Geothermal Reservoir Temperature Research Articles

Hydrogeochemical Characteristics and Genesis of Hot Springs in Da Qaidam Area, Northern Qaidam Margin of the Qaidam Basin

Hydrogeochemical research on fluids is an effective method to understand the formation mechanism, occurrence environment, and circulation process of groundwater. The groundwater sampling sites are located in the town of Dachaidan on the northeastern edge of the Tibetan Plateau, which was selected as the study object. Samples were collected from hot and cold springs and surface water in the area. This study is based on the analysis of water chemistry and isotopes, and aims (1) to discuss the chemical characteristics of groundwater in Da Qaidam, (2) to estimate the deep reservoir temperatures, recharge elevation and circulation depth of geothermal waters, and (3) to figure out the heat source beneath the geothermal area and its genetic mechanism. The result showed the following: The hydrochemical type of the hot spring is Cl·SO4-Na and Cl-Na, and the hydrochemical type of cold spring is SO4·HCO3-Na·Ca and Cl·HCO3·SO4-Ca·Na. The main source of groundwater recharge is snow and ice melt water. The recharge elevation ranges from 4666.8 m to 5755.9 m. The geothermal reservoir temperature is about 119.15–126.6 °C. Ice and snow melt water infiltrate into the high mountainous areas on the north side of Da Qaidam and circulate underground through the developed deep and large fractures. Part of the groundwater migrates upwards under the water conduction of the Da Qaidam fault fracture zone to form cold springs, while another part is heated by deep circulation and exposed to the surface in the form of medium to low temperature tectonic hot springs. The research results can provide a scientific basis for geothermal resource exploitation and utilization in Qinghai Province.

Analisis Karakteristik Fluida dan Estimasi Temperatur Reservoir Desa Sawangan Kabupaten Minahasa Utara

Geothermal energy is the heat stored within the Earth’s subsurface rocks and the fluids contained within them. Indonesia, located on the Ring of Fire, has significant geothermal potential, particularly in North Sulawesi. This study aims to assess the geothermal energy potential in Sawangan Village, North Minahasa Regency, specifically at the Kepangian River hot springs. The research was conducted by analyzing the fluid characteristics and estimating the geothermal reservoir temperature using geochemical fluid analysis and geothermometer calculations. The analysis Involved laboratory testing of fluid samples, followed by data processing using Na-K and silica geothermometers, and plotting on a Na-K-Mg ternary diagram. The results indicate that the fluid type at the Kepangian River hot springs is immature water, with an estimated reservoir temperature ranging from 240.04°C to 267.01°C, which classifies it as a high-temperature reservoir.

Geochemical characteristics, Li source and genesis mechanism of thermal mineral water in Sichuan Basin, SW China

Thermal mineral water (temperature >25 °C) is a valuable resource, especially when it contains a certain amount of Li. In this study, an attempt was made to elucidate the factors affecting spatial distribution of lithium (Li) resources and interpret the formation mechanisms of thermal mineral waters in the Sichuan Basin. The spatial distribution, reservoir temperatures, and hydrochemical characteristics of thermal mineral waters were systematically analyzed in the Sichuan Basin, preliminarily revealing Li sources through hydrochemical methods. Results are showed as follows: (1) The Li-bearing (Li ≥ 1 mg/L) thermal mineral waters are mainly distributed in the southwestern part of the Sichuan Basin. There are three sites of thermal mineral waters with Li content greater than 25 mg/L with the hydrochemical type of Cl–Na type: Pengji Well (37.7 mg/L), Foguanghu Well (99.5 mg/L) and Zhougongshan New Well (118.0 mg/L). Among them, the Foguanghu Geothermal Well and the Zhougongshan New Well have high Li content and low Mg/Li (10.7 and 2.5), indicating great potential for utilization. (2) The Li-bearing thermal mineral waters are mainly formed in the fissure and pore reservoirs of the Middle–Lower Triassic. They are mainly affected by the dissolution of halite minerals and the deeply buried ancient seawater of the Triassic. The Li-bearing thermal mineral waters possess high contents of total dissolve solids (TDS) (4.3–230.0 g/L), Cl (0.7–142.9 g/L), Na (0.5–76.7 g/L), K (0.1–52.0 g/L), B (4.1–739.6 mg/L), and Li (1.5–118.0 mg/L). Moreover, the temperature of the geothermal reservoir ranges from 40 to 150 °C. The geothermal reservoir temperatures calculated by K–Mg and Mg–Li geothermometers are positively correlated with the Li content. (3) The Li source of the thermal mineral waters of the Sichuan Basin are dominated by multiple factors: first, Li concentration by evaporation, concentration and deep-seated metamorphism of ancient Triassic seawater; second, water–rock interaction between deep thermal mineral waters and mung bean rock or Emeishan basalt; and third, active tectonic activity and deep faulting induced upward flow of Li in deep fluids. This research enhances understanding of the formation of thermal mineral waters in the Sichuan Basin, offering scientific basis for the exploitation of Li resource.

