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Gas hydrate saturation at S ite C 0002, IODP E xpeditions 314 and 315, in the K umano B asin, N ankai trough
Author(s) -
Miyakawa Ayumu,
Saito Saneatsu,
Yamada Yasuhiro,
Tomaru Hitoshi,
Kinoshita Masataka,
Tsuji Takeshi
Publication year - 2014
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12064
Subject(s) - saturation (graph theory) , electrical resistivity and conductivity , clathrate hydrate , hydrate , mineralogy , analytical chemistry (journal) , water saturation , well logging , geology , porosity , chemistry , physics , geophysics , chromatography , mathematics , organic chemistry , combinatorics , geotechnical engineering , quantum mechanics
The degree of gas hydrate saturation at I ntegrated O cean D rilling P rogram ( IODP ) S ite C 0002 in the K umano B asin, N ankai T rough, was estimated from logging‐while‐drilling logs and core samples obtained during IODP E xpeditions 314 and 315. Sediment porosity data necessary for the calculation of saturation were obtained from both core samples and density logs. Two forms of the Archie equation (‘quick‐look’ and ‘standard’) were used to calculate gas hydrate saturation from two types of electrical resistivity log data (ring resistivity and bit resistivity), and a three‐phase B iot‐type equation was used to calculate gas hydrate saturation from P ‐wave velocity log data. The gas hydrate saturation baseline calculated from both resistivity logs ranges from 0% to 35%, and that calculated from the P ‐wave velocity log ranges from 0% to 30%. High levels of gas hydrate saturation (>60%) are present as spikes in the ring resistivity log and correspond to the presence of gas hydrate concentrations within sandy layers. At several depths, saturation values obtained from P ‐wave velocity data are lower than those obtained from bit resistivity data; this discrepancy is related to the presence of free gas at these depths. Previous research has suggested that gas from deep levels in the K umano B asin has migrated up‐dip towards the southern and seaward edge of the basin near S ite C 0002. The high saturation values and presence of free gas at site C 0002 suggest that a large gas flux is flowing to the southern and seaward edge of the basin from a deeper and/or more landward part of the K umano B asin, with the southern edge of the K umano B asin (the location of site C 0002) being the main area of fluid accumulation.