Search Results (1,104)

The Muji Fault Zone (MJF) in the northeastern Pamir Plateau hosts a well-developed non-volcanic geothermal system, characterized by widespread hot springs and mud volcanoes—where core processes of geothermal fluids, including atmospheric precipitation recharge, shallow crustal circulation, carbonate-driven water–rock interactions, and CO₂-rich fluid discharge, are tightly coupled with regional intense crustal deformation and frequent seismic activity. We collected and analyzed 22 geothermal water samples and 8 bubbling gas samples from the MJF periphery, finding that the geothermal waters are predominantly of the HCO₃-Ca·Mg hydrochemical type, with hydrogen (δD: −103.82‰ to −70.21‰) and oxygen (δ¹⁸O: −14.89‰ to −10.10‰) isotopes indicating atmospheric precipitation as the main recharge source. The Na-K-Mg ternary diagram classified the waters as immature, reflecting low-temperature water–rock interactions in the shallow crust (<3 km), while noble gas isotopes (³He/⁴He: 0.03–0.09 Ra, Ra = 1.43 × 10⁻⁶) and carbon isotopes (δ¹³C-CO₂) confirmed fluid origin from crustal carbonate dissolution; SiO₂ geothermometry estimated thermal reservoir temperatures at 67–155 °C. Long-term monitoring (May 2019–April 2024) of Tahman (THM) and Bulake (BLK) springs revealed significant pre-seismic anomalies: before the 2023 Tajikistan Ms7.2 and 2024 Wushi Ms7.1 earthquakes, Na⁺, Cl⁻, and SO₄²⁻ concentrations showed notable negative anomalies (exceeding 2σ of background values) with synchronous trends between the two springs. Integrating these findings, a “Fault-Spring-Mud Volcano-Earthquake” fluid response model was established, providing direct evidence of deep-shallow fluid coupling in mud volcano–geothermal fluid interactions. This study enhances understanding of the dynamic evolution of non-volcanic geothermal systems under tectonic stress and clarifies the mechanisms of hydrogeochemical variations in fault-controlled geothermal systems, offering a robust scientific basis for advancing research on tectonic–fluid interactions in active fault zones of the northeastern Pamir Plateau. Full article

Closed-loop geothermal systems (CLGSs) avoid groundwater production and offer stable deep heat supply, but their long-term performance hinges on reliable coupling between the wellbore, the near-well interface and the surrounding formation. Using the D22 well in the Xiongan New Area (deep carbonate reservoir), we built a three-domain thermo-hydraulic framework that updates CO₂ properties with temperature and pressure and explicitly accounts for wellbore-formation thermal resistance. Two geometries (U-tube and single-well coaxial) and two working fluids (CO₂ and water) were compared and optimized under field constraints. With the coaxial configuration, CO₂ delivers an average thermal power of 186.3 kW, exceeding that of water by 44.9%, while the fraction of wellbore heat loss drops by 3–5%. Under field-matched conditions, the predicted outlet temperature (76.8 °C) agrees with the measured value (77.2 °C) within 0.52%, confirming the value of field calibration for parameter transferability. Long-term simulations indicate that after 30 years of continuous operation the outlet temperature decline remains <8 °C for CO₂, outperforming water and implying better reservoir utilization and supply stability. Sensitivity and Pareto analyses identify a practical operating window, i.e., flow velocity of 0.9–1.1 m s⁻¹ and depth of 3000–3500 m, favoring the single-well coaxial + CO₂ scheme. These results show how field-calibrated modeling narrows uncertainty and yields implementable guidance on geometry, operating conditions, and wellbore insulation strategy. This study provides quantitative evidence that CO₂-CLGSs in deep carbonate formations can simultaneously increase thermal output and limit long-term decline, supporting near-term engineering deployment. Full article

