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.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/2322 |
| Date | 07 1900 |
| Creators | Latham, Thomas, Shelander, Dianna, Boswell, Ray, Collett, Timothy S., Lee, Myung |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Rights | Latham, Thomas |
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