Ongoing compression across intraplate south America: observations and some implications for petroleum exploitation and exploration

Abstract

Stress data compilations, intraplate stress field numerical models and space-based geodetic results show that the South American plate is now in horizontal compression and shortening. Plate wide deformation related to the Andean tectonics has been put in evidence by analyses of integrated visualizations of plate-scale information on tectonics, continental geology, topography/bathymetry, seismicity, stresses, active deformation, residual isostatic anomalies, fission track analyses, and seismically derived Moho depths and P and S wave velocity anomalies. Here, a few results of these analyses are presented and some implications of the ongoing compression for petroleum exploitation and exploration are discussed. A conceptual model for the plate-wide deformation is presented. The model states that in response to the compression, the lithosphere as a whole (or only the crust if thermal gradients are high enough) tends to buckle. The resulting antiforms are responsible for uplift along erosional borders of the basins, whereas the resulting synforms are sites of continental sedimentation, at basin centers. The denudation of sedimentary covers promotes the exhumation of increasingly deeper rocks and the adiabatic decompression, facilitating fusion and hence the observed Upper Cretaceous and Tertiary alkali-magmatism. The basement low topography adjacent to the retreating scarps is frequently associated with large Neogene basins (e.g. the Pantanal). The tendency to buckle is controlled by the previous lithospheric/crustal structure. The perception of ongoing compression opens up new perspectives for petroleum exploitation and exploration. The knowledge of the stress field is crucial for secondary recovery, hydraulic fracturing, fracture reservoir characterization and well design. About 82% of the total reserves are found along the actively deforming border between the South American and the Caribbean plates. The most important intraplate accumulations (about 5% of the total reserves) are found in the Southeastern Brazilian margin, which has been deformed the most with respect to other margins during the Cenozoic, and continues to be the most seismically active. These facts suggest that the actual role of the active tectonics on the petroleum accumulation patterns may have been underestimated.