Abstract

In the southern sub-Andean region of Bolivia, most of the structurally controlled hydrocarbon traps are related to the development of the Andean fold-and-thrust belt. The present study analyzed the structure and the hydrocarbon accumulations at the south sub-Andean “wedge-top.” The structural decoupling in the allochthonous section is characterized by two vertical overlapping structural levels, and the general geometry is defined as a trailing imbricate fan system.

Backthrusts, lateral ramps, and tear faults are associated with the shallow structural level. They can act either as barriers or as secondary migration pathways for hydrocarbon accumulations. Related traps show three- and four-way dip closure, but only the latter were productive. The Curiche and Tajibo gas fields are two examples that produce from Cenozoic units in this structural domain.

The deeper structural level is defined by thrust sheets with no forelimb development, generating three-way dip closure traps. The Tacobo gas field was the first Huamampampa Formation discovery of this level in the wedge-top.

Surface geology, 2-D/3-D seismic, exploratory wells, and petroleum system modeling have been integrated to analyze the development of the wedge-top structures. The timing of generation, migration, and remigration of hydrocarbons was also analyzed.

The petroleum system model shows that most of the source rocks reached the critical generation moment prior to the Andean orogeny. The generated hydrocarbon contributed to the development of detachments and thrust that were conduits of migration from the Neogene to present.