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

Abstract

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.

Comparative study of photoinduced surface-relief-gratings on azo polymer and azo molecular glass films

“…Besides that, the cantilever needs a sufficient spring constant to prevent excessive deformation during contact, and the probe tip must be rigid enough to avoid significant deformation of itself. 62 The normal working range of the probe RTESPA-525 used in this study is 1 GPa to 20 GPa, 45,56 which is compatible with the measured sample moduli at room temperature. Thus, the probe RTESPA-525 was mainly adopted for the current AFM PF-QNM measurement based on the Bruker's protocol, to ensure that the measured moduli are more accurate.…”

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

“…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. The mean elastic moduli of the medium-strength cluster, which may be attributed to the albite and ankerite minerals in shale, were consistent with the indentation moduli of feldspar reported in the literature, with a spectrum from 45 to 68 GPa, 80,81 and carbonates, ranging from 34 to 59 GPa. 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.…”

The Assessment of Organic Matter Young's Modulus Distribution With Depositional Environment and Maturity

“…This technique along with its sister technique PeakForce TM QNM TM has successfully obtained mechanical measurements of biological materials (Chopinet et al, 2013), cements (Trtik et al, 2012), and shales (Goodarzi et al, 2017). Recent research suggests that these two techniques are similar when measuring moduli in the range expected from organic matter (Graham et al, 2020). The AFM QI TM was used with the following settings: Force applied: 500 nN; Z length: 750 nm; and speed: 253 μm/s.…”