One 1km of 200C hot granite cooled

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• One 1 km³ of 200C hot granite cooled
• by 20C...
• ...delivers about 10 MW of electric power...
• ...for a period of 20 years.
•                                                 
              

www.soultz.net
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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 1200 EJ (300000 TWh),
• which corresponds to 600times the annual
  consumption in Germany.

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Source AXPO Holding, Switzerland
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A Swiss vision...
50 EGS _at_ 50 MWe
aus GASVERBUND MITTELLAND AG
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There are widely accepted operational numbers,
which are necessary for a technically feasible
and economically viable EGS system (Garnish 2002)

• heat exchange surfaces gt2.106 m2
• in a volume gt2.108 m3
• production flow-rates of 50-100 l/s
• at temperatures 150-200 C
• flow impedance lt0.1 MPa/l/s
• water losses lt10.

So far, such numbers have not yet been
demonstrated presently there is no power
generation from EGS systems.
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Table 1 Goals and achievements in EGS projects
world-wide
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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.

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T(z) Basel
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230C
T(z) Static temperature logs Well DP
23-1 Desert Peak/NV, USA
T(z)
-1 km
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Long-term production
25 MWt
Yield(t) and recovery factor depend on fracture
network
Brown et al. (1999)
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Long-term effects
500 l/s 245 MWeyr
Production stop
20 yrs
(Sanyal Butler 2005)
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125 l/s 250 MWeyr
(Sanyal Butler 2005)
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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.

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The key component an extended, sufficiently
permeable fracture network at several km depth,
with suitable heat exchange surfaces.
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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).

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Remote Sensing and Control in Reservoir
Engineering
PTQ(t), Chem. ?
Reservoir domain
Wellhead domain
pT-Borehole Simulator
FE/FD Applications for coupled hydraulic- thermal
processes
Hydraulic tests Pressure recalculation
wellhead to open hole domain (density
changes!) Flow/pressure development at reservoir
depth
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Fracture network Data range distribution
(spacing, aperture, length)
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3
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Hydraulic boundary conditions Worst case
scenarios Most probable scnarios
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Production temperatures Cooling between open
hole.and wellhead
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Thermal processes 3D-conductive/advective High
flow-rates
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3
2
1
2
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Reservoir engineering tool (1) pT- simulator
HEX-BReservoir properties from wellhead data
GPK2/GPK3 wellheads
Example European. EGS Project Soultz-sous-Forêts,
France Stimulation GPK3, 2003
Q l/s
p(z,t) tmp(z,t)
Temperature/ pressure profile, calculated
withHEX-B
Flow Exit/Entry points
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Reservoir engineering tool (2) Stimulation Code
HEX-S Coupled hydro-rock mechanical
code
stochastic structures
deterministic
Example EGS Project Coso, USA
Wellhead pressure
Deterministische Strukturen (UBI)
Stochastische Strukturen ( S UBI)
Pressure distribution in the reservoir after 24
hours reinjection with l/s
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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.

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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.

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Prof. Dr. L. Rybach GEOWATT AG Zurich Dohlenweg
28 CH-8093 Zurich, Switzerland rybach_at_geowatt.ch