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Lost circulation is a pervasive problem in geothermal wells that can create prohibitive costs during drilling. The main issue with treatment is that the mechanism of plug formation is poorly understood. Here we applied two experimental approaches to characterize the clogging effectiveness of different materials. Fracture flow tests with different geometries were conducted with various individual materials and mixtures at relevant conditions. A high-temperature flow loop system was also developed to inject single- and mixed-material plugs into a gravel pack with a non-uniform geometry to compare with the fracture tests. The fracture tests revealed that single materials tended to form no plug or an unstable plug, while mixtures of materials were uniformly better at sealing fractures. Gravel pack tests at high temperatures show most of the materials are intact but degraded. The fibrous materials can create partial or unstable plugs in the gravel pack, but mixed-material plugs are far more effective at clogging. Both test types suggest that (1) mixed materials are more effective at blocking fluid flow and (2) fibrous materials seal fracture openings better, while granular materials seal inside fractures or pore throats better. Further research is needed to study the long-term stability of different plug configurations. [ABSTRACT FROM AUTHOR]

As one of the methods to extract geothermal energy, downhole coaxial heat exchanger is widely concerned because of its high heat extraction rate and no need of re injection. However, there are few studies on the extraction of open-loop heat from a single deep geothermal shaft, and there is a lack of detailed inlet and outlet transient temperature data. In this study, the downhole coaxial open-loop heat collector is improved, and the slotted liner at the bottom of the well is used to form a free open space to improve the heat exchange. Using the improved experimental device design, the field thermal recovery test was carried out in deep geothermal well of Shengli Oilfield, Dongying, China. According to the field test results, the control equation was established, and the influence of parameters on the thermal recovery rate was studied. It is found that the improved heat output is greater than the reported value of the downhole heat exchanger with the traditional structure. After about eight days, the heat extraction rate reached a gradually stable stage. After 15 days of continuous operation, the heat output is stable at 200 kW, and the water temperature at the water outlet is 34.6 °C. [ABSTRACT FROM AUTHOR]

This work aimed to verify forecasts of temperature and mineralization of the Lower Jurassic and Lower Cretaceous waters in the Polish Lowlands, based on new geological information. In the first part of the articles series, entitled Verification of geothermal conditions in the Polish Lowlands based on data from new drilling performed in the years 2000-2022, an analysis of geothermal conditions is presented, while this work focuses on hydrogeochemical parameters, such as temperature in the top of formations and water mineralization. For this purpose, data from the Central Geological Database (CBDG), the Central Bank of Hydrogeological Data - HY DRO Bank, and from previously published scientific and research works were used. In the years 2000-2023, twenty-four exploration wells with a depth exceeding 1000 m below ground level were drilled and documented in the Polish Lowlands, providing information on the temperature and mineralization of waters taken from the Lower Jurassic or Lower Cretaceous formations. The assessment of spatial changes, as in the first part of the work, was performed with the use of QGIS Desktop 3.24.1 software, which is geoinformation software (GIS) that allows viewing, editing, and analyzing spatial data and the creation of maps. The presented analysis made it possible to make a spot, local correction of the projected course of the isoline in relation to the maps published earlier in the Atlas of geothermal resources in the Polish Lowlands. Mesozoic Formations developed in 2006, edited by Wojciech Górecki. [ABSTRACT FROM AUTHOR]

Borehole image data and a 1D-stress model built on open hole logs, leak-off tests (LOT) and image logs are used to evaluate the potential of seismicity caused by fault triggering during geothermal heat production in the city of Vienna. Data were derived from a 4220 m deep geothermal exploration well that investigated the geothermal potential of fractured carbonates below the Miocene fill of the Vienna Basin. The well penetrated several normal faults of the Aderklaa Fault System (AFS) that offset Pleistocene terraces at the surface and hence are regarded as active. Stress-induced borehole failures and 1D geomechanical modeling proves that the potential reservoirs are in a normal fault stress regime with Sv > SHmax > Shmin. While stress magnitudes in the upper part of the well (down to about 2000 m) are significantly below the magnitudes that would trigger the rupture of critically oriented faults including the AFS, stresses in the lower part of the drilled section in the pre-Neogene basement (below about 3300 m) are not. Data evidence a rotation of SHmax for about 45° at a fault of the AFS at 3694 m to fault-parallel below the fault suggesting that the fault is active. Critical or near-critical stressing of the fault is corroborated by the stress magnitudes calculated from the 1D geomechanical model. The safety case to exclude unintended triggering of seismic fault slip by developing geothermal reservoirs in close vicinity to one of the branch faults of the AFS may therefore be difficult or impossible to make. [ABSTRACT FROM AUTHOR]

The thermodynamic analysis of an increasing-pressure endothermic power cycle (IPEPC) integrated with closed-loop geothermal energy extraction (CLGEE) in a geothermal well at a depth from 2 km to 5 km has been carried out in this study. Using CLGEE can avoid some typical problems associated with traditional EGS technology, such as water contamination and seismic-induced risk. Simultaneous optimization has been conducted for the structural parameters of the downhole heat exchanger (DHE), the CO2 mixture working fluid type, and the IPEPC operating parameters. The CO2-R32 mixture has been selected as the optimal working fluid for the IPEPC based on the highest net power output obtained. It has been found that, when the DHE length is 4 km, the thermosiphon effect is capable of compensating for 53.8% of the pump power consumption. As long as the DHE inlet pressure is higher than the critical pressure, a lower DHE inlet pressure results in more power production. The power generation performance of the IPEPC has been compared with that of the organic Rankine cycle (ORC), trans-critical carbon dioxide cycle (t-CO2), and single-flash (SF) systems. The comparison shows that the IPEPC has more net power output than other systems in the case that the DHE length is less than 3 km, along with a DHE outer diameter of 0.155 m. When the DHE outer diameter is increased to 0.22 m, the IPEPC has the highest net power output for the DHE length ranging from 2 km to 5 km. The application scopes obtained in this study for different power generation systems are of engineering-guiding significance for geothermal industries. [ABSTRACT FROM AUTHOR]

High-temperature (HT) geothermal wells can provide green power 24 hours a day, 7 days a week. Under harsh environmental and operational conditions, the long-term durability requirements of such wells require special cementitious composites for well construction. This paper reports a comprehensive assessment of geothermal cement composites in cyclic pressure function laboratory tests and field exposures in an HT geothermal well (300–350 °C), as well as a numerical model to complement the experimental results. Performances of calcium–aluminate cement (CAC)-based composites and calcium-free cement were compared against the reference ordinary Portland cement (OPC)/silica blend. The stability and degradation of the tested materials were characterized by crystalline composition, thermo-gravimetric and elemental analyses, morphological studies, water-fillable porosity, and mechanical property measurements. All CAC-based formulations outperformed the reference blend both in the function and exposure tests. The reference OPC/silica lost its mechanical properties during the 9-month well exposure through extensive HT carbonation, while the properties of the CAC-based blends improved over that period. The Modified Cam-Clay (MCC) plasticity parameters of several HT cement formulations were extracted from triaxial and Brazilian tests and verified against the experimental results of function cyclic tests. These parameters can be used in well integrity models to predict the field-scale behavior of the cement sheath under geothermal well conditions. [ABSTRACT FROM AUTHOR]

