To address the challenge of rapidly and accurately quantifying the heat performance of energy tunnels under unknown operational conditions, this study proposes an intelligent predictive framework that integrates multi-physics simulation and explainable machine learning. A validated three-dimensional multi-physics model was developed in COMSOL to generate a dataset comprising 1024 simulation samples covering ten key operational parameters. Nine machine learning algorithms were employed to construct predictive models for the heat performance of energy tunnels, and Shapley Additive Explanations (SHAP) were applied to enhance model interpretability. Results demonstrate that the Support Vector Regression (SVR) model achieved the highest predictive accuracy (R² = 0.961), while the Back Propagation Neural Network (BPNN) model exhibited the lowest average absolute error (AE) on the test set (AEavg = 2.76 W/m²). The tunnel air temperature (Ta), fluid velocity (Vf), and air convective heat transfer coefficient (h) were identified as the most influential factors affecting the heat performance, with significant interactions observed among multiple parameters. This study provides a reliable data-driven basis for the intelligent prediction and optimization of energy tunnel heat performance.
{"title":"Explainable machine learning models to predict the heat performance of energy tunnels","authors":"Lifei Zheng , Wenbo Yu , Zhi Chen , Sheng Yang , Zhiying Zhong , Henglin Xiao","doi":"10.1016/j.geothermics.2025.103508","DOIUrl":"10.1016/j.geothermics.2025.103508","url":null,"abstract":"<div><div>To address the challenge of rapidly and accurately quantifying the heat performance of energy tunnels under unknown operational conditions, this study proposes an intelligent predictive framework that integrates multi-physics simulation and explainable machine learning. A validated three-dimensional multi-physics model was developed in COMSOL to generate a dataset comprising 1024 simulation samples covering ten key operational parameters. Nine machine learning algorithms were employed to construct predictive models for the heat performance of energy tunnels, and Shapley Additive Explanations (SHAP) were applied to enhance model interpretability. Results demonstrate that the Support Vector Regression (SVR) model achieved the highest predictive accuracy (R² = 0.961), while the Back Propagation Neural Network (BPNN) model exhibited the lowest average absolute error (AE) on the test set (AE<sub>avg</sub> = 2.76 W/m²). The tunnel air temperature (<em>T</em><sub>a</sub>), fluid velocity (<em>V</em><sub>f</sub>), and air convective heat transfer coefficient (<em>h</em>) were identified as the most influential factors affecting the heat performance, with significant interactions observed among multiple parameters. This study provides a reliable data-driven basis for the intelligent prediction and optimization of energy tunnel heat performance.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103508"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145332986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-11-03DOI: 10.1016/j.geothermics.2025.103517
Biao Shu , Linyu Xiang , Sen Zhang , Joseph Moore
The use of supercritical carbon dioxide (ScCO2) for heat transfer has the potential to improve the efficiency of geothermal extraction in Enhanced Geothermal Systems. In this study, experiments were conducted to investigate the effects of reservoir temperature and confining pressure on the hydraulic and heat transfer characteristics of ScCO2 in a granite fracture. Experiments were also conducted to compare the heat transfer characteristics of ScCO2 and water. At constant confining pressure, the heat transfer coefficients of ScCO2 decrease by an average of 63.8 %, 73.7 %, and 83.5 % as the reservoir temperature increases from 50 to 100, 150, and 200 °C, respectively. The reservoir temperature governs the thermophysical properties of ScCO2, and therefore the heat transfer coefficient. The specific heat capacity and density of ScCO2 contribute much more to the heat transfer coefficient than the viscosity. As the confining pressure increases from 10 to 15, 20, and 25 MPa, the heat transfer coefficient decreases by 18.6–31.6 %, 30.6–46.0 %, and 41.3–54.7 % at reservoir temperatures of 50–200 °C, respectively. At low-medium temperatures, the heat transfer coefficient of ScCO2 is 1.8 to 7.1 times higher than that of water. The findings can provide a theoretical basis for improving the efficiency of geothermal energy extraction and optimizing the design of Enhanced Geothermal Systems.
