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North and Northwest Africa
Regions
Western Sahara has no identified petroleum potential, onshore or offshore. The country lies on the edge of the West African Craton.
Most of the area, including offshore, is overlain by the Aaiun passive margin basin which was created on opening of the North Atlantic Ocean. A small port of the Palaeozoic Tindouf basin occurs in the northwest.
The Aaiun Basin is one of a series of passive margin basins that lie along the North Atlantic margin of Northwest Africa and the northeast margin of North America. It contains Mesozoic and Cenozoic continental and shallow marine sediments overlying basement of Precambrian or Paleozoic age.
The basin extends for almost 1,100 kms from the Cap Blanc Fracture Zone in northern Mauritania, north through Western Sahara into southern Morocco to the intersection of the North Canary Island Fracture Zone and the South Atlas Fault.
There are two sub-basins present separated by the Dakhla Fracture Zone. The northern part is the Boujdour sub-basin and the southern part is the Dakhla sub-basin.
The onshore eastern margin of the basin is the Palaeozoic Tindouf basin in the north and the Precambrian Reguibat Massif and Paleozoic fold belt of the Mauritinides in the south.
Stratigraphy comprises Triassic continental sediments overlain by a thick Jurassic carbonate platform. Offshore, below the present day slope and rise, the pre-Cretaceous may reach 8 kms in thickness.
The Jurassic carbonate platform was terminated in the Early Cretaceous with deposition of a thick sequence of deltaic clastics overlain by black shales and Late Cretaceous transgressive shallow marine to lagoonal sediments. These grade eastwards into continental facies.
The Late Cretaceous rocks were unconformably overlain by marine and then deltaic Paleogene sediments and a thin Neogene sequence of sandy limestones.
Globalshift recognises source, seal and reservoir rocks to be present in the Aaiun basin but no wells have been able to locate traps containing commercial accumulations of oil or gas. However it has never been fully evaluated due to disputes over territorial ownership.
History
Western Sahara has only a limited history of drilling and it has never achieved any production. Petroleum exploration activity began in the onshore Aaiun Basin in the early 1960s when the region was under Spanish jurisdiction.
The onshore area was divided into over 100 permits and by 1964 nearly 50 wells had been drilled by companies including Gulf Oil, Amoseas, Arco and Unocal. No discoveries were made although gas shows in Cretaceous clastic reservoirs were reported in several of the wells.
In the Tindouf Basin, a number of companies, including Phillips, were active, drilling around 15 wells between 1960 and 1967 with gas shows reported in two of these. The last onshore well in the country was drilled in 1973 prior to the departure of Spain.
Four dry offshore exploration wells had also been drilled between 1966 and 1970. After discoveries were made in Mauritania in 2001 both Morocco and the SADR signed deals with exploration companies.
Total and Kerr-McGee began prospecting on behalf of the Moroccan state company (ONAREP). However, in 2002 the UN concluded that, although existing permits were not illegal, further contracts would be in violation of the principles of international law.
Total pulled out in 2004 and Kerr-McGee left in 2006, pressured by NGOs and corporate groups.
Nearly a decade later in 2014 Seabird Exploration ran a seismic survey in Western Sahara’s deeper waters on behalf of Kosmos Energy who had held rights over the Cap Boujdour contract area since 2006 under a petroleum agreement with the Moroccan Office National des Hydrocarbures et des Mines (ONHYM).
A deep water well was drilled in 2015 in the block and was reported to have had gas and condensate shows.
The Aaiun basin remains barely explored. Although the onshore part of the basin has only limited prospectivity, there exists potential for oil and gas fields offshore, particularly within deep water Cretaceous fan sediments analogous to those found elsewhere along the Atlantic passive margin.
Globalshift believes that the questionable legality of exploration activity by foreign companies, related to the continued dispute between Morocco and the SADR, makes it unlikely that any production will materialise in the short and medium term.
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