Drilling optimization is essential in constructing an enhanced geothermal system (EGS) and can be facilitated through predicting the rate of penetration (ROP). The ROP evolution along the depth was forecasted by considering the current and previous ROP values as input to a gated recurrent unit (GRU)-based deep learning model. Drilling data was obtained from two geothermal wells in Pohang, South Korea. Multiple data configurations for training and testing were designed from both wells. The proximity of the training section to the target results in improved accuracy in prediction (MAPE smaller than ~ 3%). Furthermore, larger depth spans of ROPs used for training resulted in better prediction outcomes. The model trained with the entire dataset from an adjacent well exhibited well-predicted ROP values for a new drilling hole (MAPE smaller than 5–10%). From the multiple-step forecasting analysis, the error tended to sharply increase as the number of predicted ROP values increased despite a large number of the input sequence (MAPE larger than 20%). Incorporating other drilling data besides ROP evolution did not improve the prediction. By predicting ROP evolution along the depth, the GRU-based model can assist operators in optimizing drilling processes and preparing for upcoming scenarios. The model can serve as a valuable tool for enhancing drilling efficiency and effectively managing operational uncertainties. [ABSTRACT FROM AUTHOR]

Considering the abundance of renewable energy potential in Turkey, green hydrogen derived from renewable sources holds great promise as a fuel. This paper presents a model for obtaining green hydrogen from medium-temperature geothermal sources. In this model, the Zilan location in the Van province of Turkey was identified as a suitable site for electricity and hydrogen production from low or medium-temperature geothermal sources due to its significant geothermal and water resource potential. In this regard, the installed capacity of the Organic Rankine Cycle (ORC) geothermal power plant is determined by using Monte Carlo Simulation based on the characteristics of the geothermal well at this location, and subsequently, the hydrogen production performance has been evaluated by analyzing the water of Lake Van. According to the analysis results, Lake Van was found to be efficient for hydrogen production. Hydrogen production from Lake Van water was subsequently simulated using the electrolysis method with this ORC geothermal power plant. According to the findings of this model, the hourly hydrogen production potential at this location using a 1.4 MW ORC plant, based on 2022 data, was estimated to be 18.6 kg, which is projected to increase to 28 kg based on 2050 estimated data. In addition, the techno-economic analysis of this compact green hydrogen production process was conducted in the study. The production cost of 1 kg of hydrogen was calculated to be €4.91 in 2022, while it is expected to be €1.21 in 2050. These results indicate that ORC technology will become competitive in hydrogen production in the upcoming years. • Determining the installed capacity of an ORC plant using Monte Carlo simulation. • Producing green hydrogen through an ORC power plant. • Analysis of the hydrogen production potential of the relevant water source. • Selection of the suitable electrolysis unit. • Hourly hydrogen production capacity of compact facility. [ABSTRACT FROM AUTHOR]

The repetitive process of shut-in and production in geothermal wells promotes thermal stress on the wellbore components, including annular cement. A cement sheath at a relatively shallow depth undergoes the most significant stress change due to the high differential temperature between the geothermal gradient and the production fluid's temperature. Understanding the impact of cyclical thermal stresses on cement is critical for assessing the barrier integrity at a shallow depth that serves as aquifer protection. A novel large-scale setup simulating a 1.5 m-long casing-cement-casing well section was built to study the changes in cement's sealing performance of low-enthalpy geothermal wells during production. Using this setup, a cement sheath can be cured similarly to the in situ conditions, and the annular temperature can be cycled under realistic operating conditions. The change in flow rate through the cement sheath before and after cycling is quantified through leak tests. UV dye is injected at the end of the experiment to identify the location and type of damage in the cement sheath. A hydromechanically coupled finite element model was used to estimate the stress evolution in cement during the tests. The model incorporated the impact of cement hydration and strength development during curing. The numerical results were used as a guide to ensure the test design closely mimicked in situ conditions. The results show the presence of a small microannulus immediately after curing due to hydration shrinkage. Thermal cycles reduced the permeability of the microannulus. The size of the micro-annulus was observed to be sensitive to the backpressure applied to the cement sheath, indicating the need for pressure to maintain an open microannulus. Thirty-nine thermal cycles between 80 and 20 °C did not change the permeability of the cement sheath significantly. Tensile cracks in the cement sheath were not continuous and may not be a significant pathway. The new setup allows for measuring cement's effectiveness in withstanding in situ stress conditions when exposed to thermal cycles such as geothermal and CCS wells. [ABSTRACT FROM AUTHOR]

Climate change and the energy crisis forced industrialized countries to contain CO2 emissions and use indigenous renewable energy sources. Geothermal energy undoubtedly has great potential, particularly thermal energy, given that 48% of the final energy consumption in the EU20 countries in 2021 was related to heating and cooling systems. The present study verifies and compares the feasibility of realizing district heating systems in two different contexts: (i) depleted hydrocarbon fields with the repurposing of existing hydrocarbon wells into geothermal wells and (ii) areas with documented geothermal resources. The two selected case studies are located, respectively, near Romentino (Northern Italy, province of Novara) and Tuscania (Central Italy, province of Viterbo). Following an assessment of the geothermal resources in the two selected case studies, specific methodological tools have been developed to evaluate the energy demand in the municipalities and determine the projects' economics. Both case studies show positive economic indices assuming heat tariffs aligned with the values recorded in the 2020–2021 period. However, our results show how reusing hydrocarbon wells in geothermal wells constitutes an excellent opportunity to access geothermal resources, significantly reducing the necessary investment and the mining risk and strongly improving the economics of the projects. [ABSTRACT FROM AUTHOR]

Low-enthalpy geothermal wells are considered a sustainable energy source, particularly for district heating in the Netherlands. The cement sheath in these wells experiences thermal cycles. The stability of cement recipes under such conditions is not well understood. In this work, thermal cycling experiments for intermediate- and low-temperature geothermal well cements have been conducted. The samples were cured either under ambient conditions or under realistic pressure and temperature for 7 days. The samples did not show any signs of failure after performing 10 cycles of thermal treatment between 100 °C and 18 °C. We also tested cement formulations under drying conditions. Drying shrinkage is caused by a reduction in the water content of cement, which leads to capillary forces that can damage cement. Such circumstances lead to tensile stresses causing radial cracks. Most samples exhibited cracks under low humidity conditions (drying). Fiber reinforcement, especially using short PP fibers, improved the cement's resilience to temperature and humidity changes. Such additives can improve the longevity of cement sheaths in geothermal wells. [ABSTRACT FROM AUTHOR]

