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1. Overview
The Morocco Atlantic Margin extends over more than 3000 km of the shore line, from Tangier to Lagouira. The width of its shelf is variable: up to 150 km in the areas south of Agadir while it has an average of 50 km in the north. The continental slope varies from cliff like, off the Mazagan (El Jadida) plateau to gently dipping in the Tarfaya and Dakhla segments.
2. Database
Seismic Data
More than 147 734.00 Km of 2D seismic and more than 15 413.00 Km² of 3D have been acquired.
Wells Data
The entire Atlantic Margin of Morocco is under explored in terms of drilling. Only 34 wells have been drilled since 1968. 29 wells, drilled prior to 2003, aimed principally to test Jurassic carbonate objectives in the shallow water areas of the shelf. They resulted in the discoveries of light and heavy oils at Cap Juby structure as well as oil and/or gas shows in most of the other wells. The remaining 5 wells were drilled as follows:
- 3 wells in 2004, in deep offshore to test Tertiary and Upper Cretaceous at salt related structures. Besides minor oil and/or gas shows and evidence of good source rocks intervals, these wells failed to find commercial hydrocarbon accumulations.
- One well in 2008, in deep offshore, to test the Lower Cretaceous.
- One well in 2009, to test Tertiary Bright spot anomalies. This well tested gas accumulation.
3. Tectonic and Sedimentary Evolution
The Moroccan Atlantic Margin, evolved during the Mesozoic Era, as part of the Eastern Margin of the central Atlantic. The Mesozoic and Cenozoic sedimentary pile sets uncomfortably on faulted and folded Paleozoic series.
The Paleozoic succession is outcropping onshore, with ages ranging from Precambrian to Carboniferous. The thickness exceeds 10 000 m and consists mainly of siliciclastics and carbonates.
Central Atlantic Rifting began in Triassic through Lower most Lias. Pull-apart basins were oriented NNE-SSW, following the trend of the Hercynian-Alleghanian orogenic belts. The resulting half-graben type sub-basins were filled by syn-rift sedimentation, consisting of coarse continental silico-clastics, grading upward into thick salt, due to marine incursions during Upper most Triassic and Lower most Lias. In the Jurassic, marine environments prevailed and mixed carbonate with silico-clast shelf systems started to develop. Reef buildups formed on the shelf edge as well as associated environments developed in the inner platform.
Areas with narrow shelf, constituted privileged entries of clastic sediments into the basin and therefore Jurassic carbonate sediments, in these areas, are either rare or absent. Some 700m of Jurassic sands silts and shale are preserved on Fuerventura Island, indicating that clastics were transported over the shelf and out into the deep environment.
The end of Jurassic is marked by a sea level fall and short lived sub-aerial exposure of the shelf, leading to intense karstification. Relatively rapid thermal subsidence resulted in transgression, followed by progradation of mega deltaic systems across the shelf in the Lowermost Cretaceous. Laterally westward, in the paleo-deep water, seismic shows evidences of basin floor fans development. Further to the west, Lower Cretaceous distal sandy turbidites are either exposed in outcrops on the Fuerventura Island or were penetrated by DSDP wells.
The TanTan and Boujdour fans are two of the many deltaic fans that developed on the African Atlantic Margin during the Lower Cretaceous. Yet further to the south in Mauritania and Senegal, lies two other Lower Cretaceous deltas.
Local shelf edge erosion occurred in the Aptian, during a lowstand event. In present day onshore Morocco, the seismic shows evidence of time equivalent incised valley fills and thick basin floor fans attributed to this sea level fall.
From the Albian to the Turonian time sea level rise led too much of present day western Morocco forming part of a wide shelf. Sediment supply was restricted to fine grained argillaceous sediments that were washed out of the North of Moroccan Meseta, the Atlas Gulf and the Dakhla mega canyon. Up to 2000 m of silts and shales were deposited in a wedge that passively infilled the sea bed topography, created by the Lower Cretaceous TanTan system. On the shelf a landward thick wedge of sediments was deposited, related to the transgression. The Lithology is predominantly chalk and marls and contains high concentrations of organic carbon that constitute today oil shale deposits (ex. Tarfaya). These are unconformably overlain by a progradational Upper Cretaceous unit. In the deep water the lateral equivalent unit is thought to be thin and condensed.
The base of the Tertiary is marked by an erosional unconformity. Uplift of adjacent hinterlands resulted in rejuvenation and the deposition of coarse clastics, probably of Eocene age. It is likely that the shelf areas were sub-aerially exposed and sediments had by-passed the shelf in broad river systems and were deposited directly into mini basins on the slope and the basin.
