Alluvial Fan and Fan-delta Sedimentary Facies and Favorable Assemblage of Reservoir and Seal of Wushi Sag(Cretaceous) in Tarim Basin

Based on Wucan 1 well of the south depression and the north outcrop section in Wushi sag,and in combination with synthetic analysis with logging shape and seismic section,it can be seen that the study area develops much different sedimentary facies of the north and south in the Wushi sag due to the structural influence,palaeoclimate and source.The north outcrop section mainly develops shore shallow lake sedimentary facie,yet the south depression develops typical course grain alluvial fan and fan-delta sedimentary facies.The clastic rock grain of this sedimentary facies is great different and discontinuous.The extremely thick conglomerate usually contacts directly with fine sandstone,siltstone,mudstone without transition grain.The main reason come from condition of the north outcrop locating on stable structure and having farer source,but the south depression owing to the close to source of Wensu swelling and being controlled by fractures.There are two sets of combination about reservoir and seal in Wu Shi sag as follows,one is conglomerate of middle-lower strata of Yageliemu Formation-Shushanhe Formation and mudstone and gypsum mudstone of the Ku Mu Ge Lie Mu Formation,the other is the bottom glutenite of the Bashenjiqike Formation-Kumugeliemu Formation and the salt bed and gypsum mudstone of the Kumugeliemu Formation.It has been acquired oil and gas form the first set of of combination about reservoir and seal of the middle-bottom fan-delta sandstone of fan-delta front facie,which belong to the sand bar and braided channel and can from better reservoir.The sandstone of the second set of combination about reservoir and seal of the Baxigai Formation and Bashijiqike Formation has widespread distribution with dense lithology and the reservoir is very thick and longitudinal concentricity,poor porosity and permeability.Generally,it belongs to the medium reservoir and seal combination.Owing to the poor exploration,it is predicted that there is high quality reservoir facies formed in distal area from the source.