Boreholes in the Teleghma region of northeastern Algeria discharge thermal water with temperatures between 40 and 49 °C and total dissolved solids (TDS) ranging from 570 to 940 mg/L. The stable isotope compositions range from –7.8‰ to –6.2‰ for δ¹⁸O and –52.6‰ to –43.3‰ for δ²H, indicating a meteoric origin. Based on these isotopic signatures, the water is classified as immature and undersaturated with respect to the equilibrium line on the Giggenbach Na–K–Mg ternary diagram. The water exhibits a sodium–chloride (Na–Cl) facies, closely associated with Triassic formations rich in evaporitic deposits. This association was confirmed by the IIGR method, which illustrates the chemical evolution of the hydrothermal fluid as it ascends from the karstic carbonate reservoir through conduits and traverses clay formations. Consequently, computed saturation indices and applied inverse modeling significantly contributed to understanding the interactions between the hydrothermal water and the traversed rock. At the local scale, halite dissolution is the primary mineral phase driving chemical changes. Regionally, however, the processes are dominated by gypsum dissolution and cation exchange reactions between calcium and sodium ions. These findings offer valuable insights into the geochemical processes that shape the Teleghma geothermal system, with implications for resource management and potential applications. Full article

Salt lakes on the Tibetan Plateau (TP) are vital repositories of China’s strategic mineral resources, including boron and lithium. The Budongquan Salt Lake (BDQSL) in eastern Hoh Xil Basin (HXB) represents a hypersaline system with combined geothermal recharge and intense evaporation, yet its hydrochemical characteristics and B-Li enrichment mechanisms remain poorly understood. Through systematic hydrochemical and isotopic analysis (δD, δ¹⁸O, d-excess) of 69 surface samples, 14 depth-stratified profiles, and 131 regional water samples, we reveal that: (1) BDQSL exhibits extremely saline Na-Cl brines (TDS: 192,700–220,700 mg/L) significantly enriched in B and Li (45–54 mg/L), with overall spatial homogeneity and complete vertical mixing; (2) B and Li demonstrate strong correlation (R² = 0.95), controlled by coupled hydrothermal input, water–rock interaction, and evaporative concentration, with hydrothermal delivery as the predominant source; (3) depleted isotopic signatures (δ¹⁸O = −1.4‰, d-excess = −5‰) confirm intense evaporation, while upstream cascade connectivity and climate warming drive lake expansion and brine dilution, indicating transition toward lower salinity; (4) a distinctive hydrothermal–evaporative composite mineralization model differentiates BDQSL from regional mono-evaporative systems. This study elucidates B-Li enrichment mechanisms in hydrothermally active plateau salt lakes, providing geochemical constraints for resource assessment and predictive frameworks for evaluating mineral evolution under climate change. Full article

In geothermal systems, polymer injection is vital for improving the sweep efficiency of fluid, but the critical challenge is managing the fluid flow in severely fractured systems. Developing stable plugging agents for these systems is a recurring challenge, allowing the loss of the fluid into the large fractures, hence making the recovery very difficult. The fluid is crucial for several applications like power generation, heating, and cooling without producing any toxic emissions. This study presents a gel system formulated with hydroxyethyl cellulose, and a HMTA–resorcinol crosslinker system for harsh conditions of temperature and salinity. The study employed a Central Composite Design (CCD) for optimizing gel formulation. The system achieved optimal conditions at a gelation time of 0.5 h, and the properties were investigated. The experimental outcomes reveal that the polymer gel can exhibit excellent stability under harsh conditions, withstanding temperatures up to 352 °C. This confirms the robustness of the plugging agent at elevated temperatures. This study offers a sustainable and efficient solution for fluid flow control in severely fractured geothermal systems. Full article

Sustainable mine geothermal energy causes high-temperature hazards in mine roadways, severely endangering miners’ lives. There is an urgent need to enhance research on the performance of composite phase change material (CPCM) roadway cooling systems, as they can effectively control ambient temperatures. However, existing research on CPCM roadway cooling system performance remains limited. This study innovatively establishes a numerical model for a novel cascade CPCM roadway cooling system and employs the control variable method to investigate the influence of multi-parameter regulation on system performance. The study reveals that the ring pipe radius ratio significantly impacts the system’s heat exchange efficiency and temperature distribution. The optimal comprehensive system performance is achieved at an annular tube radius ratio of 2:3, where the CPCM solid phase percentage for 89.03% and the average temperature of the monitoring surface decreases by 9.54 °C. Increasing the cascaded tube spacing enhances the overall cooling effect, but cooling efficiency diminishes when the spacing exceeds 0.5 m. The CPCM phase change temperature must align with the mine’s geothermal conditions, with CPCM utilization and cooling efficiency peaking at 25 °C. The air deflector structure effectively mitigates cooling lag in the lower roadway section. At an installation angle of 30°, the expansion distance of the lower low-temperature zone increased by up to 48.89% without compromising cooling efficiency in the upper roadway section, while also delaying the recovery rate of heat damage. Full article

Hybrid geothermal–solar systems leverage complementary resources to enhance efficiency, dispatchability, and low-carbon supply. This review compares mainstream configurations (solar-preheating configurations, solar-superheating configuration, and other emerging concepts) and reports typical performance gains—thermal efficiency of 5–80% and exergy efficiency up to ~60%—observed across resource contexts. Findings indicate that preheating routes are generally preferable under medium direct normal irradiance (DNI) and operation-and-maintenance (O&M)-constrained conditions, while superheating routes become attractive at high DNI with thermal storage; integrated multigeneration systems can deliver system-level benefits for multi-energy parks and district applications. In addition, this paper identifies technical bottlenecks—source matching, storage dependence, and the absence of a unified evaluation—and summarizes control/optimization strategies, including emerging advanced artificial-intelligence algorithms. In addition, the review highlights a standardized comprehensive performance evaluation framework, which covers thermal and exergy efficiency, net power output, complexity, the levelized cost of electricity (LCOE), reliability, and storage. Finally, according to the research status and findings, future research directions are proposed, which pave the way for more effective exploitation of geothermal and solar energy. Full article

The strategic positioning of heating and cooling segments within complex non-rectangular geometries has emerged as a critical engineering challenge across multiple industries in thermal management systems for electronic components. This analysis presents a numerical inspection of buoyancy-driven convective flow and thermal transport mechnisms of nanofluids in a parallelogrammic porous geometry. A single discrete heating–cooling segment has been placed along the slanting surfaces of the geometry. The mathematical model is formulated utilizing Darcy’s law, incorporating the Tiwari and Das approach to characterize the thermophysical properties of the nanofluid. The governing model equations corresponding to the physical process are solved numerically using finite-difference-based alternating direction implicit (ADI) and successive line over-relaxation (SLOR) techniques. Computational simulations are performed for various parametric conditions, including different nanoparticle volume fractions ($\varphi =0$–$0.05$), Rayleigh numbers ($Ra={10}^1$–${10}^3$), and parallelogram geometry ($\alpha$) and sidewall ($\gamma$) tilting angles ($-{45}^{°}\le \alpha \le +{45}^{°}$ and $-{45}^{°}\le \gamma \le +{45}^{°}$), while examining the effect of discrete thermal locations. The results reveal a significant decrement in thermal transfer rates with an increasing nanoparticle concentration, particularly at higher Rayleigh numbers. The skewness of the parallelogrammic boundaries is found to substantially influence flow patterns and thermal transport characteristics compared to conventional rectangular enclosures. Further, the discrete placement of heating and cooling sources creates unique thermal plumes that modify circulation patterns within the domain. The predictions suggest profound insights for optimizing thermal management systems by employing nanofluids in non-rectangular porous configurations, with potential applications in geothermal energy extraction, electronic cooling systems, and thermal energy storage devices. Full article

The decline in the injectivity of injection wells is a serious problem in geothermal systems. In this article, we analyse the mechanisms responsible for the reduction in permeability in Lower Jurassic sandstones during the injection of cooled formation brine. Flow experiments were conducted on rock cores using three types of brines with varying degrees of contamination. The studies included microscopic analysis, scanning electron microscopy (SEM) and mercury intrusion capillary pressure (MICP) before and after the experiments. The results showed that the main factor in the decrease in permeability is the formation of a filter cake from secondary iron minerals on the front surface of the core. Filter cake formation was observed in all samples, with ferrous sediment penetrating to a maximum depth of 1.5 cm from the core front. In addition, the mobilisation of clay particles was observed, which accumulate in pore constrictions, causing additional flow restriction. Mercury porosimetry revealed significant increases in hysteresis values in the front zone (from 16.5 to 42%), indicating complex pore connectivity changes without substantial porosity reduction. The rate of injectivity decline correlates strongly with the fluid flow velocity. The results of the study provide a scientific basis for optimising reinjection processes in geothermal systems and developing strategies to prevent formation damage. Full article

