四川盆地奥陶系油气地球化学特征及成藏模式

四川盆地奥陶系油气勘探至今未获得突破,目前已发现的少量油气发现主要集中在下奥陶统南津关组和顶部宝塔组致密灰岩,由于从中获得的地球化学信息有限,制约了对奥陶系油气成藏的认识与研究。近期在奥陶系岩石样品中获得了油苗样品,为奥陶系成藏条件的深入研究提供了重要信息。通过对四川盆地北部毛坝河剖面奥陶系宝塔组生屑灰岩中发现的液态轻质油苗开展深入分析,综合运用饱和烃色谱、碳同位素组成、包裹体特征分析等方法,对比了川北地区河深1井,川中地区古隆起以及川东南地区东深1井等奥陶系成藏条件,初步明确了川北地区与川东南地区宝塔组油气来源于上覆的五峰组、龙马溪组烃源岩的供烃,具有上生下储型成藏特征;川中古隆起奥陶系油气主要接受来自下伏寒武系烃源岩的供烃,为下生上储型成藏模式。研究将进一步明确四川盆地奥陶系油气勘探潜力和方向。

Geochemistry and accumulation model of Ordovician hydrocarbon in Sichuan Basin

Oil and gas discoveries of Ordovician in Sichuan Basin are mainly concentrated in the compact limestone of Nanjinguan Formation at the bottom of Ordovician and Baota Formation at the top of Ordovician,which is characterized by fractured hydrocarbon. It is difficult to obtain samples and to study the reservoir-forming condition furtherly. Recently,oil seepage has been obtained from Ordovician rock samples,which provides important evidences for the further study of Ordovician reservoir-forming conditions. Through the analysis of liquid oil seepage found in bioclastic limestone of Ordovician Baota Formation in Maobahe section of northern Sichuan Basin,saturated hydrocarbon chromatography,characteristic analysis of inclusions and carbon isotope analysis have been comprehensively applied. By comparing the Ordovician reservoir-forming conditions of Well Heshen-1 in northern Sichuan,paleo-uplift in central Sichuan and Well Dongshen-1 in southeastern Sichuan,it is clear that the hydrocarbon of Baota Formation in northern and southeastern Sichuan originated from the overlying source rocks of Wufeng Formation and Longmaxi Formation,which have the mode of generating in the underlying formation and storing in the overlying strata. Ordovician hydrocarbon,situated in paleo-uplift in central Sichuan mainly,receives hydrocarbon from the underlying Cambrian source rocks,forming a mode of generating in the overlying formation and storing in the underlying strata. These conclusions would provide a reference for Ordovician hydrocarbon exploration prospects.