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Book Chapter

Unconventional Gas-Oil Shale Microfabric Features Relating to Porosity, Storage, and Migration of Hydrocarbons

By
Neal R. O’Brien
Neal R. O’Brien
Geology Department, State University of New York at Potsdam, New York, U.S.A. (e-mails: obriennr@potsdam.edu, cmcrobbie@gmail.com)
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Carol A. McRobbie
Carol A. McRobbie
Geology Department, State University of New York at Potsdam, New York, U.S.A. (e-mails: obriennr@potsdam.edu, cmcrobbie@gmail.com)
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Roger M. Slatt
Roger M. Slatt
Institute of Reservoir Characterization, Sarkeys Energy Center, University of Oklahoma, Norman, Oklahoma, U.S.A. (e-mail: rslatt@ou.edu)
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Elizabeth T. Baruch-Jurado
Elizabeth T. Baruch-Jurado
Sprigg Geobiological Centre, School of Physical Sciences, The University of Adelaide, SA 5005, Australia (e-mail:Elizabeth.Baruch-Jurado@upstream.originenergy.com.au)
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Published:
January 01, 2016

Abstract

There are a variety of pore types in unconventional resource mudstones and shales. The currently preferred method by geologists and petrophysicists is to examine and analyze these mudstones and shales by argonion and focused ion-beam milling to produce an ultrasmooth surface, coupled with observation under the field emission scanning electron microscope (FESEM). Potential issues with Ar-ion milled/FESEM preparation and imaging include (1) the small size of sample cubes for upscaling, (2) loss of structural fabric during the milling–imaging process, (3) fewer non-inorganic pore types observed than when observed with an unpolished surface, (4) analog use of pores from one shale to another, although the pore types and composition might differ, and (5) the creation of potential artifacts related to desiccation and rock expansion because of core retrieval and sample preparation. Conventional FESEM images obtained from freshly broken surfaces reveal much more textural detail than those obtained from ion-milled (polished) surfaces. Although conventional FESEM methodology may share some of the same limitations as Ar-ion beam-milled/FESEM technology, FESEM methodology should not be overlooked because it provides a more cost-effective and potentially more accurate analysis for estimating porosity and determining pore types and their distribution in shales. Comparison of FESEM images from ion-milled and fresh, non-ion-milled surfaces reveals that organic matter and internal organoporosity are best viewed on ion-milled surfaces, but shale microfabric and non-organoporosity is best viewed under non-milled surfaces. Complete FESEM imagery for shale characterization should include both types of analyses.

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Contents

AAPG Memoir

Imaging Unconventional Reservoir Pore Systems

Terri Olson
Terri Olson
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American Association of Petroleum Geologists
Volume
112
ISBN electronic:
9781629812755
Publication date:
January 01, 2016

References

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