Overview:
• What we want is a decision point – What is the minimum safe distance to drill close to an adjacent well?
• Variations (ratios) on the above
- Planning margin – Give the Directional Driller a margin to allow for normal steering close to the planned trajectory
- Dispensation (ratios or risk level) Lower levels of low risk wells or ones that have been depressured.
What are the Alternatives?
• Current: Separation Factor / Major Risk / Combined Covariance Methods (Statoil/OSF)
– good for near surface
- very pessimistic for deep well crossings
- misleading values for high angle crossings
• Advanced: Risk based
- good for high angle, deep crossings
- optimistic for parallel wells – near surface
- Minimum separations fade out (dilution) at low risk levels
Minimum Separation based on Risk Level
• Risk = NormSDist((Separation+Casing*Thickening) /EllipseDimension) – NormSDist(Separation /EllipseDimension)
• Minimum Separation = Inverse of the above (have to iterate, start using NormSInv)
....
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Collision Avoidance – Grand Unified Theorem
Jerry Codling - Halliburton