Environmental Research Helps Enable Rapid Growth of Geothermal Generation in New Zealand JOGMEC International Geothermal Conference, Tokyo, 14-Oct-2014 Chris Bromley, Wairakei Research Centre c.bromley@gns.cri.nz
NZ Geothermal power October 2014 ~1030 MWe (operating) ~6053 GWh/yr (2013) World s 4 th largest producer of geothermal electricity ~17% of total NZ generation + 0.5 GWe planned ~ + 1 GWe available ~ + 1.6 GWe protected Total ~ 4 GWe (1-3 km depth) + ~ 10 GWe? (3-5km depth)
Historical and Projected Growth of NZ Power Generation
Assumptions: Gas 8$/GJ Coal $5.5/GJ Carbon $12.5/t Discount 8% Use all projects Avg. Exchange rates 2011-12 Growth 1%/yr New MW needed <40yr: Geot- 1055MW (8300 GWh/yr) CCGT- 1825 Hydro- 52 Gas peak- 400 Total: 3332 MW +22000 GWh/yr Long-Run Marginal Cost of Generation From MBIE : Electricity Generation Cost Model - 2013 (MED.govt.nz)
New Zealand Geothermal drilling activity versus time What s next? Wairakei drilling up to 3km for deep reinjection
Taupo Volcanic Zone (TVZ) Vast natural energy source - Convective Hydrothermal Systems - sub-ducting Pacific Plate & back-arc rift-zone. Unproductive Developed (conventional geothermal to 3000 m : 1.5-4 GWe potential Deep Potential 500 m 2-3 km TVZ recent drilling using large rigs > 3000 m Temp. increases with depth, whilst permeability may decrease. 10 GWe? Aust-Indo Plate Pacific Plate 5-6 km
Geophysics of the Taupo Volcanic Zone Resistivity Traversing: delineates geothermal fieldsred = low resistivity at <500m depth
Quiz : what is this? 3D models of geology & reservoir properties from borehole information buried lava flow Temperature isotherm
Integrated visualisation of 3D geology, structure, alteration, geophysics and temperature assists reservoir simulation and gridded model construction Samantha Alcaraz
Environmental considerations Environmental effects uncertainty leads to precautionary approach Protection status category locks up ~40% of potential 4 GWe (1.6 GWe) Perceptions change with acquired knowledge and successful adaptive management practices, eg. injection to locally sustain pressures
Recent Research: Reduce environmental impact of geothermal development Effects of Production and Injection Subsidence mitigation methods and predictions Induced seismicity mechanisms & protocols Ohaaki subsidence
Effects on Surface Features Thermal vegetation response to system change Hot Spring restoration Pohutu Geyser, Rotorua Ecosystems
Sustainable Geothermal Development strategies Tools and policy advice for long term utilisation Reservoir simulation / management models Long-term recovery Sustainability strategies Policy review Wairakei Western borefield
TWO MAIN OPTIONS FOR GENERATION Steam Condensing Power Plant Binary Power Plant Dickson & Fanelli, 2004
Geophysics monitoring tools used to help understand changes occurring in the geothermal reservoir during production Gravity Micro-seismicity
Micro-gravity changes during production/injection reveal reservoir mass and phase changes (boiling or saturation) Trevor Hunt and Supri Soengkono
July - Oct 2008 Oct - Dec 2008 Dec Apr 2009 Induced seismicity monitoring at Rotokawa reveals fluid flow-paths & brittle-ductile zone Depth (km) Depth (km) Depth (km) Days NW-SE Distance (km) Days NW-SE Distance (km) Steven Sherburn and Stephen Bannister Days NW-SE Distance (km)
Rotokawa Steve Sherburn
Rotokawa NW-SE cross-section Steve Sherburn
Examples from Taupo Tauhara Geothermal Field subsidence micro-gravity groundwater infrared seismicity Skip?
Map of Wairakei - Tauhara Geothermal System
6280000 400 6279000 350 m North 6278000 6277000 6276000 6275000 6274000 6273000 TH15 TH08 TH07 TH16 + TH02 TH06 TH04 + TH01 THM1 TH05 TH13 TH14 TH03 TH09 TH11 TH18 TH12 Gravity change (µgal) 300 250 200 150 100 50 0 BM 53 W 100-50 1960 1970 1980 1990 2000 2010 Year Tauhara/Microgravity/W100BM53changesV2.grf 6272000 6271000 TH10 Map of gravity changes at Tauhara 2006-2009, and trends with time 6270000 2776000 2777000 2778000 2779000 2780000 2781000 2782000 2783000 2784000 2785000 2786000 m East 1 micro-gal = 10-8 m/s 2 Tauhara/Tauhara 2009-2006 with topo background.srf Positive changes (>1986 ) indicate regions of mass increase from inflowing water re-saturating steam zones
Tauhara water level changes (-7m) in the upper groundwater (1995 to 2006). The centre of the water level depression coincides with the Crown thermal area (and subsidence bowl)
Groundwater level decline (~5m in 15 years) 1974 eruption crater Broadlands Rd. Scenic Reserve hydrothermal eruption craters containing acidic hot pools
Tauhara thermal infrared (T >18 C) (A) Broadlands Road Reserve; (B) Crown Road 1m deep T profile
(From Sepulveda et al 2013) Map and vertical cross-sections of located earthquakes near Wairakei-Tauhara, for the period 2000-2009 (right), 2009-2013 (above)
Sustainability How much geothermal resource do we need? How should we sustain it for future generations? Can I have my cake and eat it too?
