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Los Humeros is one of the main Pleistocene silicic volcanic complexes and the third geothermal field in exploitation in Mexico. It is located in the eastern sector of the Trans-Mexican Volcanic Belt (TMVB) and has a long and complex geologic evolution involving the formation of at least two large nested calderas associated with very large ignimbrite-forming eruptions during the last 0.46 Ma (Ferriz and Mahood, 1984). Due to its young activity, it has an active geothermal field (Yanez and Garcia, 1980) producing about 65 MW. Several wells for both exploration and exploitation of geothermal fluids have been drilled in the caldera interior, showing the subsurface stratigraphy and structure of the volcanic center. A revised lithostratigraphic characterization of Los Humeros subsurface together with petrographic, geochemical and 40 Ar/ 39 Ar-based geochronology data support correlation of rock formations at depth with surface geology. This study shows the very heterogeneous nature of the subsurface stratigraphy of Los Humeros volcanic complex, helping to refine its internal structure and evolution. This provides a more realistic configuration of the heterogeneities of the geothermal reservoir and the vertical and lateral distribution of permeable conditions controlling the configuration of the geothermal reservoir. These results can be important to guide the prospection of potential areas for the possible expansion of the geothermal field.

Project HOTSPOT, the Snake River Scientific Drilling Project (International Continental Scientific Drilling Program), tested for deep geothermal resources and examined the petrology of volcanic rocks with three drillholes in the central and western Snake River Plain (western USA). The MH-2 drillhole targeted fractured crystalline and hydrothermally altered basalt in the area of the Mountain Home Air Force Base (Idaho) to a total depth of 1821 m. At 1745 m depth the drillhole encountered flowing artesian hydrothermal fluids of at least 150 °C. We integrate geological analyses of core, image log, and borehole geophysical data, and in situ stress analyses to describe the structural environment that produces permeability for artesian flow. The rocks in the lower 540 m of the drillhole consist of basalt flows as much as 30 m thick, altered basalt, and thin sedimentary horizons. The mechanical stratigraphy is defined by nine mechanical horizons that are in three ranges of rock strength on the basis of experimentally determined strength data, core logging, and geophysical log signatures. Hydrothermal alteration products and mineralization in the core are associated with three highly faulted sections; the lowermost section is associated with the zone of flowing thermal water. Shear slip indicators on faults observed in core indicate slip ranging from pure strike slip to normal failure mechanisms in the stronger horizons. The borehole breakouts indicate that the maximum horizontal stress, SH, is oriented 047° ± 7°, and drilling-induced tensile fractures indicate that SH is oriented at 67° ± 21°. The in situ stress orientations exhibit little variation over the depth of the measured interval, but the SH magnitude varies with depth, and is best explained by an oblique normal fault stress regime. The geomechanical model indicates that if pore pressures at depth are elevated above the normal hydrostatic gradient, as observed here, the system has the potential to deform by mixed normal and strike-slip failure. Our observations and interpretations suggest that the MH-2 borehole was drilled into oblique normal faults that intersect a buried 300°-trending fault block masked by the basaltic volcanic complex. These data indicate that the transition from the central to western Snake River Plain is characterized by complex structures developed in response to a transitional stress state related to Snake River Plain and western Basin and Range stress regimes. The western Basin and Range stress and tectonic regime may extend from northern Nevada into western Idaho and may enhance the potential for geothermal resources by creating interconnected fracture and fault-related permeability at depth.

A primary focus of geothermal seismic imaging is to map dipping faults and fracture zones that control rock permeability and fluid flow. Vertical seismic profiling (VSP) is therefore a most valuable means to image the immediate surroundings of an existing borehole to guide, for example, the placing of new boreholes to optimize production from known faults and fractures. We simulated 2D and 3D acoustic synthetic seismic data and processed it through to pre-stack depth migration to optimize VSP survey layouts for mapping moderately to steeply dipping fracture zones within possible basement geothermal reservoirs. Our VSP survey optimization procedure for sequentially selecting source locations to define the area where source points are best located for optimal imaging makes use of a cross-correlation statistic, by which a subset of migrated shot gathers is compared with a target or reference image from a comprehensive set of source gathers. In geothermal exploration at established sites, it is reasonable to assume that sufficient a priori information is available to construct such a target image. We generally obtained good results with a relatively small number of optimally chosen source positions distributed over an ideal source location area for different fracture zone scenarios (different dips, azimuths, and distances from the surveying borehole). Adding further sources outside the optimal source area did not necessarily improve the results, but rather resulted in image distortions. It was found that fracture zones located at borehole-receiver depths and laterally offset from the borehole by 300 m can be imaged reliably for a range of the different dips, but more source positions and large offsets between sources and the borehole are required for imaging steeply dipping interfaces. When such features cross-cut the borehole, they are particularly difficult to image. For fracture zones with different azimuths, 3D effects are observed. Far offset source positions contribute less to the image quality as fracture zone azimuth increases. Our optimization methodology is best suited for designing future field surveys with a favorable benefit-cost ratio in areas with significant a priori knowledge. Moreover, our optimization workflow is valuable for selecting useful subsets of acquired data for optimum target-oriented processing.

Understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids. However, in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface. This study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir. The neural network clustering technique called “self-organizing maps” (SOMs) successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source, evolution and flow pathways of geothermal fluids. Scatter plots, as shown in this study, are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth. One geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of HCO3, Ca and Sr. The second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high SO4 and Si concentrations. Former studies, i.e., Giggenbach (1988), suggested Cl, HCO3 and SO4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs. Their relation has been widely used to classify different water types in geothermal fields. However, this study showed that non-standard elements are at least of same importance to reveal different fluid types in geothermal systems. Therefore, this study is an extended water classification approach using SOM for element correlations. SOM have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications.

Has conducted research using remote sensing methods being located in the mountain complex Ijen, Bondowoso - Banyuwangi, East Java as preliminary data to assist in the design of geothermal exploration survey. Remote sensing data used are images from Landsat 8. Landsat 8 infrared thermal image is processed as land surface temperature data. Processing land surface temperature using a single band. Methods in this study begins with finding NDVI (Normal Differential Vegetation Index), which is the value used to state how dense vegetation in an area. After it obtained the value of the fraction of vegetation and emissivity of land used for the determination of the distribution of land surface temperatures. The surface temperature of this land will be used as a guide in making the design of a geophysical survey in geothermal exploration further. Because geothermal areas associated with land surface temperatures were relatively high. Based on the results of data processing of remote sensing, land surface temperatures were relatively high in the area around the Kawah Wurung and Girimulyo that has a land surface temperature ranges between 3060oC.

We present a value of information (VOI) analysis for magnetotelluric (MT) data for locating high steam flow regions of a geothermal resource. The high electrical conductivity feature in volcanic geothermal settings, known as the clay cap, can be indicative of geothermal alteration occurring just above the resource. We demonstrate how several alternative interpretations of the clay cap from one 3D electrical conductivity model can be used to estimate the value of geophysical information. Our results indicate that the final VOI estimate was not strongly dependent on the different interpretations of the clay cap. Additionally, we demonstrate how these VOI evaluations can be used to guide future drilling locations.

With high temperatures, high transmissivities, and low salinities the Malm aquifer in the Bavarian Molasse Basin, Germany, offers ideal conditions for the exploration of geothermal energy in Germany. In 2011, the Pullach geothermal doublet system was extended with a third geothermal well (Th3) to account for increasing heat demand. The third well was then used as injection well and the former injection well (Th2) was converted to a production well. Hence, for the first time in the history of geothermal exploration of the Malm aquifer, data became accessible from the formation surrounding an injection well which had been in operation for more than 5 years. This data provides access to the processes at the injection well and sets the baseline for an assessment of the long term behaviour of geothermal heat and power plants in the Molasse Basin. The increase of the production temperatures at the former injection well after conversion from injection to production went faster than expected; after 3 years of production the initial temperatures have almost been reached. This can be explained with a vertically heterogeneous distribution of the aquifer transmissivity with one thin, highly permeable layer. In this setting, the cold water forms a thin disc which extends much further from the injection well compared to a vertically homogeneous setting, with a cylindrical propagation of the injected water. Hence, in a heterogeneous setting the effective interface for conductive heat exchange between injected cool water and hot aquifer matrix with low permeability is larger. The hydrochemical data of the water from the former injection well showed a significant increase of the concentrations of calcium, magnesium, and bicarbonate, indicating dissolution of dolomite with about 0.6 mmol/L of produced water. Together with thermoelastic effects and hydrostatic stress, the dissolution significantly contributes to an increasing injectivity. The effects are overcompensating the effects of the increased viscosity of the injected cold water. Results from the hydrogeochemical model show that lower temperatures and different lithostratigraphic origin of the injected water are responsible for the dissolution. The kinetic model suggests that the dissolution takes place close to the bore hole. The data collected from the Pullach site provides experimental proof for the processes in the surrounding of injection wells, i.e., the assumed aquifer heterogeneity, the connection to overlying strata, and for the hydrogeochemical model of the Malm aquifer. The data serves as a benchmark and reference for future exploration.

Prior investigations concur that the granite plutons in Scotland which are most likely to prove favourable for geothermal exploration are the Ballater, Bennachie, Cairngorm and Mount Battock plutons, all of which have heat production values greater than 5 μW m −3 . This heat production arises from the significant concentrations of potassium, uranium and thorium in some granite plutons. A new field-based gamma-ray spectrometric survey targeted plutons that were poorly surveyed in the past or near areas of high heat demand. This survey identifies several other plutons (Ben Rhinnes, Cheviot, Hill of Fare, Lochnagar and Monadhliath) with heat production rates between 3 and 5 μW m −3 that could well have geothermal gradients sufficient for direct heat use rather than higher temperatures required for electricity generation. The Criffel and Cheviot plutons are examples of Scottish granites that have concentric compositional zonation and some zones have significantly higher (up to 20%) heat production rates than others in the same plutons. However, the relatively small surface areas of individual high heat-production zones mean that it is unlikely to be worthwhile specifically targeting them. Supplementary material: The full set of heat production data is available at https://doi.org/10.5525/gla.researchdata.302

Geothermal exploration is a complex process that spans a number of disciplines. Before a decision is made to drill a geothermal well, there is need for an extensive exploration process to determine the most suitable location. The process of evaluating and analyzing data from individual scientific disciplines can be complex and tedious. Attempts have been made at solving this problem using GIS-based tools but the uptake of these tools is often hindered by the limited knowledge of GIS by decision makers. This paper presents an approach for solving the geothermal exploration question through a web-based spatial decision support system (SDSS) that incorporates the various geosciences through a multi-criteria spatial decision analysis model. The results reveal a decision-making gap that is to be filled using a novel, automated exploration SDSS. This approach hypothesizes an easier and faster decision-making process. The research focuses on Olkaria, an active geothermal area in Kenya, East Africa and hi...

Abundant geothermal springs occur along the Moxi fault located in western Sichuan Province (the eastern edge of the Qinghai-Tibet plateau), highlighted by geothermal water outflow with an unusually high temperature of 218 °C at 21.5 MPa from a 2010-m borehole in Laoyulin, Kangding. Earthquake activity occurs relatively more frequently in the region and is considered to be related to the strong hydrothermal activity. Geothermal waters hosted by a deep fault may provide evidence regarding the deep underground; their aqueous chemistry and isotopic information can indicate the mechanism of thermal springs. Cyclical variations of geothermal water outflows are thought to work under the effect of solid earth tides and can contribute to understanding conditions and processes in underground geo-environments. This paper studies the origin and variations of the geothermal spring group controlled by the Moxi fault and discusses conditions in the deep ground. Flow variation monitoring of a series of parameters was performed to study the geothermal responses to solid tides. Geothermal reservoir temperatures are evaluated with Na-K-Mg data. The abundant sulfite content, dissolved oxygen (DO) and oxidation-reduction potential (ORP) data are discussed to study the oxidation-reduction states. Strontium isotopes are used to trace the water source. The results demonstrate that geothermal water could flow quickly through the Moxi fault the depth of the geothermal reservoir influences the thermal reservoir temperature, where supercritical hot water is mixed with circulating groundwater and can reach 380 °C. To the southward along the fault, the circulation of geothermal waters becomes shallower, and the waters may have reacted with metamorphic rock to some extent. Our results provide a conceptual deep heat source model for geothermal flow and the reservoir characteristics of the Moxi fault and indicate that the faulting may well connect the deep heat source to shallower depths. The approach of hot spring variation research also has potential benefits for earthquake monitoring and prediction.

Geological and geophysical characteristics of supercritical geothermal reservoirs in the Tohoku District, NE Japan were investigated in order to evaluate potential of future geothermal energy. Geological information in the Tohoku District (caldera, hot spring hydrothermal alteration, mine, and granitoid) and geophysical data (gravity, MT and seismicity) were accumulated into GIS database. We can evaluate present volcanism and related events, geothermal structure, depth of heat source, fracture distribution, and existence of fluid by using the GIS database. We identify the following geological features in terms of geothermal resources: “Deep fluid input”, “Magma input”, “Geothermal gradient”, and “High temperature hot spring”, and we can classify the geothermal energy and potentials as follows: “Promising”, “Probable”, “Possible”, and “Potential”.

Gaseous components are very effective indicators of deep processes in high-temperature geothermal systems. We have chosen the Kangding, Rehai, Tatun, and Yangbajing geothermal systems, from the Chinese segments of the Mediterranean-Himalayas and Circum-Pacific global geothermal belts, to analyze and compare the geochemical characteristics of gases. Results confirm that the two geothermal belts are very different as regards deep processes. Gases of the Tatun are mantle derived, which is in agreement with its island-arc tectonic setting, while the others are located in the continental collision boundary exhibiting crustal and mantle origins to a varying extent. The geothermal gases from Yangbajing show an apparently crustal origin. The isotopic composition of CO2 and He in the Tengchong geothermal region helped to identify their mantle origins. The CO2 of the Kangding geothermal system is largely derived from limestone metamorphism with only a small fraction of He coming from deep sources, likely due to active faulting in the area.

Prospecting the geothermal resources in northwest of Iran, conducted in 1975, revealed several promising areas and introduced the Sabalan geothermal field as a priority for further studies. The Sabalan Mt., representing the Sabalan geothermal field, is a large stratovolcano which consists of an extensive central edifice built on a probable tectonic horst of underlying intrusive and effusive volcanic rocks. In this study, Curie point depth (CPD), geothermal gradient and heat-flow map were constituted from spectral analysis of the aeromagnetic data for the NW of Iran. The top of the geothermal resource (i.e., the thickness of the overburden) was evaluated by applying the Euler deconvolution method on the residual gravity data. The thickness of the geothermal resource was calculated by subtracting the Euler depths obtained from the CPDs in the geothermal anomalous region. The geothermal anomalous region was defined by the heat-flow value greater than 150 mW/m2. CPDs in the investigated area are found between 8.8 km in the Sabalan geothermal field and 14.1 in the northeast. The results showed that the geothermal gradient is higher than 62 °C/km and the heat-flow is higher than 152 mW/m2 for the geothermal manifestation region; the thickness of the geothermal resource was also estimated to vary between 5.4 and 9.1 km. These results are consistent with the drilling and other geological information. Findings indicate that the CDPs agree with earthquake distribution and the type of thermal spring is related to the depth of the top of the geothermal resource.

The Thermal structure of continental crust is a critical factor for geothermal exploration, hydrocarbon maturation and crustal strength, and yet our understanding of it is limited by our incomplete knowledge of its geological structure and thermal properties. One of the most critical parameters in modelling upper crustal temperature is thermal conductivity, which itself exhibits strong temperature dependence. In this study, finite-element geothermal models of the Sydney Basin are generated through the use of deal.II finite element libraries. Basin geometry and structure is adapted from Danis, et al. (2011), which quantified the extent of Triassic sediment, Permian coal measure, Carboniferous volcanics and Basement thickness. We find that temperature-dependent thermal conductivity result in lower lateral variation in temperature compared to constant thermal conductivity models. However, the average temperatures at depth are significantly higher when temperature-dependent thermal conductivity effects are included. A number of regions within the Sydney Basin demonstrate temperature above 150C at depths of less than 2000m in these models, for instance NW of Singleton exhibits a strong thermal anomaly, demonstrating the potential for geothermal prospectivity of the region from experimentally-constrained thermal parameters. Future work will address the repeatability and application of this type of thermal model in areas of varying geology and stratigraphy, as well as refining the model by adding new variables, such as pressure or fine tuning existing variables.

Geophysical joint inversions seek to exploit the statistical fact that a model that simultaneously satisfies two or more independent data sets is more likely to represent geological ‘reality’ than a model that only satisfies a single data set. Interpreting geophysical data directly rapidly exceeds the capacity of a human as more data are added, so some form of machine assistance is usually required. Conventional inversion techniques can produce a ‘best fit’ model but this might only be one of a large range of possible models that fit the data. Bayesian inference provides a tool to evaluate the relative probability of all possible geological models in a given set, thereby quantifying the amount of information the data is actually providing. Over 2012–2014, National ICT Australia (NICTA; now Data 61) worked with a number of university, government and industry partners, with support from the Australian Renewable Energy Agency, to build a Bayesian inference software tool for geophysical joint inversions. The tool was initially directed at geothermal energy exploration but is equally applicable to investigating other geological problems. For one geothermal exploration problem, Bayesian inference allowed us to jointly invert gravity, magnetics, magnetotelluric soundings and borehole temperature records to map in three dimensions the probability of encountering granite >270°C beneath the Moomba region of South Australia. The results correlated well with an independent deterministic inversion carried out by Geoscience Australia, but provided a much richer interpretation in probability space. NICTA released the software tools as open source code on the GitHub platform.

Geothermal resources have the potential to fulfill a significant portion of the low-temperature (30–100 °C) thermal energy demand in the United States. Investment risk at the exploration stage is a primary factor limiting the development of geothermal energy projects, due to the high cost of drilling and limited reservoir data. An approach to reduce this risk is to target proven, well-characterized conventional oil and gas reservoirs. We examined the suitability of the Trenton–Black River gas fields of southern New York as geothermal reservoirs. These highly productive hydrothermal dolomite fields occur within long, narrow normal-fault–bounded, en echelon grabens that are scattered with saddle dolomite-lined vugs, fractures, and breccia. The Quackenbush Hill field was analyzed using existing data sets with geothermal purposes in mind. Key geothermal reservoir characteristics examined here include rock temperature, porosity and permeability, stimulation potential, and the risk of inducing seismicity. Results indicate that the Quackenbush Hill field would produce temperatures of ∼91 °C from a dolomite reservoir with sufficient average horizontal permeability, low vertical permeability, and significant vertical and horizontal anisotropy. In the case that adequate flow rates cannot be achieved in practice, stimulation is a feasible option from the perspective of well-field design for optimal heat sweep; however, higher-resolution data are necessary to constrain the risk of inducing seismicity. We demonstrate the technical feasibility of transitioning conventional gas fields into geothermal heat-producing reservoirs, setting the stage for future consideration of the economics of a petroleum-to-geothermal transition.

WOS: 000406808700003, The geological characteristics of a Kavaklidere geothermal field is of particular importance during the evaluation of a geothermal prospect. The field covers a 126 km(2) area between Alasehir and Salihli districts in Manisa province, Turkey. The field was mapped geologically at the scale of 1/25.000 in order to determine heat source(s) and various characteristics of rock sequences, such as their lithofacies, thickness, contact relationships, stratigraphy, and whether there are cap and/or reservoir rocks exposed in and adjacent to the field. In the Kavaklidere geothermal field, 38 fault planes in total were measured, including 7 detachment faults, 15 high-angle normal faults, 2 low-angle normal faults and 13 shear fractures/strike-slip faults (scissor faults). Temperatures in the Kavaklidere geothermal field range from 188 to 287 degrees C. Permeability in the reservoir consists of a network of fractures in hard metamorphic rocks a short distance above a granitic intrusion. In this study, in the Kavaklidere geothermal field about the formation of geothermal model, the evaluations are made about the reservoirs, cap rock, recharge, heat source and prepared geothermal model.

After early exploration during the 1980s and 1990s, the 0.3 MW Fang geothermal power plant was built as a demonstration to supply electricity to the local community. The shallow well (100 m) drilling program produced about 22 l/s of 125 °C water, and two wells to 500 m produced about 10 l/s. Due to the lack of detailed information on the geothermal system, the plan to expand to a larger power plant was halted to avoid the drilling missing the hot fluid. The plan was resumed in the last ten years starting with the magnetotelluric (MT) survey. Thirty three MT sites were deployed on the southern part of the Fang geothermal area. A remote site was installed about 600 km south of the study area for better data quality. After data processing, the data was inverted with WSINV3DMT to produce the 3-D resistivity model which clearly matches the near-surface geology and is also in agreement with the conceptual geology of the Fang geothermal system. The high resistivity zone is interpreted as the crystalline granitic rock, while the intermediate resistivity zone is associated with the Fang sedimentary basin. The resistivity contrast between the higher and lower resistivities helps reveal the orientations of the major Mae Chan Fault (MCF) and the two local faults of the area. The two main conductors of interests, C1 and C2, are directly linked to the hot fluid found at the surface. C1 is shallow (

