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Operators follow offshore Ghana trend for new prospects

Seismic, drilling interest extends to neighboring West Africa countries

Eldon Ball
Senior Editor, Technology & Economics

The center of interest off West Africa is on the exploration successes off Ghana and the implications they have for prospects offshore neighboring and nearby countries.

Production began last December at Tullow Oil’s Jubilee field – Ghana’s first deepwater oil development – and output has climbed to around 50,000 b/d since the field came onstream.

Click to Enlarge

The semisubmersible Eirik Raude operating on the Jubilee field.

Currently four wells are in service and full capacity of 120,000 b/d should be attained within six months as the remaining five producer wells are completed and come on line.

Water is being injected into two of the producing wells at a rate of 75,000 b/d, and a further four water injectors will be completed this year to maintain production levels. Gas compression commissioning has started onboard the FPSO, with gas injection to the reservoir due to start next month.

Even more significant than that milestone are the new exploration efforts popping up along the upper West Africa coastline, led by Tullow Oil, Kosmos Energy, Anadarko, and others, as operators follow what they hope is a trend that mirrors the deepwater geology offshore South America.

Last July, Tullow Oil made another potentially major oil discovery in Ghana’s deepwater play fairway. Owo-1, drilled in 1,428 m (4,685 ft) of water in the Deepwater Tano license offshore Ghana, intersected “a significant column of excellent quality light oil.” Analysis of drilling, wireline logs, and reservoir fluid samples suggest this is a large new oil field warranting further appraisal.

The deviated well, drilled by the semisubmersible Sedco 702 from a location around 6 km (3.7 mi) west of the Tweneboa wells, encountered a gross vertical reservoir interval of 154 m (505 ft), including 53 m (174 ft) of net oil pay in two zones of good-quality, stacked reservoir sandstones.

Pressure data suggest that these zones form part of the same accumulation; samples indicate a light oil (33-36º API).

Once logging operations are complete, the well will be side tracked 0.6 km (0.4 mi) to the east in an attempt to determine lateral reservoir distribution, and also to intersect a deeper part of the Owo channel system.

Owo-1 was drilled to a final depth of 3,891 m (12,766 ft). On completion of the side track, the rig will drill the Onyina-1 exploration well elsewhere in the Deepwater Tano block, targeting a large fan/channel system between the Tweneboa and Jubilee fields.

Meanwhile, Tullow’s Enyenra-2A appraisal well in the Tano license area has encountered oil in high-quality sandstone reservoirs.

The well reached a TD of 4,234 m (13,891 ft) in a water depth of 1,674 m (5,492 ft). The location is down-dip of Owo-1 (since re-named Enyenra), 7 km (4.35 mi) to the north, the aim being to appraise the field’s upper and lower channels.

Wireline logs, reservoir fluid samples, and pressure data indicate that Enyenra-2A intersected 21 m (69 ft) of net oil pay in the upper channel and 11 m (36 ft) of net oil pay in the lower channel.

Pressure data show that the oil is in communication with the Owo-1 well, and oil pressures in the lower channel suggest it may also be in communication with the deeper pools evidenced in Owo-1 and its side track.

Additionally, Enyenra-2 tested a deeper Turonian fan, intersecting 5 m (16.4 ft) of gas/condensate bearing sandstones. The extent and thickness of this zone away from the well is undergoing interpretation.

Once operations have been completed, the well will be suspended for later use. Prior to flow testing, pressure gauges will be deployed to measure reservoir connectivity.

Deepwater Millennium will stay in the block to complete drilling of the Tweneboa-4 well. The next appraisal well will be Enyenra-3A, up-dip to the north of Owo-1.

Angus McCoss, Tullow’s exploration director, said: “This represents a major step forward in the appraisal of the Enyenra-Tweneboa area and is highly encouraging for our target to declare commerciality later this year. We are now looking forward to leveraging our expertise in the Jubilee play across the Atlantic through drilling the high-risk, high-impact, Zaedyus prospect in French Guiana in March.”

Tullow has a 49.95% operated interest in Ghana’s Deepwater Tano license, and 22.9% of the adjacent West Cape Three Points (WCTP) license, extending across a total of 2,605 sq km (1,006 sq mi). It is also unit operator of the Jubilee development, with a 34% interest, while Kosmos Energy is the technical operator. Kosmos, Anadarko, Ghanaian National Petroleum Co. (GNPC), and Sabre are partners in both exploration licenses, with EO Group also present in WCTP.

Between June 2007 and September 2010, Tullow has operated or participated in 15 deepwater exploration and appraisal wells across these permits, in water depths ranging from 1,079-1,428 m (3,540-4,685 ft), with only one failure, Dahoma-1 in WCTP. Aside from Jubilee and the South-East Jubilee extension which includes Mahogany Deep, the company has achieved commercial discoveries in Turonian and Campanian intervals on Tweneboa and Owo in Deepwater Tano, and on Odum in WCTP.

More off Ghana

In February, Kosmos Energy reported its Teak-1 exploration well offshore Ghana discovered hydrocarbons. The well, in the Cape Three Points block, encountered oil, gas/condensate, and natural gas over a 576-m (1,890-ft) interval.

Logs and samples indicate the well found pay in five Campanian and Turonian sandstones with 26 m (85 ft) of oil. Samples show the Campanian reservoirs with 40º API and the Turonian with 32º API. The well is updip and northeast of Jubilee field.

The Atwood Hunter semisubmersible rig drilled the Teak-1 well in a water depth of 868 m (2,847 ft) to a total depth of 3,170 m (10,398 ft) and will now drill Teak-2. The partners plan to drill other Upper Cretaceous prospects over a sequence up to mid-2011, when the exploration period for the license expires.

