Abstract: The Pilar Basin - A New Prospect in Paraguay

Delaney, Patrick J. V. - Consultant

Until recently the southwest portion of Paraguay was considered to be a lowland underlain by Precambrian basement or by Cretaceous flood basalts. New geological and geophysical evidence indicates that the Ñeembucú area is in reality a formidable basin with a good potential for hydrocarbons. (see Fig. 1)

This area is herein called the Pilar Basin although it may only be a sub-basin of a larger feature. The surface area of the Pilar Basin in Paraguay occupies more than two million hectares and extends into Argentina where it forms part of the imperfectly identified Chaco-Paranaense Basin. The only wells that have been drilled in the area are PR-1 Pirané, T.D. 2408 meters in 1963 and FMB-1 Marcelo Boedo T.D. 1864 meters in 1964. Both wells were drilled by Y.P.F. in Argentina.

The structural setting of the basin appears to be a pull-apart basin characterized by steep basin bounding faults (NW-SE) that have a very strong magnetic expression. It is believed that these faults occurred during the Eocene, are intruded by alkaline rocks and are related to early Andean orogeny. These intrusions are different from the carbonatites of late Jurassic-Cretaceous age because the latter are related to Atlantic rifting and the Parana Basin.

Cross basin faults and strike slip faults give the impression that the Pilar Basin in Paraguay is a half graben with similarities to extensional structures found in rift zones.

The Pilar Basin is separated eastwardly from Precambrian and early Paleozoic rocks by a 30-kilometer belt of NW-SE trending an echelon shear faults. The northern extension of the basin probably connects with the Pirity Basin through the San Pedro low and around the President Haynes high. The Western limit of the basin possibly terminates in the Las Breñas high and the southern portion of the basin surely connects with the vast Parana Basin.

Aeromagnetic data indicates depth to basement to be 1700-3000 meters. It is anticipated that the stratigraphic column will be somewhat different from that encountered in the Chaco and Parana Basins.

The expected stratigraphic column along with probable source beds are shown on Fig. 2. Marine Devonian sediments similar to the San Alfredo Group of the Chaco basin are thought to be several hundreds of meters thick and to be a good source for hydrocarbons. Carboniferous diamicites of probable glacial origin and shallow marine sandstones have a good chance of containing gas.

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