曲流河浅水三角洲沉积过程与沉积模式探讨——沉积过程数值模拟与现代沉积分析的启示

发布时间：2018-09-14 10:05

【摘要】：浅水曲流河三角洲是近年来沉积学研究的热点和油气勘探的重点对象,国内外学者基于地下储层、露头、现代沉积进行了大量研究,关于浅水曲流河三角洲的沉积特征与沉积模式,不同学者往往持不同观点,在缺乏沉积过程与演化特征观察、分析的现状下,很难统一认识。基于此,本文选取鄱阳湖赣江三角洲这一典型的浅水曲流河三角洲,根据其水动力、水深、沉积物供给等数据,采用基于泥沙水动力学的沉积过程数值模拟软件(Delft3D)再现浅水曲流河三角洲的生长与演化过程,并与现代浅水曲流河三角洲对比验证,建立浅水曲流河三角洲沉积模式。研究表明:(1)在浅水环境下,曲流河三角洲快速向湖生长,三角洲前缘持续向前延伸并快速平原化,具有典型的宽平原-窄前缘的特征。三角洲垂向沉积厚度较小,但底积-前积-顶积三层结构完整。(2)浅水曲流河三角洲平原发育数条同期活跃的高弯度分流河道,在平原近端,分流河道存在频繁的侧向迁移现象,可对先期三角洲前缘、前三角洲沉积侵蚀改造,形成串珠状点坝,经长期侧向迁移可形成大规模的长条宽带状分流河道复合体,分流河道对先期沉积体的长期改造使得大部分厚层砂体呈正韵律,导致先期河口坝保存程度较低;在前缘远端,由于堤岸不稳定,分流河道往往存在决口改道现象,废弃的水道缺乏砂质沉积物供给而成为高泥质充填水道,多条废弃分流河道在三角洲平原远端形成高泥质充填河网系统。(3)浅水曲流河三角洲前缘水下分流河道是平原分流河道在水体中的短程延伸,水道长约300m,由于水体较浅,河口处水流冲刷能力较强,水携沉积物多在水下分流河道侧缘堆积形成指状坝。由于分流河道建设性极强,水下分流河道往往频繁发生决口或侧向摆动,经多期复合,可形成多分叉复合体指状坝,而前缘水下分流河道在废弃后往往被泥质充填。(4)受三角洲平原远端水道决口改道的控制,前缘多分叉指状复合坝沿岸线迁移,可形成大面积近等厚砂体。
[Abstract]:Shallow meandering river delta has been the focus of sedimentology research and oil and gas exploration in recent years. Scholars at home and abroad have done a lot of research based on underground reservoir, outcrop and modern sedimentation. Different scholars tend to hold different views on the sedimentary characteristics and models of shallow meandering river delta. In the absence of observation and analysis of sedimentary process and evolution characteristics, it is difficult to unify understanding. Based on this, this paper selects the Poyang Lake Ganjiang Delta, a typical shallow meandering river delta, according to its hydrodynamic, water depth, sediment supply and other data. The sedimentation process numerical simulation software (Delft3D) based on sediment hydrodynamics was used to reproduce the growth and evolution process of shallow meandering river delta, and compared with that of modern shallow meandering river delta, the sedimentary model of shallow meandering river delta was established. The results are as follows: (1) in shallow water environment, the meandering river delta grows rapidly to the lake, the delta front continues to extend forward and becomes plain rapidly, which has the typical characteristics of wide plain and narrow front. The vertical depositional thickness of the delta is relatively small, but the structure of the three layers is complete. (2) in the shallow meandering river delta plain, there are several simultaneously active high-bend distributary channels, and in the near end of the plain, there are frequent lateral migration phenomena in the distributary channel. The pre-delta front and pre-delta sediment erosion can be transformed to form beaded point dams, and a large scale broad-band distributary channel complex can be formed through long-term lateral migration. The long-term transformation of the distributary channel to the pre-sedimentary body makes most thick sand bodies have positive rhythm, which leads to the lower preservation degree of the pre-existing estuarine dam, and at the far end of the front edge, because of the instability of the bank of the dike, the distributary channel often has the phenomenon of diverging channel. Abandoned waterways are short of sandy sediment supplies and become high-muddy filling waterways. Many abandoned distributary channels form a high muddy filling river network system at the far end of the delta plain. (3) the shallow meandering river delta front underwater distributary channel is the short-range extension of the plain distributary channel in the water body, the length of the channel is about 300m, because of the shallow water body, In estuaries, the erosion capacity of water flow is strong, and most of the sediment carried by water accumulates in the lateral edge of underwater distributary channel to form finger dam. Because the distributary channel is very constructive, the underwater distributary channel often occurs break or lateral wobble frequently, and the multi-branched complex finger dam can be formed after multi-period compound. However, the front underwater distributary channel is often filled with mud after it is abandoned. (4) under the control of the channel of the far end of the delta plain, the front edge multi-bifurcation finger composite dam moves along the shore line, and a large area of nearly equal thickness sand body can be formed.
【作者单位】：中国石油大学(北京)地球科学学院油气资源与探测国家重点实验室;中国石油青海油田分公司井下作业公司;中国石油青海油田分公司勘探开发研究院;
【基金】：国家自然科学基金项目(编号41372116) 国家重大科技专项(编号2011ZX05009-003)联合资助成果
【分类号】：P618.13

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