Transcript Using Ground Penetrating Radar to Detect Oil in Ice and Snow

Using Ground Penetrating Radar
to Detect Oil in Ice and Snow
E. Babcock1, J. Bradford1, H.P. Marshall1, C.
Hall2, and D.F. Dickins3
1Department
of Geosciences, Boise State University, Boise ID; 2Alaska
Clean Seas, Anchorage AK; 3P.Eng., DF Dickins Associates Ltd., La Jolla CA
Overview
• Ground Penetrating Radar (GPR) theory
• Considerations for detecting oil under ice and
snow
• Demonstrations in controlled environment
spill response
• Future work
Brief History of GPR (Olhoeft, 2006)
• 1926: Radar used to sound the depth of an alpine
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glacier in Austria (Stern, 1929)
1958: USAF airplane crashed on Greenland ice
sheet as radar energy passes through surface
to layers below
1960s: GPR used to sound moon during Apollo 17
1970s: Begin widespread use of GPR as a
geotechnical tool
1980s: GPR assessed as tool for oil detection under
ice(Goodman et al., 1985 and 1987)
Fundamentals of GPR
• GPR uses electrical energy to interrogate
the subsurface
• Operates at radio frequencies
– 10 MHz to 1 GHz
• Transmit timed pulses of EM energy;
measure reflected returns, process data,
and display
Annan, 2002.
Material Electrical Properties in the Arctic
Marine Environment
Material
Relative
Dielectric
Permittivity
Conductivity
(S/m)
Velocity
(m/ns)
Wavelength
@ 500 MHz
Air
1
0
0.3
60 cm
Sea Water
88
1-5
No
propagation
No
propagation
Sea Ice
4-8
.01 - 0.1
0.134-0.150
27 cm
1.4 – 3.1
0.000001
0.25 - 0.168
50 cm
2-4
0.000010.0005
0.212
42 cm
Snow
Oil
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GPR for Oil Spill Response
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Can we detect oil under ice and/or snow?
What processing do the data require?
What resolution can the system provide?
What limitations do we experience?
What benefits does this technology provide?
System Considerations:
Data Processing
• Use standard basic processing steps
– Time zero shift
– Bandpass filter
– Spherical spreading correction
• Attribute analysis
– Instantaneous phase and frequency
– Reflection strength
– Previous work with GPR noted potential using
attribute analysis to detect oil that was not
possible with conventional analysis
System Considerations:
Antenna Frequency
• Frequency for radar survey is a trade-off
– Depth of penetration
– Quality of resolution
– System portability
• Field testing shows that GPR frequency of 500
MHz is optimal for penetration and resolution
of oil under ice
System Considerations:
Resolution and Detection
• Using 500 MHz antennas
– Detect 1-2 cm oil layer in most scenarios
– Resolve 4-5 cm oil layer
• Thin bed analysis problem
– Reflection analysis alone not enough to accurately
locate oil
– Previous work had indicated attribute analysis as
possible solution (Goodman et al., 1985)
– Consider attributes in conjunction with modeled
response
System Considerations:
Non-Uniqueness
From Bradford et al., 2008
System
Considerations:
Anisotropy
Data courtesy of Alaska Clean Seas
Control Module (Digital Video Logger)
- Sensors and Software PE Pro
www.sensoft.ca
Prudhoe Bay, April 2007
2008 Training on North Slope
Norway, 2006
• Pulse Ekko Pro GPR
• 500 and 1000 MHz
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antennas
Multi-offset acquisition to
determine effective
permittivity of ice
Pre- and post- oil
emplacement 3D
surveying over 20 x 20 m
grid
Large scale 2D profiling
GPR for Oil Spill Response: Svalbard
From Bradford et al., 2008
Controlled Spill, New Hampshire,
2004,2011-2013
• Cold Regions Research and Engineering
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Lab (CRREL), 2011 and 2012
Indoor and outdoor testing
Known ice thickness
Known oil locations
500 MHz PE Pro System
GPR for Oil Spill Response: CRREL
From Bradford et al., 2010
From Bradford et al., 2008
GPR for Oil Spill Response: CRREL 2012
GPR Limitations in the Arctic
Environment
• Variations in sea-ice conductivity and
anisotropy
• Snow may generate spurious amplitude
anomalies due to water or ice in
snowpack: solution is non-unique
• We can ameliorate these concerns by
frequent data truing and cautious
interpretation
Conclusions: What Can GPR
Do For Us in
Arctic Spill Response?
…and future research
Acknowledgements
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My advisors John Bradford and HP Marshall
CRREL and all the hardworking staff there – thanks!
Alaska Clean Seas
DF Dickins Associates Ltd
Current funding provided by
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Alaska Clean Seas
Conoco Phillips
ExxonMobil
Shell Oil
Statoil
References
Annan, A.P. 2005. Ground-Penetrating Radar. In Near Surface Geophysics, Investigations in Geophysics No. 13.
Butler, D.K., Ed. Society of Exploration Geophysicists, Tulsa, OK.
Annan, A.P. 2002. GPR – History, Trends, and Future Developments. Subsurface Sensing Technologies and
Applications, 3(4): 253-271.
Bradford, J.H. and J.C. Deeds. 2006. Ground penetrating radar theory and application of thin-bed offsetdependent reflectivity. Geophysics, 71(3): K47-K57.
Bradford, J.H., D.F. Dickins, and P.J. Brandvik. 2010. Detection of snow covered oil spills on sea ice using
ground-penetrating radar: Geophysics, 75, G1-G12, doi:10.1190/1.3312184.
Bradford, J. H., D. F. Dickins, and L. Liberty. 2008. Locating oil spills under sea ice using ground-penetrating
radar: The Leading Edge, 27,1424–1435.
Martinez, A. and A.P. Byrnes. 2001. Modeling Dielectric-constant values of Geologic Materials: An Aid to
Ground-Penetrating Radar Data Collection and Interpretation. Current Research in Earth Sciences,
Bulletin 247. Online at http://www.kgs.ukans.edu/Current/2001/martinez/martinez1.hmtl
Olhoeft, G.R. 2006. Applications and Frustrations in Using Ground Penetrating Radar. IEEE AESS Systems
Magazine, 2: 12-20.
Questions?