Nanoindentation of Horn River Basin Shales: The Micromechanical Contrast Between Overburden and Reservoir Formations
Nanoindentation of Horn River Basin Shales: The Micromechanical Contrast Between Overburden and Reservoir Formations
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DOI：
10.1029/2022jb025957
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发表时间：
2023-03
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影响因子：
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通讯作者：
T. Charlton;M. Rouainia;A. C. Aplin;Q. Fisher;L. Bowen
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作者：
T. Charlton;M. Rouainia;A. C. Aplin;Q. Fisher;L. Bowen
我们提出了一个微观力学表征页岩从霍恩河流域，加拿大西北部。页岩具有对比鲜明的矿物学和微观结构，并在现场发挥不同的地质力学作用：样品集涵盖非常规气藏和作为上部裂缝屏障的覆盖层单元。使用X射线衍射、压汞法和扫描电子显微镜（SEM）表征组成和织构。网格纳米压痕测试被用来获得页岩微观结构中的主要相的力学响应。平行和垂直于层面对样品进行压痕，以评估机械各向异性。采用SEM-EDS（能量色散X射线光谱）对网格进行化学分析，并将耦合的化学-机械数据用于统计聚类程序（高斯混合模型），以揭示每个相的机械性能。结果表明，覆盖层由具有高度各向异性弹性刚度的软粘土基质和较硬但有效各向同性的石英和长石夹杂物组成;先前已使用微震数据在更大规模上观察到覆盖层的显著各向异性。蠕变位移集中在粘土基质中，这是裂缝屏障和密封应用的关键阶段。储集层单元较硬，具有更多的各向同性力学响应，主要是由于其较低的粘土含量。尽管不同的组合物和微观结构，这些页岩（粘土/有机基质，石英/长石，白云石，方解石）的主要阶段有独特的机械签名，这将有助于识别在未来的微观力学表征，并促进其在升级方案中的使用。
We present a micromechanical characterization of shales from the Horn River Basin, NW Canada. The shales have contrasting mineralogy and microstructures and play different geomechanical roles in the field: the sample set covers an unconventional gas reservoir and the overburden unit that serves as the upper fracture barrier. Composition and texture were characterized using X‐ray diffraction, mercury injection porosimetry, and scanning electron microscopy (SEM). Grid nanoindentation testing was used to obtain the mechanical response of the dominant phases in the shale microstructure. Samples were indented parallel and perpendicular to the bedding plane to assess mechanical anisotropy. Chemical analysis of the grids with SEM‐EDS (energy dispersive X‐ray spectroscopy) was undertaken and the coupled chemo‐mechanical data was used in a statistical clustering procedure (Gaussian mixture model) to reveal the mechanical properties of each phase. The results show that the overburden consists of a soft clay matrix with highly anisotropic elastic stiffness, and stiffer but effectively isotropic inclusions of quartz and feldspar; the significant anisotropy of the overburden has been previously observed on a much larger scale using microseismic data. Creep displacement is concentrated in the clay matrix, which is the key phase for fracture barrier and seal applications. The reservoir units are harder and have more isotropic mechanical responses, primarily due to their lower clay content. Despite varied compositions and microstructures, the major phases of these shales (clay/organic matrix, quartz/feldspar, dolomite, and calcite) have unique mechanical signatures, which will aid identification in future micromechanical characterizations and facilitate their use in upscaling schemes.