03 latest development of shallow seimic exploration for sandstone type uranium 2012 iae an
1. Latest development of shallow seismic
exploration for sandstone-type uranium
deposits in Erlian Basin, China
Guilai XU
Division of Geophysical and Geochemical Exploration,
Beijing Research Institute of Uranium Geology
Email: Guilaixu@163.com
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
2. OUTLINE
1 Geological Setting
2 Reflection Survey
3 Limitations and Improvement
4 Conclusion
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
3. 1 Geological setting
Geological setting of Erlian
basin
Geological requirements
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
4. Geological setting of Erlian Basin
Overall geological characteristics in Erlian Basin
• Tectonics was dominated by
multi-cycle fold and frequent
magma activity.
• Basin was controlled by EW ,
NE strike fault and formed a
frame of 5 depressions and 1
uplift , the basin can be further
divided into tens of sags and
salients which distribute in
interphase or in parallel.
• Complex geologic conditions
make the seismic data lower in
quality
1-marginal uplift of the Basin 2-uplift in the Basin ; 3-
depression in Basin ; 4-Sub-depression of the Basin ;
5-Area of project ; 6-Geological section
Fig.2-1 Structural Units of Erlain Basin in Inner Mongolia
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5. Geological setting of Erlian Basin
Llayer depth
is from tens
of meters to
hundreds of
meters.
G1 Section of Nuheting-Qihargertu ( 努和廷 - 齐哈日格图 )
1 - Paleogene ; 2 - Erlian Formation of Later Cretaceous ; 3 - Saihan Formation
of Earlier Cretaceous ; 4 - Tengger Formation of Earlier Cretaceous ; 5 -
Nonconformity ; 6 - sand body ; 8 - curve of electronic resistivity ; 9 - uranium
mineralized body
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
6. Geological setting of Erlian Basin
Layer depth
is only tens
of meters
G2 Section of Nuheting Deposit 努和廷矿床剖面
1 - Paleogene ; 2 - Upper member of Earlier Cretaceous Later Formation ; 3 -
Lower member of Later Cretaceous Erlian Formation ; 4 - Earlier Cretaceous Saihan Formation
of ; 5 - Sandstone ; 6 - Mudstone ; 7 - lithologic boundary ; 10 - uranium
ore-body and its number ; 11 - Borehole and its number
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
7. Geological setting of Erlian Basin
Layer depth is
from tens of
meters to
about two
hundred
meters.
G3 Section of Baiyingwula 白音乌拉剖面
1 - Lithologic type ( mudstone-coarse sandstone ); 2 - Gamma logging curve ; 3
- Strata contact zone ( upper : disconformity ; lower : angular unconformity );
4 - uranium ore-body ; 5 - frount of redox zone ; 6 - Yierdingmanha Formation 伊
尔丁曼哈组( E2y ); 7 - Saihan Formation ; 8 - Tenger Formation 腾格尔组
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
8. Geological requirements
The objectives of surveying :
• Determine the distribution of
sandstone layers
• Determine bedrock conditions
(0~1000m)
• Locate faults
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9. 2 Reflection survey
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10. 2 Reflection survey
• Advantages
• Waves
• Principle
• data acquisition
• data processing
• worked in Erlian Basin and problems ?
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11. Advantages
• In seismic reflection surveys, the travel-time of
waves reflected from subsurface interfaces is
measured directly to obtain information about
depths and geometrical shapes of the interfaces.
• The reflection method differs from the refraction
method mainly in its use of smaller source-
detector distances so that the seismic wave
travel is predominantly vertical rather than
horizontal. The frequency of reflection signals
tends to be higher than that of refracted pulses.
High resolution in depth is obtained.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
12. Advantages
• Widely applied to resource, engineering and
environmental problems.
such as mapping of fracture zone; reflection
profiling in groundwater studies; delineation of
bedrock valley; detection of faults and cavities;
and so on.
To meet the geological requirements for
sandstone-type uranium deposits in Erlian
Basin, reflection survey should be the primary
choice for it .
