The weight indicator shows 230,000 lbs. The block and lines weight 30,000 lbs. A pump pressure gauge in line with the drillpipe shows 7,000 psi. The drillpipe is 5" by 4.276" by 19.5 ppf and the average weight per foot of the steel in the drillpipe is 21.4 lb/ft. What is the real tension in the drillpipe at the rotary table and at a depth of5,000 feet?
The inside end area of 5" drillpipe = 0c/4) 4.2762 = 14.360 sq. in.
Treal = 230,000 - 30,000 + 7,000 * 14.360 = 300,520 lb (rotary table)
Treal = 300,520 - 21.4 * 5,000 = 193,520 lb (at 5,000 ft)
Drag loads may be measured with the weight indicator or estimated with equations.
The differences in the pick-up and slack-off weights from the free rotating weight are the pick-up drag and the slack-off drag.
Pick-up drag = 250,000 - 200,000 Slack-off drag = 200,000 - 170,000
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