Oil and Gas Potential of the Prerif Foreland Basin, Onshore Northern Morocco

Abstract

The PreRif Basin in northern onshore Morocco may contain major oil and gas reserves. This foreland basin is located between the Tertiary‐Recent Rif Orogen to the north and the stable Moroccan Meseta to the south; for the purposes of this paper, it includes the Rharb Basin, an area of strong Neogene subsidence which extends offshore to the west. Prospective sandstone and carbonate reservoirs are present at a number of stratigraphic levels, ranging in age from Triassic and Jurassic to Miocene and Pliocene. Lower and Middle Jurassic shales and carbonates constitute potential source beds for “thermal” oil and gas; biogenic gas is generated within Miocene/Pliocene shales. Potential source beds are expected to have reached thermal maturity in the deepest portions of the present basinal area since the Late Miocene. Seals are provided by intraformational shales, transgressive shales of Tertiary age, Triassic evaporites, and by a thick, complex glidemass (or “olistostrome”) of late Miocene (Tortonian) age. Multiple traps can be expected; they will include anticlines, fault closures, salt‐tectonic features, and structural‐stratigraphic traps. Gravity‐defined low areas in the northern portion of the basin are probably the main generative depocentres. Lateral oil and gas migration has occurred on a regional scale since the Late Miocene, and has continued to the present day. A Jurassic Petroleum System includes the surface oil seeps and shut‐in oilfields of the Sidi Cacem area along the basin's southern flank. A Miocene Petroleum System supplies gas production in the Rharb Basin. The prospective area covers some 15,000 sq. km. Available reconnaissance data include published gravity, magnetic, seismic, and surface‐geological surveys. Modern airborne surveys of prospective areas should be followed by detailed exploration, including 3‐D seismic surveys. New recoverable field reserves may lie in the range of 50 to 150 million barrels oil‐equivalent per discovery; several new discoveries can be expected, leading to new total reserves possibly totalling 0.5 billion barrels oil‐equivalent.

Punctuated Neogene tectonics and stratigraphy of the African-Iberian plate-boundary zone: concurrent development of Betic-Rif basins (southern Spain, northern Morocco)

“…On account of comparisons with the Saiss Basin (see above), it is surmised that coeval, partly calcareous strata have been laid down in the Southern Gharb Basin, similarly onlapping the Moroccan Foreland. The olistostrome is interpreted to be an unconformable, gravity-driven sedimentary unit that slid southward into the Western Prerif Foreland Basin, simultaneously with late Tortonian thrust loading of the adjoining External Rif and subsidence of Moroccan Foreland, carrying olistolites derived from tectonically-deformed and uplifted parts of the emergent External Rif (Pratsch, 1996). The overlying transgressive-regressive sequence is equivalent to the Marine Marl Formation of the Saiss Basin (Akrech Sequence of Barbieri & Ori, 2000).…”

“…8) Chaotic mass-flow deposits (olistostromes, sedimentary klippes) like those encountered in the Nador Basin are found throughout the External Rif. In particular, they occur at the uprooted nappe system of the Prerif thrust zone forming the Tortonian tectonosedimentary complex of overthrusting, diverticulate gliding nappes, or Prerif Allochthon (Frizon de Lamotte, 1987;Flinch, 1996;Pratsch, 1996;Chalouan et al, 2001). The emplacement of this major allochthonous unit occurred in the Moroccan Foreland, which includes this huge accretionary wedge, the Gharb and Saiss Basins in the west (see below) and the Taza-Guercif Basin and some smaller extensional basins in the east.…”

“…1; Flinch et al, 1996;Berástegui et al, 1998) and the Prerif Allochthon ( Fig. 1; Frizon de Lamotte, 1987;Flinch, 1996;Pratsch, 1996), this tectonosedimentary mélange consists of gravity-driven olistostromes and other allochthonous deposits incorporating strongly deformed Mesozoic and younger rock material detached from their original base and thust outward from the Betic-Rif orogen into the adjacent basin (Flinch, 1996). …”

“…Three principal sequences of Neogene age are distinguished in the Northern Gharb Basin: a basal Miocene sequence, an overlying Late Miocene olistostrome that is part of the Prerif Allochthon, and a cover sequence of Late Miocene and Plio-Quaternary age (Flinch, 1996;Pratsch, 1996). The basal Miocene sequence consists of Langhian-Serravallian and Tortonian marls and limestones (Flinch, 1996), which accumulated during a compressional tectonic regime founding the western Prerif foredeep (Litto et al, 2001 (Pratsch, 1996). The overlying transgressive-regressive sequence is equivalent to the Marine Marl Formation of the Saiss Basin (Akrech Sequence of Barbieri & Ori, 2000).…”

Central Atlantic margin basins of North West Africa: Geology and hydrocarbon potential (Morocco to Guinea)

“…A Miocene age foredeep is developed in the Rabat area, south of the Rharb Basin, which extends offshore into the Atlantic (Flinch, 1993;Pratsch, 1996). The arcuate fold and thrust belt extends some 450 km westward from the Straits of Gibraltar, and there is general younging of the thrust sheets westward (Fig.…”