GROUND DEFORMATION DUE TO STEAM CAP PROCESSES AT REYKJANES, SW-ICELAND: EFFECTS OF GEOTHERMAL

EXPLOITATION INFERRED FROM INTERFEROMETRIC ANALYSIS OF SENTINEL-1 IMAGES 2015-2017

Mylène Receveur (1), Freysteinn Sigmundsson(1), Vincent Drouin(1,2), Michelle Parks (3)

(1) Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland(2) National Land Survey of Iceland, Akranes, Iceland

(3) Icelandic Meteorological Office

myr2@hi.isFinal Master project

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Highlights• Time series analysis from 2015 to 2017 using

Interferometric analysis of C-band Sentinel-1A and Sentinel-1B data

• Determination of the parameters for the deformation source using probabilistic inversion

• Models of deformation processes, considering pressure/temperature and production data

2Source :Mylene Receveur

Source :European Space Agency (ESA)

Source : Mylène Receveur

Introduction Data Time series analysis Modeling Interpretation Conclusion

• High temperature geothermal system

• 17 production and 5 injection wells in 2015-2017

• Commissioning of the 100 Mwe power plant in 2006

Average yearly next extraction of geothermal fluid 1970-2016 (Vatnaskilreport, 2017)

Pre

ssu

re (

ba

r) 2

00

6-2

01

7

3Source: HS-Orka; Thorvaldsson & Arnarsson, Vatnaskil report, 2017; Khodayar et al., 2016

Introduction Data Time series analysis Modeling Interpretation Conclusion

2005-2016 Inferred cumulative vertical displacement: -0,26 mContraction towards the center of deflation: 0.14 m.

Envisat track 173 Envisat track 138

2005-2008

Envisat T173: -33mm/yr

Envisat T138: -28 mm/yr

Parks et al. (2018)

TSX track T26 TSX track T1102009-2016

TSX T26: -24 mm/yr

TSX T110: -21 mm/yr

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Phase change in range (rad)

Phase change in range (rad)

Introduction Data Time series analysis Modeling Interpretation Conclusion

a) Geometry for ascending and descending near-polar orbits.

b) Projection of heading h and LOS vectors l onto the ground plane (Wortham, 2014).

𝐷𝑒𝑠𝑐𝑒𝑛𝑑𝑖𝑛𝑔 𝑇155

𝐴𝑠𝑐𝑒𝑛𝑑𝑖𝑛𝑔 𝑇16

𝑑𝐿𝑂𝑆 = − ҧ𝑑 • ത𝑢

ത𝑢𝑇16 = [−0.545 0.123 0.830]

ത𝑢𝑇155 = [0.605 0.123 0.787]

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Sentinel-1 mission: two satellites, two tracks

▪ 104 and 107 Single Look Complex images from T16 and T155 between October 2014 – January 2018

▪ 1 image every 12 days, 5 x 20 m resolution

▪ Processing: ISCE software

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Introduction Data Time series analysis Modeling Interpretation Conclusion

▪40 interferograms

▪804 days

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▪47 interferograms

▪942 days

Perpendicular baseline

o S1Ao S1B

Introduction Data Time series analysis Modeling Interpretation Conclusion

Velocity maps▪Resolution:

40 x 40 m

▪Sub-circular subsidence bowl centered on the most productive area (Gunnuhver hot spring)

▪Linear deformation: 16 mm/yr in the satellite LOS

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Time series analysis for a set of point situated in the center of the most deforming area (black squares):

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Introduction Data Time series analysis Modeling Interpretation Conclusion

Decomposition into near-vertical and near-east displacement components

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𝑛𝑈 =𝑑𝐴 + 𝑑𝐷

1.617 𝑛𝐸 =𝑑𝐴 − 𝑑𝐷

−1.149

Near-eastNear-vertical

-25 mm/yr

+4 mm/yr

-10 mm/yr

(mm/yr) (mm/yr)

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Introduction Data Time series analysis Modeling Interpretation Conclusion

Horizontal Okada sill with uniform closing and contracting penny shaped crack

▪Input: LOS average velocity maps

▪Contraction of a rock body under pressure change in a homogeneous, isotropic and elastic half-space

