Southern Basins
Summary
The southern Falklands are surrounded by three interconnected basins: the Falkland Plateau Basin to the east, the South Falkland Basin to the south, and the Malvinas Basin within Argentine waters to the west. Although all connected, each of the three basins exhibits its own unique structural style. These three basins are isolated from the North Falkland Basin, and have a completely different infill, which is more marine than the predominantly continental North Falkland Basin.
Five wells have previously been drilled in the southern basins in Falklands’ waters. One was dry, one failed to reach its drilling objective after encountering gas shows, two were plugged and abandoned after encountering gas that did not flow to surface and one resulted in the Darwin gas condensate discovery.
Structure
The Falkland Plateau Basin is a passive margin basin beneath 200-2500m of water to the east of the Falkland Islands. It is bounded to the west by the Falklands Platform and to the south by the Scotia/South American plate boundary. The basin may be underlain by thinned continental crust and is connected to the Malvinas Basin through the Falkland Chasm. The Basin has Cretaceous passive margin-type rocks similar to the Falkland Plateau Basin, and early extension was followed by post-rift sag through the Cretaceous and Cenozoic.
The basin is contiguous with the Malvinas Basin to the west and the Falkland Plateau Basin to the east, but has a somewhat different structural style. It exhibits numerous major normal faults downthrowing to the north, and developed in a foreland basin setting in front of the thrust front at the plate boundary. The normal faults in the foreland basin and the thrust faults in the plate boundary zone often display reactivation into recent times. Much of the normal faulting in the basin was probably of Jurassic through Early Cretaceous age, contemporaneous with the deposition of sediments in the actively rifting trough.
Source Rock
Good quality oil-prone source rocks of late Jurassic to early Cretaceous age have been proven on the Maurice Ewing Bank to the east of the Falklands, and the presence of hydrocarbons in four of the five wells drilled in the Falkland Plateau and South Falkland Basins indicates the presence of source rocks locally.
Reservoirs
The Southern Basins contain Permo-Triassic, Mesozoic, and Cenozoic sediments that have the potential to be reservoir rocks. The Lower Cretaceous Springhill Formation is the main reservoir in the Argentine part of the Malvinas Basin and may extend into the South Falkland Basin and Falkland Plateau Basin. Sediments from the Falklands Platform area could improve reservoir quality locally. Reservoirs may also be found in lowstand systems-tract wedges and in major regressive systems that prograded eastwards and southeastwards off the Falklands platform.
Exploration to date
Five wells have been drilled in the southern Falklands' waters, with one currently underway. Each well was drilled for a different purpose and yielded varying results. Some were plugged and abandoned as dry holes, while others were abandoned after discovering gas or oil that was not commercially viable. The wells were drilled to test anticlinal closures, tilted fault block traps, stacked seismic high amplitude events, mid Cretaceous fan systems, and Springhill Formations. Seventeen or so wells have been drilled in the Argentine part of the Malvinas Basin, with some limited success. The Southern Basins are at the earliest stage of exploration.
Play Types
The potential 'play' types for the basins include different types of wedges, rollovers, traps, structures, and stratigraphic changes at different levels of Jurassic and Cretaceous sandstones. There are also probable Permo-Triassic rocks in structural traps sealed by Jurassic volcanic rocks or Cretaceous-Cenozoic mudstones.