Hot Aquifer Research Articles

Integrated Carbon Sequestration\u2013Geothermal Heat Recovery: Performance Comparison Between Open and Close Systems

In this paper, the lateral boundaries for a theoretical homogeneous, isotropic, horizontal, 3-dimensional sedimentary hot aquifer were prescribed by either unhindered open to fluid and heat flow, or compartmentalised fully close boundary conditions. CO2 injection was administered through three well patterns of varying well spacing and numbers: 3 × 3 (5 injection wells and 4 production wells, 750-m well spacing), 5 × 5 (13 injection wells and 12 production wells, 500-m well spacing), and 7 × 7 (25 injection wells and 24 production wells, 375-m well spacing). To assess the effects of boundary conditions and well spacing on a combined carbon sequestration–geothermal heat recovery process, number of output metrics such as net cumulative CO2 stored, volumetric storage efficiency, geothermal heat recovery and pressure build-up were quantified in 54 simulation runs. Based on the assumption made and conditions that the simulation, it was shown that for a typical and more common fewer well number cases, the open versus close boundaries have critical role in determining the effectiveness of operation. (a) Open boundary conditions may counter-intuitively lead to heat recovery relative deficiencies if the pressure gradient stays largely towards the outside of the system (pressure of system > pressure of surrounding). This, however, will benefit CO2 injectivity and storage efficiency by providing escape paths for fluids (CO2 and brine). (b) Close boundary conditions will universally be beneficial for fluid and heat production purposes; however, the excessive pressure build-up can significantly affect the operation duration length. For economically unjustifiable cases with high number of wells, the effects of boundary conditions were shown to be reduced by effective fluid extraction from the medium, thereby enhancing the geothermal heat recovery and avoiding pressure build-up. The research delineated no significant effect of boundary conditions on salt precipitation.

GEOCHEMICAL CHARACTERISTICS OF THE GEOTHERMAL FLUIDS IN THE AKROPOTAMOS AREA (MACEDONIA, NORTHERN GREECE)

The geothermal field of Akropotamos produces fluids at temperatures up to 90oC. The waters from wells AKR-1, AKR-3, AKR-4, AKR-5 and AKR-6 at 30 86oC and TDS of 3.1-30.7 g/l are classified as Na-Cl type. The water from well AKR-2 at 46oC with TDS of 2.15 g/l belongs to Na-HCO3Cl type. The cold and sub-thermal waters (16.4- 27oC) in the area are considered as fresh or low salinity waters (TDS: 0.31-4.34 g/l) of various mixed types. The Na-Cl geothermal waters can be divided into two categories due to two different hot aquifers: (a) Τhe first shallow aquifer contains high salinity waters (TDS: 27.4 30.7 g/l) at 30-48oC located within sands, sandstones and gravels. (b) Τhe second deeper reservoir composed of calcareous conglomerates and sandstones contains lower salinity waters (TDS: 3.1-5.08 g/l) at 83-90οC. The contribution of seawater to the chemical composition of the thermal waters in the shallow aquifer system seems to be important. With the aid of chemical geothermomometers applied to the geothermal water from well AKR-1, the deep temperature has been estimated to be >120oC. Significant quantities of CO2 are encountered in wells AKR-1 and AKR-3.

Application of vertical electrical sounding method to identify distribution of hot groundwater around the hotsprings in geothermal prospect area

Field survey with geoelectric method has been conducted in the Songgoriti geothermal prospect area, Malang, Indonesia. This area is located between Mount Arjuno and Mount Welirang. The aim of this study is to identify the distribution of hot groundwater. Subsurface resistivity data acquisition is done by using Vertical Electrical Sounding (VES) in the four sounding points around the hotsprings with a maximum path length of 160 meters. Data from this measurement is the apparent resistivity that be a response model of the subsurface rock model parameters at each depth. The true resistivity of the subsurface model parameters is determined by inversion modeling. Result of data processing generates a resistivity model of each layer of rock at depth. This study successfully estimate the hot groundwater aquifer layer in the study area. The layer of hot groundwater aquifer is identified by low resistivity in the VES-1 point, VES-2 point and VES-3 point with different depth and thickness. Resistivity of hot groundwater layer is about 19.5–43.1 ohmmeter with the largest thickness in VES-3 point with the direction of orientation from Mount Welirang to southeast.

