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Xianxian geothermal exploitation area is one of the areas with the best occurrence conditions of geothermal resource in North China, rich in medium and low temperature geothermal resource, and is a typical carbonate geothermal field. However, its hydrogeochemical evolution process is not clear, and no complete conceptual model of geothermal genesis has been established to guide the exploration, development and utilization of geothermal resource in the area. It restricts the sustainable development of regional geothermal resource and the realization of carbon emission reduction targets. In this study, geothermal fluids in the area were collected for testing and analysis in terms of hydrochemical characteristics and stable isotopes. Based on systematic geochemical research, the formation mechanism of geothermal fluids was analyzed, and a conceptual model of geothermal genetic in the study area was established. The main understanding is as follows: the hydrochemical type of geothermal water in the study area is Cl-Na type, and the water-rock interaction is not balanced. The formation of geothermal water in the area is affected by the infiltration of atmospheric precipitation, and it is terrestrial leached water. The flow path of geothermal water is long, the water circulation is slow, and the metamorphism is deep. Dolomite, calcite and gypsum dissolution are the main sources of Mg2+, Ca2+, , and in geothermal water, besides, other minerals containing calcium and magnesium are also part of their sources. The source of geothermal water recharge is atmospheric precipitation, and the recharge elevation of geothermal water is about 619–1069 m. The age of the geothermal water is between 16 000 and 18 000 years. The sulfur in geothermal water mainly comes from the leaching of sedimentary layer. [ABSTRACT FROM AUTHOR]

Geophysical surveys discovered low resistivity values that, in combination with geochemical and structural data, indicate the presence of a previously unrecognized geothermal system with a possible maximum size potential similar to that of the presently installed capacity of the Cerro Prieto geothermal field. The only evidence of a hydrothermal system in the San Felipe Valley are warm groundwater wells and four intertidal hot springs. Exploration at San Felipe was part of a research project that included geological, geochemical and geophysical studies, which indicated the presence of low resistivity anomalies and high temperature at depth; the geological survey provided evidence of active fault systems that may act as channels for convective heat transport. Estimation of the energy potential of the San Felipe prospect using the heat in place method yielded a 50% probability of more than 300 MW that would add to the 570 MW of the Cerro Prieto geothermal field and can supply almost 40% of the state of Baja California electricity demand. The Baja California Peninsula is not connected with the national grid and has one of the highest electricity prices in Mexico, which should be an incentive to develop this clean energy source. The results of this work support the recommendation to pursue further advanced exploration of this prospect. [ABSTRACT FROM AUTHOR]

As volcanoes are closely related to the living environment of humans, in particular via natural hazards and geothermal energy, scientific studies on volcanic edifice structures are required. Ulleung Island is a Quaternary volcanic island located in the mid-western East Sea (Sea of Japan). In this study, we conducted an audio-frequency magnetotelluric (AMT) survey to image the substructure of the Ulleung volcanic edifice. In addition, the electrical structure was interpreted from the geothermal system perspective, geochemical compositions of volcanic rocks, and the possibility of the presence of a magma reservoir. AMT data were obtained from 25 stations and processed using the remote reference technique. Then, the three-dimensional (3-D) approach was reasonably adopted according to dimensionality analysis. Before conducting the 3-D inversion, the effects on topography and ocean were analyzed using a simplified 3-D synthetic model, because Ulleung Island is surrounded by sea and the topography is undulating. Most AMT stations on Ulleung Island are distorted by topographical and oceanic effects; in particular, oceanic effects are significant at frequencies lower than 10 Hz. The 3-D inversion was conducted with full impedance components and vertical magnetic transfer functions in a frequency range of 10,000–1 Hz. The results show that the Ulleung volcanic edifice is characterized by two layers of electrical structures as follows: near-surface resistive anomalies and an underlying conductive layer. Considering the high geothermal gradient on Ulleung Island, we suggest that the conductive layer of the volcanic edifice is due to hydrothermal alteration of basaltic rocks, with a potential heat source underneath. Based on the geochemical characteristics of the Ulleung volcanic rocks, the possibility of heat transfer from a trachytic magma reservoir within the shallow crustal is suggested. In summary, this study presents a geological interpretation of shallow volcanic structures beneath Ulleung Island and the possibility of an active magma reservoir as a potential heat source for the volcanic edifice. [ABSTRACT FROM AUTHOR]

