Sometimes it is important to ascertain the actual depth from which a 

 sample comes, as, for example, when a show of oil is observed. In this case 

 the bit is lifted slightly off bottom, but rotation of the drill pipe and circulation 

 of the drilling mud are continued. Cuttings already in the mud column are 

 thus brought to the surface though no additional hole is cut. The last chips to 

 reach the surface are from the bottom of the hole. When the bit is again lowered 

 and drilling resumed, the first chips to come over the top are from the circulated 

 depth and slightly below. Samples marked "Cir. 30 min." or "Cir. 1 hr." refer 

 to the process just described. 



When a bit is to be replaced, it is necessary to shut down the mud pumps 

 and pull the drill pipe out of the hole. This procedure may require several hours. 

 A new bit is attached, and the drill pipe is made up and run back into the hole. 

 The process is called making a trip. When making a trip, and for some time 

 after one is made, there may be an excessive amount of caving into the hole. 

 Therefore, it is to the advantage of the microscopist, when drilling records are 

 available, to indicate on the log strip where trips were made so that he will 

 be prepared in advance for extraneous materials in the samples. 



Cable-Tool Cuttings 



A cable-tool string consists of a cylindrical bit with a chisel-like cutting 

 end, a sliding steel linkage called jars, a drill stem somewhat smaller in diameter 

 than the bit and several feet long, and a steel wire rope or drill line from which 

 the entire assemblage is suspended. The other end of the drilling line is attached 

 to a heavy walking beam on the drilling rig. This beam rocks up and down 

 when power is applied, and in so doing lifts the tool string up several feet and 

 then allows it to fall back to the bottom of the hole, where the chisel end of the 

 bit chips away the solid rock. A slight torque taken in the drilling line causes the 

 bit to rotate slowly with each stroke of the tool string. 



Cuttings are removed with a bailer, which is a steel pipe from 10 to 30 feet 

 long. A gravity-operated valve at the bottom opens or closes according to the 

 driller's manipulation of the suspending line. 



Before drilling is begun, a bailer of water is lowered and dumped into the 

 well. The bit is then run in, and the churning operation just described is begun. 

 When several feet of new hole have been cut and the softer portions of the 

 formations have made a thin mud, the bailer is again run into the hole to re- 

 move the mud and drilled chips. A portion of the mud is caught at the surface 

 in a sample box or bucket, the cuttings are recovered, washed and dried, and 

 placed in bags numbered with appropriate depths. 



Cable-tool cuttings are usually much finer than the samples from rotary 

 holes. Even if large pieces are chipped out by the bit, the repeated churning 

 continues to break them into finer particles. 



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