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

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Presentation on theme: "How EGS is investigated in the case of the Larderello geothermal field ? Guido Cappetti Enel – Generation and Energy Management – Geothermal Production."— Presentation transcript:

1 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 February 2006

2 1 /16 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

3 2 /16 Uso: aziendale Temperature distribution at 3000m depth, in Italy

4 3 /16 Uso: aziendale 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 First test in Larderello 1913 First 250 kW unit in Larderello

5 4 /16 Uso: aziendale Top of the shallow Carbonate Reservoir Temperature distribution in the Larderello area

6 5 /16 Uso: aziendale 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 Years GWh/yr Deep exploration m Reinjection / Injection Stimulation of low productivity wells Deep exploration m Reinjection / Injection Stimulation of low productivity wells

7 6 /16 Uso: aziendale Deep exploration and development

8 7 /16 Uso: aziendale Top of the shallow Carbonate Reservoir Temperature distribution in the Larderello area

9 8 /16 Uso: aziendale Conceptual model of the Larderello Geothermal field

10 9 /16 Uso: aziendale Temperature distribution at 3000 m b.s.l. Temperature distribution in the Larderello area

11 10 /16 Uso: aziendale Reinjection

12 11 /16 Uso: aziendale Intensive exploitation of the Larderello-Valle Secolo area has gradually depleted the fluid inside the reservoir. Intensive exploitation: field depletion

13 12 /16 Uso: aziendale 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

14 13 /16 Uso: aziendale 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

15 14 /16 Uso: aziendale Stimulation activities/EGS

16 15 /16 Uso: aziendale 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

17 16 /16 Uso: aziendale 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

18 17 /16 Uso: aziendale Acid attack Lab Tests Tests at batch conditions: temperatures in the range °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

19 18 /16 Uso: aziendale Equipment for Lab tests

20 19 /16 Uso: aziendale Lab tests

21 20 /16 Uso: aziendale Lab tests

22 21 /16 Uso: aziendale Field tests  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)

23 22 /16 Uso: aziendale Improvement of well production characteristics by the injection of cold water Field tests

24 23 /16 Uso: aziendale  The deep drilling activity pointed out the presence of productive layers up to depths of m, 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

25 24 /16 Uso: aziendale Larderello/Travale Steam production history

26 25 /16 Uso: aziendale Power development Positive results of deep drillings, stimulations and reinjection 12 new units (314,5 MW) started up in the period units, for a total of 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 Larderello (20 MW)

27 26 /16 Uso: aziendale Electricity generation and steam flow-rate in the Larderello geothermal field

28 27 /16 Uso: aziendale Years MW USA: The Geyser production trend

29 28 /16 Uso: aziendale 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 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 Systems

30 29 /16 Uso: aziendale 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 EGS Considerations about EGS

31 30 /16 Uso: aziendale 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”

32 31 /16 Uso: aziendale Thanks for your attention!


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