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Confidence in surveys
19 March 2018
Gents,
What are your thoughts on the relevance of Survey confidence levels; that is to say what is the most sensible number of Standard Deviations and at what confidence level?
I was wondering how changing these values can "massage" EOU's and so wondered the feelings of the community on this issue?
4 answer(s)
NickG
Consultant
GeoPetra Ltd
Total Posts: 9
Join Date: 16/11/15
Hello,

I am not sure that my reply specifically answers your  question, however ... Steve Sawaryn has written several SPE technical papers on directional survey calculations and also EOU, the details of which are as listed below.

Regards, Nick Gibson, GeoPetra Ltd

(1) A Compendium of Directional Calculations Based on the Minimum Curvature Method in www.onepetro.org/journal-paper/SPE-84246-PA

(2) A Compendium of Directional Calculations Based on the Minimum Curvature Method--Part 2: Extension to Steering and Landing Applications in www.onepetro.org/journal-paper/SPE-159840-PA

(3) Explicit Calculation of Expansion Factors for Collision Avoidance Between Two Coplanar Survey-Error Ellipses in www.onepetro.org/journal-paper/SPE-159840-PA

(4) Well Collision Avoidance Management and Principles in www.onepetro.org/conference-paper/SPE-184730-MS

(5) Well Collision Avoidance - Separation Rule in www.onepetro.org/conference-paper/SPE-187073-MS
PDM_LLC
Owner
Proximity Drilling Mgt
Total Posts: 7
Join Date: 27/11/17
So, in some respects, the question comes down to "How well do you know your current location (MSA updates)?" and "How good is your latest survey and what is the impact on the downhole e.o.u.?"
PDM_LLC
Owner
Proximity Drilling Mgt
Total Posts: 7
Join Date: 27/11/17
Perhaps I can add some flavor to this discussion with the following comment(s). First, a great deal of effort is understandably directed toward reducing final survey ellipses/ellipsoids of uncertainty to the smallest possible.size. This is entirely understandable as the need for collision mitigation increases with closer spacings.

However, a similar effort must be directed toward real-time survey management and forward planning. We know where the offset wells are but need to know equally the location and direction / plan forward of a new-drill !!
PDM_LLC
Owner
Proximity Drilling Mgt
Total Posts: 7
Join Date: 27/11/17
Chris, this is a very good question. Lack of response is disappointing, particularly with the upcoming ISCWSA meeting next week. I will say that a few years ago I was involved in an effort to ensure that expanded well plan ellipses due to last minute discovery of a "bad" survey in an offset well would not lead to unacceptable collision risk. Kudos to the Operator who had the staff to review offset well surveys and discover this problem.
Posted by

Chris Henderson

Directional Driller

SPREADAssociates

Total Posts: 129
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