Sustainable Utilization of Geothermal Resources Renewable: Recovery rates governed by enhanced recharge driven by strong pressure and temperature gradients initially created by fluid and heat extraction. *T (recovery) = (PR-1) T (extract) PR= ratio of extracted to natural heat flow Cycle durations to meet demand (daily or seasonal) or extended : 100 yrs Pressure (bars) at - 500m 60 55 50 45 40 35 30 25 20 15 ON draw-down OFF recovery pressure temperature ON drawdown OFF recovery 300 250 200 150 0 50 Years 100 150 200 Cyclic utilization and recovery Resource recovery time depends on deep recharge rate. (Here PR=2). Temperature (degc) Resource utilization alternates between geothermal systems to maintain continuous energy output. Resource Rotation or heat-grazing rather than heat-mining (*from Mike O Sullivan)
Earths stored heat = 10 31 Joules (plenty to go around) Heat flow to surface = 47 TWatts (10 KW per person) Average = 87 mw/m 2 (ie needs 1 hectare/house) But at Craters of the Moon (Wairakei)= 1 KW/m 2
Adaptive Reinjection Strategy - objectives: 1) Avoid contamination of streams 2) Avoid rapid return of injected fluid 3) Minimise excessive pressure drawdown. 4) Use deeper or peripheral injection aquifers, of lower chemical quality. Quiz: Is 100% reinjection necessary? Issues to consider - recharge rates, evolution of 2-phase zones, total energy recovered, fracture flow, etc. Adopt flexible and adaptive injection strategy
Surface thermal features hot spring changes Orakei Korako
Shallow reinjection can affect (enhance or suppress) surface thermal features ROTOKAWA Ed s Spring shallow reinjection raised pressures and caused discharge of a natural acid chloride pool 2000-2004. When injection rates reduced, spring discharge ceased. MOKAI: (near reinjection area)..increase in steaming ground & expanded thermal vegetation (2000-2004), then less steam, more liquid overflows and hydrothermal eruptions (2006-7), then reduced overflow when local injection reduced (new strategy worked)
Wairakei enhancements Silica wing sculpture, growing in the Wairakei drain a microbial-sinter ecosystem Wairakei Terraces artificial geyser and terraces using waste hot water from reinjection pipeline Spa Stream - steam heated groundwater at Otumuheke Spring, Taupo (increased 50 o C from 1960-1995), an enhancement from Wairakei pressure drawdown. (Balance this effect against nearby chloride springs at Spa Sights which ceased discharging).
Hot spring recovery through pressure control. Rotorua and its Geysers Since 1987, a bore closure and reinjection policy has raised pressures, rejuvenated thermal features, lead to more active geysers and a hydrothermal eruption (Kuirau Park)
THE FUTURE : Optimum Environmental Management Balance adverse & beneficial effects Enhance thermal features and ecosystems Stage developments to reduce risk Manage resources flexibly to allow recovery/remediation Manage subsurface pressures through adaptive reinjection Waimangu Frying Pan lake Sustain resources for the long term.using cyclic utilisation strategy Wairakei drain silica deposit
Questions for the future : TVZ natural heat flow is ~ 4 GW th ; useable heat to ~3 km is ~4 GW e ; How robust are estimates of economic geothermal resource potential of TVZ? 10 GW e /100 yrs, at 3 to 5 km, & at super-critical Temperature/Pressure? What resource proportion should be kept in protected category? Hot spring at Atiamuri an untapped resource Wairakei borefield : 56 yrs old, good for another 50 yrs?.. What then..?
Limit of shallow seismicity >400 after Heise et al., (2006) Realizing NZ s deep geothermal potential will involve developing the ability to identify or create deep fractures
Future Visions : Extra GW of geothermal resource potential (>2025)? 1) buffer for demand growth 70 MW e /yr; 2) backup (rotational heat grazing, allowing for recharge); 3) export to Australia; 4) energy intensive industries; 5) electric vehicles (1GW e, 30 PJ/yr saves $5B/yr, if fleet fully converted?) New research directions: hotter and deeper (4-5 km) & better use of lower enthalpy water NZ geothermal industry growth will depend on growing a bigger renewable energy market.
Conclusions and Questions What is Vision for New Zealand s Geothermal Future: Roots (deep, super-critical T/P, fracture stimulation) Model refinement (accurate predictions) Economic bi-products (bacteria, minerals, gases) Efficient use - Hybrids (power, heat and vehicles) Connections (cable to Australia?) Geothermal extraction is sustainable & hot springs are also sustained Geothermal brine reinjection is safe in terms of groundwater effects Fracturing to stimulate fluid flow is safe Peer-review process allows for adaptive field management
THANK YOU Chris Bromley Wairakei Research Centre, Taupo Email: c.bromley@gns.cri.nz Thanks also to Duncan Graham for some of these beautiful thermal feature photos
Key Messages 1. Renewable (geothermal) energy is crucial for the long-term future of all mankind. NZ baseload geothermal : ~17% of electricity and 10 PJ/yr direct heat. Applied research has given us a global technological advantage. We developed cost-effective and environmentally-benign development strategies. 2. Borehole data for monitoring & 3D models of reservoir properties. Geophysics monitoring : gravity, resistivity, micro-earthquakes, velocity & deformation. Integrated interpretation with geochemistry and hydrothermal alteration. Result: better conceptual understanding, improved simulation of reservoir behaviour, and more astute reservoir management. 3. Geothermal resource use can be sustainable. Utilisation won t cause adverse environmental effects, or detract from tourism assets Requires : calibrated simulation modelling of long-term reservoir behaviour; adaptive management to facilitate flexible injection and production strategies; & advanced monitoring of reservoir behaviour to inform decision-making. 4. What additional future use could be made of surplus geothermal resources? 3 GW(e) of power: export to Australia by cable; electrify transport sector? 1 GWth (31 PJ) of hot water: establish district heating, attract energy industry?