Assessment of heat mining and hydrogeochemical reactions with data from a former geothermal injection well in the Malm Aquifer, Bavarian Molasse Basin, Germany

With high temperatures, high transmissivities, and low salinities the Malm aquifer in the Bavarian Molasse Basin, Germany, offers ideal conditions for the exploration of geothermal energy in Germany. In 2011, the Pullach geothermal doublet system was extended with a third geothermal well (Th3) to account for increasing heat demand. The third well was then used as injection well and the former injection well (Th2) was converted to a production well. Hence, for the first time in the history of geothermal exploration of the Malm aquifer, data became accessible from the formation surrounding an injection well which had been in operation for more than 5 years. This data provides access to the processes at the injection well and sets the baseline for an assessment of the long term behaviour of geothermal heat and power plants in the Molasse Basin.The increase of the production temperatures at the former injection well after conversion from injection to production went faster than expected; after 3 years of production the initial temperatures have almost been reached. This can be explained with a vertically heterogeneous distribution of the aquifer transmissivity with one thin, highly permeable layer. In this setting, the cold water forms a thin disc which extends much further from the injection well compared to a vertically homogeneous setting, with a cylindrical propagation of the injected water. Hence, in a heterogeneous setting the effective interface for conductive heat exchange between injected cool water and hot aquifer matrix with low permeability is larger.The hydrochemical data of the water from the former injection well showed a significant increase of the concentrations of calcium, magnesium, and bicarbonate, indicating dissolution of dolomite with about 0.6mmol/L of produced water. Together with thermoelastic effects and hydrostatic stress, the dissolution significantly contributes to an increasing injectivity. The effects are overcompensating the effects of the increased viscosity of the injected cold water. Results from the hydrogeochemical model show that lower temperatures and different lithostratigraphic origin of the injected water are responsible for the dissolution. The kinetic model suggests that the dissolution takes place close to the bore hole.The data collected from the Pullach site provides experimental proof for the processes in the surrounding of injection wells, i.e., the assumed aquifer heterogeneity, the connection to overlying strata, and for the hydrogeochemical model of the Malm aquifer. The data serves as a benchmark and reference for future exploration.

El Cobreloa: A geyser with two distinct eruption styles

AbstractWe performed field measurements at a geyser nicknamed “El Cobreloa,” located in the El Tatio Geyser Field, Northern Andes, Chile. The El Cobreloa geyser has two distinct eruption styles: minor eruptions and more energetic and long‐lived major eruptions. Minor eruptions splash hot water intermittently over an approximately 4 min time period. Major eruptions begin with an eruption style similar to minor eruptions, but then transition to a voluminous liquid water‐dominated eruption, and finally end with energetic steam discharge that continues for approximately 1 h. We calculated eruption intervals by visual observations, acoustic measurements, and ground temperature measurements and found that each eruption style has a regular interval: 4 h and 40 min for major eruptions and ∼14 min for minor eruptions. Eruptions of El Cobreloa and geochemical measurements suggest interaction of three water sources. The geyser reservoir, connected to the surface by a conduit, is recharged by a deep, hot aquifer. More deeply derived magmatic fluids heat the reservoir. Boiling in the reservoir releases steam and hot liquid water to the overlying conduit, causing minor eruptions, and heating the water in the conduit. Eventually the water in the conduit becomes warm enough to boil, leading to a steam‐dominated eruption that empties the conduit. The conduit is then recharged by a shallow, colder aquifer, and the eruption cycle begins anew. We develop a model for minor eruptions which heat the water in the conduit. El Cobreloa provides insight into how small eruptions prepare the geyser system for large eruptions.

Cultivating Yet-to-be Cultivated Microbes: The Challenge Continues

Cultivating Yet-to-be Cultivated Microbes: The Challenge Continues

Domain‐level identification and quantification of relative prokaryotic cell abundance in microbial communities by Micro‐FTIR spectroscopy

Domain-level identification of microbial cells or cell-like structures is crucial for investigating natural microbial communities and their ecological significance. By using micro-Fourier transform infrared (micro-FTIR) spectroscopy, we established a technical basis for the domain-level diagnosis and quantification of prokaryotic cell abundance in natural microbial communities. Various prokaryotic cultures (12 species of bacteria and 10 of archaea) were examined using micro-FTIR spectroscopic analysis. The aliphatic CH3 /CH2 absorbance ratios (R3/2 ) showed domain-specific signatures, possibly reflecting distinctive cellular lipid compositions. The signatures were preserved even after chemical cell fixation (formaldehyde) and nucleic acid staining (DAPI) processes - techniques that are essential in studying microbial ecology. The micro-FTIR technique was successfully applied for quantification of the bacteria/archaea abundance ratio in an active microbial mat community in a subsurface hot aquifer stream. We conclude that the micro-FTIR R3/2 measurement is both fast and effective for domain-level diagnosis and quantification of first-order prokaryotic community structures.

