Summary

Typical of most shale plays, the reservoir quality of the Marcellus shale is reported to change spatially from good to poor, without clear understanding of the underlying controls. In a resource-recovery operation, one must understand the bulk behavior of the rocks in response to an applied stress state. However, in order to appropriately model shale, which is a heterogeneous composite material, one must also understand the behavior of the various individual constituents, each with a distinct material character. Changes in primary sedimentary characteristics, inclusive of mineralogy, texture, and organic matter abundance, define lithofacies within the Marcellus, and we are probing the manner in which lithofacies variations influence the mechanical properties of the shale. Capitalizing on the successes of methods developed to investigate manmade composites, we adopt micro- and nanoindentation procedures to analyze geological samples. Nanoindentation is particularly useful for its ability to reveal properties of individual constituents, a task not easily accomplished in shale due to the small constituent size. We show that nanoindentation and micro-fracture experiments have potential to provide detailed information about the spatial variation of the mechanical properties in these rocks at the scale of the fundamental constituents, but such experiments are highly affected by experimental conditions. We provide an analysis of our results, discuss their validity, and provide insight regarding how to recognize and account for experimental artifacts at this scale.

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