THE METHOD OF CURVED ELECTRICAL PROBES 



237 



-area. The plane-table grid also had the outlmes of the road, diagnostic orien- 

 tation features, trigonometrical points situated within the limits of visibil- 

 ity, etc. 



At the edges, the plane table grids overlapped by not more than 2 points, 

 with a spacing of over 1000 m. 



The profiles were connected in accordance with the "Directions for ge- 

 odesical work in geophysical surveys in the petroleum industry". 



The centres of the azimuthal probes were placed directly on the road. 

 The generator group was placed near the probe centre. To obtain the left 

 branches of the KS curves, an AMNB arrangement was used with feed 

 electrodes placed along the road, and also in quadrilateral arrangemenf. 

 Measurements with the AMNB arrangement were set up to half-spacing of 

 the feed electrodes equal to 200-600 m, and were usually carried out with 

 an electrical prospecting potentiometer. The quadrilateral measurements 

 (under favourable conditions) were made in the range of working distances 

 from 200 to 1000 m. 



Measurements with the azimuthal arrangement were commenced with 

 a distance between the centres of the feed and measuring lines of 500-1000 m. 

 When transferring from the AMNB arrangement to the quadrilateral or 

 azimuthal arrangements, the measurements were repeated at 1-2 points. 

 When carrying out azimuthal probes, the field laboratories were placed 

 along the road and measurements were made of the difference in potentials 

 at various distances from the probe centres (Fig. 7). These distances were 

 selected the same as with the usual probes (500, 700, 1000, 1300, 1800, 2500 m. 

 etc.). 



Observations with the azimuthal arrangement were made according to 

 a special procedure, which involved all the necessary information on the 

 direction of the feed and measuring lines, and was arranged as follows: 



Az. No. Azimuth AB = Marking at the centre 



Here the 2nd column gives the number of the pegs for which the measur- 

 ing lines should be unreeled. The 3rd and 4th columns give the distances 

 R between the centre of the feed line and the centre of the measuring hne and 

 angle between the feed line and the section connecting the centres of 

 the feed and measuring lines. The distances and angles were measured 



