1 ) Overview
The Tadla-Haouz Basin covers an exploration area of about 22 453 km² in central Morocco between the main cities of Marrakech, Beni Mellal and Khouribga. It is an intracratonic exploration area.
2 ) Data base
A total of 2 906 Km of seismic lines was acquired out from 1960 to 1999 and 4 exploratory wells (KMS-1, DRZ-1, KAT-1 and KAT-2) and 20 core drills (BJ -101 to 118 and TAN-101) were drilled. All wells and core drills are located in the north of the basin.
3 ) Tectonic and Sedimentary Evolution
3-1 ) Tectonic Evolution
Three main tectonic events affected the Tadla basin:
- The Hercynian orogeny started by the end of Devonian and has deformed the Paleozoic series.
- The Jurassic-Triassic rifting phase, created the High Atlas trough along the southern limit of the Tadla Basin.
- The Atlasic tectonic event, occurred during the late Cretaceous and Tertiary resulted in folding and thrusting.
3-2 ) Sedimentary Evolution
The Paleozoic section, from Lower Cambrian to Permian, is represented by sands, shales glacio-marine deposits, organic rich graptolitic shale, carbonates and deep water turbiditic facies. During Triassic most of the Tadla-Haouz area was emergent except the southern part of the basin with fluvial to shallow marine sediments followed by wide spread salt intercalated by basalts.
During Jurassic time, most of the Tadla-Haouz basin was emerged until the marine transgression occurred during Cenomanian with mainly carbonate, marls, anhydrates and red-brown shales sedimentation.
The Eocene Sedimentation is lagoonal phosphatic marls passing into wide spread marine limestones and organic-rich marls.
4 ) Petroleum system
4-1 ) Source rocks
The Silurian black graptolitic hot shales represent the most important source rocks with TOC analysis of both outcrop and well samples gave values ranging from 0.9 to 12.5%. Maturity is ranging from mature to overmature. Similar black graptolic shales exist in the lower Devonian and Ordovician with TOC values up to 5.7% and 6% respectively.
Other source rocks with TOC values up to 6.5% have been identified in the Visean with 1.5% average TOC values.
The cretaceous contain also very organic rich up to 14.75% but immature source intervals. However additional overburden provided by the over-thrusting front of the Atlas, may contribute to the maturation of these source rocks.
4-2 ) Reservoir Rocks
Upper Ordovician shallow marine sandstone, Carboniferous sandstone, conglomerate, turbiditic sands, platform reefal limestone and Permian sandstones are the main paleozoic reservoirs rocks.
The basal Triassic sandstone (over 10% porosity) and the Dogger sandstone (over 10% porosity) are the main Mesozoic reservoir rocks.
4-3 ) Traps
- Large anticline which formed during the early stages of the Hercynian tectonic event
- Triassic Horsts and hinges of tilted blocs
4-4 ) Seals
Efficient seal with different ages have been proven by drilling. Cap rocks are present in the Paleozoic as Ordovician, Silurian, Devonian and Carboniferous shales. Meso-cenozoic cap rocks are represented by Triassic red shales, salt, Dogger shales and Cretaceous shales and marls.
5 ) Play Concepts
Two play concepts were developed in the basin:
The Paleozoic play concepts with Paleozoic source rocks described previously.
The source rocks. The oil seep, reported from the site of Ait Adel Dam, is a good evidence of the presence of maturation. Mesozoic Play concepts identified in the south of the basin and separated from the first one by salt and shales with mainly Cretaceous
6 ) Prospects
The recent interpretation of the reconnaissance seismic grid (although very loose) allowed identification of four-type play concepts aiming at different levels of the stratigraphic section. Most of them are in subthrust setting located at the northern front of the Central Atlas fold belt.
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Basin
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Tadla – Haouz Basin
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Basin type
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Triassic Rift – Paleozoic basin
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Area
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22 453 km²
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Exploratory wells
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4
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2D Seismic/3D Seismic
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2.905,30 Km of 2D / 60,00 Km² of 3D
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Source Rocks
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Silurian black graptolitic hot shales and the black graptolic shales that exists in the lower Devonian and Ordovician; the Visean; the Cretaceous formations
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Reservoir Rocks
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Upper Ordovician shallow marine sandstone, Carboniferous sandstone, conglomerate, turbiditic sands, platform reefal limestone and Permian sandstones; the basal Triassic sandstone; the Dogger sandstone
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Seal Rocks
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Ordovician, Silurian, Devonian and Carboniferous shales; Triassic red shales, salt, Dogger shale and Cretaceous shales and marls.
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