Geology and fluid chemistry of the Fushime geothermal field, Kyushu, Japan

The Fushime geothermal field is located in a depression close to the coast line. The system is characterized by very high reservoir temperature (>350°C), and a high salinity production fluid. Geological analysis shows that the main reservoir in this field occurs in a fractured zone developed around a dacite intrusion located in the center of the field. High permeability zones recognized by drilling data are found to be associated with fault zones. One of these zones is clearly associated with a NW–SE trending andesite dike swarm which was encountered in some wells.Alteration in the system can be divided into four zones, in order of increasing temperature, based on calcium–magnesium aluminosilicate mineral assemblages: i.e., the smectite, transition, chlorite and epidote zones. The feed zone is located in the chlorite and epidote zones, which can be further divided into three sub-zones according to their potassium or sodium aluminosilicate mineralogy, from the center of the discharge zone: K-feldspar–quartz, sericite–quartz, and albite–chlorite zones.Chloride concentration of the sea-water is 19,800 mg/l, and Br/Cl mole ratio is 1.55. Based on geochemical information, the reservoir chloride concentration of this field ranges from 11,600 to 22,000 mg/kg. The Clres (Cl in reservoir), Br/Cl ratios and stable isotope data indicate that the Fushime geothermal fluid originated from sea-water and is diluted by ground water during its ascent. Some fluids produced from geothermal wells show low pH (about 4). It is thought that sulfide mineral (PbS, ZnS) precipitation during production produces this acidic fluid.     

Influence of water–rock interactions on fracture permeability of the deep reservoir at Soultz-sous-Forêts, France

Circulation of geothermal fluids through granitic fractured reservoirs leads to chemical reactions, modifying the porosity and permeability of the rock mass. FRACHEM, a thermo-hydraulic-chemical coupled computer code, was developed specifically to predict changes in the geothermal reservoir of the Soultz-sous-Forêts Enhanced Geothermal System (EGS) located in Alsace, France. This code can simulate fluid–rock interactions and determine the dissolution/precipitation reactions of eight minerals in the Soultz granite (i.e. carbonates, pyrite, silicates and aluminosilicates). Numerical simulation results of long-term fluid circulation through the 5000-m deep Soultz reservoir are comparable to those determined for the shallow reservoir and confirm the role played by carbonates in the evolution of reservoir porosity and permeability. Moreover, experiments with FRACHEM in simulating short-term fluid flow during hydraulic and/or chemical stimulations have demonstrated that the code could prove an efficient tool in reservoir engineering and management.     

High-temperature fluid flows in the dachny field of the Mutnovsky hydrothermal system, Russia

High-temperature hydrothermal reservoirs typically have complex structures that are difficult to characterize even after a number of wells have been drilled. The most effective methods for characterizing the flow regime within a reservoir are: (1) three-dimensional mapping of the geological structure, temperature, pressure and permeability; (2) interpretation of tracer tests and reservoir fluid chemistry; and (3) flow test data analysis. (It is assumed that the petrophysical parameters of the various lithologic units have been determined on the basis of core and geophysical log data.) When these methods are applied to the Dachny reservoir of the Mutnovsky geothermal system, they yield the distribution in the field of lithologies, temperatures, phases and pressures, as well as the characteristics of the high-temperature fluid circulation (natural state initial and boundary conditions for the associated heat transfer problem).     

Geochemistry and groundwater contamination in the La Selva geothermal system (Girona, Northeast Spain)

Hot spring waters of the La Selva geothermal system show high concentrations of Cl, F, Ca, Na, K, Li, Si, As, Ba, and Rb, whereas cold waters show low salinity, high concentrations of NO₃, and significant As content when mixed with geothermal waters.Modeling of the geothermal fluids indicates that the fluid is supersaturated with aragonite and calcite, which matches the travertine precipitation close to the present discharge areas. Moreover, the barite and fluorite are also are near equilibrium levels, indicating possible control of Ba and F solubility by these mineral phases, which also precipitate in some discharge areas. Likewise, the fluid is supersaturated with respect to quartz, indicating the possibility of siliceous precipitation near the discharge areas of the present geothermal fluids.Taking into account the Na-K, Na-K-Ca, and SiO₂-temperature geothermometers, the temperature of the reservoir may be estimated to be about 135 °C.The chemistry of the geothermal fluids has changed from a recent high-enthalpy system, which precipitated siliceous deposits, to the present low-enthalpy system, which precipitates carbonated deposits (travertine).Multivariate analysis of the groundwater shows high correlations between K, Ca, As, Br, Ag, and Ba, suggesting that As is introduced to the environment via geothermal fluids. Moreover, As concentrations in hot groundwater are associated with high concentrations of Li and Si, as has been observed in other geothermal fields. Metal concentrations in the hydrothermal deposits show high values of Ag, As, Ba, Pb, Sb, and Zn, mainly in the siliceous deposits of the town of Caldes de Malavella, where the geothermal system deposited materials with high As concentrations (123-441 ppm).The similarities between the geochemical characteristics of the hydrothermal deposits and the groundwater suggest that the metals in these deposits and fluids have the same origin.     

地热流体的腐蚀与结垢控制现状

在地热发电或直接利用过程中,与地热流体（液体或蒸汽）接触的设备、管道或管件存在着腐蚀和结垢现象,往往成为地热开发利用的技术瓶颈。因此,开展地热流体的腐蚀与结垢控制技术研究至关重要。本文主要分析了近年来国内外在地热流体的腐蚀和结垢控制方面的研究进展,包括选材、涂层、流体预处理、化学添加剂等控制方法,并提出了进一步的研究方向,包括全面的地热流体腐蚀结垢趋势预测及地球化学模拟,结垢机理研究,涂层和基底的结合力和耐久性研究,阴极保护以及复合控制方法开发等。     

四川地热流体水文地球化学及同位素特征简析

四川省范围内有沉积盆地型和隆起山地型两类地热资源,共划分五个地热区。从五个区采取的205组水样的水文地球化学特征及184组2H、18O和61组14C特征分析显示,四川省各地热区地热流体基本来自于大气降水补给,地热流体的水文地球化学和同位素特征与其所属的热储类型和热储开放性有关。盆地型热储主要为岩溶层状热储,山地型热储主要是变质岩为主的裂隙带状热储和层状带状复合型热储。盆地型热储开放性较山地型弱,地热流体矿化度和理疗元素含量均比山地型高,易形成深埋藏的卤水,地下水平均径流时间较山地型长。本研究可为四川省地热资源未来的开发利用规划提供参考。     

The precipitation of solids from potential heat exchange fluids for use in a hdr geothermal system in granite

An important consideration in the development and operation of a Hot Dry Rock geothermal system is the selection of a heat transfer fluid and the chemical composition of this fluid during circulation. The chemical reaction of the circulation fluid with the reservoir rock may lead to the undesirable corrosion or scaling of the reservoir itself, or associated engineering structures. Two potential circulation fluids for use in a high temperature (200°C) HDR system in granite in SW England, are a dilute (TDS < 120mg/1) groundwater, and a modified seawater composition. The reaction of these fluids with granite has been evaluated experimentally, with particular emphasis upon the characterisation of solid precipitates. Secondary solids associated with the reaction of groundwater with granite consist of clay and Ca-zeolite. Product fluids were alkaline (pH 9.1), of low salinity (TDS < 600mg/1) and were relatively benign for heat exchange purposes. The amount of clay precipitated may be linked to the amount of Mg in the fluid, but is less than 0.5 wt percent of the initial solid starting material. Chemical analysis of precipitated clay by analytical transmission electron microscopy reveal a range of composition between illite and smectite. Secondary solids associated with seawater-granite reaction include anhydrite, magnesium hydroxide sulphate hydrate (MHSH) and clay. The precipitation of MHSH and clay is instrumental in governing the low pH (pH 3.5) of the product fluid, which would pose problems concerning the corrosion of pumps, heat exchangers, etc in a possible HDR geothermal system. The suitability of each of the potential heat exchange fluids may be linked to their initial Mg contents which govern the acidity of the reacted fluid and the amount of precipitated clay.     

A helium isotope perspective on the Dixie Valley,Nevada, hydrothermal system

Fluids from springs, fumaroles, and wells throughout Dixie Valley, NV were analyzed for noble gas abundances and isotopic compositions. The helium isotopic compositions of fluids produced from the Dixie Valley geothermal field range from 0.70 to 0.76 Ra, are among the highest values in the valley, and indicate that ∼7.5% of the total helium is derived from the mantle. A lack of recent volcanics or other potential sources requires flow of mantle-derived helium up along the valley bounding Stillwater Range Front Fault, from which the geothermal fluids are produced. Using a one-dimensional flow model, a lower limit fluid flow rate up through the fault of 7 mm/yr is estimated, corresponding to a mantle ³He flux of ∼10⁴ atoms m⁻² s⁻¹.A comparison between the fluids from Dixie Valley springs, fumaroles, and wells and the fluids produced from the geothermal field reveals a mixing trend between the geothermal fluid and younger, cooler groundwaters. The exceptions are those features that either emanate directly from the Stillwater fault or wells that penetrate and extract fluids from the fault zone, all of which have helium isotopic compositions that are indistinguishable from the geothermal production fluids. The results of our study indicate that the Stillwater Range Front Fault system must act as a permeable conduit that can sustain high vertical fluid flow rates from deep within the crust and crust-mantle boundary and that high permeability may exist along most of its length. This suggests that the geothermal potential of the Stillwater fault may be significantly greater than the 6–8 km long system presently under production. Since all the numerous springs, wells, and fumaroles in the valley also contain a fluid component that is indistinguishable from the geothermal/Stillwater fault fluid, the potential for an additional deeper and more pervasive geothermal system also exists and should be further evaluated. Furthermore, we suggest that elevated helium isotope compositions in regions with little or no recent magmatism are an indicator of the deep crustal permeability that is required to drive and sustain extensional geothermal systems.     

Changes in thermodynamic conditions of the ahuachapán reservoir due to production and injection

Since large-scale exploitation of the Ahuachapán reservoir began in 1975 large changes in the reservoir thermodynamic conditions have occurred. Drawdown of up to 15 bars and significant temperature changes have been observed in the wellfield. Temperatures have declined due to boiling in the reservoir in response to the pressure drawdown; localized and minor cooling due to reinjection of spent geothermal fluids have also been observed. There are indications of cold fluid influx deep into the reservoir from the west and north. Reservoir temperatures show that a significant amount of hot fluid recharge comes to the wellfield from the southeast, and temperatures also indicate that the recharge rate has increased with time as pressure declines in the reservoir. Chemical analyses of the produced fluids show that most wells are fed by a mixture of geothermal fluids and cooler, less-saline waters. The cold water inflow has increased due to exploitation, as demonstrated by decreased salinity of the produced fluids.     

Hydrogeochemistry and geothermometry of Changal thermal springs,Zagros region,Iran

This study addresses the hydrogeochemistry of thermal springs that emerge from the Asmari limestone in a gorge at Changal Anticline in the vicinity of the Salman-Farsi dam. The Changal thermal springs vary in temperature between 28 and 40 °C. Chemical and isotopic compositions of the thermal waters suggest two distinct hydrogeological systems: a deep, moderate-temperature (∼40 °C) geothermal system recharged by deeply circulating meteoric waters, and a shallow cold aquifer system related to local groundwater. The source geothermal fluid temperature was calculated using different geothermometers and mineral saturation indexes. Based on chemical and isotopic data, it is hypothesized that: (1) mixing occurs between the ascending geothermal water and shallow cold water; (2) the resulting thermal waters reaching surface are a mixture of 80% local, shallow meteoric water and 20% geothermal water; and (3) the circulation depth of the meteoric water is about 1500 m. The thermal reservoir temperature is estimated to be between 70 and 80 °C according to calculations using different geothermometers and computation of saturation indices for different solid phases.     

Geothermal resources in the Asal Region,Republic of Djibouti: An update with emphasis on reservoir engineering studies

Three independent geothermal systems have been identified, so far, in the Asal region of the Republic of Djibouti (i.e. Gale le Goma, Fiale and South of Lake). Six deep wells have been drilled in the region, the first two in 1975 and the others in 1987–88. Well A2 was damaged and wells A4 and A5 encountered impermeable yet very hot (340–365 °C) rocks. Wells A1, A2, A3 and A6 produce highly saline (120 g/L TDS) fluids leading to mineral scaling. Well test data indicate that the reservoir might be producing from fractured and porous zones. The estimated permeability-thickness of the deep Gale le Goma reservoir is in the 3–9 darcy-meter range. Lumped-parameter modeling results indicate that well A3 should be operated at about 20 kg/s total flow rate and that injection should be considered to reduce pressure drawdown. The estimated power generation potential of well A3 is 2.5 MWe, and that of all Asal high-temperature hydrothermal systems is between 115 and 329 MWe for a 25-year exploitation period.     

Chemical and physical reservoir parameters at initial conditions in Berlingeothermal field,El Salvador: a first assessment

A study has been madeto obtain the main chemical and physical reservoir conditions of the Berlin field (El Salvador)before the commencement of large-scale exploitation of the geothermal resource The upflowzone and the main flow path within the geothermal system have been determined from the arealdistribution of chemical parameters such as Cl concentrations ratios such as Na/KK/Mg,K/Ca,and temperatures computed from silica concentrations and cation ratios Gas compositions havebeen used to calculate reservoir parameters such as temperature steam fraction and P_CO2 The computer code WATCH (new edition 1994) hasbeen used to evaluate the temperature of equilibration between the aqueous species and selectedalteration minerals in the reservoir The fluid in Berlin flows to the exploited reservoir from thesouth entering it in the vicinity of well TR-5 Along its flow-path (south–north direction) thefluid is cooled by boiling and conductive cooling The chloride-enthalpy diagram indicates theexistence of a parent water with a chemical composition similar to well TR-5 that boils and theresidual brine produces the fluid of well TR-3 which is very concentrated in salts The fluid ofTR-5 is probably produced from this parent water generating the fluids of wells TR-2 and TR-9by boiling and the fluids of wells TR-1 and TR-4 by conductive cooling The computed values forthe deep steam fraction clearly indicate that this is a liquid-dominated system with computedtemperature values decreasing from 310°C (upflow zone) to about 230°C from south to north© 1999 Published by Elsevier Science Ltd on behalf of CNR All rights reserved     

New geothermometers for carbonate—evaporite geothermal reservoirs

Two new Ca/Mg and SO₄/F geothermometers specific for carbonate-evaporite geothermal reservoirs are proposed. General considerations on waters interacting with such rocks suggest that Ca²⁺, Mg²⁺, CO²⁻₃, SO²⁻₄, F⁻ and SiO₂ are compatible components of the pertinent thermodynamic system and, therefore, their activities are fixed by five solid phases at equilibrium conditions. Geothermometric elaboration is based on the assumption that the five solid phases are represented by pure calcite, dolomite, anhydrite, fluorite and an SiO₂ mineral, e.g. quartz or chalcedony or amorphous silica. Pressure and ion association effects are not taken into consideration. Preliminary applications both to thermal waters and geothermal wells are promising. These new geothermometers could be widely used in the geothermal exploration of areas with carbonate-evaporite reservoirs, such as the two main geothermal fields of Italy, Larderello and Mt. Amiata. Further calibration by experimental studies and additional data from geothermal boreholes is needed, however, to test the practical reliability of the new geothermometers.     

Three-dimensional imaging of a geothermal system using temperature and geological models derived from a well-log dataset

The accurate imaging of geothermal systems from the ground surface down to great depths is an interdisciplinary problem common to geothermal resource exploration and development. Rocks can be characterized mainly in terms of their lithology, mineralogy, fracture distribution, permeability, thermal conductivity and porosity, and similarly the geothermal fluid (and its circulation) by its geochemistry, flow pattern, velocity, temperature and pressure. Some of these data are obtained by well logging and from laboratory tests conducted on drillhole cores. In general, the distribution of geothermal wells is not random, and well data are limited in terms of quantity and depth range. Accordingly, a sophisticated spatial modeling technique is indispensable in the three-dimensional imaging of geothermal systems. We describe a versatile 3-D modeling method that can be used to determine the temperature, flow velocity, and distribution of geological units within a geothermal field based on well log data. The model results for the Hohi geothermal area, Japan, provide plausible estimates of temperature, flow velocity, and geology to a depth of 3000 m. Superimposition of the three spatial models we obtained shows that, at Hohi, two geothermal reservoirs are localized near highly fractured fault zones that provide paths for the ascent of thermal fluids from depth.     

The oxygen isotope exchange between carbon dioxide and water in the Larderello geothermal field (Italy) during fluid reinjection

