The extensive use of fossil fuels worldwide is one of the major reason of the global climate crisis. Renewable energy is the most promising source used all over the world to reduce the reliance on fossil fuels. Geothermal energy is considered a trustworthy alternative energy source to replace fossil fuels due to its versatility and sustainability. Despite the geothermal energy’s major advantages, the usage of geothermal energy is still limited due to the high costs of conventional exploration techniques and the low accuracy results of these techniques, specifically in the wildcat areas. To address these challenges in exploration phases, satellite-based remote sensing data can be used to lower the early-phase exploration costs. This study aims to develop an early-phase geothermal exploration model that utilises remote sensing data through a machine learning approach. Lineament Density (LD), Hydrothermal Alterations (HA), and Land Surface Temperature (LST) were the most common geothermal surface manifestations used in the model as inputs. These inputs were integrated with K-means and Random Forest (RF) algorithms owing to their capability of handling large and complex datasets. In this study, Buharkent and Germencik geothermal fields from Türkiye were selected as study areas due to their substantial reserves and long-term production, and mature field characteristics. The results of the analysis revealed that the model accuracy was 79% and 59% in Buharkent and Germencik fields, respectively. The study’s findings demonstrate that satellite-based remote sensing data, when combined with machine learning techniques, can be considered a supportive tool for geothermal exploration alongside conventional methods.
{"title":"Early-phase geothermal prospecting using remote sensing and machine learning: application to Buharkent and Germencik fields, Türkiye","authors":"Hakan Oktay Aydınlı, Gordana Kaplan, Saye Nihan Çabuk","doi":"10.1016/j.geothermics.2026.103603","DOIUrl":"10.1016/j.geothermics.2026.103603","url":null,"abstract":"<div><div>The extensive use of fossil fuels worldwide is one of the major reason of the global climate crisis. Renewable energy is the most promising source used all over the world to reduce the reliance on fossil fuels. Geothermal energy is considered a trustworthy alternative energy source to replace fossil fuels due to its versatility and sustainability. Despite the geothermal energy’s major advantages, the usage of geothermal energy is still limited due to the high costs of conventional exploration techniques and the low accuracy results of these techniques, specifically in the wildcat areas. To address these challenges in exploration phases, satellite-based remote sensing data can be used to lower the early-phase exploration costs. This study aims to develop an early-phase geothermal exploration model that utilises remote sensing data through a machine learning approach. Lineament Density (LD), Hydrothermal Alterations (HA), and Land Surface Temperature (LST) were the most common geothermal surface manifestations used in the model as inputs. These inputs were integrated with K-means and Random Forest (RF) algorithms owing to their capability of handling large and complex datasets. In this study, Buharkent and Germencik geothermal fields from Türkiye were selected as study areas due to their substantial reserves and long-term production, and mature field characteristics. The results of the analysis revealed that the model accuracy was 79% and 59% in Buharkent and Germencik fields, respectively. The study’s findings demonstrate that satellite-based remote sensing data, when combined with machine learning techniques, can be considered a supportive tool for geothermal exploration alongside conventional methods.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103603"},"PeriodicalIF":3.9,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976969","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 : 2026-01-16DOI: 10.1016/j.geothermics.2026.103602
Ming Min , Qiang Zhang , Xiao-Suo Wu , Bin-Song Jiang
The growing development of deep geothermal energy resources, where rock masses are subjected to high temperatures and significant plastic deformation, demands constitutive models that accurately capture this complex behavior. This study presents a novel thermomechanical constitutive model within a strain-softening framework, which uniquely integrates the coupled effects of temperature (T), confining pressure (σ3), and plastic shear strain (γp). Its primary innovation lies in explicitly formulating the cohesion (c), internal friction angle (φ), and dilation angle (ψ) as functions of both γp, T and/or σ3. This nonlinear evolution function is is underpinned by systematic triaxial compression tests on thermally-treated granite specimens, which reveal that c, φ, and ψ undergo initial increasing followed by an exponential decay with increasing γp. Notably, T and σ3 play a critical role in modulating the evolution law of these fitting parameters. The proposed model, implemented in FLAC3D via a secondary development scheme, successfully reproduces the nonlinear deformation and strain-softening behavior observed in experiments. An engineering case study demonstrates that conventional models assuming constant temperature (T = 25°C) underestimate radial displacements around a deep circular opening by up to 188%, compared to simulations incorporating the proposed model with a realistic nonlinear thermal field. These findings emphasize the critical importance of incorporating thermo-mechanical-plastic coupling in the design and analysis of deep geothermal environments.
