Abnormal coal seam gas occurrence characteristics and the dynamic disaster control technologies in the magmatic rock intrusion area

To study the effect of magmatic rock occurrence on coal gas dynamic disasters, the thermal metamorphism of magmatic rocks intruding into coal measure strata and the variation of coal chemical structural and physical properties are studied comprehensively using the methods of theoretical analysis, laboratory testing, numerical simulation and engineering practice. Then, the mechanism of coal and rock gas dynamic disasters under the conditions of magmatic rock occurrence is discussed and the key control technologies are proposed. The results show that(1) the magma cools and transfers heat to the surrounding rocks through the heat conduction. The thermal evolution and thermodynamic contact metamorphism of magma not only increase the metamorphic grade and make it present the characteristics of zoning distribution, but also result in that the trend of deoxidation, dehydrogenation and carbon enrichment in coals become gradually evident.(2) The tectonic stress caused by the magmatic rock intrusion and the thermal evolution of magma is easy to cause the tectonic coalification of the underlying coal seams and the pores in coals are severely damaged. These result in the increase of the coal pore volume and specific surface area, and the enhancement of the ad-/desorption ability of coals to gas.(3) In the magmatic rock occurrence area, the secondary hydrocarbon generation in coals and the trap effects of the tight magmatic rocks result in that the gas content and gas pressure of the underlying coal seams increase greatly, which increases the risk of the coal and gas outburst.(4) When the impact load produced by the thick and hard magmatic rocks breakage is applied to the underlying coal seams, the stress superposition is equivalent to the increase of the buried depth of coal seams and causes the plastic failure of coals. In addition, the energy superposition makes the potential disaster-causing energy of coal and gas increase, which is the main factor of the coal gas dynamic disaster. On this basis, the sensitive index system and the control technologies for the accurate prediction of coal and rock dynamic disasters in the magmatic rock intrusion area were put forward combining with the occurrence characteristics of coal seams and gases.