Highlights: MVT-related elements show a specific enrichment pattern in a geothermal scale.Comparison with fluid parameters suggests pressure reduction and CO2 degassing as basis for mineral formation and element enrichment.Exchange processes at the contact surface mineral-fluid and changes in the redox potential allow for element-specific concentration changes.Methane oxidation and sulfate reduction cause major chemical changes.Isotope data track the observed chemical variations. [ABSTRACT FROM AUTHOR]

In Gulu area, geothermal waters show a high concentration of alkali metals (Li, Rb and Cs) and some other typical pollution elements, e.g. As, Sb and Tl. They are also enriched in the geothermal deposits during the phase separation of silica sinter and residual geothermal water. A comprehensive sequential extraction was carried out on the Gulu silica sinter. The results indicated that significant Li and K amount is bound to the Fe-Mn oxide and the residual fractions of sinter while, the elements (B, Cs, Rb, As, Sb and Tl) are predominantly concentrated in the sinter crystal lattices. In addition, the elemental distribution law during phase separation of the residual geothermal water and associated evapoconcentrated deposits is also uncovered in this study. With the respect to the system of the natural silica sinters precipitated from the mother geothermal water, complex variations occur during the trace elements partition between the mother water and associated deposits under evapoconcentration. Thus, the miscellaneous minerals (Li, Rb, K, Cs and B) are also distributed in the solid phases when special minerals such as opal, borax or sylvite precipitate from the residual fluids. This confirms that the valuable minerals of K, B, Cs, Rb or Li can precipitate when the geothermal water is evapoconcentrated to a certain degree and within a very concentrative stage of density. However, these elements are remarkably depleted in the residual geothermal fluid at the stages corresponding to the precipitation of these minerals while they are highly enriched in the mother fluid during the late stages of the evapoconcentration. Thus, it can be stated for the first time that the high concentration of these elements in the residual waters at the final stages will be certainly used in the future. In contrast, the concentration of pollution elements (As, Sb and Tl) of the geothermal solids is higher in the early stage of the opal precipitation, while it is lower in the later stages. The concentration of these elements (As, Sb and Tl) in residual geothermal fluids distinctly increases and is very high at the final stages of the evapoconcentration. This scenario indicates that large quantities of toxic elements such as As, Tl and Sb may degrade the surface and ground waters resources located at or near the geothermal water by mixing process making them unsuitable for drinking or irrigation. Thus, in addition to the thermal energy provided, the geothermal area are very important prospect for exploration and extraction of the mineral resources of the elements such as K, Li, B, Rb or Cs that have very significant economic value. However, percentages of trace elements such as Li, Tl, Rb and K in the exchangeable and carbonates fractions of this sinter suggested that they could become rapidly bioavailable in the geothermal environment. [ABSTRACT FROM AUTHOR]

The gravity and magnetic data sets over a geothermal source are investigated to explore the geological features and geothermal system manifestations. The raw gravity data sets are firstly corrected for drift, latitude and free-air effects to obtain free-air anomalies. A new approach is utilized for Bouguer and terrain corrections. The model space, which is the mass from the reference surface to the ground surface, is parameterized by a very accurate and advanced meshing algorithm (octree and quadtree). The gravity effect of the model space is computed via numerical forward modelling and is considered as the Bouguer and terrain corrections. These corrections are subtracted from the free-air anomalies, which yields the complete Bouguer anomaly. The computed Bouguer anomalies are de-trended and transferred to residual anomalies by methods including polynomial fitting and two-stage methods. The residual gravity anomalies are inverted to obtain the subsurface density distribution. The density contrasts are estimated by minimizing the data and model objective functions through an efficient algorithm. The probable source of the geothermal system and other new gravity anomalies are successfully detected and inverted contrary to the results in previously published papers. The residual magnetic anomaly is also inverted and the obtained geometrical and physical parameters of the source body including minimum depth, shape and susceptibility are very close to the previous results. The new detected gravity anomaly and the main magnetic anomaly in the overlapped area of gravity and magnetic grids are located at almost the same place with almost the same depths, which confirms their probable common source. We developed the open source package (http://docs.simpeg.xyz/content/tutorials/03-gravity), which is accessible through SimPEG (Simulation and Parameter Estimation in Geophysics), for inverting the gravity and magnetic data sets. [ABSTRACT FROM AUTHOR]

Thermal fracturing in reservoir rocks can cause significant increase in permeability. The change in permeability due to fracturing was predicted using the change in elastic wave velocity, density, and elastic moduli. Westerly granite samples were thermally treated to 250, 450, 650 and 850 °C. Increasing the temperature produces an increase in fracture length, aperture and density that is isotropically distributed. The permeability was measured at 10, 30 and 50 MPa effective pressure using deionized water as the pore fluid. The permeability was correlated to P- and S-wave velocities, bulk density, and static bulk modulus that were measured at similar effective pressures on the same suite of samples. Kachanov's (Elastic solids with many cracks and related problems, in: John, Theodore (eds) Advances in applied mechanics, Elsevier, pp 259–445, 1994) model was used to calculate the evolution of fracture density. Closure of fracture, due to increasing effective pressure, caused the permeability and fracture density to decrease, and the other parameters to increase. Thermal treatment caused a systematic increase in permeability and fracture density, and a decrease in the other parameters. Empirical relationships with high correlation coefficient exist between permeability and the other parameters for both dry and saturated conditions, which vary with effective pressure. Overall, we conclude that the elastic wave velocity, density and bulk modulus can be used to predict the change in permeability due to isotropic fracturing. However, a reliable method would be required to upscale these laboratory measurements for modelling and describing the permeability within a granitic reservoir. [ABSTRACT FROM AUTHOR]

In this study, Shengli fault depression, Tangyuan fault basin, and northern Songliao Basin in Yitong-Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly. Based on the temperature of the deep thermal reservoir, the hydrothermal fluid channel, caprock thickness, and the mode of heat transfer, which are the main factors controlling the geothermal reservoir formation, we examined geothermal resource system of the underground HDR in this area. First, we inversed the aeromagnetic data, calculated the Curie isotherm depth, analyzed the geothermal distribution characteristics, and estimated the temperature of the deep heat source. Second, we applied the controlled source audio frequency magnetotelluric (CSAMT) and magnetotelluric (MT) methods to obtain the deep electrical structure of the study area. We determined the thickness of the caprock and the hydrothermal fluid channel. Finally, we obtained the borehole geothermal steady-state temperature measurement data and water sample chemical analysis data from the logging temperature curves of 24 wells to infer the mode of heat transfer. Based on the results, we built a model of the geothermal system of the sedimentary basin in this area. The results show that the depth of Curie isotherm in the study area is 17–39 km. The resistivity of sedimentary caprock in the north of Songliao basin is low, and there exists a deep heat source, which is mainly thermal convection. In contrast, in Shengli and Tangyuan fault basins, heat conduction is dominant. Based on the geothermal system model, we conclude that the area from Daqing to Lindian in Songliao basin has a thermal-convection-dominated sedimentary basin geothermal system. Heat exchange is realized by the upwelling of mantle-derived thermal materials through fracture channels. The thick sedimentary caprock reduces the heat loss. It can be a target for sustainable development and utilization of HDR. [ABSTRACT FROM AUTHOR]

