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This method accounts for variations in both inclination and azimuth. It is easy to calculate and, as long as wells are surveyed at the same interval, it can provide some useful comparisons. Dividing by 90 simply expresses the simplified index as a number of right angles generated. In the following simple well shapes, a perfect well would have a TI of 1.0.
If the high side component is the build or the drop, th l l compon n s h ‘Eff c u n’. Effective Turn is the dogleg in the lateral plane across the well bore. This is NOT the azimuth change (unless horizontal).
Effective Turn = Turn x sin(Inclination) and measures the lateral component of dogleg
Here is a step by step process to calculate the tortuosity index.
1. For each survey interval find the Build Angle
Change in Inclination = dInc = Inc – prev inc
2. Find the Effective Turn Angle
Change in Direction = dDir = Dir – prev Dir if absolute value dDir > 180 then dDir = dDir - 360 * sign(dDir) (shortest way round) Effective Turn = dDir * sin(Inclination) (use final inclination in the interval)
3. Accumulate absolute values of dinc to find Total Vertical Curvature TVC 4. Accumulate absolute values of Effective Turn to find Total Lateral Curvature TLC 5. Vertical Tortuosity Index = TVI/90, Lateral Tortuosity Index = TLC/90 6. Tortuosity Index = SQRT( VTI^2 + LTI^2 )
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