pulses which are emitted approximately 20 times each second, with a frequency 

 spectrum of about 10-20 kilocycles per second. The transmitter is separated by 

 a 6-foot acoustic insulator from a single receiver which consists of a stack of 

 tourmaline crystals. Each pulse is automatically timed over the distance repre- 

 sented in the illustration by time interval t% and is recorded to form a continuous 

 log. Logging may be conducted at speeds up to 100 feet per minute. 



CABLE 



BUMPER ••■■ 



TRANSMITTER 



INSULATOR 



RECEIVER 



GEOPHONE 



Figure 21-1. Continuous velocity logger. 



The instrument is capable of continuous operation at temperatures up to 

 350F and at pressures up to 15,000 psi. Over-all length of the tool is 11 feet, 

 the outside diameter is 3% inches, and its vertical movement is controlled by a 

 standard cable and hoist truck of the type operated by Schlumberger. The nose 

 of the instrument is equipped with an adapter to which a well geophone may be 

 attached. Thus, both tools can be run in the hole simultaneously. The log is 

 ordinarily recorded on the "out run" without interruption, but may be taken 

 between shot levels of a geophone survey. 



The standard well geophone now provided for use with the Seismograph 

 Service Corporation logging operations is a development of Gulf Research and 

 Development Corporation. This well phone is a high-gain, pressure-sensitive de- 

 tector having relatively low sensitivity to movement of the cable and to other 

 vertical movements. Figures 21-2 and 21-3 are photographs of the instruments 

 and a typical velocity logging truck. 



The logging truck is shown in Figure 21-2 and a close view of the CVL 

 surface instruments as mounted in the truck for convenient operation is shown 

 in Figure 21-3. In the center of Figure 21-3 is the CVL 2-pen recorder which 



410 



