GNS Science
Sustainable and environmentally-sound
development strategies addressed through
international collaboration
Chris Bromley*, Gudni Axelsson, Mike Mongillo
*Chairman IEA-GIA
GNS Science, Wairakei Research Centre, Taupo
WGC2015, Melbourne, 21st April 2015
Sustainability I, 7J, Rm 216, 1:20 pm
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Introduction: Key Concepts
• IEA- Geothermal collaboration www.iea-gia.org
• Sustainable utilisation
• Adaptive and flexible injection strategies
• Environmentally-sound mitigation measures
• Minimize adverse effects : selective target injection
• Risk reduction from well failures : eg (n-1) strategy
• Optimize recharge enthalpy : target the drawdown
• Rotational ‘heat grazing’ for long-term renewal
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1. Sustainable Use (protocols, tools, long-term models, system roots)
2. Monitoring methods
3. Reservoir modelling issues
4. Strategies for protected areas with significant surface thermal features
5. Mitigation of adverse environmental effects, identify risks & minimize hazards (e.g. hot spring loss, subsidence)
IEA-Geothermal Annex I Cooperation
Sustainability, Monitoring, Adaptive Management & Environmental Mitigation
GNS Science
Sustainable Utilisation• Reservoir modelling scenarios & strategies
• Staged capacity increments
• Reduced risk to grow investor/regulator confidence
• Heat ‘grazing’ or ‘cyclic’ utilisation
• Recovery time : T (rec) = (PR-1) T(extraction) *
PR= (extraction/natural) heat flow rate
• Dynamic recovery factors : change with time
• Examples: Wairakei, Kawerau, Svartsengi,
Larderello, Laugarnes, Paris Basin, etc…* From O’Sullivan & Mannington 2005)
GNS SciencePR=heat extraction flowrate/natural heat flowrate
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Options for
cyclic
utilisation
‘Cyclic’ development concept (Olkaria, Axelsson, 2010). In Scenario B, the
short term production is greater (350 kg/s), but cycles on/off. Average
pressures are better supported in B than in A, by improving the balance
between mass/energy extraction and recharge. Another option could be to
shorten the off-periods to 10 years, but keep on-periods at 50 years for several
cycles, then allow much longer recovery period.
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Sustainable Use Flowchart
a ‘snakes and ladders’ approach
1. Exploration & Resource
Assessment
2. Initial Capacity for Staged Approach
3. Natural-State Simulation Model
6. DecideTiming of Multiple Stage
Expansions
5. Calibrate Reservoir Model
4. Produce & Monitor Reservoir Response
7. Expand & Stimulate Reservoir
Response
8. Achieve Enhanced Hot
Recharge
9. Apply Adaptive Reinjection Strategy
12. Decide Long-Term Strategy :
Rotate(heat-grazing)
11. Make-up Drilling Options: in or out
10. Refine Simulations (loop back to 6 or 9);
13. Refine Resource Boundary Conditions
14. Improve Simulations (loop
back to 11)
15. CELEBRATE SUCCESS!
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Environmentally sustainable
management techniquesAdaptive resource management :
• Flexible locations & rates of extraction/injection
• Plan well layouts and connections for flexibility
• Maintain surplus capacity (n-1) & monitor bores
• 2-phase boiling or saturation effects on springs
• Strike a balance of effects
• Avoid-remedy-mitigate adverse effects
• Promote-encourage-enable beneficial effects
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Sustainable Use ExamplesWairakei borefield and five
Power Stations
56 years and still expanding
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Larderello – Italy, 103 years
old, aging gracefully, along
with some grey-haired IEA-
Geothermal members
Svartsengi - 38 years
old, geothermal heat-
park in Iceland, a
combined heat &
power plant, with spa
(the ‘Blue Lagoon’)
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Laugarnes (Reykjavik, Iceland)
sustainable low temperature geothermal
The Pearl restaurant and hot water tanks
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Sustainable Direct Use (Cascaded)
how to keep your prawns
warm…
…but eat them too…
Wairakei Prawn Park (22 years, sustainable)
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The Geysers, USA
production decline has
stabilized (~1000 MWe)
following
supplementary water
injection
U13
U16
SONOMA
U18
U20
CALISTOGA W FORD FLAT
U14
U5/6
U7/8
U11
U17
U12
BEAR CN
0 1.0 2.0
MILES
Hi Pt Tank
Terminal Tank
NON-SRGRP INJECTION WELLHEAD
SEGEP PIPELINESRGRP PIPELINESRGRP INJECTION WELLHEAD
SEISMIC STATIONS
Calpine
NCPA
STRONGMOTION
LBNLCALPINENCSN
SRGRP WELL STUDY AREA
1,8
08,0
00 E
391,000 N
1,7
59,0
00 E
431,000 N
From Majer 2013
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Sustainability and Recoverability of Hot Spring flow-rates
Rotorua and Pohutu Geyser (New Zealand)
Evidence of hot spring recovery through shallow pressure control….Since 1987, a partial bore closure and reinjection policy has raised pressures,
rejuvenated thermal features, & lead to more active geysers
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Sustainability Protocol :
Goals proposed for geothermal development ….
