with caution; the difference between the nominal hole diameter, given by the 

 drill bit size, and the actual hole diameter shown by the microcaliper gives the 

 exact mud cake thickness only if the formation under consideration has not 

 caved. 



Laboratory investigations and field tests are in progress in order to select 

 more appropriate electrode spacings, whereby the influence of the mud cake on 

 the MicroLaterolog readings could be further reduced. 



New Developments 



Three paths of future development of the electric log are obviously open 

 and are being vigorously investigated at the present time. Indications are 

 very optimistic that results from these investigations will be available in the 

 near future. 



The first of these is the further development of interpretation techniques 

 of the presently available logs. This is a subject of constant study. 



The second is the combination of various tools to provide for simultaneous 

 recording. As two or more services are combined, their effectiveness will be 

 increased and their cost decreased. 



The third and possibly the most important is the trend toward focused 

 types of logs. Since the borehole, mud-invaded zone, and surrounding beds 

 cause the departure of apparent readings from true readings, focusing to elim- 

 inate the effect of these factors will definitely improve the usefulness of the log. 



During 1956, an induction-electric log combination that was introduced is 

 being widely used. It is a simultaneous recording of a short normal of 16 inches, 

 an induction log of 40-inch spacing, and an SP curve. This combination is 

 restricted to fresh muds and reads close to true formation resistivity without 

 distortions common to multiple-electrode-spaced logs. The correlation between 

 the new induction-electric log combinations and the old standard electric log 

 presents no problem inasmuch as the short normal and SP curves are common 

 to both. Identification of productive zones is much simpler with this new com- 

 bination, and it lends itself to quick and easy interpretation. 



In the future an induction-Laterolog combination is expected to give a 

 superior log in regions of medium- and high-resistivity formations for both 

 fresh and salty muds. 



USES AND The main applications of electric logging are 



INTERPRETATION OF the following: delineation of formations and 



ELECTRIC LOGS determination of their boundaries, investiga- 



tion of porosity and fluid content, investiga- 

 tions in oil-base mud and empty holes, etc. 



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