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
13. Waves
Homogeneous, unlimited medium
(Body waves)
Longitudinal = primary = compressional
Transverse = secondary = shear
Homogeneous half-space Earth’s surface
(Surface waves)
Rayleigh
Love
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
14. Waves -Seismic record
Direct wave
Refraction wave
Reflection wave
Surface wave
Air wave
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
15. Principle
A seismic reflector is a boundary between Major changes in
beds with different properties. There may properties usually
be a change of lithology or fluid fill from
Bed 1 to Bed 2. These property changes
produce strong,
cause some seismic waves to be reflected. continuous reflectors .
seismic
source geophone
In y
co ra
Bed 1 m ed
in ct
g le
lower velocity ra
y R ef
higher velocity Re
f ra c
ted
ray
Bed 2
Seismic (acoustic) impedance Z = product of velocity v and density ρ
Seismic interface ~ the change in seismic impedance
Seismic interface ~ geological boundary
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
16. Data acquisition
ρ1,2 density of rock
v1,2 wave propagation velocity
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
17. Data processing
1. Preprocessing
Demultiplex, Reformat, Edit, Geometric spreading
correction, Set up field geometry, Application of field
statics
2. Deconvolution
3. CMP sorting
4. Velocity analysis
5. Residual statics correction
6. Velocity re-analysis
7. NMO correction
Muting, Stacking
8. Time-variant band-pass filtering
9. Migration
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18. worked in Erlian Basin
With fast development in nuclear power and
more demand for nuclear fuel in China, more
and more seismic exploration work has been
done every year since 1995, especially in Erlian
Basin for the past several years. So far more
than seven hundred kilometer’s line length has
been surveyed. The survey results including
mapping of the geological structures with the
depth range from 200m to 1000m ,played a very
important role in evaluating uranium deposit
condition in the area.
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19. field work
Drilling Geode
NZ96
Truck for
dynamite
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
20. Field parameters
Name Value
Num. of cha. 96
offset 20m
Geophone Frq. 10Hz
Geophone sp. 10m
Record length 2s
Shot interval 20m
Depth of sh.hole 4m
Amount of dyna. 2kg
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21. Seismic record
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22. Stacked seismic section
③ 几张剖面
Section of part line 3
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23. Stacked seismic section
• L4
Section of part line 4
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24. Stacked seismic section
Section of part line 5
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25. Problems?
However, almost there is not reflection in the
sections between 0 and 150ms, and this doesn't
meet the geological requirements. (0…1000m).
The depth of Nuheting deposit is only tens of
meters.
图 7-1 反射波地震勘探盲区
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
26. 3 Limitations and Improvement
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
27. 3 Limitations and Improvement
• Limitations
• Improvement
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
28. Limitations
Two basic factors govern whether or not
a potential reflector can be detected and
imaged by seismic reflection techniques:
the difference in acoustic impedance
between the target or horizon and its
surroundings, and
its geometry
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
29. Limitations
First factor- the difference of acoustic impedances
The acoustic impedances (velocity-density products) of
common rock types and ores are well known from
laboratory and logging measurements.
As a rule of thumb, an impedance (Z) difference of 2.5
x 105 g/cm2s between two rock types having velocities v1
and v2 and densities ρ1 and ρ2 will give a reflection
coefficient App, of 0.06, which is sufficient to give a
strong reflection if the geometry is appropriate.
a pp ρ 2 v2 − ρ1v1
reflection coefficient: App = =
ap ρ1v1 + ρ 2v2
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( 给出二连盆地浅部值 )
中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
30. Limitations
Second factor - Geometry
The second factor that governs whether or not a target be
resolved is its geometry, especially its size and depth of burial.
If d, t and z represent the diameter, thickness and depth of
burial of a deposit, respectively, and v and f are the average
formation velocity and the seismic wave frequency used in
surveying, the minimum thickness that can be resolved by
reflection can be estimated from the quarter wavelength
criterion (Widess, 1973):
tmin = v/(4f)
Thinner targets can be detected, but reflection amplitudes will
be attenuated by the interference of reflections from the upper
and lower surfaces of the target.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
31. Limitations
Similarly, it is important that moderate
acquisition parameters should be set in order to
getting the reflection event strongly, even under
ideal conditions. Especially, in reflection survey “
optimum window” has to be concerned.
“optimum window” is that range of source-
geophone separations that allows the target
reflector to be observed with minimum
interference from other events.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
32. Limitations
Almost no reflection event can be detected in layers
between 0 and 150ms because of several adverse
factors such as small reflection coefficient (0.01),
low fold coverage near the surface and partly
outside the optimum window. This is called 'blind
zone' in the stacked section.
