Deep Geothermal Water Research Articles

Quantitative evaluation of sustainable development ability of deep buried geothermal water coupled with key index factors

ABSTRACT Scientific evaluations of the sustainable development ability of deep-buried geothermal water are essential to fully utilizing these resources while simultaneously minimizing negative environmental effects. However, due to the multi-source and variability of accumulated information in the process of geothermal water development, the precise identification of spatial differences in sustainable development capabilities is still in the exploratory stage. Taking geothermal water of thermal reservoirs with buried depths of 1000–1200 m and 1200–1400 m of downtown Kaifeng City China as an example, the exploitation potential, well distribution density, geothermal gradient, water level decline rate, recharge volume, and specific yield are selected as index factors. The weights of index factors are determined based on the gray correlation analysis method, and the sustainable development ability of the geothermal water is quantitatively evaluated using fuzzy variable set theory. Our research shows that the geothermal water resources of the 1000–1200 m deep thermal reservoir in Kaifeng can be divided into three sustainable development ability zones: ‘weakest’, ‘medium’, and ‘strong’. Moreover, the 1200–1400 m deep thermal reservoir can also be divided into three sustainable development ability zones: ‘weakest’, ‘weak’, and ‘strongest’. This research work provides a direction for the rational development and scientific protection of geothermal water.

Upgrading a District Heating System by Means of the Integration of Modular Heat Pumps, Geothermal Waters, and PVs for Resilient and Sustainable Urban Energy

Krakow has an extensive district heating network, which is approximately 900 km long. It is the second largest city in terms of the number of inhabitants in Poland, resulting in a high demand for energy—for both heating and cooling. The district heating of the city is based on coal. The paper presents the conception of using the available renewable sources to integrate them into the city’s heating system, increasing the flexibility of the system and its decentralization. An innovative solution of the use of hybrid, modular heat pumps with power dependent on the needs of customers in a given location and combining them with geothermal waters and photovoltaics is presented. The potential of deep geothermal waters is based on two reservoirs built of carbonate rocks, namely Devonian and Upper Jurassic, which mainly consist of dolomite and limestone. The theoretical potential of water intake equal to the nominal heating capacity of a geothermal installation is estimated at 3.3 and 2.0 MW, respectively. Shallow geothermal energy potential varies within the city, reflecting the complex geological structure of the city. Apart from typical borehole heat exchangers (BHEs), the shallower water levels may represent a significant potential source for both heating and cooling by means of water heat pumps. For the heating network, it has been proposed to use modular heat pumps with hybrid sources, which will allow for the flexible development of the network in places previously unavailable or unprofitable. In the case of balancing production and demand, a photovoltaic installation can be an effective and sufficient source of electricity that will cover the annual electricity demand generated by the heat pump installation, when it is used for both heating and cooling. The alternating demand of facilities for heating and cooling energy, caused by changes in the seasons, suggests potential for using seasonal cold and heat storage.

Hydrogeochemical Characteristics and Conceptual Model of the Geothermal Waters in the Xianshuihe Fault Zone, Southwestern China.

Abundant geothermal waters have been reported in the Yalabamei, Zhonggu, Erdaoqiao, and Yulingong geothermal areas of the Xianshuihe Fault Zone of western Sichuan, southwestern China. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrochemical and deuterium-oxygen (D-O) isotopic studies. Shallow geothermal waters represented by geothermal springs and shallow drilled water wells are divided into two hydrochemical groups: (1) the Ca–Na–HCO3 type in the Erdaoqiao area, and (2) Na–HCO3 in other areas. Deep geothermal waters represented by deep drilled wells are characterized by the Na–Cl–HCO3 type. The major ionic compositions of geothermal water are primarily determined by the water–rock interaction with silicate and carbonate minerals. The reservoir temperatures estimated by multi-geothermometries have a range of 63–150 °C for shallow geothermal water and of 190–210 °C for deep geothermal water, respectively. The δ18O and δD compositions indicated geothermal waters are recharged by meteoric water from the elevation of 2923–5162 m. Based on the aforementioned analyses above, a conceptual model was constructed for the geothermal system in the Xianshuihe fault zone.

Reconstruction of different original water chemical compositions and estimation of reservoir temperature from mixed geothermal water using the method of integrated multicomponent geothermometry: A case study of the Gonghe Basin, northeastern Tibetan Plateau, China

The Gonghe geothermal field, northeastern Tibetan Plateau, China, is considered to be a potential target development area for Hot Dry Rock (HDR) resources, where the first Chinese Enhanced Geothermal System (EGS) research project is likely to be located. This area has formed typical layered geothermal reservoirs in a sedimentary basin with an anomalously high geothermal gradient (more than 55 °C/km), and the hydrothermal systems at different depths are connected by hidden faults. To investigate the geothermal structure and geochemical characteristics, water samples from the Gonghe geothermal field were collected and measured. The method of Integrated Multicomponent Geothermometry (IMG) was used to analyse the mixing processes and to estimate the reservoir temperatures. Due to significant differences in the Al and Mg concentrations between shallow and deep reservoirs, the IMG method, which uses measured and optimized values to reconstruct the composition of shallow and deep geothermal water, was successfully applied to constrain the mixing processes. This study predicted three typical geothermal reservoirs at different depths, and it quite accurately estimated the reservoir temperatures. The methodology of the present work can also be used in other geothermal fields with similar geological and geothermal conditions, to reconstruct the original deep and shallow water compositions from mixing processes, estimate reservoir temperatures, and build conceptual geothermal reservoir models.

Hydrochemistry and geothermometry of geothermal water in the central Guanzhong Basin, China: a case study in Xi’an

The Xi’an geothermal field is a typical medium–low-temperature group of geothermal reservoirs in the Guanzhong Basin. Three distinct groundwater systems occur in this field: the cold groundwater (CG) system (quaternary cold-water reservoir with a depth of less than 300 m); the shallow geothermal water (SGW) system (the Quaternary, Zhangjiapo Group, and Lantian-Bahe Group thermal reservoirs with depths ranging between 300 and 2000 m); the deep geothermal water (DGW) system (the Gaoling Group, Bailuyuan Group, and Proterozoic crystalline rock fissure thermal reservoirs, with depths of more than 2000 m). The chemical composition of the CG system consists of HCO3–Ca and HCO3–Ca–Mg water types with a low Total Dissolved Solids’ (TDS) content. The chemical composition of the SGW system consists of SO4–Na and SO4–HCO3–Na water types that have resulted from the partial mixing with water from the CG system through fault structures. Calculations suggest that about 39.4–42.7% of the water in the SGW system was derived from the CG system. The chemical composition of the DGW system consists of SO4–Na and SO4–Cl–Na water types with elevated TDS, F−, SiO2, and high ion concentrations due to the long residence time of water in this largely closed system. The use of geothermometers, multiple mineral equilibrium calculations, and the silica-enthalpy mixing model suggests that temperatures in the SGW and DGW systems lie in the range of 40–85 °C and 94.7–135 °C, respectively. The chalcedony geothermometer is considered to provide the most reliable temperature estimates of the shallow reservoir, whereas the quartzb (maximum steam loss 100 °C) and Na–K geothermometers are considered to provide the most reliable estimates for the deep thermal reservoir. The results of a Q-cluster classification of the water agree well with the field classification of the sampled waters, and the associations of the principal variables obtained by the R-cluster method are consistent with the results obtained by the conventional hydrogeochemical assessment of the samples.

Systematic Analysis of Geothermal Resources in the Coastal Bedrock Area of Chunxiao Town (China) by Using Geochemistry and Geophysics Methods

Geochemical and geophysical investigations were carried out to obtain more evidence of the potential of geothermal resources in Chunxiao Town (China). Hydrochemical data indicate the possible existence of mixing process between deep geothermal water and shallow groundwater. Analysis with SiO2 geothermometer shows that the geothermal reservoir temperature was estimated around 40–60 °C. In addition, combination investigations with CSAMT, radioactive radon, and soil thermal-released mercury detection reveal the specific location of the conduction fractures for thermal water circulation. Furthermore, the drilling work shows the deep thermal water temperature of >55 °C and the thermal water yield of 300 m3/d. All these results could provide important guidance for the scientific exploration and effective utilization of geothermal resources in coastal area.

Synthesis of geochemical techniques to identify the origin and multistage evolution of saline water in a complex geothermal system

Elucidating brine origin and evolution is a fundamental but not easy task especially for coastal geothermal systems with possible marine constituents and multistage evolution, as subsequently physical, chemical and biological alteration processes may mask the original and early-stage signatures. Here chemical and isotopic characteristics of water (D and 18O) and dissolved constituents (13C, 14C, 11B and 87Sr/86Sr) have been utilized to investigate the source and multistage evolution of the Jimo coastal geothermal system in eastern China, with dramatic differences of geochemical characteristics observed within a 0.2 km2 area. Results show that geothermal water is derived from paleo-meteoric water and has undergone a 3-stages evolution that involves: (1) Dissolution of marine halite and potash salts in the deep reservoir; (2) Water-rock reactions especially cation exchange produces a Cl-Na-Ca type water as deep geothermal water upwells along the fault zone; (3) A minor (<0.3%) addition of fossil seawater to the shallow aquifer that produces Cl-Na type waters in the west, whereas sulfide oxidation and dissolution of aluminosilicate and carbonates in the east produces Cl-Na-Ca type waters. The methodology utilized in this study offers a means of examining other similar complex geochemical systems having a multistage evolution.

Renewable Energy Sources in the Lubusz Voivodship (Poland). The Present Conditions and Perspectives for Development

The article presents the present situation in terms of energy production from renewable energy sources and perspectives for development, based on research on the existing resources and possibilities of using them. The Lubusz Voivodship is not an important energy producer in Poland. In terms of the amount of energy produced it comes twelfth out of sixteen voivodships. The annual energy production from renewable energy sources is 290,9 GWh, which is 11.6% of the total energy produced. At the end of 2014 there were 73 licensed installations producing electrical energy from renewable energy sources in the Lubusz Voivodship with a total capacity of 189 MW. The largest amount of energy is produced by a pumped storage power plant (91,3 MW). The total capacity of the licensed installations using RES in the Lubusz Voivodship rose from 103 MW in 2007 to about 189 MW in 2014. Research on the existing resources indicates that it is possible to develop RES. Preparations are under way to build 66 new wind farms with a total capacity of 1834 MW [35], 89 photovoltaic power plants with a total capacity of 468 MW, 21 water power plants with a total capacity of about 60 MW, 54 biogas power plants with a total expected capacity of about 67 MW. The total capacity of the RES installations that are planned to be built by 2023 will be 2469 MW. Therefore, in the coming years the installed capacity of RES installations will increase 13 times in the Lubusz Voivodship. There are still no plans to use the energy of deep geothermal waters due to low profitability.

The deep-subsurface sulfate reducer Desulfotomaculum kuznetsovii employs two methanol-degrading pathways

Methanol is generally metabolized through a pathway initiated by a cobalamine-containing methanol methyltransferase by anaerobic methylotrophs (such as methanogens and acetogens), or through oxidation to formaldehyde using a methanol dehydrogenase by aerobes. Methanol is an important substrate in deep-subsurface environments, where thermophilic sulfate-reducing bacteria of the genus Desulfotomaculum have key roles. Here, we study the methanol metabolism of Desulfotomaculum kuznetsovii strain 17T, isolated from a 3000-m deep geothermal water reservoir. We use proteomics to analyze cells grown with methanol and sulfate in the presence and absence of cobalt and vitamin B12. The results indicate the presence of two methanol-degrading pathways in D. kuznetsovii, a cobalt-dependent methanol methyltransferase and a cobalt-independent methanol dehydrogenase, which is further confirmed by stable isotope fractionation. This is the first report of a microorganism utilizing two distinct methanol conversion pathways. We hypothesize that this gives D. kuznetsovii a competitive advantage in its natural environment.

Understanding the Burial and Migration Characteristics of Deep Geothermal Water Using Hydrogen, Oxygen, and Inorganic Carbon Isotopes

Geothermal water samples taken from deep aquifers within the city of Kaifeng at depths between 800 and 1650 m were analyzed for conventional water chemical compositions and stable isotopes. These results were then combined with the deuterium excess parameter (d value), and the contribution ratios of different carbon sources were calculated along with distributional characteristics and data on the migration and transformation of geothermal water. These results included the conventional water chemical group, hydrogen, and oxygen isotopes (δD-δ18O), dissolved inorganic carbon (DIC) and associated isotopes (δ13CDIC). The results of this study show that geothermal water in the city of Kaifeng is weakly alkaline, water chemistry mostly comprises a HCO3-Na type, and the range of variation of δD is between −76.12‰ and −70.48‰, (average: −74.25‰), while the range of variation of δ18O is between −11.08‰ and −9.41‰ (average: −10.15‰). Data show that values of d vary between 1.3‰ and 13.3‰ (average: 6.91‰), while DIC content is between 91.523 and 156.969 mg/L (average: 127.158 mg/L). The recorded range of δ13CDIC was between −10.160‰ and −6.386‰ (average: −9.019‰). The results presented in this study show that as depth increases, so do δD and δ18O, while d values decrease and DIC content and δ13CDIC gradually increase. Thus, δD, δ18O, d values, DIC, and δ13CDIC can all be used as proxies for the burial characteristics of geothermal water. Because data show that the changes in d values and DIC content are larger along the direction of geothermal water flow, so these proxies can be used to indicate migration. This study also shows demonstrates that the main source of DIC in geothermal water is CO2thathas a biological origin in soils, as well as the dissolution of carbonate minerals in surrounding rocks. Thus, as depth increases, the contribution of soil biogenic carbon sources to DIC decreases while the influence of carbonate dissolution on DIC increases.

Characterizing the hydrogeochemistry of two low-temperature thermal systems in Central Mexico

Two low-temperature geothermal systems located at the Trans-Mexican Volcanic Belt with presence of fluoride and arsenic were studied with the aim to determine hydrogeochemical indicators of the toxic elements' presence, and to propose adequate geothermometers. The hydrogeological and geochemical study was carried out in Ixtapan de la Sal and Tonatico (IxS-T) and Santa Cruz de Juventino Rosas (JR), both located at the limits of the Trans-Mexican Volcanic Belt (TMVB). In these regions, low-temperature geothermal activity is present (T=32–47°C), and various fault and fracture systems have been identified. Several faults are active, enabling the upward flow of deep geothermal water. The geothermal waters of IxS-T manifest in the form of springs and have high Na+ and Cl− concentrations, whereas those of JR are captured in wells and mainly present high Na+ and HCO3– concentrations. The hydrochemistry of water samples was analyzed to determine the dominant hydrogeochemical processes in both regions. These data were also useful for understanding the natural origin of the high levels of arsenic and fluoride reported in the water, which are likely due to mineral dissolution processes. The concentrations of these elements surpassed the permissible limits according to Mexican law (Astot=0.025mg/L; F−=1.5mg/L) and represent a toxicity risk for the local populations. The groundwater at JR supplies all needs of the local population, while the water at IxS-T is mainly used for recreational and health spa purposes. Increasing trends of As and F− in the sedimentary aquifer of IxS-T are related with the increase in TDS, Cl−, HCO3– and SiO2, while silicate alteration releasing Na and HCO3– are related with As and F− presence in the volcanic aquifer of JR. Reservoir temperature was adequately estimated with K2/Mg and Na-K-Ca (Mg corrected) geothermometers at IxS-T, and with chalcedony and quartz geothermometers at JR.

Hydrogeochemical characteristics and genesis of the high-temperature geothermal system in the Tashkorgan basin of the Pamir syntax, western China

High-temperature geothermal systems in China, such as those found in Tenchong and Tibet, are common. A similar system without obvious manifestations found in the Tashkorgan basin in the western Xinjiang Autonomous Region, however, was not expected. The results from borehole measurements and predictions with geothermometers, such as quartz, Na-K and Na-K-Mg, indicate that the reservoir temperature is approximately 250–260°C. Geothermal water is high in Total Dissolved Solids (>2.5g/L) and SiO2 content (>273mg/L), and the water type is Cl·SO4-Na, likely resulting from water-rock interactions in the granodiorite reservoirs. Based on isotope analysis, it appears to be recharged by local precipitation and river water. Evidence from the relationships between major ions and the Cl and molar Na/Cl ratio suggests mixing between deep geothermal water and shallow cold groundwater during the upwelling process. Mixing ratios calculated by the relationship between Cl and SiO2 show that the proportion from cold end-members are 96–99% and 40–90% for riparian zone springs and geothermal water from boreholes, respectively. Active regional tectonic and Neo-tectonic movements in the Pamir syntax as well as radioactive elements in the granodiorite reservoir of the Himalayan stage provide basis for the high heat flow background (150–350mW/m2). NNW trending fault systems intersecting with overlying NE faults provide circulation conduits with high permeability for geothermal water.