The Central Asian Orogenic Belt (CAOB) represents one of the largest Phanerozoic accretionary orogenic systems globally, with its easternmost segment located in Northeast China. This study integrated broadband magnetotelluric (MT) surveys, geochemical analyses, and high-pressure, high-temperature electrical conductivity experiments to elucidate the deep structural characteristics and tectonic evolution of the Heihe-Hegenshan Suture (HHS) within the CAOB. A dense MT profile survey comprising 15 stations was deployed across the HHS, revealing distinct high-conductivity anomalies interpreted as the suture zone and associated tectonic features. Geochemical and petrophysical analyses of representative andesite and granite samples under simulated crustal conditions (573–973 K, 1.0 GPa) provided critical constraints for MT data interpretation. The integration of MT inversion results with aeromagnetic and Bouguer gravity anomaly data delineates the strike and spatial extent of the HHS, confirming its continuity and northward extension beyond previously recognized limits. Numerical modeling of geothermal gradients and electrical conductivity–depth relationships highlights the dominant role of hydrothermal fluids and alteration minerals in controlling shallow high-conductivity anomalies (<5 km), while deeper structures (>5 km) reflect temperature-controlled rock conductivity. These findings offer novel insights into the lithospheric-scale architecture and geodynamic processes governing the HHS, advancing our understanding of complex accretionary orogenesis in the CAOB. Full article

Amid the global energy transition, geothermal energy, as a clean, stable, and renewable energy source, serves as a core direction for energy structure optimization. The development of medium-deep geothermal reservoirs is dominated by thermo–hydro–mechanical (THM) multi-physics coupling effects, yet the quantitative regulation laws of their operational parameters remain unclear. In this study, a numerical model for geothermal extraction considering THM multi-physics coupling was established. Using the single-factor variable method, simulations were conducted within the set parameter ranges of injection–production pressure difference, well spacing, and injection temperature. The spatiotemporal evolution characteristics of the temperature field, the dynamic temperature–pressure responses at the midpoint of injection–production wells and production wells, and efficiency indicators, such as instantaneous heat extraction power and cumulative heat extraction, were analyzed and quantified. The results show that a larger pressure difference accelerates the expansion of the cold zone in the reservoir, which improves short-term heat extraction efficiency but increases the risk of long-term thermal depletion; a smaller well spacing leads to higher initial heat production power but results in lower long-term cumulative heat extraction due to rapid heat consumption; within the normal temperature range of 16–24 °C, the injection temperature has a negligible impact on heat extraction efficiency. This study clarifies the regulatory laws of operational parameters and provides theoretical support for well pattern design and injection–production process optimization in medium-deep geothermal development. Full article

The sustainable exploitation of geothermal energy is often challenged by issues such as groundwater level decline and thermal attenuation. This study focuses on the sandstone thermal reservoir in Linqing City, Shandong Province. A three-dimensional thermo-hydro-mechanical (THM) multi-field coupling numerical model is developed to simulate the evolution of geothermal water levels and temperature fields under varying reinjection rates. The model was validated against observed water level and temperature data, showing maximum deviations of 1.62 m and 0.6 °C. Simulation results indicate that increasing the reinjection rate mitigates water-level decline but accelerates thermal breakthrough, expanding the low-temperature zone. At a 100% reinjection rate, the minimum temperature at the bottom of the thermal reservoir decreases to 63.6 °C, and the low-temperature area extends to 11.61 km². Moderate reinjection rates help to slow thermal energy loss while maintaining reservoir pressure and stabilizing water levels. This study reveals the dual effects of reinjection rate on the balance of geothermal system and puts forward suggestions on optimizing well spacing according to the simulated advance rate of cold waterfront, so as to ensure sustainable thermal recovery. It provides theoretical basis and numerical simulation support for reinjection strategy optimization and well spacing design of similar geothermal fields in Linqing and North China Plain. Full article