Geothermal energy is a renewable energy that has not been utilised as solar, wind, and biomass energy because of the cost of exploration, cost of implementation, and possible environmental concerns such as enhancing the chances of earthquakes, and tremors.The remote sensing technique and Surface Energy Balance model was proposed to determine the absorbed terrestrial radiation and other salient parameters. Forty years remote sensing dataset (1980–2019), was obtained from the MERRA-2 for three hundred and two (302) locations across Nigeria. The acquired thermal parameters were processed using known models. The heat catchment with the highest magnitude of 330.244 W/m2 are found in Nembe, Okirika, Yenagoa (Niger-Delta basin); 334.198 W/m2 in Ozubulu, Oguta, Obolo (Anambra basin); 332.877 W/m2 in Okitipupa, Atijere (Dahomey basin); 318.021 W/m2 in Eban, Mokwa (Bida basin); 318.682 W/m2 in Kumaganum, Gashua, Geidam (Chad basin); 321.050 W/m2 in Kuchi, Gwandi, Gwadabawa (Sokoto basin); 289.247 W/m2 in Gombe, Potiskum, Kafarati (Upper Benue basin); 312.964 W/m2 in Lokoja, Otukpa (Mid-Benue basin); and 338.962 W/m2 Malumfashi, Kano (Basement Complex). Likely geothermal wells were listed within the research. It is recommended that more ground measurements should be carried out in the basement complexes and sedimentary basins of Nigeria. [ABSTRACT FROM AUTHOR]

To understand the heat transfer performance of the middle-deep U-bend geothermal well, the 2500 m deep U-bend geothermal well was taken as the research object at the Hebei University of Engineering. This study established a mathematical and physical model of heat transfer in a U-bend geothermal, and the influence of geothermal gradient and lithologic changes on heat transfer performance was considered. The established model was verified based on the experimental data. Numerical simulation results show that a reasonable reduction of inlet temperature can increase thermal power. The thermal power of the geothermal well will increase by about 40 kW for every 1°C reduction of inlet temperature. The thermal power can be increased with a reasonable increase in the flow rate of the circulating fluid, but the increment of the thermal power decreases gradually. The simulation results show that the thermal power and outlet temperature of a deep U-bend geothermal well can be effectively improved by appropriately reducing the inlet temperature, increasing the flow rate, increasing the collection length, increasing the well depth, increasing the insulation length of the vertical well section and using low thermal conductivity insulation materials. The research results from this study could provide a reference for the heat transfer system optimization of the middle-deep U-bend geothermal well. [ABSTRACT FROM AUTHOR]

This study presents a new model to predict the static formation temperature in multiple geothermal fields using multiple machine learning algorithms. Both artificial intelligence and non-artificial intelligent algorithms were used for this prediction. The model developed in this study predicts static formation temperature using several machine learning algorithms, including artificial neural networks, fuzzy logic, k-nearest neighbors, and random forest algorithms. Results are compared with the real temperatures obtained from two geothermal wells. The random forest, fuzzy logic, and k-nearest neighbors algorithms outperformed the artificial neural network, with the random forest algorithm achieving higher accuracy. The MAE of the random forest algorithm was 0.7% and the RMSE was 0.9%. The MAE values for the other machine learning algorithms ranging from 1.5 to 8.4%, and the RMSE values ranged from 2 to 20.8%. Artificial intelligence methods were found to be more accurate than non-artificial intelligence (mathematical) methods, with varying percentages. The results generated by the unique new model computation and the measured test data are substantially matched when compared to computed data and observed temperature data. The novelty of this newly developed artificial intelligence model is that it serves as a practical and inexpensive tool for static formation temperature determination in geothermal and petroleum wells. [ABSTRACT FROM AUTHOR]

Hot spring biofilms are stable, highly complex microbial structures. They form at dynamic redox and light gradients and are composed of microorganisms adapted to the extreme temperatures and fluctuating geochemical conditions of geothermal environments. In Croatia, a large number of poorly investigated geothermal springs host biofilm communities. Here, we investigated the microbial community composition of biofilms collected over several seasons at 12 geothermal springs and wells. We found biofilm microbial communities to be temporally stable and highly dominated by Cyanobacteria in all but one high-temperature sampling site (Bizovac well). Of the physiochemical parameters recorded, temperature had the strongest influence on biofilm microbial community composition. Besides Cyanobacteria, the biofilms were mainly inhabited by Chloroflexota, Gammaproteobacteria, and Bacteroidota. In a series of incubations with Cyanobacteria-dominated biofilms from Tuhelj spring and Chloroflexota- and Pseudomonadota-dominated biofilms from Bizovac well, we stimulated either chemoorganotrophic or chemolithotrophic community members, to determine the fraction of microorganisms dependent on organic carbon (in situ predominantly produced via photosynthesis) versus energy derived from geochemical redox gradients (here simulated by addition of thiosulfate). We found surprisingly similar levels of activity in response to all substrates in these two distinct biofilm communities, and observed microbial community composition and hot spring geochemistry to be poor predictors of microbial activity in the study systems. [ABSTRACT FROM AUTHOR]

Geothermal energy is a new renewable and clean energy source with low cost and wide distribution. In the process of production and reinjection of geothermal well system (mainly including facilities such as wellbore, downhole casing, wellhead device and surface pipe sink), due to various factors such as temperature, pressure, pH, flow velocity, degree of supersaturation, and presence of other salts and ions interfering in solution, precipitation is easily formed, resulting in the phenomenon of scaling in geothermal well system. This phenomenon can seriously affect the normal production operation of the geothermal well system, reduce the service life of the equipment, and cause a series of problems such as energy waste and economic loss. This paper presents a review of recent research progress on scaling and scale inhibition in geothermal well systems. The mechanism of scaling in geothermal well systems, as well as the main technical means of scale inhibition and removal currently adopted were introduced. The future research directions of scale inhibition and descaling in geothermal well systems are also presented. [ABSTRACT FROM AUTHOR]

The absence of regional electrical data has constrained our comprehension of the deep geological structures in the Jizhong Depression. This limitation has impeded the exploration of factors and principles governing geothermal reservoirs. Historically, studies on these factors primarily centered on geothermal field attributes, such as anomalous geothermal flux, geothermal gradients, and deep Moho variations. In our research, we undertook an exhaustive interpretation of extended-period magnetotelluric readings. This was amalgamated with prior regional geological and geophysical studies to discern deep geological structural details pertinent to geothermal resource components, encompassing heat sources, pathways, reservoirs, and cap rocks. Our analysis spanned the foundational surface of the Cenozoic era, fault configurations, carbonate formation distribution, and layers with low velocity yet high conductivity. We also statistically evaluated geothermal wells, their density, and the water temperature attributes across various structural entities. This aided in comprehending how structural units influence thermal well features. Our research delineated the spatial interrelation between geothermal well distribution and deep geological structures, including carbonate rock distribution, Cenozoic thickness, fault patterns, and profound low-velocity, high-conductivity layers. Moreover, we scrutinized how structural unit types impact thermal well attributes, offering insights into the formation principles of deep carbonate geothermal reservoirs within the Jizhong Depression. Our findings suggest that the genesis of deep geothermal resources in the Jizhong Depression is swayed by regional geological conditions. Notably, the distribution of regional and especially deep geothermal wells is intimately tied to regional stratigraphy, structural designs, and profound geological structural traits. Furthermore, the temperature within geothermal wells correlates strongly with the burial depth, carbonate formation thickness, Cenozoic thickness, and proximity to fault channels responsible for fluid movement and heat transmission. [ABSTRACT FROM AUTHOR]

There are numerous natural outflows, 3 thermal baths, 9 disused geothermal wells, and 3 private companies operating in the Seferihisar geothermal system, including a power plant generating electricity. The potential of these resources is suitable for nonelectrical use of geothermal energy, such as greenhouse heating and thermal tourism. SWOT analysis method has been used to assess the pros and cons of the geothermal resource in Seferihisar, aiding the identification of suitable applications and investments for both present and future projects. The region is rich in terms of geothermal resources and has convenient access to both public and ware transport, which are described as strengths of the resource. However, poor management and an excess of licensed geothermal fields weaken the effective consumption of the system. A huge number of projects have led to opposition from environmentalist groups. The proven technology of geothermal energy has resulted in an increase in incentives and investment consolidations with governmental support. In the light of SWOT analysis, considering SO, ST, WO, and WT strategies, the untapped geothermal resources present in the Seferihisar geothermal system, combined with the natural attractions and cultural richness of the county, will contribute significantly to non-electrical/direct uses of the geothermal energy in the near future. [ABSTRACT FROM AUTHOR]

A model that can be used to quantify silica deposition from superheated depressurized steam is developed. Classical nucleation theory, agglomeration and deposition onto a wall are combined in a numerical model that calculates the concentration profile, the particle size distribution and the deposition in a flow through a pipeline after a sudden increase in supersaturation. The work presented here is an important step in understanding the mechanisms governing precipitation from supercritical and superheated steam as produced by deep geothermal wells drilled in magmatic areas. The power potential in such systems can be significantly higher than for conventional systems if utilized efficiently. The presented results can be applied to improve industrial designs and decrease energy costs. The model predicts the amount of precipitation along a pipe at various supersaturations, and the resulting deposition velocity in a straight pipe correlates fairly well with recent experimental results. There is a high number of nanocolloids formed close to the pressure reduction position, where deposition is at its maximum. Downstream, larger agglomerates develop, and deposition decreases as the number of particles and the overall concentration decreases. The local maximum deposition rate increases with increasing supersaturation. The calculations show that deposition mechanisms are as important as the chemical process of solidification when estimating where and how most material will be deposited. The rapid formation and deposition of solids predicted indicate that depressurization along with solid capture could be used to rid fluid of silica. [ABSTRACT FROM AUTHOR]

Energy losses can be significantly reduced if thermally insulating cement is used for energy storage and recovery. The thermal conductivity (TC) of the currently used cement is between 1 and 1.2 W/mK. In this study we assessed the ability of polystyrene (PS)–polybutadiene (PB)–polyacrylic acid (PAA) terpolymer (cross-linked styrene–butadiene rubber, XSBR) latex to improve thermal insulating properties and thermal shock (TS) resistance of class G ordinary Portland cement (OPC) and fly ash cenosphere (FCSs) composites in the temperature range of 100–175 °C. The composites autoclaved at 100 °C were subjected to three cycles, one cycle: 175 °C heat → 25 °C water quenching). In hydrothermal and thermal (TS) environments at elevated temperatures in cement slurries the XSBR latex formed acrylic calcium complexes through acid–base reactions, and the number of such complexes increased at higher temperatures due to the XSBR degradation with formation of additional acrylic groups. As a result, these complexes offered the following five advanced properties to the OPC-based composites: (1) enhanced hydrophobicity; (2) decreased water-fillable porosity; (3) reduced TC for water-saturated composites; (4) minimized loss of compressive strength, Young's modulus, and compressive fracture toughness after TS; and (5) abated pozzolanic activity of FCSs, which allowed FCSs to persist as thermal insulators under strongly alkaline conditions of cement slurries. Additionally, XSBR-modified slurries possessed improved workability and decreased slurry density due to the air-entraining effect of latex, which resulted in further improvement of thermal insulation performance of the modified composites. [ABSTRACT FROM AUTHOR]

Neogene basins/grabens along with exhumed core complexes make up the fundamental components of western Anatolia within the geologic framework of the Aegean Extensional Province. The Neogene basins are divided into two based on their orientation and contrasting lithostratigraphic packages: (1) the NE–SW basins that are dominated by materials either derived from the Menderes Massif and/or İzmir-Ankara-Erzincan suture zone-related units during the Lower Miocene and sedimentation that had mostly ended by the end of the latest Miocene, (2) E–W trending basins that are known to be devoid of Tethyan ophiolitic material and contain Miocene and Plio-Quaternary deposits. The relationship between the two sets of basins has been unclear, with some suggesting that E–W trending grabens are younger than the NE–SW trending grabens. Here, we reported results from the deep (up to 3840 m) geothermal wells from the Alaşehir sub-basin of the E–W trending Gediz Graben. Our analysis reveals that the Neogene graben fill is thicker than previously documented and contains ophiolite-derived clastics at its base. We proposed that the Alaşehir sub-basin has a similar early Miocene configuration as the Uşak-Güre basin and the Gediz Graben represents an inherited structure of the NE–SW trending grabens. [ABSTRACT FROM AUTHOR]

This study investigates different aspects of an innovative multi-heat recovery-based solar-geothermal polygeneration system, acclaiming the exergetic, exergoeconomic, and energetic concepts. Principally, using two renewable energy sources, the whole framework of the system encompasses Concentrated PhotoVoltaic Thermal (CPVT) solar collectors, Flat Plate Solar Collectors (FPSCs), geothermal wells, an Ejector Refrigeration Cycle (ERC) Organic Rankine Cycle (ORC) integrated with a Solid Oxide Electrolyzer Cell (SOEC), heating production units, an air dryer, and an Organic Rankine Cycle (ORC) unit. Afterward, the sensitivity analysis utilized for the parametric study makes a multi-aspects optimization in diverse scenarios in which NSGA-II, as well as, fuzzy TOPSIS and fuzzy VIKOR decision makings, are handled to designate the optimal solution. The suggested system has professionally been devised thanks to the characteristic of maximum use of energy of the streams circulated. Hence, crucial variables evaluated are more influenced by the variation in the geothermal heater pinch point temperature gradient. Also, in the optimization scenario based on unit cost of products / exergy efficiency, the TOPSIS selects the optimal objectives of 4.29%/1.13 $/GJ, while the VIKOR selects 4.06%/1.07 $/GJ, respectively. [Display omitted] • Multi-aspect study and multi-criteria optimization of novel polygeneration system. • Use of two renewable energy sources (solar/geothermal) through multi heat recovery. • Employing NSGA-II optimization and fuzzy TOPSIS and fuzzy VIKOR decision makings. • Outcomes are more sensitive to geothermal heater pinch point temperature difference. • TOPSIS selects the highest exergy efficiency, while VIKOR introduces the lowest costs. [ABSTRACT FROM AUTHOR]

