TARD, F., Elf (Congo); and J. AMARAL,W. BEYDOUN, J. J. BITEAU, D. DEREGNAUCOURT, and A. MANUEL, Elf Exploration (Angola)

Abstract: Angola: Challenges for Exploration of Tertiary Plays in Ultra-Deep Waters

Angolan deep waters of the Lower Congo Basin has recently become one of the most prolific petroleum provinces in West Africa (rec. reserves of 4 billions barrels in tertiary turbiditic plays). Recent giant field discoveries on deep water blocks have triggered new prospective opportunities for the future.

These sandy turbidites belong to a large detritical deposition system related with the Congo river alluvial fan. It is extending all over the margin from the Eastern stable platform down to the oceanic crust Westward. The inner part of this huge depositionnal complex is the seat of an important depocenter that induced a gravity sliding process on the salt detachment surface.Westward, the ultra deep part reveals, at the opposite, a contractional domain induced by the collision of this gravity sliding process with the oceanic crust.As a consequence, development of large compressive features observed.

In this context, a fast track approach with standard processing sequences and semi-automatic image analysis tools may not be sufficient to image and appraise turbiditic systems. Exploration efforts have to take up new challenges. Due to the increased presence of salt and local strong contractional features, appropriate seismic acquisition design, reservoir imaging while preserving amplitudes and trap geometry definition are required.

Hydrocarbon prediction is another major challenge in the ultra deep waters. Particular thermodynamic conditions, subtle traps, low burial depth and correlative biodegradation risks require a detailed approach of the petroleum system. Integration of multi-disciplinary studies (thermal gradient measurements, sea bottom cores, amplitude anomaly detection, flat events identification, etc.) improves this analysis. Consequently, the key to the exploration success, will depend on the capability of geoscientists to integrating geophysical technologies with geological processes.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England