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Water saturation effects on P-wave anisotropy in synthetic sandstone with aligned fractures

Amalokwu, Kelvin; Chapman, Mark; Best, Angus I.; Minshull, Timothy A.; Li, Xiang. 2015 Water saturation effects on P-wave anisotropy in synthetic sandstone with aligned fractures. Geophysical Journal International, 202 (2). 1088-1095. 10.1093/gji/ggv192

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This article has been accepted for publication in Geophysical Journal International ©: 2015 Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. doi:10.1093/gji/ggv192).
Geophys. J. Int.-2015-Amalokwu-1088-95.pdf - Published Version

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Abstract/Summary

The seismic properties of rocks are known to be sensitive to partial liquid or gas saturation, and to aligned fractures. P-wave anisotropy is widely used for fracture characterization and is known to be sensitive to the saturating fluid. However, studies combining the effect of multiphase saturation and aligned fractures are limited even though such conditions are common in the subsurface. An understanding of the effects of partial liquid or gas saturation on P-wave anisotropy could help improve seismic characterization of fractured, gas bearing reservoirs. Using octagonal-shaped synthetic sandstone samples, one containing aligned penny-shaped fractures and the other without fractures, we examined the influence of water saturation on P-wave anisotropy in fractured rocks. In the fractured rock, the saturation related stiffening effect at higher water saturation values is larger in the direction across the fractures than along the fractures. Consequently, the anisotropy parameter ‘ε’ decreases as a result of this fluid stiffening effect. These effects are frequency dependent as a result of wave-induced fluid flow mechanisms. Our observations can be explained by combining a frequency-dependent fractured rock model and a frequency-dependent partial saturation model.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1093/gji/ggv192
ISSN: 0956-540X
Date made live: 06 Oct 2015 13:59 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/511965

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