Based on the latest compiled 1/100 million aeromagnetic map data, the Curie point depth was estimated by power spectrum method. The calculation obtained 8004 Curie point depth values in Chinese continent. Eventually, we completely compiled the Chinese continental Curie point isotherm map. This map first fully shows the characteristics of Chinese continental Curie point depth. The study shows that Curie point isotherm is characterized by depression inside the stable blocks with the depth of 28~45 km, such as the Tarim Basin, Junggar Basin, Qaidam Basin, Hoh Xil-Bayan Har Depression area, the Yangtze Basin area, North China basin area, Songliao Basin, Erlian Basin, Bayan-Wuwei-Chaoshui basin, Pearl River Estuary-southeast Hainan basin. The Curie depth of North China basin area is shallower than Tarim continent block and Yangtze continent block, which may be related to the fact that North China block suffered a complex post-transformation which resulted in the asthenosphere upwelling and lithospheric thinning. Hoh Xil-Bayan Har block is a NWW trending Curie point isotherm depression area in northern Tibetan Plateau, where developed a large area of Triassic sedimentary strata and experienced less magmatism. The stable blocks all have uplifted Moho and depressed Curie point isotherm. Conversely, the Curie point isotherm of active orogenic belt is characterized by uplift at the depth of 18~26 km, such as the Mountain (Mtn.) area of northeast and northwest China, Qinling-Dabie area, West Kunlun-Tibet-Sanjiang-Kangdian area, the southeast coastal areas and so on. The uplift reflects the geothermal gradient difference caused by tectonic and magmatic activities. A collection of 816 heat flow data from published literatures are used to study the relationship between Curie point isotherm and heat flow. The results show that there is not a simply linear relationship between the depth and heat flow. When the depth is greater than 30 km, the heat flow values are less than 100 mW·m-2. While the Curie point depth is less than 30 km, the heat flow values vary in a wide range. The high heat flow values are mostly found in the east coast of China, southern Tibet-Sanjiang area, Qinling-Dabie area, and the east of Liaoning province, which are all characterized by uplift of Curie point isotherm. These areas are important for future geothermal exploration.

Portable x-ray fluorescence (pXRF) analyzers are widely used in the environmental and mineral exploration fields. pXRF analyzers can rapidly and inexpensively provide chemical concentrations on a variety of elements, often with detection limits of ∼1–5 ppm. We compared portable XRF results from untreated geothermal drill cuttings with laboratory XRF results from pressed pellet and lithium borate fused beads prepared from powders crushed from the same samples. It is demonstrated that the portable XRF results are accurate for many elements, particularly for those with atomic numbers greater than 17. 304 cutting samples from three drillholes in the Tauhara geothermal field were subsequently analyzed by pXRF. Downhole elemental concentrations plotted against lithological units defined on geological well logs indicate that significant variations in elemental concentrations occur, some of which correlate with logged lithology boundaries. Other chemical variations appear to define previously unrecognized subunits, as well as areas of hydrothermal alteration. We suggest that pXRF should become a routine part of the characterization of geothermal cuttings during geothermal exploration and well drilling, as the chemical results are accurate, rapid and inexpensive, and the results can be used to define lithological boundaries and potentially correlate between drillholes, therefore improving geologic, stratigraphic and hydrothermal alteration models of the geothermal field.

International audience; (U‐Th)/He ages on apatite obtained in the vicinity of the Têt fault hydrothermal system show a large variability. In the inner damage zone adjacent to the fault core, where fluid flows are concentrated, AHe ages display a large scatter (3–41 Ma) and apatite ageing. Samples from the outer damage zone show young ages with less dispersion (0.9–21.1 Ma) and apatite rejuvenation. Outside the damage zone, ages are consistent with the regional exhumation history between 20 and 12 Ma. The important age dispersion found in the damage zone is interpreted as the result of 4He mobility during fluid infiltration. Our results show that thermochronological data close to a fault should be interpreted with caution, but may offer a new tool for geothermal exploration.

This paper provides the first wide-area Interferometric Synthetic Aperture Radar (InSAR) survey of the whole eastern Trans-Mexican Volcanic Belt (42,200 km2). The aims are to identify ground deformation hotspots within major urbanized areas and rural valleys, establish baselines in geothermal exploration sites, and analyze deformation at geothermal exploitation sites and its relationship with energy production. The whole 2003−2010 ENVISAT C-band SAR archive available over the region was processed with the Small BAseline Subset (SBAS) InSAR method to retrieve over 840,000 coherent targets and estimate their ground displacement rates and time series. Land subsidence hotspots due to aquifer drawdown are found within the city of Puebla (up to −53 mm/year vertical rates, groundwater pumping for industrial use), Tlaxcala and Apizaco (−17 mm/year, industrial and public), the valley of Tecamachalco (−22 mm/year, agricultural), Tulancingo (−55 mm/year, public, industrial and agricultural), and in the eastern Mexico City metropolitan area (−44 mm/year, agricultural). The baseline for the Acoculco caldera complex shows widespread ground stability. Conversely, localized subsidence patterns of −5 to −10 mm/year exist around Las Derrumbadas and Cerro Pinto in the Serdán-Oriental basin, due to intense groundwater pumping for agriculture. A well-defined land subsidence area with −11 mm/year maximum rates is found at Los Humeros volcanic complex within Los Potreros collapse, correlating well with energy production infrastructure location and historical steam production rates. Field surveys carried out in Acoculco and Los Humeros in 2018 provide supporting evidence for the identification of hydrothermal manifestations, and understanding of the landscape and surface deformation patterns within the geothermal fields.

This study investigates the thermo-hydraulic implications of three geologic scenarios for characterizing the geothermal hydrology of Basse-Terre Island, Guadeloupe. Despite newly acquired magnetotelluric, petrophysical, and geologic data, flow patterns and heat sources have remained elusive. Our simulations were performed in 2D, on a cross section going from La Soufrière volcano in the south to the operating Bouillante geothermal field near the west coast. Simulation results are compared to geologic constraints such as the temperature profile measured at Bouillante and the timing of volcanic activity in the area, which may be indicative of new heat sources at depth. The simulations indicate that during lateral flow from La Soufrière, geothermal fluids would cool too much to explain the temperature at Bouillante. Two other scenarios were found to explain the current thermal structure of the Bouillante geothermal system: a young (ca. 5000 years) and more local magmatic intrusion at depth, or vertical corridors of enhanced permeability that tap hot and porous formations at a few km depth. Without further geologic evidence, neither of these two scenarios can be preferred. The second magma chamber scenario would indicate a more complex magmatic history of the island than previously established. The study shows that geologically constrained scenarios of regional geothermal hydrology can be meaningfully tested with current numerical simulation techniques, providing further insights for geothermal exploration.

