Applied Drilling Engineering

program in 
a given area should include average well costs due to 
drilling problems. 
In areas where formation strength is low, time 
spent drilling and tripping may account for only 
about one-half to one-third of the total time needed 
to finish the well. Shown in Table 1.10 is a detailed 
time breakdown for an offshore Louisiana well 
drilled to 10,000 ft using a small platform rig tender. 
Only about 360Jo of the time required to drill and 
complete this well was spent drilling and tripping to 
change bits. About 7% of the time was spent 
"fishing" parts of the drillstring from the hole. 
Exercises 
1.1 The following data were obtained on a diesel 
engine operating in a prony brake. 
Fuel 
Engine Speed Torque Consumption 
(rpm) (ft-lbt) (gal/hr) 
1,200 1,400 25.3 
1,000 1,550 19.7 
800 1,650 15.7 
600 1,700 12.1 
a. Compute the brake horsepower at each engine 
speed. Answer: 319.9, 295.1, 251.3, and 194.2 hp. 
b. Compute the overall engine efficiency at each 
engine speed. Answer: 0.235, 0.278, 0.297, and 
0.298. 
c. Compute the fuel consumption in gallons per 
day for an average engine speed of 800 rpm and a 12-
hour work day. Answer: 188.4 gall D. 
1.2 Compute the tension in the fast line when 
lifting a 500,000 lbf load for 6, 8, 10, and 12 lines 
strung between the crown block and traveling block. 
Answer: 95,347; 74,316; 61, 728; and 54, 113/bf. 
1.3 A rig must hoist a load of 200,000 lbf. The 
drawworks can provide a maximum input power of 
800 hp. Ten lines are strung between the crown block 
and the traveling block and the dead line is anchored 
to a derrick leg on one side of the v-door (Fig. 1.17). 
a. Calculate the static tension in the fast line when 
upward motion is impending. Answer: 24,691/bf. 
b. Calculate the maximum hook horsepower 
available. Answer: 648 hp. 
c. Calculate the maximum hoisting speed. An-
swer: 106.9/t!min. 
d. Calculate the derrick load when upward motion 
is impending. Answer: 244,691/bf. 
e. Calculate the maximum equivalent derrick 
load. Answer: 280,000 lbf. 
f. Calculate the derrick efficiency factor. Answer: 
0.874. 
1.4 Compute the minimum time required to reel a 
10,000-ft cable weighing I lbf/ft to the surface using 
a 10-hp engine. Answer: 151.5 min. 
1.5 A 1.25-in. drilling line has a nominal breaking 
strength of 138,800 lbf. A hook load of 500,000 lbf is 
anticipated on a casing job and a safety factor based 
TABLE 1.10- EXAMPLE RIG TIME ANALYSIS 
FOR TENDERED RIG 
Total 
Required 
Drilling Operation 
Drilling 
Tripping 
Rigging up 
Formation evaluation and 
borehole surveys 
Casing placement 
Well completion 
Drilling problems (total) 
Mud conditioning ........ 143 
Well control operations... 12 
Fishing operations ...... 152 
Severe weather . . . . . . . . . 97 
Rig repairs . . . . . . . . . . . . . 20 
Logistics ............... 26 
Total 
(hours) 
351 
388 
348 
103 
199 
211 
450 
2,050 
Time 
Fraction 
0.17 
0.19 
0.17 
0.05 
0.10 
0.10 
0.22 
1.00 
37 
on static loading conditions of 2.0 is required. 
Determine the minimum number of lines between the 
crown block and traveling block that can be used. 
Answer: 10. 
1.6 A driller is pulling on a stuck drillstring. The 
derrick is capable of supporting a maximum 
equivalent derrick load of 500,000 lbf, the drilling 
line has a strength of 51,200 lbf, and the strength of 
the drillpipe in tension is 396,000 lbf. If eight lines 
are strung between the crown block and traveling 
block and safety factors of 2.0 are required for the 
derrick, drillpipe, and drilling line, how hard can the 
driller pull trying to free the stuck pipe? Answer: 
166,667/bf. 
I. 7 A rig accelerates a load of 200,000 lbf from 
zero to 60 ft/min in 5 seconds. Compute the load 
shown on the hook load indicator. Answer: 201,242 
lbf. 
1.8 A load of 400,000 lbf is lowered a distance of 
90 ft using the auxiliary drawworks brakes. Compute 
the heat that must be dissipated by the brake cooling 
system. Answer: 46,213 Btu. 
