Characterization of the Source Horizons Within the Late Cretaceous Transgressive Sequence of Egypt

Abstract

Source rocks were deposited in northeastern Africa during a major Late Cretaceous transgression. The stratigraphic section begins with a series of phosphorites and oil shales and progresses up into an organically lean chalk. These deposits represent increasing water depths and depositional isolation from the continental landmass. Within the source sequences of the Duwi and Dakhla formations in the eastern desert of Egypt, variations in the organic matter are recorded. Understanding the systematics of this variability and predicting the geochemical attributes of the source system away from control can be important to resource assessment. Even though a general increase in both organic richness and liquid hydrocarbon generation potential is observed from the base to the top f the source section in Egypt, no clear, predictable trends are evident. The variability observed in source quality is best explained in a sequence stratigraphic framework. In Egypt, three third order eustatic cycles can be identified. The best oil-prone source rocks occur within the condensed sections at the top of the transgressive systems tracts of the three sequences. Little to no oil-prone source potential can be identified in the highstand systems tracts, where the bulk of the organic matter exhibits gas-prone attributes.