A geothermal exploration corehole was drilled to a total depth of 1821.5 m on the Mountain Home Air Force Base near Mountain Home, Idaho. The corehole was used to collect an unusually large amount of data, including uniaxial compressive stress (UCS) experiments on core samples, to evaluate the geothermal potential of the western Snake River Plain. In addition, unlike many exploration holes in this region, a fluid entry was encountered at 1745.3 m and flowed artesian to the surface. A maximum temperature of 149.4 °C was calculated for the entry. A temperature log run on the corehole from 3 to 1675 m is nearly linear with little variation. The average geothermal gradient is 73 °C/km, and the average heat flow between 200 and 1500 m is 102 ± 15 mW/m2. Chemical analyses of a sample from the fluid entry suggest that a significant proportion of the water is not meteoric. Five geothermometers show equilibrium temperature in the range of 133–157 °C. Furthermore, based on the unconfined UCS experiments on basalt core samples, a brittle unit was found to comprise the fractured reservoir that the geothermal water flows from, while an overlying ductile unit acts as a hydrothermal caprock. This implies that the reservoir/caprock pair may be a target for future exploration wells drilled to delineate the extent of the potential resource and the boundaries of the connected fracture network.

Heat distribution estimates at the surface and shallow depths (20 cm, 100 cm, and 150cm) obtained through surface temperature surveys (STSs) in the geothermal area of the Azufral volcano found anomalies ranging between 6 °C and 20 °C. Additionally, temperature models developedthrough Landsat 8 images from the thermal infrared sensor (TIRS) reached an approximation ofthe surface heat distribution based on three images captured around the dates on which the STSswere conducted. Aggregating the normalized difference vegetation index (NDVI) (between 0.93 and-0.563) and the topography (elevations between 2800 and 3800 m above sea level) in cross-sections using spatial analysis techniques, this study assessed the positive and negative anomaliesexhibited by these three variables within the geothermal area. Further, using Pearson coefcientestimates as a quantitative method for analyzing the correlations between the different models generated, a strong positive correlation (between 0.19 and 0.46) is denoted between deeptemperatures against the different surface temperatures calculated for each day using Landsat8 TIRS. La estimación de la distribución de calor en superfcie y a profundidades someras (20 cm,100 cm y 150 cm) por medio de los sondeos superfciales de temperatura (SST) para el área geotérmica del volcán Azufral encontró anomalías entre los 6ºC y los 20ºC. A su vez, se realizaron modelosde temperatura mediante imágenes Landsat 8 del sensor TIRS (por sus siglas en inglés), que permitieron alcanzar una aproximación de la distribución de calor en superfcie con tres imágenes confecha de toma cercanas a las fechas de levantamiento de los SST. Integrando el índice de vegetaciónde diferencia normalizada (NDVI, por sus siglas en inglés) (entre 0,93 y -0,563) y la topografía (alturasentre 2800 msnm y 3800 msnm) en secciones cruzadas mediante técnicas de análisis espacial, seanalizaron las anomalías positivas y negativas de estas tres variables en el área geotérmica. Con laestimación del coefciente de Pearson como método cuantitativo para el análisis de las correlacionesentre los diferentes modelos generados, se denota que existe una fuerte correlación positiva (entre0,19 y 0,46) entre las temperaturas en profundidad contra las temperaturas para cada uno de los díascalculados con Landsat 8 TIRS.

The European-Mexican geothermal GEMex project aims at developing geothermal energy in the easternmost region of the Trans-Mexican Volcanic Belt. Two sites under development by the Comisión Federal de Electricidad (Mexican National Power Company) are investigated to assess possible superhot resources and to develop an Enhanced Geothermal System, respectively in Los Humeros and Acoculco. European and Mexican partners constructed preliminary 3D geological models in a collaborative way. They were based on data available at the beginning of the project, including geological maps, cross-sections and well logs. To complement the existing knowledge, geological and geochemical field campaigns were conducted. Data from these surveys have been used to update the preliminary models of both sites. Geophysical surveys are ongoing. The results of this update were dedicated to improve the overall interpretation of the geothermal system in Los Humeros and Acoculco. They were also used as input for further simulations based on the geometry of the updated geomodels. The update presented in this paper is an intermediate step previous than further integration. The last phase of the geomodelling process will consist in integrating geophysical information to strengthen the geothermal interpretation of both sites.

Geophysical exploration in unconventional geothermal reservoir is challenging because of the lack of structures with specific geophysical signature such as a clay cap above volcanic geothermal reservoirs. The combination of several geophysical methods such as magnetotelluric (MT), gravity and seismic methods provides complementary insight into the geothermal reservoir. We present a joint inversion approach of ambient noise surface wave and gravity constrained by the 3D distribution of electrical resistivity. The method is applied to analyze the potential of unconventional deep geothermal resources in the French Massif Central (FMC). We coupled the resistivity, density and shear wave velocity with a linear correlation. We characterized the common properties in relation to the geological domains down to about 10–15 km. We validated the proposed approach on a synthetic model derived from models obtained from each independent geophysical method. The joint inversion limited the non-uniqueness of the gravity and the ambient noise tomography inversion and allow to recover the features of the synthetic models. We applied the method to real field data acquired in the Sioule Valley, Massif Central, France. The joint features observed in the geophysical models suggest a deep heat source associated with a possible shallow (∼6–8 km) brittle–ductile transition. A large fault zone, the Pongibaud Fault zone, seems to become listric and connect the surface to this transition zone to possibly constitute a permeable path for water circulation.

