济阳坳陷桩西潜山披覆构造带桩96井区沙二段扇三角洲沉积特征

Sedimentary study on fan delta of buried-hill draping structural belt in Sha Ⅱ member-case study of Zhuang 96 block,Jiyang depression

在沙二段沉积时期,济阳坳陷桩西潜山披覆构造带曾短暂暴露出水面,形成低缓的隆起,下伏沙三段遭受侵蚀,在隆起的周围形成"草帽边"砂体,该类砂体常被认为是滩坝砂。通过岩心观察和小层平面沉积相研究发现,这些砂体实际上属于沿低隆起区周围展布的扇三角洲沉积。其形成与下伏碎屑物质松散、剥蚀与搬运速率相对较快密切相关。这些扇三角洲一般规模较小;水下分流河道较发育,且侧向迁移频繁;分流河道间泥质沉积比较少见,砂体的侧向连通性较好;波浪对扇三角洲前缘砂体的改造作用较强,含大量螺屑的席状砂较常见。桩96井区沙二段扇三角洲的发现,不仅揭示了一种新的扇三角洲发育背景,而且有助于了解该类砂体的沉积和储层特点。

During the depositional period of Es2,buried-hill draping structural belt in Zhuangxi area of Jiyang depression was ever briefly exposed,and therefore,gentle lower uplift was formed and the underlying Es3 was eroded,forming the 'peripheral edge' sand body which is often considered as shore and bar sand.Through detailed observations and small core layer plane sedimentary facies research,it is found that this sand body is actually developed around the lower uplift of fan delta depositional facies.Its occurrence is closely related to the underlying loose debris,relatively quick erosion and fast transports ion rate.The fan delta is generally small;and distributary channel sand bodies are well developed,and the lateral migration is frequent;argillaceous sedimentary is rare between distributary channels,and the lateral connectivity is good;the modification of waves on fan delta front of sand body is appar-ent,and sheet sand containing large amount of snail fragment is common.The discovery of fan delta in well Zhuang 96 area not only reveals a new kind of fan delta development background,but also favors the understanding of sedimentary and reservoir characteristic of this kind of sand body.