Geothermal Site Research Articles

Permeability estimating beyond boreholes from electrical conductivity data determined from magnetotelluric sounding: Soultz-sous-Forêts site (France) case study

Permeability of intact and fractured core samples collected in EPS1 borehole at the Soultz-sous-Forêts geothermal site (France) is used for neural network permeability prediction beyond the borehole location using electrical conductivities obtained by 2-D inversion of the magnetotelluric (MT) profile data. The estimates of prediction accuracy as a function of depth indicate that the average relative accuracy of permeability prediction from electromagnetic (EM) data, for example, at double borehole depth ranges from 93% to 97% depending on rock fracturing. Permeability predicting by ANN trained on intact permeability values results in its lower-bound assessment (in contrary to upper-bound values, which could be predicted by ANN trained on “equivalent" permeability values determined using 2-D flow model or depth dependence of fracture apertures. It is shown that the EM forecast of cross-well permeability gives an idea of the overall distribution of this parameter in the section while the comparison of this prediction with the temperature model is fairly conclusive for locating the most promising sites and depths for geothermal exploration. On the other hand, the EM-based permeability prediction could reveal practically impermeable domains in the sedimentary cover and granitic basement where drilling of exploration boreholes is inadvisable. Based on the 2-D MT sounding data, permeability model of the Soultz-sous-Forêts geothermal site is built. The model, in particular, revealed a 500 m thick poorly permeable belt in the sedimentary cover, presumably formed by the precipitation of secondary hydrothermal minerals during cooling. The belt can be considered as a transition zone between conductive (above) and convective (below) heat transfer mechanisms hypothesized earlier based on the analysis of geotherms from different boreholes.

Fractal characteristics of fractures in crystalline basement rocks: Insights from depth-dependent correlation analyses to 5 km depth

The scaling laws describing the spatial arrangement of fractures along six deep boreholes penetrating the crystalline rocks in the Rhine Graben were derived using a correlation analysis. Five of the wells, two to 5 km depth, were located at the Soultz geothermal site and one well to 5 km depth was located at Basel, some 150 km from Soultz. Five datasets were derived from borehole imaging logs, whilst one stemmed from the analysis of 810 m of continuous core at Soultz. The two differed inasmuch as the core dataset included essentially all fractures, whereas the image log dataset had few fractures narrower than 1–3 mm. The results of the analysis for all image datasets showed that the spatial arrangement of fractures followed fractal behavior at all scales from meters to several hundred meters, the largest scale amenable to assessment, and that the fractal dimensions were confined to the narrow range 0.85–0.9. However, the core dataset showed significant deviation from fractal behavior, the best-fit fractal dimension of 0.8 being somewhat lower than values obtained from imaging logs in neighboring wells. Eliminating fractures with apertures less than 1 mm from the core dataset to improve comparability led to even lower fractal dimension estimates, indicating the discrepancy was not due to imaging log resolution. Analysis of successive depth sections of the core log suggested the discrepancy was due to the presence of a localized zone between 1750 and 2070 m where the fractal organization is disturbed or takes a lower dimension than elsewhere. Aside from this zone, no systematic variation of fractal dimension with depth was observed in any dataset, implying that a single exponent together with intensity adequately describes the arrangement of fractures along the entire length of the boreholes. The results are relevant to the parameterization of DFN models of deep rock masses. • The fracture population derived from image logs followed fractal statistic with very similiar fractal dimensions. • The core-derived fracture dataset showed significant deviation from fractal behavior. • No systematic variations of fractal dimension with depth were observed in any of the datasets.