A coupled study on deep cores from the Paris basin brings new insights for the geothermal potential of the area on both sedimentary and basement geological units. Petrophysical and petrographic results of continental successions from Upper Triassic formations show that the western edge of the Paris basin can deliver fairly good reservoir properties (5-23% porosity and 5-800 mD permeability) with a the best quality index found in fluvial facies types along the continental deposition profile. The burial of the sedimentary sequence affects the reservoir quality with appearance of several diagenetic phases (dolomite and calcite cements) and feldspar dissolution to a lesser degree. In parallel, an analytical work is conducted on basement rocks from deep cores and combines petrography and petrophysics for identifying potential structures for hot water circulation in the Variscan basement, displaying mineralogical testimonies of paleofluids. These targets in the Paris basin are part of a broad scale European project called MEET, for Multidisciplinary and multi-context demonstration of EGS exploration and Exploitation Techniques and potentials. This project aims to increase the geothermal market at European scale by means of original exploitation techniques and the identification of untapped geothermal resources of various geological contexts of Europe.

The belief that resource abundance equates to energy security is roundly debunked in Indonesian geothermal. Indonesia’s copious geothermal reserves remain untapped. Experts cite the usual culprits: unreliable long-term contracts, ambivalent government support, and lukewarm investors investment appetite. In this paper, we argue that the real constraints lie in investors’ unresolved contradictions: Quick to complain about government’s unreliable and shifting stance, investors look to the same counter-party to guarantee their “iron-clad power purchase agreements (PPAs)” to secure their returns. To unleash Indonesia’s geothermal potential, we propose adopting slim-hole drilling technologies to reduce costs, while facilitating sequential commitments. This could enhance strategic flexibility that lowers the costs of good failures while facilitating the adoption of resource insurance to de-risk geothermal exploration and drilling. To sustain these benefits, “cheap” energy policy needs to be phased out to allow a restructured PT Perusahaan Listrik Negara’s (PLN) to flourish by embracing commercially viable strategic approaches.

In March 2016, arguably the most ambitious 4D (3D space + over time) active-source seismic survey for geothermal exploration in the U.S. was acquired at Brady Natural Laboratory, outside Fernley, Nevada. The four-week experiment included 191 vibroseis source locations, and approximately 130 m of distributed acoustic sensing (DAS) in a vertical well, located at the southern end of the survey area. The imaging of the geothermal faults is done with reverse time migration of the DAS data for both P-P and P-S events in order to generate 3D models of reflectivity, which can identify subsurface fault locations. Three scenarios of receiver data are explored to investigate the reliability of the reflectivity models obtained: (1) Migration of synthetic P-P and P-S DAS data, (2) migration of the observed field DAS data and (3) migration of pure random noise to better assess the validity of our results. The comparisons of the 3D reflectivity models from these three scenarios confirm that sections of three known faults at Brady produce reflected energy observed by the DAS. Two faults that are imaged are ~1 km away from the DAS well; one of these faults (middle west-dipping) is well-constructed for over 400 m along the fault’s strike, and 300 m in depth. These results confirm that the DAS data, together with an imaging engine such as reverse time migration, can be used to position important geothermal features such as faults.

The assessment of geothermal potentials over part of the upper Benue trough corresponding to Kaltungo, Guyok, Lau and Dong areas, North Eastern Nigeria using spectral depth analysis of aeromagnetic data has been carried out. The study area is bounded by latitudes 9o00’N and 10o00’N and longitudes 11o00’E and 12o00’E. This research work is necessitated by the need for renewable and alternative sources of energy for use in Nigeria. Regional/residual separation was carried out on the total magnetic field using polynomial fitting method of order one. The residual map was divided into nine overlapping blocks for the spectral analysis. The centroid depths and depth to top of basement were obtained from the plot of log of power spectrum against wavenumber. These two parameters were used to estimate the Curie point depth using , where and are Curie depth, centroid depth and depth to top of basement respectively. The results from the spectral analysis suggested that in the parts of the Upper Benue trough, the basement is deepest at the south western portion towards the Lau area and varies between 0.55 and 3.8 km, while the centroid depth varies from 7.26 to 18.00 km. From the same portion of the trough, the Curie-point depths vary between 12.43 and 33.91 km and the corresponding geothermal gradient and heat flow values varying from 17.10 to 46.66 0C/km with an average of 30.75 0C/km and 42.75 to 116.65 mW/m2 with an average of 75.91 mW/m2 respectively. The maximum heat flow is found around the south western portion of the study area (Lau). The entire study area with high heat flow values might probably be good sources for geothermal and thereby recommended for both geothermal exploration and exploitation.

Exploration of the geothermal resources in the Beijing–Tianjin–Hebei region has been kept for tens of years, and the recent success of geothermal exploration in the Xiongxian County provides a new model for the utilization of geothermal resources in this area. This research integrates the formation of temperature obtained from hydrocarbon drilling, experiments of reservoirs’ micro-characteristics and physical property, and employs the previous works on the regional geological settings to investigate the geothermal reservoirs and geothermal status. The microphotography indicates that the reservoir space is dominated by supergene karst in the Wumishan Formation which is mainly controlled by the topography when the interval emerged. The groundwater in the Pre-Paleogene has the similar composition of the hydrogen and oxygen isotope with the atmospheric precipitation, and the salinity of the groundwater has an increasing trend from the Taihang Mountain and the Yanshan Mountain to the depocenters, which indicates the groundwater originates from the atmospheric precipitation of the Taihang Mountain and the Yanshan Mountain and transports to the depocenters. The thermal conductivity of the lower carbonate rocks is much higher than the upper clastic intervals. This difference makes the upper clastic intervals of the Paleogene and the Neogene good seals for geothermal reservoirs and leads to the regional anomaly of the terrestrial heat flow: the intrabasin highs have a thicker thickness of the Pre-Paleogene carbonate deposition with high thermal conductivity, which results in high efficient thermal transmission and high terrestrial heat flow. Consequently, this research suggests that the intrabasin highs and slopes are the favourable areas for geothermal exploration with reservoirs of good quality, high terrestrial heat flow and efficient groundwater supply, and several areas were selected to be the potential targets for the Wumishan Formation and the Pre-Paleogene.

