p and s wave velocities in rock as a function of pressure and temperature
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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

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p and s wave velocities in rock as a function of pressure and temperature

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
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.

tof and depth
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.

samples
Samples
  • Outokumpu Deep Drilling Project (2516 m)
device requirements
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

22 mm

25 mm

possible measurement setups
Possible measurement setups
  • Uniaxial
  • Multianvil
  • Hydrostatic pressure
timetable
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

Pressure monitoring

Heating

Temperature monitoring

Transducer cooling

Ordering parts

Planning the measurement procedure

Assembling the setup

Programming the DAQ software

Validation

device vp and vs
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 mode well present
    • Caused by silver epoxy?
  • Removable delay lines
    • Fused quartz
    • Brass
  • Water cooling
  • No load over the piezo crystal
device pressure simulation
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
device pressure
Device: pressure
  • Generating: 15 ton jack borrowed from Department of Chemistry
  • Measuring: Sensotec Model 53 (max 23 ton) + Lebow 7528 amplifier
device pressure1
Device: pressure
  • Problem with sample durability
  • Solved with a brass jacket
  • Splitting sample holder allows sample removal after compression
device temperature simulations
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
device temperature
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
device data acquisition
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
device
Device
  • Transducers
  • Delay lines
  • Heating element and sample
  • Thermocouple
  • Load cell
  • Water cooling tubes
  • Jack
preliminary results
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
pressure test
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
tof time of flight through the delay lines
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
damping the transducers
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)

damping test ok
Damping test - ok
  • Reduced ringing time and increased bandwidth
outcome of applying the backing
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
new transducers
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
new thermal simulations
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=10ºC

h = 20-70mm

T(t=0)=350ºC

D = 25-62 mm

slide27
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

slide28
Temperature distribution in the sample and the upper transducer

Sample D = 25,5 mm, h = 24 mm

t = 200s.

Sample D = 62 mm, h = 70 mm,

t = 400s.

other updates
Other updates
  • PC controlled pressure generation
  • Separate heating of samples to increase the throughput rate
new frame
New frame
  • Compressed air controlled one way hydraulic cylinder replaced with electric motor controlled two way hydraulic cylinder
modification for hydraulic control
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
testing new hydraulics
Testing new hydraulics
  • Pressure increase at 0,1 s intervals
  • OK for loads over 3000 kg
testing of new hydraulics
Testing of new hydraulics
  • Pressure decrease at 0,1 s intervals
  • No control of outcome when decreasing pressure
more control needed
More control needed
  • Manual shut off valve, needle type control
  • Slows down the flow of the hydraulic oil
control achieved
Control achieved
  • Needle valve can be adjusted to allow precise control of the load
conclusions
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
future tasks
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
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