Stratigraphy and Facies Distribution of Lower Devonian F4 Unit in Zarzaitine Oilfield, Illizi Basin, Algeria
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摘要: 区域构造-沉积演化背景与研究区大量岩心、测井资料分析相结合的沉积相分析表明, 下泥盆统F4层段属于处于陆隆部位的半深海背景下的海底扇沉积.以F4层段中部稳定发育的深海泥岩段为区域对比标志层, 将其分为上部和下部2个旋回, 分别对应2期扇体的形成与发育过程.以各扇体内部较为稳定的泥岩为次级对比标志层, 可进一步将各扇体划分出相当于砂层组级别的地层单元, 由此建立了F4层段具有时间意义的地层对比格架.在分析各扇体沉积亚相类型与成因机制的基础上, 认为F4层段储层成因类型主要包括辫状水道复合体、沉积型水道和水道末段舌状体3种类型.在高精度时间地层格架内, 分析了储集砂体平面展布规律, 并提出F4层段海底扇至少存在来自北西西和东南2个方向的物源供给体系, 属于多点物源和砂质扇成因类型.该研究不仅为重力流沉积层序地层划分和对比提供了研究思路与方法, 同时也为F4层段剩余油的分布研究提供了可靠的地质模型, 为油藏的深入开发挖潜提供了科学依据.Abstract: Based on cores and well logs, the analyses of tectono-sedimentary setting and facies show that F4 unit formed by submarine fan located in the continental rise. Lower Devonian F4 unit can be divided into upper cycle and lower cycle by a correlating fan-wide marine mud datum called "middle mud", which correspond individual the two-stage of the submarine fan evolution. Each cycle can be subdivided into several sub-cycles by mudstone or thin bedded siltstone, and mudstone which can be traced in the interior fan, thereby establishing the cronostraticframe of F4 unit. In light of the analysis of subfacies and their mechanisms, the reservoir types of F4 unit include braided channel-complex, sedimentary channel and tongue-like body. Facies distribution maps in the precision stratiraphic framework indicate that the submarine fan sediments formed F4 unit were supplied from at least two sources, i.e., northwest and southeast. The genetic type of F4 unit is a multiple point-source sand-rich fan. This study provides not only correlation strategy of submarine fan, but also a reliable geological model for the further development of F4 unit.
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Key words:
- facies /
- stratigrapgy /
- gravity flow /
- F4 unit /
- Illizi basin /
- Algeria /
- sedimentation /
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图 3 岩心图版
a.Zr140, 1 483.0 m, 泥砾岩相;b.Zr83, 1 267.6 m, 泥砾岩相;c.Zr140, 1 474.0 m, 块状层理砂岩相;d.Zr140, 1 457.2 m, 块状层理砂岩相;e.Zr140, 1 487.35 m, 交错层理砂岩相;f.Zr140, 1 473.4 m, 交错层理砂岩相;g.Zr140, 1 461.2 m, 波状层理砂岩相;h.Zr140, 1 438.8 m, 波状层理砂岩相;i.Zr515, 1 509.9 m, 砂泥薄互层相;j.Zr515, 1 495.4 m, 砂泥薄互层相;k.Zr140, 1 440.2 m, 灰黑色泥岩;l.Zr140, 1 434.8 m, 紫色虫孔泥岩;m.Zr140, 1 492.3 m, 微断层;n.Zr80, 1 272.5 m, 砂球枕构造;o.Zr140, 1 440.7 m, 液化构造;p.Zr140, 1 471.4 m, 重荷模;q.1 484.4 m, 植物碳屑;r.Zr515, 1 362.4 m, 鲍马序列A-C-E;s.Zr515, 1 360.1 m, 鲍马序列B-C-E
Fig. 3. Core assemblage
图 6 重力流流变学机制的变化导致沉积物沉积构造和结构的差异(据Ganni, 2004修改)
a.粘性碎屑流;b, c.非粘性碎屑流;d, e, f.密度流;g.浊流(鲍马序列);h.浊流(高密度流)
Fig. 6. Difference in structure of gravity flow sedimentation
表 1 F4层段岩相类型
Table 1. Type of litho-facies in F4 unit
类型 厚度 岩石类型 颜色 结构 构造 成因机制 发育程度 砂质泥砾岩相 0.1~0.5 m 砂质支撑泥砾岩 红/紫/绿/灰色 分选差, 泥砾磨圆中等 包卷层理, 揉皱构造 滑塌/碎屑流/水道底部 中等 块状层理砂岩相 0.2~3.0 m 中细砂岩夹少量泥质漂砾 灰色 分选中等, 磨圆较好 无构造, 局部见泄水/火焰状/碟状构造 碎屑流为主, 局部颗粒/液化流 普遍 交错层理砂岩相 0.2~0.4 m 中细砂岩为主 灰色 分选一般, 磨圆较好 槽状交错层理, 或泥砾定向排列显示 低密度碎屑流 少量 波状层理粉砂岩相 0.1~0.3 m 粉砂岩/泥质粉砂岩 灰色 分选好, 磨圆好 波状、爬升/透镜状层理 低密度浊流, Tc-d段 局部 砂泥薄互层相 0.1~0.6 m 粉砂岩和泥岩 灰/黑色 分选中等, 磨圆较好 波状层理, 互层层理 低密度浊流, Td-e段 中等 暗色泥岩相 0.05~0.10 m 泥岩 灰/灰黑色 块状, 局部见虫孔和植物碎屑 悬浮沉积作用 中等 -
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