TY - JOUR
T1 - Strength characteristics of sediments from a gas hydrate deposit in the Krishna–Godavari Basin on the eastern margin of India
AU - NGHP Expedition 02 JAMSTEC Science Team
AU - Hirose, Takehiro
AU - Tanikawa, Wataru
AU - Hamada, Yohei
AU - Lin, Weiren
AU - Hatakeda, Kentaro
AU - Tadai, Osamu
AU - Wu, Hung Y.
AU - Nomura, Shun
AU - Abe, Natsue
AU - Gupta, Lallan P.
AU - Sugihara, Takamitsu
AU - Masaki, Yuka
AU - Kinoshita, Masataka
AU - Yamada, Yasuhiro
N1 - Funding Information:
The authors are thankful to the Ministry of Petroleum & Natural Gas within the Government of India, Oil and Natural Gas Corporation Limited (ONGC), Directorate General of Hydrocarbons (DGH), Oil India Ltd, GAIL (India) Ltd, Indian Oil Corporation Ltd and all other NGHP partner organizations for providing the opportunity to contribute to the NGHP-02 Expedition and this special issue of the Journal of Marine and Petroleum Geology. The technical and science support from Japan Agency for Marine-Earth Science and Technology (JAMSTEC), United States Geological Survey (USGS), U.S. Department of Energy (US-DOE), the National Institute of Advanced Industrial Science and Technology (AIST), Geotek Coring, and Schlumberger is gratefully acknowledged.
Funding Information:
The authors are thankful to the Ministry of Petroleum & Natural Gas within the Government of India, Oil and Natural Gas Corporation Limited (ONGC), Directorate General of Hydrocarbons (DGH), Oil India Ltd, GAIL (India) Ltd, Indian Oil Corporation Ltd and all other NGHP partner organizations for providing the opportunity to contribute to the NGHP-02 Expedition and this special issue of the Journal of Marine and Petroleum Geology. The technical and science support from Japan Agency for Marine-Earth Science and Technology ( JAMSTEC ), United States Geological Survey ( USGS ), U.S. Department of Energy (US-DOE), the National Institute of Advanced Industrial Science and Technology (AIST), Geotek Coring, and Schlumberger is gratefully acknowledged.
Publisher Copyright:
© 2018 Elsevier Ltd
PY - 2019/10
Y1 - 2019/10
N2 - Knowledge of the strength of sediments overlying sub-seafloor gas-hydrate deposits is crucial for predicting borehole and seafloor stability during hydrate extraction. Ideally, sediment strength should be determined along a continuous downhole profile from the seafloor to the hydrate reservoir, but few such profiles have been obtained. In this study we used cores retrieved at Site NGHP-02-23 in the Krishna–Godavari Basin in unconfined penetration tests on split cores and in triaxial deformation experiments on hydrate-free sediment samples. Although penetrometer tests identified relatively low strength (70–250 kPa) likely due to hydrate dissociation in the hydrate-bearing interval 90–300 m below seafloor (mbsf), sediment strength exceeded 350 kPa in the intervals 140–170 and 250–270 mbsf, each of which lies just above a zone of high gas-hydrate concentration. The average stress ratio of triaxial strength at 4% axial strain to effective mean stress (qε=4%/p’) of hydrate-free silts was about 0.67 throughout the Hole. An exception to this trend was in fine sands from 280 mbsf in the deeper gas-hydrate zone, where the stress ratios were greater than 1.0. The stress ratios of hydrate-bearing sediments in the deeper gas-hydrate zone that were reported from the pressure-core measurements were far greater than those of any hydrate-free sediments for a given effective mean stress. The high-strength intervals in silty sediments we identified by the penetration tests could be associated with zones of high hydrate concentration. Because high-strength layers in fine-grained silty sediments commonly exhibit lower permeability than sandy layers (potential hydrate-host), they may act as seals that assist the precipitation of hydrate below them.
AB - Knowledge of the strength of sediments overlying sub-seafloor gas-hydrate deposits is crucial for predicting borehole and seafloor stability during hydrate extraction. Ideally, sediment strength should be determined along a continuous downhole profile from the seafloor to the hydrate reservoir, but few such profiles have been obtained. In this study we used cores retrieved at Site NGHP-02-23 in the Krishna–Godavari Basin in unconfined penetration tests on split cores and in triaxial deformation experiments on hydrate-free sediment samples. Although penetrometer tests identified relatively low strength (70–250 kPa) likely due to hydrate dissociation in the hydrate-bearing interval 90–300 m below seafloor (mbsf), sediment strength exceeded 350 kPa in the intervals 140–170 and 250–270 mbsf, each of which lies just above a zone of high gas-hydrate concentration. The average stress ratio of triaxial strength at 4% axial strain to effective mean stress (qε=4%/p’) of hydrate-free silts was about 0.67 throughout the Hole. An exception to this trend was in fine sands from 280 mbsf in the deeper gas-hydrate zone, where the stress ratios were greater than 1.0. The stress ratios of hydrate-bearing sediments in the deeper gas-hydrate zone that were reported from the pressure-core measurements were far greater than those of any hydrate-free sediments for a given effective mean stress. The high-strength intervals in silty sediments we identified by the penetration tests could be associated with zones of high hydrate concentration. Because high-strength layers in fine-grained silty sediments commonly exhibit lower permeability than sandy layers (potential hydrate-host), they may act as seals that assist the precipitation of hydrate below them.
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U2 - 10.1016/j.marpetgeo.2018.08.017
DO - 10.1016/j.marpetgeo.2018.08.017
M3 - Article
AN - SCOPUS:85054458135
VL - 108
SP - 348
EP - 355
JO - Marine and Petroleum Geology
JF - Marine and Petroleum Geology
SN - 0264-8172
ER -