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.
Header Label-Expanded Header (Term)-Definition
| Easting (m) | interpolated E-W map coordinate (in specified units) of the primary well |
| Northing (m) | interpolated N-S map coordinate (in specified units) of the primary well |
| TVD True Vertical Depth (m) | the true vertical depth (in specified units) of the centre of the primary well |
| Inc - Inclination | the inclination vector direction of the centre of the primary well |
| Azi – Azimuth | the azimuth vector direction of the centre of the primary well |
| MD (m) – Measured Depth (m) | the measured depth (in specified units) of the centre of the primary well |
| 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. |
| Semi Minor (m) | the length (in specified units) of the axis at right angles to the semi major axis in whatever plane of projection is used. |
| 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 – Nearest 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 |
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