Error Model Documentation Archive
This page is an archive of mostly historical technical documents relating to the error model. These documents help to explain or clarify parts of the error model, but should be considered as historical context since details may have changed since they were produced.
The latest details of the the error model can be found here.
Uncertainties in Connection with the Determination of Wellbore Positions
PhD Thesis by Roger Ekseth
Roger Ekseth's 1998 PhD thesis was one of the principal contributions to the early development of the ISCWSA error model. In particular, Roger did much of the work on the depth model that we currently use. It's fitting that we can now host his thesis on the ISCWSA page making it more widely avaiable and also acknowlege the contribution that Roger made.
Corrections to Roger Ekseth's 1998 PhD Thesis (2012)
This document includes some errata from the published document, with corrections from Roger, Torgeir Torkildsen and Jon Bang (some of the later handwritten changes are not included in the thesis download above).
Some historical documents written by Steve Grindrod at Copsegrove Developments:
Test Profile Differences (2020) - discusses some of possible differences in interpretation of the three standard error model test profiles.
Depth Error Term Values (2009) - an explanation of the terms used in the fixed and floating MWD models.
MWD Toolface Independant Terms (2009) - explains the derivation of the toolface independant sensor terms.
MWD Toolface Independant Tool Error Terms (2011) - shows the changes required to move from a Rev2 to a Rev3 version of the MWD error model.
Additional Tool Error Models (2013) - an early extension of the ISCWSA documented set from MWD to MWD+IFR/IIFR etc.
Error Model Terms for IGRF and HDGM (2012) - a presentation by Stefan Maus to the error model committee justifying term magnitudes for the IGRF and HDGM models. See also the following presentations from main ISCWSA meetings which touch on the same subject:
Release and Validation of the High Definition Geomagnetic Model 2011
Systematic and Random Contributions to the Disturbance Field (IFR 2) (2014)
Two mathematical derivations from Chad Hanak at Superior QC:
Correct Vertical Well Weighting Functions for Cross-Axis Accelerometer Bias Terms
A rigorous derivation of the accelerometer sensor terms in the singular case where the well is vertical.
Mathematical Deriviation of the XCLA Weighting Function (added 16/9/22)
A document deriving the XCLA error term.
History of ISCWSA MWD Model Revisions
A spreadsheet detailing the MWD and MWD+Axial variants of the model at each revision. (added 23/9/22)
OWSG Toolcodes - Previous Release (2015)
The error model maintenance committee is now responsbile for a standard set of models. These have been update to the latest release, revision 5 which now replaces these older versions. Although now out of date, copies of the earlier models are included below for reference.
These documents were created by Steve Grindrod from Copsegrove.
OWSG Rev2 Diagnostics SetA SetB
Flowchart for Selection of OWSG Models
Example worksheets for Rev4 (= OWSG Rev2) on the test wells: