Site Selection for DOE/JIP Gas Hydrate Drilling in the Northern Gulf of Mexico Page: 3 of 12
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Salt has also spread laterally on the lower slope to
form the Sigsbee Escarpment, one of the most
prominent features of the margin. Minibasins in
the shelf and upper slope are generally filled while
those in the lower slope are still filling .
Numerous canyons have also incised the margin.
The youngest of these is the Mississippi Canyon,
which provided a pathway for sediments to move
from the Mississippi River onto the Mississippi
Fan. The pathways associated with some of the
older canyons (e.g., Alaminos, Bryant, Keathley,
and Green Canyons) are obscured by younger salt
movement, deposition, and tectonism (e.g., ).
Detachment faults soling into salt are common in
the Gulf, and have created large gravity-driven,
generally buried, salt-cored foldbelts in sediments
near the Sigsbee Escarpment, such as the Perdido
Foldbelt in the western Gulf and the Mississippi
Fan Foldbelt in the east [16, 171.
Figure 1: Bathymetric map of the northern
Gulf of Mexico showing three sites
recommended for 2008 JIP gas hydrate
drilling program (AC818, GC955, and
WR313) together with the location of holes
drilled in 2005 (KC and AT). The axis of
fold 3 of the Perdido Foldbelt is labeled in
yellow where it crosses the AC818 site.
Superimposed on this complex morphology is a
near-seafloor hydrate stability zone that increases
from zero thickness at the pressure-temperature
conditions on the upper slope to an estimated
1,150 m thickness at mid-slope water depths .
Stratigraphic and structural disturbances are
common in the shallow section, with faults, mass
wasting, gas chimneys, and overpressured zones
being typical of the variability [19, 20]. Thermal
anomalies from 3 to 10 times background values
can also occur locally near seep sites and mud
volcanoes [9, 21, 22]. The hydrate stability zone,
therefore, includes sedimentary, chemical,
thermal, and tectonic processes that occur and
continue to occur at multiple spatial and temporal
In this paper, "site" is used to define an area of
interest for drilling, generally described in terms of
one of the lease blocks that includes well
information and is near the structural or
stratigraphic features of interest. Multiple drilling
locations exist at each site. Sites have been
identified as potentially having gas hydrate in
reservoir units through the application of geologic
and geophysical models and approaches. Drilling
locations are chosen to implement a sampling
strategy designed to maximize specific
information to be obtained by drilling at a site.
During the JIP site selection process, several
approaches were adopted for identifying sites and
locating drilling targets. Industry-standard 3D
multichannel seismic data were used for
stratigraphic mapping, seismic facies analyses,
structural interpretations, and identification of
features associated with free gas. Geophysical
approaches used during the site selection process
have included qualitative analyses of peak-trough
relationships in seismic traces to infer occurrences
of free gas, gas hydrate, and water-saturated
lithologies. Quantitative well-log analyses have
also been essential, with gamma ray logs used to
infer lithologic variations. When available, sonic
and resistivity logs were used to constrain
potential gas hydrate saturations. A centerpiece of
the geophysical analyses has been the inversion of
the 3D seismic data, coupled with lithologic
information from well-logs to estimate gas hydrate
saturations [23-26]. Results of these inversions
are described below. Details of the site selection
process and information about sites not chosen for
further analysis are given elsewhere .
After much consideration, the JIP site selection
team identified Alaminos Canyon 818, Green
Canyon 955, and Walker Ridge 313 as having
characteristics consistent with the goals of
sampling gas hydrate in coarse-grained sediments
in a variety of structural or stratigraphic plays in
the deepwater northern Gulf of Mexico. Table 1
provides basic information at the three sites
0 10 M
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Hutchinson, D. R.; Shelander, D.; Dai, J.; McConnell, D.; Shedd, W.; Frye, M. et al. Site Selection for DOE/JIP Gas Hydrate Drilling in the Northern Gulf of Mexico, article, July 1, 2008; Vancouver, British Columbia. (https://digital.library.unt.edu/ark:/67531/metadc895823/m1/3/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.