GEOPHYSICS LETTERS

56 Seismic study to recognize reef reservoirs.The logged velocity trace, the interval velocity and the formation densitylog plotted on a suitable time scale when overlain and spliced into aseismic section, velocity contrasts well aligned with appropriate peaksand troughs (McQuillin et ai, 1984). The acoustic impedance andinterval velocity as a seismic parameter determined from well log data(sonic and density logs), and the density (from density log) can be usedto interpret the lithology (Sheriff, 1995). ~The seismic parameters derived from the sonic and density log data, suchas the acoustic impedance, interval velocity and density can be used tointerpret the lithology and tied to the seismic sections as follows:The first step in this case study includes the calculation of the intervalvelocity from the sonic log, determine the density from density log andcalculating the corresponding acoustic impedance in the two wells-224and 252 taken as examples. The next step includes the plotting ofdensity, velocity and acoustic impedance versus depth to the two wellsas represented on Fig. (4) and (5), on the plotted curves we candifferentiate the Nullipore rock by its characteristic moderate density,velocity and acoustic impedance, which is characteristic feature toporous carbonate (which may be reefs), from the overlying high density,velocity and acoustic impedance which represent anhydrite (southGharib formation), also differentiate it from the underlying beds whichrepresent low density, velocity and acoustic impedance which representthe pre-Miocene shale, this indicate how the density, velocity andacoustic impedance parameters are used as lithologic indicator, where itis used to identify the Hammam Faraun sequence as pours carbonatewhich may be carbonate build-up(reefs).The plotted curves density, interval velocity and acoustic impedance towell-252 taken as an example in this case study, are used to recognizethe reflection events (sequences) on the seismic section. Where byoverlie or spliced these curves into the seismic Line-8, which runadjacent to well-252. The main shifts on the plotted curvescorresponding to the top and bottom of Hammam Faraun Member willbe aligned with the appropriate peaks and trough on the seismic sectionwhich represents the top and bottom reflectors of the Hammam FaraunMember on the seismic section as represented on Fig. (6).