Geothermal Water Research Articles

Geothermal prospecting of a tropical geothermal field – field investigation and water geochemistry of Ambitle Island, Papua New Guinea

ABSTRACT Five sets of water samples were collected in airtight containers using strict sampling protocols for chemistry and isotope analysis. The isotope samples were collected in amber bottles, while the others were collected in 250, 500 ml, and 1L clear containers and treated respectively. Samples were airfreighted to GNS Science for analysis. Ambitle Island’s thermal waters show two distinct characteristics: heated meteoric and mixed geothermal waters. Samples from Nanum and Matangkapok exhibit meteoric water characteristics and are observed to be secondarily heated by mixing with other water sources. Waramong and Balamuson demonstrated high reservoir temperatures, 252 and 260 °C, respectively, and are observed to be a mixture of seawater, meteoric waters, and the deep reservoir. Further work is recommended for comprehensive mapping and sampling, covering alteration minerals, gas, and condensate sampling, and geophysical surveys such as magnetotellurics (MT) and resistivity, to delineate and establish the extent of the reservoir that will subsequently determine the viability of the geothermal field for power generation and other purposes.

Assessment of geothermal waters in Yunnan, China: Distribution, quality and driving factors

Assessment of geothermal waters in Yunnan, China: Distribution, quality and driving factors

Copper Slag Cathodes for Eco-Friendly Hydrogen Generation: Corrosion and Electrochemical Insights for Saline Water Splitting

The increasing demand for sustainable energy and clean water has prompted the exploration of alternative solutions to reduce reliance on fossil fuels. In this context, hydrogen production through water electrolysis powered by solar energy presents a promising pathway toward a zero-carbon footprint. This study investigates the potential of copper slag, an abundant industrial waste, as a low-cost electrocatalyst for the hydrogen evolution reaction (HER) in contact with saline water such as 0.5 M NaCl and seawater, comparing the electrochemical response when in contact with geothermal water from El Tatio (Atacama Desert). The physicochemical characterisation of copper slag was performed using XRD, Raman, and SEM-EDS to determine its surface properties. Electrochemical evaluations were conducted in 0.5 M NaCl and natural seawater using polarisation techniques to assess the corrosion behaviour and catalytic efficiency of the copper slag electrodes. The results indicate that copper slag exhibits high stability and promising HER kinetics, particularly in seawater, where its mesoporous structure facilitates efficient charge transfer processes. The key novelty of this manuscript lies in the direct revalorisation of untreated copper slag as a functional electrode for HER in real seawater and geothermal water, avoiding the use of expensive noble metals and aligning with circular economy principles. This innovative combination of recycled material and natural saline electrolyte enhances both the technical and economic viability of electrolysis, while reducing environmental impact and promoting green hydrogen production in coastal regions with high solar potential. This research contributes to the value of industrial waste, offering a viable pathway for advancing sustainable hydrogen technologies in real-world environments.

Chloride and combined chemical attack of saline solutions on modified oil well cement pastes

Abstract The effect of complex geothermal water composition in comparison with that of a single NaCl solution was studied on cement pastes prepared by partial substitution of cement with silica fume and metakaolin in different proportions. After 90 days of hydration in solutions or water, TGA, XRD, FTIR, ion chromatography, SEM, volume change, and compressive strength (CS) measurements were used to evaluate the impact of solutions on the systems. Higher Al3+ content in blended samples resulted in a greater ability to bind chlorides in Cl–AFm. A lower amount of free Cl− restrained delayed ettringite formation. Less significant volume changes together with the formation of C–(A–)S–H phases promoted by both solutions led to lower porosities and higher CSs than those of referential paste. NaCl solution showed a bigger negative influence than the geothermal one.

