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This has the disadvantage that it can be optimistic. In a worst case scenario it can even miss a potential collision situation as in figure 88b. This represents the same target and planned well as in the above example but the conditions have varied such that the lateral uncertainty is now much larger.
Figure 88b: Separation vector method
20.4 Pedal Curve Method
The second method for calculating separation factor is the pedal curve method. This overcomes the previous problem by projecting the extremities of the ellipses onto the separation vector.
Figure 89a: Separation factor – pedal curve method
However, whereas the separation vector method can be too optimistic, this one has the opposite problem of sometimes being too pessimistic. In figure 86a the two wells are crossing safely in 3D space but using this method calculates a collision risk when in fact there is not one.
Figure 89b: Separation factor – pedal curve method
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