CORE ORIENTATION 



91 



This device has been well tried in California oil wells 

 and has yielded reliable results. Its chief drawbacks are 

 that for very narrow diameters its mechanism is too com- 

 plicated and delicate ; thus it has a critical limiting borehole 

 width. It can not be used for the continuous survey of bore- 

 holes, being essentially a core-orientating instrument. 

 While it does not interfere with the ordinary coring opera- 

 tions and requires no special lowering proc- 

 ess or apparatus, it is confined to rotary 

 boring methods. 



The ingenious notion underlying the 

 apparatus is extended in Riemer's apparatus 

 wherein the surge effect of an annulus of 

 mercury is utilized to produce somewhat 

 similar results. 



Macready's Method. — This interesting 

 modern method was devised by George A. 

 Macready of Los Angeles and can be utilized 

 at depths exceeding 6,000 ft., though 



ooo 



Fig. 45. Fig. 45a. 



Fig. 45. — Borehole apparatus records. {By the courtesy of George A. 

 Macready.) 



Fig. 45a. — Types of compass pendulum photographs. 



the greatest run to date is only 3,780 ft. It has been devel- 

 oped and employed in the Trinidad asphalt deposits, the 

 Venezuelan petroleum fields and the western oil areas of 

 America. It is suited to holes of fairly small diameter. 



