Evolution of Deep Water Confined Channels, Offshore Angola: Results from Integrated Cores, Logs, and Seismic Interpretation

Chen, Jiajie¹, Chris Tuttle² (1) Marathon Oil Company, Houston, TX (2) Marathon Oil Company, Houston,

Miocene-Oligocene deep water reservoirs in offshore Angola have been a focus point for multi-company exploration activities, most fields being considered for project sanction. Effectively evaluating these reservoirs and providing objective reserve estimates requires a thorough understanding of the depositional environment and stratigraphic framework, as well as the evolution of the channel systems through time, thus that the confined channels can be recognized within the framework, and the stacked reservoir sands can be well defined.

We used core data to describe depositional facies and assemblages. We then compared cores and logs to understand the petrophysical signatures of lithofacies. Once core-log consistency was achieved, the relationship was used to infer depositional facies and sequences from logs for not-cored intervals. In the four reservoirs concerned, we defined 6-7 third order sequences for the intervals of interests. These sequences are traceable in high resolution seismic data, although cross-field correlation may be difficult. The confined channels are generally controlled by the sequence stratigraphic boundaries. Using these boundaries as controlling horizons, simultaneous seismic inversion was conducted. The results of such an approach, when tied with detailed core and log interpretation, clearly delineate the shape, aspect ratio of the channel systems, evaluation and distribution of channel systems over time, and existence of some sheet sands. Once petro-elastic modeling is conducted, we can associate the rock properties with seismic attributes and model the reservoir under a better controlled structure, stratigraphy, and petrophysical framework.