When cementing geothermal wells in dry hot rocks, the bottom temperature is often as high as above 200 ℃. Aiming at the problem of strength decline of cement paste caused by high temperature at the bottom of the well under dry-hot rock conditions, this paper directly starts from the chemical composition of cement, and improves this problem by adjusting the ratio of C3S and C2S, and compounding low-heat portland cement with lower calcium-silicon ratio under the synergistic effect of silicon powder. Firstly, the mechanical properties of multiphase C3S-C2S mineral system are the best when C3S∶C2S=1.0. Combined with XRD, TGA and SEM tests, it is known that the reduction of calcium-silicon ratio has a positive effect on the formation of favorable phase xonotlite. Lowgrade cement with lower calcium-silicon ratio is introduced to strengthen G-grade cement. The results show that the compressive strength of "30% G-grade +70% low-grade cement" composite cement system (the ratio of C3S to C2S is 1.07) is 27.34 MPa under the action of 40% silicon powder. The high temperature resistance of cement paste can be greatly improved from the cement itself by properly adjusting the mineral composition in cement to make the ratio of C3S to C2S about 1.0. [ABSTRACT FROM AUTHOR]

The Hellisheidi geothermal power plant, located in Iceland, is a combined heat and power double-flash geothermal plant with an installed capacity of 303.3 MW of electricity and 133 MW of hot water. This study aimed to elucidate the environmental impacts of the electricity and heat production from this double-flash geothermal power plant. In this vein, firstly, the most updated inventory of the plant was generated, and secondly, a life-cycle assessment approach based on the exergy allocation factor was carried out instead of applying the traditionally used allocations in terms of mass and energy. The functional unit was defined as the production of 1 kWh of electricity and 1 kWh of hot water for district heating. The life-cycle stages included the (i) construction, (ii) operation (including abatement operations and maintenance), and (iii) well closure of the geothermal plant. All of the life-cycle stages from construction to dismantling were considered. Finally, the results on the partitioning of the environmental impact to electricity and heat with exergy allocations showed that most of the impact should be charged to electricity, as expected. Furthermore, the distribution of the environmental impacts among the life-cycle stages determined that the construction stage was the most impactful for the electricity and heat production. This result was attributable to the large consumption of steel that was demanded during the construction of the geothermal power plant (geothermal wells, equipment, and buildings). Impacts due to the abatement stage demonstrated that this stage satisfactorily reduced the total impact attributed to the three life-cycle stages of the geothermal power plant. [ABSTRACT FROM AUTHOR]

Based on the geothermal geological conditions and the geothermal resources development and utilization data of Nanyang Basin for many years, the geothermal fields in the basin are divided according to the study of fault structures. According to the pumping test data of geothermal wells, the permeability coefficients of the thermal storage aquifers of the geothermal wells were calculated using the steady-flow Dupuit formula and Kusakin's empirical formula. In this paper, the water conductivity of thermal reservoir is calculated by using the method of line diagram and recovery water level, and the characteristics of thermal reservoir aquifer group, geothermal fluid-flow field, and hydrochemistry are described systematically. Based on the analysis method of groundwater exploitation potential index, the development and utilization potential of geothermal resources is studied, which has certain reference significance for the development and utilization of geothermal resources of sedimentary basins. [ABSTRACT FROM AUTHOR]

Geothermal well recharge is one of the main measures to maintain the production capacity of geothermal field, and sandstone reservoir recharge is a very difficult work. Taking the Leling area as an example, the permeability, porosity, throat characteristics and rock mechanical properties of sandstone thermal reservoirs were studied to clarify the main geological controlling factors that affecting the recharge of sandstone thermal reservoirs. The numerical simulation model of "one mining one irrigation" geothermal development system is established to study its heat transfer characteristics. The results show that the physical properties and water quality characteristics of sandstone thermal reservoir in Leling area meet the sandstone recharge conditions. The larger the distance between the mining and filling wells is, the longer the time required for the thermal breakthrough of the mining wells is, and the smaller the variation range of the mining temperature is. When the reinjection volume of the reinjection well is 65 m³ per hour, the reasonable well spacing with the production well is about 300 m. When the horizontal well distance is constant, with the increasing of flow, geothermal water connection time is faster, the average porosity >30%, the average permeability >1100 mD, the average cumulative thickness of sand layer is greater than 195 m is more conducive to geothermal tail water recharge. In geothermal reinjection field test, the reinjection rate is 100%, the maximum reinjection volume is 82 m³ per hour and reinjection operation is stable. [ABSTRACT FROM AUTHOR]

Understanding injection‐induced microseismicity in geothermal systems can provide insight into reservoir connectedness. However, fault and reservoir complexity are difficult to represent in simple analytical models, which makes it difficult to discern clear relationships from incidental associations. Here, we have used data‐driven models to study how fluid injection and microseismicity are related in the Rotokawa (New Zealand) and Hellisheiði (Iceland) geothermal fields. We tested two classes of model: (a) lagged linear regression of seismicity rate as a function of well injection rates; and (b) systematic extraction of injection time series features that are then evaluated for associations with the seismicity. These models allowed us to determine which wells had the greatest correlation with microseismicity and to explain this association in a reservoir context. Finally, exploring different data types and transformations, we were unable to establish a link between rapid changes in injection rate and seismicity spikes, as suggested by some theoretical models. Plain Language Summary: To better understand the small earthquakes triggered in geothermal fields, we used two kinds of data‐driven models: time series feature engineering (a machine learning method) and the non‐negative linear regression method. We applied these techniques to microearthquakes recorded in the Rotokawa geothermal field, New Zealand, and the Húsmúli reinjection area in the Hellisheiði field, Iceland. We searched for associations and patterns hidden within the noisy injection and seismicity data. These patterns are further complicated by the complex injection schedules that involve several wells that switch off and on over time. We found a stronger association between injection and long‐term microseismicity rate as opposed to short‐term fluctuations driven by noise. We showed that particular injection wells are strongly associated with the microseismicity, which we interpret in terms of reservoir connectedness and stress changes in the rock. We found that injection rate and volume are the most useful data for understanding microseismicity, whereas there was no evidence that rapid injection rate changes triggered seismicity at these two locations. Key Points: Relative associations of geothermal wells with seismicity rate are evaluated using regression analysis and time series feature engineeringReservoir operational changes such as injection transfers between wells can affect the association between wells and microseismicityThere is a stronger correlation between injection and long‐term seismicity rate than short‐term seismicity rate at Rotokawa and Hellisheiði site [ABSTRACT FROM AUTHOR]

Induced seismicity observed during Enhanced Geothermal Stimulation at Otaniemi, Finland is modeled using both statistical and physical approaches. The physical model produces simulations closest to the observations when assuming rate‐and‐state friction for shear failure with diffusivity matching the pressure build‐up at the well‐head at onset of injections. Rate‐and‐state friction implies a time‐dependent earthquake nucleation process which is found to be essential in reproducing the spatial pattern of seismicity. This implies that permeability inferred from the expansion of the seismicity triggering front (Shapiro et al., 1997, https://doi.org/10.1111/j.1365-246x.1997.tb01215.x) can be biased. We suggest a heuristic method to account for this bias that is independent of the earthquake magnitude detection threshold. Our modeling suggests that the Omori law decay during injection shut‐ins results mainly from stress relaxation by pore pressure diffusion. During successive stimulations, seismicity should only be induced where the previous maximum of Coulomb stress changes is exceeded. This effect, commonly referred to as the Kaiser effect, is not clearly visible in the data from Otaniemi. The different injection locations at the various stimulation stages may have resulted in sufficiently different effective stress distributions that the effect was muted. We describe a statistical model whereby seismicity rate is estimated from convolution of the injection history with a kernel which approximates earthquake triggering by fluid diffusion. The statistical method has superior computational efficiency to the physical model and fits the observations as well as the physical model. This approach is applicable provided the Kaiser effect is not strong, as was the case in Otaniemi. Plain Language Summary: Around 60,000 earthquakes are recorded during a span of 50 days where large volumes of water were injected underground for the stimulation of a geothermal well at Otaniemi, near Helsinki, Finland. We compare the observations with numerical simulations to analyze the physical processes that have driven these earthquakes. A model based on physics finds that it is important to use a friction law that includes friction's dependence on slip‐rate and state variables to match the observations. In particular, the model allows relating the spatio‐temporal evolution of seismicity with fluid pressure diffusion in the sub‐surface. An empirical statistical model is also developed using the recorded catalog. The statistical model is shown to perform well in the particular case of the Otaniemi stimulations. The models provide insight into the physical processes that govern induced seismicity. The models presented in this study could help safer operations or the design of mitigation and optimization strategies that may help improve the efficiency of geothermal energy extraction. Key Points: We model induced seismicity from a geothermal well stimulation operation near Helsinki, Finland, using physical and statistical approachesHydraulic diffusivity may be misestimated by the triggering front without accounting for nucleation effects from rate‐and‐state frictionNucleation effects are expected to be significant at short‐time scale injections commonly employed in geothermal well stimulation operations [ABSTRACT FROM AUTHOR]

Reducing the heat loss in wellbore is the key for efficient development of geothermal resource. It is a reliable solution to establish a long-term stable wellbore with good thermal insulation through cementing. In this paper, the cement-based composite thermal insulation material was prepared by using cement as the cementing material, hollow glass beads, foaming agent and stabilizer as main raw materials, and other conventional admixtures. Foams and hollow glass beads can introduce gas with low thermal conductivity into cement, so as to improve the thermal insulation of composite material. Foams are produced by chemical forming process, using foaming agent, which is prepared according electrochemistry and thermodynamics, and the foam stabilizer helps foam distribute in cement slurry stably and uniformly. 10–13% hollow glass beads can significantly reduce the thermal conductivity of hardened cement, without significant adverse effects on the rheology and strength of the material. The thermal conductivity of the composite thermal insulation material can be as low as 0.2998 W·(m·K)−1, which is 62% lower than that of conventional cement, while the compressive strength is 6.10 MPa, meeting the engineering requirement. A thermal-conductivity prediction method is proposed correspondingly based on Maxwell model, and the prediction error of the newly established model is within 2%. This research can provide technical support for efficient development of geothermal resources. [ABSTRACT FROM AUTHOR]

Recently, the development and exploitation of renewables-driven multigeneration systems can be a sensible solution to reduce the limitations of fossil energies and their negative environmental impacts. The combination of two geothermal and solar energies, in addition to reducing the installation costs of solar systems, can support the efficiency improvement of the geothermal-driven energy systems. In addition, the use of suitable downstream cycles in such energy conversion processes can improve thermodynamic and economic performances. The coefficient of performance offered by a generator absorber heat exchanger-based refrigeration cycle can be higher than that by the ejector and absorption refrigeration processes. A comprehensive thermodynamic-conceptual and exergoeconomic evaluations as well as two-objective optimization on a new geothermal-driven multigeneration system, based Sabalan geothermal wells, has been developed in this paper. The proposed system is able to produce power, heating, cooling, and hydrogen fuel. In the developed configuration the geothermal source is considered as the main source of energy production and a linear Fresnel reflector-based solar unit produces a portion of the required thermal power of the system. Further, a single-flash cycle, a water electrolysis unit (based on alkaline electrolyzer cell), and a generator absorber heat exchanger unit are embedded to generate various forms of energy. The overall outcomes indicated that the proposed system can produce 4.1 MW of electric power, 1.67 MW of heating load and 1.46 MW of cooling load. In addition, the hydrogen production rate of the energy process is equal to 5.75 kg/h. In such a context, the considered process can achieve energy and exergy efficiencies of almost 34.2% and 66.3%, respectively. Based on the optimization findings, the energy efficiency can be improved by approximately 9.75% according to the optimal input data. Additionally, the total product unit cost rate can be reduced by almost 4.3% at the same time. Relying on a parametric analysis, variables affecting the performance of the considered system are identified. The conceptual design of the solar unit is also presented regarding the geographical and climatic data of the desired region. [ABSTRACT FROM AUTHOR]

The physicochemical and isotopic characteristics of groundwater and dissolved gas of central Mexico provide valuable information about the geologic and tectonic context of the area. Low–high- enthalpy manifestations (up to 98 °C in springs and more than 100 °C in geothermal wells) are distributed within the San Juan del Río, Querétaro, and Celaya hydrologic basins, located at the boundary between the current Mexican magmatic arc and an extensional continental area with intraplate volcanism called Mesa Central Province. Groundwaters in the study area represent a mixture between the cold water end- member with a Ca2+-Mg2+-HCO3- composition and a hydrothermal end- member enriched in Na+, K+, SO42−, and Cl-. Cold and hot groundwaters δ²H and δ18O plot along the same evaporation lines and do not exhibit a magmatic input. Dissolved and free gas do not show a typical volcanic composition signature. He and Ne isotope composition provide evidence of an important contribution of non-atmospheric noble gases. Although helium composition mainly has a crustal origin (21–83%), the mantellic contribution (1–39%) is higher than expected for an area lacking recent volcanism. A volatile- rich magma aging at depth was discarded as the source of this mantellic helium signature but points out a recent mantellic contribution. Thus, we propose that mantellic helium comes from the sublithospheric mantle into the shallow crust through the highly permeable tectonic boundaries between the geologic provinces, namely the N−S Taxco−San Miguel de Allende and Chapala-Tula fault systems. Mantellic helium flow rates through these fault systems were estimated to have values ranging from 0.1 m/yr to 2.9 m/yr. This He flux range implies that aside from subduction, mantle volatile degassing enhanced by crustal fault systems is the main degassing process in the region studied. [ABSTRACT FROM AUTHOR]

The U-shaped well geothermal production system is proposed on the basis of abandoned oil wells which can achieve the non-interference conversion of "heat extraction without water". Compared with the fracturing enhanced geothermal system, the U-shaped well system is more stable and more achievable. However, there is no comprehensive parametric study of the heat extraction performance of U-shaped well geothermal production system. In this paper, the thermal-hydraulic model of U-shaped geothermal production system is established based on the abandoned oil well. The temporal and spatial evolution of temperature field is analyzed, radiation range of the temperature drop is calculated, the effects of well-layout parameters on heat extraction performance are investigated. For well-layout parameters, the optimal horizontal section length is 1500m, the optimal insulation material length is 1000m. For the engineering parameters, the optimal injection rate is 1500m3/d and the optimal injection fluid temperature is 288.15K to obtain a higher heat extraction power. The discontinuous mode can sustainably guarantee better heat extraction performance compared with continuous mode. These findings can provide some reasonable suggestions for the deep geothermal development. [Display omitted] [ABSTRACT FROM AUTHOR]

