Successes in Cauvery basin

IF there is one sedimentary basin in the country that has posed a sustained challenge for nearly four decades to geoscientists looking for oil and gas, it is the Cauvery basin in Tamil Nadu. For the Oil and Natural Gas Corporation, prospecting for hydrocarbons in the basin has meant acquiring a substantial amount of geoscientific data, reviewing them, undertaking three-dimensional seismic surveys and then drilling wells.

"In exploration, you have to be a die-hard optimist," says V.C. Ramaiah, General Manager-Basin Manager. ONGC's aggressive exploration has led to the discovery of a number of oil and gas fields, both onland and offshore in the basin. The basin has thus earned a place on the oil map of the country. In 1989, it was promoted from being a Category II basin to a Category I basin; it was thus put on a par with basins such as Cambay, Upper Assam and Mumbai offshore.

ONGC produces hydrocarbons from both onland and offshore sites in the Cauvery basin. Over the years, the production of crude oil from onland wells here has been going up, and it is currently about 1,100 tonnes a day. The PY-3 offshore field producesabout 4,500 barrels a day. The sale of natural gas to industries is around 6.5 lakh cubic metres a day now.

The discovery of gas in the Perungulam field in Ramanathapuram district in 1994 added a new dimension to the exploration drive. Since then, many more gas fields have been discovered in the Ramnad sub-basin - at Periyapattinam, Ramanavalasai and Kanjirangudi. Considering the possibility of onland gas sites extending to the adjoining offshore areas in the Palk Bay and the Gulf of Mannar, ONGC is carrying out special seismic surveys, called "telesis", in offshore areas. The processing and interpretation of the data from the surveys have led to the identification of several drillable prospects in the Palk Bay and in the shallow waters of the Gulf of Mannar. One such prospect, PBS-1, a major portion of which falls in the Palk Bay region and the rest onland, was drilled onland in 2001. It yielded a large quantity of gas. Efforts are under way to hire a suitable offshore rig to drill in the shallow waters (at a depth of 10 metres).

Offshore fields such as PY-3 and PY-1 were awarded to multinational companies under the Centre's policy of inviting both Indian companies and MNCs for exploration and exploitation. A certain area was carved out of PY-3 and offered for joint venture development. The companies involved are ONGC, Hardy Oil and Exploration of the United Kingdom, Tata Petrodyne and Hindustan Oil Exploration, Baroda. ONGC holds a 40 per cent interest in the PY-3 field. More wells were drilled recently in PY-3.