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24. o uos y
24.1 Illustrating tortuosity
This has been variously defined as the variability in dogleg severity or the unnecessary undulations in the wellpath. Essentially tortuosity describes a lack of smoothness in the well trajectory and the greater the tortuosity the greater the likelihood of problems when running casing or excessive drillpipe stress when rotating in hole. One simple presentation of tortuosity is to plot the dogleg severity against measured depth.
Figure 109: Plotting the dogleg severity against measured depth.
However, on its own, this is hard to interpret in a measurable way. Clearly, the well is tortuous but how can we define acceptable tortuosity? If the wellplan had prescribed a 4 deg/100 build rate, it would be inappropriate to penalise a dogleg severity of 4 deg/100. The real problem is when the dogleg severity varies too much and a 4 deg/100 build is constructed with dogleg severities of 0 to 12 varying wildly during the build section. A well which smoothly followed the wellplan would have very little variation in dogleg severity. Figure 109 is the well plan for the well above.
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