0306 silas simi yu 02
TRANSCRIPT
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APPLICATION OF MICRO SEISMIC METHODSAPPLICATION OF MICRO SEISMIC METHODS
TO GEOTHERMAL EXPLORATIONTO GEOTHERMAL EXPLORATION
Silas M. Simiyu
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BASIC REQUIREMENTS FOR A
GEOTHERMAL SYSTEM
1. Heat Source
Magma Body related to volcanic activityDeep circulating fluids along Deep faults
May be a Radioactive plutons
2. ReservoirFluid availability and recharge
Pathways/conduits along which fluids will
circulateStatus of the reservoir
Liquid/water dominated
Steam/Vapour Dominated
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SEISMIC WAVES
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TYPE AND PROPERTIES OF SEISMIC
WAVES
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P and S Wave Properties
Compressional (P) WaveCompressional (P) Wave
Motion through compression & dilatationalMotion through compression & dilatationaltransfer of energytransfer of energy
Propagates through solid and liquid mediaPropagates through solid and liquid media
Dependent on the density and ElasticDependent on the density and Elastic ModuliModuli
Shear (S) WaveShear (S) Wave
Motion through pure shear strain.Motion through pure shear strain.
Propagation is only through solid mediaPropagation is only through solid media
Dependent on the density and ElasticDependent on the density and Elastic ModuliModuli
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MAGNITUDE DETERMINATION
-10
-5
0
5
10-10
-5
0
5
10
P SCoda Length
Vertical
Radial
Transverse
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Time [Seconds]
0
510
15
20
25
Magnitude determination
Mc= 2log[C] + 0.00325d-0.97,
d = epicentral distance [km],
C = duration earthquake coda [sec].
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Effect of Media on P and S Wave
Transmission velocity 1
Normal
Low
High
Low
Low
Poissons Ratio
() -MaterialStrength
HighVery lowLowDuctile material
Very Low
(~1.4)
NormalLowRocks (Steam
filled pores)
High (~2.1)V. LowNormalRocks (water
filled Pores)
Normal (~1.71)V. HighV. HighSolid Rocks
Infinite (Very
High)
0V. LowLiquid (Water,
Magma)
Vp/VsVsVpMedia
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Effect of Media on P and S Wave
2Transmission velocity 2
Very low
Decrease
Decrease
Decrease
Increase
Poissons
Ratio ()
DecreaseIncreaseDecreasePore Pressure(Less Fluid)
NormalDrasticDecrease
DecreaseRocks -Brittle toDuctile transition
IncreaseTends to ZeroDecreaseLiquefaction
DecreaseIncreaseDecreasePhase Change
(Liquid to vapour)
IncreaseDecreaseIncreasePore Pressure
(More fluid)
Vp/VsVsVpMedia
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Seismic Methods
Active SourceActive SourceArtificial Sources (Dynamite,Artificial Sources (Dynamite, AirgunAirgun, weight drop), weight drop)
Reflection MethodReflection Method Refraction MethodRefraction Method
Shallow Geotechnical StudiesShallow Geotechnical Studies
Passive SourcePassive SourceNatural Seismicity (MicroNatural Seismicity (Micro--Earthquakes)Earthquakes)
Event distribution with depthEvent distribution with depth
Wave velocity, attenuation and SWave velocity, attenuation and S--wave shadow zoneswave shadow zones
Active faults and permeable zonesActive faults and permeable zones
SS--wave shadows can indicate partial melt and magma chamberswave shadows can indicate partial melt and magma chambers
Ground noise generated by the geothermal system (from boilingGround noise generated by the geothermal system (from boiling
and/or convective flow)and/or convective flow)
Hydraulic fracturing and tensile cracking of cooling intrusionsHydraulic fracturing and tensile cracking of cooling intrusions
VolcanoVolcano--Seismic Hazards analysisSeismic Hazards analysis
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ACTIVE SOURCE METHODS
Refraction Seismology
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Active Source
Kenya Rift Axis Refraction Profile
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Active Source
Kenya Rift Axis Refraction
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0 20 40 60 80 100 120 140 160 180 200 220
Distance (km)
-15
-10
-5
0
Depth
2
3
4
5
6
7
Vp (km/s)SUSWAOLKARIAMENENGAI
Figure 1.2. Seismic Velocity model along the Rift axis showing high velocity zones beneathMenengai, Olkaria and Suswa Volcanic centers based on the KRISP 1985-1990axial model by Simiyu and Keller, 2000.
