ESCHARD, REMI, and GUY DESAUBLIAUX, Institut Francais du Petrole; RUEIL MALMAISON, France; DJAMEL BEKKOUCHE and AICHA HAMEL, Sonatrach,Algeria

Abstract: Stratigraphic Architecture Of The Triassic Series In The Saharan Province, Algeria

The Triassic reservoir is one of the most productive reservoirs in Algeria. Reservoirs were deposited in fluvial and evaporitic environments with complex depositional processes controlled by tectonism. A basin-scale regional synthesis has been performed to better understand the stratigraphic architecture of the Triassic series (using new palynological datings, 130 wells with good core control, and outcrop studies).

In the Saharan province, Upper Triassic series are directly onlapping the erosional Hercynian unconformity, with fluvial valleys incising into older Paleozoic series. During Carnian times, an extensional phase induced the formation of large North-South horsts and grabens. In the Illizi-Berkine graben, alluvial fans were associated to the main border faults, and interfingered with floodplain deposits towards the graben axis. Further down shallow marine and lagoonal dolomites were deposited during transgressive events. In the Oued Mya graben, braided and sandy anastomosed channels formed extensive sand sheets, alternated with mud-rich floodplain units. During Norian times, fault activity decreased, and a thermal subsidence regime caused a general tilt of the whole province northwards, associated with a backstepping of the fluvial system; horsts were progressively onlapped, and an evaporitic basin was initiated in the North (braided deltas interfingered with sabkha deposits).

Petrographical and petrophysical studies, combined with this sequence stratigraphic analysis, led to a better characterization of reservoirs (with eight depositional sequences identified and dated, and their internal stratigraphic architecture charaterized).

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