{"title":"Experimental investigation of the heat transfer characteristics of supercritical CO2 in a single granite fracture","authors":"Biao Shu , Linyu Xiang , Sen Zhang , Joseph Moore","doi":"10.1016/j.geothermics.2025.103517","DOIUrl":"10.1016/j.geothermics.2025.103517","url":null,"abstract":"<div><div>The use of supercritical carbon dioxide (ScCO<sub>2</sub>) for heat transfer has the potential to improve the efficiency of geothermal extraction in Enhanced Geothermal Systems. In this study, experiments were conducted to investigate the effects of reservoir temperature and confining pressure on the hydraulic and heat transfer characteristics of ScCO<sub>2</sub> in a granite fracture. Experiments were also conducted to compare the heat transfer characteristics of ScCO<sub>2</sub> and water. At constant confining pressure, the heat transfer coefficients of ScCO<sub>2</sub> decrease by an average of 63.8 %, 73.7 %, and 83.5 % as the reservoir temperature increases from 50 to 100, 150, and 200 °C, respectively. The reservoir temperature governs the thermophysical properties of ScCO<sub>2</sub>, and therefore the heat transfer coefficient. The specific heat capacity and density of ScCO<sub>2</sub> contribute much more to the heat transfer coefficient than the viscosity. As the confining pressure increases from 10 to 15, 20, and 25 MPa, the heat transfer coefficient decreases by 18.6–31.6 %, 30.6–46.0 %, and 41.3–54.7 % at reservoir temperatures of 50–200 °C, respectively. At low-medium temperatures, the heat transfer coefficient of ScCO<sub>2</sub> is 1.8 to 7.1 times higher than that of water. The findings can provide a theoretical basis for improving the efficiency of geothermal energy extraction and optimizing the design of Enhanced Geothermal Systems.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103517"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145474205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-23DOI: 10.1016/j.geothermics.2025.103479
Xiaoxiao Yin , Bowen Xu , Jian Shen , Zhenhai Zong , Guangyao Zhang , Zhilong Liu , Jinghong Hu
Geothermal reservoir dynamic monitoring and research serve as the key scientific foundation for optimizing resource development, ensuring sustainable utilization, and mitigating exploitation risks. This paper systematically compiles nearly 50 years of geothermal utilization demand and management policies in Tianjin, along with data on application scenarios, extraction/injection volumes, thermal reservoir water levels, hydrochemical components, wellhead temperatures, and thermal reservoir temperatures for both porous (e.g., Guantao Formation) and fractured (e.g., Wumishan Formation) reservoirs. It analyzes the relationships among market demand, policy regulation, and the dynamic characteristics of reservoir resources. The findings indicate: (1) Reduced consumption is the direct cause of the shift from declining to recovering water levels. Although porous and fractured reservoirs respond synchronously, their patterns differ. In porous reservoirs, abrupt shutdowns of unlicensed wells led to a sharp decline in non-reinjected extraction, causing water levels to transition from rapid decline to rapid and then slow recovery (a "V"-shaped response). In contrast, fractured reservoirs exhibited gradual consumption reduction due to sustained reinjection increases, resulting in a shift from slow decline to slow and then rapid recovery (a "U"-shaped response). (2) Hydrochemical components in both reservoirs remained stable, with no significant alteration to the subsurface chemical environment, though calcium carbonate scaling in some wells impaired reinjection efficiency. (3) Overly low reinjection temperatures in porous reservoirs risked cold front migration from injection wells, posing thermal breakthrough threats, whereas fractured reservoirs maintained stable temperatures—especially near deep conductive faults, demonstrating high exploitation potential due to deep heat sources. Tianjin’s large-scale reinjection practices hold significant implications for reestablishing thermal reservoir equilibrium, offering valuable insights for sustainable geothermal development in similar regions.
{"title":"Geothermal resource development and reservoir dynamics in Tianjin, China","authors":"Xiaoxiao Yin , Bowen Xu , Jian Shen , Zhenhai Zong , Guangyao Zhang , Zhilong Liu , Jinghong Hu","doi":"10.1016/j.geothermics.2025.103479","DOIUrl":"10.1016/j.geothermics.2025.103479","url":null,"abstract":"<div><div>Geothermal reservoir dynamic monitoring and research serve as the key scientific foundation for optimizing resource development, ensuring sustainable utilization, and mitigating exploitation risks. This paper systematically compiles nearly 50 years of geothermal utilization demand and management policies in Tianjin, along with data on application scenarios, extraction/injection volumes, thermal reservoir water levels, hydrochemical components, wellhead temperatures, and thermal reservoir temperatures for both porous (e.g., Guantao Formation) and fractured (e.g., Wumishan Formation) reservoirs. It analyzes the relationships among market demand, policy regulation, and the dynamic characteristics of reservoir resources. The findings indicate: (1) Reduced consumption is the direct cause of the shift from declining to recovering water levels. Although porous and fractured reservoirs respond synchronously, their patterns differ. In porous reservoirs, abrupt shutdowns of unlicensed wells led to a sharp decline in non-reinjected extraction, causing water levels to transition from rapid decline to rapid and then slow recovery (a \"V\"-shaped response). In contrast, fractured reservoirs exhibited gradual consumption reduction due to sustained reinjection increases, resulting in a shift from slow decline to slow and then rapid recovery (a \"U\"-shaped response). (2) Hydrochemical components in both reservoirs remained stable, with no significant alteration to the subsurface chemical environment, though calcium carbonate scaling in some wells impaired reinjection efficiency. (3) Overly low reinjection temperatures in porous reservoirs risked cold front migration from injection wells, posing thermal breakthrough threats, whereas fractured reservoirs maintained stable temperatures—especially near deep conductive faults, demonstrating high exploitation potential due to deep heat sources. Tianjin’s large-scale reinjection practices hold significant implications for reestablishing thermal reservoir equilibrium, offering valuable insights for sustainable geothermal development in similar regions.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103479"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145121010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-11-04DOI: 10.1016/j.geothermics.2025.103515
Abdul Karim , Kwonye Kim , Hobyung Chae , Jinhwan Oh , Yujin Nam
According to a recent International Energy Agency (IEA) report, ground source heat pump (GSHP) technology is receiving increasing attention as it can play a major role in carbon neutrality and building energy reduction. GSHP systems have been applied to commercial buildings since the 1960s and have evolved through the adoption of diverse technological innovations. GSHPs are recognized as a key carbon-reduction technology and have been studied mainly in North America and Northern Europe. However, considerable research and development is being conducted in Asia, and the number of applications in large buildings is also increasing. In this study, research publications and operation data of GSHP systems over the past 15 years were analyzed to examine the trends in the research focus and system performance. Furthermore, the performance of GSHP systems was analyzed by region and climate based on the system performance data obtained from experiments and analysis, and the differences were quantitatively presented. As a result, the average coefficient of performance COP of the GSHP system in actual operation was 4.7 for cooling and 4.2 for heating. Moreover, higher latitude were found to be more favorable for cooling performances, whereas lower latitudes were more favorable for heating.Over the past 15 years, GSHP research has expanded beyond ground heat exchanger designs, hybrid technologies, and AI-driven optimization to include emerging topics such as energy geostructures, integration with district heating and cooling networks, advanced sensing and Digital Twin frameworks, and long-term thermal energy storage, with much of this work concentrated in Northeast Asia and Europe.
{"title":"Latest trends and new approaches in ground source heat pump systems: A comprehensive review of performance, sustainability, and future directions","authors":"Abdul Karim , Kwonye Kim , Hobyung Chae , Jinhwan Oh , Yujin Nam","doi":"10.1016/j.geothermics.2025.103515","DOIUrl":"10.1016/j.geothermics.2025.103515","url":null,"abstract":"<div><div>According to a recent International Energy Agency (IEA) report, ground source heat pump (GSHP) technology is receiving increasing attention as it can play a major role in carbon neutrality and building energy reduction. GSHP systems have been applied to commercial buildings since the 1960s and have evolved through the adoption of diverse technological innovations. GSHPs are recognized as a key carbon-reduction technology and have been studied mainly in North America and Northern Europe. However, considerable research and development is being conducted in Asia, and the number of applications in large buildings is also increasing. In this study, research publications and operation data of GSHP systems over the past 15 years were analyzed to examine the trends in the research focus and system performance. Furthermore, the performance of GSHP systems was analyzed by region and climate based on the system performance data obtained from experiments and analysis, and the differences were quantitatively presented. As a result, the average coefficient of performance COP of the GSHP system in actual operation was 4.7 for cooling and 4.2 for heating. Moreover, higher latitude were found to be more favorable for cooling performances, whereas lower latitudes were more favorable for heating.Over the past 15 years, GSHP research has expanded beyond ground heat exchanger designs, hybrid technologies, and AI-driven optimization to include emerging topics such as energy geostructures, integration with district heating and cooling networks, advanced sensing and Digital Twin frameworks, and long-term thermal energy storage, with much of this work concentrated in Northeast Asia and Europe.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103515"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145474467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-27DOI: 10.1016/j.geothermics.2025.103503
Y.A. Popov, E.M. Chekhonin, E.G. Savelev, R.A. Romushkevich, M.Y. Spasennykh
For the first time in the marine geothermal research practice, multiscale rock heterogeneity and anisotropy were studied with continuous thermal property profiling on whole core column from shallow stratigraphic wells on the Kara Sea shelf that improved heat flow assessment. The thermophysical core logging technology, which allows specialists to provide continuous non-destructive profiling of rock thermal properties with spatial resolution of 1 mm, was utilized for the first time in marine wells. This approach yielded high-quality data on thermal conductivity, volumetric heat capacity, and thermal diffusivity for all drilled 916 full-size core samples, accounting for their thermal heterogeneity and anisotropy. Additionally, 30 core samples were selected based on thermal profiling results for extended thermophysical studies: 25 samples were scanned after additional saturation, 5 samples were prepared and studied within the temperature range from 20 to 80 °C using the divided bar technique, and 5 samples were studied at increased up to 5 MPa uniaxial pressure. Heat flow was estimated using the equivalent thermal conductivity, which was determined accounting for each core sample length, macro- and microanisotropy of the rocks, the core decompression, the drying of samples during transportation and storage, and thermobaric conditions of the drilled sediments. The research aims to create a database on geothermal characteristics to improve the reliability of hydrocarbon exploration and development on the studied territory of the Kara Sea shelf. The applied technology for experimental geothermal research allows specialists for extensive and more representative studies of the subsurface geothermal characteristics on the shelf, compared to the traditional approaches that rely on measurements in near-bottom sediments.
{"title":"Marine geothermal study in shallow stratigraphic wells on the Kara sea shelf: high-resolution thermal conductivity and temperature data","authors":"Y.A. Popov, E.M. Chekhonin, E.G. Savelev, R.A. Romushkevich, M.Y. Spasennykh","doi":"10.1016/j.geothermics.2025.103503","DOIUrl":"10.1016/j.geothermics.2025.103503","url":null,"abstract":"<div><div>For the first time in the marine geothermal research practice, multiscale rock heterogeneity and anisotropy were studied with continuous thermal property profiling on whole core column from shallow stratigraphic wells on the Kara Sea shelf that improved heat flow assessment. The thermophysical core logging technology, which allows specialists to provide continuous non-destructive profiling of rock thermal properties with spatial resolution of 1 mm, was utilized for the first time in marine wells. This approach yielded high-quality data on thermal conductivity, volumetric heat capacity, and thermal diffusivity for all drilled 916 full-size core samples, accounting for their thermal heterogeneity and anisotropy. Additionally, 30 core samples were selected based on thermal profiling results for extended thermophysical studies: 25 samples were scanned after additional saturation, 5 samples were prepared and studied within the temperature range from 20 to 80 °C using the divided bar technique, and 5 samples were studied at increased up to 5 MPa uniaxial pressure. Heat flow was estimated using the equivalent thermal conductivity, which was determined accounting for each core sample length, macro- and microanisotropy of the rocks, the core decompression, the drying of samples during transportation and storage, and thermobaric conditions of the drilled sediments. The research aims to create a database on geothermal characteristics to improve the reliability of hydrocarbon exploration and development on the studied territory of the Kara Sea shelf. The applied technology for experimental geothermal research allows specialists for extensive and more representative studies of the subsurface geothermal characteristics on the shelf, compared to the traditional approaches that rely on measurements in near-bottom sediments.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103503"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-10-10DOI: 10.1016/j.geothermics.2025.103507
Yuhzong Liao , Guiling Wang , Wei Zhang , Hanxiong Zhang , Jiyun Liang , Yufei Xi
