RAHMANI, ATHMANE, and SALAH HAOUCHINE, Sonatrach Exploration, Houari Boumediene University of Sciences and Technology, Algiers, Algeria

Abstract: Structural Evolution and Implication of Fractures Distribution - Ahnet Basin, Algeria

The Ahnet Basin is located on the saharan platform, in central Algeria, between the Azzene Ridge to the West and Idjerane Spur to the East.

The first exploration has started in this part in the late 1950s. Many gas fields were discovered.

The sedimentary fill, mainly Palaeozoic shales and sandstones, occur at the surface and has a thickness ranging from 4,000 to 2,000 m. The main source rocks are Silurian, Middle and Upper Devonian shales. Potential reservoirs occur in the Ordovician and Lower Devonian sandstones. For the Ordovician, gas production is related to the fractures. Recorded flow rates range between 200,000 and 250,000 cubic-meters per day. Both structural and stratigraphic traps can be expected in the future.

The structural configuration of the Ahnet basin results from three main tectonic events, a rifting phase in the Infracambrian to lower Ordovician, post-rift sedimentation from the Ordovician to the end of Palaeozoic and inversion at the late of the Carboniferous.

Numerous folds of complex geometries are created, including both basement involved and detached structures.The geometry of the anticlines results from the combined effects of both wrench and compressional motions.

The density and orientation of the natural fractures depend of the interaction between the regional stress and the direction of the Panafrican faults in the basement.

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