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Abstract: Continental Integration of Gravity and Magnetic Data for South America Help to Define Basin Structures

Fairhead, J. D., Getech; Blitzkow, D. - Escola Politecnica da Universidade de São Paulo

Since 1988, GETECH has undertaken two major compilation studies in South America (South American Gravity Project, 1988-91; South American Magnetic Mapping Project 1993-96). These studies have reprocessed all available gravity and magnetic data into unified continental data sets suitable for evaluating the hydrocarbon potential of the sedimentary basins onshore and offshore. Between 1991-98 a major campaign has been undertaken to further improve the resolution of the gravity field in many countries of South America by updating the original studies with significant amounts of new data, while offshore GETECH has reprocessed the marine gravity and satellite derived gravity data to further improve their resolution.

For Brazil, original gravity and magnetic data were provided by academic, Government agencies including CPRM and Petrobras. New gravity data collected by EPUSP and IBGE over 1991-98 period have helped to infill the large gravity gaps in central and northern Brazil. Offshore Brazil, GETECH has reprocessed and unified all Petrobras' marine and bottom meter proprietary data and reprocessed the satellite altimeter data of the GM of GeoSat and ERS1. In parallel with these studies, a new 3' digital terrain model has been generated for onshore and offshore Brazil. These data when combined provide more reliable Bouguer and Isostatic residual anomalies as well as better derivative anomalies which help to define better basin structure onshore and along the continental margin.

Examples of the interpretation power that gravity and magnetic data can have to our understanding of the morphology, depth and structure of basins is demonstrated in the Sub Andean Depth to Basement Study undertaken by GETECH and Earthfield Technology Inc. using these data sets from Venezuela to northern Argentina. While offshore Brazil, the integrated satellite, land and marine gravity data have been analysed using Euler deconvolution and horizontal derivative methods. When such data are used to constrain plate reconstruction between Brazil and West Africa implications on source and reservoir distribution can be made. These offshore interpretations are the focus of two poster papers (Sessions P8 &P24).

Research completed by GETECH in early 1998 on The Ultimate Resolution of Satellite Gravity Data indicates that significant improvements to the existing satellite gravity solutions are possible, particularly in the suppression of noise at wavelengths less than 30 km. This will make satellite gravity a more valuable exploration tool in offshore areas so long as the bathymetry is adequately defined.

The willing co-operation of national groups in all countries of South America, the support of the oil and mineral companies and US Government funding have contributed to the success of these compilation studies.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil