Geochemical Triggers of Coal and Gas Outbursts Derived From Rock-Eval Thermolytic Analysis

Abstract

Purpose. Investigation of the conditions for the occurrence of coal and gas outbursts from a geochemical point of view. Methodology. The paper examines and analyses the results of determining bituminous and hydrogen indices using the Rock-Eval thermolytic analysis method on safe and dangerous areas of coal seams in terms of coal and gas outbursts. Results. It was established that on safe mining seams, coal samples are within the oil window, where microcracks in the coal mass may still contain films of sorbed bituminous components (liquid hydrocarbons), which counteract the accumulation of energy of elastic deformations and the localization of gas accumulation. However, the transition from the area of liquid hydrocarbon generation to the gas window leads to a sharp increase in the volume of generated hydrocarbon gases, mainly due to the cracking of liquid hydrocarbons, that is, the emergence of geochemical triggers for the localization of coal and gas outbursts during coal mining. Scientific novelty. The new experimentally determined values of bituminous and hydrogen indices for coal seams of the Donetsk basin, and their comparison with the results within safe and dangerous mining seams, demonstrate the fact that all the studied coal samples from outburst-prone areas geometrically lie in the area of the gas window, starting from the moment of cracking of already formed liquid hydrocarbons and subsequent generation of dry hydrocarbon gases (mainly methane) due to the thermal degradation of higher carbon compounds first, and then low carbon compounds (wet hydrocarbon gases) and direct generation from the kerogen matrix. Practical significance. Established geochemical criteria that determine the conditions for the occurrence of gas-dynamic phenomena - outbursts of coal and gas during coal mining. Key words: coal and gas outbursts, bitumen index, hydrogen index, microcracks, hydrocarbon generation, gas window.