The stability of cement sheath under high temperature and high pressure is one of the most critical issues for the durability of geothermal well systems. In this study, a two-dimensional plane-strain finite element code was developed to investigate the coupled thermomechanical behaviors of the casing-cement-formation system. Different from previous linear elastic analyses, a thermoelasto-plastic constitutive model based on the thermodynamic theory was adopted for the cement sheath. It is shown that the finite element simulations using the proposed model provide a more accurate and realistic prediction of stress--strain responses of the cement sheath under high temperature. The results demonstrate that the radial stress concentration and the tensile strain concentration occur at both the cement--casing interface and the cement--formation interface, where the cement sheath is most likely to fail. High strength and low stiff- ness in the cement sheath and the formation are preferred for the integrity of the system. Both large thermal cycles and large differences between the internal fluid pressure and the external pressure should be avoided during operation. The new code is an alternative tool for guiding the geothermal well design. The finite element framework described herein is universal for other thermo-mechanical applications, such as energy foundations and energy tunnels. [ABSTRACT FROM AUTHOR]

Knowledge of fluid flow temperature along the wellbore can be useful for a realistic calculation of the total heat production in geothermal wells. Therefore, wellbore modeling is an important part of the characterization of geothermal wells and predicting their future behavior. This study describes the dynamic transport of transient heat and fluid dynamic transport inside a geothermal well and also heat loss in the surrounding rocks. The objective of this investigation is to accurately predict temperature and pressure variations within the producing well GPK2 of the geothermal site Soultz-sous-Forêts. The temperature effect of possible leakage zones in the reservoir section of the production casing was also considered. A single-phase flow modeling was carried out using Comsol software. Our study highlights that the properties of the flow (well flow rates for steady and unsteady flow), of the fluid (density, viscosity, chemical composition), and the well (diameter, length, thermal properties of environments) are parameters, which directly influence the pressure and temperature profiles of the well. A sensitivity study has been carried out to demonstrate the role that these parameters play in the heat transport occurring in this well. According to our simulated results, during the flow of hot water in GPK2 well the production temperature of water decreases by dozen degrees of its downhole temperature. It is also shown that the leakage zone affects the temperature, decreasing it at least by 1–2°C. [ABSTRACT FROM AUTHOR]

Two-phase flows are found in almost all areas of technology. For example, tubular evaporators, boiling water reactors, boiler blowdown systems, heaters, boilers, gas lift pumps, oil and geothermal wells, oil and gas pipelines, refrigerators, process pipelines, and condensers. Two-phase flows are classified as mixtures. According to the composition of the mixture are divided: (a) for single-component (or one-component) - vapor-liquid flows; (b) multicomponent - gas-liquid flows. One-component mixtures consist of the same substance in different states of aggregation. This can be not only vapor-liquid, but also a mixture of liquid or vapor with a solid phase, a water-ice mixture, or a vapor flow with ice particles, for example, in sublimation installations. Multicomponent mixtures are a combination of substances of different physical nature. These include not only gas-liquid flows, but also, for example, mixtures of air and sand, water and oil. The paper presents the main attention is paid to the movement of two-phase flows in the pipeline. [ABSTRACT FROM AUTHOR]

The Ilgın geothermal field that is the oldest and most important spa of the Konya Region is located in Central Turkey. The Ilgın geothermal field has five geothermal wells and three hot water springs with flow rates of 40–130 L/s, temperatures 26–42°C and depths of 120–300 m. In the present study, detailed hydrogeochemical investigations are carried out to understand the geothermal energy potential of the thermal waters. The chemical properties of the cold and hot waters collected from the field were determined and the classification and usage possibilities of the waters were investigated. The thermal well water samples have the same Cl, B and Li concentrations in rainy and dry seasons, but those of the other samples are variable in rainy and dry seasons. This suggests the surface water mixtures were constant in hot water wells or that the precipitation times were long. In the Li‐Rb‐Cs diagram, the Li/Cs ratios of hot waters are 6.53–8.61 in the rainy period and 6.28–8.47 in the dry period, indicating that they are derived from acidic rocks. According to their isotopic composition, it can be said that the waters are of meteoric origin. According to the Langelier, the Ryznar and the Puckorius Saturation Indexes, the waters can precipitate carbonate. The waters interacted with gypsum and anhydrite zones based on the Halite Saturation Index, while the waters are associated with dolomite‐rich rocks in terms of the Dolomite Saturation Index. Silica and cation geothermometers except Na‐K applicated to the Ilgın geothermal waters yielded similar reservoir temperature estimates (e.g., 13–76°C for rainy period, 10–80°C for dry period). However, reservoir temperature from the other estimates (Na‐K geothermometers, enthalpy‐chloride diagram and enthalpy‐silica mixture model) are higher than 103°C. Taken as whole, the temperature estimates exhibit little agreement between the different geothermometry calculations suggesting that the Ilgın geothermal waters represent immature waters, and water‐rock equilibrium in the geothermal reservoir was not fully attained. [ABSTRACT FROM AUTHOR]

The aim of the presented work was an attempt to verify the geothermal conditions in the Polish lowlands (lower jurassic and lower cretaceous reservoir) based on new geological information. The paper presents geothermal conditions in the Polish lowlands according to the state of recognition at the end of 2022 in order to update the hydrogeothermal conditions in selected regions. Based on the scientific and research works published so far as well as numerous geothermal investments, and geological information from twenty-three new exploratory drilling events performed in the years 2000-2022 (nineteen of which were performed/documented after 2006), the authors undertook to update forecasts of the top surface of lower jurassic and lower cretaceous formations, the total thickness of these formations and the potential discharge of wells. The analysis was performed using the Qgis desktop 3.24.1 software, a cross-platform and free open-source geoinformation software application (gis) that enables the viewing, editing and analyzing of spatial data and the creation of maps. The correction covered the course of the isolines on all six analyzed maps. The presented analysis made it possible to make a spot correction of the forecasted course of the isoline in relation to the maps published earlier in the Atlas of geothermal resources in the Polish Lowlands. Mesozoic formations developed in 2006, edited by Wojciech górecki. information obtained from newly drilled geothermal boreholes enabled the local correction of the forecasted values of individual parameters while maintaining the general trend. [ABSTRACT FROM AUTHOR]

