关键词: 鄂尔多斯盆地, 下古生界, 碳酸盐岩, 平凉组, 烃源岩, 油气成藏

Abstract:

The carbonate rock in Lower Ordovician Majiagou Formation of Ordos Basin is ineffective source rock because of its turbulence and rich-oxygen environment resulting in low organic matter abundance, inferior kerogen type and low hydrocarbon generation potertial. But the geological and geochemical analyses showed that there existed a set of high quality marine source rock in the platform slope facies of Middle Ordovician Pingliang Formation. The oil and gas generated from the source rock of Pingliang Formation was accumulated firstly in the central Palaeo-uplift and its surrounding regions. The thermogenic asphalt in palaeo-uplift carbonate reservoir indicated that oil accumulation completed transition from oil to gas in the Lower Crataceous. Along with the palaeo-uplift axis convection and the formation of westward monocline in the Late Crataceous, gas from the palaeo-reservoir was finally accumulated in the weathering crust of Majiagou carbonate reservoir. Pingliang series in southern and western margins of Ordos Basin was provided to be the main source for oil-type gas in Jingbian Gas Field.

Key words: Ordos Basin, Lower Paleozoic, carbonate rock, Pingliang Formation, source rock, oil and gas accumulation