperature and time affected by high temperature. © 2023 China University of Mining and Technology. All rights reserved.