GEOPHYSICS LETTERS

30 Petrophysical studiesfor recognizing reefelectro-litho zones are obtained, this compression represents thelateral vBL,ationin the section, which is a characteristic feature toreefs.The caliper log, which recorded a hole size smaller than the bit size,and the log has smooth profile, is an indicator to permeability of theformation, where only permeable beds allow mud-cake build-up. Thebed opposite the deflection on the SP log is permeable, and theamount of deflection however does not indicate the amount ofpermeability (Rider, 1986).In the case study of the Nullipore section (Hammam Faran Member)in the available wells the caliper log is not on-gauge, but its readingsare smaller than the bit size with smooth profile as represented on Fig.(14), which represents some of the recorded logs in well- 252 asexample. This case indicates that the formation (Nullipore section) ispermeable. Also the SP log on the figure showing negative deflectionwhich also indicates that the section opposite deflection (Nulliporerock) is permeable.Then bulk volume water (BVW) can be taken as indicator to Igrainsize, where the bulk volume water increasing with decreasing grainsize. Also vuggy porosity has very low values for irreducible watersaturation, and then has very low values for bulk volume water. Bulkvolume water (BVW= Sw * ) calculated at several depths of theformation, when it is constant or very close to constant, this indicatethat the formation is at irreducible water saturation (Asquith andGibson, 1982).Log derived permeability formula is only valid for estimatingpermeability in formations at irreducible water saturation, amongthese formulas is the Timur formula as follows (Asquith and Gibson,1982):Where:KI\O.5=KSwirrlOO(1\2.25/Swirr)is permeability in mi1.darcy.is porosity.is irreducible water saturation.