1 ) Overview
The onshore Meso-Cenozoic basin of Tarfaya-Lagwira covers an extensive area of about 124 821 km². It is limited to the North-East by the Anti-Atlas, to the East by the Precambrian outcrops of the Reguibat Ridge and to the West by the Atlantic Ocean.
2 ) Data Base
2. 822 Km of 2D seismic data is available in the basin witch was acquired between 1986 and 2007 and 53 exploratory wells drilled between 1960 and 1973.
3 ) Tectonic and Sedimentary Evolution.
The Tarfaya-Lagwira area is a coastal basin developed in a stable passive margin. The Precambrian and Paleozoic basement is composed of very complex structures and is divided into horsts and grabens. On this, lies the syn-rift sequence of basal-Liassic, which is composed essentially of red clastic sediments: Conglomerates, sandstones and shales. Doloretic flows are interbeded with these deposits in grabens.
During the Coniacian regression sedimentation remained only in shallow bays. At these locations such as Boukraa region, phosphate series were deposited in the Paleogene.
Seismic interpretation mapping for the different post rift sequences provide proofs of the stable nature of the passive margin in the Tarfaya-Laayoune basin. Generally the cover is very weakly deformed by the alpine orogeny, and the weak flexures and ondulations are gradually absorbed in the Meso-cenozoic series.
4 ) Petroleum System
4-1 ) Source rocks
The best mature source rocks in the basin are found Lias-Dogger elongated depocenters in the platform with TOC values varying from 1, 47 to 2, 49% and the organic matter essentially composed of type II kerogen. Maturity reached between the end of the Upper Jurassic and the beginning of the Cretaceous.
The Upper Cretaceous-Albian and Tertiary sequences represent the best source rocks in the basin, but their organic matter is immature except in the southern areas.
4-2 ) Reservoir rocks
The Lower Cretaceous contains the best reservoir rocks in the basin. The quality of these reservoirs improves from west to east with abundant alternating sandstones and sandy beds.
In the Jurassic, the reservoirs are well developed on the borders of the platform and around the depocenters. The quality of Jurassic reservoir rocks gets better in the eastern areas and the borders of the basin.
The Tertiary and the Triassic are essentially composed of lenticular sandy to sand and conglomeratic beds.
4-3 ) Seals
With the exception of the eastern areas where the Ceno - Mesozoic formations are essentially sandy to sandy-conglomeratic, all the reservoirs are provided with an adequate impermeable seal.
4-4 ) Traps
The different structural or stratigraphic traps are identified in different level of the Meso-Cenozoic sequences.
The stratigraphic plays are generally related to the prograding structures present at different level of the Meso-Cenozoic sequences (Triassic, Lower Jurassic, Lower Cretaceous and Upper Cretaceous).
5 ) Play Concepts
5-1 ) Triassic play
This leads corresponds to the Triassic progradation structures which are related to the fluvial-deltaic system deposits and listric normal fault systems, Lower Jurassic reef.
5-2 ) Jurassic plays
This leads corresponds to Daora structure, Dogger progradational series, Amseiquir structure, Lower Jurassic prograding structures
5-3 ) Cretaceous plays
This leads corresponds to fore structures of Puerto-Cansado and prograding structures
6 ) Prospects and Leads
In the north western part of the basin, the seismic coverage permitted to delineate 12 prospective structures. The main objectives are the Lower and Middle Jurassic reservoirs.
The wells drilled in the area in the sixties were off structures as shown on the newly acquired seismic.
In the southern part of the basin, the data available from numerous shallow wells and few deep wells drilled during the sixteen in the area suggest that the same play concepts developed to the north may also exist in this part of the basin.
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Basin
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Tarfaya- Lagwira Onshore
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Basin type
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Passive margin basin
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Area
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124 821 km²
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Exploratory wells
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53
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2D Seismic/3D Seismic
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2.822,00 Km of 2D
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Source Rocks
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Lias-Dogger - Upper Cretaceous-Albian: Type II kerogen
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Reservoir Rocks
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Lower Cretaceous sandstones- Jurassic carbonate and Tertiary lenticular sandy to sand and conglomeratic beds.
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Seal Rocks
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Triassic salt, Jurassic and cretaceous marls
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