A Method for Determining Target Areas of Hot Dry Rock Resources: A Case Study in Continental China

Geothermal resources have been recognized as important sources of clean renewable energy. The exploration, development, and utilization of geothermal resources, especially hot dry rock (HDR) resources, are highly important for achieving peak carbon and carbon neutrality. However, there is no comprehensive evaluation method for determining HDR target areas, and the evaluation scale and application disciplines are relatively simplistic. In this paper, we sought to optimize the identification of HDR target areas through a multiscale and multidisciplinary method and formed a set of generalized and demonstrative processes to guide the exploration of HDR resources. Through practical application to the Gonghe Basin and the Zhangzhou Basin, it was found that the comprehensive geothermal conditions of the Gonghe Basin are superior to those of the Zhangzhou Basin, and the geothermal reservoir depth, geothermal reservoir temperature, geothermal gradient, and heat flow are the four most important factors affecting hot dry rock geothermal resources. Using this method, the prioritization of target areas changes from a qualitative study to a quantitative and semiquantitative study, increasing the specificity and reliability of the decision-making process.

Representative High-Temperature Hydrothermal Activities in the Himalaya Geothermal Belt (HGB): A Review and Future Perspectives

Southern Tibet and western Yunnan are areas with an intensive distribution of high-temperature geothermal systems in China, as an important part of the Himalayan Geothermal Belt (HGB). In recent decades, China has conducted systematic research on high-temperature geothermal fields such as Yangbajing, Gudui, and Rehai. However, a comprehensive understanding has not yet been formed. The objective of this study was to enhance comprehension of the high-temperature geothermal system in the HGB and to elucidate the hydrogeochemical characteristics of geothermal fluids. This will facilitate the subsequent sustainable development and exploitation of domestic high-temperature hydrothermal geothermal resources. To this end, this study analysed geothermal spring and borehole data from the Yangbajing, Gudui, and Rehai geothermal fields. Based on previous research results, the source, evolution, and reservoir temperature characteristics of geothermal fluids are compared and summarised. The main high-temperature geothermal water in the geothermal field is derived from the deep Cl-Na geothermal fluid. Yangbajing’s and Gudui’s geothermal waters are primarily recharged by snow-melt water, while Rehai’s geothermal water is mainly recharged by local meteoric water. The average mixing ratios of magmatic water in the Yangbajing, Gudui, and Rehai geothermal fields are 17%, 21%, and 22%, respectively. The Yangbajing and Gudui geothermal fields have a relatively closed geological environment, resulting in a stronger water–rock interaction compared to the Rehai geothermal field. As geothermal water rises, it mixes with shallow cold water infiltration. The mixing ratios of cold water in the Yangbajing, Gudui, and Rehai geothermal fields are 60–70%, 40–50%, and 20–40%, respectively. Based on the solute geothermometer calculations, the maximum geothermal reservoir temperatures for Yangbajing, Gudui, and Rehai are 237 °C, 266 °C, and 282 °C, respectively. This study summarises and compares the hydrogeochemical characteristics of three typical high-temperature geothermal fields. The findings provide an important theoretical basis for the development of high-temperature geothermal resources in the Himalayan Geothermal Belt.