This study investigates fault-controlled geothermal systems in southeastern China, focusing on representative regions in Hunan, Guangdong, and Jiangxi provinces. A machine learning approach—non-negative matrix factorization with k-means clustering (NMFk)—was applied to classify geothermal water types and delineate favorable exploration zones based on hydrochemical composition, flow rate, heat flow, and fault proximity. Geothermal waters were classified into three types with distinct geochemical and geological attributes: Type A, Type B, and Type C. Representative geothermal fields—Nuanshui (Type A), Longmen and Reshui (Type B), and Chengkou (Type C)—were selected to validate the classification and analyze reservoir characteristics and genetic mechanisms. Type B geothermal water exhibits the highest exploration potential, characterized by deep circulation (1900–5300 m), high reservoir temperatures (66–143 °C), strong confinement, and enrichment in Na⁺ and Li⁺. Its formation is primarily controlled by NW-trending faults and high heat-producing granites. Type C geothermal water shows moderate potential, with the highest heat flow (83 mW/m²), deep circulation (3500–5400 m), and elevated temperatures (109–127 °C), despite lower flow rates. It is hosted in granitic reservoirs associated with NE–N-trending faults. In contrast, Type A demonstrates the lowest geothermal potential, featuring shallow circulation (900–2100 m), lower temperatures (42–75 °C), high flow rates, and enrichment in Mg²⁺, Ca²⁺, and Sr²⁺, reflecting strong meteoric recharge and limited geochemical evolution. A conceptual model is proposed in which meteoric water infiltrates through fault zones, absorbs heat during deep circulation within granitic or carbonate rocks, and ascends to form geothermal reservoirs or surface springs. The classification results align well with spatial patterns of geothermal favorability, offering a robust framework for geothermal resource assessment and supporting sustainable development strategies in southeastern China.
{"title":"Machine learning for fault-controlled geothermal systems exploration in Chenzhou and Huizhou region, Southeast China","authors":"Yuhzong Liao , Guiling Wang , Wei Zhang , Hanxiong Zhang , Jiyun Liang , Yufei Xi","doi":"10.1016/j.geothermics.2025.103507","DOIUrl":"10.1016/j.geothermics.2025.103507","url":null,"abstract":"<div><div>This study investigates fault-controlled geothermal systems in southeastern China, focusing on representative regions in Hunan, Guangdong, and Jiangxi provinces. A machine learning approach—non-negative matrix factorization with k-means clustering (NMF<em>k</em>)—was applied to classify geothermal water types and delineate favorable exploration zones based on hydrochemical composition, flow rate, heat flow, and fault proximity. Geothermal waters were classified into three types with distinct geochemical and geological attributes: Type A, Type B, and Type C. Representative geothermal fields—Nuanshui (Type A), Longmen and Reshui (Type B), and Chengkou (Type C)—were selected to validate the classification and analyze reservoir characteristics and genetic mechanisms. Type B geothermal water exhibits the highest exploration potential, characterized by deep circulation (1900–5300 m), high reservoir temperatures (66–143 °C), strong confinement, and enrichment in Na⁺ and Li⁺. Its formation is primarily controlled by NW-trending faults and high heat-producing granites. Type C geothermal water shows moderate potential, with the highest heat flow (83 mW/m²), deep circulation (3500–5400 m), and elevated temperatures (109–127 °C), despite lower flow rates. It is hosted in granitic reservoirs associated with NE–N-trending faults. In contrast, Type A demonstrates the lowest geothermal potential, featuring shallow circulation (900–2100 m), lower temperatures (42–75 °C), high flow rates, and enrichment in Mg²⁺, Ca²⁺, and Sr²⁺, reflecting strong meteoric recharge and limited geochemical evolution. A conceptual model is proposed in which meteoric water infiltrates through fault zones, absorbs heat during deep circulation within granitic or carbonate rocks, and ascends to form geothermal reservoirs or surface springs. The classification results align well with spatial patterns of geothermal favorability, offering a robust framework for geothermal resource assessment and supporting sustainable development strategies in southeastern China.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103507"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145268815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The advantage of suitable anti-scaling technologies for individual geothermal plants would benefit from shorter development periods, making it necessary to improve the precision in evaluating a scaling technology through laboratory testing. This study focuses on developing a technology to replicate the scale formed in the Takigami binary geothermal plant. The artificial scale obtained was compared with an actual scale collected during jet washing that followed the chemical washing process in the evaporator of the Takigami binary power plant. The artificial scale was synthesized in controlled environments by removing dissolved oxygen and introducing carbon dioxide (CO2) to simulate geothermal conditions. The artificial scale resembled the natural scale, predominantly comprising silica and metal silicates. Although the scale formed in the Takigami binary geothermal plant differed from the artificial scale in terms of particle size, the size of the dispersion particles in the geothermal brine was similar to that of the dispersion particles in the synthesized solution. In addition, the amounts of enriched elements differed from those in the natural scale, with higher aluminum and lower calcium concentrations. These discrepancies highlight the need for additional adjustments in synthesis conditions to more precisely replicate the natural scaling environment. We illustrate how laboratory-scale synthesis can help successfully imitate the intricate natural scaling processes, providing valuable insights for enhancing scaling management in geothermal facilities. Optimizing the gas and chemical inputs may help further improve the precision of these simulations. The interactions between the material and solution particles need careful consideration.
