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The Canary Islands archipelago, due to their recent volcanism, are the only Spanish territory with high enthalpy geothermal resources. However, there is no evidence in the islands of endogenous fluids manifestations with the exception of the Teide fumaroles, in Tenerife. Although some efforts have been made to investigate the geothermal resources from the 1970s to the 1990s and later during the past decade, the final goal has not yet been achieved, which is to locate and define the size, shape and structure of the geothermal resource, and determine their characteristics and capacity to produce energy (Rodríguez et al. 2015). For this reason it is extremely important to use new tools that allow a better understanding of the geothermal resource. In this work we describe a probabilistic evaluation of the geothermal potential of the island of Tenerife using Geographical Information Systems (GIS) through a collection of geological, geophysical and geochemical data.The Play Fairway Analysis (PFA) was used, as illustrated by Lautze et al. (2017) in a similar study for an environment having similar characteristics: the Hawaiian Archipelago. The PFA approach consists of joining information coming from multidisciplinary datasets within a probabilistic framework. Basically, the probabilities related to the presence of heat (H), fluids (F) and permeability (P) are computed quantitatively from the starting datasets and combined to obtain the probability of presence of geothermal resources and its confidence.In the present study this probabilistic method have been implemented using GIS geoprocessing tools and raster image analysis using geological (Holocene vents, volcano-tectonic structures), geophysical (seismicity, resistivity data, gravity data) and geochemical (hydrogeochemistry, soil gas emission and geochemistry, etc…).The main result of this work is a cartographic set that allow showing the areas of Tenerife with the greatest potential for geothermal exploration. Furthermore, using the statistical framework of PFA analysis, we obtained also confidence intervals on the retrieved probability maps.

Terceira Island is located in the Azores Archipelago and it lies at the intersection of four submarine volcanic ridges. Due to its characteristics the geothermal potential of Terceira Island has begun to receive some interest from researchers and decision makers from the 70s of last century, but only in 2000 an exploration license was granted in favour of GEOTERCEIRA (now EDA RENOVÁVEIS S.A.). The area of this license is located in the central part of the island in the Pico Alto Volcanic Complex, and includes the fumarolic field of Furnas do Enxofre.The main aim of this study is to provide additional information about the presence of fluids upflow regions and areas of increased subsurface permeability related to high temperature hydrothermal activity at depth, as part of an study to expand the current geothermal plant of Terceira. To achieve this objective, a soil gas and diffuse CO2 and H2S degassing survey, which included in situ CO2 emission measurements and soil temperature at 15 and 40 cm deep and the collection of soil gas samples, was performed during September 2019. 122 sampling sites were selected spaced at ~100 meters at Pico Alto Volcanic Complex. Diffuse CO2 and H2S measurements were performed according to the accumulation chamber method, using a non-dispersive infrared (NDIR) LICOR-830 CO2 analyser and ALPHASENSE H2S-BH detectors, respectively. In addition, soil gas samples were collected to analyse the He, H2, O2, N2, CO2, CH4 and CO contents and the isotopic composition of the CO2. Soil CO2 efflux values ranged between non-detectable values and 56.2 g m2 d-1, with an average of 21.7 g m2 d-1. Soil H2S efflux values ranged between non-detectable values and 0.245 g m2 d-1, with an average of 0.027 g m2 d-1. The probability plot technique applied to the soil CO2 efflux data allowed to distinguish three different geochemical populations: background, intermediate and peak represented by 36.9 %, 59.8 % and 3.3 % respectively, with geometric means of 10.8, 25.4 and 50.0 g m2 d-1 respectively. The spatial distribution of soil CO2 efflux data, constructed by means of Sequential Gaussian simulations algorithm, depicted the most important emission anomalies at the western section of the study area. These results can help to identify the possible existence of additional actively degassing geothermal reservoirs to reduce the uncertainty inherent to the selection of the area with the highest potential success in the selection of new exploratory wells at Terceira.

The exploration of geothermal resources on the island of La Palma, Canary Islands, was first conducted by the Spanish Geological Survey (IGME) from 1982 to 1984. These studies were focused exclusively on the southern part, where the last historical eruption, Teneguía, took place in 1971. This area still shows some geothermal features such us relatively high ground water temperatures (about 40ºC) and soil CO2 efflux values. Recent studies carried out at Cumbre Vieja volcano, the southern part of the island, on diffuse degassing, 3D gravimetry and Audio-MT probes point to promising results, although more studies are needed. We continue applying a multidisciplinary approach to obtain additional information about the geothermal system underlying at Palma island using novel techniques as well as tools which are appropriate to evaluate this system. For this reason, during summer 2019 a soil diffuse degassing research started at Cumbre Vieja volcano (220 km2) for geothermal exploration purposes. In this first phase of the diffuse degassing study about 1,200 sampling sites, with an average distance between sites of approximately 250 m were selected after taking into consideration the volcano-structural features and accessibility. In each sampling site in-situ soil CO2 efflux measurements were performed, and soil gas samples were collected at 40 cm depth for chemical and isotopic analysis. Spatial distribution of CO2 efflux, statistical-graphical analysis of CO2 efflux, and δ13C-CO2 isotopic data to calculate and map the volcano-hydrothermal contribution of CO2 were combined and used for geothermal exploration. The statistical-graphic analysis of the diffuse CO2 efflux values confirms the existence of different geochemical populations showing two log-normal geochemical populations, a fact that suggests the addition of deep-seated CO2. Relatively low CO2 efflux values were measured ranging from non-detected up to 72.8 g m-2 d-1, with an average value of 4.6 g m-2 d-1. The highest CO2 efflux values were measured at the north end of Cumbre Vieja, around the surface contact with Cumbre Nueva ridge. The CO2 isotopic composition, expressed as δ13C- CO2 showed the contribution of three different end-members: biogenic, atmospheric and deep-seated CO2. The results indicate that most of the sampling sites exhibited CO2 composed by different mixtures between atmospheric and biogenic CO2 with slight inputs of deep-seated CO2, with a mean value of -15.3‰, being the maximum and the minimum -2.8‰ and -25.4‰ respectively. The results showed here can help to identify the existence of zones where deep-seated actively degassing from geothermal reservoirs occurs, particularly where the interpretation and application of geophysical data might be difficult.

Switzerland is strongly promoting the development of geothermal energy extraction from low- to high-enthalpy resources. However, the broad development of geothermal energy exploitation is hindered by the lack of subsurface knowledge and the high cost of traditional subsurface exploration methods. Affordable passive seismic methods may provide valuable information about the geological structures targeted for geothermal energy extraction. In this context, we are investigating the potential of the Ambient-Noise Tomography (ANT) technique. We present past results obtained from surface-wave ANT in the Geneva basin with a sparse seismic network, and we share preliminary insights from the starting PSIGE project aiming to try refracted P-wave ANT on dense nodal networks (~500 nodes) at several Swiss geothermal exploration sites. From synthetic examples based on prior subsurface models, we discuss the expected depth of investigation and potential resolution of the method with various network configurations.

Petrophysical properties are key to populate local and/or regional numerical models and to interpret results from geophysical investigation methods. Searching for rock property values measured on samples from a specific rock unit at a specific location might become a very time-consuming challenge given that such data are spread across diverse compilations and that the number of publications on new measurements is continuously growing and data are of heterogeneous quality. Profiting from existing laboratory data to populate numerical models or interpret geophysical surveys at specific locations or for individual reservoir units is often hampered if information on the sample location, petrography, stratigraphy, measuring method and conditions are sparse or not documented. Within the framework of the EC funded project IMAGE (Integrated Methods for Advanced Geothermal Exploration, EU grant agreement No. 608553), an open-access database of lab measured petrophysical properties has been developed (Bär et al., 20182019: P3 – Database, https://doi.org/10.5880/GFZ.4.8.2019.P3). The goal of this hierarchical database is to provide easily accessible information on physical rock properties relevant for geothermal exploration and reservoir characterization in a single compilation. Collected data include classical petrophysical, thermophysical and mechanical properties and, in addition, electrical conductivity and magnetic susceptibility. Each measured value is complemented by relevant meta-information such as the corresponding sample location, petrographic description, chronostratigraphic age, if available, and original citation. The original stratigraphic and petrographic descriptions are transferred to standardized catalogues following a hierarchical structure ensuring inter-comparability for statistical analysis (Bär et al., 2019: P3 – Petrography, https://doi.org/10.5880/GFZ.4.8.2019.P3.p, Bär et al., 20182019: 3 – Stratigraphy, https://doi.org/10.5880/GFZ.4.8.2019.P3.s. In addition, information on the experimental setup (methods) and the measurement conditions are listed for quality control. Thus, rock properties can directly be related to in-situ conditions to derive specific parameters relevant for simulating subsurface processes or interpreting geophysical data. We describe the structure, content and status quo of the database and discuss its limitations and advantages for the end-user.

As many ocean basaltic volcanoes worldwide, Piton des Neiges (Reunion Island) hosts a hydrothermal system that represents a potential geothermal resource. Despite several prospection campaigns over the past decades, this potential has never been confirmed because many aspects of fluid supply and circulation remain unclear. To track the origin and fate of hydrothermal fluids, we analyzed the geochemistry of thermal springs (water and gas), by combining conventional tracers (major-trace elements and O, H, C, Sr, Li isotopes) with Cl isotopes, a geochemical tool under development. Added to literature data, our new results allow us to compare the composition of thermal springs with cold waters, rocks, gas, and fumarolic deposits from La Reunion and elsewhere, and to untwine the complex history of fluid mixing that constitutes the geothermal system of Piton des Neiges. delta O-18(H2O) and delta D-H2O values of springs (-8.67 to -4.9 and -56.3 to -23.5 parts per thousand VSMOW, respectively) are positioned close to the local meteoric water line, showing that thermal waters are of meteoric origin. However, their depletion in heavy isotopes relative to cold waters suggests a recharge strongly influenced by cyclones, with a possible contribution from high altitude (>= 2000m) rainfalls. Their absence of O-18 enrichment relative to the local meteoric water line indicates that the isotopic exchange between rocks and water is very limited, and therefore suggests that their deep temperatures are relatively low and/or the water/rock ratios are high. delta C-13 values in thermal waters (-8.0 to +3.2 parts per thousand PDB) and gases (-6.7 to -5.3 parts per thousand PDB) confirm that carbon is essentially of magmatic origin, which we interpret as supplied by regional degassing of La Reunion hotspot. Major-trace elements and Sr-87/Sr-86 (0.704142 to 0.704336), delta Li-7 (+2 parts per thousand and +34.8 parts per thousand LSVEC), and delta Cl-37(-0.35 parts per thousand and +0.40 parts per thousand SMOC) compositions show that three additional processes contribute to the mineralization of thermal waters: 1) interaction with basalt at temperatures >= 50 degrees C, 2) very limited seawater contamination (< 3 mol parts per thousand), and/or 3) leaching of trachyte or scrubbing of fumarolic gas or condensates emitted by a shallow trachytic magma in the volcanic edifice. The geothermal system of Piton des Neiges is thus the result of meteoric water interaction with a trachytic heat source (as a solidified intrusion or a magma pocket), unrelated to the CO2 flux. We also emphasize that thermal waters at Piton des Neiges are exceptionally isolated from seawater compared to other geothermal systems in ocean island volcanoes worldwide, which implies a heat source located above the seawater/freshwater interface. These inferences are of critical importance for the future geothermal exploration on the island, as they suggest that the geothermal resource is within reach of relatively shallow drilling depths (

Geothermal energy is one of the most promising renewable energies due to its high load factor. This work is devoted to presenting the conceptualizations and research advances made at Shenzhen University on the exploration and utilization of low/medium-temperature geothermal energy based on the geothermal resource potential and characteristics of the Guangdong-Hong Kong-Macao Greater Bay Area. The results indicate that the geological structure and lithology of this area are conducive to the formation of geothermal conditions. The geothermal flow and geothermal gradient in this area are higher than the average values in southern China. The total hydrothermal resources and hot dry rock geothermal resources amount to 1.8 × 1017 kJ and 4.0 × 1017 kJ, respectively. To enhance the permeability of geothermal reservoirs, especially hot dry rock reservoirs, the volumetric fracturing technique, which is based on three-dimensional fracture mechanics, and the fatigue pneumatic fracturing technique are proposed to stimulate geothermal reservoirs. The advances in theoretical and experimental research and some noteworthy future research topics on volumetric fracturing and fatigue pneumatic fracturing techniques are summarized. To increase the efficiency of low/medium-temperature geothermal power generation, conceptualizations of magnetic levitation power generation technology and thermovoltaic power generation technology for geothermal power generation are proposed. This study may provide new insights into geothermal exploration and low/medium-temperature geothermal power generation.

The lateral and vertical temperature distribution in Oman is so far only poorly understood, particularly in the area between Muscat and the Batinah coast, which is the area of this study and which is composed of Cenozoic sediments developed as part of a foreland basin of the Makran Thrust Zone. Temperature logs (T-logs) were run and physical rock properties of the sediments were analyzed to understand the temperature distribution, thermal and hydraulic properties, and heat-transport processes within the sedimentary cover of northern Oman. An advective component is evident in the otherwise conduction-dominated geothermal play system, and is caused by both topography and density driven flow. Calculated temperature gradients (T-gradients) in two wells that represent conductive conditions are 18.7 and 19.5 degrees C km(-1), corresponding to about 70-90 degrees C at 2000-3000 m depth. This indicates a geothermal potential that can be used for energy intensive applications like cooling or water desalinization. Sedimentation in the foreland basin was initiated after the obduction of the Semail Ophiolite in the late Campanian, and reflects the complex history of alternating periods of transgressive and regressive sequences with erosion of the Oman Mountains. Thermal and hydraulic parameters were analyzed of the basin's heterogeneous clastic and carbonate sedimentary sequence. Surface heat-flow values of 46.4 and 47.9 mW m(-2) were calculated from the T-logs and calculated thermal conductivity values in two wells. The results of this study serve as a starting point for assessing different geothermal applications that may be suitable for northern Oman., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 934

Summary In the petroleum industry, production from low permeable reservoirs is believed to be highly influenced by the presence of open natural fractures. However, in geothermal exploration projects, natural fractures are generally not incorporated in estimating the economic viability of tight reservoir bodies. Therefore, in this study we expand on the key lessons learned from the Energy & Production industry and perform a naturally fractured reservoir characterisation study of 1) automated fault extraction, 2) image log and core data interpretation and 3) Discrete Fracture Network (DFN) modelling using Multiple Point Statistics (MPS). The workflow is exemplified on tight Triassic sandstones in the West-Netherlands Basin. Firstly, the seismic data analysis shows that the reservoir target is heavily faulted, with faults showing multiple orientations. Further, well data analysis indicate faults and fractures are most likely structurally related. Therefore, in the DFN modelling workflow, we assume fault related fracturing, so that fracture density estimations away from the well, are guided by the extracted fault model. Finally, using MPS, a reservoir scale DFN is generated and we suggest that this model can be used as input for fluid-flow models, to address the impact that natural fractures could have on geothermal production in low permeable reservoirs.

Heat source is one of the four important parameters in geothermal systems of reservoir layers, caprock layers, and fractures. Its existence will cause a very significant difference between the aquifer layer and the geothermal reservoir layer. Unfortunately, the most geothermal issue is focused on fractures and clay cap layers since the MT (magnetotelluric) method is sensitive to response to the conductive clay cap. The MT and gravity method are two powerful geophysical methods to implement in geothermal exploration. The gravity data mostly used to prompt either structure or reservoir layer. Therefore, the gravity data here will be used to map the geothermal heat source in the Mt. Lawu geothermal system. The tilt angle or tilt derivative method is applied to delineate the area and determine the depth of the heat source. The vertical derivative value of gravity obtained from upward continuation with h = 200, 400, and 600 m above sea level. The result shows that the depth of heat source in the Lawu geothermal system is estimated to be at a depth of 900 - 2896 m below sea level in the southern part of the study area. These hot rocks degrade from the South toward the Northeast of the suspected caldera zone. There is also an indication of a fault that allegedly connects the reservoir layer and the fumarole manifestation zone in the Northeast study area. Structures in this area are looking likely dominated by a normal fault and among them form a graben structure.

This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234U/230Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exploration and exploitation in the Puna Plateau region Fil: Filipovich, Ruben Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Groppelli, Gianluca. CNR Istituto di Geologia Ambientale e Geoingegneria; Italia Fil: Ahumada, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Aldega, Luca. Università degli Studi di Roma "La Sapienza"; Italia Fil: Becchio, Raul Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Berardi, Gabriele. Università Roma Tre III; Italia Fil: Bigi, Sabina. Università degli Studi di Roma "La Sapienza"; Italia Fil: Caricchi. Chiara. Istituto Nazionale di Geofisica e Vulcanologia; Italia Fil: Chiodi, Agostina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Corrado, Sveva. Università Roma Tre III; Italia Fil: De Astis, Gianfilippo. Istituto Nazionale di Geofisica e Vulcanologia; Italia Fil: De Benedetti, Arnaldo Angelo. Università Roma Tre III; Italia Fil: Invernizzi, Chiara. Universita Degli Di Camerino; Italia Fil: Norini, Gianluca. CNR Istituto di Geologia Ambientale e Geoingegneria; Italia Fil: Soligo, Michele. Università Roma Tre III; Italia Fil: Taviani, Sara. University of Milano-Bicocca; Italia Fil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Giordano, Guido. CNR Istituto di Geologia Ambientale e Geoingegneria; Italia. Università Roma Tre III; Italia

Summary The main objective of this review is to investigate if the magnetotelluric method and controlled-source electromagnetics can be successfully applied for geothermal exploration in the Netherlands. In the review the available cases are reviewed and discussed, presenting some new data and results as well. The main conclusion is that no representative case study is available to be able to make an overall conclusise statement. However, it can be concluded that both methods provide additional data for subsurface information. When compared to seismic data, the added value of the EM methods are the lower data acquisition costs and the possibility to directly relate electrical resistivity to porosity. The absence of magmatic waters and related clay alteration minerals in the Netherlands implies that an important factor for successfully applying MT for geothermal exploration is missing.The experiments in Luttelgeest (Netherlands) and Belgium proved that using the EM method, one can measure up to a depth of about 2 km below the surface. The experiments in Luttelgeest and Belgium proved that acquiring good quality EM data in Belgium and the Netherlands is possible, despite the numerous EM noise sources.

Summary The Larderello-Travale field (Tuscany, Italy) is the oldest historical areas of geothermal exploration and exploitation in the world. Two reservoirs have been progressively investigated and exploited and the current case study focuses on the deepest fractured reservoir in the southwestern area of the field. It is characterized by temperatures of 250–350°C with an initial static pressure of around 70 bar. The modeled area is historically managed by 64 producers and 12 injectors. The study consisted in a 3D static and dynamic modeling and particular attention was paid to natural fractures distribution within the reservoir. The history matching was performed on the natural state and production history which started in the nineties. The aim of the study is to give a better understanding of the production mechanism of a naturally fractured geothermal field by mean of fracture characterization and distribution. This calls for a detailed description of well productivity and interference between closed wells and groups of wells.

Geothermics : an international journal of geothermal research and its applications 87, 101876 (2020). doi:10.1016/j.geothermics.2020.101876, Published by Elsevier Science, Amsterdam [u.a.]

Among geothermal exploration methods, active surface seismic methods have played only a minor role to date. Especially in high-temperature volcanic systems, reflection seismic data often reveal poor delineation of volcanic features, due to the internal heterogeneity of volcanic sequences. To enhance the vertical resolution, one possibility is the application of downhole seismic methods like vertical seismic profiling (VSP). A test experiment was carried out in the Krafla high-temperature geothermal field, NE-Iceland, to assess the ability of VSP to image subsurface structures, such as fractures, zones of high permeability, magmatic bodies, and zones of supercritical fluids and steam. Logging in such hostile environments is technical challenging in many aspects, but mainly due to the high temperature impact on the downhole electronic components of the measuring equipment. This requires a thorough pre-examination and implementation of the measurement, especially to avoid delays and tool failures. This paper presents results of zero- and far-offset VSP data from the K-18 borehole from within the Krafla caldera, which reveal good correlation with the surrounding lithology. The raw three-component seismic data display a good signal-to-noise ratio and dominant signal frequencies between 20 and 40 Hz, down to c. 2200 m depth, for air gun and explosive sources, respectively. A zero-offset source comparison was also conducted to assess the use of different impulsive sources for future VSP surveys in similar settings. By applying a standard VSP processing, we identified stratigraphic boundaries between lavas, hyaloclastites, and intrusions, which are in good agreement with existing well data. For the zero-offset VSP, both P- and S-wave velocity models were calculated and a depth-converted corridor stack was determined. In addition, multicomponent Kirchhoff depth migration and Fresnel volume migration were tested around the borehole. The 3D results are promising, but the specific shape and lateral extent of the reflectors could not be determined due to the restriction to only two sources and the insufficient spatial coverage (aperture). Our study demonstrates that vertical seismic profiles can clearly detect variations in the subsurface volcanic stratigraphy in high-temperature geothermal fields. A more detailed reservoir characterization can be achieved by further data integration, enhanced survey design including more source positions, and improved processing and imaging techniques, such as full-waveform inversion.

Arjuno-Welirang Mountain is located in East Java province, which is a type of stratovolcano with an altitude of 3,339 m for Arjuno and 3,156 m for Welirang. The Arjuno-Welirang geothermal system is a volcanic geothermal system. Magnetotelluric is the most commonly used geothermal exploration method because of its deep penetration and sensitivity to conductive zones. The Magnetotelluric method measures 103 MT points in the field of geothermal systems in the South of Mount Arjuno-Welirang. In this study, the 3D inversion model of Magnetotelluric data was used to reduce the ambiguity of 2D Magnetotelluric inversion data. 3D Model Inversion uses WinGlink and 3DModEM. The steps of Magnetotelluric processing consist of time-domain conversion to the frequency domain, cross power selection, data smoothing, static effect correction, 2D and static strips, interpolation, masking, 3D inversion, and interpretation of inversion models. The 3D model inversion consists of 3D mesh grid parameters used by the NonLinear Conjugate Gradient Algorithm. 2D Inversion Modelling was done by the NLCG method, which produces a 2D model with an RMS error of 1.7%. 3D Inversion modeling was done by the NLCG method producing a 2D model with a value of RMS error of 2.83%. The geothermal system of the Arjuno-Welirang geothermal region consists of a layer of veil rock with a type of resistivity value of 5-11 Ωm, a middle resistivity zone with a value range of 11-76 m acting as a reservoir, and a high resistivity zone with a range of 76-500 Ωm or commonly called heat source. The results of the 3D inversion model indicated a range of low resistance types (hood rock layers) that have a thickness of 1200 - 1700 m, the value of this type of resistance is below the surface with a thickness of ±500-600 m. Thus, the Mt. Arjuno-Welirang is a geothermal prospect area.

