Untold quantities await discovery

Global Focus on Gas Hydrates Growing

No one knows for certain how much methane might be produced from gas hydrates, or even the total quantity of gas hydrates on the planet.

That doesn’t mean there aren’t some wild numbers floating around.

When the Potential Gas Committee at the Colorado School of Mines increased its estimate of United States natural gas resources by 486 trillion cubic feet (Tcf), it was major news.

The increase in U.S. production potential because of shale gas and other unconventional resource plays was called a “game-changer.”

Qatar claims the largest non-associated natural gas reservoir in the world, the North Gas Field, estimated at 900 Tcf.

By comparison, some estimates of the world’s gas hydrates production potential are well above 10,000 Tcf.

For years, the oil and gas industry viewed gas hydrates as something obscure and exotic. You can flip that around completely.

When experts talk about gas hydrates now, they use terms familiar to the industry:

  • Seismic exploration.
  • Petroleum system analysis.
  • Vertical well development.

That shift to familiar territory is probably the second most important thing to know about gas hydrates today.

The most important thing to know is that commercial production of gas hydrates is close to reality.

Or at least, closer.

And a third thing to know is that the resource potential of gas hydrates is still primarily a matter of exploration.

Japan Takes the Lead

Interest in gas hydrates production intensified last year after Japan successfully extracted and produced methane from hydrates in the Nankai Trough, said AAPG member Timothy Collett, senior scientist with the U.S. Geological Survey (USGS) in Denver.

The production test was conducted by the Japan Oil, Gas and Metals National Corporation, or JOGMEC.

“The highlight by far is the significant contribution from Japan” Collett said. “JOGMEC has the national gas hydrates program in Japan. It’s the first production test for hydrates from a marine environment.”

Collett is co-chair of the session “Global Review and Exploration for Methane Hydrates,” which will be held May 8 at the Offshore Technology Conference in Houston, where speakers will discuss developments in gas hydrates exploration as well as specifics of accumulations offshore Japan and India and in the Gulf of Mexico.

Japan’s gas hydrates program has a goal of fully understanding economic production by 2018, according to Collett.

“We’d consider that very optimistic, but they’ve shown the ability to stay on track for that date,” he said.

The United States conducts its own methane hydrates research through studies by the USGS and programs funded by the Department of Energy’s National Energy Technology Laboratory (NETL).

NETL recently issued a funding opportunity announcement aimed at an extended-duration test program in Alaska and an investigation of the occurrence and nature of methane hydrates on the U.S. Outer Continental Shelf.

Pressure Cores

Today, much of the key work on production from methane hydrates is being done in Asia.

“Japan’s been at this since 1995. We started in 2000,” said Ray Boswell, technology manager in Pittsburgh for NETL’s Natural Gas Technologies Program.

Economics and the desire to secure future energy supply are driving the Asian work on gas hydrates. Japan, Korea, China and India all have national programs targeting methane production from hydrates, Collett noted.

Japan, especially, lacks domestic energy resources and hopes to develop a gas hydrates resource. Import LNG prices in Japan reached $17 per million Btu earlier this year. At the same time, the country has moved away from nuclear power as an energy source.

In 2012, Japanese researchers obtained gas hydrates sediment samples, known as “pressure cores,” in cooperation with the USGS Gas Hydrates Project and the School of Civil and Environmental Engineering at Georgia Tech University.

“You try to keep it from dissociating,” Boswell said. “We’ve got some devices where you can collect those pressure cores and preserve them, and transfer them to other devices where you can study them.”

Then last year, JOGMEC was able to conduct an extended gas hydrates production project.

“They flowed gas to surface immediately and sustained that rate for six days,” Boswell said. “It took a considerable investment for Japan to do this.”

Only limited information about the production results have been released, so interest is high in the OTC session “Invited Organization (JOGMEC)” on May 7, where speakers will discuss the project.

A Very Good Fit

OTC this year will feature two additional sessions on gas hydrates:

“Methane Hydrate Case Studies,” also on May 7.

“Modeling and Laboratory Studies for Methane Hydrates” on May 8.

Methane can be produced from gas hydrates by various methods, but the leading contender for commercial production is depressurization, according to Boswell.

“That’s a relatively simple process of drawing from the reservoir with a pump. It might need to be augmented – add heat, enhance flow pathways,” he commented. “I think what people want to get a handle on now is what rates (of production) you will get with depressurization.”

In depressurization, a well is drilled into a gas hydrates accumulation. Water is pumped out to reduce pressure, so methane will dissociate from the gas hydrates clathrate lattice. The methane then can be produced through the wellbore.

So far, “all of the tests have been vertical,” Boswell noted. “The tests have been very scientific. They haven’t attempted to maximize production, at least not yet.”

With rates of production and potential rates of return still a mystery, whether or not gas hydrates production will be economic is an unanswered question.

“You have to answer that question based on where you’re sitting at any particular date,” Collett said.

High consumer prices for natural gas at the burner-tip in Asia may help gas hydrates look attractive economically. By contrast, resource plays in the United States have produced an abundance of natural gas at low prices.

There’s no doubt that a shift in thinking has made methane from gas hydrates more familiar as a resource in the energy industry.

“We’re not talking about dredging the seafloor. We’re talking about conventional approaches,” Collett said. “We’ve seen this very important progression in our thinking that is even now beginning to fall over into the production side.”

Hydrates “do fit the petroleum systems model well,” he noted. And studies have identified sand-dominated reservoirs as providing the most favorable potential for production.

That potential often is presented as a resource pyramid, with sands at the top, followed by clay-dominated fractured reservoirs, massive gas-hydrate formations exposed on the seafloor and low-concentration, disseminated deposits at the bottom.

It might happen that only the top of the pyramid, the most promising sands, will be true reservoirs for economic hydrates production. At the moment, nobody knows how large that resource would turn out to be.

“The U.S. program has a goal of understanding the wide range of issues associated with gas hydrates. Resource potential is one of those,” Boswell said. “One of the bigger issues is that very few of the prospective areas have been explored.”

Seismic analysis is now used to study the presence, properties and distribution of gas hydrates, especially in marine settings.

“I think,” Boswell said, “we have made a very big advance in recent years in finding that the geological-geophysical approach works.”

Getting Up to Speed

Getting a firm estimate of the world’s gas hydrates resource in place will require more exploration, and a lot more time.

Collett said he doesn’t think the numbers published so far have any relevance.

“We would never use the word ‘reserves’” when talking about methane hydrates, he commented.

For the most part, methane from gas hydrates has stayed under the radar as a potential energy source. That could be because the scientific understanding of gas hydrates as a resource is a relatively new thing.

“If you just go back 20 years, gas hydrates in nature were poorly understood,” Collett said. “They’re not completely well understood today.”

But gas hydrates have begun to emerge as a possible future energy source, and the recent work in Japan has drawn the world’s interest.

“There are four sessions (related to gas hydrates) at OTC, which is quite a big percentage of OTC’s available block of sessions,” Boswell noted. “It certainly is a good place for people to get caught up on the latest.”

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