A 20,000-ft drillstring is composed of 19,400 ft of 5-in., 19.5-lbm/ft drillpipe and 600 ft of...

 

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A 20,000-ft drillstring is composed of 19,400 ft of 5-in., 19.5-lbm/ft drillpipe and 600 ft of 8.0- x 3.0-in. drill collars. The mud density is 18 lbm/gal. Assume the drill string is suspended off bottom. a. Construct a graph of axial tension (or com- pression) vs. depth. b. Determine the maximum weight that can be applied to the bit without causing a bending mo- ment in the drillstring. Answer: 64 K-lbf. c. Assume that the driller slacks off the hook load so that the computed weight is applied to the bit. Construct a graph of axial tension (or compres- sion) vs. depth. d. Lubinski“ defines the neutral point of buck- ling as the point at which the axial compressive stress is equal to the external hydrostatic pressure. Is this true for this example? Answer: yes; p=a=18,150 psi. A 20,000-ft drillstring is composed of 19,400 ft of 5-in., 19.5-lbm/ft drillpipe and 600 ft of 8.0- x 3.0-in. drill collars. The mud density is 18 lbm/gal. Assume the drill string is suspended off bottom. a. Construct a graph of axial tension (or com- pression) vs. depth. b. Determine the maximum weight that can be applied to the bit without causing a bending mo- ment in the drillstring. Answer: 64 K-lbf. c. Assume that the driller slacks off the hook load so that the computed weight is applied to the bit. Construct a graph of axial tension (or compres- sion) vs. depth. d. Lubinski“ defines the neutral point of buck- ling as the point at which the axial compressive stress is equal to the external hydrostatic pressure. Is this true for this example? Answer: yes; p=a=18,150 psi.