Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation
Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation
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DOI：
10.1007/s00603-020-02261-6
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发表时间：
2020-10-19
影响因子：
6.2
通讯作者：
Armitage, P. J.
中科院分区：
文献类型：
--
作者：
Graham, S. P.;Rouainia, M.;Armitage, P. J.
页岩覆盖层的地质力学完整性是一系列工程和能源相关应用（包括CO2储存和非常规碳氢化合物生产）的一个非常重要的地质风险因素。本文旨在提供一套全面的高质量的纳米和微观力学数据的页岩样品，以更好地约束宏观力学性能，从页岩的微观结构成分。我们提出了第一个研究的钙质页岩的长度尺度为10 nm至100 μ m的机械响应，结合方法，涉及原子力显微镜（AFM），低负荷和高负荷纳米压痕。PeakForce定量纳米力学映射AFM（PF-QNM）和定量成像（QI-AFM）给出了杨氏模量高达25 GPa的类似结果，这两种技术产生的值为5-10 GPa的有机物。在这两种AFM技术中，只有PF-QNM在较高的模量下产生稳健的结果，与高达60 GPa的低负载纳米压痕结果相似。粘土、方解石和石英长石的测量模量分别为22 +/- 2GPa、42 +/-8 GPa和55 +/-10 GPa。对于方解石和石英长石，这些值明显低于对高度结晶相的测量。高负荷纳米压痕产生的单峰机械响应在40-50 GPa的范围内的两个样品在这里研究，与方解石的主要矿物相一致。Voigt和Reuss边界计算低负荷纳米压痕结果为各个阶段产生预期的复合值测量的高负荷纳米压痕在100-600 μ m的长度尺度。相比之下，使用来自文献的数据在更高度结晶的矿物相上测量的模量与复合值不匹配。因此，更多的重点应放在使用纳米和微米尺度的数据作为输入有效的介质模型和均匀化计划，以预测散装页岩机械响应。
The geomechanical integrity of shale overburden is a highly significant geological risk factor for a range of engineering and energy-related applications including CO2 storage and unconventional hydrocarbon production. This paper aims to provide a comprehensive set of high-quality nano- and micro-mechanical data on shale samples to better constrain the macroscopic mechanical properties that result from the microstructural constituents of shale. We present the first study of the mechanical responses of a calcareous shale over length scales of 10 nm to 100 mu m, combining approaches involving atomic force microscopy (AFM), and both low-load and high-load nanoindentation. PeakForce quantitative nanomechanical mapping AFM (PF-QNM) and quantitative imaging (QI-AFM) give similar results for Young's modulus up to 25 GPa, with both techniques generating values for organic matter of 5-10 GPa. Of the two AFM techniques, only PF-QNM generates robust results at higher moduli, giving similar results to low-load nanoindentation up to 60 GPa. Measured moduli for clay, calcite, and quartz-feldspar are 22 +/- 2GPa,42 +/- 8GPa, and 55 +/- 10GPa respectively. For calcite and quartz-feldspar, these values are significantly lower than measurements made on highly crystalline phases. High-load nanoindentation generates an unimodal mechanical response in the range of 40-50 GPa for both samples studied here, consistent with calcite being the dominant mineral phase. Voigt and Reuss bounds calculated from low-load nanoindentation results for individual phases generate the expected composite value measured by high-load nanoindentation at length scales of 100-600 mu m. In contrast, moduli measured on more highly crystalline mineral phases using data from literature do not match the composite value. More emphasis should, therefore, be placed on the use of nano- and micro-scale data as the inputs to effective medium models and homogenisation schemes to predict the bulk shale mechanical response.