The oxygen isotope compositions of CO₂ and water vapor samples collected from Larderello geothermal wells after the start of the fluid reinjection program suggest that if the oxygen isotope exchange in the vapor phase does, in fact, exist, it is a very slow process when compared with the residence time of the fluids in the geothermal reservoir. This is because carbon dioxide and water vapor phases could not have equilibrated significantly in the vapor-dominated reservoir. This conclusion implies that the oxygen isotope composition of carbon dioxide may possibly be used as a tool in geothermal exploration for revealing the presence of liquid water in deep geothermal systems. Based on the interpretation of the oxygen isotope data of the CO₂, I propose that the origin of the low oxygen isotope ratios of carbon dioxide at Larderello is the high-temperature exchange with liquid water in the lower reservoir. In Larderello, the liquid water–rock interaction in the lower reservoir may have increased the ¹⁸O/¹⁶O ratio of the recharge meteoric component. By contrast, lack of high-temperature liquid water in the upper reservoir suggests that the large “δ¹⁸O shift” described for the upper-reservoir steam during the last decades reflects varying degrees of dilution of the lower-reservoir fluid by the low-¹⁸O vaporized liquid water of meteoric origin that recharges the field at shallow depth, with local contribution from still deeper high-¹⁸O water vapor of magmatic origin. The low oxygen isotope composition of the Mesozoic carbonaceous rocks that form the upper reservoir, consequently, likely represents a “fossil” record of the past hot-water geothermal stage.     

Preliminary isotopic studies of fluids from the Cerro Prieto geothermal field

Preliminary isotopic studies of Cerro Prieto geothermal fluids and earlier studies of Mexicali Valley ground waters suggest local recharge of the geothermal system from the area immediately to the west. Oxygen isotope exchange of water with reservoir rock minerals at temperatures increasing with depth has produced fluids with oxygen-18 contents increasing with depth, and pressure drawdown in the southeastern part of the field has allowed lower oxygen-18 fluids to invade the production aquifer from above. The contents of tritium and carbon-14 in the fluid suggest only that the age of the fluid is between 50 and 10,000 years. The isotopic compositions of carbon and sulfur are consistent with a magmatic origin of these elements but a mixed sedimentary-organic origin appears more likely for carbon and is also possible for sulfur. Investigations of the isotopic compositions of geothermal and cold ground waters continue and are being expanded as fluids become available and as separation and analysis methods are improved.     

Geochemical study of fluid inclusions from the western upflow zone of the Matsukawa geothermal system,Japan

Prior to development, the Matsukawa geothermal field was partially vapor-dominated. The youngest mineral assemblage consists of early pyrophyllite, diaspore and pyrite, and later anhydrite and quartz, implying deposition from an acidic, high-temperature fluid. Fluid inclusions in anhydrite and quartz from core and cutting samples collected in wells drilled in the western upflow zone of the field were studied to characterize the temperatures and compositions of these late fluids.The results of fluid inclusion studies indicate that the temperatures during the deposition of anhydrite and quartz were up to several tens of degrees lower than the reservoir temperatures at the time of exploitation. Fluids trapped in anhydrite had temperatures of up to 257 °C, CO₂ concentrations in the 0.4–2.6 mol% range and salinities of 1.9–11.3 wt.% NaCl. This compositional variation is related to vapor loss occurring during boiling. The data suggest that the geothermal reservoir is currently being reheated by subvolcanic intrusions.     

The Iceland Deep Drilling Project: a search for deep unconventional geothermal resources

The Iceland Deep Drilling Project (IDDP) is a long-term program to improve the economics of geothermal energy by producing supercritical hydrous fluids from drillable depths. Producing supercritical fluids will require the drilling of wells and the sampling of fluids and rocks to depths of 3.5–5 km, and at temperatures of 450–600 °C. The IDDP plans to drill and test a series of such deep boreholes in the Krafla, Nesjavellir and Reykjanes geothermal fields in Iceland. Beneath these three developed high-temperature systems frequent seismic activity continues below 5 km, indicating that, even at supercritical temperatures, the rocks are brittle and therefore likely to be permeable, even where the temperature is assumed to exceed 550–650 °C. Temperature gradients are greater and fluid salinities smaller at Nesjavellir and Krafla than at Reykjanes. However, an active drilling program is underway at Reykjanes to expand the existing generating capacity and the field operator has offered to make available one of a number of 2.5 km deep wells to be the first to be deepened to 5 km by the IDDP. In addition to its potential economic significance, drilling deep at this location, on the landward extension of the Mid-Atlantic Ridge, is of great interest to the international science community. This paper examines the prospect of producing geothermal fluids from deep wells drilled into a reservoir at supercritical temperatures and pressures. Since fluids drawn from a depth of 4000–5000 m may prove to be chemically hostile, the wellbore and casing must be protected while the fluid properties are being evaluated. This will be achieved by extracting the fluids through a narrow retrievable liner called the “pipe”. Modelling indicates that if the wellhead enthalpy is to exceed that of conventionally produced geothermal steam, the reservoir temperature must be higher than 450 °C. A deep well producing 0.67 m³/s steam (2400 m³/h) from a reservoir with a temperature significantly above 450 °C could, under favourable conditions, yield enough high-enthalpy steam to generate 40–50 MW of electric power. This exceeds by an order of magnitude the power typically obtained from a conventional geothermal well in Iceland. The aim of the IDDP is to determine whether utilization of heat from such an unconventional geothermal resource at supercritical conditions will lead to increased productivity of wells at a competitive cost. If the IDDP is an economic success, this same approach could be applied in other high-temperature volcanic geothermal systems elsewhere, an important step in enhancing the geothermal industry worldwide.     

