Abstract: The Subthrust Trap beneath the Western Foothills of the Eastern Cordillera, Colombia

Mauricio A. Silva, Mauricio Osorio, Alastair Sharp

LASMO started exploration in the Espinal Block within the Upper Magdalena Valley of Colombia in 1987. Since then six exploration wells have been drilled within the block which have resulted in four New Field Wildcat successes. Two of these successes have been in subthrust configurations.

This presentation shall describe the exploration and appraisal techniques used to delimit the Venganza Field which was the first subthrust field discovery made in Colombia.

The first stages of our exploration for the subthrust trap were conventional seismic surveying, and structural modelling using the excellent geological outcrop data. These led to the formulation of the Venganza prospect which comprised tilted Late Cretaceous Guadalupe sandstones overthrusted by stratigraphically older Villeta shales.

The Venganza Prospect was drilled in 1991 and encountered the reservoir as expected directly beneath the thrust plane, and produced oil at 5800 barrels/day on test.

Subsequent to the Venganza-1 discovery, further seismic data were acquired and processed using pre-stack depth migration. These new data "verified" the Venganza geological model, and formed the basis for appraisal drilling.

The Venganza-2 appraisal well, drilled 4 km to the north of the successful exploration well, was dry and indicated that the subthrust trap configuration was much more subtle than first anticipated.

The presentation shall then demonstrate the evolution of our understanding of the subthrust trap configuration and the evolution of our search techniques for it.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela