Integration of 2-D/3-D Seismic, Regional Interpretation and Petroleum Systems Modeling to Assess the Hydrocarbon Potential of the Kwanza Basin

Rodriguez, Clara ¹; Abu, Clara ¹; Herbst, Nora ²; Kornpihl, Kristijan ³; Koeninger, Chris ¹; Uzcategui, Marjosbet ¹; Milne, Graham ¹
(1)Multi-Client, WesternGeco, Gatwick, United Kingdom. (2) Multi-Client, WesternGeco, Houston, TX. (3) GeoSolutions, WesternGeco, Aachen, Germany.

The presalt basins offshore Brazil hold the largest hydrocarbon discoveries in recent years. Interest has now risen to find analogues in the conjugate West African basins. The success of exploration in frontier areas will strongly depend on integrated workflows to image the pre-salt structures. Taking into account the seismic anisotropy in the post-salt sediments, the illumination below complex salt bodies as well as understanding the salt geometries and its interaction with carbonates and deepwater clastics are key elements of a successful depth imaging project.

With recent depth migration results of WesternGeco Multi-Client seismic data this paper illustrates a string of geological observations, regional interpretations, attribute analysis and petroleum systems modeling, bringing new insights into understanding the evolution of the deepwater Kwanza basin offshore Angola and their implication for hydrocarbon prospectivity.

Canyon erosion processes, evolution of submarine channels and depositional lobes, pockmarks, radial faulting and bathymetric highs illustrate current geomorphological processes that reflect the impact of the salt interaction with the overlaying sequences.

Interpretation shows the evolution of subsiding minibasins as a result of salt deformation which is represented by deepwater clastics deposited by meandering channels and depositional lobes changing into deepwater shale facies. Salt body interpretation supports a compressional regime in the deepwater Kwanza basin embodied by the presence of squeezed diapirs, double wavelength folds and isolated pod-like structures encased in massive salt. An extensive flat base of salt supports a typical initial evaporite basin configuration. DHI’s and presalt structures are similar to the analogue discoveries offshore Brazil with rotated basement fault blocks, syn-rift and overlying sag sequences of up to 6 km thickness. Additionally saucer-shaped and layer parallel sill structures are observed representing likely volcanic intrusions.

Petroleum systems modeling focused on the maturity assessment of pre-salt and post-salt source rock intervals. The lack of suitable calibration data was tackled by a rigorous stochastic uncertainty analysis of major input uncertainties, i.e. paleo heat flow and pre-salt facies/lithologies. The uncertainty analysis revealed varying maturity risk along the transects and a clear correlation with the overlying salt geometry.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.