Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Geology

Petrological and clay mineralogical investigations have been conducted to study the origin and distribution of clay minerals as well as the diagenetic alterations in the Jurassic lower safa reservoir bearing sandstones of the obaiyed gas/condensate field, north western desert of Egypt. Core samples selected from seven wells were qualitatively and semi-quantitatively examined using the petrographic microscope, X - ray diffraction (XRD) analysis and scanning electron microscope (SEM) equipped with backscatter (BSE) and energy- dispersive X - ray (EDX) capabilities. Several clay minerals of both detrital and diagenetic origin have been identified in the study sandstones. Both kaolinite and illite are the most dominant clay minerals recorded, followed by dickite and irregular mixed - layer illite/smectite. Smectite, chlorite, irregular mixed - layer chlorite/smectite, and regular mixed - layer illite/ chlorite were also recorded in some samples in trace amounts. The detrital clay minerals are interpreted to be incorporated into the study sandstones by several ways including mud lithoclasts, mud matrix, clay coatings, and biogenic pellets

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