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}
Pub Date : 2026-01-04DOI: 10.1016/j.geothermics.2025.103568
Chenhua Li , Xiaocheng Zhou , Miao He , Zhaojun Zeng , Yuwen Wang , Jiao Tian , Yucong Yan , Bingyu Yao , Hejun Su , Ruigang Li
Geochemical variations in thermal spring compositions are sensitive to changes in regional stress, temperature, and space conditions, which are indicators of seismic and tectonic activities. However, the temporal and spatial variations in water chemistry components and their inducing mechanisms are insufficiently understood. This study aims to evaluate the effective temporal coincidence/lag of seismic events based on the long-term continuous water chemistry monitoring of seismic areas and draw attention to water chemistry changes in thermal waters during earthquake hazard monitoring. We investigated the major elements, trace elements, and hydrogen and oxygen isotopes of 21 thermal springs along the Lancang–Gengma fault (LGF) zone, which is in a highly deformed, seismically active area of the Southeastern margin of the Tibetan Plateau. In the LGF zone, the temperatures of the studied thermal springs range from 44.7°C to 96.2°C. The reservoir temperatures range from 91°C to 195°C and the reservoir depth range from 4–9 km. According to the spatiotemporal chemical variations from two-year regular monitoring of Na+, Cl−, F−, SO42−, Li, B, δD, and δ18O in five thermal springs, the thermal springs in these fault-controlled areas are sensitive and responsive to seismic activity. Different tectonic regions exhibit significant and diverse short-term precursory anomalies in water chemistry before earthquakes with M ≥ 5.0. Their characteristics and mechanisms are region-specific, and the study area is divided into two monitoring capacity range areas. Area 1: The MG, MM and XF monitoring points located on the Baoshan block are highly sensitive to seismic responses in the SW direction of the study area. For example, continuous Na⁺, Cl−, SO42−and F− anomalies were observed in MG, MM and XF before the ML5.0 and ML5.9 Myanmar earthquakes (southwest of the study area). Area 2: The NKL and EL monitoring points located on the Simao block are highly sensitive to seismic responses in the SE direction. For instance, the Na⁺ concentrations in EL and NKL sharply increased above the normal threshold before the ML6.2 Laos earthquake and ML5.0 Honghe earthquake. Notably, significant spatial directional differences in fluid chemical responses to earthquakes were observed. This directional difference may be related to the complexity of the regional stress field in the area and the local characteristics of fault activities. The chemical composition changes of these thermal springs during fluid circulation in the LGF can be a good tracer of seismic activity.
{"title":"Tectonic controls and earthquake response of thermal fluid geochemistry in southern Yunnan, southeastern Tibetan Plateau","authors":"Chenhua Li , Xiaocheng Zhou , Miao He , Zhaojun Zeng , Yuwen Wang , Jiao Tian , Yucong Yan , Bingyu Yao , Hejun Su , Ruigang Li","doi":"10.1016/j.geothermics.2025.103568","DOIUrl":"10.1016/j.geothermics.2025.103568","url":null,"abstract":"<div><div>Geochemical variations in thermal spring compositions are sensitive to changes in regional stress, temperature, and space conditions, which are indicators of seismic and tectonic activities. However, the temporal and spatial variations in water chemistry components and their inducing mechanisms are insufficiently understood. This study aims to evaluate the effective temporal coincidence/lag of seismic events based on the long-term continuous water chemistry monitoring of seismic areas and draw attention to water chemistry changes in thermal waters during earthquake hazard monitoring. We investigated the major elements, trace elements, and hydrogen and oxygen isotopes of 21 thermal springs along the Lancang–Gengma fault (LGF) zone, which is in a highly deformed, seismically active area of the Southeastern margin of the Tibetan Plateau. In the LGF zone, the temperatures of the studied thermal springs range from 44.7°C to 96.2°C. The reservoir temperatures range from 91°C to 195°C and the reservoir depth range from 4–9 km. According to the spatiotemporal chemical variations from two-year regular monitoring of Na<sup>+</sup>, Cl<sup>−</sup>, F<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, Li, B, δD, and δ<sup>18</sup>O in five thermal springs, the thermal springs in these fault-controlled areas are sensitive and responsive to seismic activity. Different tectonic regions exhibit significant and diverse short-term precursory anomalies in water chemistry before earthquakes with <em>M</em> ≥ 5.0. Their characteristics and mechanisms are region-specific, and the study area is divided into two monitoring capacity range areas. Area 1: The MG, MM and XF monitoring points located on the Baoshan block are highly sensitive to seismic responses in the SW direction of the study area. For example, continuous Na⁺, Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>and F<sup>−</sup> anomalies were observed in MG, MM and XF before the <em>M</em><sub>L</sub>5.0 and <em>M</em><sub>L</sub>5.9 Myanmar earthquakes (southwest of the study area). Area 2: The NKL and EL monitoring points located on the Simao block are highly sensitive to seismic responses in the SE direction. For instance, the Na⁺ concentrations in EL and NKL sharply increased above the normal threshold before the <em>M</em><sub>L</sub>6.2 Laos earthquake and <em>M</em><sub>L</sub>5.0 Honghe earthquake. Notably, significant spatial directional differences in fluid chemical responses to earthquakes were observed. This directional difference may be related to the complexity of the regional stress field in the area and the local characteristics of fault activities. The chemical composition changes of these thermal springs during fluid circulation in the LGF can be a good tracer of seismic activity.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103568"},"PeriodicalIF":3.9,"publicationDate":"2026-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925314","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 : 2026-01-03DOI: 10.1016/j.geothermics.2025.103595
Ana M.B. Domingues , Andre L. Razera , Jairo V.A. Ramalho , Michel K. Rodrigues , Honório J. Fernando , Liércio A. Isoldi , Elizaldo D. dos Santos
This study presents a numerical investigation of the performance of Earth-Air Heat Exchanger (EAHE) systems equipped with galvanized structures surrounding the duct. Two geometric configurations (T- and Y-shaped) are evaluated using the Constructal Design method combined with the Exhaustive Search technique. The analysis considers the EAHE thermal potential (TPEAHE) and the maximum annual efficiency (θmax), along with a multi-objective assessment based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), in which TPEAHE is treated as a benefit criterion and installation depth as a cost criterion. The results indicate that intermediate installation depths (between 3.7 m and 5.0 m) provide better thermal performance, while deeper configurations do not necessarily result in higher TPEAHE values. The T-shaped geometry with a balanced proportion between the vertical and horizontal branches, and the Y-shaped geometry with a branching angle of 140 degrees, exhibited superior performance, with improvements above 10% and 5%, respectively, compared to the least favorable geometries. The optimized Y-shaped configuration reached θmax = 72.0%, achieving a 66.3% gain compared to a conventional case (without galvanized material). The multi-objective analysis demonstrated that there is no universally optimal geometry, but rather a set of effective solutions that emerge depending on the priorities assigned to the system's objectives.
{"title":"Performance analysis and geometric evaluation of galvanized T- and Y-Shapes for earth-air heat exchangers using constructal design","authors":"Ana M.B. Domingues , Andre L. Razera , Jairo V.A. Ramalho , Michel K. Rodrigues , Honório J. Fernando , Liércio A. Isoldi , Elizaldo D. dos Santos","doi":"10.1016/j.geothermics.2025.103595","DOIUrl":"10.1016/j.geothermics.2025.103595","url":null,"abstract":"<div><div>This study presents a numerical investigation of the performance of Earth-Air Heat Exchanger (EAHE) systems equipped with galvanized structures surrounding the duct. Two geometric configurations (T- and Y-shaped) are evaluated using the Constructal Design method combined with the Exhaustive Search technique. The analysis considers the EAHE thermal potential (<em>TP<sub>EAHE</sub></em>) and the maximum annual efficiency (<em>θ<sub>max</sub></em>), along with a multi-objective assessment based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), in which <em>TP<sub>EAHE</sub></em> is treated as a benefit criterion and installation depth as a cost criterion. The results indicate that intermediate installation depths (between 3.7 m and 5.0 m) provide better thermal performance, while deeper configurations do not necessarily result in higher <em>TP<sub>EAHE</sub></em> values. The T-shaped geometry with a balanced proportion between the vertical and horizontal branches, and the Y-shaped geometry with a branching angle of 140 degrees, exhibited superior performance, with improvements above 10% and 5%, respectively, compared to the least favorable geometries. The optimized Y-shaped configuration reached <em>θ<sub>max</sub></em> = 72.0%, achieving a 66.3% gain compared to a conventional case (without galvanized material). The multi-objective analysis demonstrated that there is no universally optimal geometry, but rather a set of effective solutions that emerge depending on the priorities assigned to the system's objectives.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103595"},"PeriodicalIF":3.9,"publicationDate":"2026-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145884499","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 : 2025-12-29DOI: 10.1016/j.geothermics.2025.103581
Lucas Bofill , Gerhard Schäfer , Guilherme Bozetti , Jean-François Ghienne , Mathieu Schuster
Sandstone aquifers lacking mudstone interbeds are often considered homogeneous. However, depositional processes and diagenesis can generate significant permeability contrasts without notable variations in granulometry. Capturing this heterogeneity in flow models is essential but challenging. Outcrop studies provide valuable analogues for subsurface conditions, revealing sedimentary architectures and facies distributions not observable from borehole data alone. This study focuses on the Lower Grès Vosgien formation in eastern France, an important aquifer hosting lithium-rich geothermal brines in the Upper Rhine Graben, deposited by braided fluvial and aeolian systems during the Lower Triassic. This work aims to evaluate the influence of decimetre- to metre-scale sandstone features on advective transport modelling, through a two-dimensional conceptual model developed using a digital outcrop model and sedimentary facies analysis. Six progressively simplified hydrostratigraphic models are tested to assess how heterogeneity and its representation affect particle residence times, breakthrough curves, longitudinal macrodispersivity, and upscaled anisotropy. Results indicate that distinguishing fluvial- and aeolian-related sandstones significantly influences both horizontal and vertical advective flow. Failure to discretise individual fluvial facies and reliance on deterministic hydraulic conductivity values led to the underestimation of preferential flow pathways, delaying the prediction of first particle arrivals. Moreover, the discretisation between fluvial and aeolian-related deposits significantly affects macrodispersion results and yields considerable anisotropy when the conceptual model is upscaled. The strong coupling between advective flow with heat transfer and solute transport underscores the critical role of the observed sedimentary heterogeneity on the accurate understanding of lithium-rich geothermal brines circulation in the matrix porosity of the Lower Triassic sedimentary successions in the Upper Rhine Graben reservoirs.
{"title":"From Outcrop to Groundwater Flow: The Impact of Overlooked Heterogeneity on Advective Transport in Lower Triassic Sandstones, Eastern France","authors":"Lucas Bofill , Gerhard Schäfer , Guilherme Bozetti , Jean-François Ghienne , Mathieu Schuster","doi":"10.1016/j.geothermics.2025.103581","DOIUrl":"10.1016/j.geothermics.2025.103581","url":null,"abstract":"<div><div>Sandstone aquifers lacking mudstone interbeds are often considered homogeneous. However, depositional processes and diagenesis can generate significant permeability contrasts without notable variations in granulometry. Capturing this heterogeneity in flow models is essential but challenging. Outcrop studies provide valuable analogues for subsurface conditions, revealing sedimentary architectures and facies distributions not observable from borehole data alone. This study focuses on the Lower Grès Vosgien formation in eastern France, an important aquifer hosting lithium-rich geothermal brines in the Upper Rhine Graben, deposited by braided fluvial and aeolian systems during the Lower Triassic. This work aims to evaluate the influence of decimetre- to metre-scale sandstone features on advective transport modelling, through a two-dimensional conceptual model developed using a digital outcrop model and sedimentary facies analysis. Six progressively simplified hydrostratigraphic models are tested to assess how heterogeneity and its representation affect particle residence times, breakthrough curves, longitudinal macrodispersivity, and upscaled anisotropy. Results indicate that distinguishing fluvial- and aeolian-related sandstones significantly influences both horizontal and vertical advective flow. Failure to discretise individual fluvial facies and reliance on deterministic hydraulic conductivity values led to the underestimation of preferential flow pathways, delaying the prediction of first particle arrivals. Moreover, the discretisation between fluvial and aeolian-related deposits significantly affects macrodispersion results and yields considerable anisotropy when the conceptual model is upscaled. The strong coupling between advective flow with heat transfer and solute transport underscores the critical role of the observed sedimentary heterogeneity on the accurate understanding of lithium-rich geothermal brines circulation in the matrix porosity of the Lower Triassic sedimentary successions in the Upper Rhine Graben reservoirs.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103581"},"PeriodicalIF":3.9,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145884580","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 : 2025-12-27DOI: 10.1016/j.geothermics.2025.103588
