Heat Flow Measurements Laboratory
The evaluation of the surface heat flow distribution (HF) is fundamental among the geothermal prospection methods, as it allows at relatively low cost the identification of thermally anomalous areas, giving also a quick quality index of the geothermal potential of an area.
Thermal methods (well thermal logs and geothermal gradients calculation; thermal conductivity measurements on rock samples) are, after all, the only ones which allow a direct measurement of the physical quantity “heat”, that is the final geothermal exploration target.
The heat flow value is obtained by the simple relationship:
Q = k x ∆t/∆z (Q = mWxm-2).
where Q is heat flow, k is thermal conductivity and ∆t/∆z is the geothermal gradient.
The main result of the heat flow lab activity are contour maps of the areas under investigation, i.e. Heat Flow maps and Geothermal Gradient maps.
These maps turn out to be the basis of the geothermal exploration, but heat flow, according to data availability and to the study target, is a parameter that well behaves in a direct comparison with several different geophysical and/or geochemical parameters, i.e. Bouguer gravity anomaly, He isotopic ratio, seismic reflectors depth (see example from the high enthalpy geothermal fields of Larderello and Mt. Amiata).
Well logging operations are currently carried out with an hand-operated tool with a 4 conductors wire teflon coated, 450 m long. Acquisition sensor is a platinum resistance Pt-100 (100 Ohms) with sensitivity +/- 0.01 °C and precision +/- 0.03 °C. Control instrument and temperature indicator “Corradi RP 2000 S”.
Thermal conductivity measurements are carried out in the lab on cores from wells or on samples from rock outcrops. Samples are prepared in the rock grinding and minerals separation Laboratory of IGG.
Two instruments with line source are currently available:
- Shotherm QTM Showa Denko;
- A self-built instrument (collaboration between IGG-CNR and IPCF-CNR), with features totally analogous to Shotherm QTM.
A third instrument is available (Isomet 2114), that can be equipped with a plane source or a Maxwell needle probe.
Thermal modeling of the areas under study is carried out with the computational codes:
- Hydrotherm 3.1 (2D) (USGS);
- Shemat 7.1 (2D – 3D) (Aachen University).
Software for contouring, charts, thermal sections:
- SURFER 13© (Golden Software);
- GRAPHER 11© (Golden Software);
- DIDGER 4© (Golden Software).
METHODS AND APPLICATIONS
Precision thermal logging finds several uses in earth sciences, beyond HF and geothermal gradient calculations. This lab experienced a long activity in groundwater circulation monitoring in a mining environment (underground salt mines), as well as in climate history reconstruction by logging thermally stabilized wells not affected by groundwater circulation. Another major issue for HF and geothermal gradients measurements are medium-low enthalpy geothermal projects, a branch of energy industry quickly growing as it complies with energy saving and environmental protection.
Field activities in the field (well logging) and in the lab (thermal conductivity measurements) results are integrated with further parameters and treated with 2D and 3D thermal modeling (Hydrotherm 3.1 and Shemat 7.1 computational codes). Thermal modeling by means of more complex codes (Tough2) has been carried out with colleagues at IGG and from foreign Universities.
PROJECTS AND SCIENTIFIC INTEREST
Collaborations with research institutions and industry provide the context for large part of the activities of the laboratory. Industry commitments represents the main funding source for the lab.
Among the others (but not only), collaborations are (or have been) active with:
- ENEL (National Electricity Board of Italy);
- Società Chimica Solvay; Steam;
- Southern Methodist University (Dallas, USA),
- Universities of Trieste, Genova, Roma, Bologna, Lugano (CH).
Thermal logging survey in geothermal gradient wells (and k measurements on core samples) in the research permit areas Scansano and Pereta in Southern Tuscany, as a commitment from Steam company.
The HF lab is also currently involved in the European Union “Horizon 2020-DESCRAMBLE (2015-2018)” for deep drilling in the Larderello geothermal field.
- Bellani S., Magro G., Gherardi F. (2015). “Heat Flow and Helium Isotopes in the Geothermal Areas of Tuscany (Central Italy)”. Geothermal Resources Council Transactions, vol. 39, p. 399-405.
- Bellani S., Gherardi F. (2014). “Thermal Features of the Pisa Plain, a Neogenic Basin in Central Italy”. –Geothermal Resources Council Transactions, vol. 38, p. 357-361.
