$£*^ 14 



ELECTRIC 

 LOGGING 



Maurice P. Tixier 



Electric logging is one of the important branches of well logging. Essen- 

 tially, it consists in recording the resistivities of the subsurface formations and 

 the spontaneous potentials generated in the boreholes. Electric logging was pre- 

 sented to the oil industry more than 20 years ago and has been accepted as one 

 of the most efficient tools in the search for and the production of oil and gas. 



FUNDAMENTALS OF With electric logging, the corresponding 



ELECTRIC LOGGING parameters are measured in situ by means of 



appropriate bottom-hole instruments and are 

 recorded continuously at the surface. The measurements are performed only in 

 the uncased portions of the boreholes. 



It has become general practice, when a hole has been drilled or at intervals 

 during the drilling, to run an electrical survey for the purpose of quickly securing 

 a complete record of the formations penetrated. This recording is of immediate 

 value for the geological correlation of the strata and also for the detection and 

 evaluation of possible productive horizons. 



In addition to the spontaneous potential curve, several different kinds of 

 resistivity curves or logs now can be recorded in the boreholes. These logs are 

 obtained by the use of different resistivity measuring devices and are designated 

 as conventional logs (normal and lateral), Laterolog, Induction log, MicroLog, 

 etc. 



An example of a conventional electric log is given in Figure 14-1. 



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