Active Source
Kenya Rift Axis Seismic Refraction Results
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Active Source -Seismic Refraction
Olkaria Geothermal Field
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Active Source -Seismic Refraction Results
Olkaria Geothermal Field
Vp
NEF
OWF
OCF
OWF OCF NEF1.9
3.3
3.6
4.2
4.5
6.4
2.8
2.2
3.5
3.5
4.3
4.3
6.5
6.3
1.9
2.2
3.1
3.8
4.3
1 2 3 4 5 6 7
Velocity (Vp)
0
2
4
6
Depth(km)
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Active Source Seismic Refraction Results
Olkaria Geothermal Field
192000 194000 196000 198000 200000 202000 204000
Grid Eastings
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
Depth(km)
2.0
2.7
3.1
3.5
4.5
5.2
5.6
OWF OCF NEF
SEISMIC SECTION ACROSS OLKARIA WEST, CENTRAL AND NORTH EAST
Velocity (km/s)
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PASSIVE SOURCE METHODS
Ground Noise Monitoring
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MNA
MNWMNE
MCA
MSWMSE
Figure 2.1. Background Seismic Noise in Menengai Area: MNA, MSE, MNE, MCA, MSW and MNW
Background Noise Monitoring
Menengai Geothermal Field
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APPLICATION OF WAVE PROPERTIES
Determine Presence of Heat SourcesDetermine Presence of Heat Sources
Seismicity Distribution With DepthSeismicity Distribution With Depth Mapping of Shear Wave Attenuating BodiesMapping of Shear Wave Attenuating Bodies
Reflected ArrivalsReflected Arrivals
Map Zones Of Reservoir RechargeMap Zones Of Reservoir Recharge
Seismic Wave Spectral AnalysisSeismic Wave Spectral Analysis
Seismicity Patterns & Velocity Ratio AnalysisSeismicity Patterns & Velocity Ratio Analysis
Evaluate Existing Reservoir PropertiesEvaluate Existing Reservoir Properties
Analysis of P & S wave Seismic Velocity RatiosAnalysis of P & S wave Seismic Velocity Ratios
Analysis of Poisson RatiosAnalysis of Poisson Ratios
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SCHEMATIC RIFT VALLEY GEOTHERMALSCHEMATIC RIFT VALLEY GEOTHERMAL
MODELMODEL
Lake
Brittle Brittle
DuctileDuctile
Heat Source
Reservoir Capping Rocks
Reservoir
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0 5 10 15 20 25 30 35 40 45 50
Kilometers
-14
-12
-10
-8
-6
-4
-2
0
Depth
MODEL OF A GEOTHERMAL SYSTEM AND SEISMICITY
DISTRIBUTION WITH DEPTH
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HEAT SOURCE -OLKARIA
Event Distribution with Depth
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23188000 192000 196000 200000 204000 208000 -8
-7
-6
-5
-4
-3
-2-1
0
Depth[km]
OWF OCF NEF-DOMES
Horizontal error
0 2000 4000 M
[b]
Vertical error
DM1KM5OS1
KR6 DM4WE2 DM5
KM6EP4
NE2
KM8 CE1NE3 DM2
KM2KR2
KM7
DM3
188000 192000 196000 200000 204000 208000
9896
000
9900000
9904000
9908000
GridNorthin
gs[m]
0 2000 4000M
[a]
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Event Distribution &
with Depth at OlkariaHeat Source and Seismic Anisotropy
0 1 2 3 4 5 6 7 8 9 10 Depth [km]
0
100
200
Events
Figure 3.4A. Histogram of earthquake frequency distribution with depth
0 1 2 3 4 5 6 7 8 9 10 Depth [km]
0
100
200
CrustStrength
Figure 3.4B. Plot of crustal strength changes with depth showing theBrittle, Brittle-Ductile transition, Ductile Zone
BRITTLE ZONE TRANSITIONZONE
DUCTILE ZONE 0.10 0.15 0.20 0.25
POISSON'S RATIO
0
1
2
3
4
5
6
DEPTH(KM)
N[39-71]E AZIMUTH
0.10 0.15 0.20 0.25
POISSON'S RATIO
0
1
2
3
4
5
6
DEPTH(KM
)
N[20-68]W AZIMUTH
Heat Source Depth Seismic Anisotropy
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190000 192000 194000 196000 198000 200000 202000 204000 206000
Grid Eastings
Hypocenter Variations at Olkaria
9896000
9898000
9900000
9902000
9904000
9906000
G
ridNorthing
Olkaria production wells.
