Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough
Santamarina, J. Carlos
Waite, William F.
Winters, William J.
MetadataShow full item record
KeywordMethane hydrate; Hydrate-bearing sediment; Nankai Trough; Physical properties; Pressure core
Natural hydrate-bearing sediments from the Nankai Trough, offshore Japan, were studied using the Pressure Core Characterization Tools (PCCTs) to obtain geomechanical, hydrological, electrical, and biological properties under in situ pressure, temperature, and restored effective stress conditions. Measurement results, combined with index-property data and analytical physics-based models, provide unique insight into hydrate-bearing sediments in situ. Tested cores contain some silty-sands, but are predominantly sandy- and clayey-silts. Hydrate saturations Sh range from 0.15 to 0.74, with significant concentrations in the silty-sands. Wave velocity and flexible-wall permeameter measurements on never-depressurized pressure-core sediments suggest hydrates in the coarser-grained zones, the silty-sands where Sh exceeds 0.4, contribute to soil-skeletal stability and are load-bearing. In the sandy- and clayey-silts, where Sh < 0.4, the state of effective stress and stress history are significant factors determining sediment stiffness. Controlled depressurization tests show that hydrate dissociation occurs too quickly to maintain thermodynamic equilibrium, and pressure–temperature conditions track the hydrate stability boundary in pure-water, rather than that in seawater, in spite of both the in situ pore water and the water used to maintain specimen pore pressure prior to dissociation being saline. Hydrate dissociation accompanied with fines migration caused up to 2.4% vertical strain contraction. The first-ever direct shear measurements on never-depressurized pressure-core specimens show hydrate-bearing sediments have higher sediment strength and peak friction angle than post-dissociation sediments, but the residual friction angle remains the same in both cases. Permeability measurements made before and after hydrate dissociation demonstrate that water permeability increases after dissociation, but the gain is limited by the transition from hydrate saturation before dissociation to gas saturation after dissociation. In a proof-of-concept study, sediment microbial communities were successfully extracted and stored under high-pressure, anoxic conditions. Depressurized samples of these extractions were incubated in air, where microbes exhibited temperature-dependent growth rates.
This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 66 (2015): 434-450, doi:10.1016/j.marpetgeo.2015.02.033.
Showing items related by title, author, creator and subject.
Waite, William F.; Santamarina, J. Carlos; Cortes, Douglas D.; Dugan, Brandon; Espinoza, D. N.; Germaine, J.; Jang, J.; Jung, J. W.; Kneafsey, Timothy J.; Shin, H.; Soga, K.; Winters, William J.; Yun, T.-S. (American Geophysical Union, 2009-12-31)Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena ...
Physical property changes in hydrate-bearing sediment due to depressurization and subsequent repressurization Waite, William F.; Kneafsey, Timothy J.; Winters, William J.; Mason, D. H. (American Geophysical Union, 2008-07-03)Physical property measurements of sediment cores containing natural gas hydrate are typically performed on material exposed, at least briefly, to non-in situ conditions during recovery. To examine the effects of a brief ...
Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments : 2. Small-strain mechanical properties Lee, J. Y.; Francisca, Franco M.; Santamarina, J. Carlos; Ruppel, Carolyn D. (American Geophysical Union, 2010-11-09)The small-strain mechanical properties (e.g., seismic velocities) of hydrate-bearing sediments measured under laboratory conditions provide reference values for calibration of logging and seismic exploration results acquired ...