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?

slide 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

slide 3 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.

slide 4 Run a multi-shot survey of the hole, or section 1If 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 with FLEXIT

slide 5 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

slide 6 1SensIT records Magnetic Field Strength & Dip Angle at each station 2Within the set thresholds (white), the measured hole azimuth is reliable; MagIC will then apply the variation. 4Outside the thresholds, (yellow) the azimuth at that station is unreliable. The MagIC quality check

slide 7 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.

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

slide 9 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 m and metres

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. It’s so simple with FLEXIT

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

slide 14 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 E Borehole Surveys