State-owned Oil and Natural Gas Corp will invest Rs 985 crore (Rs 9.85 billion) to develop the Bassein East field, which is estimated to contain 97 million tonnes of oil and oil equivalent gas.

"We plan to bring to production the Bassein East oil and gas field in 30 months," ONGC chairman and managing director Subir Raha told PTI in New Delhi.

The field is estimated to yield 6.185 million tonnes of oil and 3.175 billion cubic meters of natural gas over 2006 to 2021, he said.

Bassein (now Vasai), situated between Bombay high field to the west and Mumbai to the east, has been producing gas since September 1988. It currently produces 15 million cubic meters of gas per day. Bassein East is situated to the east and northeast of Bassein and the two are separated by a low axis.

ONGC proposes to execute the project through single tender international competitive bidding process to save time. It expects to prepare bid packages by August 31 and call offers before end-November.

The project would be completed within 30 months excluding the intervening monsoon season, Raha said.

Subsequent to Bassein East, he said ONGC has discovered oil in the west of Bassein field. It is estimated to contain 25 million tonnes of oil and oil equivalent gas reserves.

For putting to production the Bassein East field, ONGC plans to set up an integrated oil handling/water injection/gas compression platform with two unmanned well platforms. It plans to drill 19 new wells, 13 producers and 6 injectors.

Raha said the Bassein West prospect located about 15-km west of Bassein field of Mumbai offshore was taken up for exploratory drilling in 2002.

Exploratory well B-22-5 flowed oil and gas at two intervals - 1774 barrels per day of crude oil and 10760 cubic meters per day of gas at one and 1050 barrels per day of oil and 7955 cubic meters per day of gas at the other.

ONGC has completed two well exploratory campaigns that have established presence of around 25 million tonnes of oil and oil equivalent gas, he said adding "the testing results indicate presence of hydrocarbon in commercial quantity in Lower Bassein formation."

Another prospect BS-16 to the north west has been taken up for fast track delineation. The well is under testing and preliminary assessment of the data acquired indicates the well to be interesting from hydrocarbons point of view, he said.

The discoveries on east and west would supplement the decline in Bassein output expected from next year.

Bassein field, which currently produces 32 million standard cubic meters per day of gas, would hit the decline stage from next year with its production falling by as much as 3 mmscmd, sources said.

East of Bassein holds close to 3.5 trillion cubic feet of gas reserves besides some quantity of crude oil. Estimated production from the field would be of the order of 0.4 million tonnes of oil per annum and 3.4 mmscmd of gas.