Search Results (83)

As a pivotal technology and infrastructure component for modern power systems, energy storage has experienced significant advancement in recent years. A fundamental prerequisite for designing future energy storage facilities lies in the systematic evaluation of energy conversion capabilities across diverse storage technologies. This study conducted a comparative analysis between pumped hydroelectric storage (PHS) and compressed air energy storage (CAES), defining the concepts of height exergy and temperature exergy. Height exergy is the maximum work capacity of a liquid due to height differences, while temperature exergy is the maximum work capacity of a gas due to temperature differences. The temperature exergy represents innovation in thermodynamic analysis; it is derived from internal exergy and proven through the Maxwell relation and the decoupling method of internal exergy, offering a more efficient method for calculating energy storage capacity in CAES systems. Mathematical models of height exergy and temperature exergy were established based on their respective forms. A unified calculation formula was derived, and their respective characteristics were analyzed. In order to show the meaning of temperature exergy more clearly and intuitively, a height exergy model of temperature exergy was established through analogy analysis, and it was concluded that the shape of the reservoir was a cone when comparing water volume to heat quantity, intuitively showing that the cold source had a higher energy storage density than the heat source. Finally, a typical hybrid PHS–CAES system was proposed, and a mathematical model was established and verified in specific cases based on height exergy and temperature exergy. It was demonstrated that when the polytropic exponent n = 1.2, the theoretical loss accounted for the largest proportion, which was 2.06%. Full article

Taking the coastal area of Binhai County, Jiangsu Province, as an example, this study first investigated the basic natural geography and the regional geological and hydrogeological conditions of the study area, and then carried out in-depth geophysical prospecting, hydrogeological tests, geothermal temperature monitoring, hydrochemistry and isotope analyses, and other studies based on the results to comprehensively and systematically reveal the genesis mechanism of the geothermal water resources of this coastal area from multiple perspectives. The results showed the following: the geothermal water in this area mainly comes from atmospheric precipitation; the deep east–northwest interlaced fracture is the recharge and transportation channel; the Cambrian–Ordovician carbonate rock layer, enriched by the development of cavernous fissures, forms the thermal storage layer; the underground heat mainly comes from the upward heat flow along the deep fracture and the natural warming of the strata; and the thermal reservoir cover comprises Paleozoic and Mesozoic clastic rocks that have a high mud content and form a thick layer. The genesis mode of this area is as follows: the atmospheric precipitation infiltrates and is recharged through the exposed alpine carbonate fissures in the Lianyungang area, and then it is transported to the south along the large deep fracture under the action of a high hydraulic pressure head; meanwhile, it is heated by the heat flow in the deep part of the fracture and water–rock interactions with the strata occur. Geothermal water with a calculated thermal storage temperature of 83.6 °C is formed at a depth of 2.9 km, which is blocked by the intersection of the northeast and northwest fractures to form a stagnant zone in the coastal area. Full article

Carbon dioxide (CO₂) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO₂ sorption equilibria under in situ unmineable coal reservoir conditions. This paper presents novel findings on the study of the equilibrium adsorption of CO₂ on two South African coals measured at four temperatures between 30 and 60 °C and pressures up to 9.0 MPa using the volumetric technique. Additionally, the sorption mechanism and thermodynamic nature of the process were studied by fitting the experimental data into Langmuir–Freundlich (Sips), Tóth, and Dubinin–Astakhov (DA) isotherm models, and the Clausius–Clapeyron equation. The findings indicate that the sorption process is highly exothermic, as presented by a negative temperature effect, with the maximum working capacity estimated to range between 3.46 and 4.16 mmol/g, which is also rank- and maceral composition-dependent, with high-rank vitrinite-rich coal yielding more sorption capacity than low-rank inertinite-rich coal. The experimental data fit well in Sips and Tóth models, confirming their applicability in describing the CO₂ sorption behaviour of the coals under the considered conditions. The isosteric heat of adsorption varied from 7.518 to 37.408 kJ/mol for adsorbate loading ranging from 0.4 to 3.6 mmol/g. Overall, the coals studied demonstrate well-developed sorption properties that characteristically make them viable candidates for CO₂ sequestration applications for environmental sustainability. Full article

