The application of fibre optic sensors in laboratory experiments.

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Damian Benson
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9th Euroconference on Rock Physics and Geomechanics Trondheim Norway 17-21 October 2011 The application of fibre optic sensors in laboratory experiments.

1 9th Euroconference on Rock Physics and Geomechanics Trondheim Norway October 2011 The application of fibre optic sensors in laboratory experiments. Guido Blöcher 1, Thomas Reinsch 1, Harald Milsch 1, Alireza Hassanzadegan 1 & Günter Zimmermann 1 1 Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany

temperature change T = 70 C maximum pressure change p = 10

2 Motivation during geothermal power production the temperature and pressure conditions will change maximum temperature change T = 70 C maximum pressure change p = 10 MPa Impact of poro-elastics and thermo-elastics on geothermal power production

3 Motivation Validating parts of the theory of poroelasticity Optimisation of undrained compression experiments Using the s of fibre optic sensors

4 Application Determination of poro-elastic response of porous media by fibre optic sensors Effective pressure dependency of Porosity φ; Biot coefficient α & Skempton coefficient B within mechanical testing system MTS Porosity Skempton coefficient Biot coefficient

5 Porosity Direct method φ = V V p b V = V i p i b dv dv Mainguy & Longuemare, 2002 p b Indirect method i i [( 1 ϕ ) βb βs ] d( pc p p ) ϕ ( βs - βϕ ) dpp d ϕ = + Ghabezloo, Sulem, Saint-Marc, 2009 Carroll & Katsube, 1983 dp p = 0 drained hydrostatic compression jacketed specimen undrained hydrostatic compression jacketed specimen hydrostatic compression unjacketed specimen or mixture rule* *Voigt-Reuss-Hill or Hashin-Shtrikman

6 Biot Coefficient Direct method Indirect method dv p α = V dε b Kümpel, 1991 v drained hydrostatic compression jacketed specimen α =1 K K undrained hydrostatic compression jacketed specimen b Biot & Willis, 1957 Nur & Byerlee, 1971 s hydrostatic compression unjacketed specimen or mixture rule* *Voigt-Reuss-Hill or Hashin-Shtrikman

Skempton Coefficient Direct method Indirect method B = dp dp p c Skempton, 1954 drained hydrostatic compression jacketed specimen B = i ϕ * b s ( β β ) + ( β β ) Mesri, Adachi, Ullrich, 1976

7 Skempton Coefficient Direct method Indirect method B = dp dp p c Skempton, 1954 drained hydrostatic compression jacketed specimen B = i ϕ * b s ( β β ) + ( β β ) Mesri, Adachi, Ullrich, 1976 Jaeger, Cook, Zimmerman, 2007 f β β undrained hydrostatic compression jacketed specimen s b s hydrostatic compression unjacketed specimen or mixture rule* *Voigt-Reuss-Hill or Hashin-Shtrikman

8 Sensor ~0.03 cm ~ 0.5 cm

9 Fibre Optic Sensor - Calibration

10 Fibre Optic Sensor - Calibration Pressure 0-70 MPa +/- 0.5 bar Temperature Accuracy approx. 0.1 C Multiple sensors per sample

11 Potential leakage & test assembly 1. Between jacket and o-ring 2. End cap Sample Interface 3. Perforated Jacket 4. Capillary Void Space Fraction < 0.05%

12 Results Comparison compressibilityβb porosity ϕ Biot coefficient α Skempton coefficient B

13 Results Comparison compressibilityβb porosity ϕ Biot coefficient α Skempton coefficient B

14 Results Comparison compressibilityβb porosity ϕ Biot coefficient α Skempton coefficient B

15 Results Comparison compressibilityβb porosity ϕ Biot coefficient α Skempton coefficient B

16 Results Thermo-elastics

17 The poro-elastic behaviour of two different sandstones Bentheimer SS & Flechtinger SS were investigated by means of fibre optic Direct and indirect methods for porosity, Biot coefficient and Skempton coefficient measurements were compared Porosity: good agreement Biot coefficient: good agreement at higher effective pressure Skempton coefficient: excellent agreement for FlechtingerSS and poor agreement for Bentheimer SS improves undrained measurement although effective pressure can not be adjusted Temperature effect are more pronounced at high effective pressure dpp/dt=-0.017exp(0.56peff)

18 Improvement of fibre optic, e.g. test assembly, data processing, quantity of sensors New applications: Pressure distribution along fractures Pressure propagation in shales Further investigation of thermo-elastic effects by meassuring T and p simultaneously at the same point Thanks for your Attention

arxiv: v1 [physics.geo-ph] 6 Aug 2012

arxiv: v1 [physics.geo-ph] 6 Aug 2012 arxiv:1208.1233v1 [physics.geo-ph] 6 Aug 2012 NOTICE: This is the author s version of a work that was accepted for publication in International Journal of Rock Mechanics and Mining Sciences. Changes resulting