SEISMIC METHODS 



881 



Fig. 553. — Cone type rock bit. 

 (Courtesy of Hughes Tool Co.) 



fluid to clean the cutting edges of the bit, to wash the cuttings away from 

 the bottom of the hole and convey them to the surface. Where formations 

 are very hard, the cone type rock bit is used. (Fig- 

 ure 553.) 



Sizes of Drills. — Seismograph drills are 

 available in different sizes or weights. Each size 

 has advantages under different operating condi- 

 tions. Where good transportation is available, the 

 drilling is in hard formations, and a high pressure 

 is required on the cutting bit in order to secure 

 rapid and economical progress, a heavy drill is re- 

 quired. In soft formations and in swampy areas, 

 extremely light-weight drills are used. Some can 

 be carried to the drilling location by man power 

 and operated either by hand power or by light- 

 weight air-cooled gasoline engines. Such units are 

 illustrated in Figures 554, 555, and 556. These units can be disassembled 

 so that the maximum weight of any piece is approximately 100 pounds. The 

 pump illustrated is the Mayno type and the engines are 5-horsepower size, 

 with total weight of 260 pounds. 



Where larger diameter deep holes 

 are required and the additional 

 weight is no disadvantage, a size 

 ^Vi" X 6'" mud pump is preferable 

 to the 4" x S" size. 



When speed of operation is not 

 the prime consideration, portable 

 drills are well adapted to shallow 

 core drilling, seismograph shot-hole 

 and water well drilling to depths of 

 not over 300 feet. These units are 

 particularly useful in areas where 

 terrain and road conditions require 

 extreme portability. The average 

 time needed for a crew to assemble 

 a unit is about 30 minutes, and the 

 knock-down time about 20 minutes. 

 The total weight of the rig shown in 

 Figure 555 is approximately 800 

 pounds. This unit may be mounted 

 on a half -ton truck with power take- 

 off for drilling power. 



Figure 556 shows a portable drill 



Fig. 554. — Light-weight seismograph drill. •yi. f \ , • , „ j. 



(Courtesy of Geophysical Service, Inc.) With gasoline-elcctnc motor rotary 



