In order to understand the controlling effect of sedimentary characteristics,sedimen-tary environment and gravity flow on reservoir distribution and various types of hydrocarbon accumulation in alkaline lake basin,the Fengcheng Formation of Mahu Sag in Junggar Basin was selected for research.Based on the logging,rock thin section,trace elements,carbon and oxygen isotopes,hyperpycnal flow flume physical simulation experiments,the sedimentary characteristics,sedimentary environment and hyperpycnal flow features of the Fengcheng For-mation in Mahu Sag were studied.Their impact on reservoir distribution and hydrocarbon accu-mulation were determined.The results show that the Fengcheng Formation in Mahu Sag has a complete alkali lake evolution sequence,which consists of three stages,corresponding to the first,second and third member of the Fengcheng Formation,respectively.From the edge to the center of the sag,there are successively deposited sandy conglomerate belt,dolomitic sand-stone belt,shale belt and dolomitic shale belt.The sedimentary environment of the Fengcheng Formation in Mahu Sag is mainly enclosed,semi-enclosed,salt water and reductive sedimentary environment.In the process of alkaline enhancement,water layer and reducibility are enhanced.The conglomerate belt and the dolomitic sandstone belt in the shallow lake envi-ronment are tight oil exploration areas,and the shale belt and the dolomitic shale belt in the shallow lake to semi-deep lake environment are shale oil exploration areas.From the edge to the center of the sag,the particle size of the sediment of the hyperpycnal flow decreases gradu-ally,forming a reservoir with full grain sequence from conglomerate to shale.The B-type and most S-type lithofacies form tight oil reservoirs,and the S-type lithofacies superimposed with L-type lithofacies and L-type lithofacies form shale oil reservoirs.
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