30 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



Figure 8 shows a longitudinal section of the device 

 placed in casing 6 being examined. It will be seen that the 

 central body 1 of the apparatus closes the tubular wall 2 

 into a chamber. About the central body 1 are the levers 

 4 which turn on axes 3 and carry rolling calipers 5 following 

 the borehole or casing walls. These levers 4 may have 

 any suitable form in cross section, preferably a definite 

 form at their ends 8, e.g., triangular, in order to get a sharp 

 projection image which is thrown on the frosted glass 

 10 by a dry-battery lamp 9. The levers press on the casing 

 walls by the action of springs 7, pressing them against the 

 central boss on the other side of the fulcrum axes. 



Fig. 9. 



Figure 9 shows another form of construction wherein the 

 caliper system 5 and spring 7 are arranged in another order 

 of leverage. In each case springs 11 also assist springs 7 

 in centering the apparatus in the borehole or casing. A sim- 

 ple removal device is a set of hooks 12 and draw cables 13 

 uniting into a central cable. 



Fig. 10. 



Figure 10 shows the most recent form of the device 

 produced in the laboratories of the Batavian Petroleum 

 Company (Astra Romana). Here the displacement of 

 the cahper system due to diameter variation is indicated 

 optically in a magnified image. The caliper system 5 is 

 here a piston system working in a cylindrical case and 

 pressed on to the borehole or casing walls by springs 7. 

 A source of light produces a magnified image on disc 10 