A passive seismic experiment using 25 broadband and 20 short‐period stations was conducted between September 2017 and September 2018 at Los Humeros geothermal field, an important natural laboratory for superhot geothermal systems in Mexico. From the recorded local seismicity, we derive a minimum 1‐D velocity model and obtain 3‐D Vp and Vp/Vs structures of Los Humeros. We improved the classical local earthquake tomography by using a postprocessing statistical approach. Several inversions were computed and averaged to reduce artifacts introduced by the model parametrization and to increase the resolution of the investigated region. Finally, the resulting Vp and Vp/Vs structures and associated seismicity were integrated with newly acquired geophysical and petrophysical data for comprehensive interpretation. The recorded seismicity is mainly grouped in three clusters, two of which seem directly related to exploitation activities. By combining new laboratory measurements and existing well data with our Vp model, we estimate possible geological unit boundaries. One large intrusion‐like body in the Vp model, together with neighboring high Vp/Vs anomalies, hints at a region of active resurgence or uplift due to the intrusion of new magma at the northern portion of the geothermal field. We interpret high Vp/Vs features as fluid bearing regions potentially favorable for further geothermal exploitation. Deep reaching permeable faults cutting the reservoir unit could explain fluid flow from a deeper local heat source in the area., Journal of Geophysical Research: Solid Earth, 125 (12), ISSN:2169-9313, ISSN:0148-0227, ISSN:2169-9356

International audience; The subsurface temperature is one of the most crucial parameters for the development of geothermal energy. Physics-based temperature models calibrated with temperature data are especially relevant for deep geothermal exploration. We present an updated high-resolution 3D thermal model of the onshore Netherlands. We constructed the model in 7 steps, starting from a lithospheric-scale, physics-based forward model and progressively detailing and updating it using temperature data. The model is built up from 14 sedimentary layers and layers for the upper crust, lower crust, and lithospheric mantle. We assigned a-priori thermal properties for each layer and updated them through an inversion procedure by the Ensemble Smoother with Multiple Data Assimilation (ES-MDA), using 1507 temperature measurements as observations. Misfits of the prior model are significantly reduced through the data assimilation procedure, demonstrating the effectiveness of ES-MDA as a tool for calibrating temperature models, supporting high-resolution external constraints. The resulting posterior model describes the thermal state in the uppermost 10 km of the Netherlands with a horizontal resolution of 1 km, a vertical resolution of 200 m, and an overall RMS misfit of 0.7 °C.The thermal state of the deep subsurface is important for geothermal exploration that targets the deeply buried Devonian-Carboniferous carbonate formations in the Netherlands. These reservoirs are potentially suitable for industrial heating applications and electricity production. To this end, one of the main aspects of this study was to incorporate the thermal effect of hydrothermal convection within the Dinantian carbonate platforms, following the example found in the Luttelgeest-01 (LTG-01) well. Our model reveals areas in the Netherlands with potential for convection in these carbonate platforms, highlighting locations that can be suitable for deep geothermal development.

Summary The Kingdom of Saudi Arabia has bold plans to diversify its energy mix, as spelled out in the Saudi 2030 vision. One of the energy diversification targets is geothermal energy, particularly in context of low to medium enthalpy energy for space heating/cooling, and water desalination applications. Areas with low-to-medium enthalpy geothermal potential in the Kingdom are stretched along the western Arabian peninsula, a region considered to have higher geothermal gradient than the eastern side. In the early stage of a geothermal exploration study, subsurface data are essential for a first-order analysis of the thermal potential of the basin. Due to limited availability of subsurface data, especially seismic data and well data, we utilize open satellite gravity data in the Ifal Basin, one of the promising areas located in north-west Saudi Arabia and site for one of the Kingdom’s giga-projects, NEOM. We estimate temperature profiles based on gravity modelling informed by published stratigraphic data. The results indicate a geothermal gradient of 30oC/km to 35oC/km in the Ifal Basin. The temperature may reach 100oC at the basement high, and more than 200oC at the basin depocentre.

Summary There are over 300 geothermal plants operating in 35 countries. The majority of the power plants occur in geologically complex high-temperature volcanic areas and limited well success rates in these settings limits commercial returns. Future geothermal drilling will turn increasingly to sedimentary basins. In this context, there are some key similarities between the skills, understanding and data used for the exploration and exploitation of hydrocarbons and that of geothermal energy. Insights into the geoscientific challenges faced in drilling sedimentary basins will enhance our ability to evaluate and develop geothermal resources in a manner that minimises subsurface risk. This paper aims to outline the different phases of a geothermal exploration and development campaign, highlighting areas of overlap between the geothermal industry and knowledge and data from the petroleum industry. By utilising the potential synergies between the petroleum and geothermal industries, the energy industry will be well positioned to transfer from oil and gas to geothermal.

