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Scientists study new seabed energy source - 11/10/2002

New Zealand scientists are studying frozen seafloor deposits that could become an important source of energy in the future.

Scientists at the GNS Science Limited (GNS) have been studying the phenomenon known as gas hydrates - a frozen methane-water mix found in ocean sediments worldwide - for the past six years.

Gas hydrate deposits, occurring mainly in the top 500m of the seafloor, have been identified in substantial quantities off the North Island's east coast between Gisborne and Marlborough.

Potentially a multi-billion dollar resource, hydrates and the free gas that underlie them, are difficult to extract because they are volatile and awkward to bring to the surface.

Scientists estimate that worldwide, gas hydrates could hold twice the energy of all the known fossil fuel reserves on Earth.

Led by geophysicists Stuart Henrys and Ingo Pecher, scientists at GNS have found indications of frozen methane in a 40,000sqkm area in water depths ranging from 1km to 3km along the East Coast.

They have identified an 80sqkm area, about 180km east of Hastings, that could hold the equivalent of five years' worth of gas supplies from the Maui natural gas field.

Dr Henrys emphasised that scientists had not yet found a way to safely extract the methane.

Even under the seafloor, the frozen gas could be unstable. Small changes in seawater temperature and pressure could cause hydrates to break down and the methane to be released as gas.

Scientists believe that in previous periods, when the Earth's climate was warmer, huge volumes of the once-frozen methane were released into the air accelerating greenhouse conditions and tipping global climate change into overdrive.

Dr Henrys said there was intense international interest in gas hydrates partly because their instability could push global atmospheric temperatures to dangerous levels. The other incentive was their potential for replacing dwindling natural gas supplies.

The GNS team uses a combination of geological, geophysical and geochemical techniques to study gas hydrates. The work fits in well with GNS' other marine activities which include evaluating petroleum reservoirs, investigating seafloor hydrothermal vents, and mapping geological structures within New Zealand's EEZ.

Much of the initial work is based on seismic reflection techniques where sound waves are bounced off the seabed and rock layers beneath. Scientists analyse the reflected sound waves to build up a picture of the rock and sediment layers under the seabed.

Reflection methods detect a `bottom simulating reflection' (BSR) - a zone which shows up on the seismic instruments as if it was a second seafloor, 1km or so beneath the real ocean floor. Where the BSR exists, methane is believed to be trapped in ice immediately above the BSR, and with zones of free gaseous methane immediately underneath.

During the next 10 years, the GNS scientists would like to drill into the most likely areas to examine the methane deposits. Because drilling is expensive, collaboration with other countries would be needed, Dr Henrys said.