Jurassic-Early Cretaceous Sedimentary Patterns of a Central-Northern Portion of Western Desert Area

By

E. Tebaldi¹, P. Giaj-Via¹, A. Ortenzi¹, F. Golfetto¹, E. Trincianti¹

(1) ENI SpA-Agip Division, S. Donato Milanese (Milan), Italy

 An integrated sedimentological, biostratigraphic and rock microcharacterisation methodological approach applied in the Central-Northern portion of Western Desert, allowed to draw a litostratigraphic and genetic scheme of the Alam el Bueib, Masajid, Khatatba and, partially, Ras Qattara s.l., Jurassic to Early Cretaceous formations.

A detailed palynozonation provided the stratigraphic framework of the Hettangian-Early Aptian succession.

Regional sedimentological cross-sections, highlighting the basin-modifying tectonic activity at the top of Masajid Formation, framed the sequence stratigraphy of the area. The more detailed results have been obtained for the Alam El Bueib Formation, where four main depositional sequences bounded by unconformity surfaces have been recognised basinwide. The sequences are constituted by deltaic depositional systems showing a South (sandy entry point) to North (shaling out of some sandstone levels into shelfal deposits) progradational pattern. In some high areas (Mirach and Qattara Rim) the lower sequences are reduced or not deposited, while, toward South-East, the same pattern is shown by the uppermost sequence.

Rock microcharacterisation was performed in order to point-out the petrographic and pore network variables that determine the efficiency of the sedimentological facies. Quartz overgrowths precipitation resulted to be the main factor controlling reservoir quality, as, following the burial/thermal history, it may fill partly or completely the pore space. The pattern of quartz precipitation is thus the key issue for reservoir quality prediction.