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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?.

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Understanding Magnetic Disturbance & unreliable azimuths

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  1. 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? Understanding Magnetic Disturbance& unreliable azimuths

  2. 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 North Magnetic Field Strength - the force of the earth's magnetic field Magnetic Dip Angle - angle the field force lines make with the horizontal

  3. Measure local magnetic dataTake several single-shot measurements, with SensITon the ground, clear of any magnetic disturbance. Enter values into MagIC set-up, with reasonable tolerances.

  4. 1 If possible, survey before running casing. 2 Take shots at close intervals; 3m or 6m max. 3 Pull out and download SensITinto StoreIT 4 Transfer survey to MeasureIT on PC Run a multi-shot survey of the hole, or section It’s so simple with FLEXIT

  5. 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 Understanding Magnetic Disturbance& unreliable azimuths

  6. The MagIC quality check • SensIT records Magnetic Field Strength & Dip Angleat each station • Within the set thresholds (white), the measured hole azimuth is reliable; MagICwill thenapply the variation. • Outside the thresholds, (yellow) the azimuth at that stationis unreliable.

  7. MagIC quality check; adjusting the hole azimuth. • 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

  8. Plotting the hole paths, in section.The measured hole & the MagIC hole.

  9. 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 Understanding Magnetic Disturbance& unreliable azimuths

  10. Set the threshold for the magnetic environment. It’s so simple with FLEXIT

  11. Identifying magnetic disturbance. It’s so simple with FLEXIT

  12. Removing the effects of magnetic disturbance. It’s so simple with FLEXIT

  13. Plotting the hole paths, in plan.The measured hole & the MagIC hole.

  14. Plotting the hole paths, in section.The measured hole & the MagIC hole.

  15. Now I know where that drillhole went,in spite of magnetic disturbance! E N C O R EBorehole Surveys

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