The Determination of Basement Configuration for a Geologic Understanding of Gabon’s Tectonic Framework

David M. Schwartz¹, Jeff Rowe², Serguei Goussev¹, Rao Yalamanchili¹, and Afif Saad^3
1Marketing, Fugro Robertson Inc., Houston, TX
²Marketing, Fugro Airborne Surveys, Houston, TX
³Consultant, Houston, TX

Basement highs play an important role in the draping of Gamba sands to develop structures for significant hydrocarbon exploration for on and offshore Gabon. Examples are the Gamba Bigorneau High and Kaba High further to the south and, in the north, the Lambarene Horst. Some of the near-shore structures and trends can act as analogs for plays in the deeper water. The magnetic data also help to understand the overall tectonic fabric of the region and, more specifically, to investigate the relationships to basement blocks and horsts. Potential control of prospective structures might be inferred from the locations of such basement blocks. Overlying salt can negatively influence the ability to image the basement surface. The satellite-derived gravity and enhancement maps can also be used to look at overall tectonic fabric for the region.

An extensive grid of aeromagnetic data was compiled from a variety of surveys acquired by Fugro Airborne Surveys over a number of years. A number of interpretive aids such as Reduction-to-Pole (RTP) of Magnetic Anomaly, Vertical and Horizontal Derivatives and Band-pass Filters are applied to enhance the relationship between the magnetic anomalies and their causative sources. Linear features appear in a number of magnetic enhancements such as the Horizontal Gradient of RTP. Depths to magnetic sources can were computed using a variety of analytical techniques and the results were compiled to describe the magnetic basement surface. Incorporation of modeled seismic data would add calibration to specific horizons and also verify the response to basement fault blocks.

This paper represents the culmination of a progression of pilot studies each of which used more data then the previous study until the full data base was utilized. Advanced GIS techniques for presenting the data help analysts get the most value out of the entire data

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery