Geothermal Field Research Articles

Effects of fluid composition and salinity on subcritical crack growth in granite

Using the double-torsion technique, the fracture mechanical response of granite specimens was investigated under the influence of fluid with different electrolyte types and salinities. The fracture toughness (KIC) and critical mechanical energy release rate (G0) of the granite in electrolyte solution are weakened compared to those in distilled water. The KIC in all electrolyte solutions is 2.08–2.28 MPa·m1/2, which is 8.4 % − 16.5 % lower than that in distilled water, and it is insensitive to ion type and salinity. In contrast, the subcritical crack growth index (n) shows different salinity dependence in three salt (AlCl3, CaCl2, and NaCl) solutions. The slight increase in n with rising salinity of the AlCl3 solution is attributed to crack tip blunting caused by over-dissolution of minerals. The n and G0 decrease and then increase with rising salinity of CaCl2 solution, which may be related to the salinity-dependent dissolution rate of quartz and the weakening of repulsive force between crack surfaces. The n and G0 shows a negative correlation with salinity and decrease by 26.4 % and 15.4 %, respectively as the NaCl salinity increases from 0.1 M to 1.0 M. Limitations in the dissolution reactions of the main minerals (albite, biotite and diopside) is accountable for enhancement of n in silica solutions. Experimental results emphasize the critical and subcritical fracture behavior of the granite in response to chemically reactive fluids with implications for both hydraulic fracture stimulations in geothermal fields and caprock integrity for CO2 sequestration. In these applications, the fracture properties of the reservoir rock can be enhanced or weakened by changing the electrolyte type and salinity of the fluid, depending on the actual requirements.

Hydrogeochemistry of geothermal water in Huangshadong and adjacent areas of Guangdong province: Implications for water-rock interaction

Hydrogeochemical characteristics can reflect important information on the circulation processes of geothermal fluids, reservoir temperatures, etc., which are essential for exploring geothermal field evolution and the rational development of geothermal resources. 23 sets of water samples were collected from Huangshadong and adjacent geothermal fields. Major cations and anions, hydrogen and oxygen isotopes, and 14C activities were analyzed to investigate the hydrogeochemical characteristics of geothermal fluids and their formation mechanisms. Hydrogen and oxygen isotope analysis and major element chemistry indicate that the geothermal waters in the study area are mainly recharged by meteoric water. The chemical facies of the geothermal waters are mainly Na−HCO3 and Ca−HCO3, and most of the geothermal waters have high Na+ contents, which are attributed to the involvement of albite in water-rock interaction and the replacement of Na+ in rocks by Ca2+ or Mg2+ in water. Geothermometry of geothermal waters suggests that the reservoir temperatures are between 140-150 ℃, and the geothermal water circulation depths range from 2.0 to 4.3 km. The residence time of up to 17.3ka for geothermal water likely suggests the earliest precipitation recharge during the Late Pleistocene. Major element chemistry and hydrogen and oxygen isotope systematics indicate essential information on the origins of geothermal waters and water-rock interaction processes and provide a more comprehensive understanding of the geothermal system in Huangshadong and adjacent areas of Guangdong province.

Exploring chemical disposal options for non-condensable gasses in geothermal power plants: A case study of Kızıldere geothermal field (Türkiye)

