Search

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]

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]

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]

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]

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]

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]

In order to study the effect of high temperature on the permeability characteristics of the surrounding rock of the geothermal well, the steady-state method was used to conduct experiments on the permeability of sandstone under different stress states under the action of 200 °C, 400 °C, 600 °C and 800 °C. The correlation between permeability and different temperature, seepage pressure and confining pressure was studied, and a temperature–permeability (T–P) model was established based on the principle of effective stress. The experimental results show that: (1) The reduction rates of density and wave velocity increase sharply from 0.57% and 15.08% at 600 °C to 1.79% and 45.68% at 800 °C and when the temperature was equal to 800 °C, the mass loss rate and the volume increase rate reached 0.96% and 1.36%, respectively. (2) The permeability increases gradually with temperature, and the permeability below 600 °C has a small increase, and the permeability between 600 and 800 °C will have a step change. (3) The permeability of sandstone decreases gradually with the negative exponential relationship of confining pressure after high temperature treatments. (4) Based on the experimental data, the rationality of the T–P model is verified. The results of the study can provide reference value for the stability assessment of the geothermal well envelope. [ABSTRACT FROM AUTHOR]

An innovative methodology is introduced to study abandoned oil exploration drillings for possible geothermal energy production at a test area in northeast Hungary. An evaluation method supported by robust statistical analysis was elaborated to provide the possible future investors with adequate technical and earth-science related information for their decision-making processes. All the available data of 161 abandoned hydrocarbon wells, with different physical conditions, were examined based on the proposed evaluation system to provide information about the geothermal energy potential for each well, as well as over a bigger area. The abandoned wells and their environments, the quantity of stored heat, and the fluid temperature and geothermal heat were the key parameters determined, which are critical when considering geothermal energy utilization or thermal water production. The maximum amount of stored energy was determined as the sum of the amount of energy extractable from the rock and the fluid. The heat stored in the rock was determined by basin modelling. The evaluation process, using one-dimensional (1D) basin modelling and 3D lithological-stratigraphic modelling, was successfully applied in the pilot area. The maximum amount of heat stored in the fluid can be determined by subtracting the heat stored in the rock from the total heat. Drilling and completing geothermal wells are rather expensive in Hungary, depending on the depth and the types of geological formations. The application of this research could greatly reduce the cost and risk of creating new geothermal energy systems based on production wells or abandoned wells in Hungary or elsewhere. [ABSTRACT FROM AUTHOR]

Radial Jet Drilling (RJD) is a stimulation technique to increase a well's performance through creation of multiple laterals of up to 100 m long. The technique has been used in the petroleum industry for several years and recently also for geothermal reservoirs. Interpretation of well tests of a well with multiple laterals may become problematic if the effect of the laterals is not correctly modelled. In this work it is investigated what the impact of RJD laterals is on the pressure transients for both single and dual porosity reservoirs. A semi-analytic model for the calculation of the transient well pressure that accounts explicitly for the RJD well geometry is developed and validated with a detailed numerical simulation. The results show that changes in the lateral configuration affect the pressure transients significantly. In particular for single porosity media, the laterals affect the pressure transients in ways that cannot be captured by representing the stimulation by a skin factor. Since the RJD process is unsteered and the exact configuration of the laterals uncertain, the model may potentially assist in estimating the effectiveness of the stimulation such as the achieved reach of the laterals. Although the work was carried out in the context of RJD application in geothermal reservoirs, the presented model approach can be extended to multi-lateral wells in oil or gas reservoirs. [ABSTRACT FROM AUTHOR]

The Krabi saline hot spring (Khlong Thom Hot Spring) located in southern Thailand has been recognized as a unique geothermal spring attraction due to its high-salinity geothermal groundwater. Studies have been performed to understand the mechanisms of saltwater intrusion into the geothermal aquifers. However, little is known about how the high-salinity groundwater affects the local geological structures, geological materials, and groundwater aquifers. Therefore, we performed integrated geological well measurements, geophysical electrical resistivity tomography (ERT) surveys, and geochemical analyses for major ions (cations and anions) and geothermometers (silica and cation) to investigate the local geological settings and the sources of salinity in the Krabi saline geothermal system. The water samples from the natural hot spring pools and geothermal wells were uniformly of the Cl−-Na+ type with high total dissolved solids (TDS) contents ranging from 12,663 to 15,180 mg/L, but the nongeothermal water was considered to be shallow groundwater of the Na+-HCO3− type with lower TDS contents. Once the trapped saltwater intruded into the wetlands (saltmarshes), its chemical composition was modified by the freshwater/groundwater mixing processes active in the development of shallow geothermal reservoirs. However, a silica-quartz geothermometer was utilized, and the calculated reservoir temperatures ranged from 83 to 86 °C, unlike the cation and silica-chalcedony geothermometers, which were not likely to be applicable for estimating reservoir temperatures in this geothermal system. Moreover, the ion ratios indicated that the water-rock interactions occurring within the geothermal reservoir, mostly related to its nonequilibrium state, might have little effect on the quality of the geothermal groundwater. ERT interpretation was carried out to compare the characteristics of the geological materials obtained directly from the geothermal wells with their apparent resistivity values corresponding to the obtained 2D-ERT profiles. Low resistivity values, ranging from 1 to 10 Ω-m, may have arisen from the dominating influence of the freshly mixed saltwater, which mainly originated via saltwater intrusion into the shallow aquifer on the study site. Therefore, 2D-ERT can be highly useful for detecting changes in thickness and detecting the presence of local faults in the Krabi saline geothermal field. In comparison, geothermal water rose to the surface due to local faults and this finding was well associated with a tectonic junction of the Krabi geological setting. These research findings suggest that governmental agencies should consider combining the results from academic geoscience studies with business objectives to develop a sustainable developmental plan for the geothermal spring attractions of Thailand. [ABSTRACT FROM AUTHOR]

Formation blockage caused by solid particle invasion and migration is the main reason for the decline of the geothermal reinjection capacity, especially in the weakly consolidated sandstone formation. In this paper, a novel evaluation model for the formation blockage risk in the geothermal water reinjection was established based on the particle bridging principle. Three kinds of solid particles were considered in this model, including the clay-sand particles self-generated in formation, and the invasive scale and suspended particles in reinjected water. A sensitivity analysis of factors influencing formation blockage risk was carried out. The results show that when self-generated particles, suspended particles, and scale particles act alone, the reinjection capacity decreases by 46.72%, 65.44%, and 42.90% after 5 years, referring to the reinjection test of a geothermal well in Xining Basin; when the above particles act at the same time, the reinjection capacity will be lost by 97.12% after 5 years, and 0.5 years later the well will have to be shut-in. Among the sensitive factor affecting formation blockage, the key parameters are the most sensitive, followed by the reinjection pressure, and finally, the composition and concentration of solid particles have less influence. Using key parameters including deposition coefficient, starting coefficient, and K-C coefficient in this model, the deposition range, migration mass, and the porosity–permeability relationship under different blockage conditions can be described flexibly. [ABSTRACT FROM AUTHOR]

Numerical reservoir modeling plays an important role in understanding and predicting the performance of geothermal reservoirs to varying exploitation schemes. In this study, four parameters including thermal breakthrough time, water level and vertical displacement at the production wells and the recoverable energy in the licensed region are selected to assess the potential exploitation schemes. An integrated model combining the simplified 1D geothermal well model and the 3D geothermal reservoir model is developed to simulate the fully coupled thermo-hydro-mechanical (THM) processes in geothermal reservoirs including multiple wells, and the measured surface settlement data in the Geysers geothermal field is used to validate the reasonability and efficiency of the developed modeling method. A case study of the Rongcheng geothermal field, China, is presented to clarify the important role of coupled THM processes in the sustainable exploitation of geothermal resources. The results show that the developed integrated model is a robust simulation tool to understand and predict the performance of city-scale geothermal fields under different patterns of well groups. The production wells may not reach the designed lifetime due to various natural or artificial reasons, so the optimal well patterns should be designed to maximize the recoverable geothermal energy considering the natural properties of geothermal reservoirs. Highlights: Coupled thermo-hydro-mechanical processes are considered in an integrated geothermal reservoir model. Assessment criteria of sustainable exploitation of geothermal resources in the licensed region are defined. The responses of the Rongcheng geothermal field under different patterns of well groups are studied. [ABSTRACT FROM AUTHOR]

The tracer test has become one of the most important methods to determine the hydraulic connection between injection and production wells in a geothermal reservoir. Various chemicals such as fluorescein, radioactive chemicals, salts, and alcohols are used as tracers in geothermal systems. Breakthrough curves of chemical concentrations are matched with analytical models to identify the most representative reservoir model and to obtain important reservoir parameters such as swept pore volume, average fluid velocity, and dispersivity. In this study, we have used sodium fluorescein as a tracer to understand the reservoir characteristics of the Salihli geothermal field in Western Anatolia. The hydraulic connectivity between injection and production wells was identified. The study aimed to determine the most representative reservoir model for Salihli geothermal reservoir. The nonlinear least square method was applied to obtain matches between the analytical models and actual field data. The most representative model was found by evaluating the sum of the square residual. The study includes moment analysis, Dkystra-Parsons, and Lorentz coefficients for reservoir characterization. The study also used flow-capacity and storage-capacity relation to quantify reservoir characteristics for different parts of the reservoir. Fluid velocity in the Salihli geothermal reservoir changes between 2.8 and 19.2 m per hour. Calculated swept pore volume was found between 2 to 13 thousand cubic meter between injection and production wells. [ABSTRACT FROM AUTHOR]

The paper considers the development of an eco-friendly acidic composition for treating high-temperature carbonate reservoirs. The nontoxic, high-boiling glycolic acid and eco-friendly additive components makes this composition suitable for treating geothermal wells that comprise a clean energy source. [ABSTRACT FROM AUTHOR]

Zonal distribution of hydrothermal alteration in and around geothermal fields is important for understanding the hydrothermal environment. In this study, we assessed the performance of three unsupervised classification algorithms—K-mean clustering, the Gaussian mixture model, and agglomerative clustering—in automated categorization of alteration minerals along wells. As quantitative data for classification, we focused on the quartz indices of alteration minerals obtained from rock cuttings, which were calculated from X-ray powder diffraction measurements. The classification algorithms were first examined by applying synthetic data and then applied to data on rock cuttings obtained from two wells in the Hachimantai geothermal field in Japan. Of the three algorithms, our results showed that the Gaussian mixture model provides classes that are reliable and relatively easy to interpret. Furthermore, an integrated interpretation of different classification results provided more detailed features buried within the quartz indices. Application to the Hachimantai geothermal field data showed that lithological boundaries underpin the data and revealed the lateral connection between wells. The method's performance is underscored by its ability to interpret multi-component data related to quartz indices. [ABSTRACT FROM AUTHOR]

The water temperature at the outlet of the production well is an important index for evaluating efficient geothermal exploration. The arrangement mode of injection wells and production wells directly affects the temperature distribution of the production wells. However, there is little information about the effect of different injection and production wells on the temperature field of production wells and rock mass, so it is critical to solve this problem. To study the influence mechanism of geothermal well arrangement mode on thermal exploration efficiency, the conceptual model of four geothermal wells is constructed by using discrete element software, and the influence law of different arrangement modes of four geothermal wells on rock mass temperature distribution is calculated and analyzed. The results indicated that the maximum water temperature at the outlet of the production well was 84.0 °C due to the thermal superposition effect of the rock mass between the adjacent injection wells and between the adjacent production wells. Inversely, the minimum water temperature at the outlet of the production well was 50.4 °C, which was determined by the convection heat transfer between the water flow and the rock between the interval injection wells and the interval production wells. When the position of the model injection well and production well was adjusted, the isothermal number line of rock mass was almost the same in value, but the direction of water flow and heat transfer was opposite. The study presented a novel mathematical modeling approach for calculating thermal exploration efficiency under various geothermal well layout conditions. [ABSTRACT FROM AUTHOR]

