PRODUCTION PROBLEMS 1127 



15 to 20 miles, with various stations along the route. The material to be 

 transported was placed in a carrier tube and propelled to its destination by 

 compressed air. Where the carrier became lodged between stations, it 

 could be located by echo methods. 



In applying this method in long tubes, it was found that the velocity of 

 the wave in the tube varied with temperature, pressure, and humidity. It 

 was noted further that where the tubes turned corners in following streets, 

 and also where switch points or other partial obstructions were located, 

 minor reflections were obtained, in addition to the main reflection coming 

 from the blocked carrier. Changes in the velocity of the wave therefore 

 were minimized by applying correction factors between these partial 

 obstructions at known locations, or by measuring from the last recorded 

 partial obstruction at a known location to the blocked carrier. 



Sonic Method 



The sonic or pressure-wave method of determining depths to fluid 

 comprises: (1) a means for initiating the sound or pressure wave, (2) a 

 suitable wave detecting and recording apparatus, and (3) a constant-speed 

 recording system and/or timer. 



Efforts to obtain more reliable data than those given by the original 

 Batcheller procedure have yielded two general methods for initiating the 

 pressure wave : ( 1 ) a method employing a pressure impulse created by the 

 release of compressed gas from a small tank and (2) methods which employ 

 the pressure wave initiated by a cartridge. 



The first mentioned method was developed by Lehr and Wyatt.f The 

 wave is created by releasing a small quantity of gas under pressure in a 

 tank. The recorder attached to the casing head of the well comprises a 

 diaphragm-driven system that actuates a mirror utilized in the photographic 

 recording mechanism.! The second method creates the pressure wave by use 

 of a cartridge, and the reflections coming from the well are detected by a 

 microphone. The microphone may be of the electrodynamic type§ or a 

 thermistor grid.ff The output of the microphone is amplified about 50 

 decibels, and then fed to a direct-writing ink recorder. 



After the pressure wave has been generated, the echoes coming from 

 the well consist of those from the tul)ing collars, other partial obstructions 

 such as gas anchors, liner tops, tubing hangers, gas valves, etc., and the 

 reflection from the fluid level. As will be seen in a later paragraph, the 

 tubing collar reflections are useful in determining the velocity of wave 

 propagation, and are used in calculating the depth to the fluid. 



The tubing collar reflections generally are weak; to record them to the 



t Paul E. Lehr and H. D. Wyatt, "Method and Apparatus for Measuring Well Depths," 

 U. S. Patent 2,047,974, issued July 21, 1936. 



t C. P. Walker, "Determination of Fluid Levels in Oil Wells by the Pressure Wave Echo 

 Method," A.l.M.E. Petroleum Technologv, 1937, pp. 33-43. 



§ A. Wolf, "Acoustic Well-Depth Indicating," World Oil, Sept. 22, 1947. 

 tt J. J. Jakosky, "Bottom Hole Measurements in Pumping Wells," A.l.M.E. Petroleum Tech- 

 nology, Tech. Pub. 1058, 1939. 



