浅水三角洲砂体类型及沉积模式——以松辽盆地南部乾安地区白垩系姚家组一段为例

Genetic types and sedimentary model of sandbodies in a shallow-water delta:A case study of the first Member of Cretaceous Yaojia Formation in Qian'an area,south of Songliao Basin,NE China

基于露头、岩心、测井、录井数据,结合现代沉积研究,分析松辽盆地南部长岭凹陷乾安地区白垩系姚家组一段(简称姚一段)浅水三角洲不同相带内砂体类型及空间分布规律,并根据沉积过程建立浅水三角洲沉积模式。姚一段浅水三角洲平原主要发育由活动水道、边滩及汊口浅滩组成的主干分流河道砂体和复合砂体,三角洲前缘主要发育末端分流河道及河口坝砂体。三角洲在河口建设作用和随后的河流冲刷改造作用控制下逐步推进,早期三角洲前缘逐渐演化为三角洲平原,并被分流河道沉积改造,在前方河口部位不断沉积形成新的三角洲前缘。在上述沉积过程控制下,三角洲平原—三角洲前缘的主干分流河道规模逐渐减小、河口坝保存程度逐渐变好,不同类型砂体组合形成受分流河道控制的浅水三角洲沉积。乾安地区姚一段浅水三角洲主干分流河道内部的边滩和活动水道砂体储集条件最好,是岩性油藏的有利发育部位。

Based on outcrop, core, logging and mud logging data, and modern deposition analog, the sandbodies genetic types and spatial distribution in different facies belts of the shallow water delta in the first Member of Cretaceous Yaojia Formation （K2y1） of Qian＇an area in Changling sag of southern Songliao Basin were analyzed, and the sedimentary model of shallow water delta was established according to deposition process. Active channel sandbodies, point bar sandbodies and bifurcation bar sandbodies in distributary channels and complex sandbodies formed the main sandbodies in the delta plain, while terminal distributary channels and mouth bar sandbodies formed the main sandbodies in the delta front. The delta prograded gradually under the construction of river mouth and reconstruction of river erosion, the early delta front evolved into delta plain and was reformed by distributary channels, and new delta fronts were formed at the river mouth ahead constantly. Under the control of the above deposition process, the size of main distributary channels in delta plain-delta front declined, while mouth bars developed increasingly. The sandbodies of different genetic types formed framework of river-dominated shallow water delta. The point bar and active channel sandbodies in main distributary channels of the delta, with the best reservoir quality, are lithologic reservoir targets in future exploration.