Overview:
- Degauss completely using low frequency AC. If there is measureable residual magnetism it is best to leave a + pole on the top end of the motor/stab/float to cancel some of the field from the + pole on the bottom of the drillpipe / collars
- Record pre and post run residual magnetism from major parts. (motor / float / stab / XO / filter sub / HWDP
- Compare with calculated DSI from MWD sensor data
- Use at least 10 feet of non-mag spacing even when drilling N-S to avoid cross-axial errors and induced magnetism effects
- Use non-mag stabilizers and subs when possible
- BHA materials should NOT be low coercivity mild steel. Use either
– Non-magnetic
– High Coercivity (hard to magnetize and demagnetize)
- Parts that contact steel casing should be non-mag
- Assume 1000 uW poles unless any parts >5 gauss at 6” are eliminated. Then 500 uW poles are OK
- Collect statistics on pole strengths after degaussing to justify assumptions before using smaller values
- Plot Gtotal, Btotal, and Dip angles vs measured depth and look for trends
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View the entire Presentation:
Neil Bergstrom - SPE WPTS