572 



Subsurface Geologic Methods 



The multiple-shot machine is run in a protective nonmagnetic case 

 of bronze or duralumin. Since the instrument is 2^ inches in diameter, as 

 is the regular single shot, the survey barrel is 3| inches. The machine is 

 loaded into the top of the barrel. An upper substitute closes the barrel 

 mud-tight with an 0-ring seal. A tool-joint box is cut in the top of this 

 upper substitute. The groove in the bottom of the angle unit fits over a 

 corresponding tapered wedge in the bottom of the survey barrel. A tapered 



Figure 293. Starting multiple-shot machine; synchronizing surface 

 and instrument watches. 



hole is bored in the bottom bull plug in exact relationship to the wedge. 

 The multiple-shot machine is held in its barrel by tightening the expansion 

 head (fig. 292) . 



Magnetic surveys in open or uncased hole are run on drill pipe, sand 

 line, or conductor cable. The instrument, loaded with film and with fresh 

 batteries, is started. The watch that will be photographed in the machine 

 is synchronized with a similar surface watch (fig. 293). After the instru- 

 ment has been tightened in the barrel and the closure made, the assembly 

 is made up on the drill pipe (fig. 294). As the pipe is run into the well 

 stand by stand, the pipe is held motionless for two minutes whenever a 

 record is desired. These time intervals are noted on a field sheet so that 

 the correct pictures are read when the survey is developed. When a mag- 

 netic survey is run on sand line in open hole, two joints of tubing usually 

 are used as a sinker bar. The machine is run to bottom and readings are 



