Impact of Multiscale Characteristics of Heterogeneous Pore Structure and Mineralogy on Mechanical Properties of Shale

Abstract

Because of the need to artificially enhance permeability through induced fracture of mudstones, internal variations in the strength, toughness and elasticity of mudstones have been linked to reservoir performance. Mudstone mechanical properties are geologically controlled through changes in detrital and authigenic mineralogy, organic content and porosity that can be linked to deposition and diagenesis. We are investigating the impact of these geologic controls on mechanical strength and compliance from 10 μm to 10 cm scales in the Mancos Shale. We have described the range of sample lithologic variations at the sub-cm scale using a combination of optical petrography, microbeam analysis and laser scanning confocal microscopy. The samples' lithologic variations have been subdivided into macroscopic and microscopic facies. The microfacies' porosity and mineralogy were determined using dual focused ion beam-scanning electron microscopy at 10s of nm resolution. Micropillar unconfined compression testing (10 μm diameter by 20 μm length) perpendicular and parallel to bedding determined each microfacies' unconfined strength and Young's modulus. Micropillars were created with focused Ga ion milling. Micropillar compression tests were performed with a nanoindenter and flat diamond indenter. Macro-scale mechanical testing was conducted both perpendicular and parallel to bedding on the core samples from the different macrofacies using unconfined and triaxial compression tests with traditional hydraulic presses and pressure vessels. From the stress-strain paths of both micropillar and macro-scale mechanical testing, the anisotropy of elastoplastic deformation was determined. Comparison of multiscale lithologic description and multiscale anisotropic mechanical experiments is useful to directly evaluate the relationship between mechanical response and microscopic features across scales. This evaluation provides an example on how to develop multi-scale understanding of reservoir mudstones by correlating spatially extensible lithologic descriptions to multiple scales of deformation and failure. 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.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016