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Anti Collision Plots For Directional Wells

In this article, we shall discuss a simple overview on Anti Collision For Directional Drilling

  • The surveys and well plans are used to carefully map the relationship of the proposed new well to all existing wells and any proposed future wells.
  • “Spider” Plots : are usually of the horizontal projection
directional drilling Anti-collision spider plots

Definition Of Traveling Cylinder Plot (TCP).

Traveling Cylinder Plot (TCP) is one of a collection of tools that operators have traditionally used to plan and drill safely through a maze of wells.  Most common usage is on wells that are drilled from offshore platforms or wells that are drilled from land pads with multiple adjacent wells.  Their principle usage is in the vertical hole sections near the surface where collision risks are generally the highest    TCP involves imagining a cylinder with a given radius enclosing the wellbore from one depth to another, the zone of interest. Any well entering this cylinder i.e. approaching closer than the radius of the cylinder to the centralwell, is plotted and displayed graphically.    

Directional drilling traveling cylinder plot

Volumes of Uncertainty.

 The systems for surveying directional drilling wells have limited accuracy. The survey may also be subject to errors resulting from:

  1. Downhole changes in the magnetic field.
  2. Systematic errors associated with either a magnetic or gyro compass (check gyro tool for surveying)
  3. Misalignment of the tool in the hole
  4. Depth measurement, and inclination.

Ellipsoid Of Certainty Plot.

Definition: ellipsoid (3-D body) that represents the envelope of the likely position of a given well survey point based on the error.

Anti-collision Ellipsoid Of Certainty plot
Ellipsoid Of Certainty

Lead Angle:

  • Directional Wells which are drilled with rotary assemblies often have a tendency to turn or “walk” during the drilling process.
  • “Lead Angle” where the tendency is anticipated using past experience in the same or similar areas, and built into the initial directional orientation of the well
  • The use of steerable systems, while more costly, removes a lot of the guesswork and allow a straighter, more accurate hole

Well Plan Maps

The vertical projection of the actual well is plotted using the TVD and Vertical Section values from the survey calculations The Horizontal projection is plotted using the North/South and East/West coordinates  

well plan maps directional drilling vertical projection horizontal