The impact of magmatic intrusion on the microscopic composition and pore structure of coal seams in the Kailuan coalfield

With the continuous growth in global coal demand, the impact of magma intrusion on coal micro-components, pore structure, and gas storage characteristics has gradually become a significant factor influencing the economic efficiency and safety of coal mining operations. This study focuses on the Qianjiaying, Lvjiatuo, Fangezhuang, and Linxi mines in the Kailuan mining area, systematically analyzing the mechanisms of magma intrusion and its potential threats to mining safety. The study reveals that the impact range of vitrinite reflectance changes is smaller than the actual thermal influence range of magma. Magma intrusion causes significant changes in coal micro-components, particularly the carbonization of vitrinite and inertinite, as well as a marked increase in natural coke. Vitrinite is notably more sensitive to thermal effects than inertinite. Additionally, magma intrusion alters the pore structure of coal seams through thermo-mechanical coupling, significantly affecting the development of mesopores and micropores. The results show that as the distance from magma increases, micropores first increase, then decrease, and later increase again, while mesopores rapidly decrease and eventually stabilize. In areas close to the magma, pore structures tend to become more uniform, while those further from the intrusion gradually return to normal. Furthermore, magma intrusion enhances the secondary hydrocarbon generation in coal seams, producing large amounts of gas. The form of magma intrusion, whether continuous or discontinuous, has different effects on gas accumulation and release: continuous magma beds facilitate gas accumulation, while discontinuous magma dikes cause gas to escape. The findings provide important theoretical insights for coal mining, utilization, and gas prevention strategies. • Magmatic intrusion alters macerals: vitrinite reflectance zone < thermal zone; vitrinite rises, inertinite stable, coke enriched. • Intrusion reshapes pores: temperature drives maturity, pressure compresses; mesopores shrink, micropores rise then decline to stable. • Intrusion controls gas: heating boosts CH₄, CO₂; porosity loss limits adsorption; beds trap gas, dikes let gas escape.