Bombay High will see a third phase of redevelopment to coax it into yielding oil beyond 2030. ONGC has hired the global consultancy Gaffney Cline Associates to come up with a redevelopment plan for the oilfield which has been in production since 1976.

No estimate of the cost is available yet.

As with all old oilfields, the problem with Bombay High is that its yield has been declining. Outside Opec, all oilfields around the globe that have been in production for more than three decades have historically seen an 8.5 per cent annual drop in yield.

Bombay High was no exception, but with two redevelopment plans already executed, ONGC has been able to arrest the decline at 2.23 per cent. The third redevelopment will try to at least hold this rate of decline, if not pare it further.

At its peak in 1989-90, the field yielded a little over 20 mt of crude. This dropped to just 10.6 mt last year. Yet, it is still the largest productive oilfield in India, yielding 28 per cent of the 37.7 mt mined from all oilfields in the country that year. With 420 mt already extracted, Bombay High has by now exhausted more than three-fourths of the 542 mt of recoverable crude oil reserves in the offshore field. The field is estimated to have reserves of 1,728 mt of oil and oil equivalent — but not all of this can be mined.

Bombay High is ONGC’s mainstay, accounting for over 43 per cent of the company’s output of 24.4 mt last year from all hydrocarbon fields. At some point of time all oilfields die. Arvind Mahajan, executive director of KPMG India, sees the third phase as an effort to prolong Bombay High’s life.

Bombay High is vast and divided into the north and south parts. The first redevelopment of the north field began in 2001 and finished in 2007, consuming Rs 3,302 crore. This alone is expected to have benefits over two decades in the shape of 23.25 mt more of mined oil.

Simultaneously with the north, ONGC redeveloped the south field also, spending Rs 6,569 crore. The potential benefit of this over two decades is an additional 33.85 mt.

Of the potential benefit of the first phase, ONGC has already realised an additional 38 million tonnes in both parts, according ONGC group chairman AK Hazarika. The second phase of redevelopment started soon after the first was over, the cost being Rs 7,133 crore for the north field and Rs 8,813 crore for the south. This phase is over now and the third phase study initiated.

“The likely gain in the form of oil production and investment requirement (of the third phase) will only be known after this study,” Hazarika told Financial Chronicle.