Caldilinea tarbellica sp. nov., a filamentous, thermophilic, anaerobic bacterium isolated from a deep hot aquifer in the Aquitaine Basin

An anaerobic, thermophilic, filamentous (0.45 × >100 µm) bacterium, designated D1-25-10-4(T), was isolated from a deep hot aquifer in France. Cells were non-motile and Gram-negative. Growth was observed at 43-65 °C (optimum 55 °C), at pH 6.8-7.8 (optimum pH 7.0) and with 0-5 g NaCl l(-1) (optimum 0 g NaCl l(-1)). Strain D1-25-10-4(T) was a chemo-organotroph and fermented ribose, maltose, glucose, galactose, arabinose, fructose, mannose, sucrose, raffinose, xylose, glycerol, fumarate, peptone, starch and xylan. Yeast extract was required for growth. Sulfate, thiosulfate, sulfite, elemental sulfur, nitrate, nitrite and fumarate were not used as terminal electron acceptors. The G+C content of the DNA was 61.9 mol%. The major cellular fatty acids of strain D1-25-10-4(T) were C(17 : 0), C(18 : 0,) C(16 : 0) and iso-C(17 : 0). The closest phylogenetic relative of strain D1-25-10-4(T) was Caldilinea aerophila STL-6-O1(T) (97.9 % 16S rRNA gene sequence similarity). DNA-DNA relatedness between strain D1-25-10-4(T) and Caldilinea aerophila DSM 14535(T) was 8.7 ± 1 %. On the basis of phylogenetic, genotypic and phenotypic characteristics, strain D1-25-10-4(T) represents a novel species within the genus Caldilinea, class Caldilineae, phylum Chloroflexi, for which the name Caldilinea tarbellica sp. nov. is proposed. The type strain is D1-25-10-4(T) ( = DSM 22659(T) = JCM 16120(T)).

Isolation and characterization of Thermanaerothrix daxensis gen. nov., sp. nov., a thermophilic anaerobic bacterium pertaining to the phylum “ Chloroflexi”, isolated from a deep hot aquifer in the Aquitaine Basin

A new strictly anaerobic thermophilic multicellular filamentous bacterium (0.2–0.3 μm × >100 μm), designated GNS-1 T, was isolated from a deep hot aquifer in France. It was non-motile, and stained Gram-negative. Optimal growth was observed at 65 °C, pH 7.0, and 2 g L −1 of NaCl. Strain GNS-1 T was chemoorganotrophic fermenting ribose, glucose, galactose, arabinose, fructose, mannose, maltose, sucrose, xylose, raffinose, pyruvate, and xylan. Yeast extract was required for growth. The end products of glucose fermentation were lactate, acetate, CO 2, and H 2. The G + C content of the DNA was 57.6 mol%. Its closest phylogenetic relative was Bellilinea caldifistulae with 92.5% similarity. Based on phylogenetic, genotypic and phenotypic characteristics, strain GNS-1 T (DSM 23592 T, JCM 16980 T) is proposed to be assigned to a novel species of a novel genus within the class Anaerolineae (subphylum I), phylum “ Chloroflexi”, Thermanaerothrix daxensis gen. nov., sp. nov. The GenBank accession number is HM596746.

Internal corrosion of carbon steel piping in hot aquifers service

Internal corrosion of carbon steel pipelines is a major problem encountered in water service. In terms of prediction of the remaining lifetime for water pipelines based on the corrosion allowance, the three main approaches are corrosion modelling, corrosion inhibitor availability, and corrosion monitoring. In this study we used two theoretical corrosion models, CASSANDRA and NORSOK M-506 of quite different origin in order to predict uniform corrosivity of hot aquifers in eight different pipelines. Because of the varying calculation criteria for the different models, these can give very different corrosion rate predictions for the same data input. This is especially true under conditions where the formation of protective films may occur, such as at elevated temperatures. The evaluation of models was conducted by comparison using weight-loss coupons and three corrosion inhibitors were obtained from commercial suppliers. The tests were performed during the 60-day period. Even though inhibitors? efficiencies of 98% had been achieved in laboratory testing, inhibitors? availabilities of 85% have been used due to logistics problems and other issues. The results, given in mmpy, i.e. millimeter per year, are very consistent with NORSOK M-506 prediction. This is presumably because the model considers the effect of the formation of a passive iron carbonate film at temperatures above 80 ?C and significant reduction in corrosion rate. Corrosion inhibitor A showed a better performance than inhibitors B and C in all cases but the target corrosion rates of less than 0.1 mmpy were achieved for all inhibitors. The chemical type of corrosion inhibitor A is based on quaternary amines mixed with methanol, isopropyl alcohol, xylene and ethylbenzene. Based on the obtained results the carbon steel lifetime of 30 years, provided proper inhibitors are present and 3mm corrosion allowance, can be achieved for hot aquifers service with presented water compositions.

Methylothermus subterraneus sp. nov., a moderately thermophilic methanotroph isolated from a terrestrial subsurface hot aquifer

A novel methane-oxidizing bacterium, strain HTM55(T), was isolated from subsurface hot aquifer water from a Japanese gold mine. Strain HTM55(T) was a Gram-negative, aerobic, motile, coccoid bacterium with a single polar flagellum and the distinctive intracytoplasmic membrane arrangement of a type I methanotroph. Strain HTM55(T) was a moderately thermophilic, obligate methanotroph that grew on methane and methanol at 37-65 °C (optimum 55-60 °C). The isolate grew at pH 5.2-7.5 (optimum 5.8-6.3) and with 0-1 % NaCl (optimum 0-0.3 %). The ribulose monophosphate pathway was operative for carbon assimilation. The DNA G+C content was 54.4 mol% and the major fatty acids were C(16 : 0) (52.0 %) and C(18 : 1)ω7c (34.8 %). Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain HTM55(T) was closely related to Methylothermus thermalis MYHT(T) (99.2 % 16S rRNA gene sequence similarity), which is within the class Gammaproteobacteria. However, DNA-DNA relatedness between strain HTM55(T) and Methylothermus thermalis MYHT(T) was ≤ 39 %. On the basis of distinct phylogenetic, chemotaxonomic and physiological characteristics, strain HTM55(T) represents a novel species of the genus Methylothermus, for which the name Methylothermus subterraneus sp. nov. is proposed. The type strain is HTM55(T) ( = JCM 13664(T) = DSM 19750(T)).

Mud plumbing system of an isolated phreatic eruption at Akita Yakeyama volcano, northern Honshu, Japan

A small phreatic eruption occurred on 16 August 1997 at the flank of a dacite lava dome of Akita Yakeyama, northern Honshu, Japan. Air-falls and viscous mudflows were discharged from two craters. Mudflow effusion preceded discrete explosions, followed by a fine ash discharge. The air-fall deposit consists of an upper fine ash deposit and a lower ballistic-dominated, poorly sorted tephra in which ranges in grain size from fine ash to blocks of ca. 50 cm. Both air fall and mudflow deposits were composed of fine mud and coarse lithic fragments, which contained abundant liquid water. Lithic fragments comprise fresh dacite of the host lava dome and hydrothermally altered stratocone andesite. Intensely altered andesite fragments contain quartz, cristobalite, andalusite, pyrophyllite, 7 Å-kaolin, and anhydrite. Some mineral assemblages indicate hydrothermal temperatures greater than 300 °C. Rare sandstone fragments are likely to be lacustrine from ca. 1000 m depth. The surface morphology of the mudflow deposits indicates that the mud contained ca. 30 vol.% water. The cube-root similarity rules on crater size and the cloud shape of buried explosions provided energy of 3–5 × 10 9 J at depths of 6–10 m, based on the observed crater size (20 m) and fountain-like cloud shape. The depth estimate is consistent with the abundance of coarse dacite fragments derived from shallow lava in the explosion deposit. Thermodynamic energy release of ca. 1 × 10 11 J was calculated based on the following estimated parameters: product volume of 1 × 10 3 m 3, hydrothermal temperatures of 300–350 °C, and pressures of 11–24 MPa corresponding to the estimated source depth. The thermodynamic estimation represents the total energy released during the eruption, whereas the similarity rule yields an energy value as created by discrete explosions. Mud ascended from a hot aquifer at 1000 m depth, first effused as a mudflow, and was then expelled explosively from another crater. Explosivity depends on the shallow geologic structures. Reduction of pressure within the shallow permeable breccia resulted in effusive mudflow, whereas overpressure, confined by rigid dacite lava, yielded explosive eruptions. The mud plumbing system, which includes deep-aquifer mud and shallow explosions, seems to be typical of phreatic eruptions.

