The origin and formation of CO2 gas pools in the coal seam of the Yaojie coalfield in China

High concentrations of CO2 have been observed in the No. 2 coal seam in the Yaojie coalfield. A number of instantaneous CO2 outbursts occurred during coal mining. The CO2 concentration range in the eastern coalfield is 18.79 to 96.6%. The delta C-13(CO2) values are mainly in the range of -5.0 parts per thousand to +1.0 parts per thousand (PDB), suggesting an inorganic origin of CO2. The He-3/He-4 ratios are (0.6-25.9) x 10(-8), and the R/Ra is 0.0042-0.185, which is a characteristic of crust-derived CO2 gas. The dynamic-thermal metamorphism of the F19 ductile-brittle shear zone is believed to result in the release of CO2 from basement marble formations, which show an inorganic source of CO2 in the Yaojie coalfield. The regional geological evolution and multi-periodical F19 fault movement control the formation, migration, and accumulation of the CO2, in addition to the development of CO2 gas pools in the Yaojie coalfield. The F19 fault played multiple roles in the generation, transport, and sequestration of gas during the CO2 formation. The displacement of CH4, carbonate generation, and pore structure transformation of coal due to a series of physical and chemical effects occurred after CO2 flux into the coal seams. (C) 2010 Elsevier B.V. All rights reserved.