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03 latest development of shallow seimic exploration for sandstone type uranium 2012 iae an Presentation Transcript

  • 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 BasinLlayer depthis from tensof meters tohundreds ofmeters. 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 BasinLayer depthis only tensof 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 BasinLayer depth isfrom tens ofmeters toabout twohundredmeters. 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. PrincipleA seismic reflector is a boundary between Major changes inbeds with different properties. There may properties usuallybe a change of lithology or fluid fill fromBed 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 2Seismic (acoustic) impedance Z = product of velocity v and density ρSeismic interface ~ the change in seismic impedanceSeismic 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 BasinWith fast development in nuclear power andmore demand for nuclear fuel in China, moreand more seismic exploration work has beendone every year since 1995, especially in ErlianBasin for the past several years. So far morethan seven hundred kilometer’s line length hasbeen surveyed. The survey results includingmapping of the geological structures with thedepth range from 200m to 1000m ,played a veryimportant role in evaluating uranium depositcondition 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 section③ 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 thesections between 0 and 150ms, and this doesntmeet the geological requirements. (0…1000m).The depth of Nuheting deposit is only tens ofmeters. 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. LimitationsFirst 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. LimitationsSimilarly, it is important that moderateacquisition parameters should be set in order togetting the reflection event strongly, even underideal conditions. Especially, in reflection survey “optimum window” has to be concerned.“optimum window” is that range of source-geophone separations that allows the targetreflector to be observed with minimuminterference 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. ImprovementThe 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. ImprovementThe processingprocedures are asfollows:① Original datainputA strong Rayleighwave signal isobserved in thebottom-left side ofthe 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. Improvement② 2-D Fourier transformationand 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. Improvement③ parameters calculationAn initial geological model (redline) was built based ondispersion curve (blue dots)plotted using 2D-Fouriertransformation. When thedispersion curve of the model(red dots) is close to observedcurve (blue dots), the rockmechanical parameters of themodel represent the actualparameters of the investigated Plot showing the results ofsite. 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. ImprovementThis is part of theseismic explorationprofile of the ErlianBasin in 2011. Notonly geologicalformations buried atdepths between 0—200m are delineating,but also locations ofsome shallow faultsare 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