-7.5
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
Depth
EVENTS HYPOCENTER VARIATIONEVENTS HYPOCENTER VARIATION
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Active Source Seismic Refraction Results
Olkaria Geothermal Field
191000 193000 195000 197000 199000 201000 203000
Grid Eastings [m]
989900
0
9901000
9903000
9905000
GridNorthin
gs[m]
5
10
14
17
18
20
22
24
26
28
30
32
34
36
3840
DOMES
EPF
NEFOCF
OSF
OWF
Resistivity [ Ohm-m]
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1
2
3
4
16
2021
22
DM1
DM4
DM5
NE3
OS1
SM6
KM11
KM12
KM8
OR1
OR2
OR3
OR4
180000 185000 190000 195000 200000 205000 210000 215000 220000
Grid Eastings
9885000
9890000
9895000
9900000
9905000
9910000
9915000
GridNorthings
LONGONOTCALDERA
OLKARIA
LAKENAIVASHA
Recording stationEvent EpicenterNAIRAGIEENGARE
Shear Wave attenuation
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SHEAR WAVE ATTENUATION:SHEAR WAVE ATTENUATION:
RAYPATH SECTION ACROSS OLKARIARAYPATH SECTION ACROSS OLKARIA
KM5WE2
EVENT 2
EVENT 13
KM11 KM12 DM5EP4 NE5 KM2
EVENT 8
OR2
EVENT 18
178000 182000 186000 190000 194000 198000 202000 206000 210000
Grid Eastings
-20
-15
-10
-5
0
Depth
[Km]
OHC GFC
Normal raypath
Attenuated raypath
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Possible Seismic S-wave attenuating Bodies [Semi-Fluidized]
EPFNEF
DOMESOWF OW-01
3D PLOT OF DEPTH TO ATTENUATING HEAT3D PLOT OF DEPTH TO ATTENUATING HEAT
SOURCES BENEATH OLKARIA AREASOURCES BENEATH OLKARIA AREA
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HEAT SOURCE -SUSWA
Event Distribution with Depth
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SEISMIC EVENTS DISTRIBUTIONSEISMIC EVENTS DISTRIBUTION
SU01
SU02
SU03
SU04
SU05
SU06
SU07
SU08
SU09
SU10
SU11
SU12
SU13
SU14
SU15
SU16
196000 200000 204000 208000 212000
9864000
9868000
9872000
9876000
9880000
GridNo
rthings[m]
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196000 200000 204000 208000 212000
Grid Eastings [m]
-10000
-8000
-6000
-4000
-2000
0
Depth(m)
SEISMIC SECTION SHOWING EVENTSEISMIC SECTION SHOWING EVENT
DISTRIBUTION ACROSS SUSWA CALDERADISTRIBUTION ACROSS SUSWA CALDERA
-----------Outer Caldera-----------
-Inner Caldera-
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196000 200000 204000 208000 212000
Grid Eastings [m]
9864000
9868000
9872000
9876000
9880000
GridNorthings[m]
[a] 5001500 m
196000 200000 204000 208000 212000
Grid Eastings [m]
[b] 15002500 m
196000 200000 204000 208000 212000
Grid Eastings [m]
[d] dept >3500 m
196000 200000 204000 208000 212000
Grid Eastings [m]
9864000
9868000
9872000
9876000
9880000
GridNorthings[m]
[c] 25003500 m
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800
1100
1400
2000
2600
3200
196000 200000 204000 208000 212000
9864000
9868000
9872000
9876000
9880000
SU01
SU02
SU03
SU04
SU05
SU06
SU07
SU08
SU09
SU10
SU11
SU12
SU13
SU14
SU15
SU16
Average EventDepth
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196000 200000 204000 208000 212000
Grid Eastings
-15
-11
-7
-3
1
Dept
h[km]
Outer Caldera
Inner Caldera
HEAT
SOURCE
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HEAT SOURCE -MENENGAI
Event Distribution with Depth
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38MN01MN02
MN03
MN04
MN05
MN06
MN07MN08
MN09MN10
MN11
MN12
MN13
MN14
MN15
160000 165000 170000 175000 180000 185000
Grid Eastings (m)
9965000
9970000
9975000
9980000
9985000
9990000
GridNorthings Kabarak
Majani Mingi
Rongai
NAKURUURBAN AREA
Lake NakuruNational Park
BahatiSettlement
Bahati
ResidentialArea
LakeNakuru
ToEldoret
