Airborne Resistivity Mapping with Helicopter TEM: An Oil Sands Case Study S. Walker and J. Rudd,...

Airborne Resistivity Mapping

with Helicopter TEM:An Oil Sands Case Study S. Walker and J. Rudd, Aeroquest International

Ltd.

KEGS Symposium: Geophysical Contributions to New Discoveries

Exploration ’07, Toronto, September 2007

Airborne Resistivity Mapping with Helicopter TEM



Acknowledgements• Husky Oil• Doug Oldenburg, Scott Napier

and Roman Shekhtman (UBC-GIF)• Jim Henderson (AGL)• Aeroquest International




Outline• Introduction• Geologic Setting• EM System Descriptions• Qualitative Data Comparison• Quantitative Comparison• Conclusions




Introduction• Oil Sands prospect in Northern Alberta• Test survey flown for Husky Oil• Provided three lines of comparison data




Geologic SettingGeologic

UnitResistivity (Ωm)

Thickness (m)

Overburden

100’s 0 – 200

Clearwater Formation

2-10 0 – 30

McMurray Formation

100 – 1000

50 – 100

DevonianBasement

1 – 1000 N/A

Glacial cover

Shale

Oil Sands

Limestonewith/withoutsalt water




EM System Descriptions• AeroTEM IV (Aeroquest)

– Helicopter TEM• 90 Hz, Triangular pulse, 190,000 Am2

• Z comp., 17 off-time gates (2.01 – 5.13 ms)

• GeoTEM (Fugro)– Fixed-wing TEM

• 30 Hz, Half-sine pulse, 690,00 Am2

• X comp., 14 off-time gates (4.58 – 15.59 ms)

• Resolve (Fugro)– Helicopter FEM

• 5 coplanar freq. (400, 1500, 6200, 25k, 100kHz)




Qualitative Comparison• Common first step• Data or image based• Focus on northern most line

Line 1

Line 2

Line 3




Features in Data• Paleo-channel• Depth to the

Clearwater• Surface detail • Bird height

variation• Good first pass• But…

AeroTEM Z (nT/s)

GeoTEM X (pV/m2)

CP Inphase (ppm)

CP Quad (ppm)




Spatial Resolution• Detailed view of

paleo-channel data

• Sampling Freq.• Survey speed• Effect of foot print

• Need to do something else…

AeroTEM Z (nT/s)

GeoTEM X (pV/m2)

CP Inphase (ppm)

CP Quad (ppm)




Quantitative Comparison• Rigorous 1D EM Inversion• What can we see and do we believe it?• Focus on specific soundings (1, 2, 3)




Inversion Algorithm• EM1DFM and EM1DTM (UBC-GIF)

• Model: log(σ), layered earth model• Data misfit

– Chi squared, noise estimates important

• Model Norm– Flattest and smallest model

• Remember that solutions are non-unique!!

md min




Recovered Models (Stn 1)

10 Ωm ref. model 20 Ωm ref. model














Depth of Investigation Index

• Oldenburg and Li (1999)

• if R = 0: m1 = m2

– More reliable model

• as R → 1: m1, m2 → m1ref , m2ref – Less reliable model

• Apply to our models and take a look…

refref mm

zmzmzR

21

12111

)()()(




Models with DOI Index (Stn 1)

10 Ωm ref. model 20 Ωm ref. model DOI Index














Pseudo 2D Model (Line 1)

• Geologically interpretable• DOI helps know when to stop




Pseudo 3D Model




Conclusions• Helicopter TEM has worked well

in the Oil Sands• High spatial resolution• Sensitive to both near surface

and deep features• Pseudo 3D models• Start applying it in other areas

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Airborne Resistivity Mapping with Helicopter TEM: An Oil Sands Case Study S. Walker and J. Rudd,...

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