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Drilling Vessel Targets Methane Hydrates in Gulf of Mexico

The Uncle John semi-submersible drilling vessel will enter the Gulf of Mexico later this month to embark on a 35-day mission to test drilling through methane hydrates with two pairs of deep wells. Methane hydrate, which is called the "ice that burns" because it releases a flammable gas when it melts, may represent up to 200,000 Tcf of natural gas, according to the DOE's Office of Fossil Energy. But the industry is years away from understanding how to tap the resource.

The voyage, which is being led by ChevronTexaco in cooperation with DOE's National Energy Technology Laboratory (NETL), is part of a four-year, $13.6 million project, called the Gulf of Mexico Joint Industry Project, partially funded by the DOE to develop technologies that locate and safely drill through or near hydrates. It is one initiative in DOE's National Methane Hydrate R&D Program.

The Joint Industry Project has focused on two Gulf of Mexico sites: the Keathley Canyon and Atwater Valley areas on the Outer Continental Shelf offshore Texas and Louisiana. These locations, at a depth of 4,300 feet, were selected after an evaluation of sea floor geologic features and an estimation of the presence of methane hydrates.

While the potential of methane hydrates as an energy source is enormous, there is insufficient information available on its characteristics, on safety issues related to drilling through hydrates to resources below, and on the global climate impact of producing hydrates. More research also must be done on how to cost-effectively transport the gas to the surface before wide-scale production could ever take place.

Data collected during the project will be used for many different purposes, said DOE's Ray Boswell, acting technology manager for hydrates at NETL. But the project is mainly focused on the safety issues involved in drilling through methane hydrates to resources below.

Methane hydrate is sensitive to temperature changes and because of this, producing warm oil and gas from reservoirs below methane hydrate accumulations could make the sea floor and well-bore unstable.

"The idea is you are drilling through hydrates to a deeper zone and producing warm fluids that are coming up the pipe and might heat the hydrate and there might be instability in the sediment so that it might start moving," he explained. "Anything that is sitting on the surface might start moving. Pipes passing through it might experience some shear. The project's goal is to assess the safety of this.

"The way [producers handle drilling through hydrates now] is to avoid them. At some point in the future they are not going to want to avoid them any more. They are going to want to be able to know something about them and when they need to avoid them."

He said project researchers will assess their ability to determine what sites have hydrates in the subsurface before drilling. "They are working with seismic, heat flow measurement, chemistry and a bunch of different indicators to try to estimate how much hydrate will be in two locations. Then we are going to drill the wells and see how good the predictive capability currently is."

During the project, researchers plan to drill two sets of deep well pairs in the Keathley Canyon and Atwater Valley locations to collect drilling, logging, and coring data. One well pair at each location will be drilled in an area expected to contain large volumes of methane hydrate. The second well pair will be drilled where less methane hydrate is indicated, for baseline data.

Comparing the data from the two areas will provide important information about the nature of the methane hydrate in the sea floor and provide a test for estimating reserves prior to drilling. The research team will subsequently evaluate all data and integrate it into the existing database and seismic information.

A significant activity of the expedition will be the collection and preservation of methane hydrate samples for laboratory testing. The results will ultimately provide researchers with the data needed to validate gas hydrate models and improve drilling safety procedures.

"Our program also is very interested in determining the resource potential of hydrates in the Gulf of Mexico. But this particular project's goal is a safety goal," said Boswell. However, he noted that DOE is working with BP on a separate hydrate project in Alaska, where the hydrate volumes are lower but the hydrate reservoirs are much better than those in the Gulf of Mexico.

"That project is focused on [hydrate] recovery techniques and exploration techniques to define prospects, modeling to determine the economics of prospects and if we go to a third phase, there will be drilling and production testing with different production designs and stimulation techniques.

"In the Gulf we haven't gotten to that stage yet...," he said. "Right now we don't have the ability in the marine environment to identify [hydrate] prospects. There is a hydrate stability zone all throughout the Gulf of Mexico, but it is perturbed a lot by deformation, salt features, differential thermal gradients. So right now if you had to go pick a spot in the Gulf of Mexico to drill a hydrate well you would be hard pressed to do it."

Boswell said the industry is still attempting to find the right tools to identify hydrate prospects. Because of the nature of hydrates, that currently cannot be done with conventional seismic. What makes a good hydrate prospect and how that shows up on seismic data is still not clear.

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