Hope for future in methane find

By SIMON COLLINS science reporter

Huge deposits of frozen methane off the east coast of the North Island are a possible long-term replacement for the Maui natural gas field.

A survey by the Institute of Geological and Nuclear Sciences has found indications of frozen methane in a 40,000 sq km area underneath waters between 1km and 3km deep off the coast from Gisborne to Marlborough.

One 80 sq km "sweet spot" alone, about 180km east of Hastings, contains enough methane to replace Maui gas for five years.

But scientists have not found ways to extract the methane commercially.

The US Department of Energy has set a target of starting commercial production from American methane deposits by 2015.

Methane, also known as swamp gas, is released by bacteria that eat plant and animal material in swamps, landfills, rice paddies and animals' digestive tracts, as well as material washed off land by rainwater and ending up on the seafloor.

Like carbon dioxide, methane in the air absorbs some of the sun's heat, creating a natural greenhouse effect that keeps the climate around 32C warmer than it would be otherwise.

The frozen methane under the oceans - said to contain twice as much carbon as all other fossil fuels on Earth - is stable only while the water above it remains cold and heavy.

Scientists believe that in previous periods when the world's climate has warmed, huge volumes of once-frozen methane have been released into the atmosphere, reinforcing the greenhouse effect and pushing the original warming into catastrophic overdrive.

Intense research into the frozen methane is being done around the world because of the danger that it might drive global warming to disastrous levels, and because of its economic potential to replace natural gas.

Part of the New Zealand study was done last year in a joint project with Japanese and British scientists to explore the area where rock from the vast Pacific plate of the Earth's crust dives under the Australian plate along the "Hikurangi deformation front" off the east coast.

The scientists sent soundwaves into the sea to detect a "bottom simulating reflector", a zone which shows up on the seismic instruments as if it was a second seafloor, 1km or so beneath the real ocean floor.

Methane is believed to be trapped in ice immediately above the reflector, often with zones of free gaseous methane in the warmer rock immediately underneath.

Project leader Stuart Henrys said the reflector was only an indication of likely methane, and drilling would be required to prove its existence.

"What we'd like to do in the next 10 years is get down there and have a look at the methane," he said.

But drilling was costly, and was likely to require further collaboration with other countries.

He said "huge engineering problems" would have to be overcome to extract the methane from the ice structures, or "hydrates", which had trapped it.

"The danger is that if you hit a gas pocket and you are not prepared for it, you can completely blow the well out."

The chairman of the Petroleum Exploration Association, Peter Hazledine, said getting methane from ice would be more like mining than conventional oil and gas extraction.

"It's not sealed with anything, so you can't just drill into them and pump a whole lot of water into them to melt the ice, because you have nothing to trap it," he said.

"It will just bubble away.

"I don't think we'll be seeing an awful lot of methane hydrates in my lifetime."

Henrys said natural gas discovered near the same area in Hawke Bay had not proved economic to develop.

"If we are going to find a Maui, we are probably going to find it in the short term in Taranaki," he said.

"But if you are looking long term, hydrates are kind of cool.

"There are a lot of them, and in the meantime we'll learn quite a lot about natural gas systems."

Institute of Geological & Nuclear Sciences