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Case Study: Added Value of Contaminant Mapping Using
Capacitively Coupled Resistivity in Pseudo‐ 3D form Combined with
Frequency‐Domain ElectromagneticsPresenter: Adam Peake, P.Geo.
DMT Geosciences Ltd.
In Collaboration With: Christian Lavallee, Environmental Specialist.
Precision Drilling Corporation
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Overview• Site Description• Objectives• Methods / Instruments
– Advantages and Disadvantages• Survey Design• Acquisition• Results• Challenges• Added Value for Client• Conclusions
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Fence
150m
120m
EM31 Survey Extents
Well Location
Looking NW Looking NE
Looking SW Looking SE
Site Description
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• Objectives– Identify and map contaminated zone
• EM31 and OhmMapper– Pseudo‐3D OhmMapper data
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Methods / InstrumentsEM31 OhmMapper
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• Geonics EM31 MK II Conductivity Meter• GPS integrated in real time• Average over exploration extents.
• 5‐6 metres• High data density – 1 reading / second.
GPSEM31
Tx
Rx
Image from: http://asstgroup.com/techniques.html
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Advantages/Disadvantages of EM31
Advantages:• Quick• Ease of use• Site overview
Disadvantages:• Limited depth info.• Higher conductivity reduces depth of investigation.
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Conventional Resistivity
• Labour and equipment intensive.• Stationary.• Time intensive.
• Electrical Resistivity Imaging (ERI)
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Geometrics OhmMapperCapacitively Coupled Resistivity
Data Acquisition• GPS linked
Many configurations• Cable lengths• Rope lengths
GPS
Weight to preventlifting cable
Rx 5Rx 4
Rx 3Rx 2Rx 1Tx
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OhmMapper Vs. ERIDipole‐Dipole Array
http://geoscixyz.readthedocs.org/en/latest/content/DC_resistivity/DC_measurements_and_data.html
• Conventional ERI
• OhmMapper
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Advantages/Disadvantages of OhmMapper
Advantages:• Depth information • Quick ‐ Dragged• Efficient ‐ Limited personnel • Very high horizontal resolution
– 2 readings/second
Disadvantages:• Shallower depth than ERI• Higher conductivity reduces
ability to receive data • Only water resistant• Difficult to drag by hand
and/or rough terrain
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Survey design
• Reconnaissance style EM31– Identify targets and background
• Targeted Pseudo‐3D OhmMapper survey– Characterize target
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EM31 Acquisition
• EM31 = one continuous traverse, approx. 3m apart
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Short RopeLong Rope
Short Rope
Long Rope
OhmMapper Acquisition• 25 Lines ‐ 2 passes per line
– Different rope lengths• 0.625m and 2.5m
• Lines approx. 3‐5 metres apart.– Pin‐flagged.
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Results• EM31 Results• Expectation Vs. Reality• OhmMapper Results
– Challenges
• Added Value for Client• Pseudo 3D
– Possible Subsurface Propagation
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EM31 Results –With Snow
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EM31 Results – No Snow
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EM31 Results – CompareWith Snow
No Snow
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Expectation vs. RealityExample 1
Example 2
Example 3
Example 4
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OhmMapper Results• 3 Attempts – 3rd was successful.
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Challenges
• Improper coupling possibility.– Thick crust– Granular snow– Air pockets?
• Increased distance from ground surface– Capacitance inversely related to distance
Air/Loose Snow?
Loose Snow?Compact/Drifted
Interconnected Snow?
Crust Surface
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Added Value for Client
• Accurate borehole locations• Volume estimates• Possible subsurface propagation
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• Before GeophysicsSuggestedBoreholes
Accurate Borehole Locations
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Accurate Borehole Locations• After GeophysicsSuggestedBoreholes
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Accurate Borehole Locations• Before GeophysicsSuggestedBoreholes
• After GeophysicsSuggestedBoreholes
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Accurate Borehole Locations• After Actually Drilled
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Pseudo‐3D • 75 to 325mS/m• Vertical Ex. = x3
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Psuedo 3D ‐Volume Estimates• Any Conductivity (Confined depth)
Iso‐Surface Value
Volume within Iso‐Surface (m3) – Limited to 4m depth
125 mS/m 1640m3
185 mS/m 350m3
250 mS/m 129m3
300 mS/m 52m3
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Evaluation• Revisit Conductivity Iso‐surfaces• 108mS/m appears
to closer match exceeding salinity
• Upper 0.5 to 1m stockpiled in some places?
New Iso‐Surface Value Volume within Iso‐Surface (m3) –Limited to 4m depth
108 mS/m 3150m3
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Evaluation• Stockpile material?
Looking Northwest
• 108mS/m• Vertical Ex. = x3
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ckpile material?Evaluation • 108mS/m
• Vertical Ex. = x3
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ssible Subsurface PropagationEM31 OhmMapper Depth Slice – Near Surface
SouthNorth X‐section
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ssible Subsurface Propagation
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Conclusion
QuickEasyTargeted borehole locationsPossible volume savingsAnother perspective to understand all dataMight not work correctly in certain snow situations.
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Wolf
Rx 4
Rx 3
Rx 2
Rx 1
Thank you!
DMT Geosciences Ltd.Suite 415, 708-11th Ave. S.W.Calgary, Alberta,Canada, T2R 0E4403-264-9496
Suite 1030, 789 West Pender St.Vancouver, British ColumbiaCanada, V6H 1H2604-293-2800