Abstract: Oil Potential in the Malvinas Foreland Basin

Nevistic, Antonio; Jorge Cerdan; Guillermo Laffitte; Dani Crivaro; Claudio Haring; and Silvia del Vo - YPF

The deformed area of the Malvinas Basin associated with the Burdwood Bank is located northward from the South America-Scotia plate boundary and is a product of transtentional to transpressional events (fig.1).

During the Upper Eocene, the Austral Basin suffered a series of major changes in the tectonic framework. The passive margin type was replaced by strong tectonic inversion, allowing the formation of large progressively uplifting feature towards the east as a propagation of the Andean movements. The Malvinas Basin was involved in this process during the early Miocene in a direct relationship with the beginning of the maturation and migration of the hydrocarbons and the accumulation of a thick sedimentary column.

The compressive deformation in the southern Malvinas Basin was associated with flexural process that produced a deep foreland basin. This evolution was stressed due to the action of a previous transitional phase that took place at least from the Paleocene times and partially inverting previous structures.

The possible hydrocarbons could have migrated laterally to the north and northwest direction mainly through the porous levels of the Lower Cretaceous, to be trapped in the reservoirs detected in Calamar, Ciclón and Salmon wells. In the inverted area different migration pattern took place, where the updip movement was predominant and as a consequence of the shallower burial a better preservation of the hydrocarbons occurred and the existence of faults should have put in contact the generating levels with possible reservoirs in the Lower Tertiary wedges.

The seismic information and exploratory wells drilled in the Malvinas Basin detected the presence of an important hydrocarbon "kitchen" area in the southern portion of the basin. Generating levels, identified in wells located at the Northern and Western borders of the "kitchen" are marine shales of external platform assigned to Lower Inoceramus and Margas Verdes (lower to middle Cretaceous) which present a regular to good generating potential with values of COT% variable between 1 and 3 and Hydrocarbon Index near 400. The available biomarker studies showed a good correlation among shales and oils of the above mentioned wells.

The thermal modeling of wells and the stratigraphic correlation through seismic data, suggest that since the Miocene the source rocks generated and expulsed hydrocarbons toward porous levels grouped at the Springhill Fm. Using Springhill Fm. as a carrier the hydrocarbons remigrate updip towards Rio Chico High to form recognized accumulations at wells like Ciclón, Salmón and Calamar. Following this idea and taking into account that the oil generation started during the Miocene times, the migration and trapping, of part of the oil and gas generated, could have been carried along the active compressive faulting and structuration in the tertiary foreland (fig.2).

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil