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<br /> ~ <br />DIY Yfll~ u I J V~I~ II I I~I~ <br />IIII u, <br />II 111V I ~ l.. ~~~ ~ , u I I ii!~~ ~ dE II ~ ~ii~V Ifi~,i , ~ ~ uI~~I~VI d~~ ,~ ~~~ ~~I ~ ~ I <br />A FCCLEAR WELL LOGGING I6I <br />U is the volumetric photoelectric cross-section de(tned by: <br />U = P.Pn (3.5) <br />it is used in crossplots (ef. Chapter 8). <br />The Litho-Density log thus provides a way ofdirectly determining the lithology because <br />P, is a(Tected only very slightly by porosity variations and fluid-content variations. <br />A plot of P~ versus the ratio Th/K can be made in order to characterize the clay as shown <br />on the chart in Fig. 4.7. <br />am <br />'e <br />~m <br /> <br /> uwco.n] <br /> e~o.~rt c,.o.me <br /> <br />ica <br /> i ~ ~ <br /> ~ ~ ~i <br />i o~. I <br /> I i C <br /> <br />uos... <br />~ 1 <br /> i <br />- ~ u scavm <br />IW <br /> ~ .a+~.o.~~.o.m <br /> i <br />~ <br />i +.n <br />L <br />oao <br />I ~ <br />] ) 6 ~ ] ~ ~ ~0 )0 l0 00 ip0 <br />Th/N <br />Fig. 3.7. -Plot P, versus ThfK. <br />(ScGG~mberger document) <br />4.4. NEUTRON LOGS <br />Neutrons are electrically neutral particles having a mass that is almost identical to that <br />of hydrogen nuclei. <br />Fast neutrons (having high energy) are emitted either by special radioactive sources or <br />by particle accelerators. In both cases the Fast neutrons are slowed down by colliding with <br />i the nuclei of atoms, among which the most elTective are hydrogen nuclei. The slow <br />~ neutrons thus formed are then"captured" by atoms with emission ofcapture gamma rays. <br />