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The temperature prediction of geothermal reservoirs at different depths is to determine the key parameters such as thermal energy storage,heat output capacity,and the sustainable utilization period of geothermal reservoirs. Taking the geothermal wells in the Qiabuqia area of Gonghe Basin as an example, this study proposes a temperature prediction model for heat reservoirs under different constraints based on particle swarm optimization (PSO) and long short-term memory network (LSTM). The prediction effect of this model is verified by comparing with those of the BP model and LSTM model. The results show that the RMSE value,MAPE value and MAD value in the prediction results of the model are the smallest compared with those in BP and LSTM models, and the minimum RMSE value is only 1. 192. The determination coefficient of the model is 0. 929,showing a good prediction effect. This indicates that this model could realize the prediction of reservoir temperature in geothermal system,which provides references for the efficient and long-term development of geothermal system. [ABSTRACT FROM AUTHOR]

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Optimizing heat generation capacity is crucial for geothermal system design and evaluation. Computer simulation is a valuable approach for determining the influence of various parameter combinations on a geothermal system's ability to produce heat. However, computer simulation evaluations are often computationally demanding since all potential parameter combinations must be examined, posing significant hurdles for heat generation performance evaluation and optimization. This research proposes an adaptive Kriging-based heat generation performance optimization method. Firstly, a two-horizontal-well geothermal system with rectangular multi-parallel fractures is constructed. The heat production performance optimization problem is then established, and the temperature and enthalpy of the outlet water are calculated using computer simulation and Kriging. A parameterized lower confidence bounding sampling scheme (PLCB) is developed to adaptively update Kriging in order to strike a compromise between optimization accuracy and computation burden. The outcomes of the optimization are compared to those of the Kriging-based optimization approach and other common infill options to demonstrate the efficiency of the proposed method. The outlet temperature curve obtained with PLCB-AKO-1 rose for a longer time and the heat generation power curve reached a stable output without a downward trend. According to the Friedman and Wilcoxon signed ranks tests, the PLCB-1-AKO technique is statistically superior to alternative strategies. [ABSTRACT FROM AUTHOR]

Introduction: The surface expression of enhanced geothermal heat fluxes above an active hydrothermal system causes a surface thermal anomaly (ΔΌ. The thermal anomaly is expressed by the difference between the temperature within the heated zone (Th) and the temperature of non-heated surfaces (T0). Given that the resulting thermal anomaly at the surface is of extremely low magnitude (1°C-5°C at Vulcano, Italy), it is extremely sensitive to overprinting by external factors, namely, meteorological influences on surface temperature variation, such as solar heating, wind and rain. Methods: To test the sensitivity of the surface to external drivers, we installed two surface temperature measurement stations within the Vulcano's Fossa crater, one inside the thermal anomaly and one outside (separation = 50 m), with a weather station co-located with the T0 station. Time series of Th and T0 were collected for 2020, when the Vulcano Fossa hydrothermal system was at a low and stable level of activity so that external drivers would have been the main influences on Th and T0, and hence also ΔT To test for divergence from normality in terms of diurnal and seasonal variations in Th and T0, and the role of external factors in causing abnormality, we used the deep learning engine DITAN: a domain-agnostic framework to detect and interpret anomalies in time-series data. Results: During the year, DITAN found 16 cases of two types of meteorological events: intense low-pressure systems and high-intensity rainstorms (cloudbursts). Passage of 13 abnormal low-pressure systems were detected (10 between February and May, and three in December), with three abnormal rainstorm events (all in December); all three being coincident with the abnormal low pressure events. We find just two abnormalities in the time series for of Th and T0, both of which coincide with passage of abnormal low-pressure systems, and neither of which coincide with abnormal rain events. We conclude that diurnaland annual heating and cooling cycles, subject to normal meteorological inputs and at a surface above a geothermal-heated source, are immune to anomalous behaviour to the external (meteorological) variations. [ABSTRACT FROM AUTHOR]

The Woka-Cuona rift zone on the southeastern side of the Qinghai-Tibet Plateau is characterized by complex geological background conditions, comprising three independent or semi-grabens that traverse from south to north across the Himalayan and Gangdise terranes. Conducting research on the distribution patterns and genesis mechanisms of geothermal resources within the Woka-Cuona rift zone has certain guiding significance for understanding the genesis mechanisms of the geothermal system in the southern Tibetan rift and its exploitation. This paper utilized methods such as data collection, ground investigations, and geochemical analyses to analyze the distribution characteristics and evolutionary processes of geothermal waters in the Cuona rift area based on the geological background conditions of the study area. The research findings demonstrate a significant correlation between the occurrence of geothermal waters in the Cuona rift zone and geological structures, with most geothermal waters primarily distributed near intersections of graben boundary faults and east–west-trending faults. Different regions exhibit variations in the intensity of geothermal activity and geochemical characteristics, with the genesis of geothermal waters associated with deep magmatic activity, characterized by Na+ and K+ as the primary cations and Cl− as the primary anions. Geothermal waters mainly originate from atmospheric precipitation and snowmelt water from surrounding mountainous areas, with recharge elevations ranging from 4500 to 6200 m and an average elevation of 5400 m. [ABSTRACT FROM AUTHOR]

Geothermal energy holds great potential for a sustainable future, as it is a clean and weather-independent form of energy. In addition to energy production, it can also serve the population of a region through direct use. In this paper, three municipal geothermal systems (Szarvas, Nagyszénás, Békéscsaba) in the same Hungarian region which have been recently installed or expanded are presented and analysed. Here, the direct usage of geothermal energy for heating purposes is a very important issue. The three systems show several differences and to some extent face different challenges in the various phases of the projects. Particular attention has been paid to engineering solutions to the problems that arise. The challenges, such as technical difficulties during installation, maintenance difficulties, or problems arising during operation are introduced. The strengths, weaknesses, opportunities, and threats of similar geothermal systems were summarized, based on the relevant literature. These points were evaluated by their appearance and characteristics in the examined systems. This study aims to provide insights, based on recently gained experiences, into geothermal projects, thus providing feedback and practical information for researchers and practitioners. [ABSTRACT FROM AUTHOR]

Xianxian geothermal exploitation area is one of the areas with the best occurrence conditions of geothermal resource in North China, rich in medium and low temperature geothermal resource, and is a typical carbonate geothermal field. However, its hydrogeochemical evolution process is not clear, and no complete conceptual model of geothermal genesis has been established to guide the exploration, development and utilization of geothermal resource in the area. It restricts the sustainable development of regional geothermal resource and the realization of carbon emission reduction targets. In this study, geothermal fluids in the area were collected for testing and analysis in terms of hydrochemical characteristics and stable isotopes. Based on systematic geochemical research, the formation mechanism of geothermal fluids was analyzed, and a conceptual model of geothermal genetic in the study area was established. The main understanding is as follows: the hydrochemical type of geothermal water in the study area is Cl-Na type, and the water-rock interaction is not balanced. The formation of geothermal water in the area is affected by the infiltration of atmospheric precipitation, and it is terrestrial leached water. The flow path of geothermal water is long, the water circulation is slow, and the metamorphism is deep. Dolomite, calcite and gypsum dissolution are the main sources of Mg2+, Ca2+, , and in geothermal water, besides, other minerals containing calcium and magnesium are also part of their sources. The source of geothermal water recharge is atmospheric precipitation, and the recharge elevation of geothermal water is about 619–1069 m. The age of the geothermal water is between 16 000 and 18 000 years. The sulfur in geothermal water mainly comes from the leaching of sedimentary layer. [ABSTRACT FROM AUTHOR]

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Deposition of terrestrial carbonate (i.e. travertine) and silica sinter in geothermal areas is always closely linked to the presence of relevant crustal structures which enhance the permeability in the upper crust favouring the upflow of fluids to the surface. Most travertine deposits are originated by geothermal fluids stored within carbonate reservoirs in continental crust, and their morphology and areal distribution provide useful information on geometry, kinematics, and age of faults which control the fluid flow. In this paper, we focus on the tectonic control on a travertine depositional system, associated with silica sinter, developing in oceanic crust, in the Lýsuskarð volcano-geothermal area on the Snæfellsnes Peninsula, West Iceland. The presence of HCO3 and Ca in the geothermal fluids is related to chemical-physical processes linked to fluid–rock interaction that occurs in the geothermal reservoir made up of tholeiitic basalt, by fluids enriched in CO2 of deep origin (i.e. magmatic). Travertine deposits consist of mounds and slopes, which are still in formation and overlie the silica sinter deposits. Both sinter and travertine deposits derive from thermal springs aligned according to two trends: NNE-SSW and WNW-ESE. This evidence suggests the occurrence of buried, permeable, and thus active faults, which control the circulation of fluids containing HCO3 and Ca. Faults are near parallel to those which define the rift systems and transform zones in Iceland, and probably comprise the still active sector of the abandoned transform zone that, starting with the Snæfellsnes Peninsula, interrupts eastward the northern continuation of the western and eastern rift-zones in the south-central Iceland. In this setting, we refer, for the first time, travertine and silica sinter deposition to an oceanic active crustal structure. [ABSTRACT FROM AUTHOR]

Geophysical surveys discovered low resistivity values that, in combination with geochemical and structural data, indicate the presence of a previously unrecognized geothermal system with a possible maximum size potential similar to that of the presently installed capacity of the Cerro Prieto geothermal field. The only evidence of a hydrothermal system in the San Felipe Valley are warm groundwater wells and four intertidal hot springs. Exploration at San Felipe was part of a research project that included geological, geochemical and geophysical studies, which indicated the presence of low resistivity anomalies and high temperature at depth; the geological survey provided evidence of active fault systems that may act as channels for convective heat transport. Estimation of the energy potential of the San Felipe prospect using the heat in place method yielded a 50% probability of more than 300 MW that would add to the 570 MW of the Cerro Prieto geothermal field and can supply almost 40% of the state of Baja California electricity demand. The Baja California Peninsula is not connected with the national grid and has one of the highest electricity prices in Mexico, which should be an incentive to develop this clean energy source. The results of this work support the recommendation to pursue further advanced exploration of this prospect. [ABSTRACT FROM AUTHOR]

High-temperature geothermal systems hold promise for sustainable and environmentally friendly power generation. However, China's geothermal power capacity significantly underutilizes its abundant resources. This study focuses on the geothermal potential of the Pamir Plateau, particularly its northeastern edge, where complex tectonic forces converge. We aim to unveil the mechanisms driving the emergence of high-temperature geothermal reservoirs in this unique geological setting. Hydrogeochemical analysis reveals diverse profiles in geothermal water, primarily derived from atmospheric precipitation. Estimation of reservoir temperatures and simulation of geotherms unveil distinct geothermal systems. Kongur exhibits a medium–low-temperature hydrothermal system and Tashkurgan demonstrates high-temperature hydrothermal system characteristics, while the Pamir's northeastern edge hints at a potential high-temperature dry geothermal system where there might not be a fault. These findings have important implications for sustainable energy development and future geothermal exploration. [ABSTRACT FROM AUTHOR]

The part of China, east of the Hu Huanyong Line, is commonly referred to as eastern China. It is characterized by a high population density and a well-developed economy; it also has huge energy demands. This study assesses and promotes the large-scale development of geothermal resources in eastern China by analyzing deep geological structures, geothermal regimes, and typical geothermal systems. These analyses are based on data collected from geotectology, deep geophysics, geothermics, structural geology, and petrology. Determining the distribution patterns of intermediate-to-deep geothermal resources in the region helps develop prospects for their exploitation and utilization. Eastern China hosts superimposed layers of rocks from three major, global tectonic domainsd namely Paleo-Asian, Circum-Pacific, and Tethyan rocks. The structure of its crust and mantle exhibits a special flyover pattern, with basins and mountains as well as well-spaced uplifts and depressions alternatively on top. The lithosphere in Northeast China and North China is characterized by a thin, low density crust and mantle, whereas the lithosphere in South China has a thin, low density crust and a thick, high density mantle. The middle and upper crust contain geobodies with high conductivity and low velocity, with varying degrees of development that create favorable conditions for the formation and enrichment of geothermal resources. Moderate-to-high temperature geothermal resources are distributed in the MesozoiceCenozoic basins in eastern China, although moderate temperature geothermal resources with low abundance dominate. Porous sandstone reservoirs, karstified fractured-vuggy carbonate reservoirs, and fissured granite reservoirs are the main types of geothermal reservoirs in this region. Under the currently available technical conditions, the exploitation and utilization of geothermal resources in eastern China favor direct utilization over large-scale geothermal power generation. In Northeast China and North China, geothermal resources could be applied for large-scale geothermal heating purposes; geothermal heating could be applied during winter along parts of the Yangtze River while geothermal cooling would be more suitable for summer there; geothermal cooling could also be applied to much of South China. Geothermal resources can also be applied to high value-added industries, to aid agricultural practices, and for tourism. [ABSTRACT FROM AUTHOR]

The granitoids widely distributed in South China are characterized by multi-stage evolution via episodic intrusions, in a complex geodynamic setting. Since granites have high radioactive heat generation and excellent thermal conductivity, a deep moderate- to high-temperature geothermal system can be formed in the presence of high-quality, fissured granite geothermal reservoirs and thermal insulation with appropriate cap rocks. The key to exploring deep geothermal resources is to identify high-quality fissured granite geothermal reservoirs of a certain scale in a thermal anomaly zone with high background heat- flow values. To determine the controlling effects of the distribution and development characteristics of granite geothermal reservoirs on the generation and enrichment of deep geothermal resources, this study analyzed the characteristics of the geothermal reservoirs in the Huangshadong geothermal field in the Yuezhong Depression, Guangdong Province, and their controlling effects on the formation of geothermal resources. The results are as follows. The hydrothermal system in the Huangshadong geothermal field mainly distributed in the contact zones between magmatic plutons and surrounding rocks, is significantly controlled by faults, followed by neoid volcanic apparatus and magmatic activities. That is, the geothermal system therein is under joint control of structures and magmas. Moreover, fractured zones of neoid transtensional faults conduct the geothermal water in the hydrothermal system and control its shallow discharge. Therefore, the hydrothermal system in the study area is characterized by the control of transpressional tectonic zone and volcanic apparatus, and geothermal water conduction through fractured zones of transtensional faults. [ABSTRACT FROM AUTHOR]

As volcanoes are closely related to the living environment of humans, in particular via natural hazards and geothermal energy, scientific studies on volcanic edifice structures are required. Ulleung Island is a Quaternary volcanic island located in the mid-western East Sea (Sea of Japan). In this study, we conducted an audio-frequency magnetotelluric (AMT) survey to image the substructure of the Ulleung volcanic edifice. In addition, the electrical structure was interpreted from the geothermal system perspective, geochemical compositions of volcanic rocks, and the possibility of the presence of a magma reservoir. AMT data were obtained from 25 stations and processed using the remote reference technique. Then, the three-dimensional (3-D) approach was reasonably adopted according to dimensionality analysis. Before conducting the 3-D inversion, the effects on topography and ocean were analyzed using a simplified 3-D synthetic model, because Ulleung Island is surrounded by sea and the topography is undulating. Most AMT stations on Ulleung Island are distorted by topographical and oceanic effects; in particular, oceanic effects are significant at frequencies lower than 10 Hz. The 3-D inversion was conducted with full impedance components and vertical magnetic transfer functions in a frequency range of 10,000–1 Hz. The results show that the Ulleung volcanic edifice is characterized by two layers of electrical structures as follows: near-surface resistive anomalies and an underlying conductive layer. Considering the high geothermal gradient on Ulleung Island, we suggest that the conductive layer of the volcanic edifice is due to hydrothermal alteration of basaltic rocks, with a potential heat source underneath. Based on the geochemical characteristics of the Ulleung volcanic rocks, the possibility of heat transfer from a trachytic magma reservoir within the shallow crustal is suggested. In summary, this study presents a geological interpretation of shallow volcanic structures beneath Ulleung Island and the possibility of an active magma reservoir as a potential heat source for the volcanic edifice. [ABSTRACT FROM AUTHOR]

Cationic silica scale inhibitors are widely used, but are prone to precipitation and exhibit poor performance in geothermal systems. In this study, the cationic polymer polyethyleneimine ethoxylate (PEIE) was first found to have high silica scale inhibition efficiency. Three anionic polymers were added separately to PEIE solutions to alleviate the precipitation and scaling. The inhibition effect of PEIE alone and PEIE with anionic polymers were measured at 40°C without salt and 136.7°C with salt. Molecular dynamics simulation was used to investigate the inhibition mechanism. The results showed that PEIE exhibited good inhibition efficiency of 62% at 40°C without salt and 48% at 136.7°C with salt, while the addition of the anionic polymer acrylic acid‐2‐acrylamide‐2‐methylpropanesulfonic acid (AA/AMPS) to PEIE further improved to 71% and 62%. Compared with commercial inhibitors, the PEIE + AA/AMPS enhanced at least 15% scale inhibition efficiency. This is because the addition of AA/AMPS: (1) enhances the attraction of PEIE to silicic acid and inhibits the silicic acid condensation process; (2) chelates metal ions that promote condensation; and (3) enhances dispersion ability, stabilizing the colloid formed by PEIE and silicic acid. This study provides a promising new inhibitor and efficient strategy for inhibiting silica scale in geothermal systems. [ABSTRACT FROM AUTHOR]

Metallogenic models are vital to mineral exploration. However, there is debate concerning the origin of hydrothermal‐type ore deposits such as vein‐type U and W deposits. The formation, migration, heating and controls on the composition of metal‐fertile fluids in active geothermal systems provide insights into the formation of ore‐forming fluids. Fluid's metal contents are relatively high in the Yadong–Yangbajing–Naqu (YYN) geothermal belt of South Tibet, and a similar association of enrichment has been found in saline lakes of the region. This study analysed major ions and trace metal contents together with stable (O, H) isotopes of water samples from geothermal springs and wells and regional saline lakes and rivers along the Beng and YYN fault systems. Results demonstrate that metal‐fertile geothermal brines, were sourced from the Bangor saline lake. This study highlights the role of evaporation of saline lake water in the formation of metal‐fertile brines and the contrasting behaviors of U and W in hydrothermal conditions. [ABSTRACT FROM AUTHOR]

Numerous present-day hot springs in the Sulawesi region are divided into two, generally associated with non-volcanic and tectonics geothermal systems, only a small number are associated with active volcanoes, but most do not yet have data to support their utilization. Here we have conducted research at Makula Hot Springs South Sulawesi, the method used is combined geochemical analysis with an estimation of subsurface temperature by using the geothermometer at three sites at Makula Hot Springs. The percentage values of HCO³ˉ, Clˉ, and SO₄²ˉ ion content in hot water samples were analyzed, indicating that the hot springs area was included in the chloride water type. While the results of the estimation of subsurface temperature by using the geothermometer Na - K from the three sites each show the following temperatures: Site I is 124.69℃, Site II is 122.65℃, and Site III is 114.75℃. All sites result in estimations suggested including the low enthalpy which has a temperature limit of <125℃. Furthermore, using the geothermometer Na - K - Mg is known, and the hot springs in the area are included in the partial equilibrium. Geothermal energy in the study area is used for public swimming baths, the development of a tourist attraction, and potentially for a power plant. However, it is still necessary to investigate the geothermal characteristics to maximize the utilization of the hot springs in this area. [ABSTRACT FROM AUTHOR]

To better understand the geothermal system of the Gonghe Basin, we deployed 471 magnetotelluric survey points with an average distance of 2~3 km, covering the eastern and southern areas of the Basin. We used ModEM inversion software to carry out 3D inversion of 431 survey points and established a 3D-electrical model at a depth of 50 km in the area. The resistivity model shows that the low resistivity in the shallow part of the basin is related to the Cenozoic loose sedimentary cover, while the resistivity values of the mountains around the basin and the magmatic rock uplift zone are higher. The electrical model also shows that the high-conductivity layer is widely distributed in the middle and lower crust (15~35 km) of the basin, and direction of the high-conductivity layer is consistent with that of NW–SE fault in the basin. These high-conductivity layers may be the principal reason for the high heat flow values in the Gonghe Basin. Our resistivity model also shows that there is an obvious discontinuity between high- and low-resistivity blocks at different depths in the middle and upper crust. These discontinuities are consistent with the faults observed on the surface, which are related to the strong topographic relief. Our electrical model shows that these faults in the middle and upper crust are connected with the high-conductivity layer as the channel of heat transfer to the shallow part. Finally, the heat energy is enriched in the Triassic granite to form dry hot rock (HDR). The 3D-magnetotelluric imaging results depict the 3D-distribution characteristics of the geothermal system in the eastern and southern parts of the Gonghe Basin. [ABSTRACT FROM AUTHOR]