The travertines of the Fitero thermal springs, with more than 98% of aragonite in most of the samples, are studied in this paper. The main objective is to improve the general understanding of aragonite precipitation, since the deposits of almost pure aragonite are very scarce. This study presents a complete mineralogical and isotopic characterisation, including the evaluation of the δ18O and δ13C fractionation during precipitation, as valuable information for paleoclimate and paleoenvironmental studies. Samples of a laminated travertine deposit constituted by almost pure aragonite were taken from a pipe discharging water at 40 °C. Waters suffered an important CO2 outgassing, as suggested by the geochemical calculations and the δ13C values of travertines and waters. This outgassing triggers the oversaturation and precipitation of carbonate phases. Temperature seems to be the main factor controlling the precipitation of aragonite or calcite, as checked by studying another travertine sample with higher calcite content. Various δ18O isotope fractionation equations for aragonite and calcite were used. The results indicate that precipitation took place close to equilibrium according to some of these equations. The fact that the equilibrium is maintained in a natural system with an important CO2 loss is surprising. However, it can be explained by an HCO3−–water oxygen isotopic equilibrium and a direct transfer of the HCO3− isotope signal to the carbonate without fractionation due to the fast CO2 loss and precipitation. Finally, considering other natural aragonite samples, a fractionation equation is defined for natural aragonite in the temperature range between 23 and 80 °C. [ABSTRACT FROM AUTHOR]

The Southern Volcanic Zone of the Andes has a high potential in terms of geothermal resources and is an exceptional and poorly explored natural laboratory to study the interplay between tectonic stresses, thermal damage, low-permeable crystalline rocks, and fluid flow. Permeability is mostly related to the damage zones associated with the faults controlling regional tectonics, namely, the Liquiñe–Ofqui Fault System and Andean Transverse Faults. This research presents a laboratory approach comprising a characterization of the analogue host rock from a shallow, low-to-medium temperature geothermal system surrounding the Liquiñe area in Southern Chile (39°S) to better constrain intrinsic and extrinsic factors which allow permeable pathways to exist. We analyse the effect of thermal stress at 25, 150, and 210 °C in a granodiorite, measuring some petrophysical properties before and after applying thermal damage, and then loaded the samples until failure. We also compared petrophysical properties with the fracture network characterization using X-ray microcomputed tomography imaging, segmentation, and fluid flow computational simulations. The results show that thermal stress produces intercrystalline microcracks, which result in: (1) an increase in capillary absorption; (2) a decrease in ultrasonic wave velocities; (3) a decrease in compressive strength; (4) a decrease in fracture aperture, and (5) fluid flow simulations indicate that permeability is similar at different temperatures. We conclude that for the granodiorite host rock of the Liquiñe geothermal system, the combined effect of thermal stress, even at low temperature, may constitute an effective mechanism for sustaining permeability at shallowest depths. [ABSTRACT FROM AUTHOR]

The development of the Rittershoffen deep geothermal field (Alsace, Upper Rhine Graben) between 2012 and 2014 induced unfelt seismicity with a local magnitude of less than 1.6. This seismicity occurred during two types of operations: (1) mud losses in the Muschelkalk formation during the drilling of both wells of the doublet and (2) thermal and hydraulic stimulations of the GRT-1 well. Seismicity was also observed 4 days after the main hydraulic stimulation, although no specific operation was performed. During chemical stimulation, however, no induced seismicity was detected. In the context of all field development operations and their injection parameters (flow rates, overpressures, volumes), we detail the occurrence or lack of seismicity, its magnitude distribution and its spatial distribution. The observations suggest the presence of the rock stress memory effect (Kaiser effect) of the geothermal reservoir as well as uncritically stressed zones connected to the GRT-1 well and/or rock cohesion. A reduction of the seismic rate concurrent with an increase of injectivity was noticed as well as the reactivation of a couple of faults, including the Rittershoffen fault, which was targeted by the wells. These results are derived from the homogeneous and consistent catalogue of more than 1300 local earthquakes that is provided. This reference catalogue is based on a standard detection method, whose output was manually verified and improved. The given absolute locations have been computed in a calibrated, geologically realistic 3D velocity model. Our work builds on previous analyses addressing the seismicity induced by the GRT-1 hydraulic stimulation and places the results into a historical context, thus considering the full dynamics of the observed phenomena. This paper also complements existing descriptions of the hydrothermal characteristics of the deep reservoir by providing insights separate from the wells. [ABSTRACT FROM AUTHOR]

