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Experimental observation of water saturation effects on shear wave splitting in synthetic rock with fractures aligned at oblique angles

Experimental observation of water saturation effects on shear wave splitting in synthetic rock with fractures aligned at oblique angles
Experimental observation of water saturation effects on shear wave splitting in synthetic rock with fractures aligned at oblique angles
Fractured rocks are known to exhibit seismic anisotropy and shear wave splitting (SWS). SWS is commonly used for fractured rock characterization and has been shown to be sensitive to fluid type. The presence of partial liquid/gas saturation is also known to affect the elastic properties of rocks. The combined effect of both fractures and partial liquid/gas saturation is still unknown. Using synthetic, silica-cemented sandstones with aligned penny-shaped voids, we conducted laboratory ultrasonic experiments to investigate the effect fractures aligned at an oblique angle to wave propagation would have on SWS under partial liquid/gas saturation conditions. The result for the fractured rock shows a saturation dependence which can be explained by combining a fractured rock model and a partial saturation model. At high to full water saturation values, SWS decreases as a result of the fluid bulk modulus effect on the quasi-shear wave. This bulk modulus effect is frequency dependent as a result of wave-induced fluid flow mechanisms, which would in turn lead to frequency dependent SWS. This result suggests the possible use of SWS for discriminating between full liquid saturation and partial liquid/gas saturation.
Fracture and flow, Body waves, Seismic anisotropy
0956-540X
17-24
Amalokwu, K.
fcdac4d2-28d3-45db-9ceb-394a8956399e
Chapman, M.
7419ece0-c965-4eea-b535-1d8185511ea0
Best, A.I.
cad03726-10f8-4f90-a3ba-5031665234c9
Sothcott, Jeremy
71ab4088-7b13-46d6-9e28-67538a02d595
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Li, X.Y.
fd02439f-9147-468e-8837-420c899152f5
Amalokwu, K.
fcdac4d2-28d3-45db-9ceb-394a8956399e
Chapman, M.
7419ece0-c965-4eea-b535-1d8185511ea0
Best, A.I.
cad03726-10f8-4f90-a3ba-5031665234c9
Sothcott, Jeremy
71ab4088-7b13-46d6-9e28-67538a02d595
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Li, X.Y.
fd02439f-9147-468e-8837-420c899152f5

Amalokwu, K., Chapman, M., Best, A.I., Sothcott, Jeremy, Minshull, T.A. and Li, X.Y. (2015) Experimental observation of water saturation effects on shear wave splitting in synthetic rock with fractures aligned at oblique angles. Geophysical Journal International, 200 (1), 17-24.

Record type: Article

Abstract

Fractured rocks are known to exhibit seismic anisotropy and shear wave splitting (SWS). SWS is commonly used for fractured rock characterization and has been shown to be sensitive to fluid type. The presence of partial liquid/gas saturation is also known to affect the elastic properties of rocks. The combined effect of both fractures and partial liquid/gas saturation is still unknown. Using synthetic, silica-cemented sandstones with aligned penny-shaped voids, we conducted laboratory ultrasonic experiments to investigate the effect fractures aligned at an oblique angle to wave propagation would have on SWS under partial liquid/gas saturation conditions. The result for the fractured rock shows a saturation dependence which can be explained by combining a fractured rock model and a partial saturation model. At high to full water saturation values, SWS decreases as a result of the fluid bulk modulus effect on the quasi-shear wave. This bulk modulus effect is frequency dependent as a result of wave-induced fluid flow mechanisms, which would in turn lead to frequency dependent SWS. This result suggests the possible use of SWS for discriminating between full liquid saturation and partial liquid/gas saturation.

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Amalokwu et al GJI 2015 - SWS oblique angles.pdf - Accepted Manuscript
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More information

Published date: January 2015
Keywords: Fracture and flow, Body waves, Seismic anisotropy
Organisations: Ocean and Earth Science, Marine Geoscience

Identifiers

Local EPrints ID: 374122
URI: https://eprints.soton.ac.uk/id/eprint/374122
ISSN: 0956-540X
PURE UUID: fd511823-1af8-4ed9-9126-ac82b078c342
ORCID for T.A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

Catalogue record

Date deposited: 04 Feb 2015 16:16
Last modified: 06 Jun 2018 12:53

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