7 research outputs found
SUBSURFACE CHARACTERIZATION OF THE HYDRATE BEARING SEDIMENTS NEAR ALAMINOS CANYON 818
Gas hydrate has been identified by drilling in Alaminos Canyon block 818, within the Perdido
Fold Belt, outboard of the Sigsbee Escarpment, in approximately 2750 meters (9000 feet) of
water. At the location of the AC818 #1 (“Tigershark”) well, the gas hydrate occurs within the top
20 m (65 feet) of an approximately 90 meter (300 feet) thick Oligocene Frio sand, a volcaniclastic
sandstone rich in lithic fragments, feldspar, and volcanic ash. The Frio reservoir is folded into a
4-way closed anticline. At the crest of the anticline, the sand is partly eroded and is
unconformably overlain by 450 m (1500 feet) of Pleistocene shale and sand. The unconformity
surface is also in a 4-way closed geometry and defines the top of the hydrate reservoir at the well.
The rock is poorly consolidated and has porosity as high as 42% from log data. LWD logs
indicate that the hydrate zone has high resistivity and high P-velocity (2750 mps: 9000 fps). The
underlying wet sand at the base of the gas hydrate stability zone (GHSZ) has low resistivity and
P-velocity (Vp: 1500 mps: 5000 fps). The very low Vp indicates the presence of low-saturation
free gas ("fizz gas"). The large velocity contrast creates a strong response in seismic data which
was inverted into a 3D gas hydrates saturation (Sgh) volume. Elsewhere in the GHSZ, seismic character was used to predict predominant sediment facies. Relative high stand facies, which are
more clay-rich, will generally be characterized by more continuous and parallel seismic
reflectors. In contrast, relative low stand facies, which have more sand content, will be
characterized by more hummocky, discontinuous seismic character and will often lie on erosional
surfaces, particularly in uncompacted sediments. Understanding the stratigraphy throughout the
section is important, since sand will often provide beneficial reservoir conditions, while clay will
provide more impervious sealing qualities. The seismic interpretation also identifies migration
pathways, such as faults and gas chimneys, and the presence of available gas, which are necessary
to charge reservoirs within the HSZ.Non UBCUnreviewe
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SITE SELECTION FOR DOE/JIP GAS HYDRATE DRILLING IN THE NORTHERN GULF OF MEXICO
In the late spring of 2008, the Chevron-led Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) expects
to conduct an exploratory drilling and logging campaign to better understand gas hydrate-bearing sands in
the deepwater Gulf of Mexico. The JIP Site Selection team selected three areas to test alternative
geological models and geophysical interpretations supporting the existence of potential high gas hydrate
saturations in reservoir-quality sands. The three sites are near existing drill holes which provide geological
and geophysical constraints in Alaminos Canyon (AC) lease block 818, Green Canyon (GC) 955, and
Walker Ridge (WR) 313. At the AC818 site, gas hydrate is interpreted to occur within the Oligocene Frio
volcaniclastic sand at the crest of a fold that is shallow enough to be in the hydrate stability zone. Drilling
at GC955 will sample a faulted, buried Pleistocene channel-levee system in an area characterized by
seafloor fluid expulsion features, structural closure associated with uplifted salt, and abundant seismic
evidence for upward migration of fluids and gas into the sand-rich parts of the sedimentary section.
Drilling at WR313 targets ponded sheet sands and associated channel/levee deposits within a minibasin,
making this a non-structural play. The potential for gas hydrate occurrence at WR313 is supported by
shingled phase reversals consistent with the transition from gas-charged sand to overlying gas-hydrate
saturated sand. Drilling locations have been selected at each site to 1) test geological methods and models
used to infer the occurrence of gas hydrate in sand reservoirs in different settings in the northern Gulf of
Mexico; 2) calibrate geophysical models used to detect gas hydrate sands, map reservoir thicknesses, and
estimate the degree of gas hydrate saturation; and 3) delineate potential locations for subsequent JIP drilling and coring operations that will collect samples for comprehensive physical property, geochemical and other
analysesNon UBCUnreviewe