Precise knowledge of the subsurface thermal field plays a key role in the assessment of geothermal targets. Unfortunately, deep underground temperature data is generally scarce and a matter of research. To achieve first estimates for subsurface temperatures, steady-state conductive thermal modeling is commonly applied. Thereby the rock thermal conductivity is an essential parameter, which is usually determined under ambient laboratory conditions. To arrive with in situ thermal conductivity, the ambient values need to be corrected for in situ temperature and pressure. In this paper, we apply different conversion functions for the correction of thermal conductivity and study the impact on the resultant temperature and heat flow prognoses for a synthetic, upper crustal sedimentary and a magmatic scenario along 2-D geological cross sections. Application of the correction functions results in maximum temperature prognosis uncertainties of about 8 °C and 55 °C at 2 km depth and at 8 km depth, respectively. The effect positively correlates with the magnitude of the basal heat flow used in modeling. In contrast to the heat flow determined at depth, the resulting surface heat flow is only minor affected by the different correction functions applied. In addition, the modeled temperature at depth is strongly dependent on the type and sequence of application of the pressure and temperature correction equations.

The Argentinean Andean region hosts a vast geothermal resource clustered by active magmatic and tectonic activity. One of the most studied geothermal areas is the Tuzgle-Tocomar geothermal system in Central Puna (NW Argentina). However, despite the existence of several studies since the 1970′s highlighting the geothermal potential of the area, only highly schematic and dissimilar conceptual models have been proposed for the Tocomar Geothermal System. This study presents new detailed geological-structural and hydrogeochemical data, together with in-situ permeability analysis of fault zones and Raman spectroscopic characterization of hydrothermal-alteration minerals. The electrical generating capacity has also been evaluated using the volumetric method and a stochastic approach. A new comprehensive conceptual model of the studied area was constructed highlighting the role of the Calama-Olacapato-El Toro (COT) fault-system in the circulation of hydrothermal fluids. The reservoir of the Tocomar geothermal system has a Na+-Clˉ(HCO3)ˉ composition and an estimated temperature of ∼235 °C. Such a reservoir is hosted in fractured Ordovician rocks and controlled by the COT-like Chorrillos transpressive fault at 1000–1500 m depth b.g.l. The water isotopic data and hydrological features indicate a regional recharge beyond the Tocomar sub-basin boundaries (>5000 m a.s.l.). Additionally, the main hydrothermal reservoir receives inputs of magmatic fluids from the degassing of the intra-crustal rhyolitic magma chamber of the Tocomar volcanic center. The Monte Carlo simulations suggest that the Tocomar geothermal system has a probable power production capacity above 1.23 MWe (P90), 6.18 MWe (P50) and 11.67 MWe (P10) at different confidence levels. All calculations were biased towards minimum values, thus a tighter definition of the resource size and fracture porosity would significantly impact on the predictions. Notwithstanding, the strategic position of the Tocomar geothermal field encourages move forward towards more in-depth exploration phases.

The Spessart Spa at Bad Soden-Salmunster extracts carbon dioxide bearing thermal brine from three wells. To utilise the thermal brine for balneology in the spa it is necessary to heat the brine, given that the maximum temperature is ‘only’ 23.7 °C. The management of the spa intends to lower financial expenses by increasing the utilisation of renewable energies. This has led to the investigations presented here, focussing on whether hotter brine could be produced by deepening existing wells or drilling new deeper wells. Additionally, optional heat supply from shallow geothermal systems is examined. The wells of Bad Soden-Salmunster are the deepest drill holes in the region reaching a depth of 539 m. Since there are neither deeper wells nor available geophysical exploration data, predicting the geological structure of the deeper underground is a challenging aspect of this exploration. Therefore, a multimethod approach has been chosen here. Firstly, a combination of historical data and new measurements is used to discuss origin and genesis of the thermal brine. Secondly, using literature data and an outcrop analogue study, the geological units beneath Bad Soden-Salmunster are predicted and assigned petrophysical properties. Thirdly, the open-flow potential of the used wells and data from pumping tests are evaluated. Finally, the geothermal potential of the reservoir at Bad Soden-Salmunster is estimated. The chosen multimethod approach is shown to provide a comparatively quick and cost efficient option for establishing a reliable database that enables geothermal exploration decisions as well as future simulations of different geothermal utilisation scenarios.

The important scientific questions that will form the basis of a full proposal to drill a deep well to the ductile–brittle transition zone (T>400 ∘C) at Newberry Volcano, central Oregon state, USA, were discussed during an International Continental Drilling Program (ICDP) sponsored workshop held at the Oregon State University-Cascades campus in Bend, Oregon, from 10 to 13 September 2017. Newberry Volcano is one of the largest geothermal heat reservoirs in the USA and has been extensively studied for the last 40 years. The Newberry Deep Drilling Project (NDDP) will be located at an idle geothermal exploration well, NWG 46-16, drilled in 2008, 3500 m deep and 340–374 ∘C at bottom, which will be deepened another 1000 to 1300 m to reach 500 ∘C. The workshop concluded by setting ambitious goals for the NDDP: (1) test the enhanced geothermal system (EGS) above the critical point of water, (2) collect samples of rocks within the brittle–ductile transition, (3) investigate volcanic hazards, (4) study magmatic geomechanics, (5) calibrate geophysical imaging techniques, and (6) test technology for drilling, well completion, and geophysical monitoring in a very high-temperature environment. Based on these recommendations, a full drilling proposal was submitted in January 2018 to the ICDP for deepening an existing well. The next steps will be to continue building a team with project, technology, and investment partners to make the NDDP a reality.

