6 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



of the hole.^ On the other hand, percussive borers claim 

 that curvature is more easily detected and rectified by a 

 reciprocating action especially by a free-falling tool.^ 



With regard to rotary boreholes a perusal of Table IV 

 will well repay the reader. The table is taken from a 

 compilation^ covering 255 California boreholes bored by 

 the rotary system. The total depth was 1,158,542 ft. 

 and the total number of measurements 13,150. As addi- 

 tional proof of this almost universal deviation of deep holes 

 we may cite the recent researches of D. R. Snow and H. B. 

 Goodrich^ carried out upon some 90 wells in the Seminole 

 oil field of America. These holes have been drilled since 

 1927 and show the data collected in Table V. 



Table V. — Summary of Results of 90 Oil Wells 

 {After Snoiv) 



Total surveyed: 377,719 ft. 



Total vertical correction: 9,290 ft. (per well, 103 ft.). 



Average angle of deflection: 12 deg. 44 min. 



In some relatively shallow boreholes, as in the concentric 

 circumferential suites of boreholes preliminary to sinking 

 shafts by the freezing process or by cementation, extreme 

 accuracy of data respecting the course of the holes is of 



1 Diamond Drilling, U. S. Dept. Commerce, Bur. Mines, Bull. 243, p. 60. 



2 Cf. Organ des Verein der Bohrtechniker, No. 23, p. 279, 1910. 



^ A. Anderson of Fullerton, California, in Oil Weekly, October, 1929. 

 *See also Oil Gas Jour n., p. 32, Mar. 14, 1929, and p. 218, Apr. 4, 1929. 



