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Pressure data acquired through logging operations indicates the potential for a significant oil column down-dip, which could fill the entire 150 sq km closure. Although evaluation is still at an early stage, with further appraisal drilling, Ngassa has the potential to be the largest oil field in the basin to date.
Ngassa-2 is a deviated well drilled from the Angara spit, 3.5 km from the crest of the structure, and to a total depth of 3,392 metres beneath the lake. Logging, downhole pressure testing and sampling confirmed the presence of moveable oil which has been recovered to surface. Reservoir quality is excellent and the oil is of a similar quality to that encountered in the Mputa and Kingfisher discoveries.
A deeper 15 metre gross sand was determined to be water wet at this location. These, and other sands, however have the potential to contain oil elsewhere in the Ngassa structure and will be tested through future offshore appraisal drilling.
Wireline log characteristics indicate that the reservoirs seen in Ngassa-2 are equivalent to those encountered in the Kingfisher discovery some 40 km southwest, pointing to significant lateral reservoir extent. This de-risks the down-dip potential, the remaining amplitude-supported prospectivity within the overall Ngassa closure and the neighbouring offshore prospects such as Pelican.
The well has been suspended as an oil producer, for future production testing, thereby completing the current Block 2 exploration programme. Exploration drilling activity is expected to re-commence in late 2009 in Block 1.
Tullow has interests in three licences in the Lake Albert Rift Basin in Uganda. Tullow operates Block 2 with a 100% interest and has a 50% interest in Blocks 1 and 3A which are operated by Heritage Oil (50%).
Commenting today, Angus McCoss, Exploration Director, said:
“The discovery of a significant oil field at Ngassa, with the potential to be the largest in the basin, is a major achievement for Tullow. The follow-up potential in the overall Ngassa closure has been substantially de-risked by this find and we look forward to realising the upside through appraisal and further exploration drilling. We are now focusing on the considerable follow-up to the Buffalo-Giraffe discovery in Block 1, appraisal activities in Block 2 for development planning and timely production from the basin.”