The existence of high-temperature geothermal anomalies in the Gonghe Basin on the northeastern margin of the Tibetan Plateau has highlighted a new perspective on the geothermal system of the Himalayan-Tibetan Plateau orogen. In this study, we collected 32 groups of liquid and gas samples from geothermal water, rivers, and boreholes in the Gonghe basin to analyze hydrochemistry, stable isotopes, and geochronology, which allow us to further reveal the geothermal fluid circulations of geothermal reservoirs. The ion contents of liquids identify two distinguished types of water, namely the Na-SO4-Cl type primarily from geothermal water and the Na-SO4-HCO3 and Na-Ca-CO3-SO4 types primarily from cold water. The compositions of the hydrogen and oxygen isotopes of the samples indicate geothermal waters were recharged by atmospheric precipitation and 3000–4600 m high snow mountain meltwater, which may have experienced circulation of 16,300–17,300 years and mixtures of submodern and recent recharge water sources evidenced by isotopes of 3H, 13C, and 14C data. The 3He/4He ratios of these geothermal waters varying from 0.03 to 0.84 Ra further highlighted a crustal-dominated heat source in the region. The deep thermal reservoir temperature in the Gonghe Basin at 160 ± 10 °C and the depth of circulation of geothermal water is 2200–2500 m. Based on this evidence, we have established a geothermal fluid circulation model and refined the exchange processes of fluids and geothermal heat, further enriching the details of the geothermal system in Gonghe Basin. [ABSTRACT FROM AUTHOR]

Morocco has an important geothermal potential materialized by its several thermal springs which constitute an essential surface geothermal indicator. These springs are dispersed throughout the country and present in every major structural domain. However, a significant amount is concentrated in the northern and northeastern areas. Associated with the great hydrothermal system of eastern Morocco, the thermal spring of Goutitir emerges in the Meso-Cenozoic sedimentary formations located east of the Guercif Basin, composed of a mixture of clays, carbonates, and marls, covered in unconformity by Quaternary tabular molasses. The upflow of the thermal water is dependent of Alpine faults systems with N30 and N100 directions, which are probable reactivated Hercynian structures that facilitate its circulation to the surface. The Goutitir spring has been studied by an interdisciplinary approach to identify the origin of the thermal water, the rock–water interactions, and the reservoir temperatures, contributing to the establishment of the conceptual model of the associated hydrothermal system. This thermal water is of chloride-sodium type with a hyperthermal character (43–47 °C). The isotopic composition (δ18O = −8.7 to −8.35‰; δ2H = −58.6 to −54.3‰) indicates a meteoric origin and a recharging zone located at around 2000 m of altitude. The chemical composition allows to classify the water as chloride-sodium hydrochemical facies, stabilized at ~100 °C in crystalline basement rocks, which, according to seismic data, are located at ~3 km depth. The concentrations, patterns, and correlations of trace elements point out water–rock interaction processes between the deep water and basic magmatic rocks. The integration of the chemical and isotopic data and the surface geological context shows that the Goutitir water flows within a hydrothermal zone were basic to ultrabasic lamprophyres rich in gabbroic xenoliths outcrop, witnessing the existence, at depth, of basic plutons. Moreover, near the source, these veins are strongly altered and hydrothermalized, showing late recrystallization of centimetric-sized biotites. The chloride-sodium composition of this water may also be a testimony to the presence and reaction with the overlying Triassic saline and gypsiferous and Meso-Cenozoic mainly carbonated formations. [ABSTRACT FROM AUTHOR]

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Geothermal is a renewable energy source, but this is not as often seen as other renewable energy sources, such as solar, wind, hydro, etc. Several applications could be implemented through geothermal energy, and heating & cooling systems are one of them. Because of the limits of technology, it is hard to improve cooling systems as an application. To address long-term sustainable space heating and cooling, it is imperative to develop geothermal technology. It is known as the oldest, most flexible, most adaptable, and most prevalent approach toward using renewable energy. Therefore, this review has reviewed the global development and challenges of geothermal energy for cooling systems. There are large reserves of geothermal energy available around the world, and numerous scholars have emphasized its importance, but due to a lack of knowledge, no operational work has been done in using these systems for cooling up to this point. This review paper examines globally available geothermal energy sources and technologies for environmentally friendly and sustainable cooling supplies. Finally, the benefits and challenges of geothermal systems for cooling are outlined to promote local, regional, and global investment in utilizing these resources for cooling. [ABSTRACT FROM AUTHOR]

Numerical modeling is used to understand the regional scale flow dynamics of the fault‐hosted orogenic geothermal system at the Grimsel Mountain Pass in the Swiss Alps. The model is calibrated against observations from thermal springs discharging in a tunnel some 250 m underneath Grimsel Pass to derive estimates for the bulk permeability of the fault. Simulations confirm that without the fault as a hydraulic conductor the thermal springs would not exist. Regional topography alone drives meteoric water in a single pass through the fault plane where it penetrates to depths exceeding 10 km and acquires temperatures in excess of 250°C. Thermal constraints from the thermal springs at Grimsel Pass suggest bulk fault permeabilities in the range of 2e−15 m2–4.8e−15 m2. Reported residence times of >30,000 and 7 years for the deep geothermal and shallow groundwater components in the thermal spring water, respectively, suggest fault permeabilities of around 2.5e−15 m2. We show that the long residence time of the deep geothermal water is likely a consequence of low recharge rates during the last glaciation event in the Swiss Alps, which started some 30,000 years ago. Deep groundwater discharging at Grimsel Pass today thus infiltrated the Grimsel fault prior to the last glaciation event. The range of permeabilities estimated from observational constraints is fully consistent with a subcritical single‐pass flow system in the fault plane. Plain Language Summary: Observations from warm springs discharging through a fault at Grimsel Pass (2,164 m.a.s.l.) in the Swiss Alps are used to constrain a numerical model of the deep water circulation feeding the springs. The springs are known to have been active for at least 3.3 million years and to be due to ascent of meteoric water that penetrated to depths exceeding 10 km, where it acquired temperatures above 250°C. Simulations show that the circulation along the fault connects a meteoric recharge zone at high altitude to the west with a sub‐vertical permeable discharge zone at Grimsel Pass. A key unknown is the permeability of the fault. Temperature, discharge rate and chemical composition of the spring water depend on flow conditions at depth and can be used to estimate the fault's bulk permeability. Our study shows that the range of fault permeabilities can be narrowed down to roughly half an order of magnitude: 1e−15 m2–5e−15 m2. This permeability range is consistent with a currently stable, single‐pass flow pattern. Long water‐residence times inferred from the isotopic composition of the spring water suggest low recharge rates during the last glaciation and the dominance of a multi‐pass flow pattern during that time. Key Points: The topography in the Grimsel region drives meteoric water to depths exceeding 10 km, causing discharge of thermal water at Grimsel PassBased on thermal and chemical constraints from the spring water, the bulk fault permeability is in the range of 2e−15 m2–4.8e−15 m2Recent periods of glaciation changed the pattern of flow in the fault plane and are likely the reason for fluid residence times >30,000 years [ABSTRACT FROM AUTHOR]

Estimating deep geothermal reservoir temperatures is an essential mission of geothermal exploration and development. The thermal reservoir temperature estimated directly using geothermometry without comparative analysis is often far from the actual temperature. In this paper, taking the typical geothermal systems in the Xiamen Island–Zhangzhou area of southeastern China as an example, different methods such as a water–rock equilibrium analysis, SiO2 geothermometer, multi-mineral equilibrium diagram, and silica-enthalpy mixing model are used to make a quantitative and qualitative analysis of the chemical equilibrium of minerals and fluids in the geothermal system. Finally, the applicability of different methods was compared and analyzed, and the geothermal reservoir temperature was estimated using the appropriate method. The results show that the calculated results of the Si-enthalpy mixing model of a typical geothermal system in southeastern China are significantly high. At the same time, the SiO2 geothermometer (without vapor loss), which is closest to the results of the multi-mineral equilibrium diagram, was chosen as the geothermal reservoir temperature of the geothermal system in the study area. This study can provide a reference for the future selection of methods of deep geothermal reservoir temperature estimation in similar areas. [ABSTRACT FROM AUTHOR]

This paper proposes a variable time step, second-order time filter algorithm for the closed-loop geothermal system for the first time. The algorithm is easy to implement in programming, which greatly improves calculation efficiency, while improving the accuracy of convergence. Theoretically, we mainly analyze the stability and the convergence of the algorithm in the case of variable time steps. Finally, numerical experiments confirm the theoretical results and show that the algorithm can simulate geothermal system well. [ABSTRACT FROM AUTHOR]

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Geothermal manifestations in Parangtritis, Indonesia, known as Parang Wedang Hot Spring, indicate a geothermal system in the subsurface. This circumstance motivated our research to model the Parang Wedang geothermal system in order to determine its subsurface conditions. Geological mapping, the geophysical method, and geochemical analysis were integrated to produce a conceptual model of the Parang Wedang geothermal system. The study area consists of structural hills, karst hills, and eolian plains with andesite breccias, limestone, andesite, and sand deposits as lithological variations. The results of magnetic modeling indicate that the research area is associated with the presence of an andesite intrusion and shows a NE-SW trending geological structure that is thought to be a path for hydrothermal fluid to the surface. Geochemical analysis was performed at two hot springs with temperatures of 47 °C and 49 °C. Geothermometer calculation showed that the geothermal reservoir in Parang Wedang has a temperature of 100 to 120 °C, a depth of about 180 to 285 m, and can be classified as a low enthalpy geothermal system. [ABSTRACT FROM AUTHOR]

Real time prediction of energy consumption is the basis of energy conservation and emission reduction. Aiming at the problems of large prediction error and poor effect, a real-time prediction method of energy consumption of geothermal system of public buildings based on wavelet neural network is proposed. Firstly, the energy consumption of geothermal system in public buildings is analyzed, the wavelet neural network is designed, the neural network is optimized and solved by genetic algorithm, and the necessity of constructing the real-time prediction model of energy consumption based on wavelet neural network is established. Then it introduces the basic principle of model establishment, wavelet analysis, and shows the role of wavelet analysis in prediction model. Finally, based on the distribution structure of public buildings, this paper analyzes the energy consumption system of geothermal system, constructs the energy consumption prediction method, analyzes the overall temperature regulation energy consumption prediction principle of building geothermal system, and realizes the real-time prediction of energy consumption of geothermal system of public buildings. The experimental results show that the energy consumption real-time prediction results of the designed method are basically similar to the actual prediction values, and the prediction efficiency is high, which can effectively reduce the energy consumption of the geothermal system of public buildings. [ABSTRACT FROM AUTHOR]

Geothermal resources as clean and renewable energy can be utilized for agriculture, tourism, and industry. The assessment of geothermal potential and the study of genetic mechanism of the geothermal system is an essential part of geothermal resource development. In this study, 16 steady-state temperature logs are obtained in the mountainous area on the northern margin of North China. Thermal conductivity and heat production rates are tested or collected from more than 200 rock samples of these wells and outcrops around the study area. Based on these data, for the first time, the detailed delineations of temperature distributions, genetic mechanisms of geothermal systems, and resource potential of Hot Dry Rock in the study area are achieved. The heat flow map indicates a low heat flow state with an average value of 53.1 mW/m2 in the study area, which is lower than the average value of 62.5 mW/m2 in mainland China. The distribution of hot springs in the area is mainly controlled by fault systems. Heat flow only exhibits a minor effect on the temperature of hot springs and geothermal wells. On this basis, the deep temperature distribution within 3–10 km depths of the study area is calculated using the one-dimensional steady-state heat conduction equation. With it, the reservoir depths of hot springs are estimated to be 3–5 km with temperatures ranging from 70°C to 110°C. Furthermore, a conceptual model for the geothermal system in the study area is derived. According to the results, Northeastern Chengde and northern Beijing exhibit the highest temperatures at all depths. Similar patterns are observed in the temperature distribution maps and the heat flow map, which suggest that the deep temperature distribution is mainly controlled by regional heat flow. With the depth increases, the temperature shows larger variation at each depth level, which is possibly caused by the heterogeneity of crustal composition. According to our resource assessment by volumetric method, the exploitable potential of Hot Dry Rock within the depth of 7–10 km of the study area is equivalent to about 3.1 × 1011 tons of standard coal, but the barrier is still existing for development under the current technical and economic conditions. [ABSTRACT FROM AUTHOR]

This study presents the characteristics of the Lahendong geothermal working area (GWA) in terms of the geological, geophysical, geochemical, and environmental implications. The investigated area is located in the Sulawesi North Arm, where the volcanic arc extends from Sangihe Island to Minahasa with two major strike-slip faults. NE-SW (northeast-southwest) trending faults control the thermal surface manifestation. The geothermal field is grouped into two hydrochemical systems: acid-sulphate-chloride (acid reservoir) and chloride (closer to neutral) types. The environmental implication analysis shows that the North Sulawesi province is experiencing water shortages due to excessive mining activities, inadequate wastewater management, and periods of drought. Although geothermal wastewater is being re-injected, the possibility of water contamination by hazardous materials from geothermal power plant activity is still evident. This study reviews the actual geothermal utilisation in the form of the 120 MWe power plant, the 500 kWe binary power plant, while the heat from geothermal energy is used for palm sugar production. Furthermore, the article also analyses the potential of the rational use of geothermal resources in this area. As a result of the high salinity and silica concentration of the brine, the geothermal wastewater should be treated before further utilisation and it potentially benefits both local communities and geothermal companies. [ABSTRACT FROM AUTHOR]

