鄂尔多斯盆地吴起地区侏罗纪早中期河流沉积及油气分布

应用现代沉积学理论,结合岩心观察描述、钻井、测井等资料,对鄂尔多斯盆地吴起地区侏罗纪早中期富县组到延安组延10、9、8期的沉积体系、岩相古地理特征及演化进行了详细研究,认为早侏罗世富县组和中侏罗世延安组延10期为深切河谷充填的辫状河沉积,延9和延8期则发育曲流河沉积.这2种河流沉积经历了有规律的继承性演化:富县组河谷充填作用最强,辫状河道砂体沉积厚度最大.延10期河谷进一步填平补齐,河谷斜坡上次级河道溯源增长、侧向侵蚀使河道变宽,漫滩分布面积减小.延9和延8期,古地形差异进一步减弱,河流转型为曲流河,河道和漫滩沉积均发育.吴起地区侏罗纪早中期河流发育辫状河和曲流河2种河流沉积模式.沉积相对富县组-延安组延8油层组油藏分布起主要控制作用,油气聚集主要受河道砂体展布控制,储层发育的河道砂体是该区今后勘探的主要目标.

Study on fluvial deposits and oil & gas distribution of early and middle Jurassic in Wuqi area,Ordos Basin

On the basis of core observation,well drilling data,logging data and so on,the characteristics and evolution of the sedimentary system from Fuxian Formation to Yan10,Yan 9,Yan 8 reservoirs of Yan'an Formation of early and middle Jurassic in Wuqi area,Ordos Basin are studied in detail using modern sedimentology theory.It is held that Fuxian Formation of early Jurassic and Yan10 reservoir of middle Jurassic are dominated by deep valley filling braided fluvial deposits,and Yan 9 and Yan 8 reservoirs are dominated by meandering fluvial deposits.The two types of fluvial deposits experienced regular inherited evolution.The braided sand-body of Fuxian Formation is the thickest because of the strongest valley packing action.During Yan10 period,the filling process continued,headward erosion was developed on the sub-valley slopes,the channel grew wider due to lateral erosion and the distribution range of flood plain reduced.During Yan 9 and Yan 8 periods,river became meandering river,and fluvial was present in Yan 9 and Yan 8 Reservoirs and channel and flood plain deposits were developed because of the reduction of the elevation difference of ancient landform.Braided river and meandering river depositional models were developed in early and middle Jurassic in Wuqi area.The hydrocarbon accumulation is controlled by the channel sandstones,which may be regarded as the target for further exploration of oil and gas.