duplication achieved between the separate runs is excellent. Not only were the 

 logs run three weeks apart, but the first log was recorded with automatic track- 

 ing techniques while manual tracking was used to record the second log. 



The second illustration, demonstrating the faithful reproduction of formation 

 characteristics, displays the type log produced in isotropic media of salt and 

 anhydrite. Constant velocity conditions are expected to exist and are so recorded 

 on the log (fig. 21-19) by the extremely smooth curves shown. The lithology is 

 apparent from the velocities recorded: anhydrite approximately 20,000 feet per 

 second and salt approximately 15,000 feet per second. Also, fidelity of recording 

 is not affected by the highly saline drilling fluid. 



The low velocity deflection shown at the top of the salt plug results from a 

 solution cavity and can be corrected by use of caliper data. In general, it is 

 found that drilling in the softer formations results in larger hole diameter. This 

 condition, therefore, occasionally produces an expected correlation between the 



VELOCITY -THOUSANDS OF FT./ SEC. 



15 20 25 



T I 1 1 1*11 11*1111 



.• :J-.H 



15 20 25 



* i i I 1*1 I IITIHI 



550' 



Figure 21-18. Velocity logs illustrating duplication in same well. 



423 