The heterogeneous distribution of minerals in different rock types poses several challenges for assessing thermal conductivity, heat flow and temperature of sedimentary basins, especially when databases coming from the oil sector are the only source of information. The objective of this study was to develop a new methodology that uses well log data to better infer the thermal conductivity variations of sedimentary formations in order to evaluate heat flow and extrapolate temperature at depth. The methodology was applied to the St. Lawrence Lowlands basin, with constrains from the available oil and gas database not designed for geothermal exploration purposes. The main idea was to analyze quantitatively well log data with an inversion approach from limited reference wells and derive empirical relationships to calculate a thermal conductivity profile for each available well. Pressure and temperature corrections were then considered. These continuous logs of thermal conductivity were used to estimate the Earth’s heat flux density using bottomhole temperatures and to extrapolate temperature at depth. A modified version of Poisson’s equation was solved by the finite difference method for this purpose. The average temperature and its standard deviation obtained with this approach for the St. Lawrence Lowlands at 1000, 2500 and 5000 m depth is approximately 32 ± 6.9 °C, 63 °C ± 12.7 °C and 119 °C ± 28.3 °C, respectively. Moreover, temperature ranges from 19 to 52 °C, 41 to 112 °C and 75 to 236 °C at 1000, 2500 and 5000 m depth, respectively.

Regular annual reports issued by the Ministry of Electricity and Energy show that the established power generating capacity of Egypt is based mainly on oil and natural gas resources. Due to its high energy demand, Egypt needs clean, renewable, alternative energy sources. From this perspective, it is earnestly imperative to utilize geothermal resources to produce power and add to the Egyptian energy supply in a clean and efficient way. This paper reviews the state-of-the-art geothermal resources in Egypt with an emphasis on the current investigation utilizing aeromagnetic data. Power spectral analysis was applied to the aeromagnetic data to estimate the Curie point depth (CPD), heat flow and geothermal gradient. The CPDs range from 8.6 to 35.7 km, the derived geothermal gradients vary from 16.3 to 67.4 °C/km, and the heat flow values range from 47.1 to 195.5 mW/m2. The relation between the CPDs and seismic activity was also examined. Most of the earthquakes that originated in areas with CPDs of less than 25 km are considered promising regions for geothermal exploration, especially in the Gulf of Suez. The results of the current study may guide governmental and private sectors interested in the geothermal energy industry to select the most appropriate geothermal power plant sites in Egypt.

Once a geothermal site has been selected for exploration, a full understanding of the formation temperature distribution on the surface and in the underground reservoir is always needed to assess the geothermal capability and productivity. Commercially available electronic measuring instruments cannot overcome the highest downhole temperatures obtained in the world’s deepest and hottest geothermal reservoirs. In this study, fiber optic Bragg grating (FBG) measurement technology is utilized applied in an attempt to replace more expensive electronic sensors and to obtain more accurate downhole pressure and temperature data. This has been our target since 2013. For this purpose, a portable pressure and temperature (P/T) optic fiber wire-line instrument prototype was developed, and it can measure up to 1500 m in depth. The prototype was named SINOTECH-OPTIC-P/T in 2015. It has been tested in various well types, including a hot spring well and a pioneering geothermal exploration well (JY-01). The primary results have proved to be satisfactory. This paper summarizes the temperature and pressure measurement results obtained in JY-01 well at Sanshing geothermal site in I-lan County, Taiwan. The maximum measured well depth was 1200 m, and data measured includes a downhole temperature profile with the maximum temperature of around 75 °C.

The Los Humeros geothermal field is the third most important producer of geothermal electricity (70 MW) in Mexico. Geothermal fluids are hosted in fractured andesitic lavas and mostly consist of high enthalpy steam with limited water content (vapor fraction > 0.9). Despite the high reservoir temperature (~300–400 °C), thermal manifestations at the surface are scarce and locally appear as steaming grounds, weak steam vents and advanced argillic alteration. Geothermal fluid upflow from the reservoir towards the surface is limited by welded ignimbrite deposits that act as a low-permeability barrier. In this study, we present the first measurements of CO2, CH4 and H2S degassing rates from the soil performed at Los Humeros. Flux measurements were complemented with δ13C composition of degassing CO2 and soil temperatures to discuss gas origin and thermal anomalies. We measured high soil degassing rates (up to 7530 g m−2 d−1 CO2, 33 g m−2 d−1 CH4 and 22 g m−2 d−1 H2S) in three localized areas (Humeros North – HN, Humeros South – HS and Xalapazco – XA) as well as high soil temperatures reaching the boiling temperature at the local altitude (90.6 °C). The particular location of these three areas suggests that the steam-dominated reservoir degases to the surface through permeable faults crossing the ignimbritic deposits. The remaining surveyed areas are characterized by weak CO2 fluxes (≤44 g m−2 d−1), non-detectable CH4 and H2S fluxes, and lower soil temperatures (5–21 °C). The compositions in δ13CCO2 from HN-HS-XA areas (δ13CCO2 = −7.94 to −2.73‰) reflect a magmatic source with some possible contribution from the sedimentary basement, as well as fractionation induced by boiling and CO2 dissolution in shallow water bodies. We also discuss the processes causing the spread in CO2/CH4 flux ratios. Finally, we estimate the heat output from the three high degassing areas to a value of 16.4 MWt.

In this paper a relatively inexpensive and efficient strategy for geothermal exploration by using geochemical prospecting tools to determine the placement of initial exploratory well(s) is proposed. The method involves categorizing the hierarchy of thermal manifestations from which the presence of a buried thermal anomaly can be identified in a given geothermal area, and then locating the centre of the thermal anomaly. This is done by using simple, easy to obtain data on the depth, temperature, and some common chemical parameters determined in wells of the shallow unconfined aquifer, from which thermal gradients can be calculated if the temperature of the local rainfall is known. The proposed strategy was applied by the author in Yemen; on a national scale in 2001–2006 ( Minissale et al., 2007 ), and a local scale in 2007–2010 in the Dhamar region ( Minissale et al., 2013 ). In the paper about the Dhamar area, briefly summarized here, how the placement of its first exploratory well was determined is described. The methodology proposed is particularly effective and convenient in developing countries, such as those located along the African Rift, e.g. Zambia and Malawi, where geothermal exploration is still in its infancy, and where waiting for expensive geophysical investigations might postpone the development of geothermal resources for decades.