During the Upper Eocene and Lower Oligocene, gradual peneplanation led to a decrease in the energy of the system and the deposition of finer grained sediments. In the mid-Oligocene re-newed uplift, probably associated with the uplift of the Moroccan Mesetas and inversion of the Atlas Gulf, to form the Atlas mountain chain, led to tremendous influx of silico-clastic sediments that were transported westward, to form a depositional thick in the deep water area.
A second cycle of course, then fine grained clastics, have been established from the Late Oligocene to the present day. At the same time, further offshore, the Eastern Canary Ridge has been extruded, forming the Canary Islands.
During the Mesozoic and the Cenozoic times, the Pre-Cambrian and Hercynian granites as well as the Palaeozoic meta-sediments, of the fold belts, provided the main hinterland of the margin basins.
4. Petroleum Systems
4-1. Hydrocarbon Occurrences
Discovered oil accumulations, even small, as well as oil and gas shows, recorded in numerous exploratory wells, are strong proof of active petroleum systems.
Indeed, In Tarfaya offshore area, the MO-2 well tested 2,377 BOPD of 12° API from the Upper Jurassic. The oil was biodegraded due to erosion caused by the Oligocene unconformity and sub-aerial exposure of the reservoir to weathering. At the same salt cored structure, the MO-8 well discovered 38° API light oil accumulation in Middle Jurassic carbonates.
In the Agadir shallow offshore, AGM-1 well encountered traces of live oil in siltstones over 1,000 m feet interval in the Lower Cretaceous. BTS-1 well recorded 35° API oil shows in the Upper Cretaceous shale.
In the Agadir onshore, HB-1 and TGA-1 wells had shows in the Lower Cretaceous sand.
4-2. Source Rock
The organic-rich blak shales of Mid-Cretaceous age (Albian to Cenomanian), With TOCs up to 19%, are cropping out along the coast line from TanTan to Layoune in the south as well as at the vicinity of Tangier in the North. They were also encountered in Amber-1 and RAK-1 wells in deep Agadir offshore, in 51A-1 well drilled offshore of Dakhla and in DSDP sites 137,138,369,370/416,398 in the eastern side of the Central and North Atlantic. These records confirm the widespread deposition of organic rich shale at this time. Site 369 had Apian-Albian marls with TOC of 1-9% and site 370 up to 3%. Marcan-1 Well, offshore of Agadir city had over 1,000 meters of Albian shales with TOC up to 2.5% and 57% of type II kerogen, 25% type I/II and 18% type III.
Deeper in the stratigraphic section, Lower Oxfordian marls, with an average TOC of 4,5%, are proven to be the source rocks of the Sidi Rhalem oil field in onshore Morocco. They should be present in the offshore and have likely sourced the Cap Juby heavy oil discovery.
The Lower Jurassic, Toarcian source rocks with TOC up to 8%, reported in DSDP-547 and at the Canary Islands (Fuerteventura) outcrops, could have sourced the offshore Cap Juby light oil discovery as well as the oil shows encountered in Guettata wells in the onshore of Essaouira Basin.
4-3. Reservoir Rock
Several silicoclastic or carbonate reservoir intervals have been penetrated in onshore and offshore exploratory bore holes as well as in DSDP wells. Furthermore the coeval stratigraphic unit of these reservoir intervals has been identified at outcrops.
- Tertiary reservoirs :
The Tertiary silicoclastic reservoirs developed, due the rapid uplifts and erosions that the High and Anti Atlas Mountains underwent during the Eocene, the Oligocene and Miocene. Tertiary outcrops, even though rare and thin, consist of fluvial polygenic conglomerate sandstones and shale. The absence of thick Tertiary foreland basins onshore, suggests that these clastics, shed from the Paleozoic hinterland, were transported into offshore areas. Tertiary age turbidities, outcropping in the Canary Islands, support the concept. It is worth noting that the seaward distribution of Tertiary clastics was strongly dependent upon the salt controlled topography.
- Upper Cretaceous Reservoirs
Tow reservoir intervals of Coniacian and Maastrichtian age are well documented from surface geology. They crop out at the western High Atlas fold belt and they consist of shallow marine clean medium to fine grained sandstone. In RAK-1 well, drilled in deep offshore of Agadir, a total of 19 individual thin sand beds were interpreted from log, 5 of which are confirmed by side wall sections. These five SWS samples are generally clean to partly shaly, well sorted, upper very fine to lower fine sand, mostly disaggregated, with minor quartz cement. The average thickness is 1.5 m, but varies from 4.1 m to 0.3 m and their porosity varies from 14 to 29%.13 thin beds totaling 22.6 m with a N/G ratio of 12.5%.