In Gulu area, geothermal waters show a high concentration of alkali metals (Li, Rb and Cs) and some other typical pollution elements, e.g. As, Sb and Tl. They are also enriched in the geothermal deposits during the phase separation of silica sinter and residual geothermal water. A comprehensive sequential extraction was carried out on the Gulu silica sinter. The results indicated that significant Li and K amount is bound to the Fe-Mn oxide and the residual fractions of sinter while, the elements (B, Cs, Rb, As, Sb and Tl) are predominantly concentrated in the sinter crystal lattices. In addition, the elemental distribution law during phase separation of the residual geothermal water and associated evapoconcentrated deposits is also uncovered in this study. With the respect to the system of the natural silica sinters precipitated from the mother geothermal water, complex variations occur during the trace elements partition between the mother water and associated deposits under evapoconcentration. Thus, the miscellaneous minerals (Li, Rb, K, Cs and B) are also distributed in the solid phases when special minerals such as opal, borax or sylvite precipitate from the residual fluids. This confirms that the valuable minerals of K, B, Cs, Rb or Li can precipitate when the geothermal water is evapoconcentrated to a certain degree and within a very concentrative stage of density. However, these elements are remarkably depleted in the residual geothermal fluid at the stages corresponding to the precipitation of these minerals while they are highly enriched in the mother fluid during the late stages of the evapoconcentration. Thus, it can be stated for the first time that the high concentration of these elements in the residual waters at the final stages will be certainly used in the future. In contrast, the concentration of pollution elements (As, Sb and Tl) of the geothermal solids is higher in the early stage of the opal precipitation, while it is lower in the later stages. The concentration of these elements (As, Sb and Tl) in residual geothermal fluids distinctly increases and is very high at the final stages of the evapoconcentration. This scenario indicates that large quantities of toxic elements such as As, Tl and Sb may degrade the surface and ground waters resources located at or near the geothermal water by mixing process making them unsuitable for drinking or irrigation. Thus, in addition to the thermal energy provided, the geothermal area are very important prospect for exploration and extraction of the mineral resources of the elements such as K, Li, B, Rb or Cs that have very significant economic value. However, percentages of trace elements such as Li, Tl, Rb and K in the exchangeable and carbonates fractions of this sinter suggested that they could become rapidly bioavailable in the geothermal environment. [ABSTRACT FROM AUTHOR]

Many meteoric‐recharged, fault‐hosted geothermal systems in amagmatic orogenic belts have been active through the Pleistocene glacial/interglacial climate fluctuations. The effects of climate‐induced recharge variations on fluid flow patterns and residence times of the thermal waters are complex and may influence how the geothermal and mineralization potential of the systems are evaluated. We report systematic thermal‐hydraulic simulations designed to reveal the effects of recharge variations, using a model patterned on the orogenic geothermal system at Grimsel Pass in the Swiss Alps. Previous studies have shown that fault‐bounded circulation of meteoric water is driven to depths of ∼10 km by the high alpine topography. Simulations suggest that the current single‐pass flow is typical of interglacial periods, during which (a) meteoric recharge into the fault is high (above tens of centimeters per year), (b) conditions are at or somewhat below the critical Rayleigh number, and (c) hydraulic connectivity along the fault plane is extensive (an extent of at least 10 km into increasingly higher terrain is required to explain the 10 km penetration depth). The subcritical condition constrains the bulk fault permeability to <1e‐14 m2. In contrast, the limited recharge during the numerous Pleistocene glaciation events likely induced a layered flow system, with single‐pass flow confined to shallow depths while non‐Rayleigh convection occurred deeper in the fault. The same layering can be observed at low aspect ratios (length/depth) of the fault plane, when the available recharge area limits flux through the fault. Plain Language Summary: Many fault‐hosted geothermal systems in mountainous regions have been active through the Pleistocene glacial/interglacial climate fluctuations. As a result of climate change, meteoric recharge into these systems has changed over time, affecting geothermal circulation in the fault and hence influencing the geothermal and mineralization potential of the systems. We present a series thermal‐hydraulic simulations designed to reveal the effects of recharge variations, using a model patterned on the orogenic geothermal system at Grimsel Pass in the Swiss Alps. Previous studies have shown that fault‐bounded circulation of meteoric water is driven to depths of ∼10 km by the high alpine topography. Simulations suggest that the current single‐pass flow pattern is typical of interglacial periods, during which (a) meteoric recharge into the fault is high, (b) the contribution of buoyancy as a driving force for fluid flow is low, and (c) hydraulic connectivity along the fault plane is extensive. The deep, single‐pass flow pattern constrains the bulk fault permeability to <1e‐14 m2. In contrast, the limited recharge during the numerous Pleistocene glaciation events likely induced a layered flow system, with single‐pass flow confined to shallow depths while slow non‐Rayleigh convection occurred deeper in the fault. Key Points: Gradients in topography can drive meteoric water to depths exceeding 10 km where it acquires temperatures in excess of 250°CRecharge limited conditions induce a layered flow system in orogenic faults with shallow single pass flow and deep non‐Rayleigh convectionIf the depth of meteoric infiltration is known, a minimum length of the fault plane can be estimated [ABSTRACT FROM AUTHOR]

The gravity and magnetic data sets over a geothermal source are investigated to explore the geological features and geothermal system manifestations. The raw gravity data sets are firstly corrected for drift, latitude and free-air effects to obtain free-air anomalies. A new approach is utilized for Bouguer and terrain corrections. The model space, which is the mass from the reference surface to the ground surface, is parameterized by a very accurate and advanced meshing algorithm (octree and quadtree). The gravity effect of the model space is computed via numerical forward modelling and is considered as the Bouguer and terrain corrections. These corrections are subtracted from the free-air anomalies, which yields the complete Bouguer anomaly. The computed Bouguer anomalies are de-trended and transferred to residual anomalies by methods including polynomial fitting and two-stage methods. The residual gravity anomalies are inverted to obtain the subsurface density distribution. The density contrasts are estimated by minimizing the data and model objective functions through an efficient algorithm. The probable source of the geothermal system and other new gravity anomalies are successfully detected and inverted contrary to the results in previously published papers. The residual magnetic anomaly is also inverted and the obtained geometrical and physical parameters of the source body including minimum depth, shape and susceptibility are very close to the previous results. The new detected gravity anomaly and the main magnetic anomaly in the overlapped area of gravity and magnetic grids are located at almost the same place with almost the same depths, which confirms their probable common source. We developed the open source package (http://docs.simpeg.xyz/content/tutorials/03-gravity), which is accessible through SimPEG (Simulation and Parameter Estimation in Geophysics), for inverting the gravity and magnetic data sets. [ABSTRACT FROM AUTHOR]

Geothermal energy, as a safe, stable and low-cost clean power resource, has been highly recommended in recent years. Geothermal system, the basic unit for the study of geothermal genesis, can be divided into 2 types including heat conduction and heat convection, and further subdivided into 5 subtypes of sedimentary basin, geopressure, dry hot rock, magmatic intrusion and deep circulation in terms of geological environment and heat transfer mode. This paper reviews the concept and research history of geothermal system, and discusses the main controlling factors and heat transfer mechanism of the two types of geothermal system. [ABSTRACT FROM AUTHOR]