Formation and Evolution Mechanisms of Geothermal Waters Influenced by Fault Zones and Ancient Lithology in the Yunkai Uplift, Southern China

Geothermal systems play a crucial role in understanding Earth’s heat dynamics. The Yunkai Uplift in southern China exemplifies a geothermally rich region characterized by ancient lithologies and high heat flow. This study investigates the geochemical characteristics of geothermal waters in the Yunkai Uplift. Both geothermal and non-thermal water samples were collected along the Xinyi–Lianjiang (XL) Fault Zone and the Cenxi–Luchuan (CL) Fault Zone flanking the core of the Yunkai Mountains. Analytical techniques were applied to examine major ions, trace elements, and dissolved CO2 and H2, as well as isotopic characteristics of O, H, Sr, C, and He in water samples, allowing for an investigation of geothermal reservoir temperatures, circulation depths, and mixing processes. The findings indicate that most geothermal waters are influenced by water–rock interactions primarily dominated by granites. The region’s diverse lithologies, change from ancient Caledonian granites and medium–high-grade metamorphic rocks in the central hinterland (XL Fault Zone) to low-grade metamorphic rocks and sedimentary rocks in the western margin (CL Fault Zone). The chemical compositions of geothermal waters are influenced through mixing contacts between diverse rocks of varying ages, leading to distinct geochemical characteristics. Notably, δ13CCO2 values reveal that while some samples exhibit significant contributions from metamorphic CO2 sources, others are characterized by organic CO2 origins. Regional heat flow results from the upwelling of mantle magma, supplemented by radioactive heat generated from crustal granites. Isotopic evidence from δ2H and δ18O indicates that the geothermal waters originate from atmospheric sources, recharged by precipitation in the northern Yunkai Mountains. After infiltrating to specific depths, meteoric waters are heated to temperatures ranging from about 76.4 °C to 178.5 °C before ascending through the XL and CL Fault Zones under buoyancy forces. During their upward migration, geothermal waters undergo significant mixing with cold groundwater (54–92%) in shallow strata. As part of the western boundary of the Yunkai Uplift, the CL Fault Zone may extend deeper into the crust or even interact with the upper mantle but exhibits weaker hydrothermal activities than the XL Fault Zone. The XL Fault Zone, however, is enriched with highly heat-generating granites, is subjected more to both the thermal and mechanical influences of upwelling mantle magma, resulting in a higher heat flow and tension effect, and is more conducive to the formation of geothermal waters. Our findings underscore the role of geotectonic processes, lithological variation, and fault zone activity in shaping the genesis and evolution of geothermal waters in the Yunkai Uplift.

A multi period community energy system optimization model for Arctic and Northern communities considering both thermal and electric loads

Abstract Remote communities across the Arctic continue to rely heavily on fossil fuels for energy sources, which is environmentally damaging and decreases energy security in these regions. Energy system planning models can help communities transition to renewable energy and displace the need for imported diesel. Many studies have developed generation expansion planning (GEP) models to make staged investment decisions. However, few models integrate both electricity and thermal energy needs. In this work, space heating via surface geothermal water is integrated directly into a mixed integer linear programming GEP optimization model, validated on a case study in Pilgrim Hot Springs, Alaska. It was found that a renewably-powered system consisting of wind, solar, and battery storage units was economically superior to a system with diesel, saving over $3457 per year in annualized costs. An analysis of generator capacity lumpiness revealed that a purely renewables system with a hypothetical 20 kW wind turbine (WT) could meet the energy needs of the community for an annualized cost of $13 525, a 24% decrease when compared to a system using a commercially available 100 kW WT. The recommended system met the expressed preferences of the case study community in achieving diesel independence.

Numerical investigation of groundwater aging and thermal processes in confined-unconfined basins with asymmetric flow patterns: The Buda Thermal Karst, Hungary

Abstract Groundwater temperature and age are crucial proxy data that play a fundamental role in understanding regional-scale groundwater flow systems and managing drinking and geothermal water resources. To investigate groundwater flow as well as heat and age mass transport processes in a complex hydrogeological system with deep carbonate sequences and adjoining sedimentary basins (DCSBs), numerical simulations were carried out in two-dimensional synthetic and two- and three-dimensional field-based conceptual environments. The simulations carried out for the Buda Thermal Karst (BTK), Hungary, revealed that the increasing asymmetry in the water table and the appearance of DCSB-type heterogeneity could affect the transition from advection-dominated to conduction- and diffusion-controlled transport processes in the models. However, simultaneously, both effects significantly influence the intensity of groundwater flow. Thermal buoyancy was superimposed on the water table-controlled forced convection (mixed convection), causing significant age mass accumulations in the closed convection cells. To quantify and track the changes in physical processes in the DCSB-type system, the simultaneous use of monitoring parameters calculated in the different parts of the model domain (e.g., unconfined vs confined), contours of groundwater age and temperature, and histograms of normalized groundwater age are presented. The numerical results from the preliminary three-dimensional model were compared to the 14C observation data in the BTK. The groundwater age calculated in the model was of the same order of magnitude as the results of 14C dating from samples taken at different depths in the unconfined and confined parts, and from the deeper mixing zone of the BTK.

Hydrochemical Characteristicsand Evolution of GeothermalWaters from the Gudui–Riruo Geothermal Field, Southern Tibet

The Gudui–Riruo geothermal system, located inthe southernTibet, exhibits higher temperatures compared with other geothermalsystems at similar depths in China. However, the origin and circulationmechanisms of the geothermal water in the Gudui–Riruo geothermalfield remain unclear. Therefore, this study offers a detailed comparativeanalysis of hydrochemical and hydrogen–oxygen isotopic characteristicsof geothermal waters from five geothermal manifestation zones withinthe Gudui–Riruo geothermal system, aiming to improve the understandingof their genesis and circulation mechanisms. Hydrochemical characteristicsindicate that the geothermal waters are notable variations in differentmanifestation zones in the study area. Na–Cl-type geothermalwaters are present in the Buxionglanggu (BXLG), Shagalangga (SGLG),and Babudemi (BBDM) zones, whereas Na·Ca–Cl·HCO3 type waters are distributed in the Chaka (CK) and Riruo (RR)zones. The geothermal waters originate from a common deep parent geothermalfluid with the Cl concentration and enthalpy of 645 mg/L and 1757J/g °C, respectively. Hydrogen and oxygen isotopic characteristicsreveal that the primary source of the Gudui–Riruo geothermalwaters is high-altitude atmospheric precipitation, with about 14%to 18% attributed to mixing with magmatic water. Based on the geologicalbackground of the southern Tibetan Plateau and the hydrochemical andisotopic characteristics of the geothermal waters in the study area,a genesis circulation model for the Gudui–Riruo geothermalsystem is established. Infiltrating meteoric water mixes with residualmagmatic fluid to create the parent geothermal fluid, which then ascendsalong fractures and experiences various cooling processes, resultingin hot springs that exhibit varying hydrochemical characteristics.Based on hydrochemical analysis, five cooling processes have beenidentified for geothermal waters ascending from the reservoir to thesurface: conductive cooling, adiabatic cooling, mixing with cold groundwater,and combinations of these processes.

Fluoride levels in water sources inside the crater of Furnas volcano: Potential health implications for local communities and tourists.

Fluoride, a naturally occurring mineral, is widely recognized for its dual role in human health. At optimal concentrations, it provides dental benefits; however, excessive fluoride can lead to dental and skeletal fluorosis. Volcanic regions are known for their geothermal water sources that contain elevated levels of fluoride, raising concerns about potential health impacts on local populations. This study focuses on the Furnas volcano region at the Island of São Miguel, Azores, where natural springs are promoted for their therapeutic and medicinal properties. However, these springs also raise concerns about health risks due to fluoride exposure, as they are freely consumed by locals and tourists without any formal treatment or monitoring. Eighteen water samples were collected from natural springs in the village of Furnas. In situ measurements were taken forphysicochemical parameters such as pH, temperature, and conductivity. Fluoride concentrations were quantified using a potentiometric method with a fluoride ion-selective electrode. To assess risks, we estimated daily fluoride intake (DFI) and calculated the Hazard Quotient (HQ) for both children and adults. The fluoride concentrations in the samples ranged from 0.47mg/L to 5.48mg/L, with 72% exceeding the recommended limit of 1.5mg/L for drinking water. Significant correlations were found between temperature, conductivity, and fluoride concentration. Hazard Quotient values indicated potential health risks for children consuming untreated spring water. Waters categorized as hypothermal exhibited significantly lower fluoride concentrations compared to mesothermal, thermal, and hyperthermal samples. These findings highlight the impact of volcanic activity on fluoride levels in the natural springs of Furnas, emphasizing the need for regular monitoring and public awareness. While these waters are frequently consumed for their perceived health benefits, elevated fluoride levels may pose health risks to residents and tourists, demanding informed decision-making and enhanced water safety measures.