Low-to-medium temperature geothermal fluids in the granite regions of southeastern China are an important renewable energy resource, but they are also a source of contamination containing highly toxic elements such as fluoride and arsenic. This study analyzed the origin of the geothermal fluids in a regional-scale hydrogeological unit in the city of Xiamen, China, based on isotope and hydrochemical analyses. The Br/Cl ratios suggested that the inland geothermal fluid is merely recharged by rainwater from the mountain edge, while the coastal geothermal fluid is originally recharged by the seawater and later mixed with rain-derived groundwater. The geothermal water featured high SiO2 and detectable Zn concentrations. The former reflects the significant water–granite interaction along the flow path, and the latter indicates the active hydraulic connection between surface waters, shallow aquifers and deep geothermal fluids. High radon content was detected near the deep conductive fault adjacent to a geothermal well, demonstrating that the fault damage zone acts as a major conduit for upward transport of the deep geothermal fluid. As a result, the fault damage zones developed in the granite are necessary for the formation of geothermal water, which leads to the uneven distribution of geothermal water in the subsurface. High-temperature geothermal water can be found in those regions with fairly sparse fault damage zones. In contrast, in the region with high-density fault activities, the active communication between shallow cool water and deep geothermal fluids can decrease the water temperature. [ABSTRACT FROM AUTHOR]

Achieving crack propagation and rapid deterioration of high-temperature rock masses by using cooling shocks is important for improving the efficiency of low-permeability oil and gas production, geothermal well pumping, and other engineering facilities. In this study, the temperatures of four groups of granite samples with holes were set as 150, 350, 550, and 750 °C. To study the crack propagation in high-temperature granite suffering from different cooling shocks, the cooling shock temperatures were set as −20, 0, 20, and 25 °C in experiments and an RFPA2D-Thermal numerical simulation. The results indicated that in the range of 350–550 °C, there is a critical temperature for the sudden change of the crack macroscopic shape. Numerous open cracks appeared on the rock surface, and the thermal damage caused by the cooling shocks was significantly enhanced within the temperature range. Additionally, under the action of the cooling shocks, cracks were initiated in the high-temperature granite at the boundary of the cooling shock hole and the sample and extended radially to the interior of the sample. Moreover, in the process of crack propagation, there was always an annular heat-balance zone inside the rock. Thus, the cracks generated at the boundary of the cube are not connected to the cracks formed at the center hole. A larger temperature gradient in the rock led to a higher crack propagation rate, larger penetration depth, and higher density of cooling-induced cracks. The results of this study can not only improve the permeability of reservoir rocks but also have important reference value for rock engineering in high-temperature environments. [ABSTRACT FROM AUTHOR]

Geothermal district heating development has been gaining momentum in Europe with numerous deep geothermal installations and projects currently under development. With the increasing density of geothermal wells, questions related to the optimal and sustainable reservoir exploitation become more and more important. A quantitative understanding of the complex thermo-hydraulic interaction between tightly deployed geothermal wells in heterogeneous temperature and permeability fields is key for a maximum sustainable use of geothermal resources. Motivated by the geological settings of the Upper Jurassic aquifer in the Greater Munich region, we develop a computational model based on finite element analysis and gradient-free optimization to simulate groundwater flow and heat transport in hot sedimentary aquifers, and numerically investigate the optimal positioning and spacing of multi-well systems. Based on our numerical simulations, net energy production from deep geothermal reservoirs in sedimentary basins by smart geothermal multi-well arrangements provides significant amounts of energy to meet heat demand in highly urbanized regions. Our results show that taking into account heterogeneous permeability structures and a variable reservoir temperature may drastically affect the results in the optimal configuration. We demonstrate that the proposed numerical framework is able to efficiently handle generic geometrical and geological configurations, and can be thus flexibly used in the context of multi-variable optimization problems. Hence, this numerical framework can be used to assess the extractable geothermal energy from heterogeneous deep geothermal reservoirs by the optimized deployment of smart multi-well systems. [ABSTRACT FROM AUTHOR]