3D deep geoelectrical exploration in the Larderello geothermal sites (Italy)

The paper describes a new experimental deep electrical resistivity acquisition (down to 1600 m) for exploring deep and shallow geothermal systems. The test site is located in the Larderello geothermal area, the oldest geothermal field in the world under exploitation for power production. In this area, many data have been acquired in the frame of previous exploration projects but nowadays several critical issues are still matter of debate: permeability distribution, depth and volume of the magmatic heat source, supercritical fluid condition at depth, and the occurrence of low resistivity anomalies in a dry-steam crystalline and carbonate reservoir. In order to develop new methods for contributing to the hydrothermal reservoir issues, an experimental high resolution 3D Surface-Hole Deep Electrical Resistivity Tomography (SH-DERT) was designed and the Venelle2 well in the Larderello geothermal site, hosted in the crystalline units, was used for the experiment. The design of the in-hole experiment and the results of the deep geoelectrical survey are hereby presented. SH-DERT was properly designed to face extreme conditions at depth characterizing the geothermal well. It provided a 3D resistivity distribution. Transmitting and receiving electrodes were distributed on a large surface (6 km2) and in the Venelle2 well (down to 1600 m). The in-hole electrical cable was equipped to be able to operate in very high temperature conditions. The experiment represents a challenge and an opportunity for the applied geophysics in geothermal areas, where a lowest resistivity is highlighted in a zone above the reservoir and the resistivity of the reservoir is higher. Moreover, the relationship between temperature, clay alteration and resistivity can define a challenger to enable better prediction of reservoir temperature distribution from resistivity measurements. It is a potential improvement of the reservoir knowledge and a useful success for exploration drilling.

Seismic interpretation pitfalls caused by interference effects, exemplified by seismic modeling of outcropping chalk successions

Interference and inherent resolution limitations are well-recognized problems in reflection seismic data and have over time led to misinterpretations. Acquisition of seismic data containing a broad range of frequencies, including high frequencies, does not solve this problem but merely moves the problem to a finer scale. Forward seismic modeling of known geologic scenarios is a valuable tool for studying anticipated seismic responses of successions with a given set of geologic and/or rock physical characteristics and for predicting interpretational challenges. We perform finite-difference-based seismic forward modeling on a conceptual geologic model derived from outcropping chalk sections in southeast Denmark and evaluate possible pitfalls that may hamper interpretation of seismic data acquired from strata with similar characteristics. We demonstrate that interbedded strata with contrasting physical properties and variable thickness can result in interference effects resembling faults and fractures. The result has significance for characterization, e.g., geothermal sites, potential CO2 storage targets, groundwater reservoirs, and hydrocarbon exploration sites, in which the proper imaging of faults and fractures from seismic data is an essential task.

Three-dimensional time-lapse inversion of transient electromagnetic data, with application at an Icelandic geothermal site

SUMMARY Transient electromagnetic (TEM) is an efficient non-invasive method to map electrical conductivity distribution in the subsurface. This paper presents an inversion scheme for 3-D TEM time-lapse (TL) data using a generalized minimum support (MS) norm and its application to monitoring conductivity changes over time. In particular, two challenges for TL TEM applications are addressed: (i) the survey repetition with slightly different acquisition position, that is, because systems are not installed and (ii) non-optimal data coverage above the TL anomalies, for instance, due to the presence of infrastructure that limits the acquisition layout because of coupling. To address these issues, we developed a new TEM TL inversion scheme with the following features: (1) a multimesh approach for model definition and forward computations, which allows for seamless integration of data sets with different acquisition layouts; (2) 3-D sensitivity calculation during the inversion, which allows retrieving conductivity changes in-between TEM soundings and (3) simultaneous inversion of two data sets at once, imposing TL constraints defined in terms of a generalized MS norm, which ensures compact TL changes. We assess the relevance of our implementations through a synthetic example and a field example. In the synthetic example, we study the capability of the inversion scheme to retrieve compact time-lapse changes despite slight changes in the acquisition layout and the effect of data coverage on the retrieval of TL changes. Results from the synthetic tests are used for interpreting field data, which consists of two TEM data sets collected in 2019 and 2020 at the Nesjavellir high-temperature geothermal site (Iceland) within a monitoring project of H2S sequestration. Furthermore, the field example illustrates the effect of the trade-off between data misfit and TL constraints in the inversion objective function, using the tuning settings of the generalized MS norm. Based on the results from both the synthetic and field cases, we show that our implementation of 3-D TL inversion has a robust performance for TEM monitoring.

GPR Application on Geothermal Studies: The Case Study of the Thermal Baths of San Xusto (Pontevedra, Spain)

Geophysical studies are frequently used on the geothermal field to define and characterize deep structures. However, shallow investigations are also needed for understanding the origin and local potential structures of a promising geothermal site. In this research, it is intended to present a review of the possibilities of the application of ground-penetrating radar (GPR) on the study of geothermal resources and how this geophysical technique can contribute to improving the energy use of these thermal resources. For this, the specific case of application to the investigation of the thermal baths of San Xusto (Pontevedra, Spain) is included in this work, whose interest for the region makes it necessary to perform an in-depth analysis of the original thermal structure. A GPR survey with frequency antennas of 200 and 500 MHz was conducted. Additionally, chemical analyses were performed to characterize the thermal water in the San Xusto site. As a result, a hot spring was detected by identifying reverberation phenomena in GPR imaging due to the presence of metal compounds and silica. Locating the origin of the thermal springs could allow for a more efficient use of the thermal resources as well as the hydrothermal possibilities of the area.

Geothermal renewable energy prospects of the African continent using GIS

Geothermal energy potential is identified through the deep investigation of geological, geothermal, and geophysical information over a small area; however, this task is both expensive and complex. Geographic Information Systems (GIS) can integrate different types of data (or thematic layers) over large regions and use them to identify zones of high geothermal potential. In this study, we use GIS as a tool to construct the first regional-scale geothermal potential map of Africa from different datasets. The key objective of this study is to estimate the geothermally promising areas within Africa by integrating geological thematic layers (rock units and faults), geophysical layers (heat flow derived from aeromagnetic data and seismicity), and geothermal layers (hot springs and volcanoes) within the GIS database. A weighted overlay technique within the GIS environment is applied to these data to generate the geothermal potential map. The result shows 14 regions with a high geothermal favorability index. The geothermal potential map of Africa is useful for targeting and exploring new geothermal renewable energy sites and can reduce exploration costs and pinpoint investigation areas during preliminary geothermal studies.

Unraveling the origin of geothermal heat in absence of recent volcanism: The Santiago Papasquiaro hydrothermal area, Central-Eastern Sierra Madre Occidental, México

In western Mexico, the central part of the Sierra Madre Occidental (SMO) large igneous province hosts several thermal springs with groundwater temperatures up to 74 ºC within late Eocene to Oligocene extensional structures. Given that in this region the last pulse of silicic volcanism ended >30 Ma ago this hydrothermal activity cannot be associated with cooling magma chambers and/or ongoing crustal thinning as in conventional geothermal sites. A possible explanation for the anomalous water temperature includes two non-mutual excluding processes: 1) heat production by radioactive decay of abundant U, Th, K radioisotopes in the silicic rocks forming the upper crust of the SMO and accumulated below the low conductive sediments filling the tectonic depressions, and 2) water heating by convection through deeply rooted faults. To prove this hypothesis, we studied the Santiago Papasquiaro hydrothermal area, located at the intersection between the NNW trending Santiago Papasquiaro half-graben and the NW trending San Luis-Tepehuanes fault system. We provide a detailed stratigraphy of the area supported by new U-Pb ages and we estimated heat production with in-situ gamma ray measurements of radioelements (U, Th, K), and groundwater He isotopes analyses.The stratigraphy of the region consists of 1) a Late Cretaceous-Paleocene continental volcanosedimentary succession (Garame Group), 2) Early Eocene rhyolitic lavas and ignimbrites, 3) Late Eocene volcanosedimentary succession, 4) Late Eocene-Early Oligocene pyroclastic succession capped by rhyolitic lavas and domes, and 5) a siliciclastic succession (Papasquiaro Formation) filling the graben interbedded with minor basaltic lavas (∼12–11 Ma) in its upper part. We also mapped two intermediate composition intrusive bodies, a Late Cretaceous (66 Ma) granodiorite and a Late Eocene (∼39 Ma) diorite.Heat production values are in the range of 1 µWm−3 to 8 µWm−3, with extreme values up to 310 µWm−3 for carbonaceous beds within the Garame Group. Late Cretaceous to Eocene volcanosedimentary and volcanic successions have lower heat production values than the Oligocene volcanic succession and the Oligocene-Quaternary siliciclastic succession. As a whole, heat production of Santiago Papasquiaro rocks exceeds the average for the upper crust as well as that of continental granite/rhyolite, being in the range of the high heat production granites worldwide, and above plutonic and volcanic rocks from other areas of Mexico. Noble gasses isotopes show a major crustal radiogenic input (79.4–96.1%), consistent with the radiogenic heat source hypothesis for the thermal springs, and a secondary mantle input (1.9 – 9.4%), which can be related to the ascent of mantle fluids through a deep crustal zone at the intersection of the regional structures. The isotopic He composition differs from the volcanic geothermal systems of Mexico such as Los Azufres, Los Humeros and from the unconventional geothermal area of the Juchipila Graben, located 300 km southeast in the same tectonic setting. The first two nearly represent a binary mixture between mantle and air saturated water end-members, whereas the latter also includes a minor crustal signal. Modeling of He isotopes data confirm that the 3He signature is associated to the ascent of mantle fluids through a deep crustal zone of highly fractured rocks at the intersection of regional structures. The signal of mantle fluids is diluted over the time by 4He sourced from the Oligocene high-heat production rocks.

Polyphasic Analysis Reveals Potential Petroleum Hydrocarbon Degradation and Biosurfactant Production by Rare Biosphere Thermophilic Bacteria From Deception Island, an Active Antarctic Volcano.

Extreme temperature gradients in polar volcanoes are capable of selecting different types of extremophiles. Deception Island is a marine stratovolcano located in maritime Antarctica. The volcano has pronounced temperature gradients over very short distances, from as high as 100°C in the fumaroles to subzero next to the glaciers. These characteristics make Deception a promising source of a variety of bioproducts for use in different biotechnological areas. In this study, we isolated thermophilic bacteria from sediments in fumaroles at two geothermal sites on Deception Island with temperatures between 50 and 100°C, to evaluate the potential capacity of these bacteria to degrade petroleum hydrocarbons and produce biosurfactants under thermophilic conditions. We isolated 126 thermophilic bacterial strains and identified them molecularly as members of genera Geobacillus, Anoxybacillus, and Brevibacillus (all in phylum Firmicutes). Seventy-six strains grew in a culture medium supplemented with crude oil as the only carbon source, and 30 of them showed particularly good results for oil degradation. Of 50 strains tested for biosurfactant production, 13 showed good results, with an emulsification index of 50% or higher of a petroleum hydrocarbon source (crude oil and diesel), emulsification stability at 100°C, and positive results in drop-collapse, oil spreading, and hemolytic activity tests. Four of these isolates showed great capability of degrade crude oil: FB2_38 (Geobacillus), FB3_54 (Geobacillus), FB4_88 (Anoxybacillus), and WB1_122 (Geobacillus). Genomic analysis of the oil-degrading and biosurfactant-producer strain FB4_88 identified it as Anoxybacillus flavithermus, with a high genetic and functional diversity potential for biotechnological applications. These initial culturomic and genomic data suggest that thermophilic bacteria from this Antarctic volcano have potential applications in the petroleum industry, for bioremediation in extreme environments and for microbial enhanced oil recovery (MEOR) in reservoirs. In addition, recovery of small-subunit rRNA from metagenomes of Deception Island showed that Firmicutes is not among the dominant phyla, indicating that these low-abundance microorganisms may be important for hydrocarbon degradation and biosurfactant production in the Deception Island volcanic sediments.

