Geothermal Energy最新文献

Sustainable utilization of sandstone geothermal resources is a worldwide challenge due to limited natural recharge and rapid aquifer clogging associated with reinjection of return water back into reservoirs. In the Dezhou area of the North Shandong Plain (NSP), China, technical solutions for successful reinjection have been developed and applied based on nearly 30 years of production experience from the Guantao geothermal reservoir. These solutions include drilling large-diameter reinjection wells, filtration systems, oxygen-free configuration, back-pumping, and acidification. To further investigate the reservoir properties, a pumping test, three reinjection tests, and a tracer test were carried out in a dedicated experimental field setup in Dezhou, which included one regular diameter production well and one large diameter reinjection well. This study integrates effective reinjection technologies with long-term sustainability assessment, providing a comprehensive framework for managing low-temperature sandstone geothermal systems. Based on long-term water-level monitoring data and lumped parameter modelling, a sustainable yield assessment of the reservoir in the urban Dezhou area has been performed, with the deepest permissible water level at 150 m below ground surface over a 100-year time frame. The results suggest that reinjection is the dominant factor influencing sustainability. When the reinjection rate approaches 90%, the sustainable yield corresponds to an average value of 1300 L/s during the space heating period and 500 L/s annually. Using volumetric energy balance calculations, the average thermal energy loss over 100 years of reinjecting cooled return water is estimated to constitute 3% and 8% of the total energy stored relative to the volumes of the closed and open lumped parameter models, respectively. This indicates that the cooling assessment of reinjection should further concentrate on the cooling distribution in the reservoir and the decrease in reservoir temperature in particular locations. This study emphasizes the importance of integrating reinjection strategies with sustainability assessments and highlights the need for continued long-term geothermal resource management research for porous sandstone reservoirs.

This study explores the application of a gas lift system for extracting geothermal fluids from enhanced geothermal systems (EGS) with reservoir temperatures exceeding (400^{circ })C ((752^{circ })F) and depths up to 15 km (9.3 mi). Using a validated numerical pressure gradient model, 15 different 3D-printed gas sparger designs were tested through over 100 scaled experiments. The investigation focused on critical parameters, including the submergence ratio, venturi area, orifice size, and orifice count. The optimal sparger featured a venturi area of 95% and 51 orifices, which increased the flow rate by 24% and efficiency by 30% compared to a baseline design without a sparger. Although partial blockage of orifices reduced performance, it did not critically affect system operation, demonstrating the sparger's robustness. Numerical extrapolation to a 4000 ft deep EGS well indicated that optimized spargers could increase the pressure gradient by 10% on average, resulting in a 30% boost in water production at the same wellhead pressure and injection flow rate as a setup without a sparger. These results highlight the potential for gas lift systems with optimized spargers as an efficient, low-maintenance alternative to conventional pumps in harsh EGS geothermal environments.

Triassic sandstones of the Middle and Upper Buntsandstein are highly suitable for ground source heat pump (GSHP) systems. Thus, knowledge of their thermal properties, which can be measured or estimated by theoretical models, is crucial. However, the transferability of estimated thermal conductivities to the field scale has not yet been thoroughly examined. Therefore, in this study, the thermal and lithological properties of 156 core samples from a borehole in the Buntsandstein are analysed in the laboratory. Various theoretical models are applied and compared to the laboratory-derived thermal conductivities. The best agreement is achieved with the Voigt-Reuss-Hill model with an average thermal conductivity of 4.5 W m⁻¹ K⁻¹ and an RMSE of 0.7 W m⁻¹ K⁻¹ (T = 20 °C). The results of this model are compared to depth-specific, effective thermal conductivities from an enhanced thermal response test (ETRT). These effective thermal conductivities range between 2.3 and 6.1 W m⁻¹ K⁻¹ with an average of 4.7 W m⁻¹ K⁻¹. We demonstrate that some theoretical models can provide an initial estimation of the effective thermal conductivity of sandstones when groundwater flow is negligible. However, the accuracy of the estimation is limited by sample quantity and model assumptions.

