Multiscale Approach for Mechanical Characterization of Organic-Rich Shale and Its Application

Abstract

Mechanical behavior of organic-rich shale strongly influences the stimulation performance of hydraulic fracturing. This article presents an approach for the characterization and evaluation of mechanical properties of shale at different scales. Nanoindentation and modulus mapping were performed to measure the Young’s modulus and stiffness coefficients of the main constituents in shale at the mineral scale. The contact area of the nanoindentation on quartz is approximately 3.79 × 105 nm2, whereas the contact areas of modulus mapping are almost below 7.85 × 103 nm2. This comparison indicates that modulus mapping has higher resolution and is more suitable for the characterization of clay minerals. At the core scale, microindentation was applied to investigate the macroscopic properties. From the statistical analysis, we find that the quantity of the successful microindentation should be more than 70 to obtain effective results. In addition, an upscaling method was proposed to predict the macroscopic properties. Both of the predictions from the Mori-Tanaka (MT) model and the self-consistent method agree well with the microindentation results, but the results from the MT model show stronger anisotropy. Finally, we provided a new brittleness index (BI) and an example to estimate the mechanical properties along the well with the mineralogical logging data.