ToBarin
go
ToNy
ahuru
ru
ToNairobi
MENENGAI
CALDERA
-8
-7
-5
-4
-3
-2
SEISMIC SECTION SHOWING EVENTSEISMIC SECTION SHOWING EVENT
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Men. CalderaNorthWest SouthEast
165000 167500 170000 172500 175000 177500 180000
Distance (M)
-8
-6
-4
-2
0
D
epth(Km)
Olbanita
SEISMIC SECTION SHOWING EVENTSEISMIC SECTION SHOWING EVENT
DISTRIBUTION ACROSS MENENGAI CALDERADISTRIBUTION ACROSS MENENGAI CALDERA
SEISMIC RAYPATHS ACROSS MENENGAISEISMIC RAYPATHS ACROSS MENENGAI
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SEISMIC RAYPATHS ACROSS MENENGAISEISMIC RAYPATHS ACROSS MENENGAI
CALDERACALDERA
Bahati
MN01MN02
MN03
MN04
MN05
MN06
MN07
MN08
MN09MN10
MN11
MN12
MN13
MN14
MN15
160000 165000 170000 175000 180000 185000
Grid Eastings (m)
9965000
9970000
9975000
9980000
9985000
9990000
GridNor
things
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RESERVOIR CHARACTERIZATION
Vp/Vs Velocity Ratios
Olkaria
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9903000
9
904000
9905000
GridNo
rthings[m]
OW-703OW-704
OW-705
OW-709
OW-710
OW-711
OW-713
OW-714
OW-718
OW-722
OW-723
OW-724
OW-726OW-727
OW-707
OW-716
OW-30OW-32
78
82
87
90
92
93
95
98
Bars
9903000
9904000
9905000
GridNorthings
[m]
OW-703OW-704
OW-705
OW-709
OW-710
OW-711
OW-713
OW-714
OW-718
OW-722
OW-723
OW-724
OW-726OW-727
OW-707
OW-716
OW-30OW-32
1.63
1.64
1.66
1.67
1.69
1.73
1.75
1.78
Pressure at 500 m.a.s.lPressure at 500 m.a.s.l
Velocity Ratio DistributionVelocity Ratio Distribution
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9864000
9869000
9874000
9879000
15
35
55
75
95A RESISTIVITY (Ohm-m)
9864000
9869000
9874000
9879000
-200
-100
0
100
200
B AEROMAGNETIC (Gammas)
9864000
9869000
9874000
9879000
-140
-100
-60
-20
20
60
100
140C RESIDUAL GRAVITY (gu)
1.9
2.0
2.1
2.2
2.3
2.4
[a] Vp 1000
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3.5
3.8
4.1
4.4
4.7
5.0
[c] Vp 3000
2.02
2.03
2.04
2.05[f] Vp/Vs 3000
1.84
1.86
1.88
1.90
1.92
1.94
[e] Vp/Vs 2000
1.60
1.65
1.70
1.75
1.80
[d] Vp/Vs 1000
1.9
2.0
2.1
2.2
2.3
2.4
[a] Vp 1000
2.5
2.8
3.1
3.4
3.7
[b] Vp 2000
RESERVOIR COMPARISSON: Vp/Vs RATIOSRESERVOIR COMPARISSON: Vp/Vs RATIOS
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RESERVOIR COMPARISSON: Vp/Vs RATIOSRESERVOIR COMPARISSON: Vp/Vs RATIOS
MENENGAI OLK-NEAST
OLK-EAST SUSWA
OLK-CENTRALOLK-SOUTH
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196000 200000 204000 208000 212000
Grid Eastings[m]
9864000
9868000
9872000
9876000
9880000
GridN
orthings[m]
1.58
1.62
1.66
1.70
1.74
1.78
1.82
Vp/Vs Ratio
HOT
UPFLOW
COLD
INFLOW
Outflo
w
Outflow
Inner and outerCaldera walls
Site 1
Site 2
Site 3
COL
DIN
FLO
W
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160000 165000 170000 175000 180000 1850009965000
9970000
9975000
9980000
9985000
9990000
Rongai
ToEldoret
ToBaringo
ToNyahu
ruru
ToNairobi
1.5
1.7
1.7
2.0
Vp/Vs Ratio
Figure 5.1. Average Vp/Vs rartion variations in the Menengai study area showing proposedtest drill sites [Stars], interpreted upflow zones and fluid recharge for the system
MN01
MN02
MN03
Cold Water
ColdWa
ter
Cold
Water
ColdW
ater
ColdW
ater
UPFLOW
UPFLOW
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VOLCANO-SEISMIC HAZARDS ANALYSIS
THETHE B VALUEB VALUE RELATIONSHIPRELATIONSHIP
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THETHE B VALUEB VALUE RELATIONSHIPRELATIONSHIP
0.0 1.0 2.0 3.0
MAGNITUDE
0.0
1.0
2.0
3.0
4.0
LOG
(N)
Menengai =1.21
Suswa =1.09
Olkaria =1.05
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THANK YOU