Subsurface Logging Methods 503 



20. What advantages does induction logging have over electric logging? 



21. The radioactive log involves the gamma and neutron curve. Upon 

 what principles are these curves based? 



22. What rock types are most radioactive? Which are least radioactive? 



23. Why is the neutron curve sometimes referred to as the "hydrogen 



" o 



curve : 



24. Which radioactive curve is used for defining probable porous zones 

 in a well section? 



25. What are the applications of the radioactive well log? 



26. Carefully study figure 203 which shows the response of radioactivity 

 and electric logs in usual formations. 



27. What does the caliper-log profile show, and for what purpose is it 

 used? 



28. For what purposes are thermal surveys of drill holes made? 



29. The cooling or warming of a drilling mud at any given depth depends 

 on what factors? 



30. Why it is necessary to circulate the drilling fluid before running a 

 temperature survey? 



31. How long should the drilling fluid remain stationary before a temper- 

 ature survey is made? 



32. In the section "Well Logging by Drilling — Mud and Cutting Analy- 

 sis," the term "sand or lime-index curve" is used. What is the value 

 of these curves? 



33. Periodic testing of drilling-mud qualities is required for successful 

 completion of a well. Why? 



34. What size sample is used in the spectrochemical logging method? 



35. What is the standard method of graphically representing spectro- 

 chemical data? 



36. What is meant by "drill-time logging"? 



37. Study figure 218 which correlates the electrical profile with the pene- 

 tration-rate log. 



38. What are the applications of a drill-time log? 



39. How are drill-time logs prepared? 



40. What factors control penetration rate? 



41. Compare the relationship of the driller's log to other log data given 

 in figure 221. 



42. Upon what principle is composite-cuttings-analysis logging based? 



