塔里木盆地东河塘石炭系障壁岛后冲溢扇研究

Study on the Carboniferous Washover Fan Behind Barrier lsland ln Donghetang of Tarim Basin

本文充分运用地质、测井、地震资料，对塔里木盆地东河塘石炭系障岛壁岛后冲溢扇进行了研究。从岩性特征、结构、沉积构造、垂向层序、地球物理、沉积背景、古地理条件等几个方面，详细阐述了冲溢扇的沉积特征。概括总结了冲溢扇的沉积模式，并对冲溢扇含油气性进行了论述，指出冲溢扇沉积特征研究不仅可以丰富沉积学理论。

In recent 20 years,while having payed attention to studying the modern barrier island sedimentary systems,reople have made some researches on sedimentary characteristics of washover fans associated with barrier island and pointed out that there are many washover fans in ancient barrier island sedimentary sequences,which opens up a new field for oil-gas exploration.Directed by modern sedimentary theory,authors studied the Carboniferous washover fans behind barrier island in the Donghetang area of the Tarim basin by full uses of geological,logging and seismic data.The washover fan can be divided into sandstone type and limestone type.The former consists of siltstone,fine sandstone and brown mudstone with graded and parrallel beddings.In the sandstone,quartz and chert content is 80%～90%,there are some normal and multicrystal oolites in it.The latter is made up of brecciated tearing debris,fine silt and quartz,chert,coarse silt,which are associated with grey brown siltstone and grey green arenaceous limestone vertically.Grain probability curves of the washover fan almost are characterized by two segments with high content of suspension substance which is up to 30%.The thickness of sandstone type washover fan vertical sedimentary structure sequence,which can be described as “Bouma sequence AE,AAA and ABE”,is 40～60 cm.The washover fan of limestone type shows massive structure as a whole, and there developed limestone brecciated with various size and shape,suspending among lime mud and silty sand,and sedimentary thickness is about 1 m,which is associated with normal tidal flat lagoon mud.Affected by storm factor,tempestuous current carrying a great deal of basinal debris passed over barrier island,and formed washover fans extended toward lagoon about 1 kilometer in length and about 10 square kilometer in area in atidal flat lagoon environment at the back of barrier island.The washover fan has good reservoir potential and pinches out quickly laterally,therefore,it′s favorable for forming updip pinch-out oil-gas pool which has been found in the Carboniferous stfata in the Lunnan area of the Tarim basin.