Pre-Jurassic Paleogeomorphology and Its Influence on Oil Accumulation:Case of Yan'an Formation in QY Area,Ordos Basin
In order to clarify the control effect of paleogeomorphology on the reservoir distribution in the Lower Jurassic in Ordos Ba-sin,and to determine the specific relationship between different paleogeomorphology units and petroleum accumulation,the Yan'an For-mation of the Jurassic system in the QY area of the southwestern Ordos Basin was taken as an example,based on the study of stratigra-phy,structure,and sedimentary facies,the ancient landforms of the Jurassic system in the research area were restored using the im-pression method,and the distribution characteristics of the ancient landform units in the area were characterized.Finally,the relation-ship between the planar distribution characteristics of the Yan'an Formation oil reservoirs in the study area were analyzed,and the pa-leogeomorphological units,the controlling role of the pre Jurassic paleogeomorphology on oil reservoir enrichment was determined.The results show that five kinds of paleogeomorphological units are developed in the study area,namely highlands,slopes,river valleys,branch river valleys and inter-river hills,respectively.With respect to the distribution of different paleogeomorphological units,the south-west and northeast area are dominated by highlands,and river valleys,respectively.But,middle area is mainly dominated by slopes,branch river valleys,and some of the dismembered highlands.The influence of paleogeomorphology on petroleum enrichment can be re-flected not only in the controlling of sedimentary facies,but also in the types of reservoir traps and migration pathways.The petroleum ac-cumulation models can be divided into two types,including flank accumulation in river valley,and accumulation in paleo-highland.This research can provide a theoretical basis for predicting the petroleum distribution law of Yan'an Formation in the study area.
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