The solfataric soil sediments of the hot springs of Sikkim located at Yume Samdung and Lachen valley were studied for deciphering the bacterial diversity. The main aim here is to present a comparative study and generate a baseline data on the post-monsoon seasonal variation for the months of October and December, analyzed through 16S rRNA V3-V4 amplicon sequencing. The results have shown that there is not much variation at phylum level in the month of October in all the three hot springs such as New Yume Samdung (NYS), Old Yume Samdung (OYS), and Tarum (TAR) hot spring. The abundant phyla mainly present were Firmicutes, followed by Proteobacteria, Actinobacteria, and Bacteroidetes. Similarly, in the month of December, Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were prevalent; however, the percent relative abundance of these phyla in the month of December is relatively less. Besides this decrease in percent abundance, it was interestingly seen that relatively more phyla were found contributing towards the bacterial diversity in the month of December. Similar to phylum level, at genus level, there was not much variation seen among various prevalent genera of the three studied hot springs in both months. The major genera prevalent in both months among all the three hot springs were followed by Bacillus, Desulfotomaculum, Lactobacillus, and Paenibacillus. A similar trend was also seen at gene level that relative abundance of various genera was higher in the month of October but more genera were found to be contributing towards bacterial diversity in the month of December. Few distinct genera were found to be more abundant in the month of December such as Rhodopirellula and Blastopirellula. The results may conclude that there is not much variation in the abundance and type of bacterial communities during the post-monsoon season in the month of October and December. However, this may be assumed that there is the accumulation or increase in the bacterial communities during the winter (relatively higher temperature among hot springs) and may favor few mesophilic and more thermophilic communities as well., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

More than 185 hot springs have been recently discovered in the eastern Tibetan Plateau geothermal belt (also called the Kangding-Litang-Batang geothermal belt) (98-102°E, 28-32°N). Among them, more than 60% of springs have temperatures of >40 °C, and 11 springs have temperature higher than the local water boiling point. These hot springs are mostly exposed near the fault or valley areas, as bandings in reservoirs of Triassic carbonate rocks and clastic quartz sandstone or in fractured granite and intrusive rocks. The geothermal belt can be subdivided into the Batang-Xiangcheng geothermal field, the Ganzi-Litang geothermal field, and the Luhuo-Kangding geothermal field, which are controlled by the Jinsa fault, Xiangcheng fault, Litang fault, and Xianshuihe fault, respectively. Radiogenic heat from the Mesozoic and Cenozoic granites, possible ductile crustal flow beneath the lower crust, and frictional heat generated by active strike-slipping along faults are the significant heat resources for the geothermal genesis. Frictional heat caused by the slipping along the Xianshuihe fault is the main thermal source for the Luhuo-Kangding geothermal field, whereas magma melting heat is the main source for the Batang-Xiangcheng geothermal field. Glacier water and river water are the main water supply sources, and the fracture serves as the main channel for runoff and hot water flow. The activity intensity and magnitude of the Kangding-Litang-Batang geothermal anomaly were lower than those of the geothermal fields of Yangbajing and Tengchong in the central and southern Tibetan Plateau, respectively, which indicates that the eastern Tibetan Plateau has a strong heat flow background. [ABSTRACT FROM AUTHOR]