The Jimo hot spring in Shandong Peninsula, China, is a typical coastal geothermal system. The geothermal water has a very high salinity (10.8 g/L) and the origin of the salt is key to utilization of this geothermal resource. A systematic investigation of the hydrochemistry and isotopes (δ11B, 87Sr/86Sr, δ18O, δD, 13CDIC and 14CDIC) of water from 14 geothermal wells was conducted. The results show that the geothermal waters from the high-temperature center and eastern part of the geothermal field are Cl-Na·Ca-type waters with Br/Cl (8 × 10−4–1.0 × 10−3), Na/Cl (0.63–0.70) and δ11B values (15.9–17.2‰) that are lower than those of seawater. The western geothermal waters are dominated by Cl-Na-type waters with Br/Cl and Na/Cl values similar to those of seawater. The depleted δD and δ18O compositions and the corrected 14CDIC age suggest that Jimo geothermal waters are mixtures of late Pleistocene to early Holocene and younger meteoric waters. An improved Br/Cl-Na/Cl diagram, ion mass balance calculations and δ11B values indicate that halite and K-salt dissolution and subsequent cation exchange formed the dominant Cl-Na·Ca-type geothermal water, and this was then modified into a small amount of Cl-Na-type water in the western area by mixing with minor seawater entrapped in the unconsolidated sediments. The 87Sr/86Sr ratios (0.710613–0.710726) of the geothermal waters reflect water–rock reactions in the sandstone. The improved Br/Cl-Na/Cl diagram, Piper plot and boron isotopic dataset containing saline waters from coastal geothermal systems worldwide further confirm that the salinity in the Jimo geothermal water originated from dissolution of marine evaporites. [ABSTRACT FROM AUTHOR]

We describe the design and implementation of a traffic light system (TLS) created for the stimulation phase of a 6.1-km-deep geothermal well in the Helsinki area, Finland. Because of the lack of local seismic data to calibrate the TLS, the TLS thresholds have been proposed on the basis of two parameters: acceptable ground motion levels and probabilities to reach these levels, which were then used to establish TLS magnitudes. A peak ground velocity (PGV) of 1 mm/s associated with a ML ≥ 1 event, or a ML ≥ 1.2 event alone, triggered an Amber alert. A PGV of 7.5 mm/s associated with a ML ≥ 2.1 event triggered a Red alert, where ML was a local "Helsinki" magnitude. Specific thresholds based on PGV and peak ground acceleration were gathered for critical infrastructure sites and related to earthquake magnitudes in a probabilistic way. The implementation of the TLS during the stimulation showed that the selected thresholds were reasonably conservative. Some of the Amber events were reportedly felt or heard, but the public opinion remained very favourable to the project. Measured ground motions were too low to have any impact on the built environment and the stimulation was able to proceed without being impaired by the occurrence of a Red event. Seismic data acquired during the stimulation and lessons learnt are presented and used to revisit the TLS thresholds for potential future stimulations. [ABSTRACT FROM AUTHOR]

CCWater is a computer program developed for the application of extensively being used triangular diagrams for chemical classification and for identification of equilibrium conditions of waters. The program for these diagrams were developed as a Microsoft Excel™ spreadsheet application and compiled using Visual Basic™ 6.0, which has enabled to execute an Excel™ file from a program created by Visual Basic™ 6.0. The performances of all the four diagrams were validated by applying for the same chemical concentration data of the waters that was used by the original authors of these diagrams. The results obtained from this program were consistent with those of the original authors of these diagrams. As an example, CCWater is applied for chemical characterization of thermal waters from springs and geothermal wells of five geothermal fields of Mexico, in which four are electricity producing fields (Cerro Prieto, CPGF; Las Tres Vírgenes, LTVGF; Los Azufres, LAGF, and Los Humeros, LHGF) and the fifth geothermal field (La Primavera, LPGF) is in exploration stage. Majority of the reservoir temperatures estimated by Na/K geothermometers from geothermal well waters of CPGF, LAGF, LTVGF, and LPGF are within the limits of accepted differences (within ±20%) comparing to the average BHTs of the respective geothermal well. The good performances of the geothermometers in predicting the reservoir temperatures from well waters is expected because the well waters are fully equilibrated and are of Cl type, thus fulfilling the basic requirements. In contrary, though the spring waters of LHGF and LAGF are of HCO3 type (immature) and exhibited no equilibrium conditions, they also predicted reliable reservoir temperatures. This unusual but important observation in the behavior of the spring waters of LHGF and LAGF was made possible to known by chemical classification of these waters in to different groups and estimation of the reservoir temperatures by considering each water type of a geothermal field as a separate group. This application has shown the importance of chemical type of water and the existing chemical equilibrium conditions in successful using these waters in estimation of the reservoir temperatures, and hence the necessity of the computer program like CCWater. The software CCWater is easy to use, reliable, freely available and will be useful in the application of ternary diagrams for chemical characterization and to evaluate the equilibrium conditions of geothermal waters, particularly during the initial stage of geothermal exploration. [ABSTRACT FROM AUTHOR]

