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Preferred orientation and elastic anisotropy of illite-rich shale

Hans-Rudolf Wenk, Ivan Lonardelli, Hermann Franz, Kurt Nihei and Seiji Nakagawa
Preferred orientation and elastic anisotropy of illite-rich shale
Geophysics (April 2007) 72 (2): E69-E75


Shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals. This orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals. A new method is introduced that uses high-energy synchrotron X-rays to obtain diffraction images in transmission geometry and applies it to an illite-rich shale. The images are analyzed with the crystallographic Rietveld method to obtain quantitative information about phase proportions, crystal structure, grain size, and preferred orientation (texture) that is the focus of the study. Textures for illite are extremely strong, with a maximum of 10 multiples of a random distribution for (001) pole figures. From the three-dimensional orientation distribution of crystallites, and single-crystal elastic properties, the intrinsic anisotropic elastic constants of the illite aggregate (excluding contribution from aligned micropores) can be calculated by appropriate medium averaging. The illitic shale displays roughly transverse isotropy with C (sub 11) close to C (sub 22) and more than twice as strong as C (sub 33) . This method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy.

ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 72
Serial Issue: 2
Title: Preferred orientation and elastic anisotropy of illite-rich shale
Affiliation: University of California, Berkekey, Department of Earth and Planetary Science, Berkeley, CA, United States
Pages: E69-E75
Published: 200704
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 41
Accession Number: 2007-114243
Categories: Economic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N44°30'00" - N49°00'00", W116°01'60" - W104°01'60"
Secondary Affiliation: HASYLAB, DEU, Federal Republic of GermanyChevron Energy Technology Company, USA, United StatesLawrence Berkeley National Laboratory, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 200747
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