{"title":"Mechanical behavior and constitutive model of thermally damaged granite: Insights from experiments","authors":"Ming Min , Qiang Zhang , Xiao-Suo Wu , Bin-Song Jiang","doi":"10.1016/j.geothermics.2026.103602","DOIUrl":"10.1016/j.geothermics.2026.103602","url":null,"abstract":"<div><div>The growing development of deep geothermal energy resources, where rock masses are subjected to high temperatures and significant plastic deformation, demands constitutive models that accurately capture this complex behavior. This study presents a novel thermomechanical constitutive model within a strain-softening framework, which uniquely integrates the coupled effects of temperature (<em>T</em>), confining pressure (<em>σ</em><sub>3</sub>), and plastic shear strain (<em>γ</em><sup>p</sup>). Its primary innovation lies in explicitly formulating the cohesion (<em>c</em>), internal friction angle (<em>φ</em>), and dilation angle (<em>ψ</em>) as functions of both <em>γ</em><sup>p</sup>, <em>T</em> and/or <em>σ</em><sub>3</sub>. This nonlinear evolution function is is underpinned by systematic triaxial compression tests on thermally-treated granite specimens, which reveal that <em>c, φ</em>, and <em>ψ</em> undergo initial increasing followed by an exponential decay with increasing <em>γ</em><sup>p</sup>. Notably, <em>T</em> and <em>σ</em><sub>3</sub> play a critical role in modulating the evolution law of these fitting parameters. The proposed model, implemented in FLAC3D via a secondary development scheme, successfully reproduces the nonlinear deformation and strain-softening behavior observed in experiments. An engineering case study demonstrates that conventional models assuming constant temperature (<em>T</em> = 25°C) underestimate radial displacements around a deep circular opening by up to 188%, compared to simulations incorporating the proposed model with a realistic nonlinear thermal field. These findings emphasize the critical importance of incorporating thermo-mechanical-plastic coupling in the design and analysis of deep geothermal environments.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103602"},"PeriodicalIF":3.9,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976970","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 : 2026-01-16DOI: 10.1016/j.geothermics.2026.103599
Samuel Rybár , Michal Nemčok , Lucia Ledvényiová , Přemysl Kyselák , Ľubomír Sliva
This study investigates the geothermal potential of the Czech sector of the Vienna Basin, a region traditionally explored for hydrocarbons, through the integration of seismic and fluid data. The analysis focuses on low-temperature geothermal systems (<150°C) hosted by Badenian and Sarmatian (Langhian–Serravallian) sedimentary sequences. Seismic interpretation identifies key structural features, including the Steinberg Fault Zone, serving as a recharge area, and the Lanžhot–Hrušky Fault Zone, representing a discharge area of a topography-driven geothermal fluid-flow system connected by a network of densely spaced aquifers. Hydrogeochemical analyses reveal total dissolved solids ranging from 3400 to 21,000 ppm and fluid inflow rates from 0.5 to 14.5 m³/h. Current limitations include incomplete data coverage and relatively low geothermal gradients; however, the availability of extensive hydrocarbon infrastructure and a large well database provides a unique opportunity for geothermal exploration and redevelopment. Deepening of selected wells in the most promising areas could increase reservoir temperatures, improving the economic efficiency of future geothermal projects. This study provides the first integrated structural and hydrogeothermal interpretation of the Czech sector of the Vienna Basin. The results identify a topography-driven geothermal circulation system controlled by the Steinberg and Lanžhot–Hrušky Fault Zones, linking recharge and discharge zones across multiple Badenian and Sarmatian aquifers. These findings establish a well-constrained conceptual framework for the basin’s geothermal system and demonstrate the potential for direct-use applications based on existing exploration data.
{"title":"Geothermal potential of the Czech Vienna Basin: Structural and fluid-flow dynamics of a former pull-apart basin","authors":"Samuel Rybár , Michal Nemčok , Lucia Ledvényiová , Přemysl Kyselák , Ľubomír Sliva","doi":"10.1016/j.geothermics.2026.103599","DOIUrl":"10.1016/j.geothermics.2026.103599","url":null,"abstract":"<div><div>This study investigates the geothermal potential of the Czech sector of the Vienna Basin, a region traditionally explored for hydrocarbons, through the integration of seismic and fluid data. The analysis focuses on low-temperature geothermal systems (<150°C) hosted by Badenian and Sarmatian (Langhian–Serravallian) sedimentary sequences. Seismic interpretation identifies key structural features, including the Steinberg Fault Zone, serving as a recharge area, and the Lanžhot–Hrušky Fault Zone, representing a discharge area of a topography-driven geothermal fluid-flow system connected by a network of densely spaced aquifers. Hydrogeochemical analyses reveal total dissolved solids ranging from 3400 to 21,000 ppm and fluid inflow rates from 0.5 to 14.5 m³/h. Current limitations include incomplete data coverage and relatively low geothermal gradients; however, the availability of extensive hydrocarbon infrastructure and a large well database provides a unique opportunity for geothermal exploration and redevelopment. Deepening of selected wells in the most promising areas could increase reservoir temperatures, improving the economic efficiency of future geothermal projects. This study provides the first integrated structural and hydrogeothermal interpretation of the Czech sector of the Vienna Basin. The results identify a topography-driven geothermal circulation system controlled by the Steinberg and Lanžhot–Hrušky Fault Zones, linking recharge and discharge zones across multiple Badenian and Sarmatian aquifers. These findings establish a well-constrained conceptual framework for the basin’s geothermal system and demonstrate the potential for direct-use applications based on existing exploration data.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103599"},"PeriodicalIF":3.9,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976971","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 : 2026-01-13DOI: 10.1016/j.geothermics.2026.103600
Yixuan Wang , Xun Zhou , Jingru Ma , Bin Fang , Ye Shen , Ruige Chen , Yanqiu Wu , Yanxiang Shi , Mengying Chen , Qiqi Liu , Tong Zhang , Guangbin Tao , Linyang Zhuo
Hot springs in the Chengde region of northern Hebei Province, China, occur in scattered locations influenced by varied geological structures. Twenty-eight water samples from 10 sites were analyzed to investigate hydrogeochemistry and geothermal behavior. Stable isotopes indicate meteoric recharge at elevations of 861–1938 m, with northern springs near active faults showing more depleted signatures, reflecting deeper circulation. The waters are weakly alkaline, low- to moderate-TDS, and mainly HCO3·SO4–Na and HCO3–Na types. Na+ derives from silicate weathering and cation exchange, SO42- from evaporite dissolution and pyrite oxidation, and HCO3- from CO2-driven carbonate dissolution. Trace elements (Li, Rb, Cs, Sr, Ba) vary systematically among groups, indicating differences in reservoir lithology and circulation depth; carbonate dissolution is a major Sr and Ba source. Mineral saturation and ion concentrations reflect contrasting water–rock interaction intensities. Reservoir temperatures from silica geothermometers and the SiO2–enthalpy model range from 50 to 143 °C, with circulation depths up to approximately 4500 m and cold water mixing ratios of 46–93%. Springs linked to faults and lithological contacts generally have higher temperatures and deeper flow paths, whereas those in bedrock fractures are shallower and more affected by mixing. These findings highlight the combined influence of topography, geological structure, and lithology on geothermal circulation, providing a geochemical framework for geothermal exploration and resource assessment in intracontinental regions.
{"title":"Hydrogeochemical characteristics and geological controls of thermal springs in the Chengde Area, North China","authors":"Yixuan Wang , Xun Zhou , Jingru Ma , Bin Fang , Ye Shen , Ruige Chen , Yanqiu Wu , Yanxiang Shi , Mengying Chen , Qiqi Liu , Tong Zhang , Guangbin Tao , Linyang Zhuo","doi":"10.1016/j.geothermics.2026.103600","DOIUrl":"10.1016/j.geothermics.2026.103600","url":null,"abstract":"<div><div>Hot springs in the Chengde region of northern Hebei Province, China, occur in scattered locations influenced by varied geological structures. Twenty-eight water samples from 10 sites were analyzed to investigate hydrogeochemistry and geothermal behavior. Stable isotopes indicate meteoric recharge at elevations of 861–1938 m, with northern springs near active faults showing more depleted signatures, reflecting deeper circulation. The waters are weakly alkaline, low- to moderate-TDS, and mainly HCO<sub>3</sub>·SO<sub>4</sub>–Na and HCO<sub>3</sub>–Na types. Na<sup>+</sup> derives from silicate weathering and cation exchange, SO<sub>4</sub><sup>2-</sup> from evaporite dissolution and pyrite oxidation, and HCO<sub>3</sub><sup>-</sup> from CO<sub>2</sub>-driven carbonate dissolution. Trace elements (Li, Rb, Cs, Sr, Ba) vary systematically among groups, indicating differences in reservoir lithology and circulation depth; carbonate dissolution is a major Sr and Ba source. Mineral saturation and ion concentrations reflect contrasting water–rock interaction intensities. Reservoir temperatures from silica geothermometers and the SiO<sub>2</sub>–enthalpy model range from 50 to 143 °C, with circulation depths up to approximately 4500 m and cold water mixing ratios of 46–93%. Springs linked to faults and lithological contacts generally have higher temperatures and deeper flow paths, whereas those in bedrock fractures are shallower and more affected by mixing. These findings highlight the combined influence of topography, geological structure, and lithology on geothermal circulation, providing a geochemical framework for geothermal exploration and resource assessment in intracontinental regions.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103600"},"PeriodicalIF":3.9,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976968","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 : 2026-01-09DOI: 10.1016/j.geothermics.2026.103598
Yifan Zhang, Pradeepkumar Ashok, Dongmei Chen, Eric van Oort
Drilling and other well construction operations in high-temperature geothermal wells face a fundamental challenge: preventing downhole tool failure caused by exceeding temperature limits. Tripping into such wells needs to be staged to lower the possibility of thermal tool damage. This study investigates the bottomhole assembly (BHA) temperature evolution, cooling effectiveness, and operational design of staged trip-in practices in geothermal and other high-temperature wells. A thermo-hydraulic modeling framework is developed, combining a full-well finite volume model (FVM) with a lumped BHA-wellbore model, to capture transient well thermodynamics during drilling and staged trip-in operations. Model validation using Utah Forge Well 16B(78)-32 data shows that the root mean square error (RMSE) of bit/BHA temperature prediction ranges from 4°F (2.2°C) to 8°F (4.4°C). Sensitivity analyses demonstrate that the maximum stage length remains under 4-5 stands when tripping into wellbores with near-field formation temperatures in the range of 250°F (121°C) to 320°F (160°C) unless significant well geometry or mud property changes occur. The only strategy that consistently extends downhole sensor survivability beyond 8-10 stands is BHA external thermal insulation. Simulation results demonstrate that adding a field-proven 0.15 in (3.8 mm) coating with thermal conductivity of 9 BTU.in/hr/ft2/°F (1.30 W/m/K) can reduce BHA temperatures by up to 30°F (17°C), compared to unprotected configurations under these downhole conditions. The modeling and analysis can also help identify scenarios where staged circulation is insufficient and continuous circulation (i.e., circulation while making connections) is required to maintain safe tripping BHA temperatures. These findings provide practical and insightful guidance for the design of effective cooling strategies during geothermal and high-temperature oil and gas well drilling and tripping operations, ensuring safer and more efficient operations in extreme downhole thermal environments with a lowered risk of BHA component failure.
