Multi-scale evaluation of mechanical properties of the Bakken shale

Understanding mechanical properties of shale has been the topic of research in the past decade due to its importance in hydraulic fracturing and rock physics modeling. Since shales are highly heterogeneous in constituent components, detailed understanding of mechanical properties in a multi-scale (nano, micro, macro and field) is vital and can present various results. In this study, we used a combination of analytical methods including high-resolution mineral mapping (MAPS), programmed pyrolysis and nanoindentation to identify mineralogy, geochemistry and nanomechanical characteristics of the Bakken shales in Williston Basin, North Dakota. Nanoindentation measurements were done both parallel and perpendicular to the bedding plane to examine mechanical anisotropy. Data were analyzed via multivariate statistical deconvolution technique (maximum likelihood approach and expectation–maximization algorithms) to reveal different mechanical phases, considering their Young’s modulus and hardness. Based on recognized components in the samples and measured values, Young’s modulus was upscaled through effective medium theory. Results showed that total organic carbon (TOC) content has a decreasing effect on Young’s modulus values. It was found that mechanical anisotropy increases with an increasing TOC content. Finally, upscaled Young’s modulus results were compared with reported measurements on core plugs which was found in a reasonable agreement.