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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. H æggström 1 and L. J. Pesonen 2 V. Kananen 1 and M. Perä J. Haapalainen 1 and R. Lehtiniemi 3 P. Heikkinen 4 and I. Kukkonen 5. 1 Electronics Research Unit - PowerPoint PPT Presentation
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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
7.12.2007 Ilkka Lassila
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.
Location of the FIRE reflection seismic lines.
7.12.2007 Ilkka Lassila
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.
7.12.2007 Ilkka Lassila
Samples
Outokumpu Deep Drilling Project (2516 m)
7.12.2007 Ilkka Lassila
Device: requirements
Vp and Vs measurements preferably simultanously
10 m/s accuracy
Controlled pressure 0 - 300 MPa (15 ton for OKU samples)
Controlled temperature 20-300ºC
Data acquisition Preferably automatic
25 mm22
mm
7.12.2007 Ilkka Lassila
Possible measurement setups
Uniaxial
Multianvil
Hydrostatic pressure
7.12.2007 Ilkka Lassila
Timetable
Material considerations
Mechanical design
Ultrasonic testing and designingTransducers, pulser / signal generator, amplifiers, switches, oscilloscope
Pressure generating Pressure monitoring
Heating Temperature monitoring
Transducer cooling
Ordering parts
Planning the measurement procedure
Assembling the setup
Programming the DAQ software
Jan Feb Mar Apr May Jun Jul
Validation
7.12.2007 Ilkka Lassila
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 useAt first only the shear crystal was in use
Longitudinal mode well presentLongitudinal mode well present
Caused by silver epoxy?Caused by silver epoxy?
Removable delay lines Fused quartz
Brass
Water cooling No load over the piezo crystal
7.12.2007 Ilkka Lassila
Device: pressure simulation
Pressure simulations by Mr. Haapalainen Device can withstand the required pressure
Fused quartz can be used as a delay line material in case of
no roughness
7.12.2007 Ilkka Lassila
Device: pressure
Generating: 15 ton jack borrowed from Department of Chemistry Measuring: Sensotec Model 53 (max 23 ton) + Lebow 7528 amplifier
7.12.2007 Ilkka Lassila
Device: pressure
Problem with sample durability Solved with a brass jacket Splitting sample holder allows sample removal after
compressioncompression
7.12.2007 Ilkka Lassila
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 Transducer temperature stays below solder melting / epoxy
softening temperaturesoftening temperature
7.12.2007 Ilkka Lassila
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 Thermocouple inside the sample holder
7.12.2007 Ilkka Lassila
Device: Data acquisition
US signals: 5072 PR, LeCroy 9410, GPIB, PC, LabVIEW, Matlab
Thermocouple and load cell: AD-conversion and transfer to PC with NI PCI-6024E
7.12.2007 Ilkka Lassila
Device
Transducers Delay lines Heating element and sample Thermocouple Load cell Water cooling tubes Jack
7.12.2007 Ilkka Lassila
Preliminary results
7 samples from Outokumpu Deep Drill Core T: 300ºC20ºC, Load: 7000 kg 500 kg (resembling
the conditions in the Earth’s crust) Results comparable with literature values
0 0.5 1 1.5 2
x 106
4000
4500
5000
5500
6000
Vp(
m/s
)
T*load(ºC kg)0 0.5 1 1.5 2
x 106
3000
3500
4000
Vs(
m/s
)
T*load(ºC kg)
7.12.2007 Ilkka Lassila
Pressure test
The error if we don’t measure
the compression of the
sample? Compression = 0,1 mm
(Δhsample- Δhno sample)
Error Vp = 24-33 m/s Error Vs = 15-18 m/s
Pressure test without sample
48.6
48.7
48.8
48.9
49
49.1
49.2
49.3
mea
sure
d h
eig
ht
(mm
)
1000 kg
13000 kg
Pressure test with sample
70.5
70.6
70.7
70.8
70.9
71
71.1
71.2
71.3
mea
sure
d h
eig
ht
(mm
)
1000 kg
13000 kg
7.12.2007 Ilkka Lassila
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
7.12.2007 Ilkka Lassila
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
Egypt. J. Sol., Vol. (23), No. (2), (2000)
7.12.2007 Ilkka Lassila
Damping test - ok
Reduced ringing time and increased bandwidth
7.12.2007 Ilkka Lassila
Transducers without backing
7.12.2007 Ilkka Lassila
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
7.12.2007 Ilkka Lassila
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: stainless steel
No separate delay lines
7.12.2007 Ilkka Lassila
New transducer drawings
7.12.2007 Ilkka Lassila
New transducer
7.12.2007 Ilkka Lassila
New thermal simulations
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)
T(t=0)=350ºC
T=10ºC
T=?
h = 20-70mm
D = 25-62 mm
7.12.2007 Ilkka Lassila
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 Sample D = 62 mm, h = 70 mm
7.12.2007 Ilkka Lassila
Temperature distribution in the sample and the upper
transducer
Sample D = 25,5 mm, h = 24 mmt = 200s.
Sample D = 62 mm, h = 70 mm,t = 400s.
7.12.2007 Ilkka Lassila
Other updates
PC controlled pressure generation Separate heating of samples to increase the throughput
rate
7.12.2007 Ilkka Lassila
New frame
Compressed air controlled one way
hydraulic cylinder replaced with
electric motor controlled two way
hydraulic cylinder
7.12.2007 Ilkka Lassila
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 closed no change
7.12.2007 Ilkka Lassila
Testing new hydraulics
Pressure increase at 0,1 s intervals OK for loads over 3000 kg
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 0,5 1 1,5 2 2,5 3
throttle time (s)
load
(kg
)
7.12.2007 Ilkka Lassila
Testing of new hydraulics
-2000
0
2000
4000
6000
8000
10000
12000
14000
0 0,05 0,1 0,15 0,2 0,25
throttle time (s)
load
(kg
) Pressure decrease at 0,1 s intervals No control of outcome when decreasing pressure
7.12.2007 Ilkka Lassila
More control needed
Manual shut off valve, needle type control Slows down the flow of the hydraulic oil
7.12.2007 Ilkka Lassila
Control achieved
0,00E+00
1,00E+03
2,00E+03
3,00E+03
4,00E+03
5,00E+03
6,00E+03
7,00E+03
8,00E+03
loa
d (
kg
)
measuredload
targetload
Needle valve can be adjusted to allow precise control
of the load
0,00E+00
1,00E+03
2,00E+03
3,00E+03
4,00E+03
5,00E+03
6,00E+03
7,00E+03
loa
d (
kg
)measuredload
targetload
7.12.2007 Ilkka Lassila
Measurement diagram
7.12.2007 Ilkka Lassila
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
7.12.2007 Ilkka Lassila
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