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Using 3D Seismic Imaging for Mine and Mineral Exploration G. Schuster University of Utah.

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Presentation on theme: "Using 3D Seismic Imaging for Mine and Mineral Exploration G. Schuster University of Utah."— Presentation transcript:

1 Using 3D Seismic Imaging for Mine and Mineral Exploration G. Schuster University of Utah

2 Outline Reflection Imaging Principles Reflection Imaging Principles Case History: 3D Seismic Potash Case History: 3D Seismic Potash Case History: 2D Tomography Case History: 2D Tomography Case History: Crosswell Case History: Crosswell Summary Summary

3 Seismic Section Depth Time

4 Depth Time Depth=vel*T Depth Resolution =  Horiz. Resolution >  = 10 m = 60 m

5 2-D Seismic Survey 6 km 30 m

6 3-D Seismic Survey 6 km 30 m

7 2D vs 3D TopView

8 Outline Reflection Imaging Principles Reflection Imaging Principles Case History: 3D Seismic Potash Case History: 3D Seismic Potash Case History: 2D Tomography Case History: 2D Tomography Case History: Crosswell Case History: Crosswell Summary Summary

9 Potash Geology (Pruegger & Nemeth) Sakatchewn Province: 12 km/12 km Potash mine 1 km depth Sakatchewn Province: 12 km/12 km Potash mine 1 km depth Geology Geology Potash Salt Limestone KarstReefs 12 km 200 m

10 Potash Geology Sakatchewn Province: 12 km/12 km Potash mine 1 km depth Sakatchewn Province: 12 km/12 km Potash mine 1 km depth Geology Geology Potash Salt Limestone KarstReefs 12 km 200 m Can Seismic Predict Disturbances?

11 3D Seismic Parameters Receiver line interval = 180 m Receiver line interval = 180 m Survey Area 15 km Survey Area 15 km2 Source line interval = 300 m Source line interval = 300 m 550 traces/shot 550 traces/shot 60 m shot/recievr interval 60 m shot/recievr interval 150 Hz Dynamite, 12-fold, 30 m 150 Hz Dynamite, 12-fold, 30 m 1/3 million dollars 1/3 million dollars

12 Top View of Mine (z=1 km) Disturbance 10 km 10 km 15 m 5 m = Seismic Anomaly?

13 Collapsed Breccia 15 m Breccia Limestone

14 Collapsed Breccia 10 m

15 Summary 3D Seismic Sections Boreholes Top Salt

16 3D Seismic Depth Slices and Cross Sections Mine Entry 1 km Cross section Cross Sections Depth Slices

17 Boreholes+Logs Winnipegosis Limestone Mine Integrated Lanigan Data 200 m

18 Red Bed Limestone Gamma Log Potash 200 m

19 “Looking Down” View

20 Limestone 200 m Mine Roof Mine Room

21 Mine near potash above limestone Limestone Subtle Sags = Collapse Zones

22 1.0 km 0.0 km SeismicInterpretation

23 Prugger and Nemeth Summary We found a number of inconsistencies with our data (eg.- seismic depth conversion, borehole orientation, coordinate conversion) once everything was put together in GOCAD. We found a number of inconsistencies with our data (eg.- seismic depth conversion, borehole orientation, coordinate conversion) once everything was put together in GOCAD. We use GOCAD (almost every day) to view various types of data simultaneously Data formats are well described, so we’ve generally found adding data to be easy. $333K, Seismic-> Rooms, anoamlies

24 WHAT’S NEXT FOR POTASHCORP ? We are building a “MODEL3D” earth model from 3D seismic & well-logs, which results in a velocity VOXET. This is then used to depth- migrate the seismic data, resulting in an improved seismic depth-image.We are building a “MODEL3D” earth model from 3D seismic & well-logs, which results in a velocity VOXET. This is then used to depth- migrate the seismic data, resulting in an improved seismic depth-image. We plan to keep adding data, minesite by minesite, and we want make GOCAD conveniently available at all our mine divisions.We plan to keep adding data, minesite by minesite, and we want make GOCAD conveniently available at all our mine divisions.

25 Outline Reflection Imaging Principles Reflection Imaging Principles Case History: 3D Seismic Potash Case History: 3D Seismic Potash Case History: 2D Tomography Case History: 2D Tomography Case History: Crosswell Case History: Crosswell Summary Summary

26 Mineral Geology Western State: Large mining operation over many km, but at shallow depth (30 m) Western State: Large mining operation over many km, but at shallow depth (30 m) Geology Geology ?????? km 20 m

27 Goal: Cheaply Find Lateral Extent of Play Geology Geology ?????? km 20 m Soln: 2-D Refraction Tomography

28 Seismic ImagingofAnomaly Seismic Imaging of Anomaly Velocity Anomaly

29 Seismic ImagingofAnomaly Seismic Imaging of Anomaly Velocity Anomaly

30 Seismic ImagingofAnomaly Seismic Imaging of Anomaly Fast Time Velocity Anomaly

31 Seismic ImagingofAnomaly Seismic Imaging of Anomaly Velocity Anomaly Fast Time Slow Time

32 Seismic ImagingofAnomaly Seismic Imaging of Anomaly 3.0 m

33 Discretize Earth Model into Grid of Unknown Velocities

34 One Traveltime Equation for Each Measurement

35 T = L /v + L /v + L /v

36 Many Traveltime Equations for Each Shot T = L /v + L /v + L /v

37 Field Data Thirty-one shots and 120 traces Thirty-one shots and 120 traces total 3188 traveltimes picked. total 3188 traveltimes picked. Shot interval: 20 m Shot interval: 20 m geophone interval 5 m geophone interval 5 m Source frequency 40 Hz. Source frequency 40 Hz. Record length 1 sec. Record length 1 sec. sample interval 0.5 millisecond. sample interval 0.5 millisecond.

38 Seismic Refraction Data Common Shot Gather – Line 2 WestEast Created with Vista

39 Seismic Data Acquisition Parameters

40 Seismic Refraction Data Ray Path Density Velocity Profile Ray Density Plot Line 1 – Final Model (3 rd Schedule) 55 m No Salt 46 m No Salt 20 m Hit Salt Well Tunnel Surface Depth & Distance in Meters

41 Summary $5K, Seismic-> Mapped Lateral extent of Play extent of Play 4:1 Offset-Depth ratio Less Resolution Than Reflection 4 More surveys

42 Conclusions 3D Seismic Reflection Mine Survey: > $50K several sq. km Depth Resolution = 5-20 m Offset Resolution = m Requires Expert Processing Refraction Tomography: > $5K several km Always works, moderate expertise, 4:1 offset/depth ratio

43 Crosswell Traveltime Tomography Time

44 0 90 Offset (m) Depth (m) P 0 90 Offset (m) S m/s m/s Fault Model

45 0 90 Offset (m) Depth (m) P 0 90 Offset (m) S m/s m/s A B C A B C D Fault Tomogram

46 B A C D Offset (ft) Depth (ft) P Offset (ft) S ft/s ft/s W Texas Tomogram

47 Crosswell McElroy Data (m/s) Depth (m) 201 shots from depths of 811 to 963 m 186 hydrophones from depths of 822 to 963 m Shot, hydrophone interval 0.76m Maximum source freq Hz 846m 920m 887m Distance (m)

48 270 0 V Depth (ft) 3150 V Receiver Well Source Well Crosswell McElroy Comparison

49 Poisson Ratio Comparison 0 Offset (ft) Depth (ft) Visco. 184 A B

50 Summary $25K, Seismic-> Mapped Lateral extent of Play extent of Play 3 m Resolution!


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