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The elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems

Bu, Q.T.; Hu, G.W.; Ye, Y.G.; Liu, C.L.; Li, C.F.; Best, A.I.; Wang, J.S.. 2017 The elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems. Journal of Geophysics and Engineering, 14 (3). 555-569. https://doi.org/10.1088/1742-2140/aa6493

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This is an author-created, un-copyedited version of an article published in Journal of Geophysics and Engineering. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.1088/1742-2140/aa6493.
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Abstract/Summary

Knowledge of the elastic wave velocities of hydrate-bearing sediments is important for geophysical exploration and resource evaluation. Methane gas migration processes play an important role in geological hydrate accumulation systems, whether on the seafloor or in terrestrial permafrost regions, and their impact on elastic wave velocities in sediments needs further study. Hence, a high-pressure laboratory apparatus was developed to simulate natural continuous vertical migration of methane gas through sediments. Hydrate saturation (S h) and ultrasonic P- and S-wave velocities (V p and V s) were measured synchronously by time domain reflectometry (TDR) and by ultrasonic transmission methods respectively during gas hydrate formation in sediments. The results were compared to previously published laboratory data obtained in a static closed system. This indicated that the velocities of hydrate-bearing sediments in vertical gas migration systems are slightly lower than those in closed systems during hydrate formation. While velocities increase at a constant rate with hydrate saturation in the closed system, P-wave velocities show a fast–slow–fast variation with increasing hydrate saturation in the vertical gas migration system. The observed velocities are well described by an effective-medium velocity model, from which changing hydrate morphology was inferred to cause the fast–slow–fast velocity response in the gas migration system. Hydrate forms firstly at the grain contacts as cement, then grows within the pore space (floating), then finally grows into contact with the pore walls again. We conclude that hydrate morphology is the key factor that influences the elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.1088/1742-2140/aa6493
ISSN: 1742-2132
Date made live: 28 Apr 2017 12:21 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/516946

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