高温地热井的钻井和其他建井作业面临着一个根本性的挑战：防止井下工具因温度超标而失效。下入此类井需要分级，以降低热工具损坏的可能性。本研究研究了地热井和其他高温井的井底钻具组合（BHA）温度变化、冷却效果以及分段起下钻的操作设计。开发了一种热水力建模框架，将全井有限体积模型（FVM）与集总bha -井筒模型相结合，以捕获钻井和分段起下钻过程中的瞬态井热力学。使用Utah Forge Well 16B(78)-32数据进行的模型验证表明，钻头/BHA温度预测的均方根误差（RMSE）范围为4°F（2.2°C）至8°F（4.4°C）。敏感性分析表明，当下入近场地层温度为250°F（121°C）至320°F（160°C）的井时，除非井的几何形状或泥浆性质发生重大变化，否则最大段长度保持在4-5°F以下。将井下传感器的生存能力持续延长至8-10架以上的唯一策略是BHA外部保温。模拟结果表明，添加经过现场验证的0.15 in （3.8 mm）涂层，导热系数为9 BTU。在这些井下条件下，与不受保护的配置相比，1.30 W/m/K可以将BHA温度降低30°F（17°C）。建模和分析还可以帮助识别分段循环不足的情况，以及需要连续循环（即在连接时进行循环）以保持起下钻BHA温度的情况。这些发现为地热和高温油气井钻井和起下钻过程中有效冷却策略的设计提供了实用和有见解的指导，确保在极端的井下热环境下更安全、更高效地作业，同时降低BHA组件失效的风险。
{"title":"Tripping and staging into geothermal wells while assuring thermal protection of downhole tools and sensors","authors":"Yifan Zhang, Pradeepkumar Ashok, Dongmei Chen, Eric van Oort","doi":"10.1016/j.geothermics.2026.103598","DOIUrl":"10.1016/j.geothermics.2026.103598","url":null,"abstract":"<div><div>Drilling and other well construction operations in high-temperature geothermal wells face a fundamental challenge: preventing downhole tool failure caused by exceeding temperature limits. Tripping into such wells needs to be staged to lower the possibility of thermal tool damage. This study investigates the bottomhole assembly (BHA) temperature evolution, cooling effectiveness, and operational design of staged trip-in practices in geothermal and other high-temperature wells. A thermo-hydraulic modeling framework is developed, combining a full-well finite volume model (FVM) with a lumped BHA-wellbore model, to capture transient well thermodynamics during drilling and staged trip-in operations. Model validation using Utah Forge Well 16B(78)-32 data shows that the root mean square error (RMSE) of bit/BHA temperature prediction ranges from 4°F (2.2°C) to 8°F (4.4°C). Sensitivity analyses demonstrate that the maximum stage length remains under 4-5 stands when tripping into wellbores with near-field formation temperatures in the range of 250°F (121°C) to 320°F (160°C) unless significant well geometry or mud property changes occur. The only strategy that consistently extends downhole sensor survivability beyond 8-10 stands is BHA external thermal insulation. Simulation results demonstrate that adding a field-proven 0.15 in (3.8 mm) coating with thermal conductivity of 9 BTU.in/hr/ft<sup>2</sup>/°F (1.30 W/m/K) can reduce BHA temperatures by up to 30°F (17°C), compared to unprotected configurations under these downhole conditions. The modeling and analysis can also help identify scenarios where staged circulation is insufficient and continuous circulation (i.e., circulation while making connections) is required to maintain safe tripping BHA temperatures. These findings provide practical and insightful guidance for the design of effective cooling strategies during geothermal and high-temperature oil and gas well drilling and tripping operations, ensuring safer and more efficient operations in extreme downhole thermal environments with a lowered risk of BHA component failure.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103598"},"PeriodicalIF":3.9,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925309","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 : 2026-01-09DOI: 10.1016/j.geothermics.2026.103596
Aastha , Emma Bramham , Andy Nowacki , Nick Shaw , Anette Mortensen , David Healy
Permeability in the Þeistareykir geothermal system of Iceland is structurally controlled. Natural fracture networks are abundant in Þeistareykir and contribute significantly to fluid flow. Understanding which features enhance permeability and hydraulic conductivity, and how their properties interact with lithology and reservoir structure, is key to predicting reservoir behaviour. To address this, we utilise a range of borehole data to characterise natural fractures in terms of their occurrence, orientation, relative distribution, their relationship with the major lithological units and permeable flow zones in the subsurface. Results show systematic variations in fracture density, thickness, and distribution pattern across different lithologies and depths, with orientations ranging from NNW-SSE, N-S, NNE-SSW to NE-SW. Fractures exhibit the highest intensity in the deeper acidic intrusive units or coarser grained basalt with a predominant N-S-trend and bimodal dip distribution. However, permeability is controlled by a complex interplay of fracture geometry, openness and connectivity rather than simply high fracture abundance or a preferential set of fractures. Permeable feed zones show diverse structural expressions, ranging from high-density fracture clusters and large-aperture fractures to intensely fractured damage zones and multiple intersecting fracture sets. These findings demonstrate that the structural character of the potential fluid-flow channels is highly variable in Þeistareykir. The results of this study can be incorporated into fracture and flow models to enhance our understanding of the permeability distribution and fluid pathways in the Þeistareykir geothermal system.
{"title":"Fracture properties, structural heterogeneity, and permeability in the Þeistareykir geothermal system, NE Iceland","authors":"Aastha , Emma Bramham , Andy Nowacki , Nick Shaw , Anette Mortensen , David Healy","doi":"10.1016/j.geothermics.2026.103596","DOIUrl":"10.1016/j.geothermics.2026.103596","url":null,"abstract":"<div><div>Permeability in the Þeistareykir geothermal system of Iceland is structurally controlled. Natural fracture networks are abundant in Þeistareykir and contribute significantly to fluid flow. Understanding which features enhance permeability and hydraulic conductivity, and how their properties interact with lithology and reservoir structure, is key to predicting reservoir behaviour. To address this, we utilise a range of borehole data to characterise natural fractures in terms of their occurrence, orientation, relative distribution, their relationship with the major lithological units and permeable flow zones in the subsurface. Results show systematic variations in fracture density, thickness, and distribution pattern across different lithologies and depths, with orientations ranging from NNW-SSE, N-S, NNE-SSW to NE-SW. Fractures exhibit the highest intensity in the deeper acidic intrusive units or coarser grained basalt with a predominant N-S-trend and bimodal dip distribution. However, permeability is controlled by a complex interplay of fracture geometry, openness and connectivity rather than simply high fracture abundance or a preferential set of fractures. Permeable feed zones show diverse structural expressions, ranging from high-density fracture clusters and large-aperture fractures to intensely fractured damage zones and multiple intersecting fracture sets. These findings demonstrate that the structural character of the potential fluid-flow channels is highly variable in Þeistareykir. The results of this study can be incorporated into fracture and flow models to enhance our understanding of the permeability distribution and fluid pathways in the Þeistareykir geothermal system.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103596"},"PeriodicalIF":3.9,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925306","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 : 2026-01-09DOI: 10.1016/j.geothermics.2026.103597
Yue Shen , Yuanzhi Cheng , Zhonghe Pang
The Chabu geothermal field, located on the Xainza-Dinggye Rift, is demonstrated to be a product of the tectonic-heat flow couple under plate collision, where an extensional fault network exerts the primary control on heat and fluid transport. Based on magnetotelluric (MT) data from 76 stations, we constructed a three-dimensional resistivity model to investigate the heat source, fluid pathways, and tectonic controls on the geothermal system. The model reveals a shallow low-resistivity anomaly associated with hot spring discharge and a large-scale low-resistivity body of ∼18–20 km depth in the middle to upper crust. The low-resistivity body is interpreted as a heat source resulting from asthenospheric upwelling and partial melting of the lithosphere. These two anomalies are linked by a fault-controlled, vertically aligned low-resistivity conduit that likely serves as a channel for upward fluid migration. This channel is controlled by the intersection of the deep and large fracture in the EW direction and the SNNE direction in the region, demonstrating the significant control effect of the southern Tibetan extension structure on the migration path of thermal fluids. Studies show that the Chabu geothermal system is the product of the tectonic-heat flow couple under the background of plate collision. The extensional fault network controls both the migration of heat and the development of the hydrothermal circulation system. The results of this study provide new geophysical evidence and theoretical support for the formation mechanism and resource evaluation of the rift-type geothermal system in the South Tibet Plateau.
