CHAPTER 9 

 DUTIES AND REPORTS OF A SUBSURFACE GEOLOGIST 



GEORGE W. JOHNSON 



The work of a subsurface geologist as he "sits on" a well may be 

 divided into two general categories: collecting and assembling data, and 

 reporting. Such work will be rather generally described first; then 

 specific examples of field practices will be given. 



Duties of a Subsurface Geologist on an Exploratory Well 



It is common practice during exploratory drilling for a geologist to 

 "sit on" the well. His responsibilities are to assimilate and evaluate all 

 subsurface geologic and frequently engineering data during penetration. 

 These responsibilities include (1) collecting, preparing, examining, de- 

 scribing, and shipping ditch, core, gas, and fluid samples; (2) keeping 

 the log of the well up to date; (3) recommending coring, formation tests, 

 and logging surveys; (4) evaluating all oil and gas shows; (5) witnessing 

 or supervising formation tests; (6) following drilling operations in con- 

 tiguous areas; (7) selecting proper casing points; (8) forecasting possible 

 strata that may cause drilling difficulties; (9) running salinity and water- 

 loss tests on mud; (10) submitting geologic progress and summary 

 reports; and (11) cooperating with the petroleum- and production-en- 

 gineering personnel and with the subsurface laboratory. 



Well Log 



The well-site geologist is called upon to keep a current log of the well 

 at all times. All pertinent data such as lithology, cored intervals, electric 

 profile, casing records, tested and perforated intervals, hole deviation, 

 the formation-test summary, and oil and gas shows should be plotted on 

 tracing cloth, thus permitting periodic progress copies of the logs to be 

 submitted to the home office. 



Ditch Sampling 



Ditch samples should be taken at ten-foot intervals down to the 

 proximity of important markers and at five-foot or lesser intervals there- 

 after until the desired point is established. Fresh ditch samples should be 

 examined by ultraviolet light through all possible producing intervals 

 while drilling is in progress. 



There is always an interval between the time at which a formation 

 is drilled and that of the return of its fragments to the surface. This 

 time interval depends on such factors as the size, rate, and efficiency of the 

 circulation pumps, the mud viscosity, and the diameter and depth of the 

 hole. When these variables are known, the approximate time lag can be 

 calculated and adjustments of sample depth made. The adjustments can be 