The measurement of ground deformation during a volcanic eruption is one of the main tools for the monitoring of active volcanoes. The deformation is caused by processes that are occurring in the chamber-conduit system, as well as in the geothermal systems that are heated by ascending magma. The influence of the magma chamber and, to a lesser degree, of the conduit on deformation in host rocks is sufficiently well known theoretically, but no studies have been made to investigate the effects of a hydrothermal system on measurable ground deformation during a volcanic eruption. We made a comparative study of the ground deformation due to two deformation-initiating sources: a fissure conduit with a specified excess pressure and a hydrothermal system that was heated by magma flow. We show that the vertical deformation due to the activity of a geothermal system can exceed that due to magma flow by factors of several times. The spatial distributions of the deformation are also substantially different. The vertical displacement due to a geothermal system has its maximum above the fissure conduit, while when the pressure varies in the conduit it induces a local subsidence of the ground; the maximum ground uplift is at a distance of approximately twice the depth to the top of the conduit. The influence of the geothermal system should be incorporated in interpretations of data that come from the monitoring of active volcanoes. [ABSTRACT FROM AUTHOR]

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Flow of undersaturated water in limestone aquifer can cause continuous permeability growth due to dissolution. We have simulated the evolution of permeability field of a 3-D porous limestone aquifer subjected to geothermal temperature gradient and vertical through-flow. The upward flow through porous limestone results in dissolution since calcite is a retrograde soluble mineral. In addition to permeability growth by promoting more dissolution, through-flow also inhibits Rayleigh Benard convection. To understand the temporal evolution of permeability and flow fields, we have performed several simulations with various combinations of initial permeability and through-flow magnitude. Since our computational domain is different in size and boundary conditions from past studies related to buoyant convection in porous medium, we have carried out simulations without reactive alteration to distinguish the hydrothermal systems as stable or unstable. The permeability growth is insignificant in the central part of the reservoir as the temperature gradient vanishes due to forced convection. Permeability growth is more near the edges, where temperature gradients are significant due to conductive heat transfer from the boundaries. For small magnitudes of through-flow, convection rolls are formed near the corners. However, the growth is very localized and rolls never form when magnitude of through-flow is large. [ABSTRACT FROM AUTHOR]

The uplift of the Tibetan Plateau has caused the development of many high-enthalpy geothermal fields that are rich in exploitable rare and dispersed resource elements. However, the mechanism of the unusual enrichment of these resource elements is still unclear. From a geochemical viewpoint, including major chemical compositions, some rare and dispersed resource elements and trace elements in geothermal water and some river samples from the northern Lhasa block (saline lake area), the southern Lhasa block (Gangdise volcanic belt) and Tethyan Himalaya in Tibet, this study provides new insights into the mechanism of the hydrochemical evolution of the Tibetan geothermal system. The Cl-type geothermal waters in the Gangdise volcanic belt and Tethyan sedimentary area show similar chemical characteristics that are apparently different from that of surface cold waters. The concentrations of Sb, Tl, As, K, Cs, Li, Rb, Ga, B, Cl, Th, Sc, Mn, V, and Ti in Cl-type geothermal waters are at least one order of magnitude higher than those in surface cold waters, but the concentrations of Ca, Mg, Ni, Cr, Zn, Fe, Co, Cu, Pb, and U in Cl-type geothermal waters are slightly higher or even lower than those in surface cold waters. Some rivers and streams in Tibet also show high concentrations of toxic elements. These rivers and streams are mainly polluted by geothermal spring discharge and are unsuitable for drinking. Some ions and elements (such as Ca, Mg, Ba, Sr, SO and Mn) in HCO -type geothermal waters from sedimentary rocks are affected by the availability of soluble minerals such as calcite, dolomite and gypsum. However, the other dissolved elements in HCO-type geothermal waters show the characteristic of mixing Cl-type geothermal waters with surface cold waters. The origin of deep fluids in Cl and HCO-type springs is related, and this origin probably involves the contribution of crustal partial melting rather than single rock leaching. Thus, deep circulating groundwater mixes with residual magmatic fluids and evolves into the unusual enrichment of geothermal mineral resources. [ABSTRACT FROM AUTHOR]

