--> ABSTRACT: Exploration in Fold-Thrust Belt of Cretaceous Subbasin, Northwest Basin, Argentina: Search for Another Caimancito, by James S. Dean; #91022 (1989)

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Exploration in Fold-Thrust Belt of Cretaceous Subbasin, Northwest Basin, Argentina: Search for Another Caimancito

James S. Dean

For the first time since the discovery of the prolific Caimancito field by State Oil Company Y.P.F. in 1968, Argentina's "Houston Plan" has given foreign operators a shot at exploring for analogous accumulations in the structurally complex Cretaceous portion of the sub-Andean foldbelt. A careful reevaluation of the some two dozen dry holes drilled by Y.P.F. in search of a look-alike field suggests that the majority lacked both adequate seismic control to define trap geometry and favorable "timing" for hydrocarbon charge relative to structural growth. As a result, explorationists armed with quality seismic and paying special attention to source rock richness and maturity face a virtually unexplored frontier region.

Although structural traps in the foldbelt have traditionally been regarded as simple anticlines, many are highly variable in their size, orientation, and internal complexity depending on the degree of transpression from the several wrench fault zones that run oblique to the Andean compressional front and the interaction between simple thrusts and rejuvenated normal faults that originated early in the rift history of the Cretaceous aulacogen. With the notable exception of paleohighs in the area of the Zapla arch, Santa Barbara massif, and Metan arch, deformation in the foldbelt is among the most recent in the Andean trend, being mainly Pliocene-Pleistocene in age.

The Yacoraite Formation of Maestrichtian-Paleocene age, a heterogeneous package of peritidal carbonate and restricted marine-lacustrine organic-rich shale with a well-defined clastic shoreface facies along the basin margin, is a combination source rock-reservoir couplet and comprises the primary target in the foldbelt. Reservoir development is erratic but aided by crestal fracturing. The low regional geothermal gradient and relatively recent burial history is a plus for deep drilling but precludes some areas of the foldbelt from charging shallow structures, especially as the recent deformation limits both fetch area and long-distance migration.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.