Multi-isotope characteristics and residence time of saline geothermal waters in the coastal area of Xiamen bay, southeast China

Multi-isotope characteristics and residence time of saline geothermal waters in the coastal area of Xiamen bay, southeast China

Research progress in isotope geochemistry of geothermal water systems

Research progress in isotope geochemistry of geothermal water systems

Fluoride enrichment in geothermal waters based on H, O, Sr, and Li isotopes of the Taiyuan Basin, North China

Fluoride enrichment in geothermal waters based on H, O, Sr, and Li isotopes of the Taiyuan Basin, North China

Genesis Mechanism of Geothermal Water in Binhai County, Jiangsu Province, China

Taking the coastal area of Binhai County, Jiangsu Province, as an example, this study first investigated the basic natural geography and the regional geological and hydrogeological conditions of the study area, and then carried out in-depth geophysical prospecting, hydrogeological tests, geothermal temperature monitoring, hydrochemistry and isotope analyses, and other studies based on the results to comprehensively and systematically reveal the genesis mechanism of the geothermal water resources of this coastal area from multiple perspectives. The results showed the following: the geothermal water in this area mainly comes from atmospheric precipitation; the deep east–northwest interlaced fracture is the recharge and transportation channel; the Cambrian–Ordovician carbonate rock layer, enriched by the development of cavernous fissures, forms the thermal storage layer; the underground heat mainly comes from the upward heat flow along the deep fracture and the natural warming of the strata; and the thermal reservoir cover comprises Paleozoic and Mesozoic clastic rocks that have a high mud content and form a thick layer. The genesis mode of this area is as follows: the atmospheric precipitation infiltrates and is recharged through the exposed alpine carbonate fissures in the Lianyungang area, and then it is transported to the south along the large deep fracture under the action of a high hydraulic pressure head; meanwhile, it is heated by the heat flow in the deep part of the fracture and water–rock interactions with the strata occur. Geothermal water with a calculated thermal storage temperature of 83.6 °C is formed at a depth of 2.9 km, which is blocked by the intersection of the northeast and northwest fractures to form a stagnant zone in the coastal area.

Mine Water as an Energy Source: Overview of Technical Basics, Existing Plants, and Monitoring Results

Abstract As a renewable energy source, geothermal mine water systems utilize abandoned mines for heating and cooling and contribute to the reduction of CO2 emissions. There are five different systems for mine water heat recovery, including both open and closed types. A comprehensive review of geothermal mine water systems worldwide, both planned and existing, as well as their accompanying studies, shows that such systems have already been installed as heating and cooling applications at more than 51 sites. Approximately 85 MW of heating and 20 MW of cooling capacity worldwide are currently provided by geothermal mine water systems, and due to rising energy prices, new systems are increasingly being planned and installed. Most systems have supplied single properties with heating and cooling capacities below 200 KW; however, a trend towards larger systems that are able to provide energy for entire neighborhoods or districts can be observed. In this study, a comparison of monitoring results of four locations in Europe and North America shows that the parallel use of mine water for heating and cooling can achieve seasonal performance factors (SPF) of up to 10 for the overall system. Thus, even with high electricity prices, operational costs for geothermal mine water energy of between 5 and 10 ct/kWh heat are possible. Therefore, depending on fossil energy prices, performance factors of over 3 (Europe) or over 3.5 (USA) are feasible.

