Strength characteristics of sediments from a gas hydrate deposit in the Krishna–Godavari Basin on the eastern margin of India

NGHP Expedition 02 JAMSTEC Science Team

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)348-355
Number of pages8
JournalMarine and Petroleum Geology
Volume108
DOIs
Publication statusPublished - 2019 Oct

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Geophysics
  • Geology
  • Economic Geology
  • Stratigraphy

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