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Abstract: Tertiary Petroleum System, a New Play in the Deep Offshore of the Congolese Basin

Mauriaud, P.; Drapeau, D. - Elf Congo; Levache, D.; Kothe, A.; Reynaud, F. - Elf

Exploration of the Offshore Congo Basin focused on pre-salt source rock and pre/post salt (cretaceous) seals and reservoirs. The results of MOHO M1 in mid 1995 established the existence of a post-salt petroleum system and thus conforted the exploration of the Tertiary series.

The Tertiary petroleum system consists of upper Albian, to lower Tertiary (Madingo) source rocks, Miocene reservoirs and seals:

- Maturation of the type II source rocks and migration occurs at present time.

- The reservoirs are Miocene clastics sediments deposited by gravity flow in slope and basin environment. The porosity and permeability values are exceptionally good. The best reservoirs occur in channels and proximal levees facies. Two origins are recognized for the sediments. In the southern part of the basin, sediments came from the Congo River. They are characterized by stacked channelized systems extending in a EW direction. In the northern part of the basin the gravity deposits came from the congolese platform and transitted by deep NE-SW oriented incisions of the slope.

- The seals are interbedded Miocene to Pliocene shales.

- The traps are both stratigraphic and structural.

If well calibration is still scarce, seismic data, mainly 3D is of very good quality. The critical factor, so far, is the quality (density and viscosity) of hydrocarbons. The understanding of the thermal regime, origin of the hydrocarbon, burial history, evolution of biodegradation will be a key to efficiently explore this new domain.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil