Miscellaneous Subsurface Methods 



511 



than with the knuckle joint. In operation the latter tool is rotated con- 

 tinuously. As illustrated in figure 243, the knuckle joint is essentially a 

 universal ball-and-socket joint, with the lower drill collar held at a fixed 

 angle by a spring-actuated cam. A short drill collar carries a pointed 



TABLE 26 



Eastman Full-Gauge Whipstock 



pilot bit at the bottom end and a reamer on the upper end. Either drag- 

 or rock-type bits and reamers may be used on a knuckle joint. Table 27 

 shows the three diameters in which knuckle joints are made and the recom- 

 mended hole sizes in which they are used. 



The procedure for running a knuckle joint is outlined below. (Also 

 see figure 244.) The tool should be run after the use of a flat-bottomed 

 bit. The knuckle joint is attached directly to the drill pipe (without a 

 drill collar) to obtain maximum flexibility. The tool is lowered to the 

 bottom of the hole and faced so that the bit is in the desired direction. 

 Mud circulation is started and the pumps are allowed to run slowly. The 

 tool is spudded lightly a number of times so that the pilot bit will form 

 a pocket at one side of the hole. The tool is set down on bottom and 

 drilling is commenced by slow rotation of the drill pipe. Light but con- 

 stant pressure is kept on the bit. At no time should the knuckle joint be 

 allowed to "drill off" or rotate without weight on bottom. After the tool 

 has drilled enough deflected "rathole" for the body to enter the deflected 

 hole, the ball-and-socket action is restricted, and the entire assembly drills 

 as a unit. About twenty feet of "rathole" is drilled. The amount of 

 weight applied to the bit and the type of formation in which the drilling 

 is done determine the amount of deflection made in the well. After the 

 "rathole" is made, the tool is withdrawn from the hole, which is opened 

 to full gauge by means of a pilot reamer. 



The Eastman full-gauge knuckle joint is very similar to the regular 

 knuckle joint except that it is designed to drill a nearly full-gauge hole. 

 The differences in the construction of the two tools can be seen from 

 comparing figures 242 and 243. Since the reamer is almost equal in size 

 to the hole in which the tool is run, no reaming of the deflected hole is 

 necessary after the full-gauge knuckle joint has been used. Thus, the 

 operator is able to go back in the hole with a full-gauge drilling bit and 

 proceed without making a special round trip to ream. In deep wells this 



