Abiod Formations, Tunisia - looks encouraging: ABIOD FORMATION
The Abiod formation of Campanian/Maastrichtian age is essentially composed of carbonates, generally, chalky limestones and it derives its name from Oued el Abiod, where the type section was described by P.F. Burollet in 1956.
It is divided into three members:
A) A lower carbonate member comprising chalky mudstone, rich in foraminifera (Globigerinidae, Globotruncanidae, and Orbitoides) also containing frequent fragments of pelecypods and echinoids. This member rarely exceeds 70 ft in thickness.
B) A middle member is an argillaceous limestone rich in benthic foraminiferous such as Pseudotextularia and Neoilabellina. It is normally of the order of 100 ft thick.
C) The upper carbonate member is the most important from the economic point of view because it often has porosities in excess of 20% and fracture permeabilities of 1-3 Darcies.
It comprises three submembers starting with a chalky limestone having rare thin argillaceous bands and a basal calcareous glauconitic sandstone. It grades into a more interbedded chalk and light gray marl which when drilled becomes a sticky amorphous mass. These two sub-units reach a combined thickness of about 230 ft.
RESERVOIR FACIES
The principal reservoir facies of the Abiod is a massive chalk with very rare green marl horizons.
It is irregularly stratified with slumps and turbidite fan deposits that enhance the porosity to good reservoir quality. The turbidities are composed of calcarenite and nodular fragments of Inoceramus, Echinoides, and rudistids frequently dolomitized and brown in color.
This member can exceed 600 ft in thickness. The upper member is overlain by the El Haria shale formation, an extensively distributed excellent seal for this carbonate reservoir.
The Abiod formation extends over most of northern and eastern Tunisia, is known to outcrop in the north and west, and is present in wells throughout the pelagian shelf from Cap Bon to the Gulf of Gabes.
It gives a clear response on the sonic velocity log but in several recent wells has not exhibited any oil or gas shows during drilling, although it has produced more than 3,000 b/d of oil under subsequent test.
Nondeposition occurred in the area of Tunisia southwest of the city of Kairouan known to paleogeographers as Kasserine Island.