To overcome this limitation, we have devised the
way to delineate the near-surface layers (0-
200m)with rock mechanical parameters derived
from surface wave processing.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
33. Improvement
Principle of rock mechanical parameter processing
Among all seismic waves, the surface waves are closely related to
the rock mechanical parameters. For lateral horizon, the
dispersion characteristics of the Rayleigh wave mostly reflect the
elastic parameters of the formation, especially the shear wave
velocity. Based on the theory of surface wave in a layered
medium, the rock mechanical parameters of a stratigraphic
model can be inverted by corresponding surface wave
dispersion data, and inversion result is mainly dependant of
stratigraphic shear wave velocity, thickness and density. Hence,
based on the basic principle mentioned above, rock mechanical
parameters are calculated by inversion of the Rayleigh wave
dispersion curves.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
34. Improvement
The rock mechanical parameters can be calculated
are as following:
• ① Dynamic elastic modulus---the ratio of stree :
strain (1 + µ )(1 − 2 µ )
E =V ρ 2 d d
d mp
1− µ (1)
d
• ② Dynamic Poisson’s ratio---the ratio of rock
horizontal strain : vertical strain
V − 2V 2 2
2(V −V ) (2)
µ = d
mp
2
ms
2
mp ms
• ③ Dynamic shear modulus
E
=V ρ
G =
(3)
d 2
2(1 + µ )
d ms
d
• ④ Dynamic bulk modulus
E
K =
3(1 − 2 µ )
d
d
(4) d 34
35. Improvement
Basic requirements of data acquisition
Corresponding to the characteristics of Rayleigh wave
of low frequency, low phase velocity and dispersion, it
should be concerned about the acquisition
parameters as follows:
• Small offset
• Low sampling rate
• Small spread length
• Moderate seismic records length
• Low frequency geophone
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
36. Improvement
Development of the processing software
A processing software was developed by our group,
to calculate rock mechanical parameters. The main
functions include original seismic record
introduction, 2-D Fourier transformation, the
extraction fundamental mode, inversion and storage
of the result. The successful development of this
software provides an important technical
foundation tool for acquiring geological information
in the ‘blind zone’ of reflection seismic exploration.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
37. Improvement
Processing System for Rock
Mechanical Parameters
The main interface of rock mechanical parameters processing software
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
38. Improvement
The processing
procedures are as
follows:
① Original data
input
A strong Rayleigh
wave signal is
observed in the
bottom-left side of
the right figure.
Original single shot record
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39. Improvement
② 2-D Fourier transformation
and determination of peaks in
fundamental mode spectrum.
2-D Fourier transformation of
original seismic records is needed
to obtain dispersion curves. The
energy spectrum can be shown
clearly in frequency—wave number
domain. The transformation result
is shown in right Fig. The variation
of the fundamental mode of the
energy spectrum with frequency is Distribution of the fundamental
shown as a white shadow in the mode of the energy spectrum in
section. frequency—wave number domain
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
40. Improvement
③ parameters calculation
An initial geological model (red
line) was built based on
dispersion curve (blue dots)
plotted using 2D-Fourier
transformation. When the
dispersion curve of the model
(red dots) is close to observed
curve (blue dots), the rock
mechanical parameters of the
model represent the actual
parameters of the investigated Plot showing the results of
site. the processing
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
41. Improvement
④ Construction of the resulting section
Using the processing steps mentioned
above, files including a set of rock
mechanical parameters can be obtained
respectively. various rock mechanical
parameters profiles are generated by
another software.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
42. From the top to
bottom of the figure:
Density,
Poisson’s ratio, Shear
modulus, Elastic
modulus, Bulk
modulus,
P-wave velocity,
S-wave velocity
The ratio of P-wave
velocity and S-wave
velocity.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
43. Improvement
This is part of the
seismic exploration
profile of the Erlian
Basin in 2011. Not
only geological
formations buried at
depths between 0—
200m are delineating,
but also locations of
some shallow faults
are determined.
Map of the results from a composite section
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
44. Map of the results from part of line3 strata column
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
45. • 处理结果和钻孔图
Map of the results from a composite section
in 2011
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46. 4 Conclusion
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
47. Conclusion
Shallow seismic exploration technique has been
carried out for sandstone-type uranium deposit
exploration and applied to the Erlian Basin, Inner
Mongolia autonomous region, China, for several
years. Primary achievements are as follows:
• ⑴ Sandstone and mudstone buried at depths
between 0 and 200m can be layered by
calculating rock mechanical parameters, and also
determined locations of shallow faults. So new
parameters are provided for the assessment of
sandstone-type uranium deposits.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
48. Conclusion
⑵ The successful development of the
rock mechanical parameter software has
provided a way to delineate shallow
layer formation, which eliminates the
'blind zone‘, which overcomes the
existence of a ‘blind zone’ in reflection
seismic exploration.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
49. Conclusion
⑶ Based on the method of rock mechanical
parameters, geological formation information at a
depth of 0—200m can be obtained without
increasing any field workload. Our research group is
planning to write an application standard for
shallow seismic exploration technique for the
exploration of sandstone-type uranium deposits.
This standard will lay a foundation for the use and
application of the rock mechanical parameters
method in nuclear geology system in China.
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
50. Thank you
for your attention!
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中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology