Magnetic Variation Services
- Part of Helmrich and Payne Technologies (Tulsa, OK)
- MagVAR – MWD Survey Specialists. Based In Denver
- Motive Drilling – Directional Advisory system. Based in Dallas
- Terravici - Rotary Steerable. Based in Houston
- MagVAR Products and Services:
- Accurate Magnetic Models – both Global and Local (IFR1)
- Real-time QC and corrections of magnetic MWD
- Local magnetic observatories
- Aeromagnetic and drone services
How to Determine the needed amount of Non-magnetic Spacing in a BHA
- Magnetometers must be spaced far (!!?) from ferromagnetic (steel) components of the BHA to reduce magnetic interference
- This DrillString magnetic Interference (DSI) will be in the long (Z) axis
- Spacing from magnetic sources must be sufficient to keep the azimuth error consistent with error model in use
- DSI depends only on the distance and the strength of magnetization
- Total magnetization is the vector sum of residual (semi-permanent) and induced (temporary) magnetization.
- Non-Mag will always be needed for magnetic MWD
- Gyro alternatives are not yet practical
Interference is from Residual + Induced Magnetism
- Magnetic Model using ViziMag
- 3.18 External field is 50 uT
- Size is 10x10 m (Not to Scale - Illustration only)
Why is shorter non-mag spacing desirable?
- Reduces Bit-Sensor Spacing
- Makes steering easier – less projection needed
- Directional Driller ‘sees’ trajectory changes earlier
- Earlier detection of external magnetic interference
- Better anticollision warning indicator
- Allows optimizing sensor location to reduce Sag error
- Saves non-mag costs including Lost in Hole (LIH)
- Drawback: increased DrillString Interference (DSI)
- DSI is virtually all in the Z-Axis direction
Magnetic Field drops off as inverse square of distance
- Magnetic Interference is typically modeled as a number of monopoles
- Principle of Superposition allows any magnetic field to be modeled as the sum of monopole fields.
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View the entire Presentation:
Non-Magnetic Spacing with Axial Corrections
Neil Bergstrom, P.E.