Gas desorption index of drill cuttings affected by magmatic sills for predicting outbursts in coal seams

摘要

Magma intrusion events accelerate the thermal evolution of coal seams, which could change their adsorption-desorption characteristics and increase the outburst risk. To study the effects on the coal seam desorption index of drill cuttings under the magmatic sill, we compared and analyzed multiple physical parameter variations and desorption characteristics of the no. 10 coal seam in the normal and thermal evolution zone in the Haizi and Yangliu mines under a thick sill. Lab simulation, theoretical analysis, and field validation were used for determination of the coal seam gas desorption index. The results indicated that the metamorphic grade of the no. 10 coal seam is increased under the sill, and the coal sample desorption rate and desorption quantity were enhanced by the sill's heat effect, which could also make the coal seam gas desorption index of the drill cutting indexes Delta h(2) and K-1 based on desorption characteristics increase, in addition to increasing the coal risk. The influence on gas desorption indexes Delta h(2) and K-1 could be reflected by the value D which shows a proportional trend; the effect on the coal seam of the Haizi coal mine with a 120-m-thick sill is stronger than in the Yangliu mine with approximately 70 m. In addition, with the increase in the thickness of the sill, the gas desorption index becomes larger; the Delta h(2) of the no. 10 coal seam could have higher reliability than K-1 in the normal and thermal evolution area. And the linear relationship between Delta h(2) and K-1 will not change under different situations.