Miscellaneous Subsurface Methods 531 



above the bit, applying weight to the drill pipe and rotating the pipe about 

 sixty r.p.m. with moderate pump speed. After drilling this distance, a 

 single-shot reading would be taken either through a trigger bit, in a non- 

 magnetic drill collar, or with an open-hole single shot to determine 

 whether the drift and direction were in accordance with the plan. The 

 location of the well at this point would be plotted on the plan and section. 

 If it were found that the course of the well was not as desired, another 

 deflecting tool would be set to keep the well on course. The maximum 

 angle and correct direction are attained by using different drilling set- 

 ups and setting deflecting tools. Then it is probable that long drill collars 

 would be used above the bit to maintain the course of the hole in a straight 

 line. Changes in any of the factors which aff^ect the directional work 

 would not be made unless a single-shot picture was taken to check the 

 eff"ect of the last setup used. Techniques in drilling directional wells and 

 maintaining them on their true courses vary greatly with different forma- 

 tions. Types of drilling equipment, bits, reamers, and drill collars and 

 methods of surveying, as well as the relation of the course of the hole to 

 the structure, are factors to be considered. 



Few ironclad rules can be followed, as directional-drilling techniques 

 are learned only by experience. Certain basic methods influence the in- 

 crease or decrease of drift. An increase in the angle of drilling is ac- 

 companied by the application of weight to the drilling bit, moderate 

 rotation speeds, and moderate pump pressure. Drift generally is gained 

 by using a short drill collar and a roller reamer directly above the bit. 

 If it is necessary to increase drift quite rapidly, the drill collar may be 

 omitted, but the well possibly may wander from its course. Reduction of 

 drift generally is accomplished by the use of sharp bits, light drilling 

 weight, fast rotation, and high pump pressure. Decrease in drift can be 

 assisted by using a long drill collar above the bit with a roller reamer at 

 the top of the drill collar. After a start has been made in reducing drift, 

 the application of weight often will increase the rate of straightening the 

 hole. 



Little definite evidence that any type of bit will consistently turn 

 a well to the right or to the left has ever been presented. Many factors 

 influence the course of a directional well. Most directional drilling 

 engineers base their usage of bits upon experience in the field in which 

 they are working or in fields having similar drilling conditions. Some 

 bits have been designed especially for use in directional drilling work. 

 Most of the deflecting tools set, after the drift has been increased to its 

 maximum, are to correct the directional course of the hole. As the drilling 

 proceeds, the engineers plot the location of the well on the proposal as 

 single-shot readings are taken. The location of the well within the cylin- 

 ders is the basis for their recommendations as to methods to be used in 

 drilling. Aside from noting the effect of different drilling setups and 

 methods which they recommend, the control men try to anticipate and 



