Burden, Paul A.1
(1)Exploration, Tullow Oil South Africa, Cape Town, South Africa.
Exploration of the northern areas of the Albert Rift Basin straddling the Victoria Nile River in Exploration Area 1 (EA-1) and the northern portion of Exploration Area 2 (EA-2) began in 2007 with the acquisition of a fairly sparse grid of 2-D seismic by Tullow, the operator of EA-2 and Heritage, operator of EA-1.
Interpretation showed large NW-SE trending faults cross-cut by secondary E-W trending faults. The intersection of the two fault trends combined with structural dip towards the SW led to the definition of a number of triangular shaped fault traps each bounded by two faults with monoclinal dip to the SW towards a potential 'source kitchen' beneath Lake Albert. Some of these prospects were supported by amplitude anomalies at various levels in the interval just above the base of the rift-fill. Prospects identified included Ngege, Kasamene, Kigogole, Nsoga, Ngiri (Warthog), Rii(Giraffe) and Jobi(Buffalo).
The first boreholes drilled within the area were Ngege-1, Kasamene-1 in mid 2008 by Tullow. The former was a minor oil discovery in Upper-Pliocene fluvio-alluvial reservoirs. the latter was a more promising discovery in high quality fluvial channel sandstones in the same stratigraphic interval. Kasamene-1 was sidetracked and the reservoir cored. This was followed by another discovery, Kigogole-1, before drilling activity switched to EA-1.
The first well to be drilled by Heritage was Ngiri-1 in EA-1 south of the Victoria Nile. This well was a promising discovery similar to Kasamene-1. Activity then moved to the north of the Victoria-Nile and the most significant discovery so far was made at the Jobi-1 and Rii-1, drilled at the end of 2008. These wells intersected the same large oil accumulation.
Tullow commenced drilling in mid 2009 in EA-2 and made further discoveries at Nsoga-1, Wahrindi-1 and Ngara-1 and also started an appraisal drilling program with successful wells drilled at Kigogole-3 and 5, Nsoga-5, Kasamene-2, 3 and 3A and Ngiri-2.
In 2010, 7 appraisal wells were drilled in EA-2 in the Kasamene and Kigogole/Nsoga areas whilst in EA-1 two wells were drilled, Ngiri-2, a successful appraisal of the Ngiri-1 discovery, and a new discovery at Mpyo-1.
Exploration by Tullow and Heritage over the past 3 years has opened up a major new oil play in the Victoria-Nile region. An extensive appraisal/development programme including more seismic acquisition and further drilling is ongoing. First oil production is expected by 2012.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.