Regional thermal anomalies derived from magnetic spectral analysis and 3D gravity inversion: Implications for potential geothermal sites in Tanzania

Tanzania is one of the several countries intersected by the East African Rift System (EARS) endowed by a geothermal potential that has been explored only to a limited extent. Here we present the first heat flux map over the region based on the Curie point depth (CPD) estimation from aeromagnetic data. We have estimated the base of magnetic sources as a proxy for the CPD from the radially average power spectra of the total magnetic field using the centroid and the de-fractal methods. Our results show that the CPDs range ca. 11 to 43 km and are comparable to, but more detailed than global CPD estimates. The heat flow has then been computed assuming a constant thermal conductivity. In order to evaluate the results against crustal thickness, we have inverted the gravimetric regional field data constrained by the existing Moho depth from seismic receiver functions. Our analysis has revealed high heat flow values (over 100 mW/m2) along the EARS and at the Proterozoic collision boundaries that have been reactivated by the EARS. In general, the high heat flow anomalies coincide with known surface geothermal manifestations and shallow Moho depth in the range ca. 30 to 35 km. A high heat flow anomaly is also found in the central part of the Tanzanian craton, likely related to the mantle plume imaged by seismic tomography. The most interesting areas for geothermal exploration in Tanzania, according to our results, are the EARS triple junction in the Rungwe volcanic province, the north Tanzania divergent zone and the areas of the Proterozoic collision boundaries reactivated by the EARS.

Induced and triggered seismicity by immediate stress transfer and delayed fluid migration in a fractured geothermal reservoir at Pohang, South Korea

This study reveals the important role of hydromechanical responses of large hydraulic fractures in the cause and mechanisms of induced seismicity associated with the Mw 5.5 earthquake at the Pohang geothermal site, South Korea. Fractures intersecting two stimulation wells, PX-1 and PX-2, were identified through a comprehensive analysis of various data produced from drilling and hydraulic stimulations, including injection flow-pressure and seismicity data. Coupled hydromechanical numerical modeling of five stimulations performed in the PX-1 and PX-2 wells, showed that injection-induced hydraulic jacking and fracture shearing induce immediate stress transfer that plays a significant role in understanding seismic response at the Mw 5.5 fault. The friction coefficient times fluid pressure change by the PX-2 stimulations accounts for only 20% of the total CFS change at the location of the Mw 5.5 earthquake. The absence of seismic events at the Mw 5.5 fault by the PX-1 stimulations is attributed to the transfer of reduced shear stress at the PX-1 fracture due to shear slip. Kaiser effects in the seismic response observed during the PX-1 stimulation is explained by the irreversible nature of shear slip of the PX-1 fracture for the first time. In addition, post-injection seismicity, observed during the PX-2 stimulations, is attributed to a low permeability of the PX-2 fracture. The current modeling study suggests that coupled hydromechanical analysis with appropriate consideration of fractures is a powerful approach in understanding the mechanism of injection-induced seismicity in fractured geological media.

The Geothermal Artificial Intelligence for geothermal exploration

Exploration of geothermal resources involves analysis and management of a large number of uncertainties, which makes investment and operations decisions challenging. Remote Sensing (RS), Machine Learning (ML) and Artificial Intelligence (AI) have potential in managing the challenges of geothermal exploration. In this paper, we present a methodology that integrates RS, ML and AI to create an initial assessment of geothermal potential, by resorting to known indicators of geothermal areas namely mineral markers, surface temperature, faults and deformation. We demonstrated the implementation of the method in two sites (Brady and Desert Peak geothermal sites) that are close to each other but have different characteristics (Brady having clear surface manifestations and Desert Peak being a blind site). We processed various satellite images and geospatial data for mineral markers, temperature, faults and deformation and then implemented ML methods to obtain pattern of surface manifestation of geothermal sites. We developed an AI that uses patterns from surface manifestations to predict geothermal potential of each pixel. We tested the Geothermal AI using independent data sets obtaining accuracy of 92–95%; also tested the Geothermal AI trained on one site by executing it for the other site to predict the geothermal/non-geothermal delineation, the Geothermal AI performed quite well in prediction with 72–76% accuracy.

