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P- and S-wave velocities in rock as
a function of pressure and
temperature
I. Lassila 1,T. Elbra 2, E. Hæggström1 and L. J. Pesonen 2
V. Kananen1 and M. Perä
J. Haapalainen1 and R. Lehtiniemi 3
P. Heikkinen 4 and I. Kukkonen 5
1
Electronics Research Unit
2
Division of Geophysics
3
Nokia Research Center
4 Institute
of Seismology
5 Geological
Survey of Finland
Motivation - Understanding the structure of the
earth’s crust
 FIRE (Finnish Reflection Experiment) - project
 Seismic reflection and refraction measurements (longitudinal
and shear wave modes)
Photo: Seismic signal is produced by vibrators. Courtesy Jukka Yliniemi.
7.12.2007 Ilkka Lassila
Location of the FIRE reflection seismic lines.
TOF and depth
 Seismic measurements give TOF data
 Need to know Vp and Vs to calibrate the depth
Example of FIRE results from the end of line FIRE 3A in western Finland. The reflector amplitudes of a migrated section are presented as gray tone intensities.
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Samples
 Outokumpu Deep Drilling Project (2516 m)
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Device: requirements
 Vp and Vs measurements
 preferably
 10
simultanously
m/s accuracy
 Controlled pressure
0
- 300 MPa (15 ton for OKU samples)
 Controlled temperature
 20-300ºC
 Preferably
automatic
22 mm
 Data acquisition
25 mm
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Possible measurement setups
 Uniaxial
 Multianvil
 Hydrostatic pressure
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Timetable
Jan
Feb
Mar
Apr
May
Jun
Jul
Material considerations
Mechanical design
Ultrasonic testing and designing
Transducers, pulser / signal generator, amplifiers, switches, oscilloscope
Pressure generating
Heating
Pressure monitoring
Temperature monitoring
Transducer cooling
Ordering parts
Planning the measurement procedure
Assembling the setup
Programming the DAQ software
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Validation
Device: Vp and Vs
 Pitch-catch method
 Two similar transducers, both comprising shear (1,1 MHz)
and longitudinal (1 MHz) piezo (Pz-27) ceramics
 At first only the shear crystal was in use
 Longitudinal
 Caused
mode well present
by silver epoxy?
 Removable delay lines
 Fused
quartz
 Brass
 Water cooling
 No load over the piezo crystal
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Device: pressure simulation
 Pressure simulations by Mr. Haapalainen
 Device
 Fused
can withstand the required pressure
quartz can be used as a delay line material in case of
no roughness
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Device: pressure
 Generating: 15 ton jack borrowed from Department of Chemistry
 Measuring: Sensotec Model 53 (max 23 ton) + Lebow 7528 amplifier
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Device: pressure
 Problem with sample durability
 Solved with a brass jacket
 Splitting sample holder allows sample removal after
compression
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Device: Temperature, simulations
 Thermal simulations by PhD Lehtiniemi and Mr.
Haapalainen
 160
W heater is sufficient for 300ºC in case of fused quartz
delay lines
 Transducer
temperature stays below solder melting / epoxy
softening temperature
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Device: Temperature
 Heating: Nozzle heater ACIM T197 (160 W / 240 Vac)
 Max
400ºC
 Covers
the sample holder
 Cooling: Water cooler (Lauda WK502)
 Measuring: Custom AD595 based thermocouple amplifier
 K-type
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Thermocouple inside the sample holder
Device: Data acquisition
 US signals:
 5072
PR, LeCroy 9410, GPIB, PC, LabVIEW, Matlab
 Thermocouple and load cell:
 AD-conversion
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and transfer to PC with NI PCI-6024E
Device
 Transducers
 Delay lines
 Heating element and sample
 Thermocouple
 Load cell
 Water cooling tubes
 Jack
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Preliminary results
 7 samples from Outokumpu Deep Drill Core
 T: 300ºC20ºC, Load: 7000 kg  500 kg (resembling the
conditions in the Earth’s crust)
 Results comparable with literature values
4000
5500
Vs(m/s)
Vp(m/s)
6000
5000
4500
4000
0
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3500
3000
0.5
1
1.5
T*load(ºC kg)
2
6
x 10
0
0.5
1
1.5
T*load(ºC kg)
2
6
x 10
Pressure test
Pressure test without sample
49.3
the compression of the
sample?