Geochemical characteristics and potentially toxic element contents of groundwater, thermal springs, and cold springs of Taftan area in the southeast of Iran examined in two different seasons in order to assess their quality and possible contamination source. Groundwater and spring water samples were collected in May and September 2012 and analyzed for major parameters, anions, cations, and potentially toxic elements. Groundwater is the local source of drinking water and along with cold springs is used for agricultural irrigation. Thermal springs are mainly used for bathing and balneological purposes. For both wells and springs under study, boron was found to have the higher concentration than the specifications in WHO standards except for PF spring. Arsenic, Fe, Mn, Pb, and Ni in thermal springs and most of groundwater samples and cold springs indicate higher concentration than those of WHO standard. The low Na/Ca and Na/K ratios in STS and TTS thermal springs confirm these waters associated with up-flow zones, while higher Na/K ratios for cold springs reveal effects of lateral flows. Conservative elements indicate that thermal springs fall within the hydrothermal field, indicating magmatic affiliation of the thermal waters. High concentrations of trace elements and major ions in well water, thermal springs, and acidic cold springs provide evidences for water-rock interaction processes and the presence of active deep circulations. Saturation indices (SI) show that thermal waters are oversaturated with respect to quartz, chalcedony, alunite, gypsum, celestite, and barite, evident by precipitation of sulfate and siliceous minerals in the most recent precipitates of the geothermal system. The cold springs and groundwater are oversaturated with chalcedony, quartz, hematite (four water wells), and goethite (two water wells), slightly highlighting the mixing of the groundwater with thermal and acidic springs. The SI indicates that the Fe-phase minerals could control mobility of As in the groundwater of the Taftan area. The present study is addressing a significant risk of toxic elements in groundwater resource management, in the volcanic regions in the southeast of Iran, and suggests some preventive measures for controlling adverse effects of using such waters for drinking and irrigation. [ABSTRACT FROM AUTHOR]

Fluid-rock interactions alter the geochemical, isotopic, petrographic and physical character of host rocks, producing a permanent record of hydrothermal activity. Maps of altered rock properties show regular variations that disclose master geologic controls and delineate likely sites for geothermal and mineral resources. In many cases, geochemical and stable isotope data reveal the origins of thermal fluids, and they can also provide estimates of reservoir temperatures and identify zones of fluid recharge. [ABSTRACT FROM AUTHOR]

In geothermal systems, the temperature distribution of heat flow in the wellbore is dependent on the well structure and the geological conditions of the surrounding formation. Understanding of heat transfer in the tubing-casing annulus can reduce the heat losses of wellbore fluid during the production process. The present study discusses the possible means of heat transfer in the annulus, and develops a piecewise equation for estimating the convective heat transfer coefficient with a wider valid condition of 0

In this paper, the hydrochemical isotopic characteristics of samples collected from geothermal springs in the Ilica geothermal field, Eastern Anatolia of Turkey, are examined and described. Low-temperature geothermal system of Ilica (Erzurum, Turkey) located along the Eastern Anatolian fault zone was investigated for hydrogeochemical and isotopic characteristics. The study of ionic and isotopic contents shows that the thermal water of Ilica is mainly, locally fed by groundwater, which changes chemically and isotopically during its circulation within the major fault zone reaching depths. The thermal spring has a temperature of 29-39 °C, with electrical conductivity ranging from 4,000 to 7,510 µS/cm and the thermal water is of Na-HCO-Cl water type. The chemical geothermometers applied in the Ilica geothermal waters yielded a maximum reservoir temperature of 142 °C according to the silica geothermometers. The thermal waters are undersaturated with respect to gypsum, anhydrite and halite, and oversaturated with respect to dolomite. The dolomite mineral possibly caused scaling when obtaining the thermal waters in the study area. According to the enthalpy chloride-mixing model, cold water to the thermal water-mixing ratio is changing between 69.8 and 75 %. The δO-δH compositions obviously indicate meteoric origin of the waters. Thermal water springs derived from continental precipitation falling on to higher elevations in the study area. The δC ratio for dissolved inorganic carbonate in the waters lies between 4.63 and 6.48 ‰. In low-temperature waters carbon is considered as originating from volcanic (mantle) CO. [ABSTRACT FROM AUTHOR]

