Acoustic wave attenuation in the gas hydrate-bearing sediments of Well GC955H, Gulf of Mexico
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ORIGINAL RESEARCH PAPER
Acoustic wave attenuation in the gas hydrate-bearing sediments of Well GC955H, Gulf of Mexico Jiliang Wang1 · Shiguo Wu1,2 · Jianhua Geng3 · Priyank Jaiswal4 Received: 15 June 2017 / Accepted: 10 November 2017 © Springer Science+Business Media B.V., part of Springer Nature 2017
Abstract A better understanding of wave attenuation in hydrate-bearing sediments is necessary for the improved geophysical quantification of marine gas hydrates. Here we compare the attenuation behavior of hydrate-saturated vs water-saturated sediments at site GC955H, in the Gulf of Mexico, which was surveyed during the JIP Leg II expedition. We compute the P-wave attenuation of the gas hydrate bearing sediments using the median frequency shift method on the monopole waveforms. The results show that P-wave attenuation due to low saturation ( 0.4) in the hydrate-filled pores of coarse-grained sediments can be up to as much as three times more than that of the water-saturated case. The correlation analysis shows that the P-wave attenuation increases with the increasing gas hydrate saturation for the highly saturated gas hydrate-bearing sand interval while the correlation of the P-wave attenuation and hydrate saturation is weak for low saturated gas hydrate-bearing shale interval. The results show that P-wave attenuation is more likely to be used as a geophysical proxy for gas hydrate quantification of highly concentrated coarse-grained sediment rather than for that of fine-grained sediment. To examine the P-wave behavior in sand, we use the improved LCAM model, which accounts for physical factors such as grain boundary roughness and squirt flow to explain the observed differences in P-wave attenuation between hydrate and water-saturated coarse-grained sediment. Our results provide further geophysical evidences for P-wave behavior in the gas hydrate-bearing sediments in the field. Keywords Gas hydrate · Sonic attenuation · Well log · Gulf of Mexico
Introduction Gas hydrate is an ice-like compound formed by gas, most often methane, trapped within a lattice of water molecules (Sloan 1998). Hydrates are stable only within a narrow range of pressures and temperatures, which exist in some marine and arctic areas within a limited depth range that is known * Jiliang Wang [email protected] 1
Institute of Deep Sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China
2
Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
3
State Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
4
Boone Pickens School of Geology, Oklahoma State University, Oklahoma 74078, USA
as the gas hydrate stability zone (GHSZ). Gas hydrates areof great interests to both the scientific and industrial communities because they could be a potential source of energy in the future (Collett 2002); they play a significant role in the global carbon cycle (Archer 2007; Dickens et al. 1995; Ruppel 1997), and they are also a geohazar
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