Pre-Salt Prospectivity on Regional 3D Seismic Data, Campos and Santos Basins, Brazil

Berryman, Jake G.¹; Borsato, Ron¹; Hawkins, Lisa¹; Martin, Mark²; Pyett, Matthew¹; Zhu, Hongwei¹
¹MultiClient Reservoir, Petroleum GeoServices, Weybridge, United Kingdom.
²MultiCliient MegaSurveys, Petroluem GeoServices, Weybridge, United Kingdom.

Introduction:
Petroleum Geo-Services has merged 2D/ 3D seismic data in the Campos /Santos Basins of Brazil to review the offshore regional potential. The 3D alone encompasses 85,000 sq km (Campos Basin 37,000 sq km) (Santos Basin 48,000 sq km). Templates of these pre-salt discoveries will be shown, along with other undrilled pre-salt prospects.

Geology:
The onset of rifting in the Early Cretaceous (Berriasian) led to the development of a series of asymmetric horsts and grabens filled with fluvial and lacustrine sediments. As active rifting persisted, adjacent rift basins entered a sag phase. This phase was crucial in creating anoxic conditions favorable for source rock generation (Pasley et al., 1998).
The continuity of salt deposition (Ariri Formation) along the South Atlantic continental margins has led to favourable conditions for the subsequent accumulation and trapping of hydrocarbons from deeper sources. Analysis of the depositional and structural controls working in successful pre-salt fields can lead to the characterisation of successful petroleum systems and play types.

Pre-salt Prospectivity:
The sag phase strata were deposited during active extension (123-116 Ma). The Brazilian sag phase contains coarse clastic alluvial fans which grade laterally into shallow water carbonates forming the main pre-salt reservoirs. Lulu is an example of these shallow water carbonates on a structural high, contained in a stratigraphic pinch out sealed by the overlying salts of the Ariri Formation.
Reservoir lithology varies along strike depending on the prevailing Cretaceous tectonic and climatic conditions, affecting sediment supply and location of depocentres. Although many of the major Brazilian pre-salt fields are reservoired in microbialitic coquinas, age equivalent clastic units with good properties may occur.

Conclusion:
The application of geophysical data from gravity and magnetics to dual-sensor seismic and regional 2D and 3D seismic has given a greater insight into the tectonic evolution of these basins. This has led to discoveries and many prospects yet to be drilled. The pre-salt had been an unattractive and difficult target; however following the success of Lulu, exploration and production of pre-salt plays have added an estimated 8-20 bboe to Brazilian offshore reserves (Chakhmakchev and Rushworth, 2010).

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012