湖相深水块状砂岩特征、成因及发育模式——以南堡凹陷东营组为例

Sedimentary characteristics,origin and model of lacustrine deep-water massive sandstone:An example from Dongying Formation in Nanpu depression

块状砂岩因其厚度大、储层物性较好而成为深水沉积油气勘探开发中最重要的目标。沉积构造相对简单,但变化迅速且组构特征多变。为了探索不同块状砂岩的成因及其联系,建立预测性地质模型,首先将南堡凹陷东营组深水块状砂岩分为2类8种岩相和10种岩相组合,其中单期砂层顶部常含漂浮状砾石,形态多变、内外源均有。本区块状砂岩成分成熟度差,结构成熟度不稳定,粒度累积概率曲线反映了3种搬运过程:多流体改造型、三角洲前缘继承型和混杂快速冻结型。成因分析认为,块状砂岩以砂质碎屑流搬运为主,真正碎屑流和颗粒流次之,并见部分砂质滑塌成因;常与浊流、泥流、泥质滑塌沉积伴生,发育5种相序组合,其中砂质碎屑流-浊流、砂质碎屑流-泥流组合最常见。高密度流体内沉积物浓度分层与特殊的流速剖面共同控制下塑性层流与牛顿紊流间的界面控制了漂浮状砾石搬运和沉积。最后,建立了陡坡带外源型、陡坡带内源型和缓坡地内源型深水沉积过程及块状砂岩发育模式,为断陷盆地深水沉积砂岩储层的预测提供了新思路。

Massive sandstone is the most important hydrocarbon exploration target due to thick layer and well porosity in deep-water sedimentary sandstone. It is characteristic by simple sedimentary structure with floating clasts and unstable sedimentary texture. In order to study the origin and their relationships among different massive sandstones and build up the predictive geological model, the massive sandstones were divided into 8 litho-facies and 10 litho-facies assembles firstly. On the top or upper part of a single-period deep-water sandstone, the floating clasts consist of muddy, sandy or base-rock gravel can be variable in shapes and sources. In study area, massive sandstone has low maturity in composition and range widely from bad to well maturity in texture. The cumulative probability curves of grain size showed that the sediments transport processes include at least three types, multi-flow reworked type, heritage of delta front by mass transport and freezing quickly of chaotic sedimentation. Totally, massive sandstone formed mainly by sandy debris flow, secondly by true debris flow, grain flow and sandy slump associated by turbidity current, slurry flow and muddy slump. As a result of analysis of dynamics, five combination relations may be recognized. Among them, the combination between sandy debris flow and turbidity current, sandy debris flow and slurry flow were the two common types. The interfaces between lower plastic laminar flow and upper Newtonian turbulent flow in high density flow is so significant in controlling the transportation and sedimentation of floating clasts on the top of the massive sandstone. Finally, three depositional progresses and developing conceptual models of deep- water sandstones were put forward to predict the high quality sandstone reservoir in the hydrocarbon exploration in rift lacustrine basin with a new insight.