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.