Cluster 7 offshore Mumbai is a آ‘jewelآ’ ONGC missed

Vol 10, PW 8 (10 Aug 06) Exploration & Production

ONGC must be regretting its decision to offer offshore marginal fields to private developers.

Particularly the much sought after Cluster 7, which lies in the Mumbai Offshore and is made up of three fields thought by ONGC to hold pools of oil too small in size to be economically viable to develop. Cluster 7 was awarded early this year to a consortium of state-owned refiner Hindustan Petroleum, its upstream subsidiary Prize Petroleum and M3nergy of Malaysia.

Sources in the consortium tell us Cluster 7 promises to be the gold mine that ONGC has missed. Sometime in the late 1980s and early 1990s, ONGC discovered this cluster of three fields offshore Mumbai scattered over a 180-sq km area in water depths between 70 metres to 80 metres.

Of the nine wells drilled, six were dry and three reported oil shows. In 1993-94, production testing of two wells by ONGC yielded a flow rate of between 6000 and 8000 b/d oil hardly anything compared to the giant Mumbai High field just 25-km away.

Disappointed, ONGC capped the fields and in 2005 offered them to private developers along with 16 other western offshore marginal fields. Consortium sources tell us Cluster 7 was grossly underrated by ONGC.

Weve found good stratigraphic features between 1400 metres and 1800 metres, says a source. How did ONGC miss it Like everybody ONGC began testing bottom upwards.

ONGC tested zones between 1900 metres and 2000 metres. When they did not find significant flows at that level a decision must have been taken to move away since the targeted drilling depth had been probably reached by then.

No further wells have yet been drilled by the consortium at Cluster 7, but after analysis of 280-sq km old 3D shot by ONGC it is confident it can produce at least 20,000 b/d oil and approximately 1m cm/d gas. More significantly, consortium sources believe Cluster 7 holds about 45m barrels recoverable oil.

Estimates of gas reserves have yet to be made, we learn. It should become clearer during drilling.