One 1 km³ of 200°C hot granite cooled by 20°C... ...delivers about 10 MW of electric power......

Challenges

Status

Problems

Summary, outlook

L. RYBACHL. RYBACH

Prof.em. ETH Zürich, GEOWATT AG Zürich, Prof.em. ETH Zürich, GEOWATT AG Zürich, SwitzerlandSwitzerland

Enhanced Geothermal Systems:Challenges and problems ahead

EnhancedEnhanced Geothermal Systems:Geothermal Systems:Challenges Challenges and and problems problems aheadahead

ENGINE ENGINE Launching ConferenceLaunching Conference, , OrléansOrléans 13 13 FebruaryFebruary 20062006

Challenges

Status

Problems

Summary, outlook

L. RYBACHL. RYBACH



EnhancedEnhanced Geothermal Systems:Geothermal Systems:Challenges Challenges and and problemsproblems ahead ahead


One 1 km³ of 200°C hot granite cooled by 20°C...

...delivers about 10 MW of electric power......for a period of 20 years.

www.soultz.net

The estimated EGS potential is huge:

• According to a study presented by the German Parliament the total technical potential for electricity production form EGS sources amounts to about 1’200 EJ (300’000 TWh),

• which corresponds to 600times the annual consumption in Germany.

Source: AXPO Holding, Switzerland

aus GASVERBUND MITTELLAND AG

A Swiss vision...50 EGS @ 50 MWe

Challenges

Status

Problems

Summary, outlook

L. RYBACHL. RYBACH



EnhancedEnhanced Geothermal Systems:Geothermal Systems:Challenges Challenges and and problems ahead problems ahead


There are widely accepted operational numbers, which are necessary for a technically feasible and economically viable EGS system (Garnish 2002):

• heat exchange surfaces >2.106 m2

• in a volume >2.108 m3

• production flow-rates of 50-100 l/s

• at temperatures 150-200 °C

• flow impedance <0.1 MPa/l/s

• water losses <10%.

So far, such numbers have not yet been demonstrated; presently there is no power generation from EGS systems.

Project Time period

Max. rock- temp. [°C]

Reservoir depth

[m]

Well spacing

[m]

Flow- rate [l/s]

Water loss [%]

Flow impedance [MPa/l/s]

Thermal capacity [MWth]

Water through-

flow [m³]

Los Alamos (USA)

1973-1979

232 3500 150-300 ~7 <10 2.5 ~5 80 -100

Rosemanowes (UK)

1980-1993

80 2000 180-270 ~15 ~25 0.4 ~4 200 -300

Hijiori (Japan) 1985-2003

270 2200 ~130 ~12 ~25 0.3 ~7 50 -150

Soultz (F) 1989-1997

168 3500 ~450 ~26 0 0.23 ~11 ~7000

Soultz (F) (expected….)

1997- 202 5000 600-700 ~100 0 0.12 ~50 ~20'000

Goals (Garnish 2002)

150 - 200

50 - 100

<10 % 0.1

Table 1: Goals and achievements in EGS projects world-wide

Challenges

Status

Problems

Summary, outlook

L. RYBACHL. RYBACH



EnhancedEnhanced Geothermal Systems:Geothermal Systems:Challenges Challenges and and problems ahead problems ahead


So there is still quite a bit ahead…

Numerous problems must be solved to reach the numerical goals and many unknowns need to be clarified:

irregularities of the temperature field at depth

favourable stress field conditions

long-term effects, rock-water interaction

possible short-circuiting

environmental impacts like man-made seismicity

to name only a few.

Temperaturprognose für DHM Basel

T(z) Basel

?

?

0 50 100 150 200

0

1000

2000

3000

4000

5000

0

2000

4000

6000

8000

10000

12000

14000

16000

50 100150200250300350

Temperature (oC)

Dep

th (

m)

EPS1

GPK1

GPK2

RhineGraben

Dep

th (ft)

Temperature (F)

T(z) Soultz

Temperatureprofileat Soultz/F

T(z) T(z) : Static temperature logsWell DP 23-1Desert Peak/NV, USA

-1 km

230°C

Brown et al. (1999)

Yield(t) and recovery factordepend on fracture network

25 MWt

Long-term production

(Sanyal & Butler 2005)

500 l/s

245 MWeyrProduction stop

20 yrs

Long-term effects

(Sanyal & Butler 2005)

125 l/s

250 MWeyr

Induced seismicity

• Reinjection is increasingly applied at numerous geothermal production areas. This changes the pore pressure conditions and herewith the local stress field.

