Relations between tectonic evolution and coalbed methane content in Gushan coal mine of Xinggong coalfield

Abstract：The study of coalbed methane content and its controlling factors is the foundation of gas hazards forecasting and coalbed methane exploitability assessment.Based on data obtained from coal and coal mine exploration, and measured data, there is osculating relation between coalbed methane content and tectonic evolution in the area, where the burial depth of No.II1 coal seam is more than 200 m in the east of Gushan coal mine.The first hydrocarbon generation occurred with a normal paleogeothermal gradient during the end of Triassic.From the late Jurassic to the end of Cretaceous, the hydrocarbon generation reached its peak during Yanshanian orogeny caused an abnormal thermal event, which established the foundation of high gas content.The theoretic adsorption capacity is less than 15m3/t.From the late Cretaceous to the forepart of Himalayan orogeny, the groundwater migrated from the south to the deep part because the Songshan mountain was continually uplifted in the south.The coalbed methane in the shallow coal seam migrated to the deep part, and accumulated in the deep stagnant zone.In this period, The hydrodynamic was decided by techtonic setting, which controlled the migration and accumulation of coalbed methane.The coal body was seriously destroyed because of sliding structure which formed in the late Tertiary.The permeability of coal reservoir reduced which increased the adsorption capability of coal.The mylonitic coal zone formed along with sliding structure surface, which prevented coalbed methane diffusing.There probably existed hydrocarbon generation that caused by dynamometamorphism, to complement coalbed methane content.

Keyword：Gushan coal mine;tectonic evolution;coalbed methane;gas content;