Applied Drilling Engineering

Torque is transmitted to the kelly through 
kelly bushings, which fit inside the master bushing of 
the rotary table. The kelly must be kept as straight as 
possible. Rotation of a crooked kelly causes a 
Fig. 1.34- Cutaway view of example swivel. 
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whipping motion that results in unnecessary wear on 
the crown block, drilling line, swivel, and threaded 
connections throughout a large part of the drillstring. 
A view of a kelly and kelly bushings in operation is 
shown in Fig. 1.35. The kelly thread is right-handed 
on the lower end and left-handed on the upper end to 
permit normal right-hand rotation of the drillstring. 
A kelly saver sub is used between the kelly and the 
first joint of drill-pipe. This relatively inexpensive 
short section of pipe prevents wear on the kelly 
threads and provides a place for mounting a rubber 
protector to keep the kelly centralized. 
An example rotary table is shown in Fig. 1.36. The 
opening in the rotary table that accepts the kelly 
bushings must be large enough for passage of the 
largest bit to be run in the hole. The lower portion of 
the opening is contoured to accept slips that grip the 
drillstring and prevent it from falling into the hole 
while a new joint of pipe is being added to the 
drillstring. A lock on the rotary prevents the table 
from turning when pipe is unscrewed without the use 
of backup tongs. 
Power for driving the rotary table usually is 
provided by an independent rotary drive. However, 
in some cases, power is taken from the drawworks. A 
hydraulic transmission between the rotary table and 
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• 18 APPLIED DRILLING ENGINEERING 
Fig. 1.35-View of kelly and kelly bushings. 
Fig. 1.36- Example rotary table. Fig. 1.37- Example power sub. 
ROTARY DRILLING PROCESS 19 
TABLE 1.5- DIMENSIONS AND STRENGTH OF API SEAMLESS INTERNAL UPSET DRILLPIPE 
Size of 
Outer 
Weight Internal 
per Foot Diameter 
With Internal At Full 
Tensile Strength' 
Collapse Pressure• Internal Yield Pressure• D E G" 
Diameter 
(in.) 
Coupling Diameter Upset D E G" S-135" D 
(psi) 
E 
(psi) 
G" 
(psi) 
S-135 
(psi) 
1,000 1,000 1,000 
(lbf) (lbf) (lbf) 
S-135" 
1,000 
(lbf) (lbf) (in.) (in.) ~ (psi) (psi) ~ 
23fa 
23fa 
2'/'a 
2'/'a 
4.85 
6.65 
6.85 
10.40 
1.995 
1.815 
2.441 
2.151 
1.437 
1.125 
1.875 
1.187 
6,850" 11,040 13,250 16,560 
11 ,440 15,600 18,720 23,400 
12,110 
10,470 12,560 15,700 
16,510 19,810 24,760 
10,040 12,110 15,140 
7,110" 
11,350 
12,120 
10,500 
15,470 
9,910 
16,530 
14,700 18,900 
21,660 27,850 
13,870 
23,140 
17,830 
29,750 
70 98 137 176 
101 138 194 249 
136 190 245 
157 214 300 386 
194 272 350 3'12 
3'12 
3'12 
9.50 
13.30 
15.50 
2.992 
2.764 
2.602 
2.250 
1.875 
1.750 
10,350 
12,300 
14,110 16,940 21,170 10,120 
16,770 20,130 25,160 12,350 
9,520 
13,800 
16,840 
13,340 
19,320 
23,570 
17,140 
24,840 
30,310 
199 272 380 489 
237 323 452 581 
4 
4 
4'12 
4'12 
4'12 
5 
11.85 
14.00 
13.75 
16.60 
20.00 
3.476 
3.340 
3.958 
3.826 
3.640 
2.937 
2.375 
3.156 
2.812 
2.812 
8,330 
7,620 
9,510 
8,410 10,310 
11 ,350 14,630 
7,200 8,920 
10,390 12,470 
12,960 15,560 
12,820 
17,030 
10,910 
15,590 
19,450 
6,970 8,640 10,550 
7,940 
7,210 
9,200 
8,600 12,040 
10,830 15,160 
15,470 
19,500 
7,900 11,070 14,230 
9,830 13,760 17,690 
12,540 17,560 22,580 
231 323 415 
209 285 400 514 
270 378 486 
242 331 463 595 
302 412 577 742 
328 459 591 
5 
16.25 
19.50 
4.408 
4.276 
3.750 
3.687 7,390 10,000 12,090 15,110 6,970 
7,770 10,880 13,980 
9,500 13,300 17,100 290 396 554 712 
5'12 
5'12 
5 9/16 
5 9/16 
5 9/16 
6% 
6 5/e 
6% 
21.90 
24.70 
19.00'' 
