Speculative Petroleum Systems of the Southern Pelotas Basin, Offshore Uruguay

Abstract

At present commercial oil accumulations in the Pelotas Basin have not been identified (as opposed to the other basins of the Brazilian Atlantic margin), nor the current geological knowledge allows to identify proven petroleum systems. In spite of that, this basin continues to be underexplored with a total of only 18 exploratory wells drilled in an area of more than 330,000 km², all of them located in its Brazilian portion. This study focused in the Uruguayan portion of the basin that has not been drilled yet. 2D and 3D seismic data acquired in this area reveal a promising hydrocarbon potential allowing the identification of stratigraphic plays that have analogies with accumulations discovered in other basins of both sides of the Atlantic not affected by halokinetic deformation (as in French Guiana and Ghana). The main purpose of this study is to evaluate the hydrocarbon potential of the southern part of the Pelotas Basin, defining the speculative petroleum systems (based on geophysical data). Sequence stratigraphy concepts were used as the main methodology to interpret the depositional sequences from 2D seismic sections of the Uruguayan portion of the Pelotas Basin and available well data. It is possible to identify a syneclise stage that preserves Permian geological units of a prerift phase corresponding to the Paleozoic intracratonic Paraná Basin; an Early Cretaceous continental synrift phase constituted by the volcanic-sedimentary infill of halfgrabens and SDRs; and a Cretaceous to Cenozoic postrift phase represented by a sedimentary stacking associated to successive transgressions and regressions of the sea level. The sequence analyses allowed interpreting the system tracts and identifying the distribution of the main elements of the potential petroleum systems. The source rocks of the speculative petroleum systems proposed in this study for the Uruguayan portion of the Pelotas Basin are represented by a Permian restricted marine source rock of the prerift phase, and two marine source rocks of the postrift phase of Aptian-Albian (OAE 1) and Cenomanian-Turonian (OAE 2) ages. The main reservoirs proposed are continental sandstones of the synrift phase and Cretaceous and Cenozoic turbidites from the postrift phase. The main regional seals are related to the postrift phase, represented by shales of the Aptian-Albian, Cenomanian-Turonian and Paleocene marine transgressions.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015