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IODP Leg 311 - Cascadia Margin Gas
Hydrates |
Gilles Guerin, Alberto Malinverno
Expedition 311 of the Integrated Ocean Drilling
Program (IODP) investigated the occurence and the formation
of gas hydrate in the accretionary prism of the northern
Cascadia margin. The five sites visited during the expedition
defined a SW-NE transect across a ~30km wide Bottom Simulating
Reflector (BSR) that runs parallel to the coast alongmost
of the continental slope (see Figure 1).
From Site U1326, at the SW tip of the accretionary
prism, to Site U1329, the shallowest site located at the
landward limit of the BSR, the transect was designed to sample
the complexity of the evolution of a gas hydrate system (see
Figure 2).
To constrain the formation of gas hydrates
in subduction zones, Expedition 311 had an ambitious drilling
program including extensive pressure coring to recover gas
hydrate at in situ conditions. Because of the unstability
of gas hydrate at surface conditions, and of the strong response
of some logging tools such as electrical and acoustic logs
to the presence of gas hydrate, logging was a critical component
of the operations. The logging program consisted of two phases
- the first week of the expedition was dedicated to Logging
While Drilling (LWD), in order to identify intervals likely
to contain gas hydrate where pressure coring tools should
be deployed; the second phase consisted in wireline logging
following coring operations in order to complete the geophysical
characterization of the sites. |
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A
location of IODP Expedition 311 on the Cascadia margin.
B) Bathymetry and location of the different sites
visited (bathimetry courtesy of D. Kelley, J. Delaney,
and D. Glickson, University of Washington, and
C. Barnes, C. Katnick, NEPTUNE Canada, University
of Victoria; funded by the University of Washington
and the W.M. Keck Foundation.
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Seismic
section (line 89-08) showing the position of the Expedition
311 sites across the accretionary front.
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Expedition 311 Proceedings
Expedition 311 Logging Summary
Log Data
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IODP Leg 204 - Hydrate Ridge |
Dave Goldberg, Gilles Guerin
During Ocean Drilling Program (ODP) Leg 204, a total of nine
sites were
drilled through the gas hydrate stability zone on the southern
part o
Hydrate Ridge on the Cascadia accretionary margin, offshore
Oregon. For
further information regarding gas hydrates and the background
geological
setting see the Leg 204 Preliminary Report. The first part
of Leg 204 was
dedicated entirely to logging while drilling (LWD) to identify
potential gas
hydrate bearing intervals prior to coring. The data were of
excellent
quality, thus allowing optimization of the use of time-consuming
special
tools to measure in situ temperature and pressure and to retrieve
cores at
in situ pressure. The leg also included an extensive wireline
logging
program and a two-ship seismic program with the R/V Maurice
Ewing to acquire
offset and walkaway vertical seismic profiles (VSP). The log
data are
available from the ODP Logging Services database.
Initial Report
Scientific Results
Logging Summary
Log Data
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Electrical and Nuclear Resonance
measurements of Tetrahydrofuran Hydrate |
Ann Cook, Dave Goldberg
Tetrahydrofuran (THF) hydrate (20% weight THF with 80% weight
deionized
water) was synthesized in the laboratory at LDEO and brought
to the
Schlumberger-Doll research laboratory in Ridgefield, Connecticut
for
measurements of their surface area, nuclear magnetic relaxivity,
and
dielectric properties. Surface area data was collected at liquid
nitrogen
temperatures. NMR and dielectric experiments were conducted
at about 0°
Celsius.
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