Case study 2: Using seismic reflection to design a mine

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1 Case study 2: Using seismic reflection to design a mine Rob Knipe, Graham Stuart * and Stephen Freeman Rock Deformation Research & School of Earth and Environment * University of Leeds

2 Seismic Reflection technique - Geophysics Geophysics? The study of the Earth by quantitative physical methods What does geophysics measure? Electrical conductivity, density, magnetisation, velocity or reflectivity of sound waves (seismic) The geological disposal of radioactive waste 24th Oct 08 Slide 2

3 Use of 3D seismic reflection technique Non-intrusive imaging of the sub-surface Highlight regions for further (expensive) in-situ study e.g. boreholes Characterise physical properties via geophysical parameters The geological disposal of radioactive waste 24th Oct 08 Slide 3

4 What geological information is required at a candidate site? Characterisation of geological aspects includes: Long-term stability Faulting and extent of host rock fracturing Seismicity Volcanism Confirmation of volume of rock suitable for construction of disposal zones Geotechnical parameters relevant to design Groundwater flow regimes Geochemical conditions; and Mineralogy IAEA (2005) after Dr Bob Chaplow The geological disposal of radioactive waste 24th Oct 08 Slide 4

5 What geological information is required at a candidate site? Characterisation of geological aspects includes: Long-term stability Faulting and extent of host rock fracturing Seismicity Volcanism Confirmation of volume of rock suitable for construction of disposal zones Geotechnical parameters relevant to design Groundwater flow regimes Geochemical conditions; and Mineralogy IAEA (2005) The geological disposal of radioactive waste 24th Oct 08 Slide 5

6 Radioactive disposal site or Mine Radioactive waste disposal after Dr Bob Chaplow The geological disposal of radioactive waste 24th Oct 08 Slide 6

7 Radioactive disposal site or Mine? Radioactive waste disposal after Dr Bob Chaplow after Dr Bob Chaplow The geological disposal of radioactive waste 24th Oct 08 Slide 7

8 Seismic Reflection Technique time

9 Development of the interpretation The geological disposal of radioactive waste 24th Oct 08 Slide 9

10 Seismic reflection signal - vertical resolution issue Physical properties of the rock Signal wavelength Centimeters 10 s meters The geological disposal of radioactive waste 24th Oct 08 Slide 10

11 Seismic reflection signal - horizontal resolution issue Fault The geological disposal of radioactive waste 24th Oct 08 Slide 11

12 Seismic Reflection Attribute Analysis Multiple attribute and edge-detection maps on a single seismically defined horizon Composite multiple attribute map TWT - depth Range Shaded relief Dip Av. Shift and Diff. Azimuth Curvature Standard deviation Laplacian diff. The geological disposal of radioactive waste 24th Oct 08 Slide 12

Typically we map double to an order of magnitude greater number of faults than are mapped on

13 Enhanced structure imaging We have developed a series of surface stabilisation and edge detection algorithms that allow significantly greater fault mapping resolution. Typically we map double to an order of magnitude greater number of faults than are mapped on standard interpretation projects. Dip of horizon Edge detection attribute The geological disposal of radioactive waste 24th Oct 08 Slide 13

14 Seismic reflection attributes Wavelength Amplitude Time The geological disposal of radioactive waste 24th Oct 08 Slide 14

directly into CAD packages for ore evaluation The

15 Modelling the faults Create continuously defined geological volume which can be incorporated directly into CAD packages for ore evaluation The geological disposal of radioactive waste 24th Oct 08 Slide 15

so that they can be directly loaded into the mine planning software systems at the

16 Structure model and CAD wireframes 3D seismic modelling CAD Data conversion We have developed software to directly transfer seismic-structure models into CAD wireframes so that they can be directly loaded into the mine planning software systems at the full resolution and accuracy. The geological disposal of radioactive waste 24th Oct 08 Slide 16

17 Time to Depth Need to know the velocity of the rocks to convert from time to depth Can get velocity from the seismic reflection travel time (inaccurate) or borehole data (more accurate) The geological disposal of radioactive waste 24th Oct 08 Slide 17

18 Depth conversion All of the 3D geological volume is tied to all of the borehole control The geological disposal of radioactive waste 24th Oct 08 Slide 18

Depth error estimate To estimate the likely depth error away from borehole control we sequentially remove one borehole at a time recompute the full depth conversion then test the

19 Depth error estimate To estimate the likely depth error away from borehole control we sequentially remove one borehole at a time recompute the full depth conversion then test the accuracy of the prediction against the removed borehole. In this way the likely error away from the boreholes can be estimated. The geological disposal of radioactive waste 24th Oct 08 Slide 19

Both are critical for defining the confidence in both fault location and depth accuracy.

20 Confidence classification High Medium We generate confidence classifications based on the surface stability of the data and the signal to noise ratio of the data around the target. Both are critical for defining the confidence in both fault location and depth accuracy. Low Lower confidences adjacent to faults that impact the seismic Higher confidences in strong seismic imaging and stable reflector areas The geological disposal of radioactive waste 24th Oct 08 Slide 20

21 Fault position accuracy Data acquired several years ago, mining now progressed into the edge of the seismic volume accuracy of interpretation can be tested Mined faults within the seismic volume indicate fault location better than ~20m (this case ~5m) The geological disposal of radioactive waste 24th Oct 08 Slide 21

22 Targeting shafts and boreholes Shaft sites chosen to avoid structurally complex areas Drilling strategy has been enhanced to test mine block geological variations. Each block defined and drilled to enhance geological model of the orebody, numerous holes still ongoing. The geological disposal of radioactive waste 24th Oct 08 Slide 22

23 Generic advantages of 3D seismic reflection for mining Optimising shaft locations for minimal haulage and planning Delineate regions of homogeneous blocks before entering the ground Reducing risk on future capital expenditure programs The geological disposal of radioactive waste 24th Oct 08 Slide 23

24 Application of geological (fracture) models to enhance sub-surface understanding Have a geological depth model of the sub-surface from the 3D seismic reflection survey interpretation Can we use our observations in a borehole or at outcrop to enhance our understanding of flow in the sub-surface from our geological model? e.g. Platinum mine = layered crystalline rock with faults e.g. Coal mine = layered sedimentary rock with permeability and faults The geological disposal of radioactive waste 24th Oct 08 Slide 24

25 Faults Properties: Barriers to Flow Reduced permeability in crushed fault rock (10 5 reduction possible) The geological disposal of radioactive waste 24th Oct 08 Slide 25

26 Faults/Fractures: Conduits to flow - Impacts on long term viability of site. - Provides porosity for fluid flow. - Large surface area for fluid rock interaction / chemical exchange. - Strength of rocks The geological disposal of radioactive waste 24th Oct 08 Slide 26

27 Fault Zone Sandstone Shale The geological disposal of radioactive waste 24th Oct 08 Slide 27

$Small-scale fractures around faults MOAB FAULT, UTAH 30m Core or Outcrop: Provides databases on fault zone architecture and$ $Statistical model of fractures around the fault Power law length distribution Orientation distribution (trend, dip) Fault$

28 Small-scale fractures around faults MOAB FAULT, UTAH 30m Core or Outcrop: Provides databases on fault zone architecture and specimens small faults around one large structure. Statistical model of fractures around the fault Power law length distribution Orientation distribution (trend, dip) Fault length throw relationship Spatial distribution hierarchical clustering Statistical spatial distribution resembles natural systems The geological disposal of radioactive waste 24th Oct 08 Slide 28

29 Fluid flow through faults with differing permeability

30 Conclusions 3D seismic reflection imaging can be used for: Optimising shaft locations for minimal haulage and planning Delineate regions of homogeneous blocks before entering the ground Reducing risk on future capital expenditure programs The geological disposal of radioactive waste 24th Oct 08 Slide 30

Deep Borehole Disposal Performance Assessment and Criteria for Site Selection

Deep Borehole Disposal Performance Assessment and Criteria for Site Selection Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department