How EGS is investigated in the case of the Larderello geothermal field ? Guido Cappetti Enel – Generation and Energy Management – Geothermal Production.

How EGS is investigated in the case of the

Larderello geothermal field ?

Guido CappettiEnel – Generation and Energy Management – Geothermal Production

Engine Launching Conference

Orleans 12-15 February 2006

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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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M. AMIATA

LARDERELLO

Temperature distribution at 3000m depth, in Italy

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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).

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.

1904

•1904 First test in Larderello

•1913 First 250 kW unit in Larderello

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Top of the shallow Carbonate Reservoir

Temperature distribution in the Larderello area

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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.

The production sustainability

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Deep exploration 3000-4000 m

Reinjection / Injection

Stimulation of low productivity wells

Deep exploration 3000-4000 m

Reinjection / Injection

Stimulation of low productivity wells

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Deep exploration and development

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Top of the shallow Carbonate Reservoir

Temperature distribution in the Larderello area

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Conceptual model of the Larderello Geothermal field

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Temperature distribution at 3000 m b.s.l.

Temperature distribution in the Larderello area

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Reinjection

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Intensive exploitation of the Larderello-Valle Secolo area has gradually

depleted the fluid inside the reservoir .

Intensive exploitation: field depletion

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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.

Reinjection results

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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.

Reinjection results

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Stimulation activities/EGS

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Injection of acid mixture (HCl and HF) and water produces self-propping 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

Stimulation methodologies

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Acid attack Lab Acid attack Lab TestsTests

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 Acid attack Lab TestsTestsTests 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

- mineralogic analyses of the leached rock surface by electronic microscope and X ray

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Equipment for Lab Equipment for Lab teststests

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Lab Lab teststests

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Lab Lab teststests

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Field Field teststests 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 mInjectivity 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/barThe 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/barThe well is now producing about 250 t/h of steam (~35 MW)

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Improvement of well production characteristics by the injection of cold water

Field tests

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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

The results of the R&D in Italy

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Larderello/Travale Steam production history

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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.

4 units, for a total of 100 MW are new capacity installed both in marginal and central areas

Nuova Larderell

o(20 MW)

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Electricity generation and steam flow-rate in the Larderello geothermal field

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USA: The Geyser production trend

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Evolution of the exploitation strategies

From hydrothermal systems...

Fractured reservoirs with high permeability and fluids inside

… to Hot Dry Rocks Tight formations with high temperatures

Heat Production

Heat Production

Production of the stored fluids analysis of the field depletion

Hydraulic stimulation for the creation of an artificial fracture network

Stimulation jobs and secondary heat recovery through water reinjection/injection

Water circulation for the heat extraction

Enhanced Geothermal SystemsEnhanced Geothermal Systems

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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

Considerations about Considerations about EGSEGS

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ConclusioConclusionsns

• 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!Thanks for your attention!