Sedimentology and Depositional Setting of the Lower Miocene Asl/Hawara Member, October Field, Egypt
Quintin Davies1, Deborah Bliefnick1, William Sercombe2, Thomas Radford2
(1) Badley Ashton and Associates, Lincolnshire LN9 6PB, England (2) BP/Gupco (currently BP Kuwait), Kuwait City, Kuwait
A sedimentological and petrological evaluation of the Middle Miocene Asl/Hawara Member in October Field, Egypt was provided through a core-based study of several wells. The distribution of reservoir quality was assessed through the determination of depositional facies variation, the influence of tectonics and the nature of the diagenetic overprint with the aim of constructing a reservoir quality framework that would allow prediction of reservoir potential in future wells.
Deposition of the Asl/Hawara Member reflects syn-rift tectonics that dominated the Red Sea region during the Middle Miocene. Uplifted and rotated fault blocks provided sediment sources and established sediment bypass zones along cross faults and relay-ramps. Carbonates formed and accumulated on uplifted fault blocks while siliciclastic material was derived from exposed older source areas and erosion along transform faults. Two principal lithofacies were observed: carbonate-rich packstones/grainstones and quartz-rich sandstones. These lithofacies occur repeatedly as coarse-grained and fine-grained elements that reflect the evolution of a turbidity current/fan system. Both siliciclastic and carbonate lithologies were reworked and ultimately transported to topographic lows surrounding fault blocks.
Reservoir quality is controlled by a combination of primary depositional fabric and subsequent diagenetic modification. Thick, porous sandstones tend to retain their primary interparticle porosity whereas thinner interbedded sandstone and carbonate lithologies are typically extensively cemented and contain relatively isolated macropores.
Paleotopographic highs will, therefore, provide poor reservoir targets due to the lack of siliciclastic material and abundance of carbonate material. Paleotopographic lows, however, will provide the best reservoir targets due to the presence of thicker, relatively uncemented sandstone units.