CHAPTER III 



INSTRUMENTAL SURVEY OF BOREHOLES 



The determination of the course of boreholes by instru- 

 mental means has occupied the minds of investigators 

 since before the middle of last century. It received great 

 impetus during the early eighties and the opening years of 

 this century. Since the World War much work has been 

 done, principally in the Mid-continent oil fields of America, 

 South Africa and Germany in devising new means to the 

 above end. From simple tests with plumbing baskets 

 and by simple fluid apparatuses the progressive trend 

 through various mechanical, optical, and photographic 

 contrivances to the highly skilled gyroscopic methods has 

 proceeded, until today the last two named means are being 

 exploited vigorously. Probably the most widely adopted 

 method in employment today is a modified form of fluid 

 method, and it is now customary for contracts in drilling 

 to specify a limiting permissible error in verticality of 1 

 part in 100. Thus we are faced with a universally applica- 

 ble standard of attainment expected of any method offered 

 in the profession. The paramount requirements which 

 have to be fulfilled by a successful device are as follows: 



a. It should record continuously on going down the 

 hole and similarly make a check record upward on extrac- 

 tion. Very few inventions meet this need. 



b. It should measure both the inclination and bearing 

 of the borehole. This could be done by simultaneous 

 registrations from one source or two initial sources register- 

 ing at the same time. It is the great time-saving 

 injunction. 



c. It should be under direct surface control with respect 

 to registration as well as depth. 



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