20.6.1 Difference between Separation Factor and Probability Based Rules

A separation factor based rule is purely geometric whereas a probability based rule relates to actual risk. For example, take two different uncertainty situations which both calculate a separation factor of 1.0. In the first case two 12-1/4” wellbores have uncertainty envelopes which are hundreds of feet across. In the second case the uncertainty envelopes only have a radius of one foot from each well centre. Clearly the second case has a much higher probability of being an actual collision than the former.

Rules merely using reported separation factor numbers will not distinguish between these two cases.