NAHIM, M., ONAREP, Rabat, Morocco

Abstract: Exploring in the Atlantic Deep Water of Morocco-A Promising Frontier

The Moroccan Atlantic deep water is a frontier area recently opened for hydrocarbon exploration.This area is NE-SW trending Mesozoic-Cenozoic sequence which lies in water depths ranging between 200-3000 m and cover an area of approximately 100.000 sq Km. Basin development which began during the Mesozoic was largely controlled by Late Triassic to Early Jurassic rifting and subsequent opening of the Atlantic. Diapiric salt structures recognised on regional seismic lines define a Late Triassic/ Early Jurassic salt basin initiated during early rifting. With continuing subsidence and marine flooding a Jurassic carbonate platform developed in the continental shelf margin while deep water sedimentation took place in the seaward area of the shelf edge.The Jurassic sequence is followed by Cretaceous and Tertiary prograding siliciclastic systems (Fig. 1).

The structure complexity of the shelf and the slope is variable along the Atlantic Margin and like onshore, exhibits a complex structural and depositional histories. In the Tarfaya-Dakhla segment, the primary play is lower Cretaceous delta front sandstones interbedded with generaly organic rich prodelta shales on downside or upside fault closure, or rollover anticlines within the growth fault complex.This growth fault system is parallel to the continental slope for 400 Km and extends seaward 50 Km.The next concept of Exploration within this area is related to the slope anticline, which is located seaward of the zone of growth faulting. Also both stratigraphic and structural traps are identified in this segment within the Upper Cretaceous.These are related to prograding complexes deposited in lowstand system tract .

In the Tarfaya-Agadir segment the concepts of exploration are related to Lower Cretaceous deltaic sandstone, Oligocene to Miocene turbidite and salt related structure (Fig.2). The turbidites were formed in response to erosional activities from the adjacent areas. Indeed, the turbidite fan and neritic sand was sourced from the adjacent High Atlas; the sand prones are due to reworking of the Lower Cretaceous and those of carbonates content are due to the erosion of Jurassic shelf .

Considering the Agadir-Essaouira segment (Fig.2) the concepts of exploration are Aptian turbidities, roll-over structures, salt related structures, salt overhangs and salt walls traps and salt injection structures.

At the coast, north of Agadir, the pre-middle Aptian is about 550 in thick.The Seri is characterized by clastics, with a sand bar at the top of the sequence. However in the offshore area of  these segments and at least in the Agadir offshore, one can presume that very little pre-middle Aptian sediments were deposited at the vicinity of Marcan-1 well. It is possible that these Lower Cretaceous sediments were deposited and then eroded by Aptian submarine currents and redeposited in the deep sea area as a fan complex at the foot of the Jurassic escarpment. In this respect, it is interesting to realize that in site 370 of the DSDP Leg 41, 800 m of Lower Cretaceous distal turbidites were encountered. It is there fore expected that thicker and better quality proximal sandstones can be found at the base of the continental slope.

During the remainder of the Cretaceous and Tertiary and in response to the atlasic movement halokinesis of the underlying Triassic/Liassic evaporates was a major control element and hence influenced the deposition of deep water turbidites. In addition to that, the atlasic movement resulted in the formation of salt dome and salt injection structure which are another concept of exploration.

In the deep sea of Rabat-Kenitra the Mesozoic passive margin sediments and the foreland basin which extend below the Rif thrust sheets are the most promising for hydrocarbon exploration. The main concepts of exploration in this zone are the up deep Cretaceous and older stratigraphic traps beyond the Prerif accretionary wedge and salt dome related structures).

In addition to these structures, numerous stratigraphic traps in the deep water region have been identified.These are the updip Cretaceous and older stratigraphic traps beyond the Prerif accretionary wedge, the traps such as salt overhangs or traps against salt walls and those of channels and sand lenses are also common in the deep water.

The hydrocarbon potential of Moroccan Atlantic deep water is supported by the presence of sediments rich in organic matter within the Lower Jurassic shale, the Albian-Cenomano-Turonian stratigraphic intervals and also the Oligocene and Middle Miocene marine clays. Potential reservoir conditions are present in deltaic systems, shelf fed turbidites and submarine sands.

Now that major oil companies have waded into deeper and deeper water to explore, the deep water basins of Morocco will play a key role in the country's push toward a major discovery.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England