STUDY ON THE SOURCE OF NATURAL GAS IN ORDOVICIAN IN TABAMIAO AREA OF NORTH ORDOS BASIN

In Tabamiao area of northern Ordos Basin, natural gas is widespread in Ordovician.However, the commercial gas is mainly produced from the weathered crust lying at the top of Ordovician. In order to track the origin of gas in Ordovician,associated condensate and indigenous gas in Ordovician carbonate source rock in upper and lower Paleozoic were correlated from such geochemical characteristics as component, compounds and isotope.Detailed study showed that (a) the commercial gas in Ordovician weathered crust in northern Tabamiao was originated mainly from coal-bearing source rock in upper Paleozoic, (b) the non-commercial gas in Ordovician in southern Tabamiao is formed on the spot, and (c) the gas below salt bed in Ordovician is also formed on the spot. The author suggested that both Ordovician weathered crust and upper Paleozoic are the superior objects for gas exploration in northern Tabamiao and upper Paleozoic is the only one of object for gas exploration in southern Tabamiao.