• At The Geysers field/California,USA a large-scale reinjection of fluids (piped to the field over long distances from a sewage plant) is underway since a few years. This creates frequent, perceptible tremors. Induced seismicity is especially relevant for the EGS technology.

Monitoring of local seismicity by a suitable seismometer array (starting well before reinjection/fracturing) is indispensable.

The key component:

an extended, sufficiently

permeable fracture network

at several km depth, with

suitable heat exchange

surfaces.

Key issue is the creation, characterization and management of an extended, sufficiently permeable fracture network at several km depth, with suitable heat exchange surfaces.

No direct observation/ manipulation is possible to achieve this; • it must be accomplished by a kind of remote-

sensing and –control; •promising developments to provide the tools

needed here are underway (e.g. the HEX-B and HEX-S software of GEOWATT).

Remote Sensing and Control in Reservoir Engineering

Fracture network Data range distribution (spacing, aperture, length)

Hydraulic boundary conditions Worst case scenariosMost probable scnarios

Reservoir domain: Wellhead domain:

Hydraulic tests Pressure recalculation wellhead to open hole domain (density changes!)Flow/pressure development at reservoir depth

PTQ(t),Chem.

?

Production temperatures Cooling between open hole.andwellhead

1

1

2

22

33

3 3

4

4

Thermal processes 3D-conductive/advectiveHigh flow-rates

pT-Borehole Simulator

HEX-B

FE/FD Applications forcoupled hydraulic-thermal processes

3D-CodeCluster

Reservoir engineering tool (1): pT- simulator HEX-BReservoir properties from wellhead data GPK2/GPK3 wellheads

Temperature/

pressure profile,

calculated withHEX-B

Example: European. EGS Project Soultz-sous-Forêts, FranceStimulation GPK3, 2003

ca. 10 Tage

p(z,t)tmp(z,t)

Flow Exit/Entry points

Q [l/s]

HEX-B

Example: EGS Project Coso, USA

-3000

-2500

-2000

-1500

-1000

x3

-5000

500x1

-5000

500

x2

XY

Z

Deterministische Strukturen (UBI)

Stochastische Strukturen ( UBI)

HEX-S

Pressure distribution in the reservoir after24 hours reinjection with l/s

time [s]

Pdh[P

a]

Flo

wra

te[l/s]

0 100000 200000 3000000

5E+06

1E+07

1.5E+07

2E+07

2.5E+07

0

10

20

30

40

50

60

70

80

90

100

Pdh B1

Qinj [l/s]

Pdh C2

Pdh C3

GPK4 Stimulation Sep.2004; Modell b1/cx

IImodl : 6.9-7.4 IImodl : 9.7-10.7

Wellhead pressure

Reservoir engineering tool (2): Stimulation Code HEX-S Coupled hydro-rock mechanical codedeterministic stochastic structures

ECONOMICS

Various economic models (for example the one at http://web.mit.edu/hjherzog/www/ developed by the IEA Geothermal Implementing Agreement) come up with favourable electricity production prices.

Such models are all based on numerous assumptions, which have not yet been substantiated.

So far there is no practical experience with real costs.

In any case, substantial front-up investment is needed since EGS technical feasibility at a given site can be demonstrated by deep drilling and circulation only.

Co-generation (and selling the heat) could secure a better price than electricity generation alone.

Challenges

Status

Problems

Summary, outlook

L. RYBACHL. RYBACH



EnhancedEnhanced Geothermal Systems:Geothermal Systems:Challenges Challenges and and problems problems aheadahead


There are great challenges but still numerous problems ahead.

The real challenge is to work for problem solutions, through a wide spectrum of disciplines: earth sciences, physics, chemistry, engineering, economics….

What will really be needed is the planning and establishment of successful EGS systems in several, contrasting geological settings;

Key issue will be remote sensing and –control in creating, characterizing and operating the fracture system at depth;

Joining forces by a broad, internationally based interdisciplinary effort like ENGINE is an important step towards the ambitious goals;

The EGS adventure resembles an Alpine tour: the difficulties and struggles underway are numerous and major, the prospect however (“the view from the top”) is rewarding.

Many thanks for your attention !

Prof. Dr. L. RybachGEOWATT AG ZurichDohlenweg 28CH-8093 Zurich, [email protected]

One 1 km³ of 200°C hot granite cooled by 20°C... ...delivers about 10 MW of electric power......

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