using 3d seismic imaging for mine and mineral exploration g. schuster university of utah

Using 3D Seismic Imaging Using 3D Seismic Imaging for Mine and Mineral for Mine and Mineral

ExplorationExploration

G. SchusterG. Schuster

University of UtahUniversity of Utah

OutlineOutline• Reflection Imaging PrinciplesReflection Imaging Principles

• Case History: 3D Seismic PotashCase History: 3D Seismic Potash

• Case History: 2D TomographyCase History: 2D Tomography

• Case History: CrosswellCase History: Crosswell• SummarySummary

Seismic SectionSeismic SectionD

epth

Dep

th

Tim

eT

ime

Seismic SectionSeismic SectionD

epth

Dep

th

Tim

eT

ime

Dep

th=

vel*

TD

epth

=ve

l*T

Depth Resolution =Depth Resolution =

Horiz. Resolution >Horiz. Resolution >

= 10 m= 10 m

= 60 m= 60 m

2-D Seismic Survey2-D Seismic Survey

6 km6 km

30 m30 m

3-D Seismic Survey3-D Seismic Survey

6 km6 km

30 m30 m

2D vs 3D2D vs 3D

TopTopViewView

Potash GeologyPotash Geology(Pruegger & Nemeth)(Pruegger & Nemeth)

• Sakatchewn Province: 12 km/12 Sakatchewn Province: 12 km/12 km Potash mine 1 km depthkm Potash mine 1 km depth

• GeologyGeologyPotashPotash

SaltSalt

LimestoneLimestoneKarstKarst

ReefsReefs

12 km12 km

200 m200 m

Potash GeologyPotash Geology• Sakatchewn Province: 12 km/12 Sakatchewn Province: 12 km/12

km Potash mine 1 km depthkm Potash mine 1 km depth

• GeologyGeologyPotashPotash

SaltSalt

LimestoneLimestoneKarstKarst

ReefsReefs

12 km12 km

200 m200 m

Can Seismic Predict Can Seismic Predict DisturbancesDisturbances??

3D Seismic Parameters3D Seismic Parameters

• Receiver line interval = 180 mReceiver line interval = 180 m

• Survey Area 15 kmSurvey Area 15 km22

• Source line interval = 300 mSource line interval = 300 m• 550 traces/shot550 traces/shot• 60 m shot/recievr interval60 m shot/recievr interval• 150 Hz Dynamite, 12-fold, 30 m150 Hz Dynamite, 12-fold, 30 m• 1/3 million dollars1/3 million dollars

Top View of Mine (z=1 km)Top View of Mine (z=1 km)

DisturbanceDisturbance

10 km10 km

15 m15 m5 m5 m

= Seismic Anomaly?= Seismic Anomaly?

Collapsed BrecciaCollapsed Breccia

15 m15 m

Breccia LimestoneBreccia Limestone

Collapsed BrecciaCollapsed Breccia

10 m10 m

SummarySummary3D Seismic Sections3D Seismic Sections

BoreholesBoreholes

Top SaltTop Salt

3D Seismic Depth Slices 3D Seismic Depth Slices and Cross Sectionsand Cross Sections

Mine EntryMine Entry1 km1 km

Cross sectionCross section

Cross SectionsCross SectionsDepth SlicesDepth Slices

Boreholes+LogsBoreholes+Logs

Winnipegosis LimestoneWinnipegosis Limestone

MineMine

Integrated Lanigan DataIntegrated Lanigan Data

200 m200 m

Red BedRed Bed

LimestoneLimestone

Gamma Log PotashGamma Log Potash

200 m200 m

““Looking Down” ViewLooking Down” View

LimestoneLimestone

200 m200 m

Mine RoofMine Roof

Mine RoomMine Room

Mine near potash above limestoneMine near potash above limestone

LimestoneLimestone

Subtle Sags = Collapse ZonesSubtle Sags = Collapse Zones

1.0 km1.0 km

0.0 km0.0 kmSeismicSeismic InterpretationInterpretation

Prugger and Nemeth SummaryPrugger and Nemeth Summary

We found a number of inconsistencies with our data We found a number of inconsistencies with our data (eg.- seismic depth conversion, borehole orientation, (eg.- seismic depth conversion, borehole orientation, coordinate conversion) once everything was put coordinate conversion) once everything was put together in GOCAD.together in GOCAD.

We use GOCAD (almost every day) to view various We use GOCAD (almost every day) to view various types of data simultaneouslytypes of data simultaneously

Data formats are well described, so we’ve generally Data formats are well described, so we’ve generally found adding data to be easy.found adding data to be easy.

$333K, Seismic-> Rooms, anoamlies$333K, Seismic-> Rooms, anoamlies

WHAT’S NEXT FOR WHAT’S NEXT FOR POTASHCORP ?POTASHCORP ?

