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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 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!

E N C O R EBorehole Surveys