1 ) Overview
The Essaouira-Haha (producer basin) is a coastal basin of central west Morocco. The basin covers approximately 11 858 Km² on the eastern Mesozoic passive margin of the central Atlantic Ocean.
2 ) Data base
Petroleum exploration started in the basin in 1950. Up to now, the basin is covered by more than 7 079.76 Km of multifold 2D seismic. In order to better vdevelop the Gas and condensate producing fields, ONHYM acquired in late 2007, 325 Km² full fold 3D seismic survey over Meskala and Toukimt areas. Also 81 wells have been drilled of which 45 for exploration and 38 for development. This continuous drilling effort leads to the discovery of seven fields, mostly producing gas.
3 ) Tectonic and sedimentary evolution
The basin is characterized by a Paleozoic sedimentary succession witch was deformed during the Carboniferous (Hercynian orogeny). Following this tectonic event, the basin evolution was controlled by Mesozoic subsidence associated with the Triassic rifting and the opening of the Atlantic Ocean. Indeed during Triassic-Early Liassic time the basin was characterized by extensional movements with faulted and tilted blocks associated with deposition of thick sequence of red beds, saliferous formations and thick dolerite flows. During Jurassic and cretaceous sedimentation was mainly controlled by eustacy and consisted of platform carbonates, interrupted by several siliciclastic intervals. Following this, thick Jurassic and Cretaceous carbonate and anhydrites were deposited .The Mesozoic section was later deformed during the (Alpine Orogeny). This structural evolution had produced fold and enhanced salt structures generating a variety of petroleum exploration objectives.
4 ) Petroleum system
4-1 ) Hydrocarbon Occurrences
The exploration effort invested in the basin was rewarded by the discovery of seven hydrocarbon Oil and gas fields:
- Four Gas fields (Kechoula, Jeer, N’Dark) with Argovian dolomite and sandstone reservoir is and Zelten field with Triassic sandstone reservoir,
- Two gas/condensate fields: Toukimt in Argovian dolomite and Meskala in Triassic sandstones,
- One oil field Sidi Rhalem with Argovian – Rauracian dolomite reservoir.
4-2 ) Source rocks
Geochemical analysis indicates that the gas and condensate fields were sourced from Silurian and Ordovician source beds (TOC values ranging from 0, 86 to 2, 35% at the oil or wet gas window). Jurassic (Oxfordian) source rocks with TOC up to 4 % are proven having sourced the Sidi Ghalem oil field.
4-3 ) Reservoir Rocks
Three main reservoirs with average porositie over 10 % are present in the Essaouira-Haha basins: Triassic, Lower Liassic Sandstones and Oxfordian carbonates. Paleozoic potential reservoirs found in outcrops, including Ordovician, Devonian and Carboniferous could exist in the subsurface. Porosity may be enhanced by fracturing due to faulting and folding.
4-4 ) Seals
Efficient cap rock is formed by Triassic-Lower Liassic salt.
4-5 ) Traps
Traps in Essaouira basin are structural (anticlines, fault tilted horsts blocks, salt pillows), stratigraphic (sand lenses, lateral facies or porosity changes) and combined.
5 ) Play Concepts
The exploration play concepts that have been matured in the Essaouira basin are of different types:
- Paleo - Highs such as horsts, and tilted blocks with Triassic sandstones and Paleozoic sandstones and / or carbonate objectives,
- Stratigraphic or combined structural and stratigraphic traps with Lower Lias sandstone objectives,
- Salt related or Atlasic deformation related structures. Exploration will aim at Middle and Upper Jurassic carbonates on anticlines and salt pillows, or on the flanks of salt diapirs or below salt overhangs.
6 ) Prospects and leads
A number of prospects have been identified in Essaouira-Haha basin (great anticline structure associated with faulted block and tilted blocks).
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Basin
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Essaouira-Haha
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Basin type
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Rift
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Area
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11 858 km²
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Exploratory wells
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45
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Oil and Gas discoveries
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Four Gas fields, two gas/condensate fields, one oil field
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2D Seismic/3D Seismic
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7 079.76 Km of 2D / 325 Km² of 3D
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Source Rocks
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Silurian black shales and Jurassic
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Reservoir Rocks
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Triassic, Lower Liassic Sandstones, Oxfordian carbonates
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Seal Rocks
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Triassic salt, anhydrites from Malm
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Hydrocarbon type
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Thermogenic Hydrocarbons
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