In an enhanced geothermal system (EGS), the use of fracking fluid generally causes changes in the geochemical properties of a hydrothermal reservoir. In this study, the geochemical changes were estimated through geochemical modelling using PHREEQC, and the modelling results were compared with field data and evaluated. As a result, the model showed an increase of the electrical conductivity in time which is consistent with the measurements. From the comparison between two results, it was found that the injected water was mixed with groundwater and the influence of the groundwater was significant when the hydraulic retention time of the fluid was longer than a day. Also, the chemical properties of the bedrock groundwater significantly could influence on the geochemical reactions in the geothermal reservoir. From the results, it can be concluded that the consideration of the chemical properties of groundwater or formation water is essential for the successful EGS operation. [ABSTRACT FROM AUTHOR]

In this paper, we study the stationary configurations of a vapor-dominated geothermal system. We propose a general mathematical model, which turns out to be a free boundary problem, and we focus on the stationary solutions. The analysis, developed considering the data of the geothermal field in Larderello, Tuscany (Italy), shows that steady-stable states may exist both when the re-injection takes place in depth and when the natural recharge is distributed both in the area occupied by vapor and in the one occupied by liquid. [ABSTRACT FROM AUTHOR]

Brady Hot Springs geothermal field has exhibited subsidence, as measured by interferometric synthetic aperture radar (InSAR). Previous studies have examined both the temporal evolution of the deformation from 2004 through 2016 and the spatial extent of the deformation, directly relating the observed subsidence to volumetric changes below the surface. We extend the modeling at Brady to analyze a data set of interferometric pairs spanning from the end of 2003 through 2018. We examine spatial and temporal trends in the observed deformation by time‐series analysis of each of the 1,656 cubic voxels in a parameterized elastic dislocation model to identify areas where the subsurface volume changes as a function of time. Joint time‐series analysis of Global Positioning System and InSAR pairs confirm significant changes in rates of volume change during time intervals when well operations were varied. The rate of subsidence increases with increased injection, consistent with the identification of thermal contraction of the rock matrix as the dominant driving mechanism. Conversely, the modeled volume increases when pumping ceases, suggesting thermal expansion of the rock matrix. Key Points: GPS and InSAR data show temporal variations in subsidence rateSpatial distribution of deformation is described by "multicube" elastic dislocation model of thermal contractionTemporal variations are related to changes in pumping by the power plant at Brady Hot Springs, Nevada, USA [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, Shengli fault depression, Tangyuan fault basin, and northern Songliao Basin in Yitong-Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly. Based on the temperature of the deep thermal reservoir, the hydrothermal fluid channel, caprock thickness, and the mode of heat transfer, which are the main factors controlling the geothermal reservoir formation, we examined geothermal resource system of the underground HDR in this area. First, we inversed the aeromagnetic data, calculated the Curie isotherm depth, analyzed the geothermal distribution characteristics, and estimated the temperature of the deep heat source. Second, we applied the controlled source audio frequency magnetotelluric (CSAMT) and magnetotelluric (MT) methods to obtain the deep electrical structure of the study area. We determined the thickness of the caprock and the hydrothermal fluid channel. Finally, we obtained the borehole geothermal steady-state temperature measurement data and water sample chemical analysis data from the logging temperature curves of 24 wells to infer the mode of heat transfer. Based on the results, we built a model of the geothermal system of the sedimentary basin in this area. The results show that the depth of Curie isotherm in the study area is 17–39 km. The resistivity of sedimentary caprock in the north of Songliao basin is low, and there exists a deep heat source, which is mainly thermal convection. In contrast, in Shengli and Tangyuan fault basins, heat conduction is dominant. Based on the geothermal system model, we conclude that the area from Daqing to Lindian in Songliao basin has a thermal-convection-dominated sedimentary basin geothermal system. Heat exchange is realized by the upwelling of mantle-derived thermal materials through fracture channels. The thick sedimentary caprock reduces the heat loss. It can be a target for sustainable development and utilization of HDR. [ABSTRACT FROM AUTHOR]

Thermal fracturing in reservoir rocks can cause significant increase in permeability. The change in permeability due to fracturing was predicted using the change in elastic wave velocity, density, and elastic moduli. Westerly granite samples were thermally treated to 250, 450, 650 and 850 °C. Increasing the temperature produces an increase in fracture length, aperture and density that is isotropically distributed. The permeability was measured at 10, 30 and 50 MPa effective pressure using deionized water as the pore fluid. The permeability was correlated to P- and S-wave velocities, bulk density, and static bulk modulus that were measured at similar effective pressures on the same suite of samples. Kachanov's (Elastic solids with many cracks and related problems, in: John, Theodore (eds) Advances in applied mechanics, Elsevier, pp 259–445, 1994) model was used to calculate the evolution of fracture density. Closure of fracture, due to increasing effective pressure, caused the permeability and fracture density to decrease, and the other parameters to increase. Thermal treatment caused a systematic increase in permeability and fracture density, and a decrease in the other parameters. Empirical relationships with high correlation coefficient exist between permeability and the other parameters for both dry and saturated conditions, which vary with effective pressure. Overall, we conclude that the elastic wave velocity, density and bulk modulus can be used to predict the change in permeability due to isotropic fracturing. However, a reliable method would be required to upscale these laboratory measurements for modelling and describing the permeability within a granitic reservoir. [ABSTRACT FROM AUTHOR]

The travertines of the Fitero thermal springs, with more than 98% of aragonite in most of the samples, are studied in this paper. The main objective is to improve the general understanding of aragonite precipitation, since the deposits of almost pure aragonite are very scarce. This study presents a complete mineralogical and isotopic characterisation, including the evaluation of the δ18O and δ13C fractionation during precipitation, as valuable information for paleoclimate and paleoenvironmental studies. Samples of a laminated travertine deposit constituted by almost pure aragonite were taken from a pipe discharging water at 40 °C. Waters suffered an important CO2 outgassing, as suggested by the geochemical calculations and the δ13C values of travertines and waters. This outgassing triggers the oversaturation and precipitation of carbonate phases. Temperature seems to be the main factor controlling the precipitation of aragonite or calcite, as checked by studying another travertine sample with higher calcite content. Various δ18O isotope fractionation equations for aragonite and calcite were used. The results indicate that precipitation took place close to equilibrium according to some of these equations. The fact that the equilibrium is maintained in a natural system with an important CO2 loss is surprising. However, it can be explained by an HCO3−–water oxygen isotopic equilibrium and a direct transfer of the HCO3− isotope signal to the carbonate without fractionation due to the fast CO2 loss and precipitation. Finally, considering other natural aragonite samples, a fractionation equation is defined for natural aragonite in the temperature range between 23 and 80 °C. [ABSTRACT FROM AUTHOR]

