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Anatomy of a gas-bearing submarine channel-lobe system on a topographically complex slope (offshore Nile Delta, Egypt)
Marine Geology ( IF 2.6 ) Pub Date : 2021-04-27 , DOI: 10.1016/j.margeo.2021.106496
Pan Li , Ben Kneller , Larissa Hansen

The characterization and predictability of submarine channel-lobe systems on topographically complex slopes have proven challenging, due to the complex responses of such systems to interacting flows and seafloor topography, in terms of their temporal evolution and spatial changes in morphology and architecture. Detailed subsurface studies can reveal important depositional and morphological elements in such settings and help develop predictive models for hydrocarbon exploration. Here, we document a gas-bearing submarine channel-lobe system on a topographically complex slope, from the Pliocene succession offshore the west Nile Delta where the Giza gas field has been discovered. Based on an integrated analysis of 3D seismic reflection and borehole data, several distinct deep-water depositional elements, including amalgamated channel-fills, aggradational channel-fills, mud-prone channel-fills, lobes, levees and mass-transport deposits are recognized. They are developed on a tectonically influenced continental slope, forming a channel-lobe system that features four main evolutionary phases over a period of ca. 0.2 Myr: 1) Channel belt incision, 2) infill of channel belt by laterally amalgamated channel deposits, 3) development of leveed aggradational channels, with lobes developed within and outside the channel belt, 4) channel avulsion led to the abandonment of the channel belt, which resulted in the formation of a new ponded lobe complex adjacent to the original channel belt.

Spatially, the channel-lobe system shows marked changes in architecture and planform morphology in the areas affected by folds and faults. As the channels cut across an faulted anticlinal structure, they show straightening with some degree of diversion on the upstream limb, while on the downstream limb, channels exhibit increased lateral migration and sinuosity, widespread high-amplitude reflections (interpreted as sand-rich channel-fills), and channelized to unchannelized (frontal/crevasse lobe) transitions. In contrast, the last-stage avulsion channel appears to divert along several normal faults at a high angle to the regional slope, and forms a ponded lobe external to the main channel-belt. This study shows how the channels and lobes throughout these evolutionary stages respond differently to the presence of folds and faults. It provides a unique analog for submarine channel-lobe systems developed over a third-order sea-level cycle with the influence of structurally induced topography. The result of this study provide insights into the spatio-temporal development of various slope channels and lobes, and may greatly enhance the prediction of associated reservoirs in deep-water systems in tectonically active area.



中文翻译:

地形复杂斜坡(埃及尼罗河三角洲近海)上的含气海底河道-波瓣系统的解剖

在地形复杂的斜坡上,海底河道系统的特征和可预测性已被证明具有挑战性,这是由于此类系统对相互作用的水流和海底地形的复杂响应,包括它们在时间上的演化以及形态和结构上的空间变化。详细的地下研究可以揭示这种环境下重要的沉积和形态元素,并有助于建立油气勘探的预测模型。在这里,我们记录了一个地形复杂的斜坡上的含气海底通道-波瓣系统,该斜坡来自尼罗河西部西部海上的上新世演替,并在此发现了吉萨气田。在对3D地震反射和井眼数据进行综合分析的基础上,几个不同的深水沉积元素(包括合并的河道填充物,可以识别出凝集性河道填充物,易淤泥的河道填充物,裂片,堤防和大量运输沉积物。它们是在受构造影响的大陆斜坡上发育的,形成了一个通道-波瓣系统,其特征是在大约一个时期内有四个主要的演化阶段。0.2 Myr:1)通道带切口,2)通过横向合并的通道沉积物充填通道带,3)发育的隆起性通道,在通道带的内部和外部均形成裂片,4)通道撕脱导致通道的放弃带,导致在原来的河道带附近形成了一个新的池塘状波群。形成一个通道瓣系统,其特征是在一个周期内有四个主要的演化阶段。0.2 Myr:1)通道带切口,2)通过横向合并的通道沉积物充填通道带,3)发育的隆起性通道,在通道带的内部和外部均形成裂片,4)通道撕脱导致通道的放弃带,导致在原来的河道带附近形成了一个新的池塘状波群。形成一个通道瓣系统,其特征是在一个周期内有四个主要的演化阶段。0.2 Myr:1)通道带切口,2)通过横向合并的通道沉积物充填通道带,3)发育的隆起性通道,在通道带的内部和外部均形成裂片,4)通道撕脱导致通道的放弃带,导致在原来的河道带附近形成了一个新的池塘状波群。

在空间上,波瓣系统在受褶皱和断层影响的区域显示出体系结构和平面形态的显着变化。当通道越过断层的背斜构造时,它们在上游肢体上表现出一定程度的拉直,而在下游肢体上,通道表现出增加的侧向偏移和弯曲度,并出现了大幅度的高反射(被解释为富沙通道)。填充),并引导到未引导(额叶/裂隙叶)过渡。相比之下,末级撕裂通道似乎沿几个正常断层以大角度转向区域斜坡,并在主通道带外部形成一个凹陷的裂片。这项研究表明了在这些演化阶段中的通道和波瓣如何对褶皱和断层的存在做出不同的反应。它为三阶海平面周期内受结构诱发地形影响开发的海底河道瓣系统提供了独特的模拟。这项研究的结果为洞察各种斜坡通道和波瓣的时空发展提供了见识,并可能大大增强构造活动区深水系统中相关储层的预测。

更新日期:2021-04-27
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