The geochemical characteristics of reinjection fluids play a crucial role in controlling water–rock interactions and the long-term stability of geothermal reservoirs. This study aims to evaluate how different fluid chemistries affect mineral dissolution–precipitation behavior and ion migration during geothermal reinjection. Five types of reinjection water—including geothermal source water (i.e., formation water from the reservoir), primary and secondary treated waters, and their mixtures—were reacted with carbonate rocks from the Wumishan Formation of the Xiong’an New Area, North China Basin, under reservoir-like conditions (70 °C, 17 MPa). A combination of batch experiments, inverse modeling using PHREEQC, and one-dimensional reactive transport simulations was employed. Results show that fluid pH, ionic strength, and saturation state significantly influence reaction pathways. Alkaline-treated waters enhanced silicate dissolution, increasing Na⁺, K⁺, and Si concentrations, while source water and its mixtures promoted carbonate precipitation, increasing the risk of clogging. Simulations revealed that the early injection stage is the most reactive, with rapid ion front advancement and strong mineral transformations. Reaction-controlled ions such as Ca²⁺ and SO₄²⁻ formed enrichment zones, while conservative ions like Na⁺ and Cl⁻ propagated more uniformly. Moderate alkaline regulation was found to mitigate carbonate scaling and improve silicate reactivity, thereby reducing permeability loss. This integrated approach provides mechanistic understanding and practical guidance for reinjection fluid design in medium-to-deep geothermal systems. Full article

The efficient utilization of renewable heat sources is important for the performance enhancement of trans-critical CO₂ heat pump systems and for promoting the transformation of energy structures. A composite-heat-source matching ratio is introduced in this article to assess the impact of a high-temperature heat source and low-temperature heat source on the performance of a novel compression/ejection trans-critical CO₂ heat pump (CTHP) system coupled with the use of composite heat sources theoretically. The research results show that the maximum reduction in the optimum gas cooler outlet pressure (P_opt,out,gc) is 3.13% with the increase in evaporating temperature (T_e), and the maximum reduction is 1.67% with the rise in the composite-heat-source matching ratio, which means that the composite-heat-source matching ratio is equally significant on the optimum high-pressure side compared to the T_e. The correlations of optimum high pressure and other optimum cycle parameters for the CTHP system, considering the composite-heat-source matching ratio, were obtained, which provide useful guidelines for optimizing the system design and selecting the appropriate operating conditions. Overall, this article will be helpful for the further development and optimization of the CTHP system, which is of great importance for increasing the utilization rate of renewable heat sources such as geothermal or air-source for urban buildings and accelerating the electrification and low-carbon transformation of terminal energy consumption. Full article

The lack of freshwater and the low efficiency of the traditional solar stills have led to the search to find a technology that can enhance desalination by use of vacuum-enhanced solar still technology. This review intends to investigate the impact of integrating a vacuum into solar stills, which include vacuum membrane distillation (VMD), nanoparticle-enhanced solar stills, multi-effect/tubular solar stills, geothermal integration and parabolic concentrator solar stills. The most important findings show that the productivity improves greatly: vacuum-assisted solar stills give up to 133.6% more product using Cu₂O nanoparticles, and multi-effect tubular stills under vacuum (40−60 kPa) show a doubling in freshwater productivity (7.15 kg/m²) in comparison to atmospheric operation. Geothermal cooling and vacuum pump systems show a 305% increase in productivity, and submerged VMD reached 5.9 to 11.1 kg m⁻² h⁻¹ with solar heating. Passive vacuum designs further reduce the energy used down to a specific cost, using as little as USD 0.0113/kg. Nevertheless, membrane fouling, initial cost, and the complexity of the system can still be termed as the challenges. This review highlights the significance of vacuum-enhanced solar stills to address the critical issue of freshwater scarcity in arid regions. The integration of vacuum membrane distillation, nanoparticle and heat recovery into vacuum-enhanced solar stills enabled us to improve the economic feasibility. We conclude that vacuum technologies significantly boost the efficiency and economic feasibility of solar desalination as a potential approach to sustainable desalination. Specifically, these inventions will contribute to providing a renewable and cost-effective solution for freshwater production. Further investigations are required to overcome the existing challenges, such as system complexity and membrane fouling, to effusively comprehend the efficacy of vacuum-enhanced solar stills to ensure sustainable water management. Full article