Geothermal energy is a promising solution to meet the increasing global energy demand while mitigate climate change. In recent years, the utilization of carbon dioxide (CO₂), especially supercritical CO₂ (SCCO₂), for geothermal energy recovery has attracted increasing attention. This study introduces and simulates a modified cyclic SCCO₂ injection method for geothermal energy recovery, marking the first exploration of its kind. We analyzed the SCCO₂ injection process under various well patterns and injection modes, comparing the cumulative energy recovery performance of cyclic and continuous injection across different models. Our findings revealed that the original reservoir dominates the initial energy production until the SCCO₂ breakthrough. After the breakthrough, cyclic injection should be utilized to enhance energy production, with higher heat extraction efficiency and the mitigation of the thermal breakthrough effect. In addition, our findings suggest that an optimal combination of cyclic and continuous injection can leverage the advantages of both strategies. Through further optimization, modified cyclic SCCO₂ injection method enhances energy production, achieving up to a 59% improvement in cumulative energy production (4.155E14J) and a 200% increase in NPV ($600,000) compared to baseline scenarios, with higher heat extraction efficiency and mitigation of thermal breakthrough effects.

The Northern Alpine Foreland Basin in southeast Germany hosts more deep geothermal plants than any other region in the country. Its primary aquifer, the Upper Jurassic, is composed of permeable carbonates containing water with temperatures exceeding (150,^{circ })C in the southern margin and low total dissolved solids ((le) 2 g/L) at depths of up to 4000 m. Its sustainable use of geothermal energy depends on an efficient exploitation strategy concerning the entire reservoir, which is influenced by the development of flow paths between production and reinjection wells. The Upper Jurassic’s waters show a carbonate signature with calcium and magnesium often replaced by sodium due to ion exchange along the infiltration pathways. These waters become undersaturated upon cooling, and dissolution around reinjection wells has been previously documented. Assessing short- to medium-term localized dissolution experimentally is challenging. While dissolution kinetics and overall volume changes have been studied in the field, microscopic changes to flow paths remain less under investigation. This study used a time-lapse experiment to evaluate microscopic changes during dissolution in limestone samples exposed to elevated (text {CO}_{2}) partial pressure in an autoclave. For an effective observation, we used artificial structures to localize the dissolution effects. Post-treatment analysis included Raman microscopy, 3D micro-scanning, confocal laser scanning microscopy (CLSM), and optical microscopy with image stacking, with a strong focus on the latter three. Each imaging method had distinct strengths and limitations. CLSM provided high-resolution surface roughness assessments but could not capture areas beneath overhangs. Optical microscopy is affordable and user-friendly and was effective for visualizing preferential dissolution pathways but lacked precise roughness information. 3D micro-scanning, despite lower resolution, uniquely resolved overhangs. The dissolution processes led to significant surface roughening, forming micrometer-scale moldic pores and preferential pathways. Artificial structures widened and deformed, with 3D micro-scanning quantifying these changes effectively and CLSM revealing fine-scale roughness details. Increased fracture surface roughness and widening of flow paths enhance water transport and dissolution, potentially accelerating thermal breakthroughs at geothermal plants. Understanding these processes is essential for predicting reservoir behavior, improving geothermal energy extraction efficiency, and exploiting aquifers sustainably.

Co-production of geothermal energy and lithium is an emerging opportunity with the potential to enhance the economic potential of geothermal operations. The economic reward of extracting lithium from geothermal brine is determined by how the lithium concentration evolves during brine production. In the initial stage, production will target lithium contained in the brine resident close to the production well. While lithium recharge, in the form of rock dissolution and inflow from other parts of the reservoir, is possible, the efficiency of such recharge depends on the geology of the reservoir. In this work, we study how structural heterogeneities in the form of fractures impact the flow of lithium-carrying brine. Using a simulation tool that gives high resolution of flow and transport in fractures and the host rock, we study how the presence of fractures influences energy and lithium production. Our simulations show that, due to heat conduction and the lack of mineral recharge from the rock, differences in fracture network geometries have a much larger impact on lithium production than energy production. The simulations thus confirm that in addition to the geochemical characterisation of lithium in geothermal brines, understanding fracture characterisation and its impact on production is highly important for lithium production.

