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    Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

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    2010JB007944.pdf (9.342Mb)
    Date
    2011-05-25
    Author
    Wang, Xiujuan  Concept link
    Hutchinson, Deborah R.  Concept link
    Wu, Shiguo  Concept link
    Yang, Shengxiong  Concept link
    Guo, Yiqun  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4642
    As published
    https://doi.org/10.1029/2010JB007944
    DOI
    10.1029/2010JB007944
    Keyword
     Gas hydrate; Saturation; Shenhu area; Fine-grained; Gas chimney 
    Abstract
    Gas hydrate saturations were estimated using five different methods in silt and silty clay foraminiferous sediments from drill hole SH2 in the South China Sea. Gas hydrate saturations derived from observed pore water chloride values in core samples range from 10 to 45% of the pore space at 190–221 m below seafloor (mbsf). Gas hydrate saturations estimated from resistivity (Rt) using wireline logging results are similar and range from 10 to 40.5% in the pore space. Gas hydrate saturations were also estimated by P wave velocity obtained during wireline logging by using a simplified three-phase equation (STPE) and effective medium theory (EMT) models. Gas hydrate saturations obtained from the STPE velocity model (41.0% maximum) are slightly higher than those calculated with the EMT velocity model (38.5% maximum). Methane analysis from a 69 cm long depressurized core from the hydrate-bearing sediment zone indicates that gas hydrate saturation is about 27.08% of the pore space at 197.5 mbsf. Results from the five methods show similar values and nearly identical trends in gas hydrate saturations above the base of the gas hydrate stability zone at depths of 190 to 221 mbsf. Gas hydrate occurs within units of clayey slit and silt containing abundant calcareous nannofossils and foraminifer, which increase the porosities of the fine-grained sediments and provide space for enhanced gas hydrate formation. In addition, gas chimneys, faults, and fractures identified from three-dimensional (3-D) and high-resolution two-dimensional (2-D) seismic data provide pathways for fluids migrating into the gas hydrate stability zone which transport methane for the formation of gas hydrate. Sedimentation and local canyon migration may contribute to higher gas hydrate saturations near the base of the stability zone.
    Description
    Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B05102, doi:10.1029/2010JB007944.
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    • Energy and Geohazards
    Suggested Citation
    Journal of Geophysical Research 116 (2011): B05102
     

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