Directional Drilling Applications & Services

The oil industry uses directional drilling operations to continuously monitor the azimuth and magnetic dip of the well path to ensure the target is reached and, for safety reasons, to avoid collisions with existing wells. An alternative approach to the gyroscopic method is to make measurements while drilling (MWD) along the well path by magnetometers housed in a tool within the drill string. These MWD magnetic surveys require real-time estimates of the Earth's magnetic field at the drilling location to correct the downhole magnetometer readings in azimuth and inclination.

The most accurate way to monitor azimuth and dip is when all sources of the Earth's magnetic field are accounted for: core and crustal fields and external field changes. To quantify the external field which can cause declination to vary sharply within a couple of minutes during a geomagnetic storm, real-time observatory-quality data can be used. This technique called interpolated in-field referencing (IIFR/IFR2) is to reduce the directional errors associated with the estimated fields at mid- and high-latitude drill sites. This improvement can vary depending on the season, local time and the phase of the solar cycle.

The BGS Global Geomagnetic Model (BGGM) is a mathematical model (or map) of the Earth's magnetic field, which includes the core and large-scale crust, but not the small-scale crust or disturbance field. For more information about our BGGM visit our BGGM page.

Annually in April. The latest version of the BGGM gives the best estimate of the magnetic field direction and strength, and a realistic uncertainty associated with these values. An annual update is needed to maintain the level of accuracy required by the industry for directional drilling.

The annual upgrades to the BGGM primarily improves the capture of the magnetic field from the Earth's core and the ever-present large-scale symmetric ring current. We integrate the latest satellite data and ground observatory data to update the time-varying spherical harmonic coefficients. Location- and time-dependent/dynamic error estimates have also been updated from newly assimilated observatory data as we enter new phase of the solar cycle. We always recommend using the latest version of the BGGM. Especially so for wells in areas of complex geology and high geomagnetic latitudes where effects of external field disturbances are prominent and well position accuracy is key.

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. By including information from near-surface total intensity anomaly compilations the resolution can be increased to 28 km.

If you are interested in dates further into the future, declination differences will be greater. If there are areas and dates for which you would like a more detailed analysis of the difference between the models, please let us know the details by emailing iifr@bgs.ac.uk and we can investigate. We do not routinely publish tables of rates of change as these are both time and location specific and thus vary considerably. This information is commercially sensitive as it is provided by the BGGM software.

The BGGM is a higher resolution model compared to freely available models such as the International Geomagnetic Reference Field (IGRF) and the World Magnetic Model (WMM). It models the magnetic signature of the large-scale core, or main field, as well as crustal field arising from small-scale local geological feature. BGGM also incorporates the annually varying part of the external field caused by the interaction between Earth's magnetic field and the Sun's solar wind.

Furthermore, in Figure 2 of the 2022 World Magnetic Model Technical Update by NOAA-NCEI and BGS, you can see a map of the differences between the WMM prediction of the rate of change of the total magnetic intensity and the latest satellite observations to the end of 2022. This divergence between a five-year prediction and observations over time is the primary reason for our annual updates to the BGGM model. BGGM better captures the declination angles closest to the magnetic poles such as in Alaska, Canada and the Barents Sea.

Freely available models, such as IGRF or WMM, do provide some limited information in this regard. However, these models are updated every five years, unlike the annual upgrade of the BGGM, so they will only provide an "average" model over the five-year period. These will not fit the true field exactly at any specific location or time but will give magnetic values that may be broadly accurate enough for purposes such as surface navigation, however, they lack the precise information needed for subsurface navigation.

In-Field Referencing (IFR), known as IFR or IFR1 is a technique to determine the vector magnetic field in the subsurface by including sources from the Earth's core and in the crust (magnetised local rocks causing crustal anomalies).

In addition to IFR1, Interpolation In-Field Referencing, known as IIFR or IFR2 is a technique to further improve the accuracy of the estimated field values provided from IFR, by including the time-varying external (or disturbance) fields measured in real-time at a nearby obsrvatory. The following components of the geomagnetic field are provided by our IFR services:

• F - total field strength
• D - magnetic declination angle
• I - magnetic dip (inclination) angle

You can download our brochure for In-Field Referencing (IFR1) and Interpolation In-Field Referencing (IFR2) services 2.96 MB pdf

BGGM is not designed to include small-scale magnetic anomalies (<28 km), though this is accounted for using our IFR services. In regions of very large crustal field gradients (e.g. Alberta), accurate geomagnetic field estimates rely on requesting IFR values. BGGM does not account for rapid external field disturbances, but real-time estimates of full field variations is included in our IFR2 service - providing F, D and I data minute-by-minute, thereby reducing uncertainty even further.

IFR1 data is in effect BGGM + crustal field variations. The resolution of the current BGGM reaches up to 28 km, but this can be improved by adding local aeromagnetic datasets. We must first establish an IFR setup at the drilling site using aeromagnetic survey data gridded to 1 km to account for small-scale crustal field anomalies caused by local geology around the drill site.

Assessing the uncertainties is part of the work we do when we set up a new field for IFR. You can reduce the uncertainty by using IFR1 compared to using BGGM alone.

IFR2 is IFR1 + real-time observatory data. IFR2 requires observatory data from one or more observatories located within 500 km of the drill site to accurately capture external field variations in real-time (or retrospectively) at the drilling site - in effect recreating a virtual observatory downhole. Applying IFR2 data at the drill site will remove the external field variation and capture local crustal field. IFR2 corrections are extremely important during geomagnetic storms but will also track the typical quiet diurnal changes in the local magnetic field. In some areas, this can exceed the ISCWSA uncertainties. The daily variation is greater in local summertime than winter and changes over the 11-year solar cycle.

IFR2 data from BGS can be accessed using a secure password-protected web service for your company to pull the data from. Data are updated every minute in near real-time (typical lag time is 2-3 minutes) so that all sources of geomagnetic disturbances are accounted for.

No, but if you are a full-license holder of the BGGM and therefore has login credentials on our system, then IFR2 can be made available quickly. Our observatory data are QC'd in real-time during normal working hours.

Yes. We will send you a quote for the current year BGGM license. Once the application is processed, the BGGM coefficient files can be integrated into the third party software either directly for Full Licence holers or via the BGGM webservice for Single User License holders.

The one-off cost to create a field set up is dependent on the location and complexity of the IFR setup work. For us to provide a formal quote for an IFR set-up we would require the coordinate location of the named field or well plan in latitude and longitude and state the datum. We would then ascertain if there were any existing IFR setups available for the operator to use and if not, we would investigate whether we have access to or are able to source aeromagnetic data. In some regions aeromagnetic data are proprietary so if it is owned by your company or the operator is willing to share the data with BGS this can accelerate the processing time.

A new IFR setup should take up to one month - but usually less - depending on the complexity of the work reflected in the charges.

Depending on the region, BGS may require permission to use data from local obsrvatories for IFR2. Through discussing with the local institute(s), we can arrive at an estimate of the budget for IFR2 service. BGS operates observatories in the UK (three sites for the North Sea), Fort McMurray (Alberta) and Jim Carrigan (North Slope, Alaska). Please email iifr@bgs.ac.uk to discuss.