▪5 model parameters

▪Results: source at 1 km depth closing by a constant rate of 4 cm/yr or a volume change ∆𝑉 = 0,9 ∗ 105𝑚3/𝑦𝑟

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-0,04 [ -0,06; -0,02]1531 [979; 1969]1357 m [666; 2156]

1161 1097; 1193700 680; 730

−9.96 −10,0;−8,5] × 10−5

Introduction Data Time series analysis Modeling Interpretation Conclusion

Relation between deformation sources and geological structure

(modified from Friðleifsson et al., 2014; Khodayar et al., 2016)

Vertical displacement map

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Reservoir volume : 3,8 𝑘𝑚3

Average reservoir thickness : 2 kmMicro-scale porosity: 15%Steam cap thickness: 300-400 mSteam cap volume: 0,6-0,8 𝑘𝑚3

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𝑑𝑣 =𝑑𝑣

𝑑𝑇𝑑𝑇 +

𝑑𝑣

𝑑𝑃𝑑𝑃 = 𝑣𝛼𝑑𝑇 − 𝑣𝑐𝑑𝑃

Introduction Data Time series analysis Modeling Interpretation Conclusion

𝑣 ∶ 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑣𝑜𝑙𝑢𝑚𝑒𝑃: 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑇: 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒𝛼: 𝐶𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒𝑟𝑚𝑎𝑙 𝑒𝑥𝑝𝑎𝑛𝑠𝑖𝑜𝑛𝑐: 𝑈𝑛𝑖𝑎𝑥𝑖𝑎𝑙 𝑝𝑜𝑟𝑜-𝑒𝑙𝑎𝑠𝑡𝑖𝑐 𝑒𝑥𝑝𝑎𝑛𝑠𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡

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Cumulative volume change 2005-2017

∆𝑉𝑡𝑜𝑡(2005−2017) = −3,9 × 106𝑚3

1) Pressure change

2) Cooling within a horizontal layer

3) Delayed rock compaction

𝑑𝑣 =𝑑𝑣

𝑑𝑇𝑑𝑇 +

𝑑𝑣

𝑑𝑃𝑑𝑃 = 𝑣𝛼𝑑𝑇 − 𝑣𝑐𝑑𝑃

Introduction Data Time series analysis Modeling Interpretation Conclusion

In a Penny shaped crack

∆𝑃 =µ

2𝑎3∆𝑉

∆𝑉𝑃𝑆𝐶= −0,7 × 105𝑚3/𝑦𝑟

with 𝑎 = 700 𝑚

µ = (1 − 20) 𝐺𝑃𝑎

∆𝑃 = 0,1 𝑡𝑜 2 𝑀𝑃𝑎/𝑦𝑟

∆𝑃 = 0,15 𝑀𝑃𝑎/𝑦𝑟 if µ = 1,5 𝐺𝑃𝑎

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∆𝑃 = 0,3 MPa in 2 years(-0,15 MPa/yr)

Introduction Data Time series analysis Modeling Interpretation Conclusion

In the Okada layer∆ℎ = 𝛾𝛼ℎ∆𝑇

= −0,04 𝑚/𝑦𝑟With 𝛾𝛼 = (1 − 5) × 10−5 °𝐶−1

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If ∆𝑇 = −4 °𝐶/𝑦𝑟ℎ = 200 𝑡𝑜 1000 𝑚

If ℎ = 400 𝑚∆𝑇 = −10 𝑡𝑜 − 2°𝐶/𝑦𝑟

1) Pressure change

2) Cooling within a horizontal layer

3) Delayed rock compaction

𝑑𝑣 =𝑑𝑣

𝑑𝑇𝑑𝑇 +

𝑑𝑣

𝑑𝑃𝑑𝑃 = 𝑣𝛼𝑑𝑇 − 𝑣𝑐𝑑𝑃

ℎ = 600 𝑚

∆𝑇2009−2015=30°C

At 925 m b.s.l

Non-linear relationship between pressure and volume change

Change in isothermal compressibility (steam zone)

