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Geoserve Logging & Tomography. Borehole Resistivity Logging and Tomography for Mineral Exploration W. Qian, B. Milkereit, G. McDowell, K. Stevens and S. Halladay www.geo-lt.com. B. A. N. M. WHY ?. Continuities of conductors between boreholes Identification of conductors offhole - PowerPoint PPT Presentation
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Borehole Resistivity Logging and Tomography for Mineral Exploration
W. Qian, B. Milkereit, G. McDowell, K. Stevens and S. Halladay
www.geo-lt.com
Geoserve Logging & Tomography
WHY ?
A
B
M
N
• Continuities of conductors between boreholes
• Identification of conductors offhole
• Mapping perfect conductors
• Mapping poor conductors
WHY NOW ?
A
B
M
N
• Forward modeling studies
• Multi-electrode array instrumentation
• Very easy to deploy
• Can acquire vast amount of data rapidly
• Battery power
• Easy data QC
• Rugged design
Advantages of the System
Zn, Pb and Ag (Modest Conductor)
Ni-Cu (Super Conductor)
Vertical Resistivity Profiling
A
B
M
N Apparent Resistivity
Borehole intersects sulfides in conductive environment
Borehole pass by sulfides in conductive environment
Log10
Borehole intersects sulfide in resistive environment
Log10
Borehole pass by sulfide in resistive environment
VRP survey in a single hole will provide:
• Bulk background resistivity
• Information about off-hole conductors
Borehole to Borehole Electrode Configuration
A
B
M
N
B3
B1
B2
Projection Plane
B3
B2
B1
DeeperDeeper
Ore zone in B2
QC Electric Current Injected between B2 and B3
Current Electrodes in B3
Cu
rre
nt E
lect
rod
es
in B
2
DeeperDeeper
Ore zone in B2
Ore zone shadow in B3
Current Electrodes in B3
Cu
rre
nt E
lect
rod
es
in B
2
QC Electric Current Injected between B2 and B3
DeeperDeeper
Ore zone shadow in B3
QC Electric Current Injected between B1 and B3
Current Electrodes in B3
Cu
rre
nt E
lect
rod
es
in B
1
B3
B2
B1
Massive Sulfide Zone
Top
Bottom
Electric Current between two adjacent electrodes in B2
Ore zone in B2
Ore zone shadow in B3
Electric Potential between two adjacent electrodes in B3 [mV]1
mA
of c
urre
nt is
inje
cted
bet
wee
n tw
o ad
jace
nt e
lect
rode
s in
B2
DeeperDeeper
Zone I
Zon
e II
QC Electric Current Injected between B1 and B3
No Electrode Coverage
No Electrode Coverage
Zon
e II
Zone I
A: alteration bleached, no significant Zn mineralization or Pyrite-content, resistivity larger than 40 ohm.m B: brecciation, matrix Pyrite rich ( 5 – 10 % Pyrite), less than 1% Zn content, resistivity between 15 and 40 ohm.m C: strong brecciation, often more than 5% Zn content, resistivity less than 15 ohm.m.
Inverse Modeling Strategy
• VRP pseudo section as starting model
• Sharp inversion of only VRP data (Initial model is the main constraint)
• Build a model from the two sharp inversion models
• Fix the near borehole properties and let the tomography inversion work on the resistivity in the central region. The resistivity values can be fixed, semi-fixed (fixed in a narrow range) or completely floating
• Fine tuning the inversion model with different geological / petrophysical constraints
• Detect conductive zones within 30 m range around the borehole
• Provide independent estimate of bulk (4 - 100 m) resistivity data for calibration / interpretation of other EM datasets
• Map conductive zones between the boreholes 180 m apart
• Works for all conductivity contrasts
• Very easy field operation procedures
Conclusions
• Field test 3D tomography methodologies
• Develop IP data interpretation
• Move towards simultaneous data acquisition in multiple boreholes
• Build cables to deploy in deeper boreholes
Outlook
• Nash Creek, Slam Exploration
• Sudbury, Camiro, NSERC, CVRD, Xstrata, First Nickel
Acknowledgement