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Prospectivity and Petroleum Systems Modelling of the Offshore Lamu Basin, Kenya: Implications for an Emerging Hydrocarbon Province

Abstract

Whilst recent years have seen major discoveries along the East African margin, the Lamu Basin in Kenya remains underexplored. Located in northern Kenya and covering both onshore and offshore, the Lamu Basin forms part of the Kenyan passive continental margin. The geology is controlled by tectonic movements that led to the break-up of Gondwana in the Jurassic and by Cretaceous activity on the Anza rift. Large discoveries in Tanzania and Mozambique indicate hydrocarbon potential in East Africa, as do heavy oil deposits on the conjugate margin in Madagascar. Exploration in the offshore Lamu Basin is limited, with only seven wells, but 52m net gas pay was discovered in channel and turbidite sands at Mbawa-1 in 2012. This indicates an active petroleum system, as do hydrocarbon shows in a number of wells and brightening on seismic data. 2D seismic interpretation will be combined with analysis of regional gravity data to constrain the tectonic history and structural geology of the offshore Lamu Basin. The survey covers from 1 – 4km water depth, and comprises 1035km of regional 2D lines, giving an overview of the basin and intersecting DSDP well 241. 9600km of new 2D seismic data currently being acquired also will be included. Seismic attributes constrain stratigraphic zones, including shale intervals providing potential source rocks, and sand-rich deposits which may act as reservoirs. Hydrocarbon plays are interpreted to range from pre-rift Karoo deposits, found in tilted fault blocks; through Jurassic syn-rift units terminating against faults and in drape and rollover anticlines; and into Cretaceous and Tertiary stratigraphic plays, reefs, turbidites and fans. The maturity and nature of source rocks in the Lamu Basin remains a key question. This study will utilise the petroleum systems concept, incorporating the presence of an active source rock a kely element along with reservoir, trap and seal, with development of the system controlled by the timing of these elements. A selected regional line traversing the northern offshore Lamu Basin from west to east is modelled and source rock intervals are identified, based on regional stratigraphy, constraining maturity and timing of generation. Combining regional studies with seismic data and the petroleum systems concept enables improved understanding of the prospectivity of the offshore Lamu Basin and indicates that all the required components of a petroleum system are present.