Scale-dependent gas hydrate saturation estimates in sand reservoirs in the Ulleung Basin,East Sea of Korea |
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| Institution: | 1. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Bldg, Corvallis, OR 97331, USA;2. Petroleum and Marine Research Division, Korea Institute of Geosciences and Mineral Resources, 124 Gwahang-no Yuseong-gu, Daejeon 305-350, South Korea;1. Chemical & Petroleum Engineering, University of Kansas, Lawrence, KS, 66045, USA;2. Petroleum Engineering, China University of Petroleum (East China), Qingdao, 266580, China;1. Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, 510640, PR China;2. Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Chinese Academy of Sciences, Guangzhou 510640, PR China;3. University of Chinese Academy of Science, Beijing, 10083, PR China;1. Institute for Geophysics, University of Texas at Austin, 10100 Burnet Road, Austin, TX 78758, United States;2. Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712, United States;1. Key Lab of Submarine Geosciences and Prospecting Techniques, MOE, College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;2. Evaluation and Detection Technology Laboratory of Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China |
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| Abstract: | Through the use of 2-D and 3-D seismic data, several gas hydrate prospects were identified in the Ulleung Basin, East Sea of Korea and thirteen drill sites were established and logging-while-drilling (LWD) data were acquired from each site in 2010. Sites UBGH2–6 and UBGH2–10 were selected to test a series of high amplitude seismic reflections, possibly from sand reservoirs. LWD logs from the UBGH2–6 well indicate that there are three significant sand reservoirs with varying thickness. Two upper sand reservoirs are water saturated and the lower thinly bedded sand reservoir contains gas hydrate with an average saturation of 13%, as estimated from the P-wave velocity. The well logs at the UBGH2–6 well clearly demonstrated the effect of scale-dependency on gas hydrate saturation estimates. Gas hydrate saturations estimated from the high resolution LWD acquired ring resistivity (vertical resolution of about 5–8 cm) reaches about 90% with an average saturation of 28%, whereas gas hydrate saturations estimated from the low resolution A40L resistivity (vertical resolution of about 120 cm) reaches about 25% with an average saturation of 11%. However, in the UBGH2–10 well, gas hydrate occupies a 5-m thick sand reservoir near 135 mbsf with a maximum saturation of about 60%. In the UBGH2–10 well, the average and a maximum saturation estimated from various well logging tools are comparable, because the bed thickness is larger than the vertical resolution of the various logging tools. High resolution wireline log data further document the role of scale-dependency on gas hydrate calculations. |
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