Geodynamic evolution of the Algerian offshore and its impact on the structural framework and play types

Abstract

The Algerian offshore extends for over 1200 km from east to west and forms the margin of the Algero-Provençal basin in its eastern part and the margin of the Alboran Sea in its western part. Parallel to this margin, there is a development of the Maghrebides which corresponds to the southern section of the Alpine thrust-belt. The structural polarity of these mountain belts is outward, away from the Mediterranean (southverging). The offshore area includes two elements of the Maghrebides: the thrust belt (inner zones, Petite and Grande Kabylie), and the outer zones west of Algiers and in the far eastern part of the Algerian offshore. Analysis of magnetic maps and seismic sections shows the existence of two different structural zones. The eastern domain shows NW-SE lineaments which accommodate the south-verging thrust of the inner zones over the foreland. These lineaments also accommodate the opening of the South Balearic basin. The western domain is characterised by E-W to NE-SW trends which have allowed the westward displacement of the Alboran block during the middle Miocene. These faults are seismically active at the present time and are associated with Plio-Quaternary volcanism. This difference in structural style is interpreted to have a direct influence on the petroleum play types. In the eastern part, plays occur within the front and back thrust belts, (e.g. Oued Gueterini field). The western zone is characterized by plays associated with strike-slip basins (e.g. Cheliff Basin). The Algerian offshore belongs to the southern margin of the Algero-Provençal and Alboran Basins (Fig. 1). In spite of the existence of seismic data dating from 1969-77, no previous study enabled us to get a clear structural image integrated within the general geologic framework of the Western Mediterranean sea. The acquisition of new seismic data in the Algerian offshore has justified a new structural reinterpretation using more up to date concepts. The main objective was to define the hydrocarbon potential of this offshore area.