Peng Dai , Tobias Dalton , Paul Eizenhoefer , Sicong Zheng , Kongyou Wu , Zhenhai Zhang , Yuntao Song , Shengdong Wang , Gege Zhang , Yimin She
The distribution of geothermal resources is strongly influenced by the surface–subsurface structural framework of a region, yet the quantitative coupling between fault systems and geothermal reservoirs remains insufficiently constrained in extensional basins. In this study, a multi-method approach integrating gas geochemistry, controlled-source electromagnetic, and geothermal well logging was applied to the Boye area to elucidate its structural–geothermal mechanism. The results reveal that the major NE–SW-trending listric normal faults with NW or SE dips dominate the structural framework and govern the spatial distribution of heat sources, reservoirs, and migration pathways. The deep carbonate geothermal reservoirs in Boye mainly consist of Middle Proterozoic (Jxw and Chg) dolomite, characterized by abundant fractures and cavities that provide effective storage space and enhance convective heat transfer, consistent with the observed reduction in geothermal gradient observed in borehole data. Geothermal accumulation in Boye are controlled by the integrated effects of source, migration, reservoir, and cap structures. Source structures facilitate the upward transfer of crust–mantle heat flow. Migration structures, comprising faults and unconformities, act as conduits that link deep sources with reservoirs. Reservoir structures include both fault-related and intra-reservoir fractures and cavities, providing favorable storage and flow conditions. Cap structures, affected by Cenozoic faulting, both govern meteoric recharge and thermal retention. This study establishes a structural–geothermal framework for the Boye area, demonstrating how extensional fault systems control heat and fluid migration, and providing a practical methodological reference for geothermal exploration in similar tectonic settings.
{"title":"Structural controls on the geothermal reservoir across the Boye Area of Jizhong Depression, Northern China","authors":"Peng Dai , Tobias Dalton , Paul Eizenhoefer , Sicong Zheng , Kongyou Wu , Zhenhai Zhang , Yuntao Song , Shengdong Wang , Gege Zhang , Yimin She","doi":"10.1016/j.geothermics.2025.103588","DOIUrl":"10.1016/j.geothermics.2025.103588","url":null,"abstract":"<div><div>The distribution of geothermal resources is strongly influenced by the surface–subsurface structural framework of a region, yet the quantitative coupling between fault systems and geothermal reservoirs remains insufficiently constrained in extensional basins. In this study, a multi-method approach integrating gas geochemistry, controlled-source electromagnetic, and geothermal well logging was applied to the Boye area to elucidate its structural–geothermal mechanism. The results reveal that the major NE–SW-trending listric normal faults with NW or SE dips dominate the structural framework and govern the spatial distribution of heat sources, reservoirs, and migration pathways. The deep carbonate geothermal reservoirs in Boye mainly consist of Middle Proterozoic (Jxw and Chg) dolomite, characterized by abundant fractures and cavities that provide effective storage space and enhance convective heat transfer, consistent with the observed reduction in geothermal gradient observed in borehole data. Geothermal accumulation in Boye are controlled by the integrated effects of source, migration, reservoir, and cap structures. Source structures facilitate the upward transfer of crust–mantle heat flow. Migration structures, comprising faults and unconformities, act as conduits that link deep sources with reservoirs. Reservoir structures include both fault-related and intra-reservoir fractures and cavities, providing favorable storage and flow conditions. Cap structures, affected by Cenozoic faulting, both govern meteoric recharge and thermal retention. This study establishes a structural–geothermal framework for the Boye area, demonstrating how extensional fault systems control heat and fluid migration, and providing a practical methodological reference for geothermal exploration in similar tectonic settings.</div></div>","PeriodicalId":55095,"journal":{"name":"Geothermics","volume":"136 ","pages":"Article 103588"},"PeriodicalIF":3.9,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145839919","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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