396 E. A. POLYAKOV 



resistivity-meter coefficient changes only by 6 per cent ^vhich is quile 

 acceptable. 



Investigations of the prototypes of the REU-57 and RSE-3-57 resis- 

 tivity-meters in bore holes have given good results, the specific resistance 

 of the drilling fluid being accurately determined, the walls not affecting: 

 the instrumental readings and the instruments staying clean and unconta- 

 minated by the drilling fluid or grease. Thus the REU-57 and RSE-3-5T 

 resistivity-meters can be recommended for serial reproduction. 



CONCLUSIONS 



(1) The existing resistivity -meters have an inconstant coefficient, which 

 causes errors in the residts of measurements. 



(2) The causes of alterations of the resistivity -meter coefficient K are: 



(a) Mutual displacement of constituent parts of the resistivity -meter and 

 changes in the size of the probe. 



(b) The influence of the surroundings. 



(c) Rearrangements of the electric field owing to changes in the fluids- 

 salinity, since the contact resistance of the metallic parts of the resis- 

 tivity-meter has no direct relationship to the resistance of the fluid. 



(3) In order to achieve a constant resistivity-meter coefficient its elec- 

 trode arrangeinent must have the electrodes A and M near to each other 

 (the electrode M is placed on the current electrode), while the electrode N 

 must enclose the electrodes A and M and must have a three-dimensional 

 shape. 



(4) Based on the electrode arrangement described two bore-hole resis- 

 tivity-meters REU-57 and RSE-3-57 have been constructed. These achieve 

 an accurate deterinination of the specific resistance of drilling fluid. 