The Southern Volcanic Zone of the Andes has a high potential in terms of geothermal resources and is an exceptional and poorly explored natural laboratory to study the interplay between tectonic stresses, thermal damage, low-permeable crystalline rocks, and fluid flow. Permeability is mostly related to the damage zones associated with the faults controlling regional tectonics, namely, the Liquiñe–Ofqui Fault System and Andean Transverse Faults. This research presents a laboratory approach comprising a characterization of the analogue host rock from a shallow, low-to-medium temperature geothermal system surrounding the Liquiñe area in Southern Chile (39°S) to better constrain intrinsic and extrinsic factors which allow permeable pathways to exist. We analyse the effect of thermal stress at 25, 150, and 210 °C in a granodiorite, measuring some petrophysical properties before and after applying thermal damage, and then loaded the samples until failure. We also compared petrophysical properties with the fracture network characterization using X-ray microcomputed tomography imaging, segmentation, and fluid flow computational simulations. The results show that thermal stress produces intercrystalline microcracks, which result in: (1) an increase in capillary absorption; (2) a decrease in ultrasonic wave velocities; (3) a decrease in compressive strength; (4) a decrease in fracture aperture, and (5) fluid flow simulations indicate that permeability is similar at different temperatures. We conclude that for the granodiorite host rock of the Liquiñe geothermal system, the combined effect of thermal stress, even at low temperature, may constitute an effective mechanism for sustaining permeability at shallowest depths. [ABSTRACT FROM AUTHOR]

The development of the Rittershoffen deep geothermal field (Alsace, Upper Rhine Graben) between 2012 and 2014 induced unfelt seismicity with a local magnitude of less than 1.6. This seismicity occurred during two types of operations: (1) mud losses in the Muschelkalk formation during the drilling of both wells of the doublet and (2) thermal and hydraulic stimulations of the GRT-1 well. Seismicity was also observed 4 days after the main hydraulic stimulation, although no specific operation was performed. During chemical stimulation, however, no induced seismicity was detected. In the context of all field development operations and their injection parameters (flow rates, overpressures, volumes), we detail the occurrence or lack of seismicity, its magnitude distribution and its spatial distribution. The observations suggest the presence of the rock stress memory effect (Kaiser effect) of the geothermal reservoir as well as uncritically stressed zones connected to the GRT-1 well and/or rock cohesion. A reduction of the seismic rate concurrent with an increase of injectivity was noticed as well as the reactivation of a couple of faults, including the Rittershoffen fault, which was targeted by the wells. These results are derived from the homogeneous and consistent catalogue of more than 1300 local earthquakes that is provided. This reference catalogue is based on a standard detection method, whose output was manually verified and improved. The given absolute locations have been computed in a calibrated, geologically realistic 3D velocity model. Our work builds on previous analyses addressing the seismicity induced by the GRT-1 hydraulic stimulation and places the results into a historical context, thus considering the full dynamics of the observed phenomena. This paper also complements existing descriptions of the hydrothermal characteristics of the deep reservoir by providing insights separate from the wells. [ABSTRACT FROM AUTHOR]

Ground deformation in volcanic areas is linked to various, often interconnected processes such as magma intrusion, pressurized fluid migration, and thermal expansion effects. The presence of active and extended hydrothermal systems plays a key role and affects the deformation phenomenon in complex ways. In this study, we propose a generalized conceptual and mathematical model, which allows retrieving the flow rate of fluid injection in a volcanic hydrothermal system, assuming a ground deformation data set as input. The basic assumption is that short‐term ground uplift episodes (with characteristic periods of less than 5 years) depend on the injection of volcanic fluids into the hydrothermal system. Then, assuming a deformation field shape independent of time and a linear time‐invariant relation between the amount of injected fluid and the resulting ground deformation, we define a Green's function as the product of spatial and temporal components. The case study is a 3‐D elastic model with permeability and porosity for the Campi Flegrei caldera, Italy. By Green's function, a 2‐km‐long source at 2.4‐km depth, which matches the interferometric synthetic aperture radar deformation, is localized and the amount of injected volcanic fluid in the last 20 years of high‐frequency deformation episodes estimated. In conclusion, we find a good agreement between the measured and estimated temporal deformation patterns and, principally, that fluid injection rates can be retrieved from the deformation field at volcanoes. Key Points: What kind of physical process could produce ground short‐term bradyseismic oscillation in calderas unrest?Linear time invariant approximation applied to multiphase thermo‐fluid dynamical evolution of the Campi Flegrei hydrothermal systemShort‐term deformation source parameters estimated by Green's function‐based inversion of the ground deformation at Campi Flegrei caldera [ABSTRACT FROM AUTHOR]

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Ground surface deformations detected with interferometric synthetic aperture radar provide valuable information for inferring subsurface reservoir processes that are difficult to observe directly. This study aims at building a reservoir model that honors the available geological, hydrological, and geomechanical data and also produces ground surface deformation consistent with interferometric synthetic aperture radar measurements at the Raft River Geothermal Field. In the thermo‐hydro‐mechanical coupled model developed, the reservoir deforms as a result of the rock's poroelastic response to changes in hydrologic pressure and thermal expansion/contraction. The results indicate that the observed deformation is the result of pressure decrease in the deep production reservoir and pressure increase in a shallower reservoir that accommodates the injected fluid (likely in the Salt Lake Formation). The combination of the uplift around injection wells with subsidence around the production wells, affected by the Bridge Fault as a flow barrier, creates a complex pattern of surface deformation in which the center of subtle subsidence significantly deviates from the location of the production wells. A parametric study suggests that (a) the Bridge Fault Zone is likely a flow barrier, (b) the surface deformation appears to be insensitive to the presence of the Narrows Structure, and (c) additional flow barriers likely exist to shape the flow system. This case study demonstrates the utility of a high‐fidelity forward model that honors available known information and thermo‐hydro‐mechanical coupled processes in understanding geothermal reservoir characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Geological storage of CO2 is currently regarded as one of the major strategies to mitigate the increasing CO2 concentrations in the atmosphere due to anthropogenic emissions from large‐scale point sources. Enhanced geothermal systems (EGS) are a novel concept in which CO2 is used as a working fluid to increase energy recovery, combined with its subsurface storage. In this study, the geothermal systems of western Anatolia are considered as potential sites for EGS, and the published hydrogeochemical data relevant to these systems are compiled and evaluated in terms of potential water/CO2/rock interaction processes. The evaluation is performed with geochemical approaches including speciation‐solubility calculations, and inverse and dedolomitization modelling. The results lead to the recognition of two different groups with respect to the effective processes: carbonate precipitation, and carbonate precipitation plus dissolution. In high‐enthalpy fields, carbonate precipitation seems to be the major mechanism, while others show the effects of both precipitation and dissolution; dedolomitization is also identified as a potential mechanism for one of the fields. These processes are examined with regard to CO2‐fixation; carbonate precipitation may lead to mineral trapping while carbonate dissolution provides additional cations to the system to react with CO2. Being relevant to CO2 storage in geothermal fields, the conclusions from this study point to the importance of temperature control for CO2 stabilization, as high temperatures seem to promote mineral trapping. The success of a CO2‐EGS project depends on complete geochemical characterization of reservoir processes with further kinetic modelling accompanying the thermodynamic modelling exemplified by this study. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]