Petrographical and petrophysical investigations of upper cretaceous sandstones of the South West Sennan field, Western Desert, Egypt

Abstract

The sandstones of the Bahariya Formation represent an important Cretaceous oil and gas reservoir in Egypt. The sandstone samples of this study originate from Abu Sennan concession in the South West Sennan (SWS) oil field that is located in the Western Desert of Egypt. The mineralogical composition for studied sandstone samples is mainly composed of detrital quartz and quartz overgrowth (69 to 82 %), kaolinite (6 to 20 %), plagioclase and microcline (2 to 9 %), and Fe-rich chlorite and framboidal pyrite (2 %). Muscovite, biotite, zircon, rutile, and apatite, as well as diagenetic calcite, are present as accessory minerals. The petrophysical properties indicate a moderate degree of diagenesis and cementation for the investigated sandstones that results in favorable reservoir conditions. We provide a detailed description of the petrophysical investigations and the resulting relationships. The magnetic susceptibility has proved to be a key parameter in evaluating porosity and permeability of the investigated sandstone samples of the SWS oil field. Obviously, Fe-rich chlorite cement that has been precipitated in the pore space control porosity, specific internal surface, and permeability. Beside the formation factor, the specific internal surface, and the imaginary part of conductivity, longitudinal and transversal relaxation times determined by nuclear magnetic resonance enable a reliable permeability prediction.