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A New Procedure for Quick Estimation of Porosity and Density of Hydrate-bearing Sediments by Using Medical X-ray CT Scanner
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  • Lallan Gupta,
  • Wataru Tanikawa,
  • Yohei Hamada,
  • Takehiro Hirose,
  • Naokazu Ahagon,
  • Takamitsu Sugihara,
  • Natsue Abe,
  • Shun Nomura,
  • Yuka Masaki,
  • Hung-Yu Wu,
  • Weiren Lin,
  • Masataka Kinoshita,
  • Yasuhiro Yamada
Lallan Gupta
JAMSTEC

Corresponding Author:gupta@jamstec.go.jp

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Wataru Tanikawa
JAMSTEC
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Yohei Hamada
JAMSTEC
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Takehiro Hirose
JAMSTEC
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Naokazu Ahagon
JAMSTEC Japan Agency for Marine-Earth Science and Technology
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Takamitsu Sugihara
Marion-Kanazawa 202
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Natsue Abe
JAMSTEC Japan Agency for Marine-Earth Science and Technology
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Shun Nomura
JAMSTEC Japan Agency for Marine-Earth Science and Technology
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Yuka Masaki
IFREE/JAMSTEC
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Hung-Yu Wu
Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology
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Weiren Lin
Kyoto University
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Masataka Kinoshita
Japan Agy Marine Sci Tech
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Yasuhiro Yamada
Kyoto Univ
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Abstract

Gas hydrates have been reported to exist in marine sediments from various parts of the world ocean. The hydrates start decomposing soon after recovery of the sediments through coring operations due to changes in ambient pressure and temperature. This decomposition leads to changes in sedimentary structures, and thus complicates physical property related measurements of the sediments by conventional methods. In this study, we used a medical X-ray CT scanner to quickly scan the recovered cores, and then used raw data from the CT, and thus avoided image processing steps, to estimate porosity and density of the sediments. The raw data were in terms of CT numbers, which were obtained by drawing a circular region of interest (ROI) to cover most of the sediments visible in a cross section XCT image of the sediments. The data were weighted for relative contribution of liquid and solid in sediments before estimating porosity. On the other hand, density was estimated by using an average CT number that was automatically calculated by the Osirix software used for drawing the ROI on an XCT image, and by using a calibration equation based on a set of standards. Although some uncertainty in estimation of relative volumes of solid, liquid and gas could not be avoided, the results obtained by this new procedure were in good agreement with those obtained by conventional methods. Since porosity and density estimates by the new procedure can be made in a matter of minutes after core recovery, it can guide progress of coring operation and further processing of hydrate-bearing sediments.