--> --> Successes, Challenges, and Future Opportunities in the Pre-Salt Kwanza and Benguela Basins of Angola: Predicating Where the Best Oil Charged Reservoirs Will be Found.

2018 AAPG International Conference and Exhibition

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Successes, Challenges, and Future Opportunities in the Pre-Salt Kwanza and Benguela Basins of Angola: Predicating Where the Best Oil Charged Reservoirs Will be Found.

Abstract

Pre-salt drilling in the Kwanza and Benguela Basins has encountered numerous successes and challenges; although significant volumes of hydrocarbons have been discovered, the types have proved difficult to predict with wells drilled on neighbouring structures encountering oil, condensate and gas, often with unexpected CO2 contamination. Furthermore carbonate reservoir presences and qualities have been found to vary over small distances and be highly dependent upon depositional environments and diagenesis. A methodology to predict reservoir facies away from well control is therefore critical to exploration success, as is the ability to better predict the hydrocarbons that might be encountered. To achieve this, a depositional sequence framework has been built, using well log and seismic data, allowing geologists to develop depositional environment models, together with the constraint of seismic facies analysis, both of which are key to identifying and de-risking new prospects. Underpinning the sequence framework is a pre-salt structural architecture model, derived from shipborne gravity data, which not only supports depositional environment & facies interpretations but also provides an understanding of where dolomitization and CO2 contamination risks are highest and where reservoirs are more likely to be oil, condensate or gas charged. In this talk, gravity modelling, 2D and 3D seismic and well log interpretation work will be presented. The methodology for developing the depositional sequence framework will be explained and multiple examples of seismic facies analysis tied to the results of key exploration wells will be shown. The presentation will explore the prediction of carbonate facies including microbial build-ups, high energy packstone shoals and oolitic grainstones as well as where dolomitization may enhance or reduce reservoir qualities. The talk will additionally demonstrate the importance of the structural architecture model in carbonate facies interpretation and show its role in explaining areas of dolomitization and CO2 contamination, allowing future explorers to account for these risks. Furthermore, the importance of model in unravelling the provenance of oil, condensate and gas charge will be shown. The conclusions of the presentation will address where future exploration in the Kwanza & Benguela Basins may best be focused together with evidence for where the best reservoir qualities may lie and why these can be predicted to be charged with oil.