• We are building a “MODEL3D” earth model We are building a “MODEL3D” earth model from 3D seismic & well-logs, which results in a from 3D seismic & well-logs, which results in a velocity VOXET. This is then used to depth-velocity VOXET. This is then used to depth-migrate the seismic data, resulting in an migrate the seismic data, resulting in an improved seismic depth-image.improved seismic depth-image.

• We plan to keep adding data, minesite by We plan to keep adding data, minesite by minesite, and we want make GOCAD minesite, and we want make GOCAD conveniently available at all our mine divisions.conveniently available at all our mine divisions.

Mineral GeologyMineral Geology• Western State: Large mining Western State: Large mining operation over many km, but at operation over many km, but at shallow depth (30 m) shallow depth (30 m) • GeologyGeology

?????? km?????? km

20 m20 m

Goal:Goal: Cheaply Find Lateral Extent Cheaply Find Lateral Extent of Playof Play

• GeologyGeology

?????? km?????? km

20 m20 m

SolnSoln: 2-D Refraction Tomography: 2-D Refraction Tomography

Seismic ImagingSeismic Imaging ofof AnomalyAnomaly

Velocity AnomalyVelocity Anomaly


Fast TimeFast Time




Fast TimeFast Time

Slow TimeSlow Time


3.0 m3.0 m

Discretize Earth Model into Grid of Discretize Earth Model into Grid of Unknown VelocitiesUnknown Velocities

One Traveltime Equation for Each One Traveltime Equation for Each MeasurementMeasurement

One Traveltime Equation for Each One Traveltime Equation for Each MeasurementMeasurement

T = T = L /v L /v + + L /vL /v + + L /vL /v

Many Traveltime Equations for Each Many Traveltime Equations for Each ShotShot

T = T = L /v L /v + + L /vL /v + + L /vL /v

TT = = L /vL /v + + L /vL /v + + L /vL /v

Field Data 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 mgeophone 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 .

Seismic Refraction DataCommon Shot Gather – Line 2

West East

Created with Vista

Seismic Data Acquisition Parameters

Seismic Refraction Data

Ray Path

Density

Velocity Profile

Ray Density Plot

Line 1 – Final Model (3rd Schedule)

55 mNo Salt

46 mNo Salt

20 mHit Salt

WellWell

Well

Tunnel

Surface

300 400 500

60

40

20

Depth & Distance in Meters

SummarySummary$5K, Seismic-> Mapped Lateral$5K, Seismic-> Mapped Lateral extent of Playextent of Play

4:1 Offset-Depth ratio4:1 Offset-Depth ratio

Less Resolution Than ReflectionLess Resolution Than Reflection

4 More surveys4 More surveys

ConclusionsConclusions3D Seismic Reflection Mine Survey:3D Seismic Reflection Mine Survey:

> $50K several sq. km> $50K several sq. kmDepth Resolution = 5-20 mDepth Resolution = 5-20 mOffset Resolution = 20-60 mOffset Resolution = 20-60 mRequires Expert ProcessingRequires Expert Processing

Refraction Tomography:Refraction Tomography:> $5K several km> $5K several km

Always works, moderate expertise, Always works, moderate expertise, 4:1 offset/depth ratio4:1 offset/depth ratio

Crosswell Traveltime TomographyCrosswell Traveltime Tomography

Time Time

00 9090Offset (m)Offset (m)

Dep

th (

m)

Dep

th (

m)

00

210210

PP


SS

23002300

36503650m/s m/s

11501150

18251825m/s m/s

Fault ModelFault Model


Dep

th (

m)

Dep

th (

m)

00

210210

PP


SS

23002300

36503650m/s m/s

11501150

18251825m/s m/s

AA

BB

CC

AA

BB

CCDD

Fault TomogramFault Tomogram

BBAA

CC

DD

00 184184Offset (ft)Offset (ft)

Dep

th (

ft)

Dep

th (

ft)

00

500500

PP

00 184184Offset (ft)Offset (ft)

SS

1400014000

2250022500ft/sft/s

77507750

1270012700ft/sft/s

W Texas TomogramW Texas Tomogram

Crosswell McElroy DataCrosswell McElroy Data

820

840

860

880

900

920

940

9600 5040302010

6505

5767

5398

5029

6136

(m/s)

Dep

th (

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. 1400 Hz

846m

920m

887m

Distance (m)

27027000

VV

Depth (ft)Depth (ft) 31503150

VV

Receiver WellReceiver Well

Source WellSource Well

Crosswell McElroy ComparisonCrosswell McElroy Comparison

Poisson Ratio Comparison

Poisson Ratio Comparison

00 Offset (ft)Offset (ft)

Dep

th (

ft)

Dep

th (

ft)

00

250250

Visco.Visco.

184184

AA

BB

0.350.35

0.00.055

SummarySummary$25K, Seismic-> Mapped Lateral$25K, Seismic-> Mapped Lateral extent of Playextent of Play

3 m Resolution!3 m Resolution!

using 3d seismic imaging for mine and mineral exploration g. schuster university of utah

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