BGS Global Geomagnetic Model

What is the BGGM?

The BGS Global Geomagnetic Model (BGGM) is a mathematical model of the Earth's magnetic field in its undisturbed state. It is revised every year to allow for the inclusion of new data collected since last revision and any development of the modelling methodology. With annual revisions it is also possible to minimise errors arising from predicting the field at some date after the time span of input data. In 2019 the maximum spherical harmonic degree increased from 133 to 1440. Degree 133, representing features of wavelength 300 km at the Earth's surface, is close to the maximum resolution that can be achieved with satellite data above 300 km altitude. By including information from near-surface total intensity anomaly compilations the theoretical resolution can be increased to 28 km.

What is it for?

The BGGM is widely used in the oil industry for directional drilling with Measurement-While-Drilling (MWD) magnetic survey tools. These tools measure the direction of the well-bore relative to the direction of the local geomagnetic field and are used to navigate wells towards precisely known underground targets. The local geomagnetic field is determined using the BGGM and the MWD data can then be used to give the drilling location in a geographic reference frame. An enhancement of this is to determine the local crustal field using either local absolute observations of the geomagnetic vector or transformation of local total intensity data collected during an aeromagnetic or marine survey. A further enhancement is to take account of the rapidly varying external field using nearby observatory data. These enhancements are referred to as In-Field Referencing (IFR)/IFR1 and Interpolation In-Field Referencing (IIFR)/IFR2 respectively.

How can I get it?

The model and associated software are available under licence from the BGS. Licence holders receive source code for incorporation into their own software throughout company, DLLs, Excel implementation examples, a Windows program for use throughout company, access to the web service and documentation.

How accurate is it?

Scalable 1-sigma error estimates are output by all BGGM software. These estimates are derived from the work published in Beggan et al (2021) SPE 204038 and presented at the SPE/IADC International Drilling Conference in March 2021. They combine errors from the unmodelled crustal field including effect of near-surface data coverage, unmodelled external field and core field prediction and are converted from XYZ to DIF taking account of main-field geometry.

Use the tool below to show estimated errors for the BGS Global Geomagnetic Model (BGGM) for a given set of coordinates and date. These are split into ISCWSA G and R for Global and Random errors which determine error propagation in industry models. Further upgrades to ISCWSA revision 5, accounting for correlated and uncorrelated errors, can be requested at contacts below.

Either enter the geodetic latitude and longitude or simply click on the map. The expected drilling date may also be set.