500 



Subsurface Geologic Methods 



with the interpretative geologic log, make it possible to pick important 

 formations tops. The geologist is present when all cores are removed, 

 and these can, if desired, be sealed preparatory to core analysis. 



Equipment is maintained for the testing of drilling-mud character- 

 istics; tests are made as often as it is desired for weight, water loss, vis- 

 cosity, filter cake, salinity, or any other properties to insure a satisfactory 

 drilling mud. 



Figure 236. A detailed microscopic examination by a competent geologist is very 

 necessary on all exploratory wells. 



The results of all tests and examinations, as well as the drilling-time 

 record, are plotted graphically on a log having a scale of five inches to 

 one hundred feet to permit the showing of as much detail as possible. 

 The first column on the final composite log denotes the characteristics of 

 the mud at the depth each check was made, as well as symbols indicating 

 new bits and circulating and coring points. The drilling-time curve in 

 the next three columns is plotted in minutes per foot, and the horizontal 

 scale is amplified to show minor variations in the drilling rate. The center 

 two columns of the log show the depth and graphic lithologic log. To the 

 right are shown the results of oil and gas tests. Since these tests are purely 

 qualitative, an arbitrary scale of 100 percent has been established to show 

 comparative readings. Oil is shown as a solid line; the "high" gas reading 



