Cretaceous Reservoirs in Tunisia

Pierre F. Burollet

During the last 30 years, several oil and gas fields have been discovered in the Cretaceous Series of Tunisia. Oil shows or presently uneconomic accumulations were found in many wells. In every case the reservoir is made of carbonate, mostly dolomitic limestone.

Thick bodies of sandstone exist in the Lower Cretaceous sequences of central and southern Tunisia. Due to active hydraulic circulation and lack of coverage until now, they have produced just water--mostly fresh water.

Carbonate development is related to two main factors: (1) a latitudinal zonation grading from an internal shelf south to the open Tethys Sea on the north and (2) local structural features such as ridges, depocenter, tilted blocks, and diapirs.

The reservoir character of the carbonates is due to various factors such as grainstone structure, reefs, moldic porosity, vadose or phreatic leaching, and fracturing.

The beds with oil and gas indications are Aptian Serdj Formation; Cenomanian reef of Isis type; Turonian reefoid talus, calcarenite, and oolites; Campanian and Maestrichtian chalky Abiod Formation, either grading to rudistid reef or fractured.

Since the exploration was led mainly to structural targets, good opportunities for discovery of stratigraphic or semistratigraphic traps remain in the field.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.