Abstract: Regional Framework of Basin Evolution in South America:
A Methodology for Hydrocarbon Exploration and Exploitation

TANKARD, ANTHONY

Over the past decade, exploration in South America has been strongly influenced by the principles of sequence stratigraphy and eustasy. This methodology has largely dominated depositional and exploration models. Are these models successful? Since 1980, many thousands of wildcat wells have been drilled in South America, but only 8% of these have resulted in hydrocarbon discoveries. Nevertheless, several resource endowment studies show that substantial oil accumulations are still undiscovered, suggesting that the exploration models need to be modified. Obviously, sequence stratigraphy is not a panacea.

An integrated approach to basin analysis better explains the distribution of petroleum occurrences. On a large scale, comparative basin prospectivity is a consequence of regional framework and tectonic evolution. Major phases of basin subsidence and deformation, recorded in the unconformity-bounded stratigraphic sequences, reflect broadscale patterns of stress field evolution. Structural styles and eustasy are believed to be a secondary response to these tectonic processes. These structural styles, the timing of their behavior, and the way depositional systems and facies associations respond to this structural behavior define the internal fabric of the sedimentary basin and hydrocarbon play development. The initiation of subsidence, especially in extensional and strike-slip basins, is reflected in structural compartmentalization. These structural compartments have unique structural, depositional, and hydrocarbon characteristics. Structural compartmentalization and its influence on deposition are reflected in the distribution of reservoirs and petroleum systems. Geothermal gradients and hydrodynamic systems also reflect the internal geometry of basins. There is a stark contrast of these characteristics between structurally compartmented extensional basins and the more uniform flexural foreland basin. For example, deep rift segments tend to be the coolest and may be associated with subnormally pressured reservoirs, compared with thinner sections, which are characterized by higher geothermal gradients and supernormally pressured reservoirs. Meteoric recharge appears to affect mostly the basin margins.

This seminar will explore an integrated basin analysis and its exploration consequences. The seminar will address structural inheritance and basin linkage on a regional scale, the response of these fabrics to different stress fields, the dynamics and timing of basin subsidence and internal deformation, and the way hydrodynamics adjusts to these conditions in controlling a variety of exploration plays.

AAPG Search and Discovery Article #90943©1996-1997 AAPG International Distinguished Lecturers