APPLICATION OF THE VELOCITY-DEVIATION LOG IN DETERMINING PORE TYPES AND PERMEABILITY TRENDS OF NUBIA S.S FORMATION, IN RUDEIS-SIDRI AREA, GULF OF SUEZ, EGYPT

The velocity-deviation log, which is calculated by combining the sonic log with the neutron-porosity or density logs, provides a tool to obtain down hole information on the predominant pore types in sandstone rocks. This information can be used to trace the down hole distribution of diagenetic processes and to estimate the causative trends in permeability. The velocity-deviation log calculated by converting porosity-log data to a synthetic velocity log using the time-average equation for the Nubia Sandstone Formation in the area of Rudeis-Sidri, Gulf of Suez, Egypt. The differences between the real sonic log and the synthetic sonic log plotted as a velocity-deviation log. These velocity-deviation logs reflected the different rock physical signatures of the different pore types; (1) Positive velocity deviation mark zones where frame forming pore types dominate, (2) Zero deviations show intervals, where the rock lacks a rigid frame, such as interparticle or microporosity and (3) Negative deviations mark zones, in which sonic log velocities are unusually low, caused, for instance, by a cavernous bore-hole wall, fracturing, or possibly by a high content of free gas. By tracing the velocity deviations continuously down hole, the diagenetic zones are identified to varying pore types. In addition, permeability trends are observed using this method depending on the influence the pore types on the permeability of the rock.