The Hydrogeochemistry of and Earthquake-Related Chemical Variations in the Springs along the Eastern Kunlun Fault Zone, China

The Eastern Kunlun Fault (EKF) is situated in an area with a history of significant seismic events, yet it has witnessed a dearth of major earthquakes in recent years. This study conducted a detailed analysis of the hydrogeochemical characteristics of the springs in the EKF and their temporal variation, aiming to address the gaps in the research on the hydrogeochemistry in the region and to investigate the changes in water chemistry during the seismogenic process. In this study, the main elements, trace elements, hydrogen isotopes, oxygen isotopes, and strontium isotopes of 23 springs in the EKF were analyzed. The results indicated that the groundwater recharge in the eastern part of the Eastern Kunlun Fault Zone mainly originates from atmospheric precipitation, as supported by its isotopic characteristics. The spring water is immature, showing weak water–rock interactions. A hydrochemical analysis classified the springs into 11 main types, reflecting varying degrees of water–rock interaction. Based on measurements using quartz geothermometers, the estimated geothermal reservoir temperatures ranged from 39.6 to 120.3 °C, with circulation depths of 1.3 to 3.8 km. By means of regularly monitoring three selected springs, this study also explored the relationship between earthquakes and hot spring chemical variations. Finally, a conceptual model of hydrogeochemistry was proposed to describe the groundwater circulation in the study area.

Assessment of the geothermal potential zone of India utilizing GIS-based multi-criteria decision analysis technique

India, with 80 % energy demand reliant on fossil fuels, is the world's third-largest greenhouse gas emitter, necessitating a shift from fossil fuels to renewable energy. While solar and wind production has grown, geothermal energy remains untapped despite enormous prospects in the country. In this regard, India's first regional-scale geothermal potential (GP) map has been prepared using a GIS based on a multi-criteria decision analysis technique. Five thematic layers (geology, fault, heat flow, thermal spring, and earthquake epicenter) have been used to calculate GP index, which is divided into high, moderate, and low categories. The result shows that most geothermal drilling sites are distributed in the high GP category zone, showing high efficacy. Further, a joint study of the geothermal surface and reservoir temperature with the present study shows that the northern and western parts of India have significant potential for geothermal exploration. Our result also reveals that the projected CO2 emissions are approximately 2.6 gigatons (which is lower than other energy sources) for an output of 10 GW using geothermal energy in the next 75 years. This study can enhance geothermal prospect identification, cutting exploration costs, and site selection, and contributing to multiple UN Sustainable Development Goals.

AOSMA-MLP: A Novel Method for Hybrid Metaheuristics Artificial Neural Networks and a New Approach for Prediction of Geothermal Reservoir Temperature

To ascertain the optimal and most efficient reservoir temperature of a geothermal source, long-term field studies and analyses utilizing specialized devices are essential. Although these requirements increase project costs and induce delays, utilizing machine learning techniques based on hydrogeochemical data can minimize losses by accurately predicting reservoir temperatures. In recent years, applying hybrid methods to real-world challenges has become increasingly prevalent over traditional machine learning methodologies. This study introduces a novel machine learning approach, named AOSMA-MLP, integrating the adaptive opposition slime mould algorithm (AOSMA) and multilayer perceptron (MLP) techniques, specifically designed for predicting the reservoir temperature of geothermal resources. Additionally, this work compares the basic artificial neural network and widely recognized algorithms in the literature, such as the whale optimization algorithm, ant lion algorithm, and SMA, under equal conditions using various evaluation regression metrics. The results demonstrated that AOSMA-MLP outperforms basic MLP and other metaheuristic-based MLPs, with the AOSMA-trained MLP achieving the highest performance, indicated by an R2 value of 0.8514. The proposed AOSMA-MLP approach shows significant potential for yielding effective outcomes in various regression problems.

Distinct response of deep and shallow geothermal reservoir temperature following earthquakes in the Kangding Fault zone hydrothermal system