- Bellani S., Gherardi F. (2013). “Thermal Overview of an Area NW of the Larderello Geothermal Field, Italy”. – Geothermal Resources Council Transactions, vol. 37, p. 231-235.
- Magro G., Gherardi F., Bellani S. (2010): “Noble gases in karstic and thermal waters of Strimon basin (Greece-Bulgaria)”. Water-Rock Interaction Symposium, Guanajuato, Mexico, p. 345-348.
- Bellani S., Gherardi F. (2009). “Thermal Modeling of an Area West of the Mt. Amiata Geothermal Field, Italy”. – Geothermal Resources Council Transactions, vol. 33, p. 431-435.
- Magro G., Bellani S., Della Vedova B. (2009). “The deep roots of the Larderello geothermal field (Italy) from heat flux and 3He anomalies”. Geothermal Resources Council Transactions, vol. 33, p. 405-409.
- Della Vedova B., Vecellio C., Bellani S., Tinivella U.,(2008). “Thermal modelling of the Larderello geothermal field (Tuscany, Italy)”. Int. Journal of Earth Sciences, 97, 317-332.
- Pasquale V., Verdoya M., Chiozzi P., Bodri L., Bellani S. (2005) “Temperature signal in the underground for climate history reconstruction in Italy”. Global and Planetary Change, 47. pp. 36-50
- Bellani S., G. Magro, A. Brogi, A. Lazzarotto and D. Liotta, (2005). “Insights into the Larderello geothermal field: structural setting and distribution of thermal and 3He anomaly”. Proceedings of World Geothermal Congress, Antalya, Turkey, 24-29 April 2005. pp. 1-4.
- Bellani S., Brogi A., Lazzarotto A., Liotta D., Ranalli G. (2004) “Heat flow, deep temperatures and extensional structures in the Larderello geothermal field (Italy): constraints on geothermal fluid flow”. Journal of Volcanology and Geothermal Research, 132, 15-29.
- Magro G., Gianelli G., Ruggieri G., Bellani S., Scandiffio G. (2003) – “Helium isotopes in paleofluids and present-day fluids of the Larderello geothermal field: Constraints on the heat source”. Journal of Geophysical Research, v. 108, n. B1, ECV3, 1-12.
- Della Vedova B., Bellani S., Pellis G., Squarci P. (2001) – “Chapter 7: Deep temperatures and surface heat flow distribution”. In: Anatomy of an orogen, The Apennines and adjacent Mediterranean basins, (Editors : Vai G.B., Martini I.P.). Kluwer Acad. Publ., Dordrecht, The Netherlands, pp. 65-76 + 2 plates.
- Bellani S., Buonasorte G., Grassi S., Squarci P. (1998): “Geological and structural features of the San Cataldo district heating project (Pisa, Italy)”. – Proceedings 5th World Renewable Energy Congress, Florence, Vol. 4, pp. 2746-2749.
- Baldi P., Bellani S., Buonasorte G., Fiordelisi A., Manzella A. (1998): “Geothermal exploration in Tuscany (Italy) for high temperature resources.” - Proceedings 5th World Renewable Energy Congress, Florence, Vol. 4, pp., 2733-2736.
- Wisian K.W., Blackwell D.D., Bellani S., Henfling J.A., Normann R.A., Lysne P.C., Forster A., Schrotter J. (1998): "Field comparison of conventional and new technology temperature logging systems" – Geothermics, Vol. 27, n.2, pp. 131-141.
- Wisian K.W., Blackwell D.D., Bellani S., Henfling J.A., Normann R.A., Lysne P.C., Forster A., Schrotter J. (1996): "How hot is it ? (A comparison of advanced technology temperature logging systems)" – Geothermal Resources Council Transactions Vol. 20, pp. 427-434
- Baldi P., Bellani S., Ceccarelli A., Fiordelisi A., Squarci P., Taffi L. (1995) : "Geothermal anomalies and structural features of southern Tuscany" - "World Geothermal Congress Proceedings"- Florence, May 1995, pp. 1287-1291.
- Bellani S., Grassi S., Squarci P.(1995) : "Geothermal characteristics of the Pisa plain" - "World Geothermal Congress Proceedings" - Florence, May 1995, pp. 1305-1308.
- Bellani S., Calore C., Grassi S., Squarci P. (1995): "Thermal prospecting in Pantelleria island (Sicily Channel, Italy)" – “World Geothermal Congress Proceedings" - Florence, May 1995, pp. 767-770.