slide 1 Understanding Magnetic Disturbance & unreliable azimuths The magnetic environment Measuring field strength & dip angle Setting the thresholds for MagIC Running a survey MagIC identifies the disturbance Adjust unreliable azimuths Calculate and plot the true hole path E N C O R E Borehole Surveys WHERE DID THAT DRILLHOLE GO?
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Understanding Magnetic Disturbance & unreliable azimuths
The magnetic environment Measuring field strength & dip angle Setting the thresholds for MagIC Running a survey MagIC identifies the disturbance Adjust unreliable azimuths Calculate and plot the true hole path E N C O R E Borehole Surveys WHERE DID THAT DRILLHOLE GO?. - PowerPoint PPT Presentation
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slid
e 1
Understanding Magnetic Disturbance& unreliable azimuths
The magnetic environment Measuring field strength & dip angle Setting the thresholds for MagIC Running a survey MagIC identifies the disturbance Adjust unreliable azimuths Calculate and plot the true hole path
E N C O R EBorehole Surveys WHERE DID THAT DRILLHOLE GO?
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Magnetic threshold and Azimuth accuracy
At any specific place on the earth's surface, these values are known.Variation - angular difference between True North and Magnetic NorthMagnetic Field Strength - the force of the earth's magnetic fieldMagnetic Dip Angle - angle the field force lines make with the horizontal
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Measure local magnetic data
Take several single-shot measurements, with SensIT
on the ground, clear of any magnetic disturbance.
Enter values into MagIC set-up, with reasonable tolerances.
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Run a multi-shot survey of the hole, or section
1 If possible, survey before running casing.
2 Take shots at close intervals; 3m or 6m max.
3 Pull out and download SensIT into StoreIT
4 Transfer survey to MeasureIT on PC
It’s so simple withFLEXIT
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Understanding Magnetic Disturbance& unreliable azimuths
This example is from a hole in Chile Collared at dip of - 67 degrees and a
direction of 270 degrees true Cased NX to 85 metres Cored NQ to 390 metres
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1 SensIT records Magnetic Field Strength & Dip Angle at each station
2 Within the set thresholds (white), the measured hole azimuth is reliable; MagIC will then apply the variation.
4 Outside the thresholds, (yellow) the azimuth at that station is unreliable.
The MagIC quality check
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• Take an average of the nearest “clean” azimuth above and below the unreliable values (yellow).
• Enter that average into the Azimuth box and click Change
MagIC quality check; adjusting the hole azimuth.
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Plotting the hole paths, in section. The measured hole & the MagIC hole.
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Understanding Magnetic Disturbance& unreliable azimuths
This example is from Scotland Collared at a dip of - 74 degrees and a
direction of 50 degrees true Depth of 120 metres; no Casing Two separate magnetic disturbances
between 48 - 60m and 78 - 84 metres
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Set the threshold for the magnetic environment.
It’s so simple withFLEXIT
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Identifying magnetic disturbance.
It’s so simple withFLEXIT
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Removing the effects of magnetic disturbance.
It’s so simple withFLEXIT
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Plotting the hole paths, in plan.The measured hole & the MagIC hole.
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Plotting the hole paths, in section. The measured hole & the MagIC hole.
Now I know where that drillhole went,in spite of magnetic disturbance!