25 February 2008
Tullow Oil plc (Tullow) announces an oil discovery on the Odum-1 exploration well in Ghana and the decision to suspend the Ngassa exploration well and redrill from an alternative location.
ODUM-1 OIL DISCOVERY
Odum-1, the second exploration well drilled on the West Cape Three Points licence offshore Ghana, has discovered a commercial light oil accumulation based on the results of drilling, wireline logs and a sample of the reservoir fluid. The well, in water depths of 955 metres, has been drilled to a depth of 3,387 metres and has encountered a gross oil column of 60 metres and 22 metres of net pay samples recovered from the reservoir indicate an oil gravity of approximately 29 degrees API.
The discovery is a stratigraphic trap in a Campanian age fan system and opens a second new play fairway in the Tano Basin. Further prospectivity in this new Campanian play has already been identified in both the West Cape Three Points and Deepwater Tano licences.
Following completion of drilling operations on Odum-1, the well will be suspended as a future development well and the Songa Saturn drillship will move to drill Mahogany-2, the next appraisal well on the Jubilee field.
While appraisal of the upside of Jubilee is ongoing, the field partnership is also working on plans for a phased development of the field. The Eirik Raude fifth generation semi-submersible has been contracted for a minimum of three years and is a critical element in our plan to target first oil in 2010.
NGASSA-1 TO BE SUSPENDED AND REDRILLED FROM NEW LOCATION
The Ngassa-1 exploration well in Block 2 Uganda commenced drilling on 17 November 2007 and the well has reached a total depth of 1,635 metres. Due to persistent borehole instability, Tullow has decided to suspend the well and redrill from an alternative location.
Drilling difficulties on Ngassa-1 were accentuated by the necessary high-angle deviation of this long-reach well through thick claystones close to a major fault zone. The well trajectory was selected on the best available 2D seismic data and on the basis of the location’s minimal environmental footprint.
Whilst drilling the shallow section, the well discovered six net metres of gas bearing sands. The thick claystone seals encountered provide good encouragement about the underlying oil prospectivity.
The substantial primary and secondary oil objectives remain undrilled so it is now planned to redrill the well from a location where subsurface conditions are expected to be more benign. The new well design will benefit considerably from the recently acquired 3D seismic and the information gained in the first hole. This information, combined with the new location, will enable the well to be drilled with a less acute trajectory and to be steered clear of identified faults. Options include a near term onshore deviated well and an offshore vertical well.
The Nabors 221 rig will now be moved to Block 3A to drill the Kingfisher-2 well during the second quarter of the year.
Commenting today, Aidan Heavey, Chief Executive of Tullow said:
"The discovery of oil in the Odum well continues the success of our exploration campaign in Ghana. This commercial discovery is located only 13 kilometres from the larger Jubilee Field and has opened up a new prospective play in the region. While the technical challenges associated with the Ngassa well are disappointing, it remains a valid high impact prospect and the new location, 3D seismic and experience of drilling Ngassa-1 should enable us to successfully drill it as part of Tullow’s Lake Albert Rift Basin campaign."