Acoustic response of gas hydrate formation in sediments from South China Sea |
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| Institution: | 1. Key Laboratory of Gas Hydrate, Ministry of Land and Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China;2. Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China;3. Oil and Gas Survey, China Geological Survey, Beijing 100029, China;4. Qinghai No.105 Coal Geological Exploration Team, Xining 810007, China;5. Guangzhou Marine Geological Survey, Guangzhou 510075, China |
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| Abstract: | Gas hydrate has been recognized as a potential energy resource in South China Sea (SCS). Understanding the acoustic response of gas hydrate formation in the SCS sediments is essential for regional gas hydrate investigation and quantification. The sediments were obtained from gravity core sampling at E 115°12.52363′ N 19°48.40299′. Gas hydrate was formed within a “gas + water-saturated SCS sediments” system. Combination of a new bender element technique and coated time domain reflectometry (TDR) was carried out to study the acoustic response of hydrate occurrence in SCS sediments. The results show the acoustic signal becomes weak when hydrate saturation (Sh) is lower than 14%. The acoustic velocities (Vp, Vs) of the sediments increase with Sh during hydrate formation, and Vs increases relatively faster when Sh is higher than 14%. These results indicate that tiny hydrate particles may firstly float in the pore fluid, which causes a significant acoustic attenuation, but has little influence on shear modulus. As time lapses and Sh approaches 14%, numerous particles coalesce together and contact with sediment particles. As a result, Vs has a sharp increase when hydrate saturation exceeds 14%. Several velocity models were validated with the experimental data, which suggests a combination of the BGTL (Biot–Gassmann Theory modified by Lee) model and the Weighted Equation is suitable to estimate Sh in SCS. |
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| Keywords: | Gas hydrate South China Sea (SCS) Acoustic response Bender element Time domain reflectometry (TDR) |
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