Updated conceptual model of Hellisheiði geothermal field

Anette K. Mortensen, Bjarni Reyr Kristjánsson,

Gunnar Gunnarsson, Ingvi Gunnarsson,

Einar Gunnlaugsson, Edda Sif Aradóttir,

Gretar Ívarsson

GGW 2016

25. november 2016

2

• Defines the natural proporties of the geothermal system

– in particular interaction between temperature, pressure,

permeability and mass/energy flow in the system

Conceptual Models of Geothermal Systems

Fractured zonePrecipitation

Recharge

InflowTemperature

Upflow

Outflow

Pressure

Permeability

Lithology

Fluid composition

Size (area, thickness)

Production

ReinjectionFractures and faults

Heat source

Conceptual Model of Hellisheiði

» Latest review in 2007» 10 years production history and much more knowledge gained

»Objective:• More clear concept of salient properties of

the geothermal reservoir and the effect of production

• Basis for management of production and reinjection in the coming years

• Foundation for future location of production wells and reinjection wells

• Updated research plan

Local Heat Sources

Heat sources and their attributes:

1. At eruptive fissure south of Skarðsmýrarfjall » High permeability and

vigorous convection

2. Mini-graben at Reykjafelli » High temperature,

lower permeability, weak convection

3. Hverahlíð – Intersecting faults» High temperature,

high permeability

Skarðsmýrarfjall

Reykjafell

Hverahlíð

HengillFormation temperature at 1000 m.u.s.l.

Initial State – Geochemical Composition

Cl/B´moleratio

Hot

ste

am p

roce

ssR

ock

ratio

Pos

s. e

ffect

of

seaw

ater

?

At least three compartments based on Cl/B ratio 10 100

Styrkur klór í jarðhitavatni (mg/kg)

1

10

100

1000

10000

Cl/B

í ja

rðhi

tava

tni

Cl/B sjór og úrkoma

Cl/B berg

Heitt gufuferli sem leiðir til of mikils bór í vatninu miðað við klór

Úrkoma Hellisheiði

Cl concentration in geothermal water (mg/kg)

Cl/B

in in

geo

ther

mal

wat

er

Precipitation at Hellisheiði

Cl/B of seawater and rain

Hot steam process, which results in high concentration of B in the water in comparison to Cl

rock

Fault Controlled Permeability

• Permeability connected to

NE-SW striking

rift faults and fissures

• Low permeability perpendicular to the orientation of main faults

Tracer Tests

Reservoir Response to Production

Decline in well outputPressure drawdownAccumulated production

kg/s pr. yr

Cooling in the Reservoir

• Up to 20°C cooling in wells at eruptive fissure• Cooling most in aquifers at 800-1400 m depth – cooling from boiling due to pressure drawdown • Cooling minimal in wells with pressure support from reinjection

Delta temp. Qz geotherm. (°C)

Cooling acc. to Qz geothermometer (°C)

Dep

th o

f aqu

ifers

(m.b

.s)

Production at Hellisheiði

Compartments Controlled by Faults and Fissures

900 kg/s

1200 kg/s

Reinjection

Production

Húsmúli

Gráhnúka

Hverahlíð

Skarðsmýrarfjall

Size of Production FieldProduction at Hellisheiði is distributed over a 14 km2 large area

» Skarðsmýrarfjall: Area: 5

km2

Output: 51 MWe Output/km2: 10 MWe/km2

» Hellisheiði and Reykjafell: Area: 9 km2

Output: 193 MWe Output/km2: 21 MWe/km2

» Hverahlíð: Area: 5 km2

Output: 53 MWe Output/km2: 11 MWe/km2

Measures:

More distributed reinjection

Enlarge production area

Current reinjection areas

Planned reinjection areas

Maintain Production