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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


                                                                       1
中核集团核工业北京地质研究院                CNNC Beijing Research Institute of Uranium Geology
OUTLINE

 1 Geological Setting
 2 Reflection Survey
 3 Limitations and Improvement
 4 Conclusion



                                                          2
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
1 Geological setting


   Geological setting of Erlian
   basin

   Geological requirements


                                                           3
中核集团核工业北京地质研究院    CNNC Beijing Research Institute of Uranium Geology
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
                                                                                         4
  中核集团核工业北京地质研究院                                CNNC Beijing Research Institute of Uranium Geology
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
                                                                                   5
中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
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
                                                                                       6
 中核集团核工业北京地质研究院                               CNNC Beijing Research Institute of Uranium Geology
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
                                                                                7
中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
Geological requirements

  The objectives of surveying :
  • Determine the distribution of
    sandstone layers
  • Determine bedrock conditions
    (0~1000m)
  • Locate faults


                                                             8
中核集团核工业北京地质研究院      CNNC Beijing Research Institute of Uranium Geology
2 Reflection survey




                                                          9
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
2 Reflection survey
    •   Advantages
    •   Waves
    •   Principle
    •   data acquisition
    •   data processing
    •   worked in Erlian Basin and problems ?



                                                               10
中核集团核工业北京地质研究院         CNNC Beijing Research Institute of Uranium Geology
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.

                                                                   11
中核集团核工业北京地质研究院             CNNC Beijing Research Institute of Uranium Geology
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 .
                                                                  12
中核集团核工业北京地质研究院            CNNC Beijing Research Institute of Uranium Geology
Waves
      Homogeneous, unlimited medium
                   (Body waves)
          Longitudinal = primary = compressional
             Transverse = secondary = shear


   Homogeneous half-space Earth’s surface
                  (Surface waves)
                        Rayleigh
                          Love




                                                                 13
中核集团核工业北京地质研究院           CNNC Beijing Research Institute of Uranium Geology
Waves -Seismic record
  Direct wave
                        Refraction wave


                            Reflection wave


  Surface wave
                                   Air wave


                                                             14
中核集团核工业北京地质研究院       CNNC Beijing Research Institute of Uranium Geology
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
                                                                                                             15
中核集团核工业北京地质研究院                                                       CNNC Beijing Research Institute of Uranium Geology
Data acquisition




        ρ1,2 density of rock
        v1,2 wave propagation velocity
                                                                16
中核集团核工业北京地质研究院          CNNC Beijing Research Institute of Uranium Geology
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

                                                                        17
中核集团核工业北京地质研究院                  CNNC Beijing Research Institute of Uranium Geology
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.
                                                                18
中核集团核工业北京地质研究院          CNNC Beijing Research Institute of Uranium Geology
field work


              Drilling                                  Geode


                                                         NZ96
  Truck for
  dynamite




                                                             19
中核集团核工业北京地质研究院       CNNC Beijing Research Institute of Uranium Geology
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
                                                                 20
中核集团核工业北京地质研究院           CNNC Beijing Research Institute of Uranium Geology
Seismic record




                                                         21
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
Stacked seismic section

③ 几张剖面




          Section of part line 3
                                                              22
中核集团核工业北京地质研究院        CNNC Beijing Research Institute of Uranium Geology
Stacked seismic section



 • L4




           Section of part line 4
                                                               23
中核集团核工业北京地质研究院         CNNC Beijing Research Institute of Uranium Geology
Stacked seismic section




          Section of part line 5
                                                              24
中核集团核工业北京地质研究院        CNNC Beijing Research Institute of Uranium Geology
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
                                                                25
中核集团核工业北京地质研究院          CNNC Beijing Research Institute of Uranium Geology
3 Limitations and Improvement




                                                         26
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
3 Limitations and Improvement

   • Limitations
   • Improvement




                                                           27
中核集团核工业北京地质研究院     CNNC Beijing Research Institute of Uranium Geology
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



                                                              28
中核集团核工业北京地质研究院        CNNC Beijing Research Institute of Uranium Geology
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

                                                                                   29
 ( 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
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.


                                                                            30
中核集团核工业北京地质研究院                      CNNC Beijing Research Institute of Uranium Geology
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.


                                                                   31
中核集团核工业北京地质研究院             CNNC Beijing Research Institute of Uranium Geology
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.

                                                                    32
中核集团核工业北京地质研究院              CNNC Beijing Research Institute of Uranium Geology
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.



                                                                          33
中核集团核工业北京地质研究院                    CNNC Beijing Research Institute of Uranium Geology
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
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

                                                                     35
中核集团核工业北京地质研究院               CNNC Beijing Research Institute of Uranium Geology
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.


                                                                    36
中核集团核工业北京地质研究院              CNNC Beijing Research Institute of Uranium Geology
Improvement

                                Processing System for Rock
                                 Mechanical Parameters




  The main interface of rock mechanical parameters processing software
                                                                            37
中核集团核工业北京地质研究院                      CNNC Beijing Research Institute of Uranium Geology
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
                                                38
中核集团核工业北京地质研究院            CNNC Beijing Research Institute of Uranium Geology
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

                                                                         39
中核集团核工业北京地质研究院                   CNNC Beijing Research Institute of Uranium Geology
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
                                                                           40
 中核集团核工业北京地质研究院                    CNNC Beijing Research Institute of Uranium Geology
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.



                                                             41
中核集团核工业北京地质研究院       CNNC Beijing Research Institute of Uranium Geology
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.
                                                         42
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
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
                                                                          43
 中核集团核工业北京地质研究院                   CNNC Beijing Research Institute of Uranium Geology
Map of the results from part of line3                   strata column
                                                                            44
中核集团核工业北京地质研究院                      CNNC Beijing Research Institute of Uranium Geology
• 处理结果和钻孔图




Map of the results from a composite section
                                 in 2011
                                                                    45
中核集团核工业北京地质研究院              CNNC Beijing Research Institute of Uranium Geology
4 Conclusion




                                                         46
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology
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.



                                                                    47
中核集团核工业北京地质研究院              CNNC Beijing Research Institute of Uranium Geology
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.


                                                              48
中核集团核工业北京地质研究院        CNNC Beijing Research Institute of Uranium Geology
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.


                                                                    49
中核集团核工业北京地质研究院              CNNC Beijing Research Institute of Uranium Geology
Thank you
     for your attention!



                                                         50
中核集团核工业北京地质研究院   CNNC Beijing Research Institute of Uranium Geology

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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 1 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 2 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 3 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 4 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 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 5 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 6 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 7 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 8 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 9. 2 Reflection survey 9 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 10. 2 Reflection survey • Advantages • Waves • Principle • data acquisition • data processing • worked in Erlian Basin and problems ? 10 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 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. 11 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 . 12 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 13 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 14 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 15 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 16 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 17 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 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. 18 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 19. field work Drilling Geode NZ96 Truck for dynamite 19 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 20 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 21. Seismic record 21 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 22. Stacked seismic section ③ 几张剖面 Section of part line 3 22 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 23. Stacked seismic section • L4 Section of part line 4 23 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 24. Stacked seismic section Section of part line 5 24 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 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 25 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 26 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 27 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 28 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 29 ( 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. 30 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. 31 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. 32 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. 33 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 35 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. 36 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 37 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 38 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 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 39 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 40 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. 41 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. 42 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 43 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 44 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 45 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology
  • 46. 4 Conclusion 46 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. 47 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. 48 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. 49 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! 50 中核集团核工业北京地质研究院 CNNC Beijing Research Institute of Uranium Geology