Oil was discovered and tested by Soekor in the A-J1 borehole drilled in 1988. Thick reservoir sandstones were intersected between 2985m and 3350m. The well was tested and flowed 191bbl per day of 360API oil from a 10m sandstone interval at about 3250m. At the time the discovery was considered to be of limited economic significance. However, significant upside potential within six prospect areas at depths of up to 800m shallower than the reservoirs in A-J1 has been identified on the 686km2 of 3-D seismic data that covers the whole of the A-J graben area. Follow-up wells will target this potential.
The A-J graben is typical a rift basin, similar to others in which major oil accumulations have recently been discovered. For example the South Lokichar basin in Kenya. The oil was generated in lacustrine source rocks that are present in the deepest parts of the basin. The oil migrated and accumulated in fluvial and lacustrine sandstone reservoirs around the basin flanks.
There is also significant potential in other rift graben to the north and south of the A-J graben and furthermore potential for significant gas discoveries in the shallower sequences above the rift graben succession over the whole block.