1. 9 A drawworks drum has a diameter of 30 in., a 
width of 56.25 in., and contains 1.25-in. drilling line. 
Calculate the approximate length of line to the first lap 
point. Answer: 368.2 ft. 
1.10 For the drawworks drum dimensions given in 
Exercise 1.9 and a fast line tension of 50,000 lbf, com-
pare the drawworks torque when the drum is almost 
empty to the drawworks torque when the drum con-
tains five laps. Answer: 65,104 ft-lbf empty; 85,938 
ft-lbf with five laps. 
1.11 Consider a triplex pump having 6-in. liners and 
11-in. strokes operating at 120 cycles/min and a 
discharge pressure of 3,000 psig. 
a. Compute the pump factor in units of gal/cycle at 
100% volumetric efficiency. Answer: 4.039 gall cycle. 
b. Compute the flow rate in gal/min. Answer: 
484.7 gal/min. 
c. Compute the energy expended by each piston 
• 
38 
during each cycle and the pump power developed. 
Answer: 77,754 ft-/bj!cycle!cylinder; 848 hp. 
1.12 A double-acting duplex pump with 6.5-in. 
liners, 2.5-in. rods, and 18-in. strokes was operated 
at 3,000 psig and 20 cycles/min. for 10 minutes with 
the suction pit isolated from the return mud flow. 
The mud level in the suction pit, which is 7 ft wide 
and 20ft long, was observed to fall 18 in. during this 
period. Compute the pump factor, volumetric pump 
efficiency, and hydraulic horsepower developed by 
the pump. Answer: 7.854 gal/c~vc/e; 0.82; 274.9 hp. 
1.13 A 1 ,000-hp pump can operate at a volumetric 
efficiency of 90UJo. For this pump, the maximum 
discharge pressure for various liner sizes is: 
Liner Size 
(in.) 
7.50 
7.25 
7.00 
6.75 
6.50 
6.00 
Maximum Discharge 
Pressure 
(psig) 
1,917 
2,068 
2,229 
2,418 
2,635 
3,153 
Plot the pump pressure flow rate combinations 
possible at maximum hydraulic horsepower using 
cartesian coordinate paper. Repeat this using log-log 
paper. 
1.14 A drillstring is composed of 9,000 ft of 5-in. 
19.5-lbm/ft drillpipe and 1,000 ft of drill collars 
having a 3.0-in. ID. Compute these items: 
a. Capacity of the drillpipe in barrels. Answer: 
159.8 bbl. 
b. Capacity of the drill collars in barrels. Answer: 
8. 7 bbl. 
c. Number of pump cycles required to pump 
surface mud to the bit. The pump is a duplex double-
acting pump with 6-in. liners, 2.5-in. rods, 16-in. 
strokes, and operates at a volumetric efficiency of 
85%. Answer: 1,164cycles. 
d. Displacement of the drillpipe in bbl/ft. An-
swer: 0.0065 bbl!ft (neglects tool joints). 
e. Displacement of the drill collars in bbllft. The 
OD of the collars is 8.0 in. Answer: 0.0534 bbl!ft. 
f. Loss in fluid level in the well if 10 stands 
(thribbles) of drillpipe are pulled without filling the 
hole. The ID of the casing in the hole is 10.05 in. 
Answer: 64ft. 
g. Loss in fluid level in the well if one stand of 
drill collars is pulled without filling the hole. Answer: 
108ft. 
h. Change in fluid level in the pit if the pit is 8 ft 
wide and 20 ft long, assuming that the hole is filled 
after pulling 10 stands of drill pipe. Answer: 2.5 in. 
i. Change in fluid level in a 3- x 3-ft trip tank 
assuming that the hole is filled from the trip tank 
after pulling 10 stands of drillpipe. Answer: 3.6ft. 
1.15 The mud logger places a sample of calcium 
carbide in the drillstring when a connection is made. 
The calcium carbide reacts with the mud to form 
acetylene gas. The acetylene is detected by a gas 
detector at the shale shaker after pumping 4,500 
strokes. The drillstring is composed of 9,500 ft of 5-
in., 19.5-lbm/ft drillpipe and 500 ft of drill collars 
having an 10 of 2.875 in. The pump is a double-
APPLIED DRILLING ENGINEERING 
acting duplex pump with 6-in. liners, 2-in. rods, and 
14-in. strokes and operates at a volumetric efficiency 
of80%.