26.3 The Existing Well Data Including Survey Tools and Depth Ranges

Any missing data within the drilling range of the new well constitutes a serious safety hazard. Whilst the legal responsibility for the completeness and quality of a survey database rests with the asset owner, in

practice, many operators do not have a formal survey focal point with responsibility for this. It is imperative that all steps be taken to ensure the quality and completeness of the data before the well is planned and

this should be formally agreed in writing with the operator and included in any new proposals.

The required data includes the surveys and the detail of the individual tool runs in each survey leg, for example:

Notes on the treatment of vertical wells:

1. If any “inclination only” surveys are part of the database, they are best entered with the inclinations set to 0.00 for the entire “inclination only” survey. A common error is to enter the actual inclination whilst
leaving the azimuth set to 0.00. This erroneously enters a well that has been drilled due north and creates a false impression that a safe clearance exists passing to the south side of the “vertical” well.

2. If the vertical well has been surveyed by “inclination only” then well planners should assume the vertical well can deviate 50 feet per thousand in any direction as the safety envelope for planning around this
“vertical” well.

3. When a ‘vertical’ well with “inclination only” surveys constitutes a high collision risk a recommended practice is to enter the “well” at least six times into the database. This should be done by entering the
actual inclinations (in six successive wells) first with azimuths of 0°, then another with azimuths of 60°, and then additional wells at azimuths of 120°, 180°, 240° and 270° successively to create an ‘Eiffel Tower’
of possible locations of the vertical well. The well planners’ and directional drillers’ software can then conduct anti-collision scans against these dummy wellbores.