Distribution characteristics and geological significance of fluorine element in hot spring water from a typical geothermal area in western Henan province, China

ABSTRACT To investigate the occurrence characteristics and fluorine enrichment mechanisms in geothermal spring water in western Henan Province of China, hydrochemical analyses were conducted on the Shangtang, Zhongtang, Wentang, Xiatang, and Jianchang hot springs in the Lushan area. The results indicated that the geothermal water in the study area was primarily HCO3·SO4 − Na, followed by SO4·HCO3 − Na, with the cation content exhibiting the trend Na+>Ca2+>K+>Mg2+, and the anion content following the order HCO3->SO42->Cl->F->NO3-. The pH ranged from 8.21 to 8.57, indicating a weak alkalinity. The chemical composition of the hot springs across different areas remained relatively consistent, suggesting similar genesis patterns and recharge sources. Correlation analysis revealed that F− was strongly associated with Ca2+ (r = 0.89) and Mg2+ (r = 0.55), whereas the correlations with Na+, K+, CO32-, and SO42- were 0.13, 0.36, 0.02, and 0.05, respectively, indicating that F– in hot springs was primarily derived from fluorspar-type, dolomite-type, and mica-type minerals. Based on regional geological data, the spatial distribution, runoff, recharge, and discharge of geothermal hot springs were controlled by regional fault structures, while the fluorine content in hot spring water was closely linked to the surrounding rocks.

Characteristics of Heat-Depleted Thermal Water Re-Injection-Induced Water–Rock Interactions in a Sandstone Reservoir Containing Carbonate and Silicate Minerals (Szentes, Hungary)

A thorough understanding of the chemistry involved in reinjecting heat-depleted geothermal water into poorly consolidated sandstone is vital for the effective design of treatments targeting subsurface rock formations. The intricate chemical interactions occurring within sandstone systems can result in the dissolution of certain minerals and the subsequent precipitation of others, which may significantly contribute to damage within the formation. This process can alter the physical properties of the rock, potentially leading to reduced permeability and other challenges in resource extraction. Thus, it is imperative to monitor not only the concentration of various chemical species present in the geothermal water and sandstone, but also the spatial distribution of these geochemical reactions. By doing so, we can better predict and mitigate their potential adverse effects on rock formations, ensuring the long-term success and efficiency of geothermal energy extraction and other subsurface activities. In this study, we conducted laboratory experiments using both model and natural formation waters, as well as rock samples, to investigate water–rock interactions in a sandstone reservoir in the Szentes area of Hungary. Geochemical models were run with two different thermodynamic databases to simulate laboratory experiments, predict the effects of heat-depleted geothermal water reinjection into the reservoir, and assess predictions of different geochemical databases. Our study shows that calcite dissolves while quartz, kaolinite, and dolomite form. Other mineral reactions, however, remain less certain. The PHREEQC database indicates chlorite dissolution along with the formation of small amounts of feldspars and hematite, whereas the Thermoddem database predicts montmorillonite dissolution and chlorite precipitation. The reservoir porosity and permeability are expected to change over time as a result of mineral reactions. Modeling results, however, indicate negligible porosity changes as the reservoir reaches equilibrium state. The general concept proposed here, which focuses on the geochemical properties of the reinjected water and reservoir, provides a framework for detailed analysis of the geothermal system—a critical step for ensuring sustainable geothermal operations.