22.20" 
25.25" 
22.20" 
25.20 
31.90" 
4.778 
4.670 
4.975 
4.859 
4.733 
6.065 
5.965 
5.761 
3.812 
3.500 
4.125 
3.812 
3.500 
5.187 
5.000 
4.625 
6,610 
7,670 
4,580 
5,480 
6,730 
3,260 
4,010 
5,020 
8,440 10,350 12,870 
10,460 12,560 15,700 
5,640 
6,740 
8,290 
4,020 
4,810 6,160 6,430 
6,170 
6,320 
7,260 
5,090 
6,090 
7,180 
4,160 
4,790 
6,275 
8,610 12,060 15,500 
9,900 13,860 17,820 
321 437 612 787 
6,950 
8,300 
9,790 
5,530 
6,540 
8,540 
365 497 696 895 
267 365 
317 432 
369 503 
307 
9,150 11,770 359 
463 
418 
489 
631 
685 881 
·Collapse. internal yield. and tensile strengths are m1nimum values w1th no safety factor. 0, E.G, S-135 are standard steel 
grades used 1n drillp1pe 5 
••Not API standard: shown for Information only. 
the rotary drive often is used. This greatly reduces 
shock loadings and prevents excessive torque if the 
drillstring becomes stuck. Excessive torque often will 
result in a twist-off- i.e., a torsional failure due to a 
break in the subsurface drillstring. 
Power swivels or power subs installed just below a 
conventional swivel can be used to replace the kelly, 
kelly bushings, and rotary table. Drillstring rotation 
is achieved through a hydraulic motor incorporated 
in the power swivel or power sub. These devices are 
available for a wide range of J:otary speed and torque 
combinations. One type of power sub is shown in 
Fig. 1.37. 
The major portion of the drillstring is composed of 
drillpipe. The drillpipe in common use is hot-rolled, 
pierced, seamless tubing. API has developed 
specifications for drillpipe. Drillpipe is specified by 
its outer diameter, weight per foot, steel grade, and 
range length. The dimensions and strength of API 
drillpipe of grades D, E, G, and S-135 are shown in 
Table 1.5. Drillpipe is furnished in the following API 
length ranges. 
Range 
1 
2 
3 
Length (ft) 
18 to 22 
27 to 30 
38 to 45 
Range 2 drill pipe is used most commonly. Since each 
joint of pipe has a unique length, the length of each 
joint must be measured carefully and recorded to 
allow a determination of total well depth during 
drilling operations. 
The drillpipe joints are fastened together in the 
drillstring by means of tool joints (Fig. 1.38). The 
female portion of the tool joint is called the box and 
the male portion is called the pin. The portion of the 
drillpipe to which the tool joint is attached has 
thicker walls than the rest of the drillpipe to provide 
for a stronger joint. This thicker portion of the pipe 
is called the upset. If the extra thickness is achieved 
by decreasing the internal diameter, the pipe is said to 
have an internal upset. A rounded-type thread is used 
now on drill pipe. The U.S. Standard V thread was 
used in early drillpipe designs, but thread failure was 
frequent because of the stress concentrations in the 
thread root. A tungsten carbide hard facing 
sometimes is manufactured on the outer surface of the 
tool joint box to reduce the abrasive wear of the tool 
joint by the borehole wall when the drillstring is rotated. 
The lower section of the rotary drillstring is 
composed of drill collars. The drill collars are thick-
walled heavy steel tubulars used to apply weight to 
the bit. The buckling tendency of the relatively thin-
walled drillpipe is too great to use it for this purpose. 
The smaller clearance between the borehole and the 
drill collars helps to keep the hole straight. Stabilizer 
subs (Fig. 1.39) often are used in the drill collar string 
to assist in keeping the drill collars centralized. 
In many drilling operations, a knowledge of the 
volume contained in or displaced by the drillstring is 
required. The term capacity often is used to refer to 
the