Magnetotelluric (MT) method is a widely used geophysical method in geothermal exploration. It is used to image subsurface resistivity structures from shallow depths up to several kilometers of depth. Resistivity imaging using MT method in high-enthalpy geothermal systems is an effective tool to identify conductive clay layers that cover the geothermal systems and to detect a potential reservoir. A resistivity model is vital for deciding the location of pilot and production sites at the early stages of a geothermal project. In this study, a 3-D resistivity model of Aluto-Langano geothermal field was constructed to map structures related to a geothermal resource . The inversion program, ModEM was used to recover the 3-D resistivity model of the study area. The 3-D inversion result revealed the three main resistivity structures: a high-resistivity surface layer related to unaltered volcanic rocks at shallow depth, underlain by a conductive zone associated with the presence of conductive clay minerals, predominantly smectite . Beneath the conductive layer, the resistivity increases gradually to higher values related to the formation of high-temperature alteration minerals such as chlorite and epidote . The resistivity model recovered from 3-D inversion in Aluto-Langano corresponds very well to the conceptual model for high-enthalpy volcanic geothermal systems. The conductive clay cap is overlying the resistive propylitic upflow zone as confirmed by the geothermal wells in the area.

A land gravity survey was carried out in the Kinigi geothermal field, Northwest Rwanda using 184 gravity stations during August and September, 2015. The aim of the gravity survey was to understand the subsurface structure and its relation to the observed surface manifestations in the study area. The complete Bouguer Gravity anomaly was produced with a reduction density of 2.4 g/cm 3 . Bouguer anomalies ranging from −52 to −35 mGals were observed in the study area with relatively high anomalies in the east and northwest zones while low anomalies are observed in the southwest side of the studied area. A decrease of 17 mGals is observed in the southwestern part of the study area and caused by the low-density of the Tertiary rocks. Horizontal gradient, tilt angle and analytical signal methods were applied to the observed gravity data and showed that Mubona, Mpenge and Cyabararika surface springs are structurally controlled while Rubindi spring is not. The integrated results of gravity gradient interpretation methods delineated a dominant geological structure trending in the NW-SE, which is in agreement with the regional geological trend. The results of this gravity study will help aid future geothermal exploration and development in the Kinigi geothermal field.

Siwa Oasis is a part of the greatest northern depression in the Egyptian Western Desert, located just 50 km east of the Libyan border. It represents one of the most interesting potential candidates for the development of the Northern Western Desert of Egypt. Temperature data from deep wells in the Western Desert of Egypt indicate low geothermal resources. Here, we present the contribution of airborne gravity and magnetic geophysical data for the preliminary exploration of geothermal potential in Siwa Oasis. To achieve this objective, a 3D inversion of aerogravity data was used to delineate the depths to basement rocks, while spectral analysis of the aeromagnetic data was used to estimate the Curie Point Depth (CPD) and provide geothermal gradient and heat flow maps for the Siwa Oasis. The depth to the Precambrian basement rock is commonly greater than 2 km, ranging from 2 km to 5 km, whereas the CPDs range from 21 km to 28 km. Our results imply an inverse relationship between these two depths, in which the deeper basement regions are associated with shallow Curie depths. The derived geothermal gradients range from 21 to 27 °C/km and the heat-flow values range from 49 to 64 mW/m2 for the study area.

Geothermal energy is a precious resource, which is widely distributed, varied, and abundant. China has entered a period of rapid development of geothermal energy since 2010. As shallow geothermal energy promoting, the depth of hydrothermal geothermal exploration is increasing. The quality of Hot Dry Rock (HDR) and related exploratory technologies are better developed and utilized. On the basis of geothermal development, this paper reviews the geothermal progress during the “12th Five-Year Plan”, and summarizes the achievements of hydrothermal geothermal and hot dry rocks from geothermal survey and evaluation aspects. Finally, the authors predict the development trend of the future geothermal research to benefit geothermal and hot dry rock research.

The goal of this study is to review 18 significant enhanced geothermal system (EGS) sites and technologies that have been applied in the European Union, Japan, South Korea, Australia and the USA. The results of earlier cases indicate that the site characteristics, such as a transtensional type setting, are a key factor of successful EGS development. This study also introduces the Enhanced Geothermal Innovative Network for Europe (ENGINE), which focuses on developing high-temperature instruments for the characterization and exploitation of supercritical geothermal reservoirs, as well as the geothermal engineering integrating mitigation of induced seismicity in reservoirs (GEISER). The energy reserves in the upper 10 km of the earth's crust are approximately 1.3 × 1027 J, which could supply the global energy use for approximately 217 million years. The exploitable geothermal potential can reach 1200 GWe based on an estimated probability of 70%. In 2050, there will be more than 70 GWe of EGS based on an estimated probability of 85%. In view of the immature technologies for EGS, the US has funded a total of 0.22 billion USD from 2007 to 2013 to develop innovative exploration, reservoir stimulation, and sustainable reservoir technologies and economic analysis models for the commercialization of EGS. The crucial issue in Taiwan's geothermal development is the enhancement of the poor productivity of geothermal production wells. Based on foreign experience, increasing the productivity by adding reinjection wells in traditional hydrothermal fields should be a feasible approach for the development of EGS in Taiwan. The study suggests that Taiwan should establish a geothermal exploration database. In addition, the enhancement of geothermal production by developing reservoir simulation and reservoir maintenance technologies will lead to cost reductions. Finally, promoting traditional hydrothermal geothermal power plants to drive EGS development will allow for the stable expansion of Taiwan's geothermal industry.