玛湖凹陷风城组沉积特征及异重流水槽模拟研究

Sedimentary characteristics and hyperpycnal flow flume simulation of the Fengcheng Formation in Mahu Sag,Junggar Basin

为厘清沉积特征、沉积环境和异重流对碱性湖盆储层分布的控制作用以及对各类型油气聚集的影响,选取准噶尔盆地玛湖凹陷风城组开展研究.以测井、岩石薄片、微量元素、碳氧同位素、异重流水槽物理模拟试验等为基础,分析玛湖凹陷风城组沉积特征、沉积环境和异重流特征,确定它们对储层分布和油气聚集的影响.研究结果表明:1)玛湖凹陷风城组沉积具有完整的碱湖演化序列,该序列由3个阶段组成,分别对应风一段、风二段和风三段,由凹陷边缘向中心依次沉积砂砾岩带、云质砂岩带、泥页岩带和云质泥页岩带;2)玛湖凹陷风城组沉积环境主要为封闭-半封闭、咸水、还原沉积环境,碱性增强过程中水体分层、还原性增强;3)滨浅湖环境的砂砾岩带和云质砂岩带是致密油勘探区域,滨浅湖至半深湖环境的泥页岩带、云质泥页岩带是页岩油勘探区域;4)玛湖凹陷风城组由凹陷边缘至中心异重流沉积物粒度逐渐变小,形成砂砾岩至泥页岩全粒序的储层.B类岩相和大部分S类岩相形成致密油储层,与L类岩相叠置的S类岩相和L类岩相形成页岩油储层.

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.