Speakers

Abiud Masinde

Abiud Masinde

Petroleum Geophysicist

National Oil Corporation of Kenya.

Abiud Masinde is a Petroleum Geophysicist at National Oil Corporation of Kenya involved in seismic processing and interpretation projects, he is also a PhD student at the University of Nairobi specializing in exploration geophysics. His research field is Simultaneous Joint Inversion in geophysical processing and interpretation. He has published 2 journal papers and attended three international academic conferences.


 ABSTRACT

SESSION 1: Petroleum prospectivity of offshore Lamu basin, Kenya:  Davie  Walu Fracture Zone

Davie Walu Fracture Zone is a 2200 km long strike slip transverse fault in the late Mesozoic along which Madagascar was separated from east coast of Africa, creating a transform margin. Gravity isostasy sourced from the International Gravity Bureau (BGI) data were filtered and processed to give the overall regional interpretation of the major and minor structures within the basin. A seismic interpretation study was undertaken on 58 migrated 2D marine seismic lines (over 5110km) acquired by Woodside Petroleum Limited in 2003 in the Lamu Basin, offshore Kenya. A synthetic seismogram was generated from which all the horizon markers were picked across all strike and dip lines to obtain varying amplitude and time values. Structural maps were generated to display the geometry of geologic features on time maps. Thickness variations and trends of target formations were derived from isopach maps.

Davie Walu Fracture Ridge (DWFR) has large positive gravity anomalies extending from the Kenyan mainland to Tanzanian offshore with a NW-SE trend. Davie Walu Fracture zone is an inverted harpoon that exhibits flower structures on seismic section due to inversion monocline. The edges of the DWFR have large-sharp negative anomalies which indicate a large vertical displacement brought by the adjacent faults along the fracture zone.  These faults assume the same trend as the DWFR marking the boundary of the Lamu basin to the NE. The displacements brought by these faults have created gravity-negative depocentres such as the Happy valley and the Tembo trough both located west of the DWFZ. Tembo trough shows little gravity variation, which implies relatively same depth. On the other hand, Happy valley portray a varying trend of sediment thickness evidenced by the negative gravity variation. It dips steeply eastwards to be offset by the DWFZ major fault. Campanian Two Way Time (TWT) map depicts large throw faults separating Happy valley from the Davie Walu Fracture Ridge. They are deep Jurassic faults oriented NW-SE that structurally binds sediment thickness to the east.
Late Miocene to Mid Miocene thickness map shows the influence of basin structures in the zone. The north-west section indicates that the accommodation space has been filled with sediments exceeding 1400ms TWT. The sediments thin out around DWFZ but thicken out by forming a wedge to the east of DWFZ. The top of this zone is interpreted as the unconformity formed after late inversion of DWFZ and Simba high. Mid Miocene to Palaeocene thickness map shows zone thickening to the west up to 2400ms TWT.

The inverted Davie Walu Fracture Ridge is underlain by an anticlinal structure. This structure is a characteristic of rotated fault blocks and faulting. The excessive erosion related to the sea level changes may have made sedimentation above Campanian to thin. Several tectonic episodes imply potential for stratigraphic trapping. There is also potential for stratigraphic traps to form in areas where depocentre have been inverted such as the inverted half graben.