- Lower Cretaceous Reservoirs
The Lower Cretaceous Reservoirs include the stratigraphic interval from Base Berriasian or Top Jurassic to Top Barremian. Stratigraphic units which are stacking patterns of fluvial to deltaic depositional facies in outcrops (red beds along the basin margin) and wells (Tan Tan and Boujdour deltas), are striking evidence of relative sea-level low-stands during the Lower Cretaceous. These low stand events were responsible for by-pass delivery of sands past the shelf edge and into the deepwater slope to base-of-slope areas, as reported in the DSDP wells and documented from the Fuerteventura (Canary Islands) outcrops. The reservoirs are believed to be low Stand deepwater turbidites sands sourced from the Hercynian massifs via widespread Lower Cretaceous fluvio-deltaic system.
- Jurassic Reservoirs
The Jurassic Reservoirs are expected to be Low Stand deepwater turbidites sands sourced from the shelf. Potential reservoir of Lower to Middle Jurassic alluvial and fluvial facies were identified at the outcrops and encountered in the Essaouira basin onshore wells. Westwards, turbidites of the same age crop out at Fuerteventura in the Canary Islands.
4-4. Seals
Each of the reservoirs intervals mentioned earlier is overlain by a sealing shale unit. The Triassic allochthonous salt, capes the Lower Cretaceous sub-salt traps. Also, the thick and widespread shale intervals of the Upper Cretaceous and the Tertiary are considered perfect and regional seals for all the underlying reservoirs.
4-5. Traps
Because of the presence of mobile Triassic salt, traps are generally salt related and of various types. The most representative are: 4-way closures highly faulted salt pillows and domes, Diapir-flank, embayment structures and combined structural and stratigraphic.
5. Play Concepts
Recent geological and seismic evaluation of the different Morocco Atlantic Margin segments led to identification of six main play concepts.
- Tertiary Play concept
The Tertiary Play Concept is workable in the entire basin and most likely inboard, Tertiary coarse sediments feed by incised slope canyon sands of Lower Tertiary, and were trapped by salt walls, to provide reservoir rocks to that would be charged from either mature Cenomanian-Turonian, or Lower Cretaceous (Apto-Albian) or Jurassic intervals (Oxfordian and Toarcian). Seals consist of Upper Cretaceous and Tertiary shale. Traps are mainly combined stratigraphic and structural.
- Upper Cretaceous Play Concept
This play concept is also workable in the entire basin and most likely inboard, where Upper Cretaceous and Tertiary sediments were trapped by salt walls to provide coarse Upper Cretaceous reservoir rocks and enough over burden to mature the Cenomanian-Turonian source rocks.
Reservoirs are Highstand siliciclastics of U. Cretaceous (Coniacian and Maastrichtian) age. Source Rocks are Upper Cretaceous (Cenomanian-Turonian black shale), Lower Cretaceous (Apto-Albian) and Jurassic intervals (Oxfordian and Toarcian) and Seals consist of U. Cretaceous Tertiary shale. Traps are stratigraphic (ponded sand in mini basins) and salt-related structures.
- Lower Cretaceous Play Concept
The targets of this play concept are located at rational depths in the upper and middle slope domains. Reservoirs are lowstand deepwater sandstone turbidites derived from the Paleozoic massifs. Source Rocks are considered to be the Lower Cretaceous Aptian-Albian shale as well as the Jurassic Oxfordian and Toarcian shale intervals. Seals are provided by Aptian to younger shale intervals. Traps are stratigraphic and structural.
- Subsalt Play Concept
This type of play does occur in the areas where the mobile salt had developed tongs, canopies and detached salt sheets. Reservoir intervals consist of lowstand deepwater sandstone turbidites. Source Rocks are considered to be the Aptian-Albian shale as well as the Oxfordian and Toarcian shale intervals. Seals are provided by allochthonous salt. Traps are stratigraphic and primarily salt-induced structures.
- Jurassic Play Concept
This play is targeted along the Jurassic shelf edge and the present upper slope domain. Reservoir intervals are expected to be formed by Lower and Middle Jurassic lowstand deepwater sandstone turbidites. Source Rocks are Jurassic or older shale intervals. Seals are insured by Cretaceous shale intervals. Traps are structural fault rotated blocs and stratigraphic reef buildups.
- Triassic/Palaeozoic Play Concept
The Triassic/Palaeozoic play is accessible mainly in the shelf. Reservoir intervals are expected to be Triassic red beds as well as fractured Palaeozoic quartzitic sandstones and carbonates. Source Rocks consist of Silurian to Devonian hot shale intervals. Seals are formed by Triassic salt and Jurassic anhydrite. Traps are anticlines and fault rotated blocs.
6. Prospects and Leads
Numerous prospects and leads, with large resource potential, have been identified in Atlantic offshore of Morocco, based on 2D and 3D seismic data.
7. Production History
MO-2 well test produced 2,377 BBOD of 12° API heavy oil, and MO-8 tested 34° API light oil.
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