1068 



EXPLORATION GEOPHYSICS 



When circulation is being lost, the mud taken by the formation is con- 

 tinually being replaced in the hole by the mud pumps. The temperatures 

 measured in the hole down to the point of lost circulation would tend to 

 be markedly cooler than the equilibrium temperature of the formations. 

 Below the point of lost circulation, the mud will have been stagnant in 

 the hole for some time, and will be practically at the natural formation 

 temperatures. A noticeable discontinuity in temperature will thus be 

 observed at that depth. 



Power Supply for Logging Operations 



The characteristics and capacity of the power supply are dependent 

 upon the type of recording and measuring equipment. When direct current, 

 usually periodically reversed by a suitable commutator device, is employed 

 for energizing the ground, the power supply may be a bank of storage 

 batteries or heavy duty dry cells. Such battery supply is usually employed 



with the mechanical type film 

 feed. This type of feed utilizes 

 a measuring sheave wheel 

 mechanically connected to the 

 lilm drive mechanism. 



When the energizing cur- 

 rent is alternating or when the 

 power must be transformed to 

 different potentials, as for sup- 

 plying the plate current in am- 

 plifying tubes or oscillators, 

 some form of alternating 

 current power supply is most 

 desirable. Alternating current 

 is also required if the inter- 

 locking synchronous motor 

 system is employed between 

 the measuring sheave wheel 

 and the film drive. The alter- 

 nating current for these pur- 

 poses may be supplied by one 

 of two convenient methods. 

 The first method utilizes a 

 bank of storage batteries, 

 usually 200 ampere-hours and 

 32 volts, which supply direct 

 current to a suitable rotary 

 converter. The output of the converter is usually 110 volts at 60 cycles, 

 which may then be transformed to any desired potential. The storage bat- 

 teries are charged by rotating or vacuum rectifier equipment whenever the 



Fig. 663. — ONAN gasoline-driven alternating current 

 power supply, a, storage batteries for starting; b, 

 alternator; c, control panel and relays; d, two-cycle 

 gasoline engine; e, demountable muffler; /, exhaust 

 line; g, air cleaner; h, carburetor. (Courtesy of John 

 C. Stick, Jr.) 



