The discovery in the well WO-24-3 is estimated to hold an in-place reserve of about 20 million tonnes, he said.
Mumbai High, India's biggest oil field, currently produces 205,000 barrels of oil per day (just over 10 million tonnes per annum) and the new find would add to that production in less than two years time.
"In all, nine objects or zones were tested and all of them were found to be hydrocarbon bearing. The last object tested flowed 3,300 barrels of oil," he said.
"This is a mid-sized discovery but a significant one," the official said.
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The new find, which comes almost 50 years after ONGC began production in Mumbai High, will help the company maintain production levels from the basin for a longer time than currently estimated.
Mumbai High is ONGC's flagship oil producing assets. It along with other small fields along the western offshore produce 16 million tonnes per annum of oil, which is 44 per cent of India's total crude oil production of 36 million tonnes.
He said the company has successfully reversed the flagging output at its western offshore fields as it strategically struck 'low-hanging fruits'.
This included completing three sub-sea wells at the Mumbai High field and using innovative technology to produce more oil B-193 satellite and D1 or NBP fields, he said.
The new discovery is close to WO-16 field and its facilities may be used to bring the find to production, he said.
Offshore fields produced 16.79 million tonnes of oil in 2016-17, up from 16.28 million tonnes in the previous year. "During FY'18, production will increase mainly from WO-16, B- 127 fields," he said without giving details.