The formation environment,hydrocarbon generating organisms,rock and mineral characteristics of the Middle-Upper Ordovician source rock layers in west margin of Ordos Basin
The Ordovician in the southwest margin of Ordos Basin has developed sedimentary layers with completely different sedimentary characteristics from central-east part of the basin,among them,the west margin developed marine source rocks in Middle-Upper Ordovician.Recent analysis on tectonic sedimentary evolution background of hydrocarbon source rock formation,hydrocarbon generating biological characteristics and rock-mineral characteristics of hydrocarbon layers,show that the development of favorable source rocks is controlled by many factors,and the distribution has certain regularity:1)the main hydrocarbon source rocks of Middle-Upper Ordovician are mainly formed under the structural background of deepening sedimentary water body.The semi deep-water slope environment,where the energy of sedimentary water body is weak and the terrigenous clastic injection is relatively slow,is the most favorable for the development of organic-rich hydrocarbon source beds.2)Although the Ordovician in the southwest margin of the Ordos Basin has diverse biological types and prosperous populations,the parent organisms(hydrocarbon generating parent materials)that can form important hydrocarbon source rocks are dominated by plankton,agnostic species(microalgae)and cyanobacteria,because the relatively reduced medium environment and appropriate deposition burial rate also play an important role in controlling the effective preservation of organic matter.3)Through X-ray diffraction phase analysis and scanning electron microscope analysis,it shows that rock forming minerals of"mud shale"is mainly quartz and feldspar particles,followed by illite clay minerals,carbonate minerals,and a small amount of pyrite,and so on.The content of clay minerals and pyrite is closely related to the abundance of organic matter.
West margin of Ordos BasinOrdovician source rockHydrocarbon generating organismWulalik FormationPetrology of source rock
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