Geothermal power plants are among the most important renewable energy power plants owing to their high-capacity factors and integrated utilization possibilities. Currently, these power plants utilize geothermal fluid to generate electricity. Although their emissions are lower than those of conventional power plants, gasses such as CO2 and H2S are released into the air from the cooling towers, particularly in flash-type geothermal power plantsTo reduce the emission of CO2 gas released from geothermal power plants, reinjection studies have mainly been carried out around the world. These types of studies require extensive analysis of underground fracture systems, detailed geosciences, and the reservoir studies. However, these studies are considered risky and expensive for most plant operators because possible changes in underground fracture systems may affect the productivity of geothermal production zones. In terms of the environmental impact, hydrogen sulfide is a more harmful gas than CO2. Effective H2S removal methods cannot be widely used, except in areas with extremely high concentrations, because they commonly incur significant costs for plant operators. Effective H2S removal methods are not widely available except for geothermal sites with high concentrations. The fact that local limit values can be exceeded in geothermal power plants with relatively low H2S concentrations, such as geothermal power plants in Türkiye, pushes plant operators to find new low-cost solutions due to high operation costs. For this reason, a treatment method that can be applied at every site and whose cost is not too high has not yet been put forward. However, NaOH is used for this purpose in geothermal fields such as steam-dominated Geyser field to increase the pH values in geothermal wells, which has been producing for a long time.In this study, field tests were carried out with five different chemicals and pure water to examine the reduction of non-condensable gasses in a geothermal power plant located in the Kızıldere (Denizli, Türkiye) geothermal field, one of the most important geothermal fields in the world. According to this, the capture of these gasses is technically possible using chemical methods, with a performance of up to 70 % observed in CO2 gas capture.However, although it is possible to capture 70 % of non-condensable gasses with such chemical methods, the consumable cost of the operation is quite high.

Relatively stable pressure effects and time-increasing thermal contraction control Heber geothermal field deformation

Due to geological complexities and observational gaps, it is challenging to identify the governing physical processes of geothermal field deformation including ground subsidence and earthquakes. In the west and east regions of the Heber Geothermal Field (HGF), decade-long subsidence was occurring despite injection of heat-depleted brines, along with transient reversals between uplift and subsidence. These observed phenomena contradict current knowledge that injection leads to surface uplift. Here we show that high-yield production wells at the HGF center siphon fluid from surrounding regions, which can cause subsidence at low-rate injection locations. Moreover, the thermal contraction effect by cooling increases with time and eventually overwhelms the pressure effects of pressure fluctuation and poroelastic responses, which keep relatively stable during geothermal operations. The observed subsidence anomalies result from the siphoning effect and thermal contraction. We further demonstrate that thermal contraction dominates long-term trends of surface displacement and seismicity growth, while pressure effects drive near-instantaneous changes.

Surveillance Data Analysis Reveals Well Performance and Reservoir Connectivity: A Case Study in Alasehir Geothermal Field

Surveillance Data Analysis Reveals Well Performance and Reservoir Connectivity: A Case Study in Alasehir Geothermal Field

Selection of Putative Polyester Hydrolases from the Metagenome of Los Humeros Geothermal Field by Means of In Silico Probes

Selection of Putative Polyester Hydrolases from the Metagenome of Los Humeros Geothermal Field by Means of In Silico Probes

Study on the Genetic Mechanism of Carbonate Rock Type Hot Mineral Water-A Case Study of Diaozhen, Jinan.

Geothermal resources are one of the most valuable resources in renewable energy because of their advantages of green environmental protection, stability, and reliability. Carbonate rock type geothermal reservoirs have great research significance. Carbonate rock type geothermal resources are abundant in the Shandong area. In this paper, we take the carbonate-type geothermal reservoir in the Diaozhen area of Jinan City as the research object, analyze the regional geothermal geological conditions, and identify the geological structure. Through physical logging exploration, hydrochemical analysis, isotope testing, and drilling exploration, we reveal the geothermal genesis mechanism and construct the genetic model of the carbonate geothermal system. The results show that Diaozhen area belongs to a low-temperature geothermal field and weak open karst thermal reservoir and that the reservoir is mainly Ordovician Majiagou group limestone. The thermal insulation caprock is the overlying Quaternary and Neogene strata with a cumulative thickness of 1376 m. The results of geophysical exploration wells and drilling data verify that the Mingshui fracture is seen around 1630-1645m, and the diorite intrusion is seen at 1610m. The Mingshui fracture connects the deep and shallow aquifers and is a geothermal fluid migration channel. The geothermal water in the Diaozhen area is mainly from the recharge of atmospheric precipitation, with a rich ion content and easy enrichment of trace elements. The regional thermal reservoir is mainly recharged by the deep circulation lateral runoff of Ordovician karst water. After long-distance deep circulation migration, groundwater continuously absorbs heat from the surrounding rock and is heated to geothermal raw water in the deep part. Deep geothermal water rises along the water-conducting fracture and mixes with shallow cold water to form shallow, low-temperature geothermal water.

Towards Improving Sustainable Water Management in Geothermal Fields: SVM and RF Land Use Monitoring

Towards Improving Sustainable Water Management in Geothermal Fields: SVM and RF Land Use Monitoring

Geothermal resource evaluation of the Middle Permian Qixia-Maokou Formation in the southern Sichuan Basin, China

The southern Sichuan Basin is an abnormal area of high present geothermal fields in the Sichuan Basin. It is a favorable area for the development of geothermal resources in the Sichuan Basin. But its evaluation of geothermal resources is lagging, which has severely affected the development of geothermal resources in the southern Sichuan Basin. In the paper, firstly, based on the temperature data of wells, the geothermal gradients and heat flows of typical wells in the study area were calculated, and the temperatures at the top and bottom of the reservoir in the Qixia-Maokou Formation were calculated using a one-dimensional steady-state heat conduction equation. Then, geothermal resource intensities and reserves of the Middle Permian Qixia-Maokou Formation in the southern Sichuan Basin were evaluated by using a method for rapidly calculating geothermal resources in sedimentary basins by multi-data fusion. Finally, suggestions for geothermal development were proposed. The results show that the geothermal gradient and heat flow values in the southern Sichuan Basin range from 15.6 to 33.70 °C/km and 49 to 85 mW/m2, respectively, and the temperature of the reservoir in the Qixia-Maokou Formation ranges from 50 to 120 °C. The geothermal resources are 3.09 × 1021 J, equivalent to 105 billion tons of standard coal, and the recoverable resources are 6.18 × 1020 J, equivalent to 21 billion tons of standard coal. The development of demonstration projects will focus on the mid- to low-temperature geothermal power generation, geothermal grain drying and geothermal agriculture in the southwestern region of the southern Sichuan Basin. The research results can provide a resource basis for the development of geothermal resources in the southern Sichuan Basin.

Geothermal Exploration in Hululais Geothermal Field, Lebong Regency, using a 1D Magnetotelluric Approach to Estimate The Depth of Reservoir Rocks

Abstract Indonesia continues to rely heavily on hydrocarbon energy sources. However, in order to ensure the country’s long-term economic growth, it must diversify its energy investments and use renewable energy sources. Through tapping into the country’s vast untapped geothermal resources, the country can meet its rising energy needs in a sustainable and effective manner, all while contributing to mitigating climate change’s worst effects. Lebong Regency, Bengkulu, Indonesia, is the site of the Hululais Geothermal Field. Geothermal energy could be extracted from the area’s hydrothermal systems, as evidenced by the existence of surface hot springs and sulfur craters. In order to determine how deep the geothermal reservoir rocks at Hululais go, a thorough investigation of the area has been carried out using the magnetotelluric (MT) technique to probe the underlying lithological conditions. More than 10 kilometers of MT data were collected across 4 different survey stations for this study’s 1D inversion. The information was gathered with the help of a Metronix ADU-07e MT instrument. The 1D occam inversion results explain the resistive zone connected to the flow of thermal fluid. Hot springs and sulfur craters can be seen on Hululais’s surface, indicating the fluid flows beneath the island’s crust. 1D Occam inversion of MT data measured in the Lebong District can identify geothermal reservoir, where the depth of the geothermal reservoir is 400 meters in subsurface, which is indicated by a high resistivity value (> 500 Ω.m).

Hydrochemical Characterization, Geothermometry, and Origin of Ain Al-Harrah Hot Spring and Its Relationship to Al-Lith Geothermal System, Saudi Arabia.

The Al-Lith geothermal field in western Saudi Arabia is a characteristic medium-high enthalpy geothermal system, exhibiting features associated with tectonic activities linked to the Red Sea rifting. Ain Al-Harrah hot spring is located in the Al-Lith field, with discharge temperatures varying from 56 to 81 °C. The determination of water temperature and composition in a geothermal reservoir is critical to the design of utilization strategies, surface production facilities, and choice of materials. This research presents a comprehensive hydrochemical characterization of the Ain Al-Harrah hot spring and its relationship with the underlying geothermal system. This study was conducted in two main phases; first, the fieldwork involved the collection of water samples from the hot spring, measuring the temperature, pH, and electrical conductivity (EC) of the water. The second phase involved laboratory analyses of the collected samples, including major and trace element analyses, isotopic analysis, and geothermometry. The dominant hydrogeochemical processes in the region were determined by analyzing the hydrochemistry of the water samples. Thermal waters analyzed exhibited high concentrations of Na+ (410-463 mg/L), HCO3 - (64.48-90 mg/L), and Cl- (472.76-581.95 mg/L), intermediate levels of K+ (50.2-93.0 mg/L), and low levels of Mg2+ (1.27-2.04 mg/L). The total dissolved solids (TDS) concentration ranges between 1830 and 2055 mg/L. The hot spring is categorized as Na-HCO3 type facies that are moderately alkaline, with pH values ranging between 7.9 and 8.2. Analysis of trace element concentrations revealed that the hydrochemical processes were primarily governed by the abundance and solubility of trace elements in the rocks surrounding the hot spring, the pH, and the temperature of the hot spring water. The stable isotope data for δD (-12.36 to 15.21%) and δ18O (-2.84 to -3.38%) provided evidence that the thermal spring is of meteoric origin. Based on Na-K-Ca, K2/Mg, and quartz geothermometers, the temperature range of the reservoir was determined to be between 150 and 205 °C. The temperature range suggests a medium-to-high enthalpy geothermal system.

Trace metal and organic biosignatures in digitate stromatolites from terrestrial siliceous hot spring deposits: Implications for the exploration of martian life

Novel biosignatures of laminated, microbial, digitate sedimentary structures – stromatolites – from modern geothermal fields of the Taupō Volcanic Zone, New Zealand, and from El Tatio, Chile, provide an opportunity to investigate evidence of extremophile life preserved in siliceous hot spring deposits, or sinters, interpreted as analogs for early life on Earth and possibly Mars. Synchrotron-μXRF, electron microprobe analysis, Raman spectroscopy, and optical microscopy are used in a coordinated approach to identify corroborating textural and chemical (organic, inorganic) evidence of life in these modern, opaline (amorphous) siliceous materials. Fluid mobile elements, such as As and Sr, track the growth history of the digitate structures. Trace element enrichments of Ca, Al, Ga, +/− Fe, Mn, As, Rb, Cs, and Sr, are identified in silicified sheaths of microbial filaments embedded within the sinter. In contrast, silicified diatoms in some sinter samples show no trace element enrichment. Gallium enrichments have also been observed in other 16 ka and Jurassic (150 Ma) microbial palisade sinter textures, suggesting the potential for preservation through geologic time, even after recrystallization to quartz. Raman analysis reveals spectra of organics, consistent with pigments for UV protection in cyanobacteria, in silicified sheaths around microbial filaments and are co-located with trace metal enrichments in digitate structures. Due to spectral bands, the location of these molecules (i.e., in the sheaths), and the sampling locations, we ascribe the spectra to scytonemin and carotenoid class molecules. The combined analytical approach outlined here provides a robust means to assess the validity of novel biosignatures, with application to the exploration of Mars, where preservation of opaline silica in >3.6 Ga deposits has the potential to preserve a range of microbial biosignatures.

The silicon isotopic compositions of silica sinters in Xizang, China: Implications for paleo-geothermal activities since 0.5 Ma B.P.

The diagenetic sequence from opal-A to opal-CT has been observed in geothermal systems worldwide. Xizang, a unique geothermal region in the world, has experienced several large-scale geothermal activities since 0.5 million years ago. The Targejia and Gulu geothermal systems were investigated in this study. The time for transformation from opal-A to opal-CT varies, indicating that the rates of silica phase transformation depend on specific conditions; however, their silicon isotopic compositions are not significantly different, ranging from −1.0‰ to −0.3‰ in Targejia and from −1.1‰ to −0.1‰ in Gulu. Additionally, silica sinters undergo varying degrees of diagenesis, as supported by different time periods and varying degrees of ordering. The δ30Si values of different phases, opal-A and opal-CT, also did not significantly change, ranging from −1.1‰ to −0.3‰ for opal-A and from −1.0‰ to −0.1‰ for opal-CT. Due to the lower dissolution rates of sediments, high aluminum content, and reduced reactivity of silica sinters, the δ30Si values of silica sinters are less susceptible to secondary modifications, and the initial information after the silica sinters formation is well preserved. Hence, the isotopic signatures of silica sinters reflect various depositional environments and can be used to reconstruct paleo-geothermal activity. The narrow range and slightly negative isotopic values of silica sinters suggest that large-scale high-temperature geothermal activity has occurred in different regions since 0.5 Ma. The diagenesis of silica sinters may have been influenced by postlarge-scale high-temperature geothermal activity. Such large-scale, high-temperature and long-term natural eruptions in geothermal fields are typically associated with magmatic activity, possibly caused by crustal remelting processes.

Mapping and resource evaluation of deep high-temperature geothermal resources in the Jiyang Depression, China

In China, geothermal resource utilization has mainly focused on resources at shallow and medium depths. Yet, the exploration of deep, high-temperature geothermal resources holds significant importance for achieving the “dual carbon” goals and the transition of energy structure. The Jiyang Depression in the Bohai Bay Basin has vast potential for deep, high-temperature geothermal resources. By analyzing data from 2187 wells with temperature logs and 270 locations for temperature measurement in deep strata, we mapped the geothermal field of shallow to medium-deep layers in the Jiyang Depression using ArcGIS and predicted the temperatures of deep layers with a burial depth of 4000 m. Through stochastic modeling and numerical simulation, a reservoir attribute parameter database for favorable deep, high-temperature geothermal areas was developed, systematically characterizing the spatial distribution of geothermal resources within a play fairway of 139.5 km2 and estimating the exploitable deep geothermal resource potential by using the heat storage method and Monte Carlo data analysis. The study reveals that the Fan 54 well block in the Boxing-Jijia region is of prime significance to develop deep, high-temperature geothermal resources in the Jiyang Depression. Strata from the Cenozoic to the Upper Paleozoic are identified as effective cap layers for these deep geothermal resources. The Lower Paleozoic capable of effectively storing thermal energy and possessing an exploitable resource volume up to 127 million tons of standard coal, is identified as a target system for the development of deep high-temperature geothermal resources, providing significant insights for the efficient development of geothermal resources in the Jiyang Depression.

Focused and Smooth Inversion2D modelling of Magnetotelluric data from the Sabalan Geothermal Field in Northwestern Iran

Magnetotelluric measurements from the Sabalan geothermal field in northwestern Iran have provided clear indications of geothermal reservoirs. This study aimed to identify shallow and deeper conductivity anomalies associated with geothermal systems in the Sabalan area. The magnetotelluric method is widely used for exploring subsurface resources, as it is suitable for detecting subsurface anomalies at significant depths. Based on modeling results, thick conductive layer was found near the surface of the Moil Valley area, where two reservoirs are embedded. The main reservoir, located on the west side of Sabalan volcano, extends from the south and southwest of Sabalan peak to the west and Moil valley. The dimensions of this reservoir are almost twice as large as the estimated volume obtained from previous studies. Another smaller reservoir is located to the north of the peak.

Image of the five elements and prediction of the geothermal field based on gravity, magnetic and magnetotelluric data in the PanZ area