Numerous studies have shown the relationship between alteration mineralogy and the characteristics of a geothermal system, as well as the fluid–rock interaction processes. Secondary minerals in such systems have been described as dependent on temperature, pH, fluid composition and lithology, with these being the main factors controlling their formation and characteristics. In this new study we establish a detailed hydrothermal mineralogy and depth zoning associated to the geothermal system of the Irruputuncu volcano. This is a currently active volcano with geothermal manifestations and is mainly composed of andesitic to dacitic lavas built on top of various ignimbrites and older lava flows. Samples were obtained from two continuous drill cores from wells PGC-01 and PGC-02. Petrographic analysis and X-ray diffraction data have shown the presence of calcite and anhydrite in association with clay minerals and interstratified clays as the main secondary mineralogy. Characterization of alteration mineralogy allowed to identify boiling and mixing of fluids as the main hydrothermal processes involved in their formation. It also permitted the identification of two alteration types, an argillic/intermediate argillic and a subpropylitic, reflecting temperatures near the 100–200 °C range and neutral to slightly acidic fluids. Secondary minerals distribution and alteration style were also used to distinguish different zones within the system, which were mainly associated with variations in permeability and fluid chemistry. Lastly, a model was developed clearly explaining previous interpretations of mineralogy and apparent electrical resistivity, giving a framework for future geothermal development in Chile and evidencing that factors such as fluid chemistry, lithology and permeability can play an equal or higher role than temperature in similar systems.

This study investigates petrological and thermophysical properties of rocks from the Estopanyà and Boix synclines (salt basins) to evaluate their potential as analogues for geothermal reservoir. A total of 45 samples were collected, including 26 carbonates, 16 arenites, and 3 altered carbonates (chalky limestones and calcitized dolomites). These samples were classified into eight distinct rock types based on 106 thin sections. Thermophysical measurements revealed mineral densities ranging from 2.64 to 2.72 g cm⁻³ and variable connected porosity (0.50–17.63%), permeability (< 0.001 to 15.30 mD, equivalent to < 10⁻¹⁸ to 10⁻¹⁴ m²), P-wave velocities (1.8–6.6 km s⁻¹ in dry and 2.7–6.3 km s⁻¹ in water-saturated samples), thermal conductivity (2.1–4.7 W m⁻¹ K⁻¹), and specific heat capacity (724–860 J kg⁻¹ K⁻¹). Correlations between thermophysical properties suggest that connected porosity predominantly influences permeability, P-wave velocity, and specific heat. In contrast, thermal conductivity is more dependent on rock composition. Key diagenetic processes such as dissolution, cementation, brecciation, and dolomitization significantly alter rock texture and composition, impacting critical thermophysical properties (e.g., thermal conductivity, permeability, and porosity), essential for geothermal reservoir potential. These alterations are particularly pronounced near the Estopanyà salt wall, indicating that fluid flow along diapir margins intensifies rock alteration. Away from the diapir margin, these effects diminish, underscoring the localized influence of salt diapirism. Results indicate that natural fluid convection likely occurred in two sedimentary units within the Estopanyà and Boix synclines. The first unit, composed of diapir-margin breccias, probably had high permeability in the past, as suggested by its present-day intense cementation. Similarly, the ongoing dedolomitization of these breccias also hints for a past dolomitization in them, which should have enhanced the thermal conductivity of this unit in the past, making it a favorable geothermal target prior to cementation and dedolomitization. The second unit consists of arenites from the Tremp Group, which exhibit sufficient permeability for fluid storage but lack the necessary permeability for natural fluid convection, in the absence of open fractures. These surface data underscore the value of outcrop analogues, demonstrating how petrological insights can reveal past geological processes that influence the thermophysical properties and reservoir potential of salt basins.