The Raft River geothermal field, located in southern Idaho, roughly 100 miles northwest of Salt Lake City, is the site of a Department of Energy Enhanced Geothermal System project designed to develop new techniques for enhancing the permeability of geothermal wells. RRG-9 ST1, the target stimulation well, was drilled to a measured depth of 5962 ft. and cased to 5551 ft. The open-hole section of the well penetrates Precambrian quartzite and quartz monzonite. The well encountered a temperature of 282 °F at its base. Thermal and hydraulic stimulation was initiated in June 2013. Several injection strategies have been employed. These strategies have included the continuous injection of water at temperatures ranging from 53 to 115 °F at wellhead pressures of approximately 275 psi and three short-term hydraulic stimulations at pressures up to approximately 1150 psi. Flow rates, wellhead and line pressures and fluid temperatures are measured continuously. These data are being utilized to assess the effectiveness of the stimulation program. As of August 2014, nearly 90 million gallons have been injected. A modified Hall plot has been used to characterize the relationships between the bottom-hole flowing pressure and the cumulative injection fluid volume. The data indicate that the skin factor is decreased, and/or the permeability around the wellbore has increased since the stimulation program was initiated. The injectivity index also indicates a positive improvement with values ranging from 0.15 gal/min psi in July 2013 to 1.73 gal/min psi in February 2015. Absolute flow rates have increased from approximately 20 to 475 gpm by February 2 2015. Geologic, downhole temperature and seismic data suggest the injected fluid enters a fracture zone at 5650 ft and then travels upward to a permeable horizon at the contact between the Precambrian rocks and the overlying Tertiary sedimentary and volcanic deposits. The reservoir simulation program FALCON developed at the Idaho National Laboratory is being used to simulate and visualize the effects of the injection. The simulation model uses a discrete fracture network generated for RRG-9 using acoustic borehole imaging and analysis of microseismic activity. By adjusting the permeability of the fractures, a pressure history match for the first part of the stimulation program was obtained. The results of this model indicate that hydraulic fracturing is the dominant mechanism for permeability improvement for this part of the stimulation program. [ABSTRACT FROM AUTHOR]

We provide the mathematical development of a gradient-based algorithm based on the augmented Lagrange approach that is applicable for multiobjective optimization. The multiobjective optimization procedures considered are the standard weighted sum and the normal boundary intersection methods as well as constrained versions of these methods developed previously by the authors to overcome non-differentiability issues. The mathematical development is general and applies to cases where nonlinear equality and inequality constraints are present, but the reservoir engineering applications considered in the paper are focused on examples where only bound constraints are present. The reservoir engineering examples considered pertain to the estimation of optimal well controls (pressures or rates at which injection and production wells are operated) that optimize three conflicting objectives involving different cost and risk measures under geological uncertainty. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1007/s12145-021-00694-3. B Correction to: Earth Science Informatics b https://doi.org/10.1007/s12145-021-00694-3 In the original published version of this article, the affiliation of first author Kazuya Ishitsuka, " B Division of Sustainable Resources Engineering, Hokkaido University, Kita-ku, Sapporo, Japan" b should be included under the affiliation section since the said affiliations was Kazuya Ishitsuka's previous affiliation. [Extracted from the article]

Two independent nuclear methods have been developed and tested for studies of mineral scaling mechanisms and kinetics related to the oil and geothermal industry. The first is a gamma transmission method to measure mass increase with a 30 MBq source of 133Ba. The other method applies radioactive tracers of one or more of the scaling components. CaCO3-precipitation has been used as an example here where the main tracer has been 47Ca2+. While the transmission method is an indirect method, the latter is a direct method where the reactions of specific components may be studied. Both methods are on-line, continuous and non-destructive, and capable to study scaling of liquids with saturation ratios approaching the solubility product. A lower limit for detection of CaCO3 with the transmission method in sand-packed columns with otherwise reasonable experimental parameters is estimated to be < 1 mg in a 1 cm section of the tube packed with silica sand while the lower limit of detection for the tracer method with reasonable experimental parameters is estimated to < 1 µg in the same tube section. [ABSTRACT FROM AUTHOR]