远源、细粒型浅水三角洲沉积特征与演化--以准噶尔盆地腹部莫索湾地区八道湾组为例

准噶尔盆地腹部中央坳陷莫索湾地区八道湾组沉积时期气候相对湿润,地形相对平缓,物源供给充足,湖岸线变化相对频繁,具备形成浅水三角洲有利条件;由于距离物源区较远,沉积砂体以细砂岩、中-细砂岩为主,粒度相对较细,垂向上形成多期正旋回沉积序列。三角洲前缘分布广、延伸长、面积大,平面主要呈朵状,由多期水下分流河道切割、叠置形成的复合砂体构成;水下分流河道砂体发育,厚度较大,数量众多,垂向相互叠置,横向互相切割,连通性较好,单砂体具有不同叠置方式,构成了主要油气储集砂体,泥岩隔层较薄,河口坝砂体不发育;总体上,形成了该区远源型、分布广、粒度较细的浅水曲流河三角洲沉积体系。不同的沉积时期,来源于两个物源方向的三角洲前缘和水下分流河道沉积形态和范围发生变化,最终形成由宽阔的复合河道砂体为主构成的浅水三角洲。

Distal Fine-grain Shallow-water Delta Sedimentary Characteristics and Evolution: A Case from Badaowan Formation in the Central Junggar Basin

The climate was relatively wet, terrain was relatively flat, water power was relatively strong, the source of supply was adequate, lakeshore line relatively frequent changes of the Badaowan Formation sedimentary period of the Mosuowan area in the Central depression of Junggar Basin, which can form shallow-water delta. Sedimentary sandbody that is formed many positive cycle sedimentary sequences vertically mainly fine and medium-fine sandstone, which is the relatively fine grain size. The delta front has a wide distribution, long extension, large area and its planar configurations are major foliaceous, which are consist of compound sandbodies by multi-subaqueous distributary channel sandbody cut and superimposition. Thick, substantial and good connectivity subaqueous distributary channel sandbodies which are vertical superimposition and transverse cut each other are well developed, shale interbeds are relative thin and mouth bar sand body is not developed. The sandbody superimposition modes can be divided into different types, which is the major petroleum reservoir. On the whole, it formed the far-source, widespread, fine-grain shallow-water delta sedimentary system. The deposition and range of delta front and subaqueous distributary channel sandbody that are from two different source direction are different in different period, which is formed shallow-water delta that is mainly composed of wide composite channel sandbody finally.