Characterization of Shale Softening by Large Volume-Based Nanoindentation

Lu, Yunhu; Liu, Yucheng; Wu, Yongkang; Luo, Shengmin; Jin, Yan; Zhang, Guoping

doi:10.1007/s00603-019-01981-8

Cited by 49 publications

(20 citation statements)

References 60 publications

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“…To access the mechanical response at length scales above ∼ 10 μm , nanoindentation is employed. A relatively wellestablished technique in geomechanics compared to AFM (Bobko and Ulm 2008;Liu and Ostadhassan 2017;Liu et al 2018;Lu et al 2019;Akono et al 2019;Abedi et al 2016), only a brief overview of the technique is provided here. For composite materials, the load applied in indentation testing is important to distinguish between local and bulk mechanical responses (Constantinides et al 2006).…”

Section: Nanoindentationmentioning

confidence: 99%

Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation

et al. 2020

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The geomechanical integrity of shale overburden is a highly significant geological risk factor for a range of engineering and energy-related applications including CO$$_2$$ 2 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 $$\upmu$$ μ 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 $$22 \pm 2\,\hbox { GPa}$$ 22 ± 2 GPa , $$42 \pm 8\,\hbox { GPa}$$ 42 ± 8 GPa , and $$55 \pm 10\,\hbox { GPa}$$ 55 ± 10 GPa 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 $$\upmu$$ μ 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.

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Section: Nanoindentationmentioning

confidence: 99%

Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation

et al. 2020

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“…In contrast, these viscoelastic parameters increased with increasing peak loads for clay minerals, which is similar to the increase in Young's modulus of clay matrix with increasing depth or peak load [55]. One possible reason may be due to grain compaction and rearrangement [56,57] and grain motion by frictional sliding [4] of clay minerals under larger peak loads, which enhances the creep deformation.…”

Section: Comparison Of the Viscoelastic Modelsmentioning

confidence: 56%

Modeling the Viscoelastic Behavior of Quartz and Clay Minerals in Shale by Nanoindentation Creep Tests

et al. 2022

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The viscoelastic behavior of minerals in shales is important in predicting the macroscale creep behavior of heterogeneous bulk shale. In this study, in situ indentation measurements of two major constitutive minerals (i.e., quartz and clay) in Longmaxi Formation shale from the Sichuan Basin, South China, were conducted using a nanoindentation technique and high-resolution optical microscope. Firstly, quartz and clay minerals were identified under an optical microscope based on their morphology, surface features, reflection characteristics, particle shapes, and indentation responses. Three viscoelastic models (i.e., three-element Voigt, Burger’s, and two-dashpot Kelvin models) were then used to fit the creep data for both minerals. Finally, the effects of peak load on the viscoelastic behavior of quartz and clay minerals were investigated. Our results show that the sizes of the residual imprints on clay minerals were larger than that of quartz for a specific peak load. Moreover, the initial creep rates and depths in clay minerals were higher than those in quartz. However, the creep rates of quartz and clay minerals displayed similar trends, which were independent of peak load. In addition, all three viscoelastic models produced good fits to the experimental data. However, due to the poor fit in the initial holding stage of the three-element Voigt model and instability of the two-dashpot Kelvin model, Burger’s model is best in obtaining the regression parameters. The regression results indicate that the viscoelastic parameters obtained by these models are associated with peak load, and that a relatively small peak load is more reliable for the determination of viscoelastic parameters. Furthermore, the regression values for the viscoelastic parameters of clay minerals were lower than those of quartz and the bulk shale, suggesting the former facilitates the viscoelastic deformation of shale. Our study provides a better understanding of the nanoscale viscoelastic properties of shale, which can be used to predict the time-dependent deformation of shale.

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“…51,52,81 For the highest-modulus cluster, the elastic modulus was up to 120 GPa, indicating that the hard cluster can be attributed to the hard minerals, like quartz and pyrite, and the tested moduli were consistent with previously reported indentation moduli. 28,80 Interestingly, only two mechanical phases were identified at site 1 rather than three distinct clusters as in other sites, as shown in Figure 9b. This demonstrates the inherent heterogeneity of shale.…”

Section: Results and Analysismentioning

confidence: 88%

“…28 Previous studies have reported that the elastic modulus of quartz was in the range of 70−110 GPa and its hardness was in the range of 12− 16 GPa. 28,80,85 Thus, we inferred that the red closed area, marked as phase 2, was most likely to feature quartz grains. Feldspar-group minerals are generally columnar or plate-like particles as a consequence of the characteristic crystalline process of formation.…”

Section: Results and Analysismentioning

confidence: 88%

“…The average value of the lowest-strength cluster was slightly higher than the indentation modulus of the reported pure clay minerals (26−34 GPa) in previous studies. 28,51,80 This is because the mean value of the loweststrength clusters was the statistical probability of the mechanical properties not only of clay minerals but also other tiny or broken granular minerals embedded in the clay matrix. Meanwhile, the mineralogy on the substrate of the indented area also has an influence on the tested value of the surface minerals, which may increase the indentation modulus.…”

Section: Results and Analysismentioning

confidence: 99%

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Probing Nanomechanical Properties of a Shale with Nanoindentation: Heterogeneity and the Effect of Water–Shale Interactions

Liu

Kang

2021

Energy Fuels

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The mechanical properties of shale are critical for the extraction of gas and oil from nanoporous shale. In this study, nanoindentation tests with the accelerated property mapping mode were used to obtain the localized quantitative mechanical properties (the elastic modulus and hardness) of the tested shale sample. X-ray diffraction was used to analyze the bulk mineral composition. The Gaussian mixture model and k-means algorithm were used to fit the data and identify distinct mineral phases based on load–displacement curves. Three clusters of different mineral phases were recognized through nanoindentation curves. Experimental results and analyses show that the nanomechanics of shale are conditioned by the mineral composition and its spatial distribution. The spatial distribution of the elastic modulus and hardness showed the high heterogeneity of shale at the nano-to-micron scale, closely related to its localized mineralogical distribution and microstructures. It was found that the plastic work induced in the nanoindentation process was different between the three mineral clusters with a plastic work ratio of 0.06–0.18, 0.32–0.38, and 0.46–0.53 in high-, medium- and low-hardness clusters, respectively. A two-term exponential relationship was observed between hardness and plastic work. For the tested Marcellus shale, obvious mechanical weakening was observed after 20 days of water vapor treatment. The elastic modulus of shale exhibited a reduction of 0.6–15%, and the hardness decreased by 8.6–17.8%. Further investigation is recommended to quantify the variations in its indent-specified mechanical properties and its direct relationship with localized mineralogy and microstructure.

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Characterization of Shale Softening by Large Volume-Based Nanoindentation

Cited by 49 publications

References 60 publications

Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation

Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation

Modeling the Viscoelastic Behavior of Quartz and Clay Minerals in Shale by Nanoindentation Creep Tests

Probing Nanomechanical Properties of a Shale with Nanoindentation: Heterogeneity and the Effect of Water–Shale Interactions

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