 Compression = 0,1 mm
(Δhsample- Δhno sample)
 Error Vp = 24-33 m/s
 Error Vs = 15-18 m/s
measured height (mm)
 The error if we don’t measure
49.2
49.1
49
1000 kg
13000 kg
48.9
48.8
48.7
48.6
Pressure test with sample
71.3
measured height (mm)
71.2
71.1
71
70.9
70.8
70.7
70.6
70.5
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1000 kg
13000 kg
TOF (time of flight) through the delay lines
 Pulse-echo measurement of the delay
line
 Subtraction of the TOF through the
delay lines from the total TOF
 Pressure and temperature effects to
the delay lines and transducers are
cancelled
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Damping the transducers
 Ringing of the piezo element makes pulse-echo (PE)
measurements difficult.
 Ringing can be reduced with applying attenuating,
material with acoustic impedance close to the piezo to the
back side of the transducer
 PE responses to water load
 a)
zero backing, b) backing of crown glass, c) backing of
tungsten-epoxy, d) backing of material with Z=Ztransducer
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Egypt. J. Sol., Vol. (23), No. (2), (2000)
Damping test - ok
 Reduced ringing time and increased bandwidth
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Transducers without backing
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Outcome of applying the backing
 No signal
 Resistance between transducer electrodes ca. 5 Ω
 Short-circuit
 Difference between test
 Amount
of tungsten in the mixture was higher
- In the test the resistance between the electrodes was ca.
500 Ω
 This type of backing method requires isolation of the
electrodes
 Instead of scraping out the backing it was decided to build
new transducers
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New transducers
 Increased sample size:
 Height
20-70 mm
 Diameter
25-62 mm
 Better modal purity required
 Mode
conversion in the gap between transducer housing
and delay line
 Material:
 No
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stainless steel
separate delay lines
New transducer drawings
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New transducer
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New thermal simulations
T=?
T=10ºC
 Stainless steel:
thermal conductivity=20 W/(m K)
Specific heat=500J/(kg K)
 Sample (rock):
thermal conductivity=2 W/(m K)
Specific heat=790J/(kg K)
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h = 20-70mm
T(t=0)=350ºC
D = 25-62 mm
 Temperature as a function of time in the middle of the
sample and on the transducer inner surface where the
piezos are fixed.
Sample D = 25,5 mm, h = 24 mm
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Sample D = 62 mm, h = 70 mm
 Temperature distribution in the sample and the upper
transducer
Sample D = 25,5 mm, h = 24 mm
t = 200s.
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Sample D = 62 mm, h = 70 mm,
t = 400s.
Other updates
 PC controlled pressure generation
 Separate heating of samples to increase the throughput
rate
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New frame
 Compressed air controlled one way
hydraulic cylinder replaced with
electric motor controlled two way
hydraulic cylinder
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Modification for hydraulic control
 Controls of the pump replaced with relay circuit that
is controlled from PC DAQ-card
 Two valves that are controlled
 Valve
1 open increasing pressure
 Valve
2 open decreasing pressure
 Valves
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closed no change
Testing new hydraulics
 Pressure increase at 0,1 s intervals
 OK for loads over 3000 kg
9000
8000
load (kg)
7000
6000
5000
4000
3000
2000
1000
0
0
0,5
1
1,5
throttle time (s)
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2
2,5
3
Testing of new hydraulics
 Pressure decrease at 0,1 s intervals
 No control of outcome when decreasing pressure
14000
12000
load (kg)
10000
8000
6000
4000
2000
0
-2000
0
0,05
0,1
0,15
throttle time (s)
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0,2
0,25
More control needed
 Manual shut off valve, needle type control
 Slows down the flow of the hydraulic oil
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Control achieved
 Needle valve can be adjusted to allow precise control
of the load
7,00E+03
8,00E+03
7,00E+03
5,00E+03
4,00E+03
3,00E+03
2,00E+03
target
load
5,00E+03
load (kg)
load (kg)
6,00E+03
6,00E+03
measured
load
4,00E+03
3,00E+03
2,00E+03
1,00E+03
1,00E+03
0,00E+00
0,00E+00
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measured
load
target
load
Measurement diagram
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Conclusions
 Device is used for measuring Vp and Vs values that are
needed to interpret seismic data
 Preliminary results ok
 At the moment system is going through some changes
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Future tasks
 Temperature inside the sample vs. on the sample surface
 Validation tests
 Implement a LVDT/gauge to measure the sample
thickness and thickness change inline
 Licentiate thesis
7.12.2007 Ilkka Lassila