Resource management / renewability target
Utilization efficiency
Research, innovation & knowledge sharing
Environmental impacts / social aspects
Energy security, accessibility, availability and diversity
(grid connections, demand patterns)
Economic and financial viability
Sustainability Indicators ……
Ruth Shorthall’s PhD topic, using case-studies from
Iceland, New Zealand & Kenya
GNS ScienceFrom Gudni Axelsson, IEA-GIA June 2012
Future utilization of deeper parts (roots) of
geothermal resources to increase sustainability Greater output than from normal-depth wells, if sufficient
permeability can be found or enhanced, because of higher
temperature and pressure, especially if super-critical
Extends resource in volume & time
Less environmental effects expected
(a) Because of greater depth
(b) Because of smaller horizontal extent
Numerous technical problems still to be overcome
Potential for applying EGS-technology (stimulation &
reinjection-production doublets)
GNS ScienceFrom Axelsson, IEA-GIA June, 2012
Tools: Geothermal Tracer Testing Has predictive power because thermal break-through time (onset of cooling) is usually
more than 2 orders of magnitude longer than tracer break-through time.
Tracer test duration is site specific and hard to estimate
Heat transfer efficiency depends on flow path surface area not on volume, so recent
emphasis is on reactive tracers
New technology : quantum dots, nano-particles, & temperature-tolerant high-sensitivity
tracers
Soultz Krafla
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Sustainable StrategiesPractical strategies for geothermal field management that optimize long-term sustainability. (Many commercial reservoir simulations only consider depletion over economic lifetimes of ~30 yrs)
1. Cyclic/intermittent utilization, depletion and recovery, relying on enhanced mass and heat recharge. Allocation of standby reserves for future use?
2. Optimize total energy yields: using high extraction rates over short duration cycles, or low extraction rates for long duration cycles. Include economic and risk factors.
3. Use ‘adaptive’ reinjection to support pressure and replace fluid, while avoiding premature cooling or suppressing natural hot recharge. Also use injection to suppress acid fluid production, and excess enthalpy steam.
4. Drill replacement or make-up wells to retain surplus production/ injection (for optimum flexibility) and to extend reservoir information boundaries.
5. Stage development sizes incrementally to test boundary conditions and recharge parameters, and also to reduce risk.
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Supplementary Slides
Reservoir Modelling Issues
&
TABLE OF BEST PRACTICE GEOTHERMAL
ENVIRONMENTAL PROCEDURES
&
New Zealand examples of surface thermal
feature changes
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Reservoir Modelling
Long-term Renewability
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Modelling Issues – prediction reliability ?• Stored heat capacity (optimistic) versus simulation models (conservative) : Philippines - Iceland
experience : Sarmiento and Bjornsson (Stanford, 2007)
• Size/temperature assumptions – 10-20 MWe/km2, use of geophysics, geochemistry, shallow
exploration wells, success/failure rate of conceptual geoscientific models?
• Boundary Recharge assumptions – better constrained by natural steady-state flow model, or
subsequent history matching.
• Pressure stabilisation : is it caused by storativity from steam cap development, or gradually enhanced
recharge of hot fluid through deep boundaries ?
• Staged step increments – how many years per step?
• Cost-benefit of drilling non-productive boundary/monitor wells to improve future capacity
predictions?
• Value of tracer tests for gross permeability structure, gravity surveys for mass and saturation
changes, and chemical monitoring for injectate returns?
• Do models confirm recovery factors of 25-30% of useable heat (to 180 oC)?
• Enthalpy, scaling and acid fluid management – detailed models of particular injection/production
scenarios to help solve specific problems ?
• Initial model boundary assumptions – effects on recharge and recovery rates?
GNS Science
Sustainability ModellingPoints for discussion and future work
• Cyclic, intermittent or rotational approach for long term strategies (heat
pumps, EGS and hydro-thermal reservoirs)
• Decline curve analysis of pressure/temperature drawdown & steam supply:
non-linear implications?