Performance of analytical techniques (SWIR imaging, XRD, EPMA) for the identification of minerals frequently formed during natural and technological geothermal processes

This study compares the performance of three analytical methods, hyperspectral imaging in the short-wave infrared range (SWIR), X-ray powder diffraction (XRD), and electron-microprobe analysis (EMPA) for the identification of minerals frequently formed during natural and technological geothermal processes. The samples from three geothermal sites in Indonesia contain a spectrum of minerals, which are characteristic for geothermal activities (alunite, jarosite, cristobalite, tridymite) and/or are involved in scaling-forming processes in geothermal plants (barite, celestine, common opal, calcite). We show and discuss the strengths and weaknesses of the individual techniques with respect to properly identifying these minerals and to approximate their relative proportions. The SWIR camera permits an unambiguous identification of only a small selection of the geothermally relevant minerals, which restricts its employment as routine tool in the context of geothermics. XRD and EPMA are more powerful techniques and deliver complementary information. In case that SWIR inactive species occur, (b) the entire spectrum of minerals present in a sample has to be unambiguously identified, (c) amorphous substances are present, (d) accurate mineral compositions are required, and (e) detailed information on minerals occurring in low abundance and grain size is warranted, the combined use of XRD and EMPA is mandatory.

An extended methodology for multi-criteria decision-making process focused on enhanced geothermal systems

When considering geothermal project development, the complex assignment of aggregating and quantifying the influencing factors and their interactions is an inevitable task that enables comprehensive assessment of the geothermal energy utilization from many different aspects. The main purpose of the scientific work is a revised set of criteria for comprehensive evaluation of geothermal project focusing on Enhanced Geothermal Systems (EGS) and considering the geological settings, technology, economic and financial aspects of project development, and societal and environmental parameters. The newly presented work is conceived as an addition to the previous work, defining and thoroughly describing twenty-eight influencing factors for evaluation of deep geothermal energy. The mentioned factors consist of 18 newly introduced criteria, 6 replaced criteria, and 4 modified criteria which are based on the extensive literature review and expertise integrating all aspects of EGS project development. One of the key findings of the presented methodology is that it provides broad assessment of an EGS project, applicable to different end-uses including only electricity generation, only heat production and combined heat and power production. The proposed methodology could serve as a preparatory guideline for more detailed analysis and calculations for a future project development, either greenfield or brownfield, encompassing technological, geological, economic, and environmental aspects. The methodology was tested in case study where two different geothermal sites were assessed for heat production and electricity production scenarios. Both sites, with their main geological parameters, resulted in production of electricity, from 263.51 GWh up to 927.69 GWh, and heat production from 334.25 GWh up to 5,207.68 GWh. Such increase of renewable energy production from geothermal source derived the avoidance of CO2 emissions ranging from 79,686 tonnes of CO2-eq up to 1,241,542 tonnes of CO2-eq. The final grades of each criterion for the heat and electricity production scenarios resulted in favor of Site 2, where better reservoir and economic performance values derived the higher final grade of site’s overall performance. The summarized results lead to a conclusion that the proposed methodology is applicable for assessment of different end-usage options for one geothermal site and for comparison of projects at different geothermal sites.

