To better determine the sweet spot in the vertical profile of the Longmaxi Formation, the shale heterogeneity was systematically investigated. A series of experiments were conducted on 40 shale samples collected from the Lower Silurian Longmaxi Formation in the Weiyuan shale gas field. The results indicated that total organic carbon (TOC), the mineral composition, methane adsorption capacity, and porosity of the four sub‐layers in the Longmaxi shale varied significantly. In terms of the TOC, the mid‐lower Long1₁¹ had the highest value, followed by Long1₁³, while the TOC values of Long1₁² and Long1₁⁴ were quite low. As for mineral composition, the mid‐lower Long1₁¹ had the highest quartz content, Long1₁² and Long1₁³ had equivalent quartz, carbonate, and clay mineral contents, and Long1₁⁴ had higher clay mineral and carbonate contents, but a lower quartz content. Shale porosity and methane adsorption capacity were the highest in the mid‐lower Long1₁¹, followed by Long1₁³, Long1₁², Long1₁⁴, and the upper Long1₁¹. The micro‐heterogeneity represented by the fractal dimension ranged from 2.590 to 2.750, with an average of 2.670. The mid‐lower Long1₁¹ had the largest fractal dimension, followed by Long1₁³, Long1₁², Long1₁⁴, and the upper part of Long1₁¹ had the smallest fractal dimension. The sedimentary environment controls the macro‐heterogeneity in the vertical profile. The micro‐heterogeneity depends on diagenesis, which can be investigated by the different effects of minerals on micropore development. The strong micro‐heterogeneity results in better preservation conditions for shale gas. The mid‐lower Long1₁¹ was rich in gas generation material (TOC) with enough storage space and is characterized by good preservation conditions, leading to the highest gas content of the four sub‐layers. In addition, the high brittle mineral content is conducive to fracturing and the formation of a fracture network. Thus, the middle ‐Long1₁¹ is the “sweet spot” in the vertical profile for the shale gas development.

中文翻译：

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龙马溪组储层非均质性及其对页岩气富集的意义

为了更好地确定龙马溪组垂直剖面上的甜点，系统地研究了页岩非均质性。对威远页岩气田下志留统龙马溪组采集的40个页岩样品进行了一系列实验。结果表明，龙马溪组页岩的四个子层的总有机碳（TOC），矿物组成，甲烷吸附能力和孔隙度存在显着差异。就TOC而言，中较低的Long1 ₁ ¹具有最高的值，其次是Long1 ₁ ³，而Long1 ₁ ²和Long1 ₁ ⁴的TOC值却很低。至于矿物成分，下中段Long1 ₁¹具有最高的石英含量，Long1 ₁ ²和Long1 ₁ ³具有相等的石英，碳酸盐和粘土矿物含量，Long1 ₁ ⁴具有较高的粘土矿物和碳酸盐含量，但石英含量较低。页岩孔隙度和甲烷吸附能力在中下部Long1 ₁ ^1中最高，其次是Long1 ₁ ³，Long1 ₁ ²，Long1 ₁ ⁴和上部Long1 ₁ ¹。分形维数表示的微异质性范围为2.590至2.750，平均为2.670。中下Long1 ₁ ¹分形维数最大，其次是Long1 ₁ ³，Long1 ₁ ²，Long1 ₁ ⁴，Long1 ₁ ¹的上部分形维数最小。沉积环境控制着垂直剖面的宏观非均质性。微异质性取决于成岩作用，可以通过矿物对微孔发育的不同影响来研究。强大的微观非均质性为页岩气的保存提供了更好的条件。中下Long1 ₁ ¹富含气体生成材料（TOC），具有足够的存储空间，并且具有良好的保存条件，从而导致四个子层中的气体含量最高。另外，高脆性矿物含量有利于压裂和裂缝网络的形成。因此，中长_{1 1} ¹是页岩气开发垂直剖面中的“最佳位置”。