1128 



EXPLORATION GEOPHYSICS 



depth of fluid in deep wells requires either (1) careful tuning of the 

 equipment or (2) high amplification. In one type of equipmentf this may- 

 be accompHshed by setting up a condition of resonance between the collar 

 echoes coming out of the well and an oscillation that takes place in the 

 tuning pipe between the recording instrument and the casing head. The 

 tuning pipe is adjusted to resonance by changing its length in small incre- 

 ments until maximum tubing collar response is obtained. Usually the 

 optimum frequency of the pipe will be the third harmonic of the tubing 

 collar reflections. This is a "cut and try" procedure. 



Fig. 700. — Reflectogram equipment for determining depth to fluid level. (Left) Direct-writing 

 ink recorder. A, 35 mm. recording paper; B, ink stylus; C, amplification control; D, frequency 

 response switch; E, sprocket feed for paper. (Right') Casing-head unit connected to well. F, micro- 

 phone chamber, connected by cable, G, to the recorder mounted in a field car; H, gun for creating 

 sound wave; /, gas line; J, oil line; K, microphone surge chamber. (Courtesy of International 

 Geophysics Company.) 



A second method for obtaining the tubing collar reflections:!: utilizes 

 much greater audio amplification of the incoming signal, followed by 

 filtering to remove the higher frequencies. Since filters are always respon- 

 sive to the harmonics as well as the fundamental frequency to which they 

 are adjusted, the recorded trace contains harmonics that often prove to be 

 sources of error when an attempt is made to count the tubing collar 

 reflections. 



A third method utilizes a tuned recording pen or galvanometer§ which 

 has been adjusted to cover the general frequency range of the incoming 

 tubing collar reflections. This tuned recorder reproduces the tubing-collar 

 frequencies and effectively suppresses the higher frequencies and well 

 noises, thereby eliminating the source of error commonly present if the 



t C. p. Walker, "Means for Measuring the Location of Obstructions in Wells," U. S. Patent 

 2,156,519, issued May 2, 1939. 



C. P. Walker, "Pressure Wave Velocity Measuring System," U. S. Patent 2,190,141, issued 

 Feb. 13, 1940. 



t A. Wolf, loc. cit. 



§ J. J. Jakosky, patents pending. 



