Nanoindentation Measurements on Rocks

Abstract

Young's modulus and hardness of shale are important parameters for the design of hydraulic fractures and the selection of proppant. Nanoindentation has shown applicability in fine grained rocks and provides a method to measure these parameters using core fragments and drill cuttings. Nanoindentation measurements on horizontal and vertical samples can be used to quantify anisotropy. Indentation Young's modulus correlates well with dynamic modulus obtained from acoustic velocity data on core plugs. Nanoindentation is thus a viable method to measure mechanical properties of fine grained shale. Young's moduli obtained by nanoindentation are related to composition and porosity, e.g., total organic carbon (TOC), porosity and mineralogy. Young's modulus showed a trends with both TOC and porosity and warrants further study to establish more robust relationships. The primary aim of this paper is to study the applicability of nanoindentation to shale and this is established by comparing nanoindentation results with standard dynamic pulse-transmission velocity measurements. Nanoindentation on Wolfcamp shale, Lyons sandstone, Sioux quartzite, Indiana limestone and pyrophyllite was performed to test whether the nanoindentation test gives representative results of the whole sample with variation in grain size. The experimental results indicate that nanoindentation measures the grain Young's modulus due to all indentations on a single grain for coarse grained rocks and thus, resulting in incorrect Young's modulus of rock. However, for rock with smaller grain (<indenter area), nanoindentation results are representative of multiple grains and hence correlating well with the dynamically determined Young's modulus.

Experimental Relationship Between Compressional Wave Attenuation and Surface Strains in Brittle Rock

“…All the peripheral surfaces of the specimens were smooth, flat, and leveled to within 0.01 mm under dry conditions using mechanized grinding. Lyons sandstone has an average grain size of about 190 μm (Bathija et al, ; Henao, ; Mighani et al, ; Ross et al, ; Shukla et al, ; Xu, Hofmann, et al, ). The bulk density of Lyons sandstone specimens was 2.52 g/cm 3 , which is similar to the value reported by Xu, Hofmann, et al ().…”

“…It is aeolian in origin and was formed through the long-term consolidation of moderately sorted fine-grained quartz sand dunes (Mighani et al, 2016;Ross et al, 2010;Shirole et al, 2017Shirole et al, , 2018bThompson, 1949). Because of this, Lyons sandstone is primarily composed of quartz (85-90%) with some presence of clay minerals (10-12%; Henao, 2017;Ross et al, 2010;Shukla et al, 2014). The sandstone block acquired for the present study was quarried from a depth of 5 m below the ground surface.…”