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Effect of Diagenesis on Geomechanical Properties of Organic-Rich Calcareous Shale: A Multiscale Investigation

Lookup NU author(s): Dr Tom Charlton, Dr Mohamed Rouainia

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

© 2021. The Authors.This study investigates the nano to core-scale geomechanical properties of a maturity series of organic-rich, calcareous shales buried to 100°C–180°C, with a focus on: (a) the mechanical properties of organic matter; (b) the elastic response and anisotropy of the shale composite at micro and core scale; and (c) the creep response. Atomic force microscopy was used to target kerogen at nanoscale resolution, and it was found that the elastic stiffness increased with thermal maturity from 5.8 GPa in an immature sample to 11.3 GPa in a mature sample. Nanoindentation testing of the shale matrix showed that diagenesis is a key factor in determining the bulk elasticity, with increasingly intense carbonate cementation at higher thermal maturities contributing to a stiffer response. A multiscale model was formulated to upscale the elastic properties from nanoscale solid clay minerals to a microcracked composite at core scale, with good predictions of the micro and core-scale stiffness in comparison to indentation and triaxial results. A negative correlation was found between the creep modulus and clay/kerogen content, with greater creep displacement observed in nanoindentation tests in the immature clay- and kerogen-rich sample compared to samples of higher thermal maturity.


Publication metadata

Author(s): Charlton TS, Goodarzi M, Rouainia M, Aplin AC, Cubillas P

Publication type: Article

Publication status: Published

Journal: Journal of Geophysical Research: Solid Earth

Year: 2021

Volume: 126

Issue: 7

Print publication date: 30/06/2021

Online publication date: 30/06/2021

Acceptance date: 08/06/2021

Date deposited: 07/10/2021

ISSN (print): 2169-9313

ISSN (electronic): 2169-9356

Publisher: John Wiley and Sons Inc

URL: https://doi.org/10.1029/2020JB021365

DOI: 10.1029/2020JB021365


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