Farther northwest along the West African Transform margin, Tullow is a participant in the recent Mercury-1 light oil discovery off Sierra Leone, drilled by the Deepwater Millennium rig.

Meanwhile, Anadarko is designing an appraisal program to be combined with the potentially high-impact Montserrado exploration well (Cobalt prospect) in the partners’ deepwater acreage offshore Liberia. First, however, rig capacity has to be secured.

Namibia

Further south, Chariot Oil and Gas has upgraded its estimate of prospective resources on its licenses offshore Namibia to 13.9 Bbbl. This follows the recent definition of the Nimrod prospect in block 2714A, and identification of 700 MMbbl of additional potential in the Tapir area of the northern blocks.

The recent resource upgrades and subsequent de-risking followed extensive in-house technical studies. Chariot continues discussions with numerous multiple potential farm-in partners, and says its data rooms have been inspected by major international oil companies. The company hopes to clinch a farm-out agreement soon.

Meanwhile, Arcadia Petroleum is looking for a deepwater rig to drill a first exploratory well late this year on license 0010 offshore Namibia. According to Tower Resources, which has a 15% interest in the permit via its subsidiary Neptune Petroleum (Namibia), processing of newly acquired 3D seismic is complete.

An initial view suggests that results of an earlier 2D seismic interpretation have been enhanced, and the large, four-way dip-closed Delta structure has been confirmed. There are also clear indicators of light hydrocarbons in the form of “pock marks” constrained below the regional seal and within the closure of the structure – Tower stresses that this is independent of hydrocarbon indications interpreted from AVO analysis of the 2D data.

Arcadia Petroleum, which is covering Tower for the cost of the first well, has accelerated its program to put in place funding and to contract a deepwater rig to drill in 4Q 2011, subject to availability.

Angola

Statoil is in line for two new operatorships offshore Angola, under the country’s pre-salt bid round in the Kwanza basin.

According to state oil company Sonangol, the Angolan government has approved Statoil’s bid to operate blocks 38 and 39, and to participate in blocks 22, 25 and 40. However, formal confirmation of the licenses is subject to the Angolan Ministry of Petroleum’s decision concerning any appeal of the jury’s decision, and the successful negotiation of contractual terms including production sharing agreements (PSAs).

If successful, Statoil will gain a 40% operating share in block 38, covering 6,298 sq km (2,431 sq mi), and the 7,800-sq km (3,011-sq mi) block 39. It will also pick up 20% of blocks 22, 25, and 40, where the respective acreage is 5,180 sq km (2,000 sq mi), 4,825 sq km (1,863 sq mi), and 7,588 sq km (2,929 sq mi).

“The Angolan pre-salt is a frontier play with high potential,” said Tim Dodson, executive vice president for Exploration. “This presents Statoil with the opportunity to access several high impact exploration prospects which are believed to be analogous to pre-salt Brazil. Securing a multiple block portfolio early on in the exploration of this new play is a big advantage. Such a strong and influential position gives Statoil exposure to significant upside potential should the play be proven.”

The Angolan Juri has awarded Eni participation and operatorship of block 35 150 km (93 mi) offshore Luanda. The deepwater block covers 4,831 sq km (1,865 sq mi) of potential pre-salt acreage.

The award involves the drilling of two wells and conducting 3D seismic surveys on a 2,500 sq km area, which will be carried out in the first five years. Eni has a 30% interest; Sonangol Pesquisa & Producao, 45%; and Repsol, 25%.

Nigeria

Mobil Producing Nigeria Unlimited (MPN), a joint venture (JV) partner of the Nigerian National Petroleum Corp. (NNPC), in November announced a rich gas condensate discovery in its operated oil mining license (OML) 104 located offshore Akwa Ibom state.

The Pegi-1 discovery well was drilled in 315 ft (96 m) of water to TD of 11,407 ft (3,477 m) beneath the Awawa field and encountered 165 net ft (50.3 m) of rich gas condensate.

According to the operator, significant additional potential remains in untested deeper targets within the Pegi fault block as well as in adjacent fault blocks.

A farm-out agreement with Starcrest Nigeria Energy Ltd. was signed by Addax Petroleum Corp. covering a PSC with NNPC on OPL 291 in deepwater offshore Nigeria.

OPL291 is 130 km (81 mi) off the Nigerian coast in water depths of 1,000 - 2,300 m (3,281 – 7,546 ft) and covers a gross area of 1,287 sq km (318,000 acres). OPL291 is adjacent to OML127 which contains the Agbami and Ikija fields, operated by Chevron, and OPL242, operated by Devon Energy.

Guinea

Hyperdynamics has released a concession evaluation of deepwater Guinea off West Africa by Netherland, Sewell & Associates Inc. covering selected leads from a 2D survey in 2009.

NSAI says its “best estimates” for the leads assessed totals 2.3 Bbbl of potentially recoverable unrisked oil. The total becomes 400 MMbbl when screened by the risk factors.

Work is under way on interpreting data from a 3,635-sq km (1,403-sq mi) 3D survey of shallow water done late in 2010.

Guinea, officially the Republic of Guinea, formerly known as French Guinea, is today sometimes called Guinea-Conakry to distinguish it from its neighbor Guinea-Bissau.

“We find the additional review and assessment by NSAI encouraging and a confirmation of our analysis of the potential prospectivity of the concession,” said Hyperdynamics’ President and CEO Ray Leonard. “The significant prospective resources in the deep water will need to be taken into account in our evolving exploration program. We still plan to spud our first exploration well in the fourth quarter of 2011.”

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