This study presents an innovative approach for repurposing depleted clastic hydrocarbon reservoirs in Hungary as High-Temperature Aquifer Thermal Energy Storage (HT-ATES) systems, integrating numerical heat transport modeling and machine learning optimization. A detailed hydrogeological model of the Békési Formation was built using historical well logs, core analyses, and production data. Heat transport simulations using MODFLOW/MT3DMS revealed optimal dual-well spacing and injection strategies, achieving peak injection temperatures around 94.9 °C and thermal recovery efficiencies ranging from 81.05% initially to 88.82% after multiple operational cycles, reflecting an efficiency improvement of approximately 8.5%. A Random Forest model trained on simulation outputs predicted thermal recovery performance with high accuracy (R² ≈ 0.87) for candidate wells beyond the original modeling domain, demonstrating computational efficiency gains exceeding 90% compared to conventional simulations. The proposed data-driven methodology significantly accelerates optimal site selection and operational planning, offering substantial economic and environmental benefits and providing a scalable template for similar geothermal energy storage initiatives in other clastic sedimentary basins. Full article

Given the high proportion of global fossil energy consumption, the Ordovician karst water in the North China-type coalfield, as a green energy source that harnesses both water and heat, holds significant potential for mitigating environmental issues associated with fossil fuels. In this work, we collected geothermal water samples and conducted borehole temperature measurements at the Xinhu Coal Mine in the Huaibei Coalfield, analyzed the chemical composition of regional geothermal water, elucidated the characteristics of thermal storage, and explored the influence of regional structure on the karst geothermal system in the northern region. The results indicate that the geothermal water chemistry at the Xinhu Coal Mine is of the Na-K-Cl-SO₄ type, with its chemical composition primarily controlled by evaporation and concentration processes. The average temperature of the Ordovician limestone thermal reservoir is 48.2 °C, and the average water circulation depth is 1153 m, suggesting karst geothermal water undergoing deep circulation. The geothermal gradient at the Xinhu Coal Mine ranges from 22 to 33 °C/km, which falls within the normal range for ground-temperature gradients. A notable jump in the geothermal gradient at well G1 suggests a strong hydraulic connection between deep strata within the mine. The heat-accumulation model of the hydrothermal mine geothermal system is influenced by strata, lithology, and fault structures. The distribution of high ground-temperature gradients in the northern region is a result of the combined effects of heat conduction from deep strata and convection of geothermal water. The Ordovician limestone and extensional faults provide a geological foundation for the abundant water and efficient heat conduction of the thermal reservoirs. Full article

Geothermal energy is typically produced from underground reservoirs using water as the working fluid to transfer heat energy to surface and eventually to the delivery point. CO₂ has been proposed as an alternative working fluid due to its improved mobility, density and its supercritical phase state, leading thus to so-called CPG (CO₂ Plume Geothermal) systems. As a positive side effect, the injected CO₂ mass circulation in the reservoir can be considered a CO₂ storage mechanism, which, depending on the size of the porous medium, may account for few millions of CO₂ tons. Moreover, the thermosiphon effect, owned to the significant change of fluid density between the injection (cold) and the production wells (hot) as well as to its change along the wells, significantly reduces the need for pumping, hence the operating costs. In this work, we setup a mathematical model that fully describes flow in the production/injection wells doublet as well as in the geothermal reservoir. Subsequently, the model is used to evaluate the sensitivity of the beneficial effects of circulating CO₂ rather than water. Parameters such as reservoir properties, injection temperature and thermal effects, are tweaked to demonstrate the sensitivity of each one to the system performance. The results can be utilized as a guideline to the design of such systems and to the emphasis needed to be paid by the engineers. Full article

The conversion and storage of renewable energy into thermal energy is an important part of the low carbon economy. The goaf of a deep mine offers the possibility of large-scale thermal energy storage due to its sufficient underground space. Since the repositories are built inside the goaf backfill and there are few studies on their heat storage capacity and effectiveness, this paper builds an experimental platform based on the similarity theory and selects the geometric similarity ratio of 1:15 to study the phase change heat storage performance of the backfill mine heat storage. Under the typical operating conditions, the temperature distribution of the PCM inside the cylindrical storage unit was analyzed. At the end of heat storage, the temperature distribution of the PCM was 0.93–0.98, but at the end of heat release, the temperature distribution of the PCM was not uniform. At the same time, the heat is reasonably corrected, so that the thermal energy charging effectiveness is increased to 0.98, and the total effectiveness of thermal energy charge and discharge remains 0.87. The parameters of the storage unit are analyzed in detail by changing the water temperature, the flow velocity and the ratio of heat storage and release time of the circulating medium. The experimental results show that when the heat release water temperature is constant and only the heat storage water temperature is changed, the higher the water temperature, the higher the total effectiveness of thermal energy charge and discharge. On the contrary, when the heat storage water temperature is constant and the heat release water temperature is reduced to 14 °C, the total effectiveness of the heat release is increased by 7.5%. When the flow state is in transition, the total effectiveness decreases. The longer the heat storage/release time, the smaller the TSTD_ave inside the PCM and the more uniform the temperature distribution. By restoring the experimental data to the engineering prototype, the repositories installed in the goaf were able to store and extract 422.88 GJ and 375.97 GJ of heat, respectively. Finally, the environmental assessment of the C-LHSU showed that the carbon emissions per unit heating area of the CFB, GWHF and GHF were reduced by 88.1%, 84.2% and 83.0%, respectively. The experimental results show that the cylindrical phase change heat reservoir has higher heat transfer energy efficiency, which provides a theoretical basis and engineering reference for efficient heat storage and utilization in deep mine goafs. Full article

