584 



Subsurface Geologic Methods 



out through a "trigger" type bit in those cases where the operator is not 

 using a nonmagnetic drill collar. 



Multiple-shot machines are not rented to operators. Surveys with 

 them are made by service company employees who are especially trained 

 to perform this type of engineering work. Charges vary with the amount 

 of hole surveyed and the type of survey run. 



Table 31 gives data on DX-type multiple-shot machines. 



Throughout the detailed discussion of well-surveying instruments 

 above it should be noted that these machines have been designed to indi- 

 cate an erroneous reading when it is taken. The drift and direction indi- 

 cating means in each of these machines are free to move at all times; no 

 locking devices are used. The instrument must be motionless, and the 

 plumb bob and compass must be allowed to come to rest before a true 

 and accurate reading can be taken. By the use of long exposure time in 

 photographic machines, movement is detected readily and another picture 



TABLE 31 

 Multiple Shot Subvey Instrument 



Standard multiple shot 



Instrument 



assembled 



tvith 10° 



unit 



Instrument 



with 90° 



combination 



unit 



Barrel 



Standard 

 bronze 



0. D. instrument 



Length instrument . 

 Weight instrument 

 Max. 0. D. barreL 



Length barrel 



Weight barrel 



Connection up 



Type connection ... 



2% in. 

 46/ff in. 

 22^ lb. 



21^ in. 

 50tV in. 

 22% lb. 



31/2 in. 



6 ft. 7 in. 



87 lbs. 



2ys in. A.P.L 



Box 



can be taken. The type "W" drift indicator, by making two determinations 

 forty seconds apart, assures a correct reading. 



The importance of surveying wells has been recognized for some 

 time, and the use of well-surveying machines is increasing rapidly. Op- 

 erators find that many times well surveys are among the most valuable 

 records to which they refer for information. 



Reasons for surveying wells are many and varied. Much could be 

 written dealing with individual instances in which surveys have made 

 large savings in the cost of drilling new wells, in which unforeseen diffi- 

 culties have been minimized by knowledge of the course of the bore, and 

 in which work-over operations have been conducted on a scientific basis 

 from survey data. 



Applications 



Some of the more common uses of surveys of wells made as they 

 are in process of drilling are noted in the following paragraphs. 



To the petroleum geologist an accurate survey of a well is of inesti- 



