Deep-Water Douala Prospectivity Transformed by the Malabo Fracture Zone

Jean Malan, Sumesh Naidoo, and Vincent Mashaba
New Ventures, PetroSA (Pty) Ltd, Parow, South Africa

The Block Q 3D seismic data set, covering the eastern half of the deep-water Block Q acreage in the central part of the Douala Basin, provides examples of NE-SW trending oceanic fracture zones, typical to the eastern Gulf of Guinea. The recent Blocks O and I discoveries to the north of Block Q proved the presence of the Miocene hydrocarbon-bearing fairway.

The Malabo Fracture Zone (MFZ) underlies the central portion of Block Q, with to the north and south four parallel trending transforms mapped out on time slices. On the 3D data the relationship between these fracture zones and the identified prospects and leads, within the Pliocene to Palaeocene interval are apparent. The vertical expression and faulting in the overlying sediments, associated flower structures, gas clouds, chimneys and escape features are clear.

In the southern portion of Block Q the intersection of the slope with the MFZ created a plunging structural nose, projecting out from the slope along the fracture zone orientation. The NW trending Lower Miocene deep-water channel fairway running along the nose was influenced by the MFZ to divert towards the SW, the trend of the MFZ. In addition to the structuration provided by the MFZ for trap formation, trapping is also reliant on up-dip stratigraphic pinch-out. The resultant deposition of ponded, banked and linear alignment of deep-water turbidites from the Cameroon shelf also occur at this junction. The deep-seated vertical faulting also has implications for hydrocarbon migration.

The Q1-well, in an expected water depth of 1300 m, is to be drilled early 2009. This well should provide further information to the control and mechanism demonstrated by the Malabo and related fracture zones on the likely hydrocarbon bearing systems and the prospectivity of the deep-water Douala Basin, which is fast becoming a prolific hydrocarbon province in West Africa.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery