Mapping of Basement Structuration From 3-D Seismic Data presented by Dr. Malcolm Francis

Abstract

Basement faults play an important role in the petroleum systems of the South-Atlantic: the rift-parallel trend defines large basins parallel to the coast which accumulate thick sediment deposits. Transfer faults that are mostly perpendicular to the rift faults appear to compartmentalize these basins. The coast-parallel basins have been mapped even from regional 2D seismic data. Rift faults and transfer faults, however, have only been identified at a large scale of 100 km from magnetic data and then verified by gravity data. Detailed mapping of these faults has only been possible with the advent of high quality 3D seismic as shown in cases like the Levantine Basin in the Mediterranean Sea. We present an example of highly accurate mapping of rift and transfer faults in the deep-water offshore South Africa. Color processing of the seismic data allows the mapping of the complete rift-induced fault system. The transfer fault pattern shows a “piano-key-like” structure similar to the pattern observed at large scale on magnetic data. From the 3D seismic data, we can map a quite regular pattern of 500 m to 1 km interval for the transfer faults, whereas the rift-parallel faults show a closer spacing of only a few 100s of meters. Both fault sets display clear throws, which seems to confirm observations from the conjugate Brazilian margin, that the rift-parallel and transfer faults appear to compartmentalize the source rock kitchens and the oil occurrence. Applying this technique to other rift basins may give valuable clues for successful exploration.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018