Characterization of Dissolved Organic Matter in Deep Geothermal Water from Different Burial Depths Based on Three-Dimensional Fluorescence Spectra

Dissolved organic matter (DOM) plays an important role in the chemical evolution of groundwater. Thus, in order to understand the composition and characteristics of DOM in groundwater, analyzed 31geothermal water samples from five aquifers (i.e., between 600 m and 1600 m) in the city of Kaifeng were analyzed and the results were compared in order to clarify their spatial distribution, characteristics, sources, and environmental influences. Results show that as the depth of a thermal reservoir increases, the ultraviolet absorption (UV254) of geothermal water does not change significantly, the concentration of dissolved organic carbon (DOC) gradually increases with depth, and the fluorescence intensity of DOM remains weak. Some differences are also evident with regard to the location and intensity of geothermal water sample DOM fluorescence peaks depending on thermal reservoir. The results of this study show that the main source of DOM in geothermal water is endogenous, derived from high stability organic matter derived from sedimentary processes and associated microbial activity. Within the three geothermal reservoir depth ranges, 600 m to 800 m, 800 m to 1000 m, and 1000 m to 1200 m, DOM components were mainly protein-like as well as soluble microbial metabolites. However, at deeper depths, within the 1200 m to 1400 m and 1400 m to 1600 m thermal reservoirs, the proportion of protein-like components in DOM decreased, while the ratio fulvic-like and humic-like components increased, leading to changes in the positions of fluorescence peaks. Finally, our results demonstrate a close relationship between the intensity of fluorescence peaks, suggesting that a number of fluorescent components may share a common source.

Fluid geochemistry and geothermometry applications of the Kangding high-temperature geothermal system in eastern Himalayas

High-temperature geothermal systems hold an enormous capacity for generating geothermal energy. The Kangding area is a typical high-temperature geothermal field in the Himalayan Geothermal Belt. Hydrogeochemical, gas geochemical and isotopic investigations were performed to identify and qualify the main hydrogeochemical processes affecting thermal water composition, including mixing and degassing, and then to estimate a reliable reservoir temperature. Nine water samples and four geothermal gas samples were collected and analysed for chemical and isotopic components. The results demonstrate the alkaline deep geothermal water is the mixtures of approximately 75% snow-melt water and 25% magmatic water. It is enriched in Na, K, F, Li and other trace elements, indicating the granite reservoir nature. The shallow geothermal water is the mixtures of approximately 30% upward flow of deep geothermal water and 70% meteoric cold water. High concentrations of Ca, Mg and HCO3 indicate the limestone reservoir nature. There is no remarkable oxygen isotope shift in the geothermal water since the rapid circulation is difficult to trigger off strong water-rock interaction. CO2 is the predominant geothermal gas, accounting for more than 97% of total gases in volume percentage. The concentration of CO2 degassing ranged from 0.4 mol L−1 to 0.8 mol L−1 via geothermometrical modelling. As a result, the geothermal water pH increased from 6.0 to 9.0, and approximately 36% of the total SiO2 re-precipitate. The sources of CO2 are the metamorphism of limestone and magmatic degassing based on the composition of carbon isotope. The appropriate geothermometers of Na-K and Na-Li yield reservoir temperature of 280 °C. The geothermometrical modelling, developed to eliminate the effects of CO2 degassing, yields temperature of 250 °C. The silica-enthalpy mixing model yields temperature of 270 °C with no steam separation before mixing.

Thermal Water's Isotope Geochemistry Study of Evros Area, NE Greece

Thermal waters from Evros area were collected and subjected to chemical and isotopic analysis in order to understand all the physicochemical mechanisms (mixing, dilution, precipitating) that contribute to the shallow and deep geothermal water tables and determine the origin of these fluids as well as their mineralization. Physicochemical characteristics EC, T°C, pH was determined at the field. The ionic concentrations of samples indicate solutions with high salinity. Two chemical water types were arisen: Na-SO4 concerning low temperatures and shallow aquifers and Na- Cl concerning high temperatures and deeper geothermal circulation. The ratio Br/Cl definitely considered marine origin indicator is the same as the sea confirming the involvement of the seawater in the geothermal system. The marine component and water-rock interaction process under high temperatures seem to contribute to the mineralization of thermal waters. Moreover, water-rock interaction process is also responsible for the alternation of δ18O values. Geothermometers concluded to a middle enthalpy geothermal field.

