"We will begin work on revival of the offshore fields from January one, that will jack up crude output by at least 50 per cent to 15 million tonnes in five years," ONGC chairman and managing director Bikash C Bora told PTI here, adding that the petroleum ministry and the director general of hydrocarbons had given necessary clearance for the entire plan.

Undertaken jointly with British consultant Geffney Cline & Associates (GCA), the exercise is expected to improve oil recovery from the current rate of 26-28 per cent to 35-40 per cent, he said.

The Rs 5,000 crore redevelopment plan for Mumbai High North would be taken up in January 2001, while that for Mumbai High South, costing Rs 2,500 crore, in April 2001, he said adding the complete recast of the offshore oil field which currently contributes around 42 per cent to ONGC's crude production is likely to be completed in four years.

ONGC produced close to 10.5 million tonne of crude and 12 million cubic metre of gas per day at its Mumbai High offshore field in 1999-2000.

The cost of crude oil produced from Mumbai High, which has reserves of about 1.64 billion tonne that could last till 2050, is only about 40 per cent of the imported crude. Bora said the entire requirement to fund the Mumbai High revamp exercise is expected to be met through ONGC's internal accruals.

"Mumbai High is going through a mid-life problem which is faced by almost all fields around the world.

We have embarked upon this exercise to arrest the decline and extend the life of the field by another 50 years at least," company sources said.

The revival package will not only help arrest decline in output, butalso give us an additional five million tonnes of crude a year, sources said.

"We are using comprehensive 3-D seismic data of the entire 1,200 sq km oilfield. This state-of-the art technique was not available in the earlier years and has now provided the clearest-ever picture of the nation's richest oilfield," they said.

With the investment in both Mumbai High and other oilfields, ONGC would be able to take its crude production to over 30 million tonnes in five years, they said, pointing out that in the absence of the revival programme of various oilfields the crude output would have declined to 20-21 million tonnes in 2005 from 24.63 million tonnes produced in 1999-2000.

Simultaneously, the Corporation has embarked on an advanced oil recovery programme, which would primarily involve water alternating gas injection and explore the possibility of using high-technology nitrogen injection, sources said, adding the programme will yield five lakh tonnes of additional crude during the current year.