For decades, researchers have dreamed about converting the vast, naturally occurring methane hydrates reserves on the North Slope into usable natural gas, but a new device could help Alaska unlock conventional natural gas fields by reversing that process.
The National Energy Technology Laboratory, an agency within the U.S. Department of Energy, is promoting a new device for making methane hydrates, a compound where molecules of methane, the main ingredient for natural gas, are trapped in cages of ice.
The device forces methane through a nozzle, chilling it to the point where it forms the crystallized hydrates. The device uses the Joule-Thomson Effect, a thermodynamic process where gas changes temperature when forced through a tiny opening. It’s the reason an aerosol can gets cold when you hold down the spray nozzle.
At a field with the right pressure, between 1,100 and 1,400 pounds per square inch, the nozzle could connect directly into the production stream, without compression.
The traditional method for making hydrates is a batch process, where methane is fed into a vessel filled with water, which is then cooled and pressurized. Not only is that process not continuous, but it’s also slow, taking six hours or more. The nozzle works in seconds.
Aren’t hydrates a problem?
Still, many who’ve heard about methane hydrates might scratch their heads to hear that someone is promoting a method for making what has traditionally been seen as a nuisance.
Hydrates can form naturally inside pipelines and wells to dangerous effect, clogging passageways that need to remain clear. That’s what happened this summer when BP tried to use a giant box to capture oil gushing from a busted wellhead in the Gulf of Mexico.
In fact, the nozzle is the opposite of most federal research into methane hydrates, which typically involves studying way to turn the ice crystals back into a gaseous state.
Over the past decade, DOE has spent millions of dollars studying methane hydrate deposits, looking for economic and environmentally conscious ways to develop the resource. Alaska is no stranger to that work, with Anadarko, BP, ConocoPhillips and the city of Barrow partnering on research projects with DOE over the past 10 years.
Hydrates vs. LNG vs. pipelines
So why is NETL interested in making methane hydrates?
“This is a whole new market for natural gas,” Charles Taylor, director of the chemistry and surface science division for NETL, told Petroleum News on Sept. 15.
Taylor said the device could unlock stranded natural gas deposits, those fields that are too small or exist too far from infrastructure to justify development and transportation costs.
Taylor said the nozzle, in many cases, would be cheaper than two other methods for transporting natural gas: super chilling it to a liquid state or building a new pipeline.
Hydrates are cheaper to make than liquefied natural gas because they form at a much lower temperature, around 14 degrees Fahrenheit for hydrates compared to minus 260 degrees for LNG. That means hydrates require less energy to produce than LNG and can be stored in simple refrigerated trucks, like those commonly used by food distributors.
As with LNG, the process of making and unmaking methane hydrates leads to a loss of some of the resource, a problem not encountered with a traditional pipeline. “You lose some with transportation, but it’s nowhere near as much as you do with LNG,” Taylor said, estimating a 10 percent loss with hydrates compared to a 25 percent loss with LNG.
A cubic foot of LNG, though, contains four times more methane than a cubic foot of hydrates, making each cargo load more valuable. Even with that advantage, Taylor believes hydrates are more cost effective. A comparison of the two technologies by Mitsui Engineering & Shipbuilding Co. supports that claim. The Japanese company concluded that, when taking the entire supply chain into consideration, the cost to produce, store and move methane hydrates “is much lower than that of LNG.”
In some cases, trucking hydrates could even be cheaper than building a new pipeline, although direct comparisons depend on factors like diesel prices and pipeline length, not to mention the possibility for increased road traffic incurred by trucking the resource.
A solution to stranded gas
But any technology aimed at stranded gas reserves should interest Alaska.
There are trillions of cubic feet of stranded proved natural gas reserves on the North Slope and for decades government and industry have floated major pipelines to un-strand them. For the first time, two current projects have held open seasons, but the success of those ventures remains uncertain and the cost of either would be undeniably large.
At the same time, policymakers are studying various in-state pipelines to direct some of that North Slope gas to local population centers around Fairbanks and Anchorage.
The new device is not an immediate alternative to either of those projects.
The NETL only filed for a patent on its nozzle in April. Taylor said it could take five to seven years to get the device on the market, even with the muscle of an industry partner.
If the nozzle is available in 2017 or sooner, it would almost certainly be on the market several years before either pipeline is built. (Those plans project a 2020 timeframe.) Still, it’s unclear whether trucking hydrates 1,700 miles to Alberta, or to other points in the Lower 48 and Canada, would be a viable alternative to a pipeline.
That said, the device could still be useful if such a pipeline is ever built.
A cost-effective way to move natural gas could connect smaller natural gas fields, like those spread across the foothills of the Brooks Range, to a larger pipeline (although trucking hydrates requires roads, a scarce commodity in much of western Alaska).
The technology could also be used to barge natural gas to remote villages along the Kuskokwim and Yukon Rivers that currently pay a premium to get diesel and heating oil.
—Eric Lidji
