Source identification of the Jurassic coalbed gas in Huangling area,Ordos basin

There are oil and gas showing in the coal exploration,shaft building and exploitation in the southern Ordos basin,associated with oil type gas,which is different from authigenic coal reservoir. In order to verify this speculation, 220 gas samples are collected from coal seam,roof,floor and the gob and tested,including heavy hydrocarbon content C2+ ,methane carbon isotope δ13 C1 ,methane hydrogen isotope δD and ethane carbon isotope δ13 C2 . The result shows that the origins of coalbed methane are mixed by coal-derived gas and oil type gas. By Schoell plate analysis,oil type mixed gas is composed by pyrolysis condensate gas,biogenic gas and oil-associated gas in coal seams and its surround- ing rocks. The oil type gas migrated from Yanchang formation shale in Triassic system by faults and fissures,and which added the gas content in the coal reservoir.