II CENTRAL & NORTH ATLANTIC CONJUGATE MARGINS CONFERENCE

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1 IB: Volume VI p II CETRAL & ORTH ATLATIC COJUGATE MARGI COFERECE Hydrocarbon Prospectivity of a ew Deepwater Petroleum Province, Offshore enegal Martin, L. (1); Effimoff, I. (2)*; Medou, J. O. (3) & Laughland, M. M. (4) (1) Consultant, Chertsey, UK. (2) First Australian Resources Ltd, Houston, TX, * presenter (3) Petrosen, Dakar, enegal. (4) Hunt Oil Company, Dallas, TX ABTRACT Recent 3D seismic offshore, deepwater enegal reveals two new hydrocarbon plays. 1. The erosion of the -Aptian carbonate shelf by the enonian unconformity with concurrent reservoir enhancing karstification of the platform and rotation due to salt withdrawal forming a broad closure. 2. A series of antonian silica-clastic and carbonate stacked upper slope fans formed from the erosional debris. A source rock kitchen has been generating oil since the Maastrichtian and feeds the two plays. KEYWORD: enegal; Hydrocarbons; Cretaceous plays; Karst unconformity; lope fans. 1. Introduction The enegalese portion of the greater MGBC Basin, located offshore and south of the Dakar peninsula and north of Gambia, is under-explored. Regional Overview- MGBC Basin Pelican 100 mmboe Late Cretaceous Aigrette 19.8 mmboe Cretaceous Tiof 380 mmboe Chinguetti 80 mmboe Tevet 41 mmboe Diam iadio ow depleted Banda 25 mmboe Cretaceous Gadiaga 14 mmboetcf enonian -Campanian Dome Flores & Gea 500mmbo-1bbo This study identifies the elements of a petroleum system and points to the exploration potential of the untested, deepwater portion of the enegalese basin margin. 3D seismic data (2050 km2) acquired in 2007 reveal the existence of a long-lived carbonate platform and associated incised canyons with genetically related down-slope debris aprons/turbidites. 167

2 2. Geological Framework eismic interpretation and multidisciplinary geologic studies indicate that the offshore region can be subdivided into two main para-sequences: the Pre-enonian unconformity section and the syn-post enonian unconformity section. Chronostratigraphy Geoseismic The pre-enonian age section includes the long-lived carbonate platform of Jurassic to Cenomanian age. Uplift and subaerial exposure of the platform during Late Cretaceous time led to karstification and erosion that we believe are key to development of fracture-related permeability in the carbonate reservoir. Uplift was likely associated with differential rotation induced by withdrawal of Triassic age salt in the southern MGBC. Erosion is marked by the enonian age unconformity that is easily recognizable on seismic and yields seismic evidence of karstified. In contrast, the syn-post enonian age section consists mainly of 168

3 stacked antonian age fans with multiple stacked amplitudes on seismic, and an overlying Tertiary age succession. Upper lope high amplitude antonian events onlapping enonianunconformity enonian unconformity surface orth fan complex Upper lope stacked high amplitude antonian fans 10 km Middle fan complex outh fan complex Paralic sands transported to slope by incised s on eroded shelf enonian Unconformity - orth Middle outh 3D perspective 3. Hydrocarbon prospectivity enegal Identified Plays L Cretaceous Carbonate helf Margin play Top Aptian 3D Line 9076 enonian Unconformity Buried hills 3D line sq km closure in highlighted area antonianfans antonian lope Fan play 3d Line 9076 High amplitude Upper slope Fan complexes Prospective dip closed Interval eocomian Top Aptian enonian Unconformity 3d Line

4 Detailed rocks physics and attribute analysis indicate that the turbidites are a mixed lithology of reworked carbonate material and paralic siliciclastic sediments. The paralic sands were transported from the shelf into the basin through incised valleys that also are clearly observable on seismic. 3D basin modeling was used to determine the timing of generation and spatial extent of the petroleum kitchen for the welldocumented age source shale that was deposited along the west African margin. ource Rock & Basin Modelling ummary METER source kitchen adjacent to identified plays R R depth ource Top 3D perspective kitchen Generation began during Maastrichtian time and continues through present-day, and the down-slope debris aprons and turbidites, as well as the karstified carbonate platform, are located either within or adjacent to the present-day kitchen. 4. Conclusions 60 Ma. 30 Ma. 0 Ma. ource rock continuously in oil window since late Cretaceous 170

5 enegal Identified Plays & Leads ummary 3D 10 km orth complex Mid complex Closure At Top eocomain Closure At top Aptian Lower Cretaceous Carbonate helf Margin structural closures antonian Upper lope tacked Fans exhibiting high amplitudes outh complex ubcrop closure Water depth meters Drawing on analogues from recent discoveries in Late Cretaceous age turbidites offshore Ghana, we believe that the enegalese offshore basin is an exciting new deepwater province along the northwest African margin. 171