Hydrogeochemistry and Heat Accumulation of a Mine Geothermal System Controlled by Extensional Faults

Given the high proportion of global fossil energy consumption, the Ordovician karst water in the North China-type coalfield, as a green energy source that harnesses both water and heat, holds significant potential for mitigating environmental issues associated with fossil fuels. In this work, we collected geothermal water samples and conducted borehole temperature measurements at the Xinhu Coal Mine in the Huaibei Coalfield, analyzed the chemical composition of regional geothermal water, elucidated the characteristics of thermal storage, and explored the influence of regional structure on the karst geothermal system in the northern region. The results indicate that the geothermal water chemistry at the Xinhu Coal Mine is of the Na-K-Cl-SO4 type, with its chemical composition primarily controlled by evaporation and concentration processes. The average temperature of the Ordovician limestone thermal reservoir is 48.2 °C, and the average water circulation depth is 1153 m, suggesting karst geothermal water undergoing deep circulation. The geothermal gradient at the Xinhu Coal Mine ranges from 22 to 33 °C/km, which falls within the normal range for ground-temperature gradients. A notable jump in the geothermal gradient at well G1 suggests a strong hydraulic connection between deep strata within the mine. The heat-accumulation model of the hydrothermal mine geothermal system is influenced by strata, lithology, and fault structures. The distribution of high ground-temperature gradients in the northern region is a result of the combined effects of heat conduction from deep strata and convection of geothermal water. The Ordovician limestone and extensional faults provide a geological foundation for the abundant water and efficient heat conduction of the thermal reservoirs.

Mechanisms of lithium and cesium enrichment in the Semi-Dazi geothermal field, Qinghai-Xizang Plateau: insights from H–O–Li–Sr isotopes

Hot springs in the southern Qinghai-Xizang Plateau show anomalous lithium (Li) and cesium (Cs) enrichment, but the mechanisms driving this enrichment remain poorly constrained. Using multi-isotope tracers (H, O, Li, Sr), we investigate the Semi-Dazi geothermal field, which hosts the Plateau’s highest recorded geothermal Cs concentrations. The system comprises two geographically separated geothermal areas: Semi and Dazi, spaced ~ 15 km apart, displaying distinct hydrogeochemical signatures. Semi hot springs show significantly higher Li (34.2 to 35.6 mg/L) and Cs (49.8 to 52.7 mg/L) concentrations than Dazi (Li: 11.4 to 21.1 mg/L; Cs: 21.5 to 37.7 mg/L). Isotopic contrasts further differentiate the areas: Semi exhibits elevated δ7Li (1.53 to 1.91 ‰) and lower 87Sr/86Sr (0.739 to 0.741), whereas Dazi shows δ7Li values of − 0.25 to 1.24 ‰ and 87Sr/86Sr ratios of 0.742 to 0.759. Two key processes govern enrichment: (1) atmospheric recharge infiltrates Li–Cs-rich strata, where high-temperature water–rock interactions (217 °C at Semi and 197 °C at Dazi reservoirs) mobilize these elements into geothermal waters; (2) phase separation during ascent causes differential steam loss (Semi: 24%, concentration factor 1.32; Dazi: 8 to 21%, 1.08 to 1.26). Secondary processes (cold water mixing, conductive cooling, mineral adsorption) further modify surface hot springs geochemistry. Semi-Dazi geothermal field illustrates how a shared geothermal system can yield chemically distinct fluids from separate reservoirs characterized by differing hydraulic connectivity and circulation pathways. Geyserite deposits and high reservoir temperatures suggest that a crustal partial melt layer adds extra heat, intensifying water–rock reactions. The occurrence of Li–Cs-rich springs on the Plateau is intrinsically linked to elevated concentrations of these elements in underlying crustal source rocks and spatially associated with deep, extensive fault systems, particularly at fault convergences. These findings underscore the necessity of multi-isotope models for interpreting geothermal Li–Cs anomalies in continental collision zones, with implications for strategic mineral exploration.

Organic Manure Tests on the Yield and Nutritional Content of the Duckweed (Lemna minor L.) Cultivated in the Geothermal Waters in Southeastern Algeria

Organic Manure Tests on the Yield and Nutritional Content of the Duckweed (Lemna minor L.) Cultivated in the Geothermal Waters in Southeastern Algeria

Delineating the controlling mechanisms of geothermal waters quality and suitability zoning in the Lower Yellow River Basin, China

Delineating the controlling mechanisms of geothermal waters quality and suitability zoning in the Lower Yellow River Basin, China