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Article

Permeability and porosity evolution in dolomitized Upper Cretaceous pelagic limestones of Central Tunisia

NEGRA Mohamed Hédi, PURCER Bruce Harold, MRABET Ali, 1994

Special Publications of the International Association of Sedimentologists, 21, 21, 309-323, Avril 1994

Résumé

Campanian-Maastrichtian sedimentation in Tunisia is dominated by well-bedded micritic limestones rich in planktonic foraminifera. However, in Central Tunisia, notably in Wadi Abiod, lensoïd bodies of massively bedded carbonates are frequently intercalated within the chalky pelagic lime mudstones. These lenses, whose properties are both sedimentary and diagenetic, correspond mainly to conglomeratic and bioclastic bodies related to gravity flows. They are affected by dolomitization, which modified several original textures. In terms of reservoir properties, this dolomitization can be destructive or constructive.

The pelagic lime mudstones have median porosities and permeabilities which are markedly lower than those of the dolomites that have replaced them locally. Although the lower porosities in the non-dolomitized micrites could result from differential compaction, the absence of visible burial compaction fabrics suggests that the more elevated porosities in the dolomites are the consequence of dolomitization. The amelioration of permeability (0.2- 300 mD) is probably the direct result of an increase in cryst