October 4-9, 2015
Gas shale has proven to be a good candidate for mechanical characterization using nanoindentation. However, this natural material composed of nano-granular clay and microscale non-clay minerals also includes within its matrix a polymeric material. This kerogen biopolymer is interbedded and intertwined with the clay and non-clay minerals at almost all scales. Figure 1(a) demonstrates the nature of interlacing that occurs between shale rock and organic matter.
Kerogen within the shale matrix has been mechanically characterized using nanoindentation to determine Young’s modulus and hardness such as in the work by Zeszotarski et al. 2004. As a polymer kerogen not only has a Young’s modulus in compression but also has a substantial Young’s modulus value in tension and much higher tensile strength than rocks in general! This fact has now been observed at the micro- and nanoscale during nanoindentation while monitoring in situ via scanning electron microscopy (SEM). Load and unload experiments with micro-Newton forces (µN) and nanometer (nm) displacements have clearly shown the elastic nature of kerogen in the shale gas matrix.
This unique experimental setup provided us not only the ability to load and fracture micro- and nano-scale kerogen-rich shale structures but also the advantage of visualizing the initiation, propagation, and ultimate failure of the beams. Subsequent high resolution imaging of the support and beam fracture faces as well as complementary EDS allowed us to analyze the grains/minerals and non-minerals associated with the fracture. Strain softening behavior was measured on this composite at the micro scale in cantilever micro-beam as shown in Figure 1 (b) and (c). This behavior of gas shale could never be captured at the macro-scale.
Younane Abousleiman, Katherine Hull, Ghaithan Al-Muntasheri, Peter Hosemann, Scott Parker, and Cameron Howard, "In-situ strain softening and strain hardening of natural geomaterials on the microscale" in "Nanomechanical Testing in Materials Research and Development V", Dr. Marc Legros, CEMES-CNRS, France Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/nanomechtest_v/44