This paper presents the techniques and results of a depth to basement inversion and modeling effort over the Guyana, Suriname, and French Guiana area of northeastern South America. A new development in the application of spectral inversion of both gravity and magnetic data has allowed us to extend the inversion over the entire study. Integrating the results of the spectral inversions with Euler deconvolution and 2-D modeling results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest have been deposited over most of the offshore area. This indicates that the USGS (2000) estimate of over fifteen BBOE for the area is highly possible.
The Guyana Basin extends from eastern Venezuela south to the Demerara Plateau. This area has been largely under explored for a variety of reasons. A few significant papers have been published on the area including Torres, et al. (2003), Workman (2004), Gouyet, et al. (2004), and the USGS (2000) assessment. These papers have emphasized the prospectivity of the area, but have not addressed in any detail the complex tectonic processes that formed the geological structures of the entire area shown in Figure 1. We have begun an analysis of the results of these processes using a variety of data and depth to basement analyses. An example of the data used, which illustrates the complexity of the structure and tectonics of the area is shown in Figure 1. The southeastern onshore area is poorly represented by the EGM96 gravity model which has a 55 kilometer, half wavelength resolution. We also used magnetic data from the South America Magnetic Mapping Project (SAMMP, Fairhead et al., 1997) which were merged with a Repsol marine survey, a Staatsoilie near shore airborne survey, and other ship-track data offshore. The well and the older seismic data is through Staatsoilie. The recent survey by Repsol provided new seismic data off the northwester part of the Demerara Rise. A seismic line from Watts and Peirce (2004) was also very useful. We have used the gravity, magnetic, seismic, well and geological data to constrain the possible tectonic scenarios. A primary first step is the integration of this wide variety of data into a GIS environment. The next is the development of a description of the basement structure using geophysical techniques, which is consistent with all of the data. The basement structure then allows us to assess the applicability of various plate reconstructs of the area which are largely unconstrained due to the subduction of much of the geological evidence. The final step is re-integration and interpretation of all data, including proprietary data and interpretations, to give the best geological and tectonic construction for the area. As part of the determination of the basement structure, some new techniques have been developed and applied. These include the use of a Tau-P approach to spectral inversion of gravity and magnetic data, and the integration of spectral, Euler deconvolution, and modeling techniques to produce a better constrained result.