Stationary regimes of nonisothermal flow of a liquid and its vapor through a porous medium in the gravity field are investigated. Possible flow types are analyzed in the plane of the determining parameters. The analytical results obtained are used in discussing the possibility of finding the pressure and temperature in the interior of a geothermal system from the parameters of the liquid and vapor flow in its permeable surface formations. [ABSTRACT FROM AUTHOR]

The transition to instability of phase interfaces in geothermal systems when a water stratum overlies a steam stratum and the most unstable mode corresponds to zero wavenumber is considered. The nonlinear Kolmogorov-Petrovskii-Piskunov equation describing the evolution of a narrow strip of weakly unstable modes is obtained. This equation is an analog of the well-known Ginzburg-Landau equation corresponding to the case of destabilization of modes with finite wavenumbers. It is shown that in the neighborhood of the critical points there exist two locations of the plane phase interface which coincide at the instant at which the instability threshold is reached and then disappear. [ABSTRACT FROM AUTHOR]

The loss of stability of a vertical phase flow in a geothermal system in which a liquid layer overlies a vapor layer is considered. The loss of stability criteria are obtained in explicit form. It is found that when the physical parameters of the system are varied the transition to phase interface instability can be realized by means of one of the following mechanisms: the transition occurs spontaneously for any perturbation wavenumber (degenerate case); an unstable wavenumber arises at infinity; the instability threshold is determined by a double zero wavenumber. In the latter case the transition to instability is accompanied by simple resonance bifurcation. As a result of this bifurcation, secondary regimes dependent on the horizontal coordinate branch off from the basic regime describing the horizontally-homogeneous vertical phase flows. [ABSTRACT FROM AUTHOR]

The Orange Mountain Basalt of New Jersey is a Mesozoic formation consisting of three units: a single lower inflated sheet lobe about 70 m thick (OMB1), a middle pillow basalt about 10 to 20 m thick (OMB2), and an upper compound pahoehoe flow about 20 to 40 m thick (OMB3). The Orange Mountain Basalt is part of the Central Atlantic Magmatic Province. Quarry and road-cut exposures of OMB1 near Paterson, New Jersey, display some unusual layering that is the focus of this study. OMB1 exposures displays the typical upper crust, core, and basal crust layers of sheet lobes but throughout the Patterson area also display distinct light gray layers of microvesicular basalt mineralized with albite directly over the basal crust and under the upper crust. The lower microvesicular layer is associated with mega-vesicular diapirs. We propose that the upper and lower microvesicular layers were composed of viscous crust that was suddenly quenched before it could devolatilize immediately before the solidification of the core. During initial cooling, the bottom of the basal layer was mineralized with high concentrations of calcite and albite during a high-temperature hydrothermal event. Subsequent albitization, as well as zeolite, prehnite, and calcite precipitation events, occurred during burial and circulation of basin brine heated by recurring Palisades magmatism below the Orange Mountain Basalt. Some of the events experienced by the Orange Mountain Basalt are unusual and place constraints on the fluid dynamics of thick flood basalt flows in general. The late penetration of vesicular diapirs through the entire thickness of the flow interior constrains its viscosity and solidification history. [ABSTRACT FROM AUTHOR]

Tulsishyam thermal springs are located in the Saurashtra region of Gujarat, India with discharge temperatures varying from 39 to 42 °C. The pH of these thermal springs varies from 7.1 to 7.4, indicating neutral character. Though these thermal springs propagate through the near surface layer of Deccan basalt, detailed geochemical analysis of the thermal waters using Piper diagram suggests that the water is interacting with the granitic basement rock. Silica and cation geothermometry estimates have reservoir temperature in the range of 138 to 207 °C categorizing it into a low to moderate enthalpy geothermal system. Furthermore, the area has high heat flow values of 53-90 mW/m2 because of shallow Moho depth. The prevailing conditions suggest that the geothermal energy can potentially be exploited through an enhanced geothermal system (EGS). The study also indicates different mineral phases that may precipitate out of water during exploitation of geothermal energy and it should be taken into account while designing an EGS for the area. [ABSTRACT FROM AUTHOR]