28 4d fixed installation seismic
➠
Gas hydrate, a substance comprised of natural gas and The most important technical accomplishments
water, is thought to exist in great abundance in nature include:
and has the potential to be a significant new energy l The collection of a comprehensive set of logging-
source to meet future energy needs. However, prior to while-drilling (LWD) data through expected hydrate-
this expedition, there was little documentation that gas bearing sand reservoirs in seven wells at three locations
hydrate occurred in resource-quality accumulations in the in the Gulf of Mexico.
marine environment. l LWD sensors provided unprecedented information on
“This is an exciting discovery because for the first the nature of the sediments and the occurrence of gas
time in the US Gulf of Mexico, we were able to predict hydrate.
hydrate accumulations before drilling, and we discovered The expedition discovered gas hydrate in both sand
thick, gas hydrate-saturated sands that actually represent and fracture dominated reservoirs.The discovery of thick
energy targets,” said US Geological Survey energy gas-hydrate-bearing sands validates the pre-drilling
programme coordinator Brenda Pierce. integrated geological and geophysical approach used to
identify the targets and provides increased confidence
Gas-hydrate-bearing sand
in assessing the energy resource potential of marine
The US Department of Energy (DOE), the US Geological gas hydrates. In the case of the Walker Ridge and Green
Survey (USGS), US Minerals Management Service (MMS) Canyon drill sites gas-hydrate-bearing sand reservoirs
and a group of international energy industry companies between 50 and 100 ft thick were discovered.
under the management of Chevron were responsible for The discovery of concentrated gas hydrates in sand
conducting this first ever drilling project with the goal reservoirs has made Walker Ridge and Green Canyon
to collect geologic data on gas-hydrate-bearing sand prime locations for future research drilling, coring, and
reservoirs in the Gulf of Mexico. production testing.
“We have also found gas hydrate in a range of The announcement by the USGS also coincided with
settings, including sand reservoirs, thick sequences of Chevron’s own announcement that it has started crude
fracture-filling gas hydrates in shales, and potential oil production from its Tahiti Field, the deepest producing
partially saturated gas hydrates in younger systems,” field in the Gulf of Mexico.
said USGS scientist Timothy Collett. “These sites should First oil from Tahiti was achieved on 5 May. Daily
provide a wealth of opportunities for further study and production is expected to ramp up to approximately
data collection that should provide significant advances in 125 000 barrels of crude oil and 70 million cubic feet of
understanding the nature and development of gas hydrate natural gas before the end of the year.
systems.”
Recoverable resources
The Tahiti Field is one of the largest in the Gulf of Mexico.
It was discovered in 2002 and is estimated to contain total
recoverable resources of 400 to 500 million oil-equivalent
barrels. The total cost for the first phase of the project is
US$2.7 billion and represents one of 40 projects in which
Chevron’s share of the investment is over US$1 billion.
The Tahiti Field is located 190 miles south of New
Orleans, in approximately 1250m of water.
“Tahiti is a significant addition to our growing reserves
and production,” said George Kirkland, executive vice
president, global upstream and gas. “It is another
demonstration of our deepwater expertise, and our ability
to execute an industry-leading queue of major capital
projects.”
Tahiti is located at Green Canyon Blocks 596, 597,
640 and 641. Primary pay sands are Lower to Middle
Miocene from 23 000 to 28 000 feet and lie below a
salt canopy ranging from 8000 to 15 000 feet thick. The
deepest producing well is more than 26 700 feet, a record
for the Gulf of Mexico. Production is from two subsea
drill centres tied backed to a floating production facility
supported by a truss spar.
Chevron holds a 58 per cent working interest in Tahiti
and is the operator, StatoilHydro holds a 25 per cent
Fig. 3. Big Wave is a survey in the Eastern Gulf of Mexico designed to working interest, and Total owns a 17 per cent working
acquire 30 000 km of data in advance of lease sales in the region. interest. l
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