Airborne Resistivity Mapping with Helicopter TEM: An Oil Sands Case Study S. Walker and J. Rudd,...
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Transcript of 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
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Acknowledgements• Husky Oil• Doug Oldenburg, Scott Napier
and Roman Shekhtman (UBC-GIF)• Jim Henderson (AGL)• Aeroquest International
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Outline• Introduction• Geologic Setting• EM System Descriptions• Qualitative Data Comparison• Quantitative Comparison• Conclusions
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Introduction• Oil Sands prospect in Northern Alberta• Test survey flown for Husky Oil• Provided three lines of comparison data
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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)
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Qualitative Comparison• Common first step• Data or image based• Focus on northern most line
Line 1
Line 2
Line 3
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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)
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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)
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Quantitative Comparison• Rigorous 1D EM Inversion• What can we see and do we believe it?• Focus on specific soundings (1, 2, 3)
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Recovered Models (Stn 1)
10 Ωm ref. model 20 Ωm ref. model
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Recovered Models (Stn 2)
10 Ωm ref. model 20 Ωm ref. model
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Recovered Models (Stn 3)
10 Ωm ref. model 20 Ωm ref. model
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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
)()()(
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Models with DOI Index (Stn 1)
10 Ωm ref. model 20 Ωm ref. model DOI Index
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Models with DOI Index (Stn 2)
10 Ωm ref. model 20 Ωm ref. model DOI Index
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Models with DOI Index (Stn 3)
10 Ωm ref. model 20 Ωm ref. model DOI Index
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Pseudo 2D Model (Line 1)
• Geologically interpretable• DOI helps know when to stop
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
Pseudo 3D Model
Airborne Resistivity Mapping with Helicopter TEM
KEGS Symposium: Geophysical Contributions to New Discoveries
Exploration ’07, Toronto, September 2007
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