MULTISCALE CHARACTERISTICS OF MECHANICAL AND COMPOSITIONAL PROPERTIES IN MANCOS SHALE

Multiscale characteristics of textural and compositional (e.g., clay, cement, organics, etc.) heterogeneity profoundly influence the mechanical properties of shale. In particular, strongly anisotropic (i.e., laminated) heterogeneities are often observed to have a significant influence on hydrological and mechanical properties. In this work, we investigate shale samples of the Cretaceous Mancos Shale to explore the importance of a variety of geologic variables, including lamination, cements, organic content, and the spatial distribution of these characteristics. Mechanical testing of the samples included: axisymmetric compressive tests to determine the mechanical properties of samples with various micro-lithofacies; Brazilian disk tests to evaluate the impact of local heterogeneity on failure characteristics; and nano-indentation to investigate heterogeneous mechanical response at the micron scale. 

Comparison of mechanical response with compositional heterogeneity is useful to mechanistically evaluate the relationship between mechanical response and micro-lithofacies features across scales. Phase field modeling was employed to evaluate crack initiation and propagation in shale during Brazilian tests using mineralogical mapping, micro-lithofacies characterization, and digital image correlation. Comparison of core-scale mechanical testing and phase field modeling results reveal the significance of microscale properties in the mechanical response on the core samples. This work provides a robust workflow to develop a multi-scale understanding of mechanical response in laminated heterolithic shale.

This work was funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE-SC0006883. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.