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The Assessment of Organic Matter Young's Modulus Distribution with Depositional Environment and Maturity

Lookup NU author(s): Thomas Fender, Dr Cees van der Land, Dr Mohamed Rouainia, Sam Graham, Dr Martin Jones, Dr Christopher Vane, Professor Thomas Wagner

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


Abstract

Quantification of risk to seal integrity in CCS, or gas extraction from hydraulic fracturing, is directly affected by the accessibility of organic pores within organic rich mudrocks. Knowledge of the host organic matter's mechanical properties, which are influenced by depositional environment and thermal maturity, are required to reduce operational risk. In this study we address the effect of both depositional environment and maturity on organic matter Young's modulus by means of Atomic Force Microscopy Quantitative ImagingTM, which is a nondestructive technique capable of nanomechanical measurements. Shales from varying marine depositional environments covering kerogen Types II (Barnett), IIS (Tarfaya), and II/III (Eagle Ford/ Bowland) are analyzed to capture variance in organic matter. The findings show organic matter has a Young's modulus ranging between 0.1 and 24 GPa. These marine shales have a bimodal distribution of Young's modulus to some degree, with peaks at between 3–10 and 19–24 GPa. These shales exhibit a trend with maturity, whereby Young's modulus values of <10 GPa are dominant in immature Tarfaya shale, becoming similar to the proportion of values above 15 GPa within the oil window, before the stiffer values dominate into the gas window. These peaks most likely represent soft heterogeneous aliphatic rich kerogen and stiff ordered aromatic rich kerogen, evidenced by the increase in the stiffer component with maturity and correlated with 13C NMR spectrocopy. These findings enable increased realism in microscale geomechanical fracture tip propagation models and may allow direct comparison between Young's modulus and Rock‐Eval parameters


Publication metadata

Author(s): Fender T, van der Land C, Rouainia M, Graham SP, Jones DM, Vane CH, Wagner T

Publication type: Article

Publication status: Published

Journal: Journal of Geophysical Research - Solid Earth

Year: 2020

Volume: 125

Issue: 12

Print publication date: 01/12/2020

Online publication date: 10/10/2020

Acceptance date: 03/10/2020

Date deposited: 16/12/2020

ISSN (print): 2169-9313

ISSN (electronic): 2169-9356

Publisher: American Geophysical Union

URL: https://doi.org/10.1029/2020JB020435

DOI: 10.1029/2020JB020435


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