{"title":"Method for imitating scale formation in the Takigami binary power plant in Oita, Japan: Establishment of primary synthesis conditions","authors":"Shota Ikemoto , Htoo Nay Wunn , Shinichi Motoda , Azusa Wada , Hirono Okano , Shinya Ui , Motoaki Morita","doi":"10.1016/j.geothermics.2025.103504","DOIUrl":"10.1016/j.geothermics.2025.103504","url":null,"abstract":"<div><div>The advantage of suitable anti-scaling technologies for individual geothermal plants would benefit from shorter development periods, making it necessary to improve the precision in evaluating a scaling technology through laboratory testing. This study focuses on developing a technology to replicate the scale formed in the Takigami binary geothermal plant. The artificial scale obtained was compared with an actual scale collected during jet washing that followed the chemical washing process in the evaporator of the Takigami binary power plant. The artificial scale was synthesized in controlled environments by removing dissolved oxygen and introducing carbon dioxide (CO<sub>2</sub>) to simulate geothermal conditions. The artificial scale resembled the natural scale, predominantly comprising silica and metal silicates. Although the scale formed in the Takigami binary geothermal plant differed from the artificial scale in terms of particle size, the size of the dispersion particles in the geothermal brine was similar to that of the dispersion particles in the synthesized solution. In addition, the amounts of enriched elements differed from those in the natural scale, with higher aluminum and lower calcium concentrations. These discrepancies highlight the need for additional adjustments in synthesis conditions to more precisely replicate the natural scaling environment. We illustrate how laboratory-scale synthesis can help successfully imitate the intricate natural scaling processes, providing valuable insights for enhancing scaling management in geothermal facilities. Optimizing the gas and chemical inputs may help further improve the precision of these simulations. The interactions between the material and solution particles need careful consideration.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103504"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145268844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-15DOI: 10.1016/j.geothermics.2025.103490
Siqi Wang , Xiting Long , Jianjun Hu , Feng Liu , Jingyu Lin
The Mianhuakeng geothermal system, hosted in a uranium-bearing granitoid environment, exhibits a high surface heat flow (62.7–90.4 mW/m2), indicating significant geothermal potential. This study integrated geochemical and isotopic analyses to elucidate the origin, evolution, and controlling mechanisms of the system. Isotopic evidence indicates that meteoric water is the primary recharge source, infiltrating to depths of 1617–4030 m, resulting in estimated geothermal reservoir temperatures ranging from 56 °C to 111 °C. Geochemical studies suggest that the mixing of deep geothermal water and water-rock interactions, such as silicate weathering (e.g., albite, biotite), sulfate dissolution (gypsum), and cation exchange, lead to the enrichment of Na+, Ca2+, SO42−, and HCO3−. Moreover, the co-dissolution of fluorite and biotite as well as the mixing of deep fluid may be the cause of the high F− level in geothermal water. The radioactive heat production of uranium-bearing granite is a major heat source in the study area that provides to the thermal regime of geothermal systems, with an average heat production rate of 5.14 μW/m3. A conceptual model based on hydrogeochemistry was proposed, providing a few new insights into the characteristics of geothermal systems in granitoid environments.
