NEW APPROACHES TO RELATING THE MACROSCOPIC BEHAVIOR OF SHALES TO PORE-SCALE CONSTITUTIVE PROPERTIES

Shales are heterogeneous fine grained rocks that possess pore sizes ranging from the nanometer to the supra-micron scale. Such small sizes are not amenable to optical investigation, which has until recently prevented pore-scale investigations into shale behavior, particularly under in situ conditions. Macroscopic thermal, hydrological, mechanical, and chemical constitutive behaviors (e.g. swelling, dry-out, yield and failure, osmotic flux) are all macroscopic manifestations of the pore-scale, i.e. nano-behavior with nanopores containing fluid phases that differ in properties from the bulk. Characterization is not just a description of what, but should also include an assessment of the how and why of constitutive behaviors. Recent technological advances are enabling an unprecedented advancement in the characterization of shale multiphysics. We examine new and on-going efforts in shale characterization, with special attention given to in situ imaging methods. These methods are yielding unprecedented understanding of shale behavior in the subsurface and attendant responses to engineering perturbations of fluid injection, waste storage, and resource extraction including geologic carbon storage. We present a novel organizing framework to describe the multiscale features and coupled processes that govern macroscopic constitutive behavior.

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.