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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


 
Chapter from: M 62: Petroleum Basins of South America 
Edited by 
A. J. Tankard, R. Suarez Soruco, and H. J. Welsink

Authors:
P. Baby, I. Moretti, B. Guillier, R. Limachi, E. Mendez, J. Oller, and M. Specht

Basin and Aerial Analysis/Evaluation

Published 1995 as part of Memoir 62
Copyright © 1995 The American Association of Petroleum Geologists.  All Rights Reserved.

 
Petroleum System of the Northern and Central Bolivian Sub-Andean Zone
P. Baby
ORSTOM
Grenoble, France
I. Moretti
IFP
Rueil Malmaison, France
B. Guillier
ORSTOM
Quito, Ecuador

 
R. Limachi
E. Mendez
YPFB
Santa Cruz, Bolivia
J. Oller
Petrolex
Santa Cruz, Bolivia
M. Specht
Total
Paris-LaDefense, France

 
 
Abstract

A coupled study of the kinematics of thrusting and hydrocarbon maturation has been carried out in the northern and central sub-Andean belt of Bolivia to define the petroleum potential of the area. In addition to the classic Devonian source rock (Tomachi-Tequeje formations to the north and Iquiri-Limoncito formations in the central area), two other source rock intervals are recognized: the Retama Formation (Upper Devonian-Lower Carboniferous) and the Copacabana Formation (Upper Carboniferous-Lower Permian). These are the most prospective units in northern Bolivia and are of marine origin. The structural style varies from north to south due to variations in the sedimentary column involved in the thrusts. The orogenic front was guided by the northern boundary of a Paleozoic sedimentary wedge. In the Boomerang area, this boundary is oriented obliquely to the regional shortening and controlled the development of a prominent transfer zone. To the north, the thrusts are wider and the amount of shortening increases. The western part of the northern sub-Andean zone is characterized by a very thick Tertiary piggyback basin fill.

Two phases of hydrocarbon maturation are recognized. The first began in Early Carboniferous and affected mostly Devonian strata. Formation of structural traps during this period occurred rarely. The entire basin was then deeply eroded in Permian-Jurassic time, causing any hydrocarbons that may have formed to be lost. The second phase of maturation was contemporaneous with Andean deformation and with the resulting burial under the Tertiary cover in the foreland basin and in piggyback basins on thrust structures. The hydrocarbon expelled during this period may fill the Andean anticlines. The known source rocks are not proven to be gas prone, but current discoveries indicate a high gas to oil ratio that may be due to secondary cracking in the source rock. Because the initial potential of the source rocks is low, expulsion of heavy compounds is expected to be weak.

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