Study regionAs part of the active Xianshuihe Fault system, the Kangding geothermal field is a representative high-temperature hydrothermal system in the southeastern Tibetan Plateau, China. The strong tectonic and hydrothermal activity serves as a unique location to study the interaction between earthquakes and geothermal fluids. Study focusWe have collected water samples taken from thermal springs and boreholes in the geothermal field to identify fluid composition and reservoir temperature of the deep granite and shallow metamorphic rock using geochemical analysis and the Integrated Multicomponent Geothermometry (IMG) method. Two typical thermal springs that offer long-term hydrochemical data were selected to investigate the effect of earthquakes on the shallow and deep reservoir temperatures. New hydrological insights for the regionThe deep reservoir temperature in the Kangding geothermal field is in the range 222 ℃ to 256 ℃, while the shallow reservoir temperature ranges from 128 ℃ to 171 ℃. Both thermal springs show changes in reservoir temperature following the 2008 Wenchuan, the 2013 Lushan, and the 2014 Kangding earthquakes. The temperature changes are similar in the deep reservoir of the two springs but different in the case of the shallow reservoir. We propose that the changes in reservoir temperature, steam fraction, and dilution factor indicate that the deep reservoir is more sensitive to earthquake-induced permeability changes than the shallow reservoir.

Reservoirs and Hydrogeochemical Characterizations of the Yanggao Geothermal Field in Shanxi Province, China

Geothermal water is the product of deep circulation within the crust, and the understanding of its hydrogeochemical process can provide effective information for integrated research on its circulation pattern and formation mechanism. Based on the geothermal geological conditions of the Yanggao geothermal field, this study analyzed water samples from thermal springs and geothermal wells in the geothermal field, ascertaining their hydrochemical components, along with their hydrogen and oxygen isotopes. Using methods like piper diagrams, ionic component ratio characterization, Na–K–Mg equilibrium diagrams, and reverse path simulations, this study elucidated the recharge source of geothermal water in the study area, revealed the water–rock interactions the geothermal water experienced, and evaluated the geothermal reservoir temperatures. The results show that the geothermal water has hydrochemical types of Na–Cl–HCO3 and Na–HCO3–Cl, and is primarily recharged by the atmospheric precipitation in the northern mountainous area. The geothermal water has experienced extended water runoff and deep thermal circulation, and its hydrochemical composition primarily results from the weathering and dissolution of silicate rocks and evaporites. The major hydrogeochemical processes of the geothermal water involve the dissolution of calcite, dolomite, gypsum, and kaolinite. In addition, the canon-exchange also changes the chemical component of the geothermal water. The SiO2 Geothermometer, a multimineral equilibrium diagram, and the silica–enthalpy model reveal the presence of deep and shallow geothermal reservoirs in the study area, which exhibit temperatures of 73 °C and ranging from 125 to 150 °C, respectively. The open geothermal reservoir environment results in the mixing of geothermal water and cold water, with shallow and deep geothermal water mixing with cold water at ratios of 57% and 76%, respectively.

Hydrogeochemical and geothermal features of thermal springs along the Ganzi-Yushu fault, eastern Tibetan Plateau and its geological implications

Important fault zone processes can be discerned from the hydrothermal fluid circulation associated with active seismic sources. This study focused on the geochemical and isotopic features of the thermal waters along the Ganzi-Yushu fault (GZYSF) located in the eastern Tibetan Plateau. 22 spring samples were collected to characterize the chemical compositions and calculate the geothermal reservoir temperatures. The hydrothermal waters are mainly recharged by meteoric water based on the δ18O and δ2H values. Immature waters with a Na + -HCO3- or Ca2+(Mg2+)-HCO3- composition were recognized in the study area, combined with the poor correlation between K+, Na+, Mg2+, HCO3− and Cl− suggesting a shallow hydrothermal fluid source. The 87Sr/86Sr ratios and high concentrations of B (from 20.3 to 9445 μg/L) and Li (from 3.04 to 2380 μg/L) show a dissolution of silicate minerals containing calcium and magnesium during fluid circulation. The geothermometry in the silicon-enthalpy system suggested equilibrium temperatures up to 146 °C, whereas most are low temperatures. The shallow geothermal fields along GZYSF show that most large earthquakes (M＞5) were distributed in the transitional zone between high-value area and low-value area of the shallow geothermal field, suggesting a potential genetic link between geothermal field structure and earthquake nucleation along active faults. In conclusion, we proposed a conceptual model to portray the fluid circulation process. Such work can provide insights into the potential geothermal resource in Tibetan Plateau, and also investigate the processes controlling the fluid chemistry and the correlation with occurrence of earthquakes in the region.

