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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
c. Calculate the maximum hoisting speed. An-
swer: 106.9/t!min.
d. Calculate the derrick load when upward motion
e. Calculate the maximum equivalent derrick
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
Determine the minimum number of lines between the
crown block and traveling block that can be used.
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
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
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
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.
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
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.
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%.```