Arsenic-contaminated drinking water and associated health risks in children from communities located in a geothermal site of Michoacán, México: Monte Carlo probabilistic method

Arsenic occurs naturally in ground and spring waters in several geothermal regions in México as a result of natural geochemical processes. Therefore, the goal of this study is to assess the probabilistic health risk in children exposed to arsenic by drinking water from communities located in the geothermal site of Zinapécuaro, Michoacán, México. The water sampling was done monthly for one year and total inorganic arsenic was determined using Hydride Generation coupled with Atomic Absorption Spectrometry. The health risk was assessed using the Monte Carlo probabilistic method. The arsenic levels in water were found to be in the range of 10.4 to 58.9 μg/L, with the highest levels from the hot springs. For children, the 95th percentile of Hazard Index was (HI) >1 for all study sites, with the highest mean (HI = 11 ± 2.9) for Taimeo’s spring water. The ingestion pathway predominantly contributed > 95% to the total health risk in comparison to the dermal exposure route. These results show the potential non-cancerous effects of arsenic in drinking water for children are high. For children and adults, the 95th percentile of Total Cancer Risk (TCR) was 4.7 × 10−4 and 1.2 × 10−3 respectively, exceeding the US EPA safe threshold of 1 × 10−4, which is an unacceptable cancer risk. Sensitivity analysis indicated that arsenic concentration in drinking water, body weight and arsenic intake for children were the most relevant variables on the output parameter HI. Consequently, the environment and health authorities must make greater efforts to provide safe drinking water to protect the residents of Zinapécuaro County.

Analysis of a basement fault zone with geothermal potential in the Southern North Sea

Extraordinary 3D seismic data from the Central Offshore Platform (Southern North Sea), complemented by information from 38 boreholes, reveal a 10 km-wide basement fault zone above which fluid anomalies emanate from sub-salt reservoirs to terminate in lower Cretaceous strata. Fluid blow-out pipes, chimneys and low-amplitude trails were mostly sourced from the region where NW-striking syn-rift faults intersect the N-striking basement fault zone. As a result, 73% of the mapped fluid-flow anomalies (94 out of 129) occur within the basement fault zone of interest or follow a N-S strike along its shoulders. We postulate a strong control of the basement fault zone on past fluid and heat flow, as basin models confirm that fluid and heat were mostly produced during the Cretaceous. Bottom-hole data record temperatures of ∼140 °C at present, highlighting the geothermal potential of the study area. These temperatures nevertheless contrast with the relatively constant gradient of ∼ 32 °C/km occurring both in and outside the basement fault zone. This work is important as its shows that past fluid and heat flow over a basement fault zone does not necessarily correlate with the existence of an enhanced hydrothermal system at present. However, as bottom-hole temperatures are within the benchmark values considered across Europe, it also stresses the importance of basement fault zones as key structures to find, and assess, as potential geothermal sites.

Multi-Method Geophysical Mapping of a Geothermal Reservoir and Buried Channel in Langfang, Northern Part of China

Geothermal resources are a clean and renewable energy source that can play a critical role in drastically reducing air pollution. The utilization of geothermal resources requires technical support to decrease the developing risk by applying an integrated interpretation of geophysical methods. In this study, we used geophysical methods in the Langfang region of China to design a workflow for the safe yield of geothermal resources. To do so, we conducted controlled-source audio-frequency magnetotelluric (CSAMT) soundings, shallow soil temperature surveys, radon gas measurements, and the microtremor survey method (MSM) at the geothermal exploration and development site. These geophysical analyses identified a geothermal reservoir and a buried channel in the region. The dominant fault developing in the area was identified as the best channel for heat and water based on the developed geothermal wells. In areas with relatively little geothermal exploration, this study provides a reference and demonstration for geothermal development.