Multi-index-weighted geothermometer estimation of geothermal reservoir temperature: Applications and future directions

Geothermal reservoir temperature (GRT) is an important factor for estimation of geothermal resources and exploitative potential. Errors in the estimated temperature of a geothermal reservoir can likely result from the use of a single geothermometer or the average. Therefore, there is an urgent need for novel and more accurate methods for estimating GRT. Taking Yitong Basin, China as the study area, this study collected water samples and measured the geothermal water temperature of 26 geothermal wells. After application of the improved entropy method (IEM) to the collected data, a multi-index weighted geothermometer (MIWG) was proposed. The MIWG provided the most accurate estimation of temperature, with average errors in temperature estimation for quartz, chalcedony, Na–K, K–Mg, and MIWG of 57.58 %, 15.86 %, 29.92 %, 42.03 %, and 11.94 %, respectively. This novel approach to estimating GRT has clear advantages, including wide applicability, and can provide a new pathway for future related research.

Geochemical Investigations of the Geothermal Waters in the Kangding Area, SW China: Constraints from Hydrochemistry and D-O-T Isotopy

Geothermal resources, as a representative of clean energy, has been paid significant attention in the world. Due to active neotectonics and widespread magmatic rocks, the abundant geothermal waters in the Kangding area have been investigated. Hydrochemistry and D–O–T isotopy studies were carried out to clarify the genetic mechanism of geothermal waters. The hydrochemical types of geothermal waters are mainly Ca2+–Na+–HCO3− type, Na+–Cl−–HCO3− type, and Na+–HCO3− type. Silicate dissolution and the cation exchange process are the water–rock interactions determining hydrochemical compositions. The recharge elevation of geothermal water was calculated to be 3034–3845 m, with an average of 3416 m. The reservoir temperatures of shallow and deep geothermal reservoirs vary from 50 to 115 °C and from 114 to 219 °C, respectively, and the mixing ratio of cold water is 0.56–0.89. These findings help to reveal the genetic mechanism of geothermal waters in the Kangding area.

Probabilistic Geothermal resources assessment using machine learning: Bayesian correction framework based on Gaussian process regression

Accurate determination of geothermal resources in the study area is of great importance for effective exploration and development. In the present study, geothermal resources in Qianguo County, Jilin Province, China, were selected as the research object, and we used the random forest sensitivity analysis method to determine the five most influential parameters among the nine parameters involved in the volumetric method: geothermal reservoir thickness (H), geothermal reservoir temperature (T), geothermal reservoir area (A), thickness porosity (Φ), and rock density (ρw). Among them, the uncertain parameters H and T show a significant positive effect on the output results. These parameters and geothermal resources estimated by volumetric method based on Monte Carlo were used as input parameters in the Gaussian process simulation, and the squared exponent (SE) with fewer hyperparameters was selected as the Gaussian process regression kernel function. During the analysis, six groups of different hyperparameter combinations were set, and the Earth Mover's distances (EMD) was applied to compare the priori distribution and simulation results with the posterior distribution (true distribution). The simulation results that are closest to the target distribution of geothermal resources were used as the final results of geothermal resources calculation. Based on the obtained results, it was concluded that the Qingshankou and Quantou formations located in the southern Changling sag have good geothermal development potential which the geothermal resources are 5.80 × 1010 kJ·km−2 and 6.22 × 1010 kJ·km−2, and the probability of occurrence is 4.65%, and 3.69%.

Numerical study of the long-term performance of EGS based on discrete fracture network with consideration of fracture deformation

During heat extraction in fractured reservoir, the perturbation of pressure, stress, temperature could alter the fracture aperture, which feeds back to the long-term performance of EGS. In this work, a 3D THM coupled model was developed for the long-term performance based on the discrete fracture network. The apparent improvement of this model is both shear dilatancy and normal closure/opening are considered in a complete constitutive relationship under the THM coupled framework TOUGH2M-FLAC3D. The feasibility is verified and validated through comparing with analytical solution and previous numerical work. In application of the new approach in a fractured reservoir, it is found that the phenomenon of channel flow will concentrate the heat mining in partial fractures, and the fracture enhancement further reinforce the channel flow. The pressure effect on fracture transfers faster than the thermal effect. In the sensitivity analysis, the zero-stress aperture has a positive impact on heat extraction. Higher thermal expansion coefficient promotes the heat extraction as well. While, the dilation angle in this work has a neglectable impact on heat extraction performance. The thermal effect accounts for the most fracture variation under high thermal expansion coefficient. Therefore, the thermal effect should be considered especially in high temperature geothermal reservoir.

