远源细粒辫状河三角洲沉积特征与单砂体构型分析

Sedimentary characteristics of distal fine-grain braided delta and architecture analysis of single sand body

关键词:  远源细粒  辫状河三角洲  沉积特征  单砂体

Key words:  distal fine-grain  braided delta  depositional characteristic  single sand body

摘要:

应用研究区丰富的取心井及密井网资料，对老君庙油田L油藏远源细粒辫状河三角洲分流河道和河口坝单砂体进行表征并明确其内部结构样式，建立远源细粒辫状河三角洲的沉积构型模式。研究表明：缓坡、距物源较远是远源细粒辫状河三角洲发育的必要条件，沉积粒度较细、沉积构造规模及单河道砂体厚度较小是其较明显的沉积特征；远源细粒辫状河三角洲平原分流河道呈交织近连片型和交织条带型两种组合样式，其中交织近连片分流河道由主干分流河道不断分叉合并而成，分流河道演化主要有3种模式，经历3个阶段，早期典型分流河道孤立分布，中期河道以决口演化模式为主成交织状分布，末期以侧向侵蚀和河道间岔口冲刷演化模式为主成近连片分布；远源细粒辫状河三角洲前缘河口坝呈大面积近连片分布，其由不同期单河口坝拼接叠置而成，前缘演化初期以坝边部部分侧向拼接样式为主，演化中期坝边部完全侧向拼接样式较常见，至演化末期河口坝间呈现坝主体完全垂向叠置和坝主体部分垂向叠置的样式。

Abstract:

Based on abundant core data and close-spacing well data, this paper analyzed the single sand body architecture and constructed the sedimentary architecture model of the distal fine-grain braided delta in Laojunmiao Oilfield. The results show that the gentle slope and the long distance to the source area are the main factors which determine the development of fine-grain braided delta. The typical characteristics of distal fine-grain braided delta include small grain size (with an average of 0.08mm), small sedimentary structure and thin channels. The distributary channel can be divided into two types:the intertexture-continuous channel and the intertexture divaricated channel. The intertexture-continuous channel is formed through the bifurcation and convergence of single distributary channels. The evolution of distributary channel has three modes, and there are three stages in the entire development of distributary channel, including the obvious isolated distributary channel, the intertexture channel in the manner of crevasse, and the continuous channel in a manner of inter channel erosion and lateral erosion for the early, middle and late stages, respectively. Delta front develops large area mouth bars due to the weak distributary channel energy and there is minimal reconstruction in the former mouth bars. The continuous mouth bars are formed by the amalgamation and superimposition of single bars. The amalgamation patterns of mouth bars are coupled with the evolution of the front delta:in the early stage, the amalgamation is characterized as weak bar edge joint. Subsequently, the amalgamation is characterized by entire bar edge joint. In the final phase, the amalgamation is characterized as weak or entire superimposition.