Deep-freeze methane may be hot state property

Tim Bradner

Conoco Phillips plans an interesting hydrocarbon test later this year: trying to extract methane gas from a hydrate on the North Slope. BP also plans a different hydrate test it will try later.

Hydrates are ice structures that form underground under certain temperature and pressure combinations. They can contain immense amounts of methane, the main chemical component of natural gas. Methane hydrates exist offshore in many places around the world, such as offshore Japan, and they may exist off the U.S.

What's important for us in Alaska is that they exist onshore in the Arctic, including the North Slope. That's because, geologists believe, hydrates that formed at the bottom of the permafrost (or underlie almost all of the North Slope) trapped methane as it seeped up from the deep rocks that are the source of the oil and gas tapped by our conventional oil fields.

Methane hydrates lie above the producing oil deposits on the North Slope and below the existing field infrastructure. This is convenient: the drill rigs, pads, roads and utility infrastructure are already close at hand. North Slope oil fields provide an ideal laboratory to test whether methane can be produced in commercial volumes from hydrates.

The implications of this are immense. If methane can be produced economically, it could add hugely to the gas resources available to support a natural gas pipeline from the North Slope. The numbers are staggering. As much as 500 trillion cubic feet (tcf) of methane could be in hydrates in accessible areas of the Slope. Compare that with the 35 tcf of conventional gas resources we now have.

But for now, this is still a science project. Producing companies have long suspected the presence of hydrates on the North Slope because they can pose drilling hazards by creating high-pressure pockets of gas. Such pockets are suspected as the cause of more than one gas blowout of wells being drilled.

In researching hydrates, the companies' first goal was to come up with a reliable way to find and identify them, which they have succeeded in doing. Phase 1 of this were tests by research groups, led by Anadarko Petroleum Corp. in 2003 and BP in 2007, to identify the presence of a hydrate through seismic profiling and then drilling a well to confirm its presence. The 2007 project also involved extracting a hydrate core for analysis. This has been done. Companies can now reliably find the hydrates.

Phase 2 is to see if methane can actually be produced from a hydrate. This is the goal of tests now under way. If those are successful, the next stage is to see if production can be economical.

If it can be, it will happen on the North Slope because the production infrastructure is there. If a gas pipeline is built to tap large conventional gas resources, it will also be able to tap these unconventional resources.

This isn't a slam dunk, though. The technical challenges are considerable. One way scientists think the methane can be produced is by gradually warming and depressurizing the frozen hydrate, allowing methane to seep out. This is the approach BP is exploring. This must be done carefully because there are worries that the hydrate might destabilize, or melt, with possible surface subsidence. Or, thawing and producing the methane may cause the hydrate to refreeze and plug the well. BP will try to find ways around this.

Conoco Phillips will try injecting carbon dioxide into the hydrate. Laboratory tests show that injecting carbon dioxide displaces methane, which comes out of the hydrate as a gas. The idea is that the carbon dioxide molecules take the place of the methane molecules in the hydrate, keeping it stable.

This could be neat, if it works. Carbon dioxide would be permanently sequestered, or stored, underground, while the methane is extracted and the hydrate is left intact.

One question the Conoco Phillips production test will attempt to answer is whether this reaction in the hydrate can occur fast enough for methane production to reach practical volumes.

The U.S. Department of Energy and several universities have partnered with industry in all of these tests.

This effort shows that despite the headaches our petroleum industry faces, with declining conventional oil production, aging infrastructure, arguments over taxes and regulatory actions, there are people in the industry who see a future for us.

By "us" I mean just that. With petroleum supporting 90 percent of our state budget and a third of our economy, we're all in this together.

Tim Bradner writes for an Alaska economic reporting service. He also consults for private clients and writes for business publications. His opinion column appears every month in the Anchorage Daily News.