Gas hydrate-bearing sediments recovered by pressure coring from the Krishna-Godavari Basin offshore India during the 2006 National Gas Hydrate Program (NGHP) expedition were characterized using the instrumented pressure testing chamber (IPTC). The IPTC studies provided longitudinal profiles of P- and S-wave velocities, electrical conductivity, and undrained penetration resistance. The formation consisted of fine-grained clayey sediments of high specific surface and high plasticity. X-ray images showed horizontal layering, pronounced heterogeneity from milli- to centimeter scales, with the presence of high-density nodules and both horizontal and sub-vertical gas hydrate lenses. Relative to reference values for sediments without hydrates, regions of high P- and S-wave velocities, low electrical conductivity, and high undrained shear strength were identified and correlated with regions of apparent high hydrate volume fractions in all tested specimens. Physical properties were monitored during the depressurization of pressure cores. The hydrate volume fraction was estimated to be 18.2%. The evolution of P-wave amplitude, electrical conductivity, and temperature showed gas generation and freshening upon phase transformation. The effect of sampling by pressure coring and the ensuing zero-effective stress condition were discussed.
ASJC Scopus subject areas
- General Chemical Engineering
- Fuel Technology
- Energy Engineering and Power Technology