Geologic structure plays an important role in controlling fluid flow in geothermal systems. In particular, very complex structural settings, consisting of many closely spaced and intersecting faults, host many geothermal systems. To elucidate the key geologic factors that affect fault-controlled geothermal circulation, it is critical to precisely characterize the structural and stratigraphic geometries in these complex settings. Here, we present a methodology and the results of 3D geologic analyses of two geothermal systems in the Basin and Range, USA. This methodology is a quantitative and geologically focused technique that can be used to precisely characterize geothermal areas, in a time when future geothermal growth demands increased exploration precision and efficiency. Surficial and subsurface geologic and geophysical data are synthesized in the construction of detailed 3D geologic maps of geothermal areas. Based on these 3D geologic maps, we examine several geologic attributes that control permeability development and geothermal fluid flow along faults. We use the stress state of faults and the distribution of structural discontinuities (i.e., fault intersections and fault terminations) to identify locations of upflow along faults in these geothermal systems. These results and the methodology presented herein are directly applicable to structurally controlled geothermal fields in the Basin and Range and worldwide. As development focus shifts toward blind geothermal resources, integration of precisely characterized subsurface structural information into exploration methods will be increasingly critical to continued growth in geothermal exploration and development.

It is important for geothermal exploration to know regional subsurface structures. The gravity survey is often used to narrow down the promising area at the early stage of geothermal exploration. The gravity survey was carried out to estimate subsurface density structure in the Kinigi geothermal field, Rwanda, in September 2015. In order to interpret the gravity anomaly distribution, 3-D gravity modeling was done by using the new program based on Gauss-Legendre integration using hexahedral elements. As the result, the computed gravity anomalies showed high gravity anomalies in northwest, the northeast, and east-southeast of the studied field and low anomalies in the southwest side of the studied field as Bouguer anomalies. The area was characterized by normal contacts with main boundary trending NW-SE direction. This boundary was estimated as main fault in Kinigi geothermal field, Rwanda. The detected fault could be a better place for installing geothermal wells for future geothermal development in the region.

Summary Deep and tight reservoirs are an important target for both Oil and Gas and Geothermal Industries. Fractures have a key role for producing from such reservoirs and therefore fracture identification is essential.In this talk we analyse the potential correlation between BHI fracture characterization results and elastic properties as output by wave-equation based AVO (WEB-AVO) inversion. WEB-AVO inversion is unique in the sense that it directly inverts for compressibility and shear compliance (inverses of bulk and shear moduli). While those parameters are already successfully used for exploration and production of hydrocarbons as well as for underground storage of CO2, here we will test their usefulness in the context of geothermal exploration.

Summary We present an experience of acoustic FWI on a noisy 2D land dataset to the end of providing a velocity model for direct geological interpretation. We first perform a dedicated processing trying to improve the data quality and we select as the input for the inversion direct, refracted and diving waves. In fact, notwithstanding the processing efforts, reflections are nearly absent. Next, we perform a sequence of FWIs. Since we wish to use the estimated velocity for the interpretation of the area, it is necessary that the estimation is not biased by unverified a-priori geological hypotheses. Therefore, to derive a low-resolution velocity model, we apply two runs of genetic-algorithm FWI (GA-FWI) with different data misfit functions based on envelopes and on waveforms. In fact, GA do not start from a given velocity model, thus risking to bias the final outcome, but from an ensemble of models randomly selected within large search ranges. The GA velocities are then used as starting model for a gradient-based FWI which yields an improved model, appropriate for evaluating different geological hypotheses. In two locations, the check-shot velocities of exploratory wells show a good matching with the 1D velocity profiles extracted from the final model.

The North German Basin is one of the three major type localities in Germany for deep geothermal energy. Here, the pore space is the dominant parameter, in contrast to fractures (Rhine Graben) and karst (Molasse Basin). To further develop the geothermal research platform Groß Schönebeck located in the Northeast German Basin, a subset of the North German Basin, we investigated the geological structure and the existence of possible fault systems in the subsurface. For this purpose, we carried out a high-resolution 3-D reflection seismic survey at the location to overcome methodical restrictions of the few 2-D seismic profiles that cross the area of interest, such as spatial focusing effects and fault imaging. The survey area extends 8 km × 8 km at the surface and focusses down to reservoir depths at 4 km. With four vibrators as source (12–96 Hz sweep, 12 s duration), we used a source line spacing of 700 m and a receiver line spacing of 400 m with both 50 m source and geophone spacing. Data processing encompassed CRS (Common Reflection Surface) stacking, post-stack time migration and depth conversion. We observed a smooth doming of the Zechstein salt from 0.6 to 1 km thickness above the continuous top of the Rotliegend Group at around 4 km depth, and the Mesozoic horizons above appear as mainly continuous reflection surfaces with gentle undulations and occasional normal faulting. We highly resolved the supra-salt sequences in the study area for the first time, which allowed us image an almost complete suite of reflectors mapped in other parts of the Northeast German Basin. However, less resolved, lower frequency images are encountered deeper than ~ 4 km. Two important factors for further field development are that we do not observe an apparent influence of crustal-scale faults, which were expected from former conceptual models for the region, and that at the current status of work, the reservoir does not show a fracture-dominated character.