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

The elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems
The elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems
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.
1742-2132
555-569
Bu, Q.T.
98108245-4ed5-4af5-bb65-11ae3df0e9d8
Hu, G.W.
2bedd39f-041d-4a1b-b0b0-5044f06f9773
Ye, Y.G.
f7bdda77-17b1-450b-805c-90e522f7bb7d
Liu, C.L.
d97a0f8e-fa4a-4f04-b7ad-e2f0e937f85c
Li, C.F.
5c19c369-ea85-49a8-9b9d-83a738410388
Best, A.I.
eb91dc86-7609-4b07-92be-2bab3bdf755f
Wang, J.S.
b6a32f99-4ade-4094-abf7-c65665e5541f
Bu, Q.T.
98108245-4ed5-4af5-bb65-11ae3df0e9d8
Hu, G.W.
2bedd39f-041d-4a1b-b0b0-5044f06f9773
Ye, Y.G.
f7bdda77-17b1-450b-805c-90e522f7bb7d
Liu, C.L.
d97a0f8e-fa4a-4f04-b7ad-e2f0e937f85c
Li, C.F.
5c19c369-ea85-49a8-9b9d-83a738410388
Best, A.I.
eb91dc86-7609-4b07-92be-2bab3bdf755f
Wang, J.S.
b6a32f99-4ade-4094-abf7-c65665e5541f

Bu, Q.T., Hu, G.W., Ye, Y.G., Liu, C.L., Li, C.F., Best, A.I. and 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. (doi:10.1088/1742-2140/aa6493).

Record type: Article

Abstract

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.

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Bu et al. - Accepted Manuscript
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Accepted/In Press date: 6 March 2017
e-pub ahead of print date: 29 March 2017
Published date: 29 March 2017
Organisations: Marine Geoscience

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Local EPrints ID: 407924
URI: https://eprints.soton.ac.uk/id/eprint/407924
ISSN: 1742-2132
PURE UUID: e0fbbb04-2501-452c-b9db-882ad0c4a5a5

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Date deposited: 29 Apr 2017 01:02
Last modified: 14 Mar 2019 05:57

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Contributors

Author: Q.T. Bu
Author: G.W. Hu
Author: Y.G. Ye
Author: C.L. Liu
Author: C.F. Li
Author: A.I. Best
Author: J.S. Wang

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