The U.S. Gulf of Mexico contains very thick and concentrated gas-hydrate-bearing reservoir rocks which have the potential to produce gas using current technology.
Recent drilling by a government and industry consortium confirm that the Gulf of Mexico is the first offshore area in the U.S. with enough information to identify gas hydrate energy resource targets with potential for gas production.
Gas hydrate, a substance comprised of natural gas and water, is thought to exist in great abundance in nature and has the potential to be a significant new energy source to meet future energy needs. However, prior to this expedition, there was little documentation that gas hydrate occurred in resource-quality accumulations in the marine environment.
“This is an exciting discovery because for the first time in the U.S. Gulf of Mexico, we were able to predict hydrate accumulations before drilling, and we discovered thick, gas hydrate-saturated sands that actually represent energy targets,” said U.S. Geological Survey Energy Program Coordinator Brenda Pierce.
The U.S. Department of Energy (DOE), the U.S. Geological Survey (USGS), U.S. Minerals Management Service (MMS) and a group of U.S. and international energy industry companies under the management of Chevron were responsible for conducting this first ever drilling project with the goal to collect geologic data on gas-hydrate-bearing sand reservoirs in the Gulf of Mexico.
“We have also found gas hydrate in a range of settings, including sand reservoirs, thick sequences of fracture-filling gas hydrates in shales, and potential partially saturated gas hydrates in younger systems,” said USGS Scientist Timothy Collett. “These sites should provide a wealth of opportunities for further study and data collection that should provide significant advances in understanding the nature and development of gas hydrate systems.”
The most important technical accomplishments include:
- The collection of a comprehensive set of logging-while-drilling (LWD) data through expected hydrate-bearing sand reservoirs in seven wells at three locations in the Gulf of Mexico.
- LWD sensors provided unprecedented information on the nature of the sediments and the occurrence of gas hydrate.
- The expedition discovered gas hydrate in both sand and fracture dominated reservoirs.
- The discovery of thick gas-hydrate-bearing sands validates the pre-drilling integrated geological and geophysical approach used to identify the targets and provides increased confidence in assessing the energy resource potential of marine gas hydrates.
- In the case of the Walker Ridge and Green Canyon drill sites gas-hydrate-bearing sand reservoirs between 50 and 100 ft thick were discovered.
- The discovery of concentrated gas hydrates in sand reservoirs has made Walker Ridge and Green Canyon prime locations for future research drilling, coring, and production testing.
Field operations during this expedition were also supported by AOA Geophysics, the Borehole Research Group at Lamont-Doherty Earth Observatory of Columbia University, Schlumberger, and the crew of the Helix Q4000 drilling vessel.
More information on natural gas hydrates:
USGS Energy Resources web site.
More informationo n gas hydrate research in the Gulf of Mexico and the results of this expedition:
National Methane Hydrates R&D web site.Christopher Mims, writing for today’s MIT Technology Review, described the new findings in detail. An excerpt of his piece:
“Last Friday, the United States Geological Survey (USGS) announced the discovery of suitable conditions for mining methane hydrates 1,000 meters beneath the seabed in the Gulf of Mexico. Together with Chevron and the U.S. Department of Energy, the USGS discovered the reserve of hydrates in high concentrations in 15-to-30-meter-thick beds of sand--conditions very much like terrestrial methane hydrate reserves, which have already yielded commercially useful flow rates. These deposits are substantially different from the gas hydrates that have previously been discovered in U.S. coastal waters, which exist in relatively shallow waters at the surface of the seabed and have become a concern for climate scientists because of their potential to melt rapidly and release large quantities of methane into the atmosphere.
In the spring of 2008, a joint Canadian-Japanese expedition in Mallik in the Northwest Territories, Canada, established that methane hydrates could be harvested by using a water pump to depressurize a well already drilled into the reserve. This involved lowering the pressure pumping out the water that naturally accumulates in the well. Crucially, it required only 10 to 15 percent of the energy represented by the gas that flowed out of the well, making it a much more viable approach than earlier methods used to harvest hydrates, which involved melting them with warm water. Standard oil and gas drilling equipment was used to reenter an old well drilled to a depth of 3,500 feet and then "refurbish" it by casing the entire well with lengths of steel tubing that cemented into place in order to prevent it from collapsing.
Hydrates require both cold temperatures and high pressure to form; eliminating either condition frees the gas from its icy cage, but past attempts to do this by heating the hydrates proved prohibitively difficult. The Canadian-Japanese expedition successfully produced up to 4,000 cubic meters of gas a day during a six-day trial in 2008 using depressurization.
‘I think [the Gulf of Mexico find] and Mallik are two revolutionary events,’ says Timothy Collett, a geologist with the USGS and one of the world's foremost authorities on gas hydrates.”
Read more at MIT Technology ReviewSOURCES: U.S. Geological Survey; MIT Technology Review