The thermal and geochemical structure of the broadlands-ohaaki geothermal system, new zealand

Fifty two wells have been drilled into the Broadlands-Ohaaki geothermal system, New Zealand, in the course of its development. Fluid samples collected from these wells and measured temperatures indicate that boiling is common within the East and West Bank production zones, separated at the surface by the Waikato River. Steam-heated waters form over the top of the system, above zones of boiling, and are also present on the margins of the system. They are C0₂-rich, and are responsible for dilution of the deep chloride fluids, particularly on the margins of the system. Thermal inversions are common on the margins of the system, associated with the steam-heated waters. The eastern portion of the East Bank and margins of the West Bank have cooled since peak thermal conditions, possibly due to dilution, as indicated by comparing fluid inclusion data with temperatures now present. However, fluid inclusion Th and Tm data indicate that boiling and dilution patterns similar to those now present have existedsince inclusion formation. The hydrothermal alteration of the silicic volcanics comprises an assemblage of quartz—albite—illite—adularia—calcite—chlorite—pyrite; epitode and wairakite are rare, and pyrrhotite, sphalerite and galena are generally confined to the margins of the system. Kaolin, Camontmorillonite, cristobalite and siderite are also present on the margins of the system to depths of 600–1200 m, and are related to the presence of the C0₂-rich, steam-heated waters. The deep production fluids originate from a parent (preboiled) fluid with a temperature of 300°C and CO₂ content of 0.6 mol. Excess enthalpy (i.e. two phase feed zone) discharges are not suitable for the calculation of activity ratios in the reservoir liquid and assessment of mineral—fluid equilibria; this is probably due to non-equilibrium distribution of gas species between liquid and vapor. However, an assessment of mineral—fluid equilibria is possible from the compositions of liquid feed wells. Based on these data, the reservoir fluids are now slightly undersaturated with respect to calcite and are in equilibrium with K-mica, pyrite and chlorite. The common presence of adularia and calcite in veins and open spaces may be due to a shift in mineral—fluid equilibria caused by extensive boiling and gas loss in fractures as compared to formation fluid. In contrast, the marginal steam-heated waters are in equilibrium with pyrite-pyrrhotite. Their lower pH values make them more undersaturated with respect to calcite and K-feldspar than the chloride fluids, due mainly to the lower temperatures and concentration of CO₂, resulting in interstratified illite-smectite and even kaolinite ± siderite stability. Dilution and cooling of the boiling fluids by the steam-heated waters has caused their shift to K-mica stability; the resulting deposition of illite in fractures of the East Bank may be responsible for the lower permeabilities here, causing excess enthalpy conditions.Steam-heated waters are common in geothermal systems throughout the world; recognition of dilution patterns helps in deducing the overall geochemical structure of each system. Knowledge of the distribution of steam-heated waters will also assist in locating upflow zones, and also allows their potential for casing corrosion and production-induced incursion to be assessed.     

Properties of geothermal fluids in Switzerland: A new interactive database

A database on geothermal fluids in Switzerland, called BDFGeotherm, has been compiled. It consists of nine related tables with fields describing the geographical, geological, hydrogeological and geothermal conditions of each sampling location. In all, 203 springs and boreholes from 82 geothermal sites in Switzerland and neighboring regions are listed in this new interactive Microsoft Access database. BDFGeotherm is a functional tool for various phases of a geothermal project such as exploration, production or fluid re-injection. Many types of queries can be run, using any fields from the database, and the results can be put into tables and printed or exported and saved in other files. In addition to describing the database structure, this paper also gives a summary of the reservoir formations, the geographical distribution of hydraulic parameters, the geochemical types of thermal waters and the potential geothermal resources associated with the sites.