Effect of Magma Intrusion on Coal Gas Outburst Indexes in China

Numerous coal and gas outburst disasters in China were caused by magma intrusion. Several outburst accidents show that the affected region of magma intrusion is the key area with abnormal gas occurrence and gas outburst disasters. The intrusive igneous rock’s occurrence, lithology and distribution form have an important impact on outburst indexes. Laboratory tests and field experimental research, analysed coal reservoirs adsorption characteristics under the function of high temperature pyrolysis and metamorphism caused by layered magma intrusion, and revealed internal relations between coal seam adsorption characteristics and outburst indexes, which were verified in the field. The results showed that under the additive effects of pyrolysis and metamorphism, the metamorphic degree of the coal seam got higher the closer the distance to the igneous rock, the adsorption characteristics of the metamorphic coal were positively correlated with gas outburst indexes. When the magma layer eroded the coal seam, along with the distance from the igneous rock, gas outburst indexes increased first, then decreased. When the layered magma intruded into the coal seam roof, coal seam gas was trapped by igneous rock, and gas outburst indexes were commonly higher, which decreased with the distance away from the igneous rock. When the layered magma intruded into the coal seam floor, the effect of high temperature pyrolysis was the strongest, and the gas outburst indexes were determined by the lithological characters of the roof.