1 ) Overview
The Guercif basin is located in the northeastern of Morocco. It is a Tertiary trough covering about 6 230 km² infilled by Triassic, Jurassic, Neogene and Quaternary deposits. Recent geological, geochemical and geophysical studies conducted in Guercif basin have defined the presence of tree petroleum systems and attractive prospects and leads from the Paleozoic to the Tertiary.
2 ) Data base
3 264 km of multi fold seismic lines have been acquired from 1968 to 2003. Four wells have been drilled: GRF-1, MSD-1, KDH-1 and TAF 1-X wells.
3 ) Tectonic and Sedimentary Evolution
3.1. Tectonic Evolution
During Triassic and Early Jurassic time, extension related to the north and central Atlantic opening created the intra-continental High and Middle Atlas troughs and produced a system of grabens and / or half grabens in these zones. The Mesozoic and Cenozoic deposits have undergone two compressional events:
An Atlasic event (Eo-Cretaceous) creating ridges and depocenters and the alpine event (post Miocene) that folded the whole Mesozoic and Cenozoic sediments.
3.2. Sedimentary Evolution
Triassic deposits are composed of fining upward sequence of conglomerates, sands and shales (TAGI), overlain by salt and basalts.
The Western part of Guercif basin is the continuity of the northeastern part of the Middle Atlas which behaved as a trough during the Jurassic time and received thick sequences of Jurassic sediments (limestone, dolomite, marls and sandstones), While the Eastern part was a platform with thin carbonate sequences.
Jurassic strata are unconformably overlain by Tertiary deposits represented by: conglomerate, sand, marls, gypsum, lignite and lacustrine limestone.
4 ) Petroleum Systems
Three petroleum systems are identified in the Guercif basin (Paleozoic, Jurassic and Tertiary Petroleum systems).
4-1 ) Source rock
Carboniferous shales are known to be potential source rocks in the area (OSD-1 well shows a good TOC values in Missour basin, and the latest discovery of gas and condensate in SBK-1 well in Talsint Area).
Domerian Inter bedded marl and limestone levels presenting TOC values of up to 8.5% in the Middle Atlas, is the main Jurassic Source Rock.
Tertiary source rocks are represented by Messinian shales with TOC values up to 2.55 % and of type II – III.
4-2 ) Reservoir Rocks
Reservoir rocks of the Paleozoic–Triassic system are represented by Carboniferous and Triassic sandstone and siltstone with a porosity ranging from 10 % to 24 %.
Potential reservoir rocks are represented also by Jurassic carbonate and sandstones (porosity varies from 6 to 20%) and also Miocene Sandy turbiditic bodies, interbeded with the marls with porosities of 13 to 30%.
4-3 ) Seals
Seals of Paleozoic and Triassic traps are represented by Triassic inter-bedded shales and salt.
Different levels of marls and shales in the Lower Jurassic, the Middle, the Upper Jurassic and the tertiary are all effective seals for the Jurassic and tertiary traps.
4-4 ) Traps
- Structural traps: Triassic faulted blocks and structures formed during the Atlasic compression.
- Stratigraphic traps: represented by reefs and lateral facies changes in the transition area between the western and the eastern part of the basin and turbiditic sands lenses represented by amplitude anomalies (Dogger and Tertiary)
5 ) Play concepts
5.1 Subsalt plays
They are represented by horsts; half grabens; roll over anticlines and faulted blocks.
5. 2 Jurassic plays
- Structural traps consist of anticlines formed during Late Middle and Early Upper Jurassic.
- Stratigraphic traps: Sand lenses (Bourached sandstones) that form interesting bright spots seen on the seismic and the likely reef build ups, are interesting traps in this area.
5. 3 Tertiary plays
Tertiary sediments deposited in the depressions and onlapping the Jurassic sequences, contain also sand bodies at various levels. Some of theses bodies are turbiditic interbeded in shale, which may source them.
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Basin
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Guercif
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Basin type
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Rift – Foreland basin
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Area
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6 230 Km²
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Exploratory wells
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4
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2D Seismic/3D Seismic
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3.291,00 Km of 2D
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Source Rocks
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Carboniferous, Jurassic and Tertiary (II-III)
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Reservoir Rocks
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Carboniferous; Triassic sandstone and siltstone; Jurassic carbonate and sandstones; and Miocene sandy turbiditic bodies.
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Seal Rocks
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Triassic inter-bedded shales and salt; marls and shales in the Lower Jurassic
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