Transcript PPTMagicMS

Understanding Magnetic Disturbance
& unreliable azimuths
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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
slide 1
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At any specific place on the earth's surface, these values are known.
Variation - angular difference between True North and Magnetic North
Magnetic Field Strength - the force of the earth's magnetic field
Magnetic Dip Angle - angle the field force lines make with the horizontal
slide 2
Magnetic threshold and Azimuth accuracy
Measure local magnetic data
Enter values into MagIC set-up, with reasonable tolerances.
slide 3
Take several single-shot measurements, with SensIT
on the ground, clear of any magnetic disturbance.
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
It’s so simple with
FLEXIT
slide 4
4 Transfer survey to MeasureIT on PC
Understanding Magnetic Disturbance
& unreliable azimuths
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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
slide 5
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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.
slide 6
The MagIC quality check
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Take an average of the nearest “clean” azimuth above
and below the unreliable values (yellow).
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Enter that average into the Azimuth box and click Change
slide 7
MagIC quality check; adjusting the hole azimuth.
Plotting the hole paths, in section.
slide 8
The measured hole & the MagIC hole.
Understanding Magnetic Disturbance
& unreliable azimuths
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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
slide 9
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It’s so simple with
FLEXIT
slide 10
Set the threshold for the magnetic environment.
It’s so simple with
FLEXIT
slide 11
Identifying magnetic disturbance.
It’s so simple with
FLEXIT
slide 12
Removing the effects of magnetic disturbance.
Plotting the hole paths, in plan.
slide 13
The measured hole & the MagIC hole.
Plotting the hole paths, in section.
slide 14
The measured hole & the MagIC hole.
Now I know where that drillhole went,
in spite of magnetic disturbance!
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