Hydrated bentonite is considered an alternative subsurface sealing/plugging material for deep geo-energy wells. However, the knowledge related to this application and the corresponding properties of bentonite is still lacking. This includes the mechanical properties at the interface of bentonite plugs with the adjacent materials (surrounding rock or casing steel) and the mechanical stability of plugs under downhole in-situ conditions. In this work, we performed experiments investigating the interface shear properties and shear strength of a bentonite plug under various settings for deep geo-energy applications, such as hydrocarbon and geothermal wells. The interface's shear properties against various adjacent materials and fluid conditions were characterized. The influence of chemical exposure, the salinity of the curing fluid, fluid pH, pressure, and temperature on bentonite's mechanical stability was evaluated in a small- and large-scale setting. The latter was performed using realistic casing sizes and placement methods, relevant for the field application. The experimental results show that the averaged shear strength of the bentonite plug interface is 13.3 kPa and 9.1 kPa when cured in freshwater and seawater, respectively. The increase in strength with increasing curing pressure, temperature, and fluid pH was characterized for the first time. The interfacial properties of cohesion and friction angle vary with different surrounding materials. They are also influenced by the saturating condition and salinity of the saturating fluid. Based on the experimental results, a bentonite plug with a minimum length of 15–43 m placed in casings of 7–5/8″ to 13–3/8″ would be sufficient to meet the necessary criteria of the Dutch regulators as an isolating material for well abandonment. Highlights: The bentonite's mechanical stability for plugging operations in deep geo-energy wells and the properties of the bentonite interface are evaluated under different in-situ downhole conditions.. The interfacial shear strength of bentonite plugs cured in freshwater and seawater is approximately 13.3 kPa and 9.1 kPa. A bentonite plug with a minimum length between 15 and 43 m, varied with casing sizes, would comply with the verification requirement of the Dutch regulators to seal deep geo-energy wells permanently. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is an emerging technology for acquiring seismic data on virtual sensors densely distributed along an optical fiber. The broadband response of the sensors, associated with the possibility of deploying fiber optic cables in harsh conditions and the relatively moderate cost of this sensing element gives clear perspectives for DAS in geothermal wells to contribute to the monitoring operations of geothermal plants. However, the technical feasibility of managing the large flow of data generated by the DAS and the suitability of the strain-rate acquisitions to monitor locally induced seismicity was yet to be assessed. We propose a monitoring concept establishing DAS as an effective component of the seismic monitoring of the Schäftlarnstraße geothermal plant (Munich, Germany). The underlying data management system links the existing on-site infrastructure, including the fiber optic cable deployed in one of the site's injection wells and the associated DAS recorder, to a cloud Internet-of-Things (IoT) platform designed to deliver both a secure storage environment for the DAS acquisitions and optimized computing resources for their processing. The proposed solution was tested over a period of six months and showed the feasibility of efficiently acquiring and processing the large flow of continuous DAS data. For seismic risk mitigation purposes, we additionally investigate the potential of the monitoring concept to tend towards real-time monitoring. The processing outcomes, focusing especially on two detected local seismic events, demonstrates the relevance of DAS from geothermal wells for the (micro)seismic monitoring of the geothermal site. Despite the noisy operational conditions, the applied processing workflow takes advantage of the sensors' high spatial density for data denoising and event triggering and highlights that higher detection sensitivity than conventional seismometers can be achieved. From a different perspective, further analyses of the DAS records confirm the logging capabilities of the technology, especially regarding well completion integrity. The 6-months test period shows that permanent DAS can be integrated as a routine seismic monitoring component of geothermal plants and advantageously complement surface seismometer based networks, especially in urban environments. [ABSTRACT FROM AUTHOR]

In China, sandstone geothermal reservoirs are large in scale and widely distributed, but their exploitation is hindered by low recharge efficiency. In this paper, an unblocking and permeability enhancement technology using a rotary water jet for low recharge efficiency wells in sandstone geothermal reservoirs is proposed to solve this problem. This paper presents a series of studies about the proposed technology, including experiments, simulation and field application. Firstly, an experiment was carried out to verify the scale removal effect of a high-pressure water jet on the inner wall of the screen tube and its impact on sandstone. Secondly, the numerical models of the rotary jet flow field in the wellbore were established by ANSYS Fluent to study the influence of parameters. Finally, based on the simulation and experiment results, a rotary jet tool applicable to unblocking and descaling low-efficiency wells was designed, and a field application for low-efficiency wells in sandstone thermal reservoirs was conducted. The study results show that the unblocking and permeability enhancement technology using a rotary water jet is effective in removing the blockages and improving the permeability near the well. In conclusion, the presented technology can solve the problem of low efficiency during the reinjection of cooled thermal waters back into sandstone geothermal reservoirs and has great effectiveness in field application. [ABSTRACT FROM AUTHOR]

Asal rift is an aerial rift segment resulting from the westward propagation of the Aden ridge into the Afar Depression. Geothermal manifestations such as hot springs and fumaroles, fault creep, conductivity anomaly, and high geothermal gradient were observed both at the surface and in the subsurface. Despite many scientific works conducted in Asal to understand the rifting mechanisms, the hydrothermal fluid circulation still needs to be evaluated since it is based on simplified conceptual models. To further contribute and progress toward a quantitative evaluation of fluid circulation, a 2D numerical model perpendicular to the rift axis was developed with the objective of better understanding the role of subsurface anisotropy in fluid flow and heat transfer in the Asal rift. Numerical modeling of multiphase flow and heat transfer was carried out with an equivalent porous medium intersected by fault zones having greater permeability. Horizontal anisotropic permeability and magmatic fluid release were taken into account with different simulation scenarios. The results indicate that fault zones act as recharge/discharge areas depending on their location, permeability, and number. Simulations considering horizontal anisotropic permeability allowed the reproduction of the thermal state observed in geothermal wells with the expected general pattern of fluid circulation in the Asal rift. Comparing our result with a recent study made with a 2D numerical modeling parallel to the rift axis, we suggest the presence of a saddle point where fluid flow is both to the northeast and to the southwest direction of the rift. Moreover, magmatic fluid release assumed in two simulation scenarios showed to have an impact on the hydrological behavior of fault zones and facilitate the development of super-critical flow at the center of the rift. [ABSTRACT FROM AUTHOR]

It is difficult for the commonly used Class G oil well cement to withstand the high-temperature environment of geothermal wells, and it is easy to deteriorate the mechanical properties and damage the integrity of the cement sheath. Industrial solid waste red mud can be used as supplementary cementing materials (SCMs) to improve its mechanical properties at high temperatures. In addition, compared to Class G oil well cement, high belite cement (HBC) has lower energy consumption and better mechanical properties at high temperatures. In this study, the mechanical properties of HBC as a gel material and quartz sand and red mud as SCMs were studied at high temperatures. The ratio of HBC to SCMs and the ratio of quartz sand to red mud in SCMs were optimized using the response surface method (RSM). The response surface was established using the three-level factorial design model, which fit well with the experimental data. The optimization results show that the best mass ratio of SCMs/HBC is 37.5% and that the best quality ratio of quartz sand/red mud is 9 under the curing conditions of 180 °C. However, the best mass ratio of SCMs/HBC is 49.3%, and the best quality ratio of quartz sand/red mud is 7 under 220 °C. With the addition of SCMs, the silicon-to-calcium ratio of HBC hydration products decreases, and high-temperature-stable xonotlite and tobermorite can be formed. After adding SCMs, the cement sample is denser without obvious cracks. [ABSTRACT FROM AUTHOR]