Spectrum Completes Subsalt Imaging in North Gabon

Spectrum’s geoscientists have completed an extensive hydrocarbon prospectivity review offshore North Gabon using 5,500 km2 of modern 3D seismic data, recently acquired to image the deep syn-rift units and to provide a regional framework for the traditional post-rift hydrocarbon plays.

Two major petroleum systems are present with source rocks and reservoirs distributed in the pre-salt syn-rift sequences and in several post-rift sequences. Each petroleum system is characterized by various source rocks, reservoirs and trapping mechanisms.

The Nyonie Deep gas discovery has proven reservoir properties in the pre-salt section syn-rift sections of Gamba Sands and Dentale Fms. Oil bearing targets are known in the clastic and calcareous deposits of the Late Cretaceous.

In the syn-rift, mostly lacustrine source rocks are expected to be oil generative from the end of the Cretaceous and Paleogene, or even later in case of a burial less than 3-4 km. Post-rift units have a number of marine source rocks, pushed into an early oil window from the Paleogene and during the Neogene, mostly as result of their close proximity to highly conductive salt bodies.

Regional extensional faults show an echelon trend with strike direction between N-S and NW-SE, generating large structural closures at base salt level, potentially over 150-200 km2, clearly visible in the initial stages of the time processing, and expected to be fully imaged by the end of the Depth Migration exercise.

Salt withdrawal occurred mainly during the Late Cretaceous-Paleogene, controlling the deposition of the post-rift sequences, which are organized in a variety of structural and stratigraphic traps, most of which remain untested. Finally, the proper imaging of subsalt traps is expected to uncover potential hydrocarbon resources, economically attractive and overlooked from the past exploration.

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