SIMPLE INTRODUCTION FOR DIRECTIONAL DRILLING ANTI-COLLISION
Directional Drilling Plots.
Spider Plots For Directional Wells.
- 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
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 central well, is plotted and displayed graphically.
Volumes of Uncertainty.The systems for surveying directional wells have limited accuracy.The survey may also be subject to errors resulting from:
- Downhole changes in the magnetic field.
- Systematic errors associated with either a magnetic or gyro compass
- Misalignment of the tool in the hole
- 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
- 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