HDGM Error model is a scaled version of the magnetic error values provided in the Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA) Measurement While Drilling (MWD) model (Reference: SPE 67616). The multiplier was derived by comparing measured Total Magnetic Field Strength values with those predicted by the geomagnetic models. The Declination and Magnetic Dip angular values were checked to confirm the same multiplier was valid. The error values in the following table may be interpreted as one standard deviation difference between a hypothetical measurement and the calculator result for a location. More details of the scaling method is available in the paper SPE 151436.
Model | |
HDGM | 0.82 |
Standard | 1.00 |
IGRF/WMM | 1.21 |
Model | ||||
MFI (nT) |
MDI (Deg) | AZ (Deg) | *DBH (Deg.nT) | |
HDGM | 107 | 0.16 | 0.30 | 4118 |
Standard | 130 | 0.20 | 0.36 | 5000 |
IGRF/WMM | 157 | 0.24 | 0.43 | 6029 |
*BH dependent error term. For example, the declination error of HDGM model in Boulder, CO (H = 20,800 nT) is calculated as √0.30^{2} + (4118/20800) ^{ 2} = 0.36°. Standard model is defined as an annually updated geomagnetic model with a spherical harmonic degree and order of 50.
For locations where magnetic survey data are not available, the HDGM software outputs the Standard ISCWSA model error, reflecting the lower resolution of the model at that location. See the following figure for HDGM’s magnetic data coverage (purple).
SPE 67616; Williamson, H. S. (2000). Accuracy prediction for directional measurement while drilling. SPE Drilling & Completion, 15(04), 221-233 https://www.onepetro.org/journal-paper/SPE-67616-PA
SPE 151436; Maus, S., M. C. Nair, B. Poedjono, S. Okewunmi, J. D. Fairhead, U. Barckhausen, P. R. Milligan, J. Matzka (2012), High Definition Geomagnetic Models: A New Perspective for Improved Wellbore Positioning, IADC/SPE Drilling Conference and Exhibition, 6-8 March 2012, San Diego, California, USA, doi: 10.2118/151436-MS https://www.onepetro.org/conference-paper/SPE-151436-MS