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THE Krishna-Godavari (KG) offshore basin is slowly but surely emerging as the Oil and Natural Gas Corporation's (ONGC) "Bombay High in gas production". Recently the ONGC discovered a huge deposit in an ultra-deep-water well there with a potential reserve of a few trillion cubic feet.
This caps a series of discoveries of big gas deposits in the KG basin since 2002 by the ONGC, Reliance Industries Limited and the Gujarat State Petroleum Corporation.
The reserves in these finds have been estimated at about 80 trillion cubic feet. The mid-year economic review for 2006-07 has called these gas discoveries "an encouraging development".
The latest discovery was in a well at 5,300 metres depth in the KG-DWN-98/2 (Krishna-Godavari Deep Water North) block in the Bay of Bengal; the reserve is estimated at 21 trillion cubic feet. The ONGC is the operator in the block with 90 per cent stake, and Cairn India Limited has 10 per cent. ONGC officials are confident that the reserve will go up to more than 20 trillion cubic feet as drilling progresses.
The targeted depth of this ultra-deep well is 6,200 m. The water depth is 2,841 metres, making drilling a challenge. Drilling began on September 19, 2006, and as on December 20 the well had been bored to a depth of 5,780 m.
The ONGC wants to test the depth of the well even beyond the basement. An ONGC official said: "Normally, the basement is made of impervious rock and is not expected to hold hydrocarbons since it has no pores. In this case, the basement may have fractures, which could hold hydrocarbons. However, the nature of the hydrocarbons, if any, can be ascertained only when drilling is complete."
The ONGC plans to drill in two other blocks, KG-DWN-98/4 and KG-DWN-98/5, as well. Seismic and geophysical studies have indicated the presence of hydrocarbons in these two blocks. Drilling for gas hydrates is also under way off the Andaman archipelago.
In 2002, the KG basin received a lot of attention when Reliance Industries Limited and its partner Niko Resources of Canada struck gas in a well with a reserve of about 14 trillion cubic feet.
In the first quarter of 2005, the ONGC found gas reserves of about three trillion cubic feet in a structure called G-1-12A.
In June 2005, it made another significant discovery of gas in GS-15 prospect. Later, in the same year, the Gujarat State Petroleum Corporation claimed to have discovered a gas reserve of several trillion cubic feet in the KG offshore basin.
On December 18, Niko Resources announced that the company and RIL had discovered an oil reserve in their gas-rich D6 block in the KG offshore basin. Reliance has made about a dozen gas discoveries in the D6 block.
T.S. Subramanian
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