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Applications of Geophysical Methods at the DOE Field Research Center, Oak Ridge
2002-2004
J.R. SheehanL.P. Beard, W.E. Doll, T.J. Gamey and D.B. Watson
Oak Ridge National Laboratory, Oak Ridge, TN
Methods Employed
• Multielectrode Resistivity• Seismic Refraction Tomography• Geophysical Logging• Azimuthal Resistivity • Crosshole Resistivity
Seismic refraction tomography data acquisition:Profiling geologic setting
• Bison EWG-1 accelerated weight-drop source, stacks of 4-8 shots
• Geometrics Strataview48-channel seismograph, 1/8ms sample interval
• 1-2m receiver spacing• 2-4m shot spacing
Seismic Refraction Tomography with well penetration (area 3)
Multielectrode Resistivity: Used to profile geologic setting and contaminants
Multielectrode resistivity data collection
• 56-electrode Sting Swift system• Data acquired on two lines, 7m apart• On Line 1, acquired one long line at
2m electrode spacing and two lines at 1m electrode spacing
• Both dipole-dipole and Schlumberger configurations tested
Resistivity with well nitrate concentrations (area 3)
Resistivity with velocity overlay
Boreholeand
Surface resultscompared (area 3)0
500
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295297299301303305307309
Elevation(m)
Velo
city
(m/s
)
Tomography
Well Log
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294296298300302304306
Elevation(m)
Res
istiv
ity(o
hm-m
)
Sting
Well Log
FW-109
Relating Drilling information to tomography result
• Depth of refusal for driven probes correlates well with the 1,000 m/s velocity contour
• Based on augerholes, the bottom of the transition zone (top of bedrock) corresponds to somewhere between the 1,500 m/s and 2,000 m/s velocity contours.
• The cores taken during augering in the vicinity of position 25 m to 35 m confirmed that bedrock in this area is about 15 m deep as estimated from the velocity profile.
• Borehole velocity logs follow the same trend as tomographic results.
Relating borehole geophysics and ground water sampling to resistivity results
• Borehole resistivity logs show the same resistivity trends as surface resistivity results
• Ground water nitrate concentrations correlate well with the surface resistivity results
Area 2 Seismic
Area 2 Seismic
0 10 20 30 40 50 60 70 80Position (m)
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Line 1 Line 2
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Field Research Center Electrical conductivity Profiling
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Depth
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Conductivity (ms/M)
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Conductivity (ms/M)
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DP12DP13
GW835
Between GW835 and TMW05
TMW05
West East
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Depth (ft)
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FW019 FW015FW021 FW027
WestEast
Data acquired by Geophex Ltd.
Area 3: EM Logging During Flow Test
• 10 wells logged repetitively over a 1-week period with EM-39 borehole conductivity logger
• A dilute KCL solution was injected in well 24 and displaced highly conductive nitrate-rich fluids.
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 014 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 028 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 046 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 062 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 078 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 095 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 119 hrs
3D: +30% change in resistivity2D: log(NO3 concentration) in mg/l
% changeresistivity log(conc)
Time 143 hrs
Time-lapse logging
• Time lapse EM logs showed a steady increase in the zone of increased resistivity as conductive fluids were displaced near the injection well.
• The resistivity pattern agreed with the flow direction and dip of the geological strata.
New Seismic and Resistivity Lines
Line A’-A: along south side of bio-oxidation tanks (F4, F5, F6)
A A’0 5 10 15 20 25 30 35 40 45Position (m)
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Line B’-B, along north side of bio-denitrification tanks (F1, F2, F3)
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Line C-C’: along east side of bio-denitrification tank F3, through tanker yard
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Line D-D’: along east side of S-3 ponds parking lot
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Low-velocity feature across thee lines
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Admin. Coord. (m)
Red areas on the lines are approximate locations of the low velocity (hole) feature with the yellow line showing the trend.
Location of Seismic Feature
Seismic FeaturePrimary zone of transport
Area 3: 2004 Seismic Refraction Tomography and Resistivity
• Resistivity shows bedrock interface, but no surprises
• Seismic data indicate a possible conduit, oriented along geologic strike, intersecting three profiles at similar depth
Azimuthal Resistivity, FRC Area 2
• To define the preferential flow direction, resistivity was measured repeatedly over a 5-day period during a flow test
• Bromide was injected at ~400 mg/L.• Injection rate: 0.5 L/min for 24 hours
followed by 24h at 3 L/min• Two significant flow directions became
apparent
Surface Resistivity, FRC Area 2
Schlumberger/Wenner inverted resistivity section across proposed bio-remediation test cell
| bio cell | WE | FW 216
Azimuthal Resistivity, FRC Area 2
FW215
TMW7 DP19s
FW212FW214
FW216-1,2
TPB16FW202-2GW835
DP13
29860
29880
29900
29920
29940
29960
51255 51275 51295 51315 51335 51355
Easting (ft)
Nor
thin
g (ft
) Monitored wells
Injection well
Bromide detected
Electrode array
Also saw Bromide in Seep1 and Seep2
Center forazimuthalresistivity
Azimuthal Resistivity, FRC Area 2electrode locations
N
Gravel Trench
Road
Iron Filings
29860
29880
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51255 51275 51295 51315 51335 51355 51375
215
216
Azimuthal Resistivity, FRC Area 2
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Hour 4
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Hour 8
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Hour 12
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Hour 16
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Hour 20
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Hour 24
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Hour 28
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Hour 32
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Hour 36
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Hour 40.5
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Hour 45
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Hour 48.5
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Hour 55
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Hour 73
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Hour 98
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Hour 123
Azimuthal Resistivity Summary
• Two directions showed most change in azimuthal resistivity: N30E, N105E
• These directions align roughly parallel with and orthogonal to the bromide solution flow direction.
Crosshole Resistivity
• Purpose: To test cross-borehole equipment and software preliminary to use at Area 2 bio-remediation test site.
• Data collected August 19-20, 2004• Area 2, between wells 228 and 229
Area 1, between wells 065 and 066
Cross-borehole resistivityArea 1
Cross-borehole resistivityArea 2
Cross-borehole Results
• Inverted crosshole resistivities are reasonable for the geological conditions and groundwater geochemistry.
• Lower resistivities starting at ~5 m depth in Area 1 are most likely the beginning of higher nitrate concentrations.
• The localized high-resistivity feature in the FW 228-229 line is likely a rock or other aquatard, such as clay.
Conclusions• Multielectrode resistivity was effective in imaging
the ionic contamination plume • Refraction tomography successfully mapped the
transition zone between saprolite and bedrock that shows a significant influence on contaminant transport
• The geophysical results were used to help select the location and depth of investigation at Area 3 for field research
• Drilling, borehole geophysics, and ground water sampling verified the geophysical results
Conclusions• Repeated EM conductivity logging during Area 3
flow test provided documentation for propagation of the injected fluid through time
• Azimuthal resistivity data acquired during flow tests (Area 2) indicates preferential pathways
• Crosshole resistivity sections in Areas 1 and 2 are in general agreement with known geology
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