Characteristics,formation environment and enrichment model of Triassic Chang 7 shale oil reservoir in Huachi area,Ordos Basin
Through the petrological characteristics and elemental geochemical testing and analysis of cores from Triassic long 7-layer drilling in Huachi area of Ordos Basin,the paleoenvironmental characteristics were ana-lyzed by using V/(V+Ni),Ni/Co,U/Th,Sr/Cu,CaO/(MgO*Al2O3),Sr/Ba,Fe/Mn,Mn/Ti,Babio values and P/Al values,combined with the content of total organic carbon,to analyze the paleoenvironmental.Paleoenviron-mental characteristics such as Ancient climate,paleosalinity and paleoredox conditions.The results show that:(1)The rocks of Triassic Chang 7 member in Huachi area of Ordos Basin are mainly dark gray mudstone,dark gray gray mudstone,silty mudstone containing carbon debris and silty mudstone rich in organic matter.Intercrys-talline pores and intergranular pores of clay minerals are the main pore types.In addition,a small number of dis-solution pores and fine fractures can be seen.(2)In the study area,the organic matter productivity was signifi-cant during the deposition period of Chang 7,and the environment was mainly freshwater with low oxygen con-tent,which was in a state of poor oxygen to hypoxia,while in the Chang 72 and 73 periods,some areas with deep water bodies had extremely strong reduction conditions,mainly warm and humid climate.Overall,it indi-cates a deep-water environment.And Chang 72 is located in the boundary zone of the deep-water area,and its water environment are obviously different from the adjacent Chang 7,and Chang 73 members,showing relatively low water depth conditions.The P/Al value and Babio value generally change in the Chang 7 member,from Chang 73 to Chang 71,they all show a process of increasing from bottom to top.(3)The paleosedimentary environment of the Chang 7 member in this area has suitable temperature and salinity conditions,coupled with the deep water and strong reduction,which jointly promote the extensive development,enrichment and preservation of organic matter.The source rock and the reservoir are interconnected through fractures,and the oil generated in the source rock is more easily transported to the reservoir layer through fractures.In addition,when the distance between the source rock and the reservoir is relatively close,the process of crude oil migration and accumulation will be more efficient,and finally form a high-quality source rock system.Source rock and reservoir configuration laid a solid foundation for large-scale enrichment of shale oil and created extremely favorable conditions.
shale oil reservoirelemental geochemistrypaleoenvironmentpaleoproductivityorganic matter enrichmentsource rock and reservoir configurationChang 7 member of Yanchang FormationTriassicHuachi areaOrdos Basin
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