Abstract Superpermeability (super-k) flow zones in carbonate reservoirs are thought to be controlled by bioturbation—related burrow networks, e.g., burrow pores of Thalassinoides. To improve the current understanding, this study investigated Thalassinoides and associated passive fill in the Upper Jubaila Member of the Upper Jurassic Jubaila Formation, central Saudi Arabia. Analysis of the elemental and mineralogical compositions of powder samples from the passive fill and burrow matrix, and thin sections of selected burrow matrix samples were conducted to determine the origin of the passive fill. The goal, herein, is to infer the flow properties of the bioturbated strata of the Upper Jubaila Member based on the occurrence of this passive fill in the burrow pores of the Thalassinoides. Compared to the burrow matrix, the analyzed passive fill exhibit marked differences in elemental composition, suggesting a much younger and different origin than that of the marine carbonates of the Upper Jubaila Member. A CaO plus MgO concentration below 28% and an elevated SiO2 plus Al2O3 concentration above 45% suggest a clay-dominated passive fill. The reddish and brownish colorations of the passive fill are attributed to the presence of iron oxyhydroxides, as indicated by the elevated Fe2O3 concentration (a mean of 5.8% ± 1.7%), and a mineralogical composition with elevated percentages of goethite and hematite. The normalized rare earth element (REE) pattern of the passive fill is consistent with that of lithogenous (siliciclastic) sources, which are likely deposited in a well-oxygenated environment, as suggested by the redox-sensitive elements and normalized REEs. These sources probably originate in hot humid environment, as indicated by the chemical index of alteration (CIA) (>80). The above geochemical data suggest that the passive fill was derived from soils similar to Mediterranean Terra Rossa soils and postdate the formation of burrow pores in the Thalassinoides-bearing strata. This could have occurred after exposure of the Upper Jubaila Member. Terra Rossa soil most likely reached the Thalassinoides-bearing strata from the surface through vertical fractures and karst features, filled burrow pores, fractures along bedding plains, and even intercrystalline pores. The occurrence of Terra Rossa soil in the burrows and intercrystalline pores of the Thalassinoides-bearing strata implies that the pore system of the Upper Jubaila Member possessed connected pathways that enabled soil infiltration followed by simultaneous precipitation in the burrows and intercrystalline pores. The presence of these connected burrow pores containing shafts with diameters ranges from 1 to 5 cm suggests a superpermeable storage capacity and presence of a superflow unit in the Upper Jubaila Member. This study provides an excellent example to better understand the controls of super-k zones in carbonate reservoirs.

中文翻译：

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沙特阿拉伯中部上朱拜拉组浅海地层生物扰动形成超渗透流动带的证据

摘要 碳酸盐岩储层中的超渗透 (super-k) 流动区被认为受生物扰动相关的洞穴网络控制，例如 Thalassinoides 的洞穴孔隙。为了提高目前的认识，本研究调查了沙特阿拉伯中部上侏罗统朱拜拉组上朱拜拉段的 Thalassinoides 和相关被动充填。对来自被动填充物和洞穴基质的粉末样品的元素和矿物组成进行分析，并对选定的洞穴基质样品进行薄片分析，以确定被动填充物的来源。本文的目标是根据 Thalassinoides 洞穴孔隙中这种被动填充物的出现来推断上朱拜拉段生物扰动地层的流动特性。与洞穴矩阵相比，分析的被动充填物在元素组成上表现出显着差异，表明与上朱拜拉段的海相碳酸盐岩相比，其起源要年轻得多，而且起源不同。CaO 加 MgO 浓度低于 28% 和升高的 SiO2 加 Al2O3 浓度高于 45% 表明粘土占主导地位的被动填充。被动填充物呈红色和褐色是由于氢氧化铁的存在，如 Fe2O3 浓度升高（平均为 5.8% ± 1.7%）以及针铁矿和赤铁矿百分比升高所表明的矿物成分。被动填充物的归一化稀土元素 (REE) 模式与岩质（硅质碎屑）源的模式一致，如氧化还原敏感元素和归一化 REE 所表明的那样，这些源很可能沉积在氧化良好的环境中。这些来源可能起源于炎热潮湿的环境，如化学蚀变指数 (CIA) (>80) 所示。上述地球化学数据表明，被动填土来源于类似于地中海 Terra Rossa 土壤的土壤，并且在含 Thalassinoides 的地层中形成洞穴孔隙之后。这可能发生在上朱拜拉成员暴露之后。Terra Rossa 土壤很可能通过垂直裂缝和岩溶特征、充满洞穴的孔隙、沿层理平原的裂缝，甚至晶间孔隙从地表到达含 Thalassinoides 的地层。Terra Rossa 土壤在含 Thalassinoides 地层的洞穴和晶间孔中的出现意味着上朱拜拉段的孔隙系统具有连通的通道，使土壤入渗，随后在洞穴和晶间孔中同时降水。这些包含直径范围为 1 至 5 厘米的竖井的连通洞穴的存在表明上朱拜拉段具有超渗透存储能力和超流单元的存在。本研究为更好地理解碳酸盐岩储层中超 k 带的控制提供了一个很好的例子。这些包含直径范围为 1 至 5 厘米的竖井的连通洞穴的存在表明上朱拜拉段具有超渗透存储能力和超流单元的存在。本研究为更好地理解碳酸盐岩储层中超 k 带的控制提供了一个很好的例子。这些包含直径范围为 1 至 5 厘米的竖井的连通洞穴的存在表明上朱拜拉段具有超渗透存储能力和超流单元的存在。本研究为更好地理解碳酸盐岩储层中超 k 带的控制提供了一个很好的例子。