Presentation on theme: "Contents The first exploitation period of Larderello"— Presentation transcript:
0 How EGS is investigated in the case of the Larderello geothermal field ?Guido CappettiEnel – Generation and Energy Management – Geothermal ProductionEngine Launching ConferenceOrleans February 2006
1 Contents The first exploitation period of Larderello The Research&Development programs, from mid ’70s:Deep explorationReinjectionStimulation jobsThe reassessment of the geothermal resourceNew exploitation strategies
2 Temperature distribution at 3000m depth, in Italy
3 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 problemsOil crisis induced a renewal of interest towards geothermal energy and new R&D were implemented.1904 First test in Larderello1913 First 250 kW unit in Larderello1904
4 Top of the shallow Carbonate Reservoir Temperature distribution in the Larderello areaTop of the shallow Carbonate Reservoir
5 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.7000Deep exploration mReinjection / InjectionStimulation of low productivity wells600050004000GWh/yr3000200010001900190419081912191619201924192819321936194019441948195219561960196419681972197619801984198819921996200020042008Years
11 depleted the fluid inside the reservoir . Intensive exploitation: field depletionIntensive exploitation of the Larderello-Valle Secolo area has graduallydepleted the fluid inside the reservoir .
12 Reinjection resultsThe 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.
13 Reinjection resultsThe 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.
15 Stimulation methodologies Injection of acid mixture (HCl and HF) and water produces self-propping effects in the fractures:Microslippage of the fracture facesRemoval of cuttings and mud deposition inside the fracturesAcid leaching of hydrothermal mineralizations present in the fracturesContraction and consequent cracking of hot rock formations due to thermal stress
16 Acid attack Lab TestsAim: Selection of the best acid mixtures for the acid attack of rock matrices and hydrothermal mineralisations of deep geothermal reservoirsTested 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 ratiosThe tests have been carried out by the Enel-Lab and by the Lab of Pisa University - Department of Earth Sciences
17 Acid attack Lab Tests Tests at batch conditions: temperatures in the range °Ctwo hours reaction time with an acid/rock ratio = 3 cm³/gTests in flowing conditions:temperatures of 30°, 50°, 70° 90 °Creaction time = 30’Tested acid mixture:9% Hcl - 1% HF; 6% Hcl - 6% HF; 6% Hcl - 3% HF; 12% Hcl - 6% HF;12% Hcl - 3% HFPerformed analyses :- weight of dissolved solids- chemical analyses of reactions products- mineralogic analyses of the leached rock surface by electronic microscope and X ray
21 Field testsWell Bagnore_25: 3397 m bottom hole. Phyllites: fractured zone near the well bottom. Acid job: injectivity improved from 3 to 15 m³/h/barWell Radicondoli_29: 4826 m bottom hole - hornfels rocks and granite from 4230 mInjectivity improved from 1 to 7 m³/h/barWell 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 rocksAcid 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)
22 Field tests Improvement of well production characteristics by the injection of cold water
23 The results of the R&D in Italy The deep drilling activity pointed out the presence of productive layers up to depths of m, in a very wide areaThe reinjection/injection strategies proved to be successful for sustaining/increasing the fluid productionThe stimulation jobs are applied successfully to increase the wells productivityReassessment of the geothermal resources has been carried out and new exploitation strategies have been adopted, based on:Heat ProductionProduction Sustainability
25 Power developmentPositive results of deep drillings, stimulations and reinjection12 new units (314,5 MW) started up in the period8 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.Nuova Larderello(20 MW)4 units, for a total of 100 MW are new capacity installed both in marginal and central areas
26 Electricity generation and steam flow-rate in the Larderello geothermal field
27 USA: The Geyser production trend 5001.0001.5002.0002.500196519701975198019851990199520002005YearsMW
28 From hydrothermal systems... Enhanced Geothermal Systems Evolution of the exploitation strategiesFrom hydrothermal systems...Fractured reservoirs with high permeability and fluids inside… to Hot Dry RocksTight formations with high temperaturesHydraulic stimulation for the creation of an artificial fracture networkProduction of the stored fluids analysis of the field depletionStimulation jobs and secondary heat recovery through water reinjection/injectionWater circulation for the heat extractionHeat ProductionEnhanced Geothermal Systems
29 Considerations about EGS What does it means to enhance a geothermal system ?to improve the knowledge of the systemto enhance the permeability of the formationto enhance the heat production through water circulationTo enhance fluid production and electricity generation
30 ConclusionsLarderello 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 systemsNow Larderello can be considered the largest worldwide example of an Enhanced Geothermal SystemThe exploitation strategies are based on the “Heat Production” and are aimed at the “Production Sustainability”