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Ghana: 'World-class' Jubilee oilfield larger than expected
THE JUBILEE oilfield, already described by Tullow Oil, the operator, as a world-class reservoir and under development for start-up in October next year, has been shown to be larger than expected. Results last month from two "bold step-out" wells, one in Kosmos' licence and one in Tullow's, have shown extensions to the southeast and to the northwest, while also confirming the excellent production characteristics of the reservoir.
The Mahogany-3 appraisal well in Kosmos' West Cape Three Points licence – but drilled by Tullow as overall operator for the field – found the hoped-for oil column in the Jubilee reservoir, but also found light crude in a deeper target. The Jubilee reservoir was thicker than expected, at 16 metres, "confirming a significant extension to the southeast", says Tullow. The lower zone found 17 metres of reservoir sandstones holding crude of 35°API, opening up further potential. The well was drilled over 5 km from the Mahogany-1 and -2 wells, increasing the known size of the field's core area. According to Kosmos, the well location was a compromise and did not penetrate the new Mahogany Deep reservoir at its thickest. The well was drilled in 1,236 metres of water by Ocean Rig's Eirik Raude semi-submersible. The other result was a production test of the Hyedua-2 well in Tullow's Deepwater Tano licence. A 41-metre column in the well's 55 metres of payzone flowed 37°API crude at 16,750 barrels a day (b/d), together with 21m cubic feet a day of gas. Tullow said the high and stable flow "from a well not even in the centre of the field" was evidence of the high reservoir quality, forecasting that production wells will be capable of delivering over 20,000 b/d each. Kosmos said the flow was limited by the equipment available on the Blackford Dolphin semi-submersible, which was working in 1,246 metres of water. Before the latest results, Tullow said Jubilee held proved recoverable reserves of 0.5bn barrels, but with the potential for 1.8bn barrels. The firm did not immediately raise its estimate, but said it was "assessing the positive impact on phase-one reserves". There are hopes of more good news soon, with the Blackford Dolphin due to carry out a production test on the Mahogany-1 discovery well and the Eirik Raude due to drill an exploration well into the nearby Tweneboa prospect. Industry sources said the high flow-rates now expected from Jubilee production wells would give Tullow the option of reducing the number to be drilled in phase one, saving on capital costs. The phase-one development has been planned with nine production wells (together with five for water-injection and three for gas-injection), with a flow of 120,000 b/d and at a cost of $3.1bn, of which wells account for $1.5bn (PE 12/08 p14). Meanwhile, as the field grows, prospects for subsequent phases of the development are firming up. According to the US' Anadarko Petroleum, a participant, as many as four floating production, storage and offloading vessels could be needed eventually. The expanding size of the field seems to have delayed the plans for its unitisation between the Tullow and Kosmos licences. Interests in Deepwater Tano are Tullow (operator), 49.95%, Kosmos, 18.0%, Anadarko, 18.0%, Ghana National Petroleum Corporation (GNPC), 10.0% (carried), and Sabre, 4.05%. Interests in West Cape Three Points are Kosmos (operator), 30.875%, Anadarko, 30.875%, Tullow, 22.896%, GNPC, 10.0% (carried), EO, 3.5%, and Sabre, 1.854%.
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