bottom. The other indicates by a slanting stroke the completion of exactly one 

 foot drilled, or two feet if set for recording on two-foot intervals. Therefore, 

 the exact depth marked by each stroke of the pen must be known and the length 

 of time occupied in the drilling must be determined. Plate 18-1 is a geolograph 

 chart showing essential data used in making a drilling-time log. 



It is strongly recommended that the geologist using complete drilling-time 

 data keep his own pipe tally. Practices differ among contractors in keeping pipe 

 tallies, but inasmuch as the object here is to know the depth indicated by each 

 mark on the chart, the geologist's tally must show all pipe in the hole at the 

 time the mark is made. This becomes most important when changes in the 

 drilling string are made, as for coring. The tally should show first the bit, subs, 

 and drill collars in the string, followed by each joint of drill pipe added. The 

 kelly should be measured accurately and its length recorded. The geologist 

 should also observe whether it is the practice of the driller to drill the kelly down 

 or make his connections with some length up on the kelly. The geolograph 

 automatically shows when a new joint of pipe is added, and the geologist should 

 write on the chart the kelly-down depth of each connection, accurate to the 

 nearest hundredth of a foot, as shown on his pipe tally. (See connections at 

 6017.27 feet and 6048.61 feet in pi. 18-1.) 



The charts are generally changed twice a day and when received for trans- 

 lating will show the date, time of chart change, depth of beginning and end of 

 each chart, and correct depth at each connection or beginning of a round trip. 

 The depth of each mark or every fifth mark between connections should then be 

 written on the chart, as 6000 feet, 6005 feet, 6010 feet, et seq., Plate 18-1. If the 

 drillers have been very careful in throwing in the clutch at the proper time, the 

 number of marks should be identical with the number of feet drilled. Often 

 this is not the case, and observation of drilling operations and experience with 

 how such discrepancies occur will show the geologist where errors take place. 

 The most common error of this type is made by the driller in failing to throw in 

 the clutch after making a connection at exactly the same depth as when it was 

 thrown out prior to making the connection. Changes in drilling weight caused 

 by settling out of rock cuttings may cause what might be called "false drilling" 

 or the redrilling of depth without drilling a new formation. Or, if the driller 

 fails to throw in the clutch as soon as the bit reaches bottom with the same 

 weight as when it left bottom, some new hole may be drilled without being 

 recorded. (See 3676 feet in figs. 18-1, 18-2.) Errors of these kinds are readily 

 understood when one realizes that the drilling crew is most busily occupied 

 when connections are made. Often the correction for depth will be made im- 

 mediately after a connection, but the geologist must use his best judgment in 

 making all corrections so that when a depth is assigned to a mark it will be 

 correct. 



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