Surface geochemical anomaly pattern of medium-to-high temperature geothermal systems in South China and its application

The existence of thermal storage will correspondingly increase the temperature of surrounding strata and promote the continuous expansion, volatilization, upward migration, and loss of gas in the strata. As a result, a low-concentration gas field will be formed in the strata above geothermal reservoirs. Geothermal reservoirs could in turn heat formation water and increase the solubility of soluble inorganic salts in the surrounding rocks and the total dissolved solids (TDS) content in the formation water. Since water can strongly wet and permeate strata, the dissolved inorganic salts migrate into upper strata along with water, giving rise to the formation of a high-concentration inorganic salt field in the strata above geothermal reservoirs. A higher geothermal reservoir temperature corresponds to more significant characteristics mentioned above. Therefore, a medium-to-high temperature geothermal system has a surface geochemical anomaly pattern of high inorganic salt concentrations and low gas concentrations (also referred to as the high-salt and low-gas pattern). This pattern is applied to the surface geochemical exploration of the two geothermal fields in Guangdong Province, i.e., the Huangshadong geothermal field in Huizhou City and the Xinzhou geothermal field in Yangjiang City, revealing low-concentration gas fields above both. The application results also show that the exposed thermal spring water in both geological fields has higher concentration of dissolved inorganic salt than the surface water and nearby seawater, forming high-amplitude anomalies on the surface above geothermal reservoirs. These characteristics, as well as the measured temperature at known geothermal wells, verify the validity of the high-salt and low-gas pattern of medium-to-high temperature geothermal systems proposed in this study. Moreover, the high-salt and low-gas pattern proposed predicts three favorable medium-to-high temperature geothermal zones in the surface geochemical exploration of the Shiba Basin near the Huangshadong geothermal field.

Hydrochemical, D–O–Sr isotopic and electromagnetic characteristics of geothermal waters from the Erdaoqiao area, SW China: Insights into genetic mechanism and scaling potential

The Erdaoqiao area has been the hot area of geothermal resource prospecting in southwestern China. Significance difference of scaling potential has been found between left and right riverbanks of the Erdaoqiao area. However, there still has no interpretation for the scaling difference since the genetic mechanism of geothermal waters remains unclear. In this study, hydrochemical, D–O–Sr isotopic and electromagnetic (EM) approaches were integrated to clarify the genetic mechanism and quantitively evaluate scaling potential of geothermal waters. All geothermal waters belonged to Ca–Na–HCO3 type and were determined by the weathering and/or dissolution of carbonates (66.87%) and silicates (31.53%) with cation exchange based on hydrochemical and Sr isotopic analyses. Na–K–Mg triangle diagram indicated they were immature water mixed by shallow cold water. Quartz geothermometer indicated the shallow reservoir temperatures (after cold–water mixing) of left riverbank (88.46 °C–90.51 °C) were higher than those of right riverbank (61.20 °C–87.89 °C). Silica – Enthalpy methods revealed the initial geothermal reservoir temperatures and cold-water mixing ratio were 102.03 °C–138.93 °C and 65.24%–85.87% in the right riverbank, 144.11 °C–146.76 °C and 73.08%–74.79% in the left riverbank of the Erdaoqiao area. D-O isotopes proposed the geothermal waters were recharged by atmospheric precipitation in the elevation of 4957 m to 5118 m. Therefore, the genetic model of geothermal waters in the Erdaoqiao area can be constructed. Stronger calcite scaling in left riverbank was attributed to deeper circulation identified by higher reservoir temperature and electromagnetic exploration. Quantitively evaluation demonstrated that the weight of scaling during 48 h in left riverbank (2968 kg) was four times higher than that in right riverbank (748 kg). The achievements of this study contribute to geothermal exploration in the Erdaoqiao and other similar areas worldwide.

