Regional Setting
The Falkland Islands are located on the south eastern margin of the South American tectonic plate which extends as far as Maurice Ewing bank to the east of the islands. It was at this location, on this ancient piece of crust, that several academic research wells were drilled in the 1970s and 1980s. The results from these wells, combined with drilling results from the Argentine Magallanes basin, demonstrated the hydrocarbon potential of the basins that lie to the south and east of the Falkland Islands.
The context for these basins was created by the break up of the Gondwana supercontinent during the Triassic and Jurassic periods. This continental mass comprised of what are now the continents of America, Africa, Antarctica, Australia and part of Asia. One of the earliest parts to fragment from the massive landmass was Antarctica. This created a small ocean basin, called the Weddell Sea, between the Falklands and Antarctica to the south. It was in this basin, that much of the petroleum system, that we believe to be active in our acreage, was deposited. In the Early Cretaceous (about 130 million years ago) the final phase of the break up of Gondwana was initiated as South America began to separate from West Africa. By 100 million years ago, the separation was complete and an open seaway existed between the Weddell Sea to the south of the Falklands and the South Atlantic to the north. The continued growth of the South Atlantic resulted in increased separation of South America and West Africa until the present day configuration was achieved.
Several basins were formed during this early break of Gondwana and some of these have become prolific oil and gas provinces (for example the Santos basin in Brazil). The South and East Falklands basins are part of a series of basins that extend onto what is now the Argentine mainland. The Magallanes basin in Argentina is a major oil and gas province and its early history shares many similarities with the East Falklands basin. The later geological history of the Falklands diverged from Argentina which was subjected to the influence of the growing Andes mountain chain to the west.
Introduction
For oil and gas deposits to form several key elements must be in place. These are: a source rock (from which the oil is generated), reservoir rock (which stores the oil in the pore spaces between the grains) and a trapping mechanism which must include a sealing formation so that the relatively buoyant oil or gas cannot escape.
Source Rocks
Source rocks were discovered in the wells (part of the deep sea research drilling programme – ODP and DSDP) drilled to the east of the FOGL licences. No oil or gas has been generated at this location due to insufficient burial of the rocks. However, these formations may be mapped from these wells into the FOGL acreage. In addition, in the Argentine basins, source rocks of the same age have generated several billion barrels of oil equivalent, confirming the model that the East Falklands basin is part of a continuous margin with similar geological characteristics, in rocks of the same age. In the FOGL acreage these source prone formations have been buried to over 3km which is sufficient (over 100 degrees Celsius) to generate oil.
Reservoirs
The North Falklands Basin was a lake throughout much of its geological history, unlike the South and East Falklands basins which are classified as 'passive margins' that developed in a fully marine setting. Published research (Richards and Hillier 2000) shows that the sediment that filled the North Falklands Basin was derived from the north and west. The South and East Falklands basins seem to have derived much of their fill from the Falkland Plateau, which includes the Falkland Islands. The Falkland Islands (see British Geological Survey) are dominantly composed of hard, old quartz rich rocks which range in age from Precambrian (older than 550 million years) to Permian (older than 260 million years). These ancient rocks erode to provide sands, which in turn will have been shed into the basin to form sandstone reservoirs to store oil and gas. The Falklands today are surrounded by beautiful sandy beaches, which were derived from these rocks. In addition, seismic analysis suggests that sands were shed into the basin during several key periods of the geologic record.
Traps
There are several potential trapping styles in the basins. Large tilted fault blocks are present in the south and north of the FOGL acreage. This is a trapping style common in the early rifted parts of basins worldwide and many of the large oil and gas fields of the North Sea (Brent for example) are in traps of this type. In the southern part of the acreage, folded rocks occur along the margin of the Scotia sea which form simple anticlinal traps. In other parts of the acreage the trap style is dominantly stratigraphic where sand bodies are mapped onlapping the basin margin, in semi isolated channel systems or submarine fans, like the recent discoveries offshore Ghana. In all cases thick, regionally extensive sealing shales form an impermeable blanket across the top of the traps.
The Plays
Geologists tend to group leads, prospects and ultimately oil and gas fields into plays (features linked by common geologic factors, such as reservoir type, structural style etc.) as a convenient classification system. There are three main plays in the FOGL acreage. The Springhill Sandstone Play, which is further subdivided into fault blocks and onlap traps, the Mid Cretaceous Basin Floor Fan Play and youngest of all, the Tertiary Channel Play which is subdivided into the Tertiary Channel Play and the Tertiary Fold Belt Play.
The Springhill Play contains about 95% of the oil and gas in the offset Argentine Magallanes basin. The oil or gas is trapped in sands which were deposited near an ancient shoreline. Many of the fields in Argentina are formed by a combination of structural and stratigraphic trapping mechanisms. Example prospects from the FOGL acreage are Endeavour, Endurance, Lutra, Inflexible and Thulla.
The Mid Cretaceous Fan Play, is developed in the northern and central portions of the East Falklands basin. Deep marine sands are shed into the basin and become large isolated stratigraphic traps. Example prospects are Scotia, Hero and Diomedea.
The Tertiary Channel Play developed following a period of uplift of the Falklands Plateau. This caused a large amount of sediment to be shed into the basin and discrete sand bodies were created, which later may have become charged with hydrocarbons. These are relatively easy to see on seismic data and form one of the main targets in the basin. The giant Loligo prospect and the potential follow up prospect, the Nimrod Complex and Vinson prospect,are examples of this play.
The Tertiary Fold Belt Play is only developed in the extreme south of the FOGL licences. The acreage in this area sits above a tectonic plate boundary, with the oceanic Scotia Sea developed to the south and the passive margin, at the east limit of the South American plate, developed to the north. Movement along this margin buckled the rocks into linear folds which may form a trapping mechanism for hydrocarbons. The deformation which drove the development of these folds is relative young (by geological standards) and took place within the last 20 million years.
The South and East Falkland basins are frontier basins with no previous commercial drilling. Although this increases the risk of drilling a dry hole it also presents a massive upside for a small company, we are not just exploring a block, licence or prospect but potentially an entirely new hydrocarbon province.
