The National Agency for the Valorization of Hydrocarbon Resources "ALNAFT"

The offshore domain

Algerian offshore geology:

From Gibraltar to the Black Sea, the Mediterranean basin is made up of a succession of basins: Western Mediterranean, Tyrrhenian, Eastern Mediterranean and Black Sea.

- The Western Mediterranean includes the Alboran Sea, the Algéro-Provencal basin, the Provençal basin, the Gulf of Valencia and the Ligurian Sea.

- The eastern Mediterranean includes the Adriatic Sea, the Jonian basin, the Herodote basin and the Levantine basin.

The Algerian offshore consists of the Alboran basin in the west, and the Algerian-Provençal basin in the Center and East.

The Algerian-Provençal basin is the western basin of the Mediterranean, it is located on the convergence zone of the African and European tectonic plates. It is formed, during the Neogene distensive phase that affected the region, of pits that descend to 3,255 m, this basin has been interpreted as a rear-arch type extension basin. Its morphology is characterized by a very narrow continental shelf and a steep slope, its sedimentary cover mainly of Mid-Plio-Quaternary Age. It rests on a substratum of variable nature and origin (volcanic or metamorphic).

Map showing the geometry of Algerian offshore basins

Map showing the geometry of Algerian offshore basins

The Algerian margin, extends from East to West, over a length of 1600 km, bordered to the South by the internal zones of the Maghrebids (ALKAPEKA) which overlap the external Tellian zones towards the South, of which it presents a strong structural heritage and a complex geodynamic history.

 The tectonic analysis resulted in an evolution in three phases:

1. 1 Syn-rift where the basin was opened in transtension from the Upper Oligocene-Aquitanian, evolving from predominantly continental sedimentation to deep marine deposits, however with volcanism.

2. Post-rift phase during which there was the development of intra-arc basins, the AlKaPeCa- Africa collision and magmatism; these series constitute a system of distal lobes

The passage of Syn-rift sequences to post-rift deposits is marked by the Langhinian transgression known by a regional MFS,

3. Inversion phase where the margin becomes active mainly from the quaternary; where Plio-Pleistocene deposits fill Messinian "carved" incisions and are dominated by deep-water turbidite deposits (channel complexes and lobe systems)

In addition to the fact that the Algerian offshore was affected by an intense tectonics generating complex geological structures, It was also affected by a geological drying episode which corresponds to the Messenian crisis due to the isolation of this basin caused by the closure of the Strait of Gibraltar.

 

Oil context of the offshore domain:

The available seismic and gravity data, as well as analysis of data from wells drilled in the region, identified the elements of the petroleum system as follows:

- The source rocks would be located in transgressive intervals of the Miocene (Langhien-Serravalien, Aquitanien-Burdigalien and Messinien) and of the Plio-Pleistocene.

- The reservoir rocks would be located in the Torto_messinian intervals with turbiditic systems

- The cover would be provided by the thick clay series of the Middle and Upper Pliocene, the Tortonian and the Serravalian.

- The traps are essentially stratigraphic