November 8-12, 2015
Organic-rich shales are heterogeneous, naturally occurring composites that act as source rocks for oil and gas, which can be extracted through the process of hydraulic fracturing. Shales are composed of clays, minerals, and evolving organic matter and developed through long periods of sedimentation and compression. An elastic modulus mapping technique based on spatially continuous dynamic nanoindentation is applied to map microscale variations in a fine-grained, organic-rich shale consisting of inorganic minerals with an inter-
penetrating network of microscale pores filled with organic matter. A sample of Bakken shale from the Williston Basin was chosen for analysis, in which the organic matter is predominantly kerogen. Figure 1 illustrates the degree of spatial variation in microstructure, with thin lathes of clay in gray, kerogen in black, and minerals including calcite and pyrite shown as larger grains in various light shades of gray. Procedures for sample preparation, scanning, and data analysis were optimized through experimentation and analysis using Hertzian contact mechanics. The magnitude of influence from surface roughness and spatially varying stiffness on property extraction were assessed and mitigated through implementing data filtering routines. As a result, spatial variation in elastic modulus was mapped at higher resolution than had previously been reported. This improvement in data extraction provides a better understanding of intergranular properties in shales and is applicable to other natural and manufactured composites containing stiff and compliant materials. The data presented here for organic-rich shales are the first of their kind and have the potential to inform procedures for upscaling to representative volume elements and developing physics-based models for assessing deformation and fracture potential.
Corinne Packard, Taylor Wilkinson, Saeed Zargari, and Manika Prasard, "Probing micro- and nano-scale elastic modulus variation in organic-rich shale—A naturally occurring composite" in "Composites at Lake Louise (CALL 2015)", Dr. Jim Smay, Oklahoma State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/composites_all/80