38 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



only one plane (a common error of borehole chart makers) 

 and it is later decided to allow for lateral directional devia- 

 tions, or for depicting any borehole data in one plane, 

 proceed thus: 



In Fig. 17a the profile of C (Fig. 17) is reproduced dotted 

 and the hole is assumed to have the C hole dips and depths 



ABC Surface 



Fig. 176. 



um^-" — ' 



Fig. 17. Fig. 17a. 



Fig. 17. — Section showing methods of plotting deviation of boreholes where 

 readings are made at intervals and angular deviation is assumed to be all in same 

 vertical plane. 



Fig. 17a. — Section showing a hole wandering in three dimensions revolved into 

 the WE plane. 



Fig. 176.— Plan of Fig. 17a. 



throughout but alters in azimuthal directions from point a 

 as shown on the left of the figure. Our problem is to 

 visualize the borehole in the WE plane as in the previous 

 Fig. 17. As ah is now bearing N.55°E. rebat it 35 deg. 

 to ah') project this line to a6^ and drop perpendicular 

 to the depth line of h at h^. (Imagine a to be the apex 

 of a cone of side and dip ah with the new ah 35 deg. out of 

 the old ah plane ; the actual depth and length of the new ah 



