1 ) Overview
The Souss basin covers an area of 7500 km². It is limited to the north by the High Atlas Mountains, to the south and east by Paleozoic outcrops of the northern flank of the Anti‑Atlas Chain and to the west, it extends into the Atlantic offshore area.
2 ) Data base
Exploration of onshore souss basin was conducted by different Societies from 1955 to present. About 906km of 2D seismic profiles has been acquired and 8 wells drilled.
3 ) Tectonic and sedimentary evolution
The Palaeozoic Basement of this Meso-Cenozoic basin was structured during the Hercynian orogeny. Basin evolution at the beginning of the Mesozoic was influenced by rifting, and later by drifting, related to the opening of the Atlantic. During this rifting period, the El Klea growth fault zone, oriented Northeast‑Southwest and downthrown to the northwest, was individualized. This major fault separated the basin into two parts: one subsiding to the northwest where Triassic and Jurassic deposits are very thick and the other one to the southeast where Triassic and Jurassic deposits are relatively thin. These deposits pinch out to the southeast towards the Anti‑Atlas.
During Oligocene time and in relation with the Atlasic tectonic phase, the El Klea fault was reactivited as a reverse fault (thrusting to the SE).
4 ) Petroleum system
4-1 ) Source rock
Geochemical Analysis were limited to the Mesozoic sedimentary section encontred in the wells indicates three main source rocks.
- A fair to good quality shaly Aptian to Albian source rock with maximum TOC of 1.39%, type III (pyrolysis), immature to early mature.
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A fair to good quality shaly Senonian source rock with maximum TOC of 1.3%, type III (pyrolysis) and immature.
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A good to very good quality shaly Dogger‑Liassic? Source rock with maximum TOC of 2.74%, type III (pyrolysis) and early mature.
Recent study indicates that Silurian source rocks are the main source beds in the Anti‑Atlas domain similar source beds could be present in the Souss basin, and may have generated hydrocarbons during the Jurassic. This hypothesis implies that exploration should aim at structural or stratigraphic traps formed prior to this Jurassic migration.
4-2 ) Reservoir Rocks
Many good reservoir rocks were identified in the basin in the Mesozoic formations.
The Triassic fluvial sandstones producing in Essaouira basin and their Equivalent in the Argana valley might occur good reservoir quality and in the Souss basin.
The Dogger‑Liassic sandstones (20% porosity), the Kimmeridgian carbonates (up to 16% porosity) and the cretaceous sandstones and carbonates (24% porosity) are the main Jurassic and Cretaceous reservoir rocks identified by wells. Paleozoïc reservoirs rocks could have also good reservoir qualities if they were fractured.
4-3 ) Seals
Rocks with good sealing capability occur at different levels of the basin stratigraphic column and are of different natures.
Shales and anhydritic Carbonates are the most common in Jurassic and the Cretaceous.
The Triassic salt is perfect seal for any sub salt accumulation.
4-4 ) Traps
So far, only structural traps such as hanging wall anticlines related to reverse faults were identified and tested. However recent studies carried out on the outcrops indicate the presence of stratigraphic traps due to lateral changes of facies, pinchout and traps bellow unconformities.
5 ) Play Concepts
Two plays concepts were identified in the basin:
5-1 ) Subsalt plays
They are represented by hercynian structures and Triassic faulted blocks sourced from Paleozoic source rocks.
5-2 ) Jurassic and Cretaceous plays
Structure generated by the reactivation of Mesozoic faults, stratigraphic traps sourced from Jurassic and cretaceous source rocks.
6 ) Prospects and Leads
Recent basin analysis studies have permitted to identify at least three leads:
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Basin
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Souss
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Basin type
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Rift
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Area
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7500 km².
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Exploratory wells
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9
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2D Seismic /3D Seismic
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907,00 km of 2D
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Source Rocks
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Aptian-Albian (III); Senonian (III); Dogger‑Lias (III); Silurian?
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Reservoir Rocks
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Triassic fluvial sandstones; Dogger‑Liassic sandstones; Kimmeridgian carbonates; Cretaceous sandstones and carbonates
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Seal Rocks
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Shales and anhydritic Carbonates from Jurassic and the Cretaceous and Triassic salt
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