{"title":"Magnetotelluric imaging of tectonic control on fluid pathways and heat sources in a continental rift geothermal system, southern tibet","authors":"Yue Shen , Yuanzhi Cheng , Zhonghe Pang","doi":"10.1016/j.geothermics.2026.103597","DOIUrl":"10.1016/j.geothermics.2026.103597","url":null,"abstract":"<div><div>The Chabu geothermal field, located on the Xainza-Dinggye Rift, is demonstrated to be a product of the tectonic-heat flow couple under plate collision, where an extensional fault network exerts the primary control on heat and fluid transport. Based on magnetotelluric (MT) data from 76 stations, we constructed a three-dimensional resistivity model to investigate the heat source, fluid pathways, and tectonic controls on the geothermal system. The model reveals a shallow low-resistivity anomaly associated with hot spring discharge and a large-scale low-resistivity body of ∼18–20 km depth in the middle to upper crust. The low-resistivity body is interpreted as a heat source resulting from asthenospheric upwelling and partial melting of the lithosphere. These two anomalies are linked by a fault-controlled, vertically aligned low-resistivity conduit that likely serves as a channel for upward fluid migration. This channel is controlled by the intersection of the deep and large fracture in the EW direction and the SN<img>NE direction in the region, demonstrating the significant control effect of the southern Tibetan extension structure on the migration path of thermal fluids. Studies show that the Chabu geothermal system is the product of the tectonic-heat flow couple under the background of plate collision. The extensional fault network controls both the migration of heat and the development of the hydrothermal circulation system. The results of this study provide new geophysical evidence and theoretical support for the formation mechanism and resource evaluation of the rift-type geothermal system in the South Tibet Plateau.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103597"},"PeriodicalIF":3.9,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925307","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 : 2026-01-07DOI: 10.1016/j.geothermics.2025.103590
Marcus L.A. do Amaral , Mayara C.O. Caldeira , Jose J.S. de Figueiredo , João Rafael B.S. Da Silveira
Geothermal energy is one of the energy resources with the potential to contribute to clean electricity generation efficiently. This study employs a Fuzzy Logic-based Multi-Criteria Decision Analysis (MCDA-Fuzzy) approach to assess the geothermal potential of an Enhanced Geothermal System (EGS) at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). The methodology integrates surface and subsurface data. Surface data include Bouguer anomaly, distance to faults and seismic epicenters, heat flow, and land surface temperature (LST), obtained from georeferenced databases and satellite imagery. Subsurface data consists of 2D sections derived from inverted magnetotelluric data, gravimetric inversion, P-wave velocity models, and basin-granitoid boundary delineation. Most data were sourced from the region’s Geothermal Data Repository (GDR). The application of the MCDA-Fuzzy methodology to surface data is compared with its application at depth to evaluate whether a surface-based assessment can provide results comparable to those obtained through geophysical modeling. The results include the construction of one geothermal potential map for the surface and six 2D maps at different depth levels, enabling a detailed spatial assessment of geothermal potential along the subsurface. We validated these maps using well-petrophysical data according to their corresponding geophysical properties. The analysis revealed that the geothermal potential estimated at the surface aligns with the distribution identified in-depth, highlighting a promising area in the eastern portion of the Utah FORGE site. It is concluded that the MCDA-Fuzzy methodology can be effectively used to assess the geothermal potential of Enhanced Geothermal Systems (EGS) using both surface data and geophysical modeling at depth, enabling the identification of promising areas for geothermal exploration with greater efficiency and lower computational cost.
{"title":"Integration of geophysical data and multicriteria decision analysis for geothermal assessment at Utah FORGE","authors":"Marcus L.A. do Amaral , Mayara C.O. Caldeira , Jose J.S. de Figueiredo , João Rafael B.S. Da Silveira","doi":"10.1016/j.geothermics.2025.103590","DOIUrl":"10.1016/j.geothermics.2025.103590","url":null,"abstract":"<div><div>Geothermal energy is one of the energy resources with the potential to contribute to clean electricity generation efficiently. This study employs a Fuzzy Logic-based Multi-Criteria Decision Analysis (MCDA-Fuzzy) approach to assess the geothermal potential of an Enhanced Geothermal System (EGS) at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). The methodology integrates surface and subsurface data. Surface data include Bouguer anomaly, distance to faults and seismic epicenters, heat flow, and land surface temperature (LST), obtained from georeferenced databases and satellite imagery. Subsurface data consists of 2D sections derived from inverted magnetotelluric data, gravimetric inversion, P-wave velocity models, and basin-granitoid boundary delineation. Most data were sourced from the region’s Geothermal Data Repository (GDR). The application of the MCDA-Fuzzy methodology to surface data is compared with its application at depth to evaluate whether a surface-based assessment can provide results comparable to those obtained through geophysical modeling. The results include the construction of one geothermal potential map for the surface and six 2D maps at different depth levels, enabling a detailed spatial assessment of geothermal potential along the subsurface. We validated these maps using well-petrophysical data according to their corresponding geophysical properties. The analysis revealed that the geothermal potential estimated at the surface aligns with the distribution identified in-depth, highlighting a promising area in the eastern portion of the Utah FORGE site. It is concluded that the MCDA-Fuzzy methodology can be effectively used to assess the geothermal potential of Enhanced Geothermal Systems (EGS) using both surface data and geophysical modeling at depth, enabling the identification of promising areas for geothermal exploration with greater efficiency and lower computational cost.