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SPECHT, MARTIN, Institut Francais de PEtrole, Ruiel-Malmaison, France, PATRICE BABY, ORSTOM, Santa Cruz, Bolivia, JAIME OLLER and GENARO MONTEMURO, YPFB, Santa Cruz, Bolivia, BERNARD COLLETTA and JEAN LETOUZEY, Institut Francais de PEtrole, Ruiel-Malmaison, France, and BERTRAND GUILLIER, IFEA, Santa Cruz, Bolivia

ABSTRACT: The Boomerang Area: An Example of Oil and Gas Fields Related to a Transfer Zone Development

We present results of a study realized from petroleum data of Yacimientos Petroliferos Fiscales Bolivianos of the most important transfer zone of the Bolivian Andean belt: the Santa Cruz transfer zone.

Frontal part of the Bolivian Andean belt consists of a thick series (6 to 8 km) of paleozoic to cenozoic sedimentary rocks thrusted eastwards on a sole thrust located in paleozoic series. The frontal part of the belt, globally N-S oriented, undergoes an important deviation East of Santa Cruz with a left lateral offset of 100 Km. Taking into account the E-W shortening direction, this transfer zone can be interpreted as a lateral ramp.

The Santa Cruz transfer zone coincide with a set of small oil and gas fields whereas frontal structures lack hydrocarbon occurrences. We are then faced with a two-fold problem: (1) what is the origin of the transfer zone ? (2) why are the oil and gas concentrated in the transfer zone ?

Our synthesis shows that the transfer zone is superimposed on the limit of a detached Paleozoic basin whose border direction is oblique to the regional shortening direction. We then interpret the oil and gas formation in two steps:

(1) source rock maturation and hydrocarbon migration towards the top of the Paleozoic sedimentary wedge before Andean deformation.

(2) hydrocarbon dismigration towards anticlinal structures developed during the lateral ramp propagation.

In order to test our interpretation we performed a set of analog model experiments whose 3D visualization was analyzed by computerized X-ray tomography.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.