Prof. Giuseppe Mandrone Prof. Cesare Comina dott. Luca Guglielmetti Dept. Earth Science, Univ. Torino (ITA) Multidisciplinary approach of geothermal prospection at Terme di Vinadio/Valdieri (Cuneo - Italy): integration of different geophysical methods aimed at geomechanical description of fracture zones in the Alps
Introduction Workflow Gological setting 3D Geological modelling Geochemistry Geophysical methods Integration of the data Estimation of the geothermal potential
Low enthalpy Medium enthalpy High enthalpy (a) (b) (c) (d) (e) < 90 <125 <100 150 190 90-150 125-225 100-200 - - >150 >225 >200 >150 >190 Rif: (a) Muffler and Cataldi (1978), (b) Hochstein (1990), (c) Benderitter and Cormy (1990), (d) Nicholson (1993), (e) Axelsson and Gunnlaugsson (2000)
THE STUDY AREA The Western Alps show widespread evidences of geothermal anomalies, represented by hot springs, usually exploited for thermal bathing. The southern part of Piedmont shows favorable conditions for geothermal investigations. The Bagni di Vinadio and Terme di Valdieri sites show the highest concentration of thermal springs and the highest temperature of the entire Western Alps. This study aims at developing a multidisciplinary concept to characterize geological and structural subsurface condition relevant to geothermal exploitation of local reservoirs in Alpine environment.
Geological observations WORKFLOW Magnetotelluric A-priori 3D geological model Gravity Geochemical investigations Calibrated 3D models Energy production Magnetic INSERIRE IMMAGINE
The Argentera Massif (AM) is a structural high of the European plate crystalline basement. This basement crops out owing to its uplift and to the subsequent erosion of the overlying Mesozoic sedimentary cover. Geologic observations THE ARGENTERA MASSIF
Geologic observations Multiscale geological and structural mapping from field and remote sensing
Geologic observations Terme di Valdieri Terme di Vinadio Already known in Roman Time Developed as Thermae in 1700 High mountain location Wilderness and isolated areas
Geochemical investigations WATER SAMPLING AND ANALYSIS Two sampling campaigns were carried out to analyze both cold and thermal springs and shallow wells. Major and trace elements, stable isotopes (δ 18 O and δ 2 H) and Tritium were analyzed. Site T max ( C) Q (kg/s) Cond max (μs/cm 2 ) ph Type Elevation recharge zone (m a.s.l.) T.U. Reservoir Temperature ( C) Bagni di Vinadio Terme di Valdieri 70.2 20 4290 9.1 Na - Cl - SO 4 1600-2200 0.6 130 62.5 50 310 9.5 Na - SO 4 1500-1800 1.6 100
3D modelling A-PRIORI 3D GEOLOGICAL MODEL The first step to integrate geological and geophysical data is to build an a- priori 3D geological model of the study areas. 3D Geomodeller by Intrepid Geophysics was the selected software.
Geophysical surveys Very nice place but Difficult to do a regular grid for geophisical measurement.
Geophysical surveys MAGNETOTELLURIC MT SURVEYS Magnetotellurics (MT) is an electromagnetic geophysical method for inferring the earth's subsurface electrical conductivity from measurements of natural geomagnetic and geoelectric field variation at the Earth's surface. Investigation depth ranges from 300 m below ground by recording higher frequencies down to 10,000 m or deeper.
403 GRAVITY STATIONS distributed along 14 profiles, with a mean stations interdistance of about 250 m. Accurate positioning of each gravity station has been obtained using two GPS. Each zone is associated with a DEM, with increasing cell size with the distance from the station Gravity stations have been processed together with 667 existing measurements of the Bureau Gravimétrique International (BGI) data set. The inversion process employed is based on a 2D compact constrained gravimetric inversion, developed from the original approach by Last and Kubik (1983), and has been implemented in Matlab environment.
Data integration BOUGUER ANOMALY IN THE ARGENTERA MASSIF Bouger Anomaly mgal -53.8-134.5 The Bouguer is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a freeair gravity anomaly. Residual Anomaly 50km filter Residual Anomaly 20km filter Residual Anomaly 10km filter 11.5 8.8 2.9-13.3-13.8-4.2 Bouger Anomaly of the Argentera Massif and residual anomalies after filtering with 50, 20, 10 km Butterworth filter
The thermae areas
2D INVERSION PROCESSING Data integration An inverse problem in science is the process of calculating from a set of observations the causal factors that produced them: calculating the density of the Earth from measurements of its gravity field.
Depth (m) S.Giovanni Fault W Data integration GEOLOGY vs GRAVITY vs MAGNETOTELLURIC S Profile 3 Profile 1 E Thermal Springs T hermal Springs NE W E Resistivity (Ωm) 200000 S NE Resistivity (Ωm) 200000 0 150000 0 150000 2000 35000 35000 2000 200 200 6500 0 Distance (m) 3600 100 3500 0 Distance (m) 9500 100 Gneiss and embrichite of the TC Central Granite Paleomilonite of the VSZ Biotitic Anatexite MAC Biotitic gneiss of the MAC Palomilonite of the FSZ
Final model Data integration
Energy production USED METHODS Integration of geochemistry, 3D modelling and geophysics (method heat in place) Temperature at the surface Temperature in the reservoir Flow rate Volume of the reservoir Porosity of the reservoir VINADIO VALDIERI T inlet 130 T inlet 100 T outlet 80 T outlet 80 Flow rate (l/s) 20 Flow rate (l/s) 50 Reservoir Volume (km3) 6 Reservoir Volume (km3) 9 Reservoir Porosity 0.02 Reservoir Porosity 0.02 Reservoir Permeability (m2) 1E-15 Reservoir Permeability (m2) 1E-15 Capacity factor 0.06 Capacity factor 0.06 Hours per Year 8000 Hours per Year 8000 Heat production (MW th) 4.18 Heat production (MW th) 4.18 NET Power production (KW el) 251 NET Power production (KW el) 251 Power Production (GWh per year) 2 Power Production (GWh per year) 2 CO2 (tons emission saved) 1400 CO2 (tons emission saved) 1400
Energy production ELECTRIC POWER 2 binary geothermal power plant 500 KW (power) 4 GW (yearly production) 1000 kwh (Italy pro capita) = 2000 persons Population: Vinadio 640, Valdieri 935 MORE PRODUCTION THAN CONSUMPTION Exceeding heat Space heating De-iceng
Energy production Frontiers in geothermal energy Hydrothermal high enthalpy systems Conventional power plant unit Big production (> 1 GW installed) A few places where it is possible to do Enhanced high-medium enthalpy (engineered) systems Medium power plant unit Production (> 0,1 GW installed) Almost everywhere possible Conventional medium enthalpy systems Low power plant unit (hundreds kw installed) Rural utility, insulate necessity, off grid location, developing country
Thanks for the attention! For more information giuseppe.mandrone@unito.it For more detail: