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Influence of fluvial crevasse-splay deposits on sandbody connectivity: Lessons from geological analogues and stochastic modelling
Marine and Petroleum Geology ( IF 3.7 ) Pub Date : 2021-03-31 , DOI: 10.1016/j.marpetgeo.2021.105060
Luca Colombera , Nigel P. Mountney

To investigate the importance of crevasse-splay elements for the connectivity of fluvial sandbodies, an integrated study has been undertaken that combines data from outcropping and subsurface fluvial successions, and modern rivers, with outputs from forward stratigraphic models and object-based modelling. Literature-derived analogue data on over 2100 crevasse-splay elements from many fluvial systems have been synthesized to obtain quantifications of the proportion and geometry of crevasse-splay units, and of their topological relationships with channel deposits. Some of the analogue data are used to inform inputs to stochastic modelling that is applied to determine how the presence of crevasse-splay deposits affects the connectivity of successions in which channel sandstones are preserved as channelized bodies or compartmentalized point-bar units.

Architectural configurations are documented that are variably characterized by (i) crevasse-splay sandbody compartmentalization, (ii) channel-sandbody connections that increase sandbody size and the likelihood of borehole connectivity, and (iii) intercommunication between different channel sandbodies. Analyses of analogue data demonstrate scaling relationships between the morphometry of crevasse-splay elements and associated channel elements and river catchments. Results also demonstrate how the proportions of channel and crevasse-splay deposits tend to covary in stratigraphic volumes. This information, when ported to stochastic models, yields results showing how the influence of crevasse-splay elements on static connectivity varies – in relative terms – as a function of architectural style, net-to-gross ratio and channel-sandbody geometry. Channel-body connections may be more important for smaller and relatively sand-poor fluvial systems, whereas mud-plug compartmentalization of splay elements may be more important for successions with larger channel-body width-to-thickness aspect ratios and lower net-to-gross ratios.

The results of this work can be applied to facilitate and improve the characterization and modelling of the static connectivity of subsurface successions that include crevasse-splay deposits. The results also reveal the possible influence of certain geological controls (channel avulsion, river-system scale, overbank cannibalization) on static connectivity.



中文翻译:

河道裂隙-张开沉积物对砂体连通性的影响:地质类似物和随机模拟的经验教训

为了研究裂隙张开要素对河流砂体连通性的重要性,已进行了一项综合研究,该研究将露头和地下河流演替以及现代河流的数据与正向地层模型和基于对象的模型的输出相结合。来自许多河流系统的2100多个裂隙扩张单元的文献衍生模拟数据已合成,以量化裂隙扩张单元的比例和几何形状以及它们与河道沉积物的拓扑关系。一些模拟数据用于为随机模型提供信息,该模型用于确定裂隙-张开沉积物的存在如何影响演替的连通性,在这些演替中,河道砂岩保存为河道状体或分隔的点状-杆状单元。

记录的建筑构型具有以下特征:(i)裂隙-张开的砂体分隔;(ii)通道-砂体连接,增加了砂体的尺寸和井眼连通性的可能性;以及(iii)不同通道的砂体之间的互通。对模拟数据的分析表明,裂隙张开单元的形态与相关河道单元和河流集水区之间的比例关系。结果还表明,地层体积中河道和缝隙-开裂沉积物的比例如何趋于平缓。将该信息移植到随机模型后,得出的结果表明,裂缝-张开元件对静态连通性的影响(相对而言)如何随建筑风格,净毛比和通道-砂体几何形状而变化。

这项工作的结果可用于促进和改善地下裂缝(包括裂隙-张开沉积物)的静态连通性的表征和建模。结果还揭示了某些地质控制措施(河道撕裂,河流系统规模,堤岸上的食人化)对静态连通性的可能影响。

更新日期:2021-04-04
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