The uplift mechanism of the rock masses around the Jiangya dam after reservoir inundation, China

During filling of the Jiangya reservoir, a multi-purpose project in China Hunan province, it was found that the dam body and the rock masses on both valley sides were uplifted to various degrees, with a measured maximum uplift of 32.6 and 19.08 mm, respectively. This rare phenomenon caused concerns from various parties. The paper presents a systematic analysis on the factors that may possibly contribute to the uplift, on the basis of a comprehensive study of the geological background of the project and the observed data. To confirm the uplift mechanism of the confined hot aquifer, 3D numerical analysis and rock mechanical model test were also carried out. It is concluded that the rise of artesian head of the confined hot aquifer as a result of the reservoir inundation is the principal factor contributing to the uplift.

Numerical Simulations of Reactive Flow in Hot Aquifers

In recent years, there has been a significant expansion in our ability to model systems that involve the interaction of fluid flow, mass transport, heat transfer, and geochemical reaction in porous media. Such scenarios arise in studies of both fundamental science, such as the effects of thermohaline flow and heat transfer in rift basins, and in the solution of applied problems, such as the response of a geothermal reservoir to the re‐injection of cool water. Numerical Simulation of Reactive Flow in Hot Aquifers presents the simulation tools that were developed by a team of researchers based in Germany.This group has a long history in analyzing geothermal systems, but the methods presented can be applied far beyond the study of geothermal reservoirs. The heart of the book is a description of the model SHEMAT. The executable code and a graphical user interface are included with the book.

THE APPLICATION OF THE TRANSIENT EM METHOD INTO THE GEOTHERMAL FIELD EXPLORATION

In this work we examine the potential of the time-domain electromagnetic method (Transient EM) in the exploration of geothermal field and the study of the geological environment. The method was applied in the geothermal field of Aristino (Alexandroupolis), westwards of the Traianoupolis, where the known hot springs exist. The EM method and more specifically magnetotellurics (MT), it has been applied in the past in Greece by various researchers, but it is the first time the TEM method is applied for geothermal exploration purposes. As it has been shown by previous works, in the wider region of Aristino an important geothermal field is developed, with geothermal fluid temperature of 30°-90° and high content of dissolved salts of 10gr/lt. These factors result to the appearance of highly conductive geoelectrical anomalies which are directly related to the geothermal field. The existence of two drillholes in the region allowed the calibration and the control of the effectiveness of the TEM method. The geophysical survey has delimited the area of local geothermal interest that is formed by hot aquifer at a relatively shallow depth, extended North of Aristino and between the main faults of the region. The two main faults are responsible for the creation of a tectonic graben in the intermediary region and the development of a highly conductive formation which correlates well with the hot aquifer tank. The geothermal fluid circulates through the faulting system having high temperature caused by the contact with magmatic masses. The application of TEM proved the operational advantages of the method in the geothermal field exploration. The relatively limited number of TEM soundings presented here does not allow the export of safe conclusions regarding the geothermal field of the wider region, although the evaluation of results based on the geological and geoelectrical data of the region is extremely encouraging and justifies the use of the TEM method in the systematic study and mapping of geothermal fields.

The use of downhole heat exchangers

The downhole heat exchanger (DHE), used extensively in Klamath Falls, Oregon, in over 500 installations, and in Turkey and New Zealand, provides heating for one or more homes, schools, and apartment buildings from a single geothermal well. The DHE eliminates the problem of disposal of geothermal fluid, since only heat is extracted from the well. The heat exchangers consist of a loop of pipes or tubes suspended in the geothermal well, through which “clean” secondary water is pumped or allowed to circulate by natural convection. The maximum output of large installations is typically less than 3 GJ/h or 0.8 MW t, with well depths up to about 150 m, and may be economical under certain conditions at a well depth of 500 m. However, the typical output for an individual home in Klamath Falls tends to be less than 265 MJ/h (0.07 MW t). In order to obtain maximum output, the well must be designed to have an open annulus between the wellbore and casing, with perforations near the top and bottom of the submerged heat exchanger, just below the water surface and at the hot aquifer at the bottom of the well. Natural convection circulates the well water down inside the casing, through the lower perforations, up through the annulus and back into the casing through the upper perforations, with the new geothermal water mixing with the old. This vertical convection cell exposes the DHE to the near-maximum temperature of the well water and thus increases the heat output of the DHE. The heat output from a DHE system is dependent on the bore diameter, casing diameter, DHE length, tube diameter, number of loops in the well, flow rate and temperature of the geothermal fluid. Based on local experience in Klamath Falls, the “rule-of-thumb” is that contractors estimate approximately “1 foot of DHE pipe per 1500 Btu/h” (5200 kJ/h/m or 1.44 kW/m) as an average output.