The Evolution and Instruction of Strontium Isotope in the Geothermal Water of Basin Type

Combined with the Guanzhong basin tectonic evolution, the data of Sr content,87Sr/86Sr ratio and hot water hydrochemistry has been used to study the supply origin and flow path of deep geothermal water in the Guanzhong central region. The Sr isotope study result shows that when accepting recharge, the geothermal water in the northwest and southeast of Xianli terrace both mainly come from northwest direction. A small amount supply source of geothermal water in the Xi 'an city is from Qinling mountain and the principal supply source comes from the west and north direction, however, geothermal water of Chang’an accepts supply from the north of Qinling mountain. Keywords: geothermal water; strontium isotope; basin type; indicating significance

Evaluation of Temperature and Mixing Process of Water in Deep and Shallow Aquifers in the Southwestern Tunisia: Case of Djerid Region

This study addresses the hydrogeochemistry of thermal and cold waters circulating in the mineralised area of the Djerid basin (South-western of Tunisia) that aimed basically at understanding the mixing processes influencing their chemical compositions. Temperature intervals are 38–75 and 24.5–26.8 °C for thermal water and cold water, respectively. Two distinct hydrogeological systems supply water either for irrigation or for drinking; they are: (1) the Continental Intercalaire geothermal aquifer (CI), and (2) the Complex Terminal aquifer (CT). Geological, geophysical, hydrogeological, hydrochemical methods are applied to reliably analyze and understand the operating model of the aquifer systems, to determine the hydrogeological, the geochemical behaviours, and the possible inter-aquifers water transfer in south western of Tunisia. The reservoir temperature is estimated to be between 60 and 104 °C according to calculations using silica geothermometers and computation of saturation indexes for different solid phases. Based on chemical and thermal data, it is hypothesized that: (1) mixing rate, which occurs between the ascending deep geothermal water and shallow cold water, is estimated from the enthalpy and chloride methods to be about 65 and 73 % respectively, (2) Mixing models can explain the temperature of the geothermal fluid component.

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France)

In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl− concentrations. Average and maximum Cl− concentrations in the recharge waters were calculated (ClRef. and ClRef.Max) to be 0.51 and 2.85mmol/L, respectively). Group A includes spring waters with Cl− concentrations that are within the same order of magnitude as the ClRef concentration. Group B includes groundwater with Cl− concentrations that range between the ClRef and ClRef.Max concentrations. Group C includes brackish groundwater with Cl− concentrations that are significantly greater than the ClRef.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO3 to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Clmolar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display 87Sr/86Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The 36Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The 87Sr/86Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.

Fluid geochemistry at the Raft River geothermal field, Idaho, USA: New data and hydrogeological implications

Following a period of exploration and development in the mid-late 1970's, there was little activity at the Raft River geothermal field for the next ~20 years. U.S. Geothermal Inc. acquired the project in 2002, and began commercial power generation in January 2008. Since 2004, U.S. Geothermal Inc. has collected geochemical data from geothermal and monitoring wells in the field, as well as other shallow wells in the area. An additional sampling program was completed in July 2010 to measure a wider range of minor and trace elements and δ18O, δD, and 3H (Tritium). The data indicate that the geothermal fluids are alkali chloride in composition, and that the fluid geochemistry is spatially variable and complex, with two compositionally-distinct deep geothermal fluids characterized by differences in K, Na, Cl, Ca, Li, and F, an intermediate fluid, and a groundwater fluid. Deep geothermal waters from the southeast part of the borefield have higher K, Na, Cl, Ca, Li, and lower F concentrations than those from the northwest, although both fluids record similar measured and geothermometer temperatures, and are produced from the same Precambrian reservoir rocks at similar depths. The higher salinities of the southeastern fluids are interpreted to result from interactions with evaporite deposits that were not encountered by the northwest fluids along their flow paths. The separation of these deep fluids within the borefield and the lack of mixing between them indicate a compartmentalized reservoir, which is attributed to a northeast-trending shear zone that appears to act as a permeability barrier. This shear zone is represented by a resistivity high as defined by magnetotelluric data.

Hydrogeological and mixing process of waters in deep aquifers in arid regions: south east Tunisia

This study addresses the hydrogeochemistry of thermal and cold waters from south east Tunisia. Temperature intervals are 38.5–68 °C and 22–27.8 °C for thermal water and cold water, respectively. Three distinct hydrogeological systems supply water either for irrigation or for drinking; they are: (1) the Continental Intercalaire geothermal aquifer (CI), (2) the Turonian aquifer and (3) the Senonian aquifer. A synthetic study including hydrochemical, hydrogeological and geothermal approaches have been applied in order to evaluate the inter-aquifers water transfer in south east of Tunisia. By using silica geothermometers and saturation indices for different solid phases, estimated thermal reservoir temperature varies between 52 and 87 °C and between 75 and 110 °C, respectively. Based on chemical and thermal data, mixing, which occurs between the ascending deep geothermal water and shallow cold water, is about 57 % cold water.