∆𝑉 = 𝑐∆𝑃𝑉

Introduction Data Time series analysis Modeling Interpretation Conclusion

𝒄 = 𝟐 × 𝟏𝟎−𝟏𝟎𝑷𝒂−𝟏

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𝒄 = 𝟏 × 𝟏𝟎−𝟗𝑷𝒂−𝟏

1) Pressure change

2) Cooling within a horizontal layer

3) Delayed rock compaction

𝑑𝑣 =𝑑𝑣

𝑑𝑇𝑑𝑇 +

𝑑𝑣

𝑑𝑃𝑑𝑃 = 𝑣𝛼𝑑𝑇 − 𝑣𝑐𝑑𝑃

Source: Thorvaldsson & Arnarsson, Vatnaskil report, 2017; Khodayar et al., 2016)

∆𝑉𝑡𝑜𝑡(2005−2017) = ∆𝑉𝑟𝑒𝑠𝑒𝑟𝑣𝑜𝑖𝑟+ ∆𝑉𝑠𝑡𝑒𝑎𝑚 𝑐𝑎𝑝 = −2,6 × 106 − 1,3 × 106 = −3,9 × 106𝑚3

Conclusion

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▪Sentinel-1 InSAR successfully captures deformation at Reykjanes using only two years of data. Ideal location at Reykjanes (flat & vegetation free area)

▪Decrease in the rate of volume change :▪ 2006-2009: -7.3 x 105 m3/yr▪ 2009-2016: -1,5 x 105 m3/yr▪ 2015-2017: -0,9 x 105 m3/yr

▪Migration of the modelled source from about 2,2 km to 1 km depth

▪Change in subsidence pattern

▪Combination of pressure, temperature and compressibility change in steam cap can explain 2015-2017 deformation

Future▪Numerical modeling of deformation processes▪Use geodetic studies to guide reinjection and

preservation of the steam cap

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Thank you !QUESTIONS ?

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Clifton, A., 2003. Fracture populations on the Reykjanes Peninsula, Iceland: Comparison with experimental clay models of obliquerifting. In: Journal of geophysical research, Vol, 108, NO. B2, 2074, doi:10.1029/2001JB000635

Drouin, V., Sigmundsson, F., Verhagen, S., Ofeigsson, B.G., Spaans, K., Hreinsdottir, S., 2017. Deformation at Krafla and Bjarnaflaggeothermal areas, Northern Vocanic Zone of Iceland, 1993-2003. In: Journal of Volcanology and Geothermal Research 344. 92-105.

Ferretti, A., Monti-Guarnieri, A., Prati, C., Rocca, F., 2007. InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation. European Space Agency. TM-19. ISBN: 92-9092-233-8 ISSN

Fialko,Y., Khazan,Y., Simons,M., 2001. Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy, Geophysical Journal International, 146, 181–190.

Friðleifsson, G.Ó., Sigurdsson, Ó., Thorbjörnsson, D., Karlsdottir, R., Gilason, Th., 2014. Preparation for drilling well IDDP-2 at Reykjanes. In: Geothermics 49. P119-126

Im, K., Elsworth, D., Guglielmi, Y., Mattioli, G.S., 2017. Geodetic imaging of thermal deformation in geothermal reservoirs –production, depletion and fault reactivation. In: Journal of Volcanology and Geothermal Research (unpublished). 13p

Khodayar, M., Nielson, S., Hickson, C., Gudnason, E.A., Hardarson, B.S., Gudmundsottir, V., Halldorsdottir, S., Oskarsson, F., Weisenberger, T.B., Bjornsson, S., 2016. The 2016 Conceptual Model of Reykjanes Geothermal System, SW Iceland. ISOR Report. Project No: 15-0230. 110p

Okada, Y. 1985. Surface deformation due to shear and tensile faults in a halfspace, Bull. Seismol. Soc. Am., 75, 1135–1154.

Parks, M., Sigmundsson, F.,Sigurdson, O., Hopper, A., in review. InSAR Analysis of the Western Reykjanes Peninsula: 2003 to 2016. Draft report.

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