Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Interpretation of Long-Offset, Prestack Depth Migrated (PSDM), Regional 2-D Seismic Data Offshore Equatorial Brazil: Tectonic Controls on Sedimentation and Comparison with Conjugate West African Margin
(1) Consultant, ION Geophysical-GX Technology, Houston, TX.
(2) Rift Institute for Teaching and Training, Las Cruces, NM.
(3) ION Geophysical-GX Technology, Houston, TX.
Recent discoveries offshore Ghana and Sierra Leone have established this area as a significant petroleum province. New regional seismic data from north Brazil demonstrate the parallels in the timing of structural and stratigraphic events on both sides of the Atlantic and thus highlight the petroleum potential of equatorial Brazil.
The data consist of newly acquired long offset (10-km, 18-sec. record), deep imaging pre-stack depth migrated (PSDM to 40 km) 2D seismic-reflection lines. In addition to the interpretation of the sedimentary wedge, the data also allow for the interpretation of deep crustal architecture along the north Brazilian margin from Foz do Amazonas in the northwest to the Potiguar basin in the southeast.
During the rift/early drift phase, narrow restricted basins between Brazil and Africa have facilitated formation of source rocks that sourced the discoveries in the Ivorian (Ghana/Ivory Coast) and Liberian (Sierra Leone/Liberia) basins. Clastic sediments, including submarine-fan facies, transported in the Late Cretaceous have formed the reservoirs for the African accumulations. Extensional, and compressional structures, forming potential traps, have also been mapped in these basins. The new data support a similar evolutionary history for the north Brazilian margin.
As Africa and South America separated from south to north creating the Atlantic Ocean, the equatorial segment was the last segment of the South Atlantic to open in the Late Cretaceous (Cenomanian, ~95 Ma). Continental margins on both sides of equatorial Atlantic primarily consist of segments which sheared against each other initially. As the spreading continued, the zones of shear movement developed into oceanic fracture zones. Major fracture zones that segment the north Brazilian margin are from north to south: St Paul’s, Romanche, and Chain/Fernando de Noronha. Tectonic boundaries of the north Brazilian basins are clearly controlled by the trends of these fracture zones as they are in west Africa. As the sea-floor spreading continued, newly created oceanic crust was segmented by these fracture zones and they produce large offsets in the present day mid-ocean ridge.
Drilling following the model from West Africa has not yet happened in Brazil so far. While active petroleum systems have been established in most of the north Brazilian basins, targets on the outer shelf/continental slope might lead to accumulations similar to those already discovered in equatorial Africa.