三角洲沉积的物理模拟

Physical simulation of deltaic deposits

为进一步清晰地认识三角洲的沉积特征及砂体发育规律,利用水槽实验对三角洲的发育过程进行了物理模拟,追踪了河口坝、分流河道和滑动-滑塌砂体的沉积过程与沉积特征。通过观察与分析,认为三角洲生长是多次侵蚀与沉积交替的结果,其中洪水期侵蚀作用小于沉积作用,表现为"填低补平";枯水期侵蚀作用大于沉积作用,表现为"削高填低"。河口坝的发育从水下浅滩开始,按照向前—垂向—向后—横向的顺序进行生长,并且存在单个河口坝的多级分流与多列河口坝的同时分流两种分流方式。三角洲平原河道演变包括河流改道与分流两种方式,分别与洪水和河口坝有关。洪水事件可以作为三角洲前缘滑动-滑塌沉积的触发因素。三角洲是河流搬运、卸载与蓄水体接受、改造沉积物动态变化过程中的产物,在此过程中形成沉积坡折带,它是优质储层发育的有利场所。

In order to fully understand the sedimentary characteristics of dehaic deposits and the development patterns of associated sand bodies, this paper presents a physical simulation of delta development through flume experiment and intro- duces the experiment results in respects of sedimentary process and characteristics of distributary channels, mouth bars, and slide-slump deposits. The experiment reveals that the development of delta is an alternating process of deposition and ero- sion. Deposition is dominant in flood season when distributary channels carry a heavy sediment load,while erosion is domi- nant in non-flood season. The growth of mouth bars initiates from an underwater shoal in an order of forward, upward, back- ward and transverse. In addition,there are two modes of bifurcation,i, e. multi-stage bifurcation by one mouth bar and sim- uhaneous bifurcation by multiple mouth bars. The channels on a deltaic plain may evolve in two modes, i. e. redirection and diversion,which are related with flood and mouth bar respectively. Flood events could be the trigger of delta front slide- slump deposits. Deltas are formed in the process of sediment transportation and sedimentation determined by the interaction of alluvial and basinal dynamics. In this process,sedimentary slope break is formed,which is favorable for the development of high quality reservoirs.