Motivation:
- MWD wellbore azimuth is determined relative to the geomagnetic field
- Converting magnetic azimuth to true azimuth requires knowledge of the direction of the geomagnetic field, at the point of measurement downhole
- Since Earth’s magnetic field varies spatially and with time, referencing against it requires measurement of the spatial and temporal variations
Magnetic Field Components: Main Field, Crustal Field, Disturbance Field
- Disturbance field components
- Stable component: originates from the ring current; varies with solar cycle
- Seasonal component: periods of months to 1 year, accounted for by global measurements and subsequent modeling
- Rapid variations: solar storms, diurnal variations, auroral events - short timescale typically less than 2 weeks, events with large magnetic swings
Source of Disturbance Field
- The solar wind deforms Earth’s fields steadily and impulsively
- This requires disturbance field monitoring to capture time variation
Disturbance Field Averages (1-sigma, magnetic storm*)
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View the entire Presentation:
On-Site Disturbance Field Measurement: A Portable Real-time Disturbance Field Monitoring Station
MagVar