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20.9 Anti-collision Scanning and Reporting
Recommended practice is to observe the following rules when scanning wells for collision risk against a subject well:
1. On first pass, scan all wells in the field. 2. Be sure to pick up all the potential hazard wells. 3. Be sure to include plugged and abandoned wells, appraisal wells, wells drilled by other operators and wells drilled by other directional drilling companies. 4. Scan all wells to all depths at a close interval (30 ft or 10 m). 5. Document that you have checked with the client and they have verified that your database contains the same number of wells located in the same locations as their database.
6. Check that the hazard wells highlighted present no surprises to the client. 7. Thereafter scan reports may be done filtering on separation factor 4.0.
20.10 The Ellipse of Uncertainty Report
The ellipse of uncertainty report required can vary from customer to customer. Terms can vary in their usage from customer to customer and from software to software. There are certain terms that must be understood. Any ambiguity arising due to customer usage or from other software programs must be understood and dealt with so as to prevent poor well planning and accidents in execution.
Below is an example of a deep, close approach report. The table following the example presents definitions of terms commonly used in ellipse of uncertainty reporting.
Figure 93: Example of a deep, close approach report.
Header Label-Expanded Header (Term)-Definition
Easting (m) Northing (m)
interpolated E-W map coordinate (in specified units) of the primary well interpolated N-S map coordinate (in specified units) of the primary well the true vertical depth (in specified units) of the centre of the primary well the inclination vector direction of the centre of the primary well the azimuth vector direction of the centre of the primary well the measured depth (in specified units) of the centre of the primary well
TVD True Vertical Depth (m)
Inc Az
Inclination
Azimuth
MD (m) Measured Depth (m)
Semi Major (m)
the length (in specified units) of the longest uncertainty axis as seen looking along the centre of the primary well. (be aware that in other software it can mean the longest axis in 3D space or the longest axis in the horizontal plane. The differences are usually small. the length (in specified units) of the axis at right angles to the semi major axis in whatever plane of projection is used.
Semi Minor (m)
PHI
Phi Angle (Orientation)
the orientation of the semi minor axis from high side
TVD Spread (m)
the TVD (in specified units) occupied by the uncertainty envelope
N’rest Well the name of the closest well at this point Cr-Cr (m) Center-Center Distance the distance (in specified units) from the centre of the primary well path to the centre of the nearest well’s path Sep Factor Separation Factor - the separation factor calculated by the specified method Inter b’dary (m) Inter Boundary Dist the distance (in specified units) from the boundary of the uncertainty surface of the primary well to the boundary of the uncertainty surface of the nearest well measured along the direction of 3D closest approach Hi-Side to Cr-Cr the orientation of the nearest well to the primary well expressed as an angle from high side of the primary well Survey Tool the current survey tool being used in the primary well Nearest Well
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