Distribution and phylogenetic diversity of the subsurface microbial community in a Japanese epithermal gold mine.

Distribution and phylogenetic diversity of microbial communities in hot, deep underground environments in the Hishikari epithermal gold mine, southern part of Kyushu, Japan, were evaluated using molecular phylogenetic analyses. Samples included drilled cores such as andesitic volcanic rock (0.95-1.78 Ma) and the oceanic sedimentary basement rock of Shimanto-Supergroup (100 Ma), as well as geothermal hot aquifer waters directly collected from two different sites: AW-site (71.5 degrees C, pH 6.19) and XW-site (85.0 degrees C, pH 6.80) at a depth of 350 mbls (meters below land surface). Based on PCR-amplified 16S rRNA gene clone analysis, the microbial communities in the drilled cores and the hot aquifer water from the XW-site consisted largely of the 16S rRNA gene sequences, closely related to the sequences often found in marine environments, while the aquifer water from the AW-site contained 16S rRNA gene sequences representing members of Aquificales, thermophilic methanotrophs within the gamma-subdivision of the Proteobacteria and uncultivated strains within the beta-subdivision of Proteobacteria. The cultivable microbial community detected by enrichment cultivation analysis largely matched that detected by the culture-independent molecular analysis.

Sulfurihydrogenibium subterraneum gen. nov., sp. nov., from a subsurface hot aquifer.

A polyphasic taxonomic study was performed on a novel facultatively anaerobic, hydrogen- or sulfur/thiosulfate-oxidizing, thermophilic chemolithoautotroph recently isolated from subsurface hot aquifer water in a Japanese gold mine. The cells were straight to slightly curved rods, with a single polar flagellum. Growth was observed at 40-70 degrees C (optimum 60-65 degrees C; 80 min doubling time) and at pH 6.4-8.8 (optimum pH 7.5). The isolate was unable to use complex organic compounds, carbohydrates, amino acids or organic acids as sole energy and carbon sources. The G + C content of the genomic DNA was 31.3 mol%. Phylogenetic analysis based on 16S rDNA sequences indicated that the isolate was closely related to an uncultivated group of micro-organisms within the order Aquificales obtained from Icelandic and Japanese hot spring microbial mats, but distantly related to previously identified genera of the Aquificales such as Persephonella, Aquifex and Hydrogenobacter. The name Sulfurihydrogenibium subterraneum gen. nov., sp. nov. is proposed for this novel species; the type strain is HGMK1(T) (= JCM 11477(T) = ATCC BAA-562(T) = DSM 15120(T)).

Isolation and metabolic characteristics of previously uncultured members of the order aquificales in a subsurface gold mine.

Culture-dependent and -independent techniques were combined to characterize the physiological properties and the ecological impacts of culture-resistant phylotypes of thermophiles within the order Aquificales from a subsurface hot aquifer of a Japanese gold mine. Thermophilic bacteria phylogenetically associated with previously uncultured phylotypes of Aquificales were successfully isolated. 16S ribosomal DNA clone analysis of the entire microbial DNA assemblage and fluorescence in situ whole-cell hybridization analysis indicated that the isolates dominated the microbial population in the subsurface aquifer. The isolates were facultatively anaerobic, hydrogen- or sulfur/thiosulfate-oxidizing, thermophilic chemolithoautotrophs utilizing molecular oxygen, nitrate, ferric iron, arsenate, selenate, and selenite as electron acceptors. Their versatile energy-generating systems may reflect the geochemical conditions of their habitat in the geothermally active subsurface gold mine.

Geothermal Convector Design: Solutions, Design Criteria, and Calculation Methods

Abstract The geothermal convector (GTC) is an unconventional system for heat extraction from a geothermal aquifer without fluid withdrawal. In this system a special two-phase thermosyphon is used. This device works with a downhole evaporator and with a condenser at the ground level. The system shares advantages and disadvantages with other downhole heat exchanger plants; for instance, a second well to return geothermal water to the aquifier is not required. Because of the limitations of the natural heal flow in the hot aquifer, however, the device is most suitable for small-to moderate-size applications. In this article, the fundamental elements required to determine the device performance and the thermal design criteria are reported and a GTC prototype is described. Designed for 70°C temperature of the geothermal water and 3 m length of the evaporator, this prototype was recently installed in a geothermal well on the island of Ischia. In this article the results of the first experimental tests are reported.