论鄂尔多斯盆地下古生界烃源岩的成藏演化特征

鄂尔多斯盆地中东部广布的下奥陶统马家沟组碳酸盐岩形成于动荡、富氧的古地理环境,因而其有机质丰度低，有机质类型差，生烃潜力低，不能成为有效烃源岩。地质和地球化学分析证实，盆地西、南缘台缘深水斜坡相的中奥陶统平凉组存在优质海相烃源岩，其形成的油气最早富集在中央古隆起及其周围；伴随着中央古隆起带轴部的向东迁移和早白垩世末盆地西倾大单斜的定型，平凉组烃源岩在早白垩世生烃高峰期生成的天然气和早期古油藏裂解气，由中央古隆起带向北东方向发生二次运聚，最终在盆地中部奥陶系马家沟组风化壳中聚集成藏，即形成靖边大气田。这一过程包含了油藏、油气共存和气藏3个成藏演化阶段，也证实了盆地西、南缘平凉组烃源岩是靖边气田油型气的主要来源。

Discussion on evolution of source rocks in Lower Paleozoic of Ordos Basin

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.