There are two problems in the prediction of the geothermal field in the PanZ area: (1) the plane scopes have some debates, and (2) the vertical scopes need to be further ascertained. Faced with these two problems, a complete set of methods was developed and summarized, and the details are as follows: a geothermal field can be divided into five elements, i.e., heat source, fault channel, thermal reservoir, cap rock and water; then, they are interpreted and imaged with the help of gravity, magnetic and magnetotelluric (MT) data; and finally, according to the integrity of five elements and the correlation between them, geothermal fields are predicted. In the PanZ area, (1) the normalized vertical derivative of the total horizontal derivative of the Bouguer gravity anomaly was applied to identify the fault channels; (2) the water was recognized using the joint interpretation results from an integrated geophysical profile with gravity and MT data instead of a single MT result; (3) the cap rock was inverted with the Bouguer gravity anomaly, using the Parker–Oldenburg inversion method, and with the help of the MT anomaly in the integrated geophysical profile, the vertical distribution of the geothermal reservoir was further ascertained; and (4) the intermediate acid magmatic rock with radioactivity, i.e., a heat source, was identified with the residual magnetic anomaly, imaged using the magnetic forward formula of the cuboid. Finally, the two geothermal fields were predicted and outlined using the above methods. A comparison of the distributions of the geothermal gradient and the outlet water temperatures of the drill holes indicated that the predicted results are credible. To better understand the effect of the method of predicting the geothermal field, a 3D geological model was constructed from the inverted results using GOCAD software, and the operating mechanism of geothermal system was analyzed based on the migration, storage, heating and insulation of the water element in the other four elements. To determine the reason for the formation of the geothermal field, the geological evolution of four elements was discussed, except the water element.

Representative High-Temperature Hydrothermal Activities in the Himalaya Geothermal Belt (HGB): A Review and Future Perspectives

Southern Tibet and western Yunnan are areas with an intensive distribution of high-temperature geothermal systems in China, as an important part of the Himalayan Geothermal Belt (HGB). In recent decades, China has conducted systematic research on high-temperature geothermal fields such as Yangbajing, Gudui, and Rehai. However, a comprehensive understanding has not yet been formed. The objective of this study was to enhance comprehension of the high-temperature geothermal system in the HGB and to elucidate the hydrogeochemical characteristics of geothermal fluids. This will facilitate the subsequent sustainable development and exploitation of domestic high-temperature hydrothermal geothermal resources. To this end, this study analysed geothermal spring and borehole data from the Yangbajing, Gudui, and Rehai geothermal fields. Based on previous research results, the source, evolution, and reservoir temperature characteristics of geothermal fluids are compared and summarised. The main high-temperature geothermal water in the geothermal field is derived from the deep Cl-Na geothermal fluid. Yangbajing’s and Gudui’s geothermal waters are primarily recharged by snow-melt water, while Rehai’s geothermal water is mainly recharged by local meteoric water. The average mixing ratios of magmatic water in the Yangbajing, Gudui, and Rehai geothermal fields are 17%, 21%, and 22%, respectively. The Yangbajing and Gudui geothermal fields have a relatively closed geological environment, resulting in a stronger water–rock interaction compared to the Rehai geothermal field. As geothermal water rises, it mixes with shallow cold water infiltration. The mixing ratios of cold water in the Yangbajing, Gudui, and Rehai geothermal fields are 60–70%, 40–50%, and 20–40%, respectively. Based on the solute geothermometer calculations, the maximum geothermal reservoir temperatures for Yangbajing, Gudui, and Rehai are 237 °C, 266 °C, and 282 °C, respectively. This study summarises and compares the hydrogeochemical characteristics of three typical high-temperature geothermal fields. The findings provide an important theoretical basis for the development of high-temperature geothermal resources in the Himalayan Geothermal Belt.

Seismic Monitoring of a Deep Geothermal Field in Munich (Germany) Using Borehole Distributed Acoustic Sensing.

Geothermal energy exploitation in urban areas necessitates robust real-time seismic monitoring for risk mitigation. While surface-based seismic networks are valuable, they are sensitive to anthropogenic noise. This study investigates the capabilities of borehole Distributed Acoustic Sensing (DAS) for local seismic monitoring of a geothermal field located in Munich, Germany. We leverage the operator's cloud infrastructure for DAS data management and processing. We introduce a comprehensive workflow for the automated processing of DAS data, including seismic event detection, onset time picking, and event characterization. The latter includes the determination of the event hypocenter, origin time, seismic moment, and stress drop. Waveform-based parameters are obtained after the automatic conversion of the DAS strain-rate to acceleration. We present the results of a 6-month monitoring period that demonstrates the capabilities of the proposed monitoring set-up, from the management of DAS data volumes to the establishment of an event catalog. The comparison of the results with seismometer data shows that the phase and amplitude of DAS data can be reliably used for seismic processing. This emphasizes the potential of improving seismic monitoring capabilities with hybrid networks, combining surface and downhole seismometers with borehole DAS. The inherent high-density array configuration of borehole DAS proves particularly advantageous in urban and operational environments. This study stresses that realistic prior knowledge of the seismic velocity model remains essential to prevent a large number of DAS sensing points from biasing results and interpretation. This study suggests the potential for a gradual extension of the network as geothermal exploitation progresses and new wells are equipped, owing to the scalability of the described monitoring system.

Harvesting Earth's heat: A deep learning Odyssey for reservoir characterization and sustainable geothermal energy management

Characterizing and predicting reservoir behavior pose significant challenges in geothermal reservoir engineering. For sustainable geothermal field management, the potential occurrence of thermal breakthroughs in producers during the injection of cold water necessitates a profound understanding of how production is influenced by the injection philosophy. The fractured nature of geothermal reservoirs adds complexity and nonlinearity to the relationship between production and injection wells. In this study, we explore alternative models to simulate reservoir behavior as substitutes for full reservoir simulations. Utilizing deep learning algorithms, we investigate two different architectures, namely the standard Long Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU). These models map injection flow rates at the injectors to tracer concentration data at the producers through layers, nodes, and activation functions. Training these models on a synthetic geothermal reservoir, Notably, the GRU architecture consistently demonstrates superior predictive capabilities across various scenarios for all three producers. Specifically, in configurations involving a target feed, the GRU model yields higher R2 values compared to its LSTM counterpart, indicating its effectiveness in capturing inter-well relationships. Furthermore, when considering all producers collectively, the GRU model exhibits a trend of lower test errors and higher R2 values, reaffirming its proficiency in modeling complex reservoir dynamics. These findings underscore the significance of GRU as a preferred choice for accurate reservoir behavior prediction. In addition to the aforementioned insights, our study contributes novel approaches to reservoir behavior prediction in the field of geothermal reservoir engineering. By leveraging deep learning algorithms, specifically the GRU and LSTM architectures, we introduce innovative methodologies for simulating reservoir behavior as alternatives to full reservoir simulations. Through comprehensive analysis, we demonstrate the superior predictive capabilities of the GRU model, particularly in capturing inter-well relationships and modeling complex reservoir dynamics.

Shallow geothermal field multidisciplinary exploration: New data from Campi Flegrei caldera (CFc) for low—middle enthalpy resource exploitation

In the framework of the GeoGrid project, with the specific goal to look for shallow geothermal resources suitable to test the developed technologies, the Agnano geothermal field, a relatively unexplored sector of the eastern Campi Flegrei caldera, was investigated through a multidisciplinary geophysical, stratigraphic and hydro-chemical surveys. Such multidisciplinary approach allows us to reconstruct the subsurface morphology below the Agnano Hyppodrome (AH), interpreted by gravimetric, seismic and stratigraphic data, as a complex structure characterized by a gradual southward and south-eastward deepening of a high-density contrast interface. Moreover, the inferred models show two pronounced lateral depressions in agreement with the existence of known lateral faults bounding the western and eastern flanks of AH, while the hydro-chemical survey of the entire Agnano caldera revealed discontinuous manifestations of thermal waters along the groundwater flow direction. Furthermore, it was found that, within the southern sector of the Agnano caldera, mineralized waters predominantly align with a primary NE-SW buried structural lineament, a feature only hypothesized in previous studies and that in this sector local fresh groundwater likely receives endogenous inputs, including CO2 at elevated temperatures, potentially leading to the mixing of seawater or deep brine. Finally, our results individuate an area north of the Agnano Hippodrome characterized by a significant presence of higher temperature mineralized water, but lacking of seawater enrichment, making it a favorable site for further exploitation of low-to-medium-enthalpy geothermal sources.