{"title":"Geothermal hydrogeochemical conditions and genesis of the Mianhuakeng uranium deposit, South China","authors":"Siqi Wang , Xiting Long , Jianjun Hu , Feng Liu , Jingyu Lin","doi":"10.1016/j.geothermics.2025.103490","DOIUrl":"10.1016/j.geothermics.2025.103490","url":null,"abstract":"<div><div>The Mianhuakeng geothermal system, hosted in a uranium-bearing granitoid environment, exhibits a high surface heat flow (62.7–90.4 mW/m<sup>2</sup>), indicating significant geothermal potential. This study integrated geochemical and isotopic analyses to elucidate the origin, evolution, and controlling mechanisms of the system. Isotopic evidence indicates that meteoric water is the primary recharge source, infiltrating to depths of 1617–4030 m, resulting in estimated geothermal reservoir temperatures ranging from 56 °C to 111 °C. Geochemical studies suggest that the mixing of deep geothermal water and water-rock interactions, such as silicate weathering (e.g., albite, biotite), sulfate dissolution (gypsum), and cation exchange, lead to the enrichment of Na<sup>+</sup>, Ca<sup>2+</sup>, SO<sub>4</sub><sup>2−</sup>, and HCO<sub>3</sub><sup>−</sup>. Moreover, the co-dissolution of fluorite and biotite as well as the mixing of deep fluid may be the cause of the high F<sup>−</sup> level in geothermal water. The radioactive heat production of uranium-bearing granite is a major heat source in the study area that provides to the thermal regime of geothermal systems, with an average heat production rate of 5.14 μW/m<sup>3</sup>. A conceptual model based on hydrogeochemistry was proposed, providing a few new insights into the characteristics of geothermal systems in granitoid environments.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103490"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145061036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-11-20DOI: 10.1016/j.geothermics.2025.103536
Tao Chen , Tong Bai , Yu Zhang , Yabin Yang , Honghao Sheng , Shuai Liu , Zongjun Gao , Fengxin Kang
Long-term and continuous exploitation of hydrothermal systems will cause a drop in groundwater level and ground subsidence. Successful reinjection is important to maintain the hydraulic head of the geothermal reservoir and to yield a sustainable utilization of geothermal energy. This study aims to investigate the reinjection mechanism by combining hydraulic and hydrothermal tests in a large-scale three-dimensional sand tank model (12 m × 6 m × 6 m). We conducted the experiments to observe the hydraulic head and temperature evolution during water reinjection at normal and heated temperatures. The experiment results are compared with the numerical results by using the SHEMAT-Suite software. The trends of hydraulic head and temperature changes match well in general, whereas heat loss due to ambient temperature and physical mechanisms such as particle rearrangement may cause differences between the experimental and numerical results. We optimize reservoir output with respect to the well spacing, porosity, and permeability of the model. Increasing porosity and permeability results in a higher geothermal energy output and better economic benefits. Meanwhile, for the well spacing, it is preferable to have a short spacing in low porosity and permeability models and a long spacing in high porosity and permeability models. The study helps understand the mechanism of reinjection in geothermal reservoirs and optimize the sandstone geothermal exploitation management strategy.
热液系统的长期持续开采将导致地下水位下降和地面沉降。成功的回注对保持地热储层水头和实现地热能源的可持续利用具有重要意义。本研究在大型三维砂槽模型（12 m × 6 m × 6 m）中，通过水力和水热试验相结合的方法研究回注机理。通过实验观察了正常和加热条件下回注水过程中水头和温度的变化规律。利用SHEMAT-Suite软件将实验结果与数值结果进行了比较。水头变化趋势与温度变化趋势总体上吻合较好，但由于环境温度和粒子重排等物理机制导致的热损失可能导致实验结果与数值结果存在差异。我们根据模型的井距、孔隙度和渗透率来优化储层产量。提高孔隙度和渗透率，可以提高地热能产量，提高经济效益。同时，在井距上，低孔渗模型宜采用短井距，高孔渗模型宜采用长井距。该研究有助于认识地热储层的回注机理，优化砂岩地热开发管理策略。
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Pub Date : 2026-01-01Epub Date: 2025-11-04DOI: 10.1016/j.geothermics.2025.103518
Xun Huang , Xingcheng Yuan , Xiyong Wu , Ying Wang , Shiming Yang , Shuang Zhao , Yangshuang Wang , Yunhui Zhang
