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- TILE C:1.111IA RAY AND SPECTRAL G,11111A RA1' LOCS - <br />It is considered that in logging potassium salts the <br />percentage of K,O can be estimated from the gamma ray <br />response. Thus, for a 6.25 inch, liquid-filled hole, <br />Edwards et a!. (1967) found a correlation of 12.6 API <br />units per 1% K,O. Obviously, [he logs must always be <br />calibrated before making generalizations of [his kind. <br />T <br />D <br />E <br />n <br />0 <br />25 <br />60 <br />•+® <br />rn <br />Figure 7.18 Glauconite causing radioactiviry in a sandstone <br />interval. Silty sands envelop this marine, Glauconite-rich sand <br />giving the sands higher gamma ray log values than the shales. <br />An oil flow confirms the reservoir characteristics. DST = Drill <br />Stem Test. •Glauconite. <br />7300'- <br />SANDS AND SILTS <br />(with heavy mineral <br />placers) <br />7500' <br />7600' <br />Ira nsgre ssive horizon <br />tidal channal <br />tida/~l/flat _ <br />/ coarsening-up <br />cycles <br />/' <br />Z_ <br />C7 <br />~ x <br />w <br />J <br />I 4 <br />U 0 <br />V <br />w <br />m <br />3 <br />O x <br />J w <br />J J <br />a a <br />2 ~ <br />N ~ <br />I U <br />2 Z <br />U <br />w Q <br />m ~ <br />Y ra dioaclive placer deposits _. <br />Sands ~~ _ Shales and Sills <br />~. <br />Figure 7.19 Heavy mineral concentrations (placer deposits) causing a spiAy gamma my log. Shales have lower gamma ray values <br />than the heavy mineral deposits (Nigeria). (Re-drawn From Serta, 1974). <br />GAMMA RAY API <br />}560 <br />E <br />zauo <br />za+p <br />UR RNIUM ppm <br />0 5 10 <br />•` <br />.\ <br />~\ <br />•1 <br />~~. <br />i\ <br />.` <br />i <br />.= <br />.\ <br />.~ <br />ti <br />I~~ vaaose sih .nn E~sperseE orga nic <br />J malt el an0 early q~d qe nelK pno5p na le <br />--•-~ srylnln es <br />Figure 7.20 Radioactivity of Ypresian (Eocene) Limestones, <br />Tunisia, related to uranium concenvations. The uranium is <br />associated with early diaeenesis, organic matter and phos- <br />phatic concentrations. (Re-drawn from Hassan, 1973). <br />135 <br />i <br />01 <br />.~ <br />°o ............. .... <br />