BEIJING, Dec 19 (Reuters) - China said it has identified a major gas hydrate reserve in the northern part of the South China Sea, joining a small group of nations in the world seeking to tap a potentially vaste future source of energy.
There is currently no technology to commercially unlock the energy also known as "flammable ice", gas frozen in ice-like crystals buried deep under the oceans and experts say commercial, scaled development could be beyond 2030.
China's Ministry of Land and Resources (MLR) announced on Tuesday it had found a gas hydrate reserve that spans 55 square kms (34 square miles) in the Pearl River Mouth basin with controlled reserve equivalent to 100-150 billion cubic metres (bcm) natural gas, according to a report carried on the ministry's website (www.mlr.gov.cn).
That would be the size of a major conventional natural gas field, like in China's top gas province Sichuan.
Guangzhou Marine Geological Survey Bureau, an MLR unit, collected samples of "high purity" gas hydrates over nearly four months of surveys and drilling of 23 wells in the waters off south China's Guangdong province.
Two gas hydrate layers with a thickness of 15-30 metres were found just below the seabed, which was at a depth of 600 to 1,000 metres.
"It marks a breakthrough in investigating the resource and proves that the Pearl River Mouth basin is rich in gas hydrate," the report said, adding China becomes the fourth country in the world to have collected sample of the methane hydrate after the U.S., Japan and India.
Che Changbo, deputy director of MLR's Geological Exploration Department, said China would collect more samples from target areas and increase research into how to tap the energy source.
"Without mature technology, nobody will be able to develop this resource," Che told Reuters by telephone.
China, the world's top energy, formally started studies of gas hydrate since 2002, when the government listed it as a national research project.
Japan, which barely has any indigenous energy resources, was probably the only country so far that has extracted gas from hydrate deposits.
In 2008, state-run Japan Oil, Gas and Metals National Corp (JOGMEC) demonstrated for the first time a nearly six-day continuous period of production of methane gas from hydrate reserves held deep in permafrost in Canada.
In March, Japan succeeded in producing 120,000 cubic metres of gas over six days from a test exploration in the Pacific Ocean off Aichi Prefecture in central Japan.
In 2010, the International Energy Agency's World Energy Outlook (WEO) estimated that methane hydrates contained almost twice as much energy as all the world's resources of gas, oil and coal combined.
Technological challenges are immense as hydrates are only stable under specific temperature and pressure.