• Make -up well drilling strategy & develop in stages -reduce risk
• Capacity factors & fluid recharge – resources are not constrained to a finite
volume
• Permeability changes with time (deposition/ dissolution; cooling cracks;
stress changes: seismicity; fracturing)
• Lessons from long-term projects, better EGS models, representative
models, shut-down economics, model sensitivity to boundary conditions,
changing permeability, interference between neighbouring systems ?
• Fully-coupled, thermal-fluid-mechanical-chemical simulators
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Adaptive Management & Monitoring • Adaptive management : adjusting locations and rates of fluid extraction and
injection.
• This will optimize sustainable use, but requires flexibility.
• Planners/regulators note : most geothermal developments more than 20 years
old have changed production-injection strategy in response to monitoring of
resource effects.
• Should always maintain some surplus production and injection capacity, and a
range of future options, in order for adaptive (flexible) management to
succeed.
• Effective monitoring of reservoir conditions (temperature, pressure and phase)
is essential.
• Tools include: bore-hole measurements, micro-gravity, seismicity, tracer
studies, and pressure interference testing.
• Monitoring results can be used to calibrate reservoir simulation models which
are used for planning.
GNS Science
Environmental
Risks Avoidance measures
Remediation
measures
Mitigation
measures
Relative
cost
Relative
Risk
1
Discharge effluent -
surface water
contamination
Reinject all
mineralised liquid
discharges
Re-instate natural
surface water quality
Replace or treat
affected water
supplies Large High
2
Discharge effluent -
groundwater
contamination
Avoid injection into
potable aquifers of
groundwater
Pump out & treat, or
reinject into
geothermal aquifer
Replace or treat
affected water
supplies Large Medium
3
Gas emissions (H2S,
Hg, CO2)
H2S abatement, NCG
injection Plant forests
Compensate or
relocate affected
inhabitants Moderate Medium
4
Hot spring
interference
Use injection to
sustain shallow
pressure/temperature
Restore dormant
thermal features by
targetted injection
Create new thermal
features using waste
hot water/steam Minor Medium
5
Induced subsidence
or heave
Use injection to
manage pressures
Repair/relocate
affected structures
Enhance public
amenities Moderate Low
6
Large magnitude
induced seismicity
Limit injection
pressure/temperature
gradients
Repair induced
seismicity damage
Construct quake-
safe public amenities Moderate Low
7
Hydrothermal
eruptions-landslides
Control shallow steam
pressure, slope
stabilisation
Repair damage,
restabilize slopes
Reconstruction,
enhance new
features Minor Low
8 Noise
Remote site selection,
low noise fans/pumps Noise screens
Compensate or
relocate residents Minor Medium
9
Powerplant/pipe
visual effects
low profile structures,
buried pipes
Camoflage painting,
vegetation screening
Tourist facility
enhancement Minor High
10
Unsustainable
utilisation rate
Conservatively sized
development stages
Production-injection
strategy changes
Retire resource to
allow recovery Large Low
Geothermal environmental risks from long-term power
station operation - avoidance, remediation and mitigation options
GNS Science
Environmental
benefits
Enhancement
options Incentive schemes
Economic-social
benefits
Benefit/
cost
1
CO2 emission
reduction (vers fossil
fuels)
Efficient direct use,
DHEs, heatpumps,
binary power-plants
Carbon credits, tax
benefits, subsidies
Reduces global
warming effects High
2
Thermal feature
enhancement
Shallow injection/
production to create/
restore hot springs,
geysers or fumaroles
Mitigation credits to
balance adverse
effects
Enhances tourist
attractions High
3
Thermal habitat
enhancement
Fencing, weed control,
plant propogation
Mitigation credits to
balance adverse
effects
Protects rare
species, increases
biodiversity Moderate
4
Wetland ecological
enhancement
Drainage into local
subsidence bowl
Land use changes,
create reserves
Recreational assets
(wildfowl, fish) Low
6
Energy utilisation
efficiency
improvements
Cascaded direct use
of waste hot water
Low cost access to
waste hot water
New businesses
(Aquaculture,
horticulture, etc) Moderate
7
Local resident social
benefits
Improve livelihood,
health,education
Revolving loans,
subsidies,
sponsorship
Improve local
employment,
standard of living Moderate
Geothermal environmental benefits - enhancements
and incentive schemes
GNS ScienceOrakei Korako
Examples of surface thermal features in
New Zealand illustrating:
Natural variation
Adverse production effects
Beneficial effects of injection management
Mitigated effects
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Rotokawa, Ed’s PoolWairakei, Craters of the Moon
Photos from personal and GNS archives
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Wairakei
Photos from personal and GNS archives
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Tauhara
Photos from personal and GNS archives