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103590"},"PeriodicalIF":3.9,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925310","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 exploitation and utilization of geothermal energy necessitate a clear understanding of the genesis mechanisms of geothermal systems. The complex geological conditions result in diverse hydrochemical characteristics of enriched geothermal waters in the Gaoligong geothermal belt, southeastern Tibetan Plateau. This study employs the Self-Organizing Map (SOM) and Positive Matrix Factorization (PMF) algorithms, along with hydrochemical and hydrogen-oxygen isotope analyses, to identify the genesis mechanisms among different types of geothermal waters. Three types of geothermal water were identified in the study area (Groups 1 − 3). For Group 1, the contribution ratio of carbonate mineral dissolution (calcite, dolomite) is 37.6 %, followed by evaporite minerals (gypsum: 17.2 %, halite: 16.6 %) and silicates (28.6 %). In Group 2, silicate minerals (Ca- and Mg-rich silicates: 41.5 %, Na-rich silicates: 30.1 %) contribute the most to the components, followed by pyrite (28.4 %). For Group 3, the components are primarily derived from silicate dissolution (sandstone: 18.0 %, granite: 31.2 %), followed by geothermal gases (25.7 %) and carbonates (25.1 %). The geothermal reservoir temperatures of Groups 1 to 3 before and after mixing are 111 °C to 61 °C, 170 °C to 78 °C, and 124 °C to 63 °C, respectively. This study identified the recharge sources, quantified the sources of the major components, and assessed the reservoir temperature. Based on these findings, the corresponding genesis mechanisms with different hydrochemical characteristics were established. This study aims to deepen the understanding of magma chamber-driven geothermal systems and provide valuable support for the development and utilization of geothermal resources worldwide.
{"title":"Hydrochemical fingerprints, source apportionment and genesis mechanism of geothermal waters in the Gaoligong Geothermal Belt, southeastern Tibetan Plateau","authors":"Jinhang Huang , Xingze Li , Xingwang Chang , Xingcheng Yuan , Xun Huang , Hongyang Guo , Yunhui Zhang","doi":"10.1016/j.geothermics.2025.103577","DOIUrl":"10.1016/j.geothermics.2025.103577","url":null,"abstract":"<div><div>The exploitation and utilization of geothermal energy necessitate a clear understanding of the genesis mechanisms of geothermal systems. The complex geological conditions result in diverse hydrochemical characteristics of enriched geothermal waters in the Gaoligong geothermal belt, southeastern Tibetan Plateau. This study employs the Self-Organizing Map (SOM) and Positive Matrix Factorization (PMF) algorithms, along with hydrochemical and hydrogen-oxygen isotope analyses, to identify the genesis mechanisms among different types of geothermal waters. Three types of geothermal water were identified in the study area (Groups 1 − 3). For Group 1, the contribution ratio of carbonate mineral dissolution (calcite, dolomite) is 37.6 %, followed by evaporite minerals (gypsum: 17.2 %, halite: 16.6 %) and silicates (28.6 %). In Group 2, silicate minerals (Ca- and Mg-rich silicates: 41.5 %, Na-rich silicates: 30.1 %) contribute the most to the components, followed by pyrite (28.4 %). For Group 3, the components are primarily derived from silicate dissolution (sandstone: 18.0 %, granite: 31.2 %), followed by geothermal gases (25.7 %) and carbonates (25.1 %). The geothermal reservoir temperatures of Groups 1 to 3 before and after mixing are 111 °C to 61 °C, 170 °C to 78 °C, and 124 °C to 63 °C, respectively. This study identified the recharge sources, quantified the sources of the major components, and assessed the reservoir temperature. Based on these findings, the corresponding genesis mechanisms with different hydrochemical characteristics were established. This study aims to deepen the understanding of magma chamber-driven geothermal systems and provide valuable support for the development and utilization of geothermal resources worldwide.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103577"},"PeriodicalIF":3.9,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925312","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 : 2026-01-05DOI: 10.1016/j.geothermics.2025.103593
Suzan Pasvanoğlu , Serkan Vural , Tekin Yeken
