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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%.