How EGS is investigated in the case of the
Larderello geothermal field ?
Guido Cappetti
Enel – Generation and Energy Management – Geothermal Production
Engine Launching Conference
Orleans 12-15 February 2006
Uso: aziendale
Contents
 The first exploitation period of Larderello
 The Research&Development programs, from mid ’70s:
Deep exploration
Reinjection
Stimulation jobs
 The reassessment of the geothermal resource
 New exploitation strategies
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Temperature distribution at 3000m depth, in Italy
LARDERELLO
M. AMIATA
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Geothermal power growth up to 80’s
In 1913, at Larderello, first unit
in operation (250 kW).

Italy was the sole country in
the world for electricity
generation from geothermal
resources up to 1958, when a
unit was installed at Wairakey
(New Zealand).
[GWh/anno]

•1904 First test in Larderello
•1913 First 250 kW unit in Larderello
Development of shallow
reservoirs of Larderello,
Travale/Radicondoli and Amiata.

Beginning of 70’s serious
production decline problems

Oil crisis induced a renewal of
interest towards geothermal
energy and new R&D were
implemented.

Anni
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Temperature distribution in the Larderello area
Top of the shallow Carbonate Reservoir
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The production sustainability
The problem of production sustainability was evidenced in the mid-‘70s, when the
boundaries of the productive areas related to the shallow reservoirs were reached.
The following R&D activities were planned to sustain production.
GWh/yr
7000
6000

Deep exploration 3000-4000 m
5000

Reinjection / Injection

Stimulation of low productivity wells
4000
3000
2000
Years
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2008
2004
2000
1996
1992
1988
1984
1980
1976
1972
1968
1964
1960
1956
1952
1948
1944
1940
1936
1932
1928
1924
1920
1916
1912
1908
1900
0
1904
1000
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Deep exploration and development
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Temperature distribution in the Larderello area
Top of the shallow Carbonate Reservoir
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Conceptual model of the Larderello Geothermal field
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Temperature distribution in the Larderello area
Temperature distribution at 3000 m b.s.l.
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Reinjection
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Intensive exploitation: field depletion
Intensive exploitation of the Larderello-Valle Secolo area has gradually
depleted the fluid inside the reservoir .
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Reinjection results
The reinjection has increased the
steam production of about 100 kg/s,
equivalent to 50 MW.
The long reinjection period has not
substantially modified the
temperature of the produced fluid.
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Reinjection results
The boiling of injected water produced additional steam devoid of gas which diluted the
primary steam and therefore allowed a reduction of the weighted average gas content, with
considerable energy savings for gas extraction from the power plant condensers.
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Stimulation activities/EGS
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Stimulation methodologies
Injection of acid mixture (HCl and HF) and water produces selfpropping effects in the fractures:
 Microslippage of the fracture faces
 Removal of cuttings and mud deposition inside the fractures
 Acid leaching of hydrothermal mineralizations present in the
fractures
 Contraction and consequent cracking of hot rock formations
due to thermal stress
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Acid attack Lab Tests
Aim: Selection of the best acid mixtures for the acid attack of rock matrices
and hydrothermal mineralisations of deep geothermal reservoirs
Tested rock samples : Phyllites, micaschists, hornfels,and granites with
some fractures filled with siliceous hydrothermal mineralizations (epidotes +
K feldspar and chlorides + K feldspar + pyrites)
Tested acid mixture : HCl + HF, at different HCl/HF ratios
The tests have been carried out by the Enel-Lab and by the Lab of Pisa
University - Department of Earth Sciences
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Acid attack Lab Tests
Tests at batch conditions:
•temperatures in the range 100 - 150 °C
•two hours reaction time with an acid/rock ratio = 3 cm³/g
Tests in flowing conditions:
•temperatures of 30°, 50°, 70° 90 °C
•reaction time = 30’
Tested acid mixture:
9% Hcl - 1% HF; 6% Hcl - 6% HF; 6% Hcl - 3% HF; 12% Hcl - 6% HF;
12% Hcl - 3% HF
Performed analyses :
- weight of dissolved solids
- chemical analyses of reactions products
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- mineralogic analyses of the leached rock surface by electronic microscope
and X ray
Uso: aziendale
Equipment for Lab tests
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Lab tests
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Lab
tests
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Field tests
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
Well Bagnore_25: 3397 m bottom hole. Phyllites: fractured zone near the well bottom.
Acid job: injectivity improved from 3 to 15 m³/h/bar

Well Radicondoli_29: 4826 m bottom hole - hornfels rocks and granite from 4230 m
Injectivity improved from 1 to 7 m³/h/bar

Well Montieri_4: granite from 2000 to 3721 m (bottom hole), characterized by high
hydrothermal alterations, temperatures of about 300 °C and low permeability.
Injectivity improved from 0.4 to 5 m³/h/bar
The well can produce 50 t/h of steam (6.5 MW)

Well Travale Sud_1: 2987 m bottom hole - hornfels rocks
Acid job: productivity increased from 30 to 110 t/h (about 15 MW)

Well Montieri_1: 2219 m bottom hole - hornfels rocks.
Acid job with 200 m³ of 12% HCl - 6% HF. Injectivity improved from 3 to 15 m³/h/bar
The well is now producing about 250 t/h of steam (~35 MW)
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Field tests
Improvement of well production characteristics
by the injection of cold water
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The results of the R&D in Italy
The deep drilling activity pointed out the presence of productive
layers up to depths of 3000-4000m, in a very wide area

The reinjection/injection strategies proved to be successful for
sustaining/increasing the fluid production
The stimulation jobs are applied successfully to increase the wells
productivity
Reassessment of the geothermal resources has been carried out and
new exploitation strategies have been adopted, based on:
 Heat Production
 Production Sustainability
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Larderello/Travale Steam production history
Steam flow-rate
Years
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Power development
Positive results of deep drillings, stimulations and reinjection
12 new units (314,5 MW) started up in the period 2000-2005
8 units, for a total of 214.5 MW, replaced old units in operation from many years
and considered “obsolete”. The new units are characterised by higher efficiency
and lower environmental impact.

Nuova
Larderello
(20 MW)
4 units, for a total of 100 MW are new capacity
installed both in marginal and central areas

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Electricity generation and steam flow-rate in the Larderello
geothermal field
Gross electricity generation
[Kg/s]
[GWh/year]
Steam flow-rate
Years
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USA: The Geyser production trend
2.500
MW
2.000
1.500
1.000
Years
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2005
2000
1995
1990
1985
1980
1975
1965
0
1970
500
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Evolution of the exploitation strategies
… to Hot Dry Rocks
From hydrothermal
systems...
Tight formations with
high temperatures

Fractured reservoirs with high
permeability and fluids inside

Hydraulic stimulation for
the creation of an artificial
fracture network

Production of the stored
fluids  analysis of the field
depletion

Stimulation jobs and
secondary heat recovery
through water
reinjection/injection


Heat
Production
Water circulation for the
heat extraction
Enhanced Geothermal Systems
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Considerations about EGS
What does it means to enhance a geothermal system ?
-to improve the knowledge of the system
-to enhance the permeability of the formation
-to enhance the heat production through water circulation
To enhance fluid production and electricity generation
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Conclusions
• Larderello has been the first geothermal system developed and
exploited in the world (over 100 years history…)
• First period of intensive explotation with “conventional” strategies,
typical of hydrothermal systems
• Now Larderello can be considered the largest worldwide example of
an Enhanced Geothermal System
• The exploitation strategies are based on the “Heat Production” and
are aimed at the “Production Sustainability”
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Thanks for your attention!
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