Environmental Research Helps Enable Rapid Growth of Geothermal Generation in New Zealand. Chris Bromley

Size: px

Start display at page:

Download "Environmental Research Helps Enable Rapid Growth of Geothermal Generation in New Zealand. Chris Bromley"

Kelley Holland
5 years ago
Views:

1 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

2 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 GWe planned ~ + 1 GWe available ~ GWe protected Total ~ 4 GWe (1-3 km depth) + ~ 10 GWe? (3-5km depth)

3 Historical and Projected Growth of NZ Power Generation

4 Assumptions: Gas 8$/GJ Coal $5.5/GJ Carbon $12.5/t Discount 8% Use all projects Avg. Exchange rates Growth 1%/yr New MW needed <40yr: Geot- 1055MW (8300 GWh/yr) CCGT Hydro- 52 Gas peak- 400 Total: 3332 MW GWh/yr Long-Run Marginal Cost of Generation From MBIE : Electricity Generation Cost Model (MED.govt.nz)

5 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.

6 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 : 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

7 Geophysics of the Taupo Volcanic Zone Resistivity Traversing: delineates geothermal fieldsred = low resistivity at <500m depth

8 Quiz : what is this? 3D models of geology & reservoir properties from borehole information buried lava flow Temperature isotherm

9 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

10 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

11 Recent Research: Reduce environmental impact of geothermal development Effects of Production and Injection Subsidence mitigation methods and predictions Induced seismicity mechanisms & protocols Ohaaki subsidence

12 Effects on Surface Features Thermal vegetation response to system change Hot Spring restoration Pohutu Geyser, Rotorua Ecosystems

13 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

14 TWO MAIN OPTIONS FOR GENERATION Steam Condensing Power Plant Binary Power Plant Dickson & Fanelli, 2004

15 Geophysics monitoring tools used to help understand changes occurring in the geothermal reservoir during production Gravity Micro-seismicity

16 Micro-gravity changes during production/injection reveal reservoir mass and phase changes (boiling or saturation) Trevor Hunt and Supri Soengkono

zone Depth (km) Depth (km) Depth (km) Days NW-SE Distance (km) Days

17 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)

18 Rotokawa Steve Sherburn

19 Rotokawa NW-SE cross-section Steve Sherburn

20 Examples from Taupo Tauhara Geothermal Field subsidence micro-gravity groundwater infrared seismicity Skip?

21 Map of Wairakei - Tauhara Geothermal System

6280000 400 6279000 350 m North 6278000 6277000 6276000 6275000 6274000 6273000 TH15 TH08 TH07 TH16 + TH02 TH06

100-50 1960 1970 1980 1990 2000 2010 Year Tauhara/Microgravity/W100BM53changesV2.

2777000 2778000 2779000 2780000 2781000 2782000 2783000 2784000 2785000 2786000 m East 1 micro-gal = 10-8 m/s 2

22 m North TH15 TH08 TH07 TH16 + TH02 TH06 TH04 + TH01 THM1 TH05 TH13 TH14 TH03 TH09 TH11 TH18 TH12 Gravity change (µgal) BM 53 W Year Tauhara/Microgravity/W100BM53changesV2.grf TH10 Map of gravity changes at Tauhara , and trends with time m East 1 micro-gal = 10-8 m/s 2 Tauhara/Tauhara with topo background.srf Positive changes (>1986 ) indicate regions of mass increase from inflowing water re-saturating steam zones

23 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)

24 Groundwater level decline (~5m in 15 years) 1974 eruption crater Broadlands Rd. Scenic Reserve hydrothermal eruption craters containing acidic hot pools

25 Tauhara thermal infrared (T >18 C) (A) Broadlands Road Reserve; (B) Crown Road 1m deep T profile

26 (From Sepulveda et al 2013) Map and vertical cross-sections of located earthquakes near Wairakei-Tauhara, for the period (right), (above)

27 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?

28 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 ON draw-down OFF recovery pressure temperature ON drawdown OFF recovery Years 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

29 Earths stored heat = 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

30 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

31 Surface thermal features hot spring changes Orakei Korako

Shallow reinjection can affect (enhance or suppress) surface thermal features

32 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 When injection rates reduced, spring discharge ceased. MOKAI: (near reinjection area)..increase in steaming ground & expanded thermal vegetation ( ), 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

and terraces using waste hot water from reinjection pipeline Spa Stream -

from 1960-1995), an enhancement from Wairakei pressure drawdown.

33 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 ), an enhancement from Wairakei pressure drawdown. (Balance this effect against nearby chloride springs at Spa Sights which ceased discharging).

34 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)

recovery/remediation Manage subsurface pressures through adaptive reinjection Waimangu Frying Pan

35 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?

36 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..?

37 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

38 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.

$Conclusions and Questions What is Vision for New Zealand s Geothermal Future: Roots (deep, super-critical T/P, fracture stimulation)$ vehicles) Connections (cable to Australia?

vehicles) Connections (cable to Australia?

39 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

40 THANK YOU Chris Bromley Wairakei Research Centre, Taupo Thanks also to Duncan Graham for some of these beautiful thermal feature photos

41 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?

Mitigating Environment Impacts of Geothermal Development IEA-GIA ANNEX 1 Workshop Taupo, 15-16th June, 2012 Report to IEA-GIA ExCo

Mitigating Environment Impacts of Geothermal Development IEA-GIA ANNEX 1 Workshop Taupo, 15-16th June, 2012 Report to IEA-GIA ExCo Chris Bromley Convenor, Wairakei Research Centre Taupo IEA-GIA, Annex