Environmental Research Helps Enable Rapid Growth of Geothermal Generation … · 2019-09-09 · GNS...

GNS Science GNS Science

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

JOGMEC International Geothermal Conference, Tokyo, 14-Oct-2014

Chris Bromley GNS Science, Wairakei Research Centre

[email protected]


NZ Geothermal power October 2014 ~1030 MWe (operating) ~6053 GWh/yr (2013) World’s 4th 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

Long-Run Marginal Cost of Generation From MBIE : Electricity Generation Cost Model - 2013 (MED.govt.nz)

New MW needed <40yr: Geot- 1055MW (8300 GWh/yr) CCGT- 1825 Hydro- 52 Gas peak- 400 Total: 3332 MW +22000 GWh/yr


New Zealand Geothermal drilling activity versus time

Wairakei drilling up to 3km for deep reinjection

What’s next ?


Taupo Volcanic Zone (TVZ) Vast natural energy source - Convective Hydrothermal

Systems - sub-ducting Pacific Plate & back-arc rift-zone.

5-6 km

Unproductive

Developed (conventional geo-thermal to 3000 m : 1.5 - 4 GWe potential

Deep Potential • recent drilling using

large rigs > 3000 m • Temp. increases

with depth, whilst permeability may decrease.

10 GWe ?

500 m

Pacific Plate

Aust-Indo Plate

TVZ

2-3 km


Resistivity Traversing: delineates geothermal fields- red = low resistivity at <500m depth

Geophysics of the Taupo Volcanic Zone


3D models of geology & reservoir properties from borehole information

Temperature isotherm

buried lava flow

Quiz : what is this ?


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

• Ecosystems Pohutu Geyser, Rotorua


Sustainable Geothermal Development – strategies

• Reservoir simulation / management models

• Long-term recovery

• Sustainability strategies

• Policy review

Tools and policy advice for long term utilisation

Wairakei Western borefield

GNS Science GNS Science Dickson & Fanelli, 2004

TWO MAIN OPTIONS FOR GENERATION

Steam Condensing Power Plant

Binary Power Plant


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 Dec – Apr 2009 Oct - Dec 2008 D

epth

(km

)

NW-SE Distance (km)

Days D

epth

(km

)

NW-SE Distance (km)

Days

Dep

th (k

m)

NW-SE Distance (km)

Days

Induced seismicity monitoring at Rotokawa reveals fluid flow-paths & brittle-ductile zone

Steven Sherburn and Stephen Bannister


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


2776000 2777000 2778000 2779000 2780000 2781000 2782000 2783000 2784000 2785000 2786000

m East

6270000

6271000

6272000

6273000

6274000

6275000

6276000

6277000

6278000

6279000

6280000m

Nor

th

+

+

Tauhara/Tauhara 2009-2006 with topo background.srf

TH01

TH02

TH03

TH04TH05

TH06TH07TH08

TH09

TH10

TH11

TH12TH13TH14

TH15

TH16

TH18

THM1

1960 1970 1980 1990 2000 2010Year

-50

0

50

100

150

200

250

300

350

400

Gra

vity

cha

nge

(µga

l)

W 100BM 53

Tauhara/Microgravity/W100BM53changesV2.grf

Map of gravity changes at Tauhara 2006-2009, and trends with time

Positive changes (>1986 ) indicate regions of mass increase from inflowing water re-saturating steam zones

1 micro-gal = 10-8 m/s2


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)


Broadlands Rd. Scenic Reserve hydrothermal eruption craters – containing acidic hot pools

Groundwater level decline (~5m in 15 years) 1974 eruption crater


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


Map and vertical cross-sections of located earthquakes near Wairakei-Tauhara, for the period 2000-2009 (right), 2009-2013 (above)

(From Sepulveda et al 2013)


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 Resource utilization alternates between geothermal systems to maintain continuous energy output.

15

20

25

30

35

40

45

50

55

60

0 50 100 150 200YearsPr

essu

re (b

ars)

at -

500

m

150

200

250

300

Tem

pera

ture

(deg

C)

pressuretemperature

ONdraw-down

OFFrecovery

ONdrawdown

OFFrecovery

Cyclic utilization and recovery Resource recovery time depends on deep recharge rate. (Here PR=2).

Resource Rotation or ‘heat-grazing’ rather than ‘heat-mining’

(*from Mike O’Sullivan)


Earths stored heat = 1031 Joules (plenty to go around) Heat flow to surface = 47 TWatts (10 KW per person) Average = 87 mW/m2 (ie needs 1 hectare/house) But at ‘Craters of the Moon’ (Wairakei)= 1 KW/m2


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’

Spa Stream - steam heated groundwater at Otumuheke Spring, Taupo (increased 50oC

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

effect against nearby chloride springs at Spa Sights which ceased discharging).

Wairakei Terraces artificial geyser and terraces using waste hot water from reinjection pipeline


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

• Sustain resources for the long

term….using cyclic utilisation strategy

Waimangu Frying Pan lake

Wairakei drain silica deposit


Questions for the future : • TVZ natural heat flow is ~ 4 GWth; useable heat to ~3 km is ~4 GWe; How robust are

estimates of economic geothermal resource potential of TVZ ? • 10 GWe/100 yrs, at 3 to 5 km, & at super-critical Temperature/Pressure ? • What resource proportion should be kept in “protected” category ?

Wairakei borefield : 56 yrs old, good for another 50 yrs?.. What then..?

Hot spring at Atiamuri – an untapped resource


Limit of shallow

seismicity

Realizing NZ’s deep geothermal potential will involve developing the ability to identify or create deep fractures

>400

after Heise et al., (2006)


Future Visions : • Extra GW of geothermal resource potential (>2025) ? 1) buffer for demand growth 70 MWe/yr; 2) backup (rotational heat grazing,

allowing for recharge); 3) export to Australia; 4) energy intensive industries; 5) electric vehicles (1GWe , 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 GNS Science Wairakei Research Centre, Taupo

Email: [email protected]

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?

Environmental Research Helps Enable Rapid Growth of Geothermal Generation … · 2019-09-09 · GNS...

Documents

Transcript of Environmental Research Helps Enable Rapid Growth of Geothermal Generation … · 2019-09-09 · GNS...