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3 <br />free-pipe travel times as seen on the log, use them. When <br />interpreting the log, a decrease in travel time (faster <br />times) with simultaneous reduction of amplitude may show a <br />de-centered tool. A 4 to 5 micro-second (us) decrease in <br />travel time corresponds to about a 35E loss of amplitude. A <br />decrease in travel time more than 4 to 5 ~ls is unacceptable. <br />PART V - LOG INTERPRETATIO:1 <br />Do not rely on the service company charts for amplitudes <br />corresponding to a good bond. These amplitudes depend on <br />many factors: type of cement used, fluid in the hole, etc. <br />To estimate bond index, choose intervals on the log that <br />correspond to of bond and 100E band. Read the amplitude <br />corresponding to l0ot ~ond from the best-bonded interval on <br />the log (NOTE: the accuracy of this amplitude reading is <br />very critical to the bond index calculations). Next, find <br />the amplitude corresponainq to of bond. Some bond logs may <br />not include a section ::t:: °ree pipe. In this instance, <br />choose the appropriate Free-pipe travel time from the <br />service company charts :or your specific tool, or from the <br />generalized chart (TABLE Z) at the end of this guidance. To <br />calculate a bond index of eoE, use the following equation: <br />A =1~ ((0. ~) log(A~) -(0.8) log(A200) l <br />80 <br />where: <br />Ago =Amplitude at 802 bond (mVj <br />Ao Amplitude at of bond (mV) <br />AlQQ Amplituae at 100E bond (mV) <br />E7(AMPLE <br />As an example, consider a bond log showing the following <br />conditions: <br />- Free pipe (OE band) amplitude at 81 mV. <br />- 100 8 bond amplitude at 1 mV. <br />Substituting the above values into the equation results in: <br />A _~O ((0.:.) 1og(91) -(0.8) lag(1) ) <br />80 <br />Ago =2 . 41mV <br />