<div><div>The Kepekler-Ilıcaboğazı geothermal field is located in northwest Anatolia, within Balıkesir Province, and comprises both thermal waters and therapeutic clay mud (Peloids). The thermal waters emerge as springs with a temperature range from 30 to 56 °C, with discharge rates of 0.01−4 L/s along a secondary fault in the North Anatolian Fault Zone (NAFZ). Only one (BK-1) production well was drilled to a depth of 390.30 m by General Directorate of Mineral Research and Exploration of Türkiye (MTA), which has a water temperature of 64 °C and a discharge rate of 15 L/<em>sec</em>. This study investigates the chemical and isotopic characteristics of thermal and cold waters using the major ion and trace element contents as well as environmental isotope compositions. The thermal waters belong to the alkaline NaCl-type, and are characterized by pH values of 6.35 and 7.90, generally higher EC (3149–3856 µS/cm), and relatively high concentrations of Cl, Na, B, As, Rb, Li, Cs, and Sr, in contrast to the cold waters, which are primarily of the CaHCO<sub>3</sub> type. Carbonate and silicate dissolution, ion exchange, and energy loss through heat conduction are processes responsible for the origin and evolution of NaCl-type water. Thermal waters tend to have lower B/Cl ratios and strong correlations between (Cl and B, Li, and Rb) trace alkali metals and Cl due to rapid, efficient upflow pathways. These features align with high vertical permeability networks that promote efficient upflow and meteoric mixing, delineating the systems of the Kepekler-Ilıcaboğazı area. By estimating reservoir temperatures using chemical geothermometers and saturation indices, reservoir temperature estimates (75–100 °C) may be affected by conductive cooling, mixing, or partial equilibration—especially as most waters plot as "immature" on Giggenbach diagrams. Chemical equilibrium studies show that the thermal waters are in equilibrium with respect to calcite, aragonite, and quartz, while undersaturated with respect to albite, anorthite, K-feldspar, and gypsum. Thermal waters are meteoric in origin as suggested by the isotope (δ<sup>18</sup>O, δ<sup>2</sup>H, <sup>3</sup>H) composition. Carbon in thermal waters is likely to originate from metamorphic CO<sub>2</sub> or marine carbonates whereas carbon in cold waters is derived from an organic source. δ<sup>34</sup>S sulfur is derived from bacterial sulfate reduction and the dissolution of marine carbonates and sulfide minerals. The study area features a fault-controlled convection deep circulation geothermal system. Thermal waters are sourced from a resource base in the upper crust, which consists of thick granitic and metamorphic rocks that reach the surface. Using the results of hydrogeology and hydrogeochemistry, a conceptual hydrothermal model of recharge, mixing, and discharge has been proposed for the formation of the thermal waters in the study area. This is the first comprehensive geochemical and isotope-based investigati
{"title":"Geochemistry and genesis analysis of the Kepekler – Ilıcaboğazı thermal waters (Balıkesir, NW Türkiye)","authors":"Suzan Pasvanoğlu , Serkan Vural , Tekin Yeken","doi":"10.1016/j.geothermics.2025.103593","DOIUrl":"10.1016/j.geothermics.2025.103593","url":null,"abstract":"<div><div>The Kepekler-Ilıcaboğazı geothermal field is located in northwest Anatolia, within Balıkesir Province, and comprises both thermal waters and therapeutic clay mud (Peloids). The thermal waters emerge as springs with a temperature range from 30 to 56 °C, with discharge rates of 0.01−4 L/s along a secondary fault in the North Anatolian Fault Zone (NAFZ). Only one (BK-1) production well was drilled to a depth of 390.30 m by General Directorate of Mineral Research and Exploration of Türkiye (MTA), which has a water temperature of 64 °C and a discharge rate of 15 L/<em>sec</em>. This study investigates the chemical and isotopic characteristics of thermal and cold waters using the major ion and trace element contents as well as environmental isotope compositions. The thermal waters belong to the alkaline NaCl-type, and are characterized by pH values of 6.35 and 7.90, generally higher EC (3149–3856 µS/cm), and relatively high concentrations of Cl, Na, B, As, Rb, Li, Cs, and Sr, in contrast to the cold waters, which are primarily of the CaHCO<sub>3</sub> type. Carbonate and silicate dissolution, ion exchange, and energy loss through heat conduction are processes responsible for the origin and evolution of NaCl-type water. Thermal waters tend to have lower B/Cl ratios and strong correlations between (Cl and B, Li, and Rb) trace alkali metals and Cl due to rapid, efficient upflow pathways. These features align with high vertical permeability networks that promote efficient upflow and meteoric mixing, delineating the systems of the Kepekler-Ilıcaboğazı area. By estimating reservoir temperatures using chemical geothermometers and saturation indices, reservoir temperature estimates (75–100 °C) may be affected by conductive cooling, mixing, or partial equilibration—especially as most waters plot as \"immature\" on Giggenbach diagrams. Chemical equilibrium studies show that the thermal waters are in equilibrium with respect to calcite, aragonite, and quartz, while undersaturated with respect to albite, anorthite, K-feldspar, and gypsum. Thermal waters are meteoric in origin as suggested by the isotope (δ<sup>18</sup>O, δ<sup>2</sup>H, <sup>3</sup>H) composition. Carbon in thermal waters is likely to originate from metamorphic CO<sub>2</sub> or marine carbonates whereas carbon in cold waters is derived from an organic source. δ<sup>34</sup>S sulfur is derived from bacterial sulfate reduction and the dissolution of marine carbonates and sulfide minerals. The study area features a fault-controlled convection deep circulation geothermal system. Thermal waters are sourced from a resource base in the upper crust, which consists of thick granitic and metamorphic rocks that reach the surface. Using the results of hydrogeology and hydrogeochemistry, a conceptual hydrothermal model of recharge, mixing, and discharge has been proposed for the formation of the thermal waters in the study area. This is the first comprehensive geochemical and isotope-based investigati","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103593"},"PeriodicalIF":3.9,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925313","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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