To achieve the goals of carbon peak and carbon neutrality, geothermal energy, as a clean, renewable, and pollution-free natural resource, has attracted attention worldwide. The Sichuan Basin in China is rich in geothermal resources, especially in the fold structure area on the southeast side. However, research on the region's formation mechanisms and quality evaluation is lacking, hindering further geothermal resource development. In this study, the hydrochemical and isotopic characteristics of 27 geothermal water samples from the fold structure area of the southeastern Sichuan Basin were investigated to elucidate the formation mechanism of geothermal water and evaluate its quality. The discharge temperatures of geothermal waters range from 32.5 to 52 °C; they have neutral pH values and are brackish with hydrochemical types classified as SO4Ca and SO4Ca·Mg. The results of δD and δ18O analysis show that the geothermal water comes from the recharge of meteoric waters. The recharge elevation and temperature are 528−1212 m and 8.5 − 14.5 °C, respectively, and geothermal waters flow along anticlinal cores from NE to SW. The main factors controlling the hydrochemical evolution of geothermal waters are calcite, dolomite, and gypsum dissolution in Triassic carbonate rocks, followed by silicate minerals and halite. Reservoir fluids are primarily composed of free ions such as Na+, Ca2+, and Mg2+, as well as complexes like CaHCO3+, CaSO4, and MgSO4. The shallow reservoir temperatures of geothermal waters range from 52 °C to 96 °C, with 20−83% of cold waters mixed with deep geothermal fluids during the rising process. The initial reservoir temperatures before mixing are between 62 °C and 183 °C, and the circulation depths range from 1383 m to 2619 m. The eastern part of the study area is the most promising development area due to its high reservoir temperatures (>90 °C) and enriched minor elements (Sr and F). However, attention should be paid to the scaling of CaCO3 and CaSO4 and the treatment of high SO42−-concentration wastewater in the development process. The research results reveal both the formation mechanism of geothermal waters and the distribution characteristics of geothermal resources, while providing valuable insights for their development in fold structure areas.
{"title":"Hydrochemical appraisal, formation mechanism, and sustainable development of fold-type geothermal waters: Insights from hydrochemistry and isotopes","authors":"Xun Huang , Xingcheng Yuan , Xiyong Wu , Ying Wang , Shiming Yang , Shuang Zhao , Yangshuang Wang , Yunhui Zhang","doi":"10.1016/j.geothermics.2025.103518","DOIUrl":"10.1016/j.geothermics.2025.103518","url":null,"abstract":"<div><div>To achieve the goals of carbon peak and carbon neutrality, geothermal energy, as a clean, renewable, and pollution-free natural resource, has attracted attention worldwide. The Sichuan Basin in China is rich in geothermal resources, especially in the fold structure area on the southeast side. However, research on the region's formation mechanisms and quality evaluation is lacking, hindering further geothermal resource development. In this study, the hydrochemical and isotopic characteristics of 27 geothermal water samples from the fold structure area of the southeastern Sichuan Basin were investigated to elucidate the formation mechanism of geothermal water and evaluate its quality. The discharge temperatures of geothermal waters range from 32.5 to 52 °C; they have neutral pH values and are brackish with hydrochemical types classified as SO<sub>4<img></sub>Ca and SO<sub>4<img></sub>Ca·Mg. The results of δ<sub>D</sub> and δ<sup>18</sup>O analysis show that the geothermal water comes from the recharge of meteoric waters. The recharge elevation and temperature are 528−1212 m and 8.5 − 14.5 °C, respectively, and geothermal waters flow along anticlinal cores from NE to SW. The main factors controlling the hydrochemical evolution of geothermal waters are calcite, dolomite, and gypsum dissolution in Triassic carbonate rocks, followed by silicate minerals and halite. Reservoir fluids are primarily composed of free ions such as Na<sup>+</sup>, Ca<sup>2+</sup>, and Mg<sup>2+</sup>, as well as complexes like CaHCO<sub>3</sub><sup>+</sup>, CaSO<sub>4</sub>, and MgSO<sub>4</sub>. The shallow reservoir temperatures of geothermal waters range from 52 °C to 96 °C, with 20−83% of cold waters mixed with deep geothermal fluids during the rising process. The initial reservoir temperatures before mixing are between 62 °C and 183 °C, and the circulation depths range from 1383 m to 2619 m. The eastern part of the study area is the most promising development area due to its high reservoir temperatures (>90 °C) and enriched minor elements (Sr and F). However, attention should be paid to the scaling of CaCO<sub>3</sub> and CaSO<sub>4</sub> and the treatment of high SO<sub>4</sub><sup>2−</sup>-concentration wastewater in the development process. The research results reveal both the formation mechanism of geothermal waters and the distribution characteristics of geothermal resources, while providing valuable insights for their development in fold structure areas.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"134 ","pages":"Article 103518"},"PeriodicalIF":3.9,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145474206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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