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Sierra Leone discovery firms up new oil province

The third well in the emerging Sierra Leone-Liberia basin has produced a third discovery for Anadarko

Anadarko’s third well in the emerging Sierra Leone-Liberia basin has produced a third discovery, lifting prospects for the new – although difficult-to-interpret – oil province. The company will now drill an appraisal well at the second discovery, and is planning to follow it with a testing programme on its finds.

Anadarko said its latest well, Jupiter-1, passed through a net 30 metres of hydrocarbon zones and did not encounter a hydrocarbon-water contact. The well, drilled in 2,199 metres of water by Transocean’s Discoverer Spirit drillship, was located 25 km west of the second discovery, Mercury, in the same block. The first discovery, Venus, which set the scene for the basin, lies about 50 km to the northwest of Mercury in the neighbouring block.

As well as being the first deep-water drillings off Sierra Leone, Anadarko’s wells have been the first to target the Sierra Leone-Liberia basin’s stratigraphic traps – more difficult to identify on seismic surveys than structural traps. The new interpretation of the geology by Anadarko, and shared by US firm Kosmos, has led to discoveries spanning 1,100 km of the West African Transform Margin – Anadarko’s Venus on the west and Kosmos’s Mahogany, now part of Jubilee field, Ghana, on the east.

Anadarko operates the two blocks covering the Sierra Leone part of the Sierra Leone-Liberia basin, SL-06 and SL-07, and also the three contiguous blocks in Liberian waters, LB-15, -16 and -17. In November, the company’s Montserrado-1 well in LB-15 found an eight-metre hydrocarbon zone from which a sample of light crude was recovered. Although non-commercial, the find established that a working hydrocarbon system exists in the eastern part of the basin.

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