Formation of the hydrothermal system from granite reservoir for power generation in igneous rock areas of South China

Hydrothermal systems occurring in granite reservoir widely exist over the world, but those can continuously supply large quantities of hot water with certain temperature for power generation are rare, e.g., TangKeng geothermal system in South China. It is unclear how the granite reservoir keeps this kind of large natural yield of geothermal water with stable temperature and the genesis study is of great importance to find similar geothermal fields for further exploitation. This paper aims to discuss the formation of TangKeng geothermal system in granite of Cretaceous period, with emphasis on heat sources, geothermal fluid circulation and reservoir temperature. Results show that average regional heat flow of 72.2 mW/m2 is composed by almost equal contribution from heat production of radioactive elements in crust and conductive heat of mantle. Extension and thinning processes of lithosphere and upwelling of magma in the asthenosphere caused the thermal erosion of the upper mantle and lower crust but doesn't induce the formation of magma chamber or partial molten in the upper crust and had very limited influences on the regional thermal state. Heat flow of the crust is mainly composed by intrusive granite pluton with high heat production value in the surface and the felsic upper crust. Geothermal fluid is recharged by the local precipitation from the surrounding mountains through regional developed NE and NW faults system. The crushed fine-middle grained biotite granite or granite with fractures and fissures of Mesozoic period provide excellent reservoir for water circulation. Interactions between regional faults and fractures in granites provide excellent conduits for additional recharge from shallow groundwater which is continuously recharged by the Rong Jiang River water during the ascending process. Reservoir temperature is calculated to be about 140–143 °C with correction of slightly CO2 degassing and mixing. Missing of caprock for most of the areas and mixing with cold groundwater during ascending process led to the occurrence of geothermal water with lower temperature of 92 °C collected at the surface.Fractured granite reservoir with high heat productivity from radioactive elements, well developed NE and NW oriented faults system and continuous recharge from local precipitation and surface water nearby are essential for the formation of this kind of hydrothermal system.

Determination of Reservoir Temperatures of Low-Enthalpy Geothermal Systems in the Sudetes (SW Poland) Using Multicomponent Geothermometers

Thermal waters from deep circulation systems are mixed with cold shallow system components during their ascent to drainage zones. In the current research, classic chemical geothermometers and geothermometric modeling using the GeoT app were employed to determine the temperatures of geothermal reservoirs in the Sudetic region. Moreover, models of primary deep components mixed with cold shallow circulation system components were used to determine their proportions, particularly water deposits. In the studied geothermal systems, the proportion of the cold component ranged from c. 46% to c. 75%. Classic cation thermometers (Na-K, Na-K-Ca) indicated a very wide temperature range and they proved rather unreliable. The reservoir temperatures estimated with silica thermometers ranged from 52 °C to 141 °C and they can be deemed more reliable. The temperatures obtained from modeling (54.5 ± 3–120 ± 4) were adopted as temperatures of waters pre-cooled conductively and then mixed with cold components. The temperatures of primary deep waters (74–225 °C) were adopted as geothermal system temperatures.

Relationship between hydrogeochemical characteristics of hot springs and seismic activity in the Jinshajiang fault zone, Southeast Tibetan Plateau

Significant anomalous hydrogeochemical changes in hot spring water are detected during strong seismic cycles. It is now necessary to clarify the relationship between tectonic movements, earthquakes and the evolution of hot springs. In this paper, laboratory analyses of major, trace elements, δD, δ18O and 87Sr/86Sr values of 28 hot spring waters in the Jinshajiang fault zone (JSJFZ) in the northwestern boundary of the Sichuan-Yunnan block were conducted. The results showed that the primary source of water for JSJFZ hot springs was atmospheric precipitation. The geothermal reservoir temperature variation based on the silicon enthalpy mixing model ranged from 73 to 272°C. And the circulation depth range was 1.2–5.4 km. The segmentation characteristics of the 87Sr/86Sr values were related to the influence of source rocks on groundwater cycle processes. A conceptual model of the hydrologic cycle of hot springs explained the spatial distribution of earthquakes associated with tectonic movements. The Batang segment had the strongest water-rock reaction, the highest reservoir temperature and the deepest circulation depth; meanwhile, it was also an earthquake prone area. The fluid circulation of the JSJFZ corresponds well with the seismicity, which indicates that the hydrological characteristics of the hot spring water in a fracture zone play a crucial role in receiving information on seismic activity.