Scaling Behavior of Thermally Driven Fractures in Deep Low‐Permeability Formations: A Plane Strain Model With 1‐D Heat Conduction

AbstractInjection of cold fluids through/into deep formations may cause significant cooling, thermal stress, and possible thermal fracturing. In this study, the thermal fracturing of low‐permeability formations under one‐dimensional heat conduction was investigated using a plane strain model. Dimensionless governing equations, with dimensionless fracture length , aperture , spacing , time , and effective confining stress , were derived. Solution of single thermal fracture was derived analytically, while solution of multiple fractures with constant (or dynamic) spacing were obtained using the displacement discontinuity method (and stability analysis). For single fracture, increases nonlinearly with and then transitions to scaling law , indicating that late‐time fracture length increases linearly with the square root of cooling time. For constantly spaced fractures, deviates from the single‐fracture solution at a later for a larger , showing slower propagation under inter‐fracture stress interaction. For dynamically spaced fractures, fracture arrest induced by stress interaction was determined by the stability analysis; the fully transient solution provides evolution of dimensionless fracture length, spacing, aperture, and pattern; a similar scaling law, with , obtained shows the effect of both stress interaction and fracture arrest. The solution and scaling law provide fast predictions for all reservoir and cooling conditions using (single) model parameter . Application to a geothermal site with demonstrates that thermal fractures reach 0.67, 6.25, and 78.00 m in length, 0.49, 2.30, and 13.00 m in spacing, and 0.43, 2.09, and 12.19 mm in aperture at 1, 100, and 10,000 days.

3D thermo‐hydro‐mechanical simulation of the behaviour of a naturally fractured petrothermal reservoir in deep Upper Jurassic carbonates of the Bavarian Molasse Basin – Case study Geretsried

AbstractBased on multi‐scale and multi‐disciplinary measured data, gathered at the Geretsried geothermal site, a 3D reservoir model of the deep and fracture‐controlled Upper Jurassic carbonates in the North Alpine Foreland Basin is generated in this work. An efficient methodology is developed to numerically simulate the coupled reservoir processes of fluid flow, heat transport and thermoporoelastic stresses resulting from possible geothermal doublet operating schemes with cold fluid injection and production profiles in an enhanced naturally fractured reservoir. A variety of numerical experiments is conducted to study the reactivation potential and dilation tendency of the fracture and fault system. Simulation results show the spatiotemporal evolution of the thermoporoelastic stresses and the zone affected after 50 years of geothermal doublet operation. From these simulations, the thermoelastic response of a geothermal doublet operating with 60 °C fluid injection temperature and 20 l/s flow rate translates into a maximum induced thermal stress of around 49.4 MPa near the injection well. In terms of a long‐term reservoir performance and fault and fracture reactivation potential, the findings reveal a negligible risk to a sustainable geothermal doublet operation.

From the Discovery of Extremozymes to an Enzymatic Product: Roadmap Based on Their Applications.

With the advent of the industrial revolution, the use of toxic compounds has grown exponentially, leading to a considerable pollution of the environment. Consequently, the development of more environmentally conscious technologies is an urgent need. Industrial biocatalysis appears as one potential solution, where a higher demand for more robust enzymes aims to replace toxic chemical catalysts. To date, most of the commercially available enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of temperature and pH (i.e., between 20°C and 45°C, neutral pH), limiting their actual application under industrial reaction settings, where they usually underperform, requiring larger quantities to compensate loss of activity. In order to obtain novel biocatalysts better suited for industrial conditions, an efficient solution is to take advantage of nature by searching and discovering enzymes from extremophiles. These microorganisms and their macromolecules have already adapted to thrive in environments that present extreme physicochemical conditions. Hence, extremophilic enzymes stand out for showing higher activity, stability, and robustness than their mesophilic counterparts, being able to carry out reactions at nonstandard conditions. In this brief research report we describe three examples to illustrate a stepwise strategy for the development and production of commercial extremozymes, including a catalase from an Antarctic psychrotolerant microorganism, a laccase from a thermoalkaliphilic bacterium isolated from a hot spring and an amine-transaminase from a thermophilic bacterium isolated from a geothermal site in Antarctica. We will also explore some of their interesting biotechnological applications and comparisons with commercial enzymes.