Flagship explorer ONGC has struck a gas reserve in the form of hydrates ­ otherwise known as 'fire ice' ­ off the Andhra coast that could turn out to be four times larger in terms of yield than Reliance Industries Ltd's discovery of 2002, India's biggest so far.The discovery was made in August last year by the second exploratory expedition under the government's gas hydrate programme in collaboration with scientists from US and Japan, which have separately inked research MoUs with India.The discovery validates the government's stress on finding alternative sources of energy and efforts to attract investments in the exploration business. It would also be a boost for PM Modi as he moves to promote a gas-based economy in tune with India's commitment to mitigate climate change. Irrespective of the cur rent depressed oil and gas price price scenario, which makes fresh investments unviable, the hydrates discovery would put India back in reckoning in terms of prospectivity . It would also return the spotlight on the eastern offshore, described as `India's gas bowl' and `India's North Sea' after Reliance's gas discovery. The region lost its glory in the aftermath of output falling from Reliance's field.Sources in the Directorate General of Hydrocarbons, the oil ministry's technical arm co-ordinating the gas hydrates programme, said the discoveries have been made in Blocks 982, D3, D6 and D9 in the Krishna-Godavari basin, off the Andhra coast.These blocks are 30 Kms south-west of Reliance industries Ltd's natural gas block KG-D6.Broadly , commercially useful gas hydrates are formed when methane or natural gas get trapped in icicles. These are found at places with extreme cold temperatures such as the Arctic region, Alaska and Siberia; or below seabed under high pressure of water depth.There are two main technologies being successfully tried to free gas ­ either by depressurising or injecting CO2 which replaces gas in the icicles.But there's a catch. Or two. Cost of production is a worry , especially in a depressed market. Technology for producing gas from hydrates is still in pilot stage ­ though considerable success in Japan, US and Canada gives hope. Indeed, Japan has declared it would start commercial gas production from its offshore hydrates from 2020 after proving commerciality of the technology by 2018. ONGC intends to benefit from Japan's experience and technology by starting pilot production from its discovery from 2017.The sources put the initial reserves potential of the hydrates at 134 tcf (trillion cubic feet). Even if ONGC manages to pump out a tenth of the reserves, the discovery could yield nearly 13 tcf of gas against RIL's 9 tcf.