Possible Controls of Andes-associated Volcanic Activity on Hydrocarbon Generation and Leakage in the On/Offshore Northern Austral Basin, Southern Argentina, South America

Sachse, Victoria F.¹; Anka, Zahie; di Primio, Rolando; Rodriguez, Jorge; and Cagnolatti, Marcelo
¹[email protected]

Although numerous oil and gas fields have been developed on- and offshore Austral Basin, southern Argentina, the processes of hydrocarbon generation and accumulation in time and space, including migration and leakage dynamics remain not completely understood. In order to better understand how the regional tectonic setting, i.e. the Andes evolution, may have influenced the HC system history, we carry out an integrated basin analysis including onshore-offshore correlations and 3D modeling of hydrocarbon generation, migration and sequestration dynamics through geologic time.

As a first step, and after the definition of the main depositional units in the Basin, information about source rocks (TOC, HI), potential reservoirs and seals were used as input for a 3D petroleum system modelling (PetroMod software). In the model source rock qualities were assigned to the Lower Cretaceous Springhill Formation (up to 6 %TOC), Lower Inoceramus and Margas Verdes Formation (>2 %TOC). Reservoirs and seals occur from Jurassic up to the Eocene, but the main reservoir is present in the Early Cretaceous Springhill Formation. An initial constant heat flow of 60mW/m2 was assigned. A recent burial depth of up to 8 km in the southernmost northern Austral Basin and shallowing up to 2.5 km on the western flank of the Rio Chico High were modelled for the base of the Early Cretaceous. Modelled vitrinite reflectance values indicate gas window or even over-mature ranges for organic matter samples from deep buried zones in the south-western basin. Lower vitrinite reflectance values were modelled for the eastern part; where maturity ranges between immature and the oil window.

These differences in maturity distribution can be explained by the differential burial depth between the west and east. However, this preliminary run of the petroleum system model not comply entirely with present-day accumulations known in the basin. Thus, either the temperatures during burial were not high enough or the modelled burial history needs refinement. Increased past-temperatures can be explained by volcanic activity during different times of Cenozoic. Identified seismic features which have been interpreted as magmatic intrusions (sills and dikes) within the sediments, and also at the surface, support this idea of increased temperature field in the past. Hence, future efforts will concentrate in refining the heat flow evolution incorporating the presence of the magmatic intrusion both in time and space.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013