Riza Nurbekova , Xiangyun Shi , Randy Hazlett , David Misch , Milovan Fustic , Reinhard F. Sachsenhofer
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The initially diverse values of <em>E</em> and <em>H</em> for the mechanical pseudophases were observed to converge to a constant value at indentations beyond 2–2.5 μm (varying between different samples), implying the existence of a minimal probing depth for assessing the bulk <em>E</em> and <em>H</em> of heterogeneous mudstone samples. The obtained bulk <em>E</em> and <em>H</em> values (8–21 GPa and 0.3–0.9 GPa, respectively) demonstrated a strong correlation with the mineralogical composition of the indented samples. Despite containing a notable proportion of mechanically stiff components (>45 vol%), the bulk mechanical parameters determined in this study were significantly lower than those reported for major shale formations such as the Barnett and Longmaxi Shale. 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引用次数: 0
摘要
在高达 4 μm 的挠曲深度范围内进行的广泛纳米压痕测试产生了一个大型数据集,为富含有机物的不同成分泥岩样品的力学性能(特别是弹性模量(E)和硬度(H))的统计评估提供了一个可行的框架。使用 K-means 算法对浅至 300-400 nm 的压痕数据进行聚类,以确定样品中的三个力学类别:软假相(如有机物、石膏和粘土矿物)、硬假相(如石英和长石)以及连接软硬矿物的过渡复合假相。据观察,机械假相最初不同的 E 值和 H 值在压痕超过 2-2.5 μm 时趋于一个恒定值(不同样品之间存在差异),这意味着存在一个最小探测深度来评估异质泥岩样品的体积 E 值和 H 值。所获得的体积 E 值和 H 值(分别为 8-21 GPa 和 0.3-0.9 GPa)与压痕样品的矿物成分密切相关。尽管含有相当比例的机械刚性成分(45% vol%),但本研究确定的块体机械参数明显低于巴尼特页岩和龙马溪页岩等主要页岩层的报告参数。造成这种差异的主要原因是样本中存在热成熟度较低的有机物(Ro < 0.6%),占样本总量的 36%,以及大量石膏(占样本总量的 15%)。所采用的方法不仅证明了选择适当的压痕深度对研究高度异质泥岩及其组成矿物的机械特性的重要性,而且还说明了使用纳米压痕法检测各种调查体积、接近宏观值和确定代表性元素体积(REV)的能力。研究结果还对所调查地层的可压裂性和总体可开采性提供了重要见解,从而加深了我们对其开采潜力的了解。
Geomechanical characterization and mineralogical correlation of compositionally diverse world-class Kazakhstani source rocks: Insights from nanoindentation testing
Extensive nanoindentation testing over a range of deflection depths of up to 4 μm yielded a large dataset, providing a viable framework for the statistical assessment of the mechanical properties, specifically elastic modulus (E) and hardness (H), of compositionally diverse organic-rich mudstone samples. The data from indentations as shallow as 300–400 nm were clustered using the k-means algorithm to identify three mechanical categories in the samples: a soft pseudophase (e.g., organic matter, gypsum, and clay minerals), a stiff pseudophase (e.g., quartz and feldspar), and a transitional composite-like pseudophase bridging the soft and hard minerals. The initially diverse values of E and H for the mechanical pseudophases were observed to converge to a constant value at indentations beyond 2–2.5 μm (varying between different samples), implying the existence of a minimal probing depth for assessing the bulk E and H of heterogeneous mudstone samples. The obtained bulk E and H values (8–21 GPa and 0.3–0.9 GPa, respectively) demonstrated a strong correlation with the mineralogical composition of the indented samples. Despite containing a notable proportion of mechanically stiff components (>45 vol%), the bulk mechanical parameters determined in this study were significantly lower than those reported for major shale formations such as the Barnett and Longmaxi Shale. This discrepancy is primarily due to the presence of organic matter with low thermal maturity (Ro < 0.6%), which constitutes <36 vol% of the samples, and a significant gypsum content, accounting for <15 vol%.
The employed approach not only demonstrated the importance of choosing the proper indentation depths for investigating the mechanical properties of highly heterogeneous mudstone rocks and their constituent minerals, but it also illustrated the capability of examining various volumes of investigation using nanoindentation, approaching macroscopic values, and identifying a representative element volume (REV). The findings also provided crucial insights into the fracability and overall producibility of the investigated formations, thereby enhancing our understanding of their extraction potential.
期刊介绍:
The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.