The analysis of metal hydride (MH) tanks requires numerical modeling, which can be complemented by analytical studies. These analytical studies are valuable for swiftly sizing efficient reservoirs intended for hydrogen or thermal energy storage systems. This study aims to develop an analytical model for estimating the filling time of various metal hydride–hydrogen storage tanks under two conditions, with and without heat reaction recovery, utilizing phase change material (PCM). Four scenarios of the metal hydride tank are considered: (i) one with an external electrical drum heater, (ii) one with an external heat transfer fluid, (iii) one with a PCM jacket, and (iv) one with a sandwiched MH-PCM configuration. Furthermore, this study investigates the influence of the MH tank design, geometric parameters (dimensions, geometry), and operational conditions (pressure and temperature) on the filling time. Overall, this investigation offers a basis for calculating the filling times of various metal hydride–hydrogen storage tank types, enabling well-informed design and system optimization decisions. Full article

Although Aquifer Thermal Energy Storage (ATES) systems are widely researched, Fractured Thermal Energy Storage (FTES) systems are comparatively underexplored. This study presents a detailed numerical model of a fractured granitic reservoir at the Bedretto underground laboratory in Switzerland, developed using COMSOL Multiphysics. Energy efficiency was evaluated across different flow rates and well configurations, including single-well and doublet systems, as well as for two different temperatures, namely 60 °C and 120 °C. The doublet configuration at an injection temperature of 60 °C with a flow rate of 2 kg/s demonstrated the highest energy efficiency among the cases studied. Potential applications for the stored heat are discussed, with scenarios including district heating for the nearby village and greenhouse heating. The results show that although FTES is associated with unique challenges, it has significant potential as a reliable thermal energy storage method, particularly in regions without suitable aquifers. It can also be considered as a cost-effective and competitive approach for climate mitigation (assuming the system is solely powered by solar-PV). This study provides insights into the viability and optimization of FTES systems and highlights the role of fracture/fault properties in enhancing energy efficiency. Full article

Aiming at the challenges of rapid heat dissipation, limited swept efficiency, and a rapid water cut increase in steam huff and puff development in heavy oil reservoirs, an alternating steam and CO₂/viscosity reducer huff and puff method for IOR was proposed. In this work, the effect of CO₂ on the physical properties of heavy oil was evaluated, and the optimal concentration of viscosity reducer for synergistic interaction between CO₂ and the viscosity reducer was determined. Next, novel huff and puff simulation experiments by three sandpack models of different sizes in series were analyzed. Then, the IOR difference between the pure steam huff and puff experiments and the steam-alternating CO₂/viscosity reducer huff and puff were compared. Finally, the CO₂ storage rate was obtained based on the principle of the conservation of matter. The results show that the optimal viscosity reducer concentration, 0.8 wt%, can achieve a 98.5% reduction after combining CO₂. The steam-alternating CO₂/viscosity reducer huff and puff reached about 45 cm at 80 °C in the fifth cycle due to the CO₂/viscosity reducer effects. CO₂/viscosity reducer huff and puff significantly reduces water cut during cold production, with an ultimate IOR 15.89% higher than pure steam huff and puff. The viscosity reducer alleviates heavy oil blockages, and CO₂ decreases oil viscosity and enhances elastic repulsion energy. The highest CO₂ storage rate of 76.8% occurs in the initial stage, declining to 15.2% by the sixth cycle, indicating carbon sequestration potential. These findings suggest that steam-alternating CO₂/viscosity reducer huff and puff improves heavy oil reservoir development and provides theoretical guidance for optimizing steam huff and puff processes. Full article

Geothermal resources are abundant in the Southern North China Basin, which is one of the prospective areas hosting low–medium-temperature geothermal resources in sedimentary basins in China. The purpose of this work is to reveal the formation and storage conditions of the geothermal resources in the western margin of the Taikang Uplift and delineate the range of potential geothermal reservoirs. This paper uses five magnetotelluric sounding profiles for data processing and analysis, including the calculation of 2D skewness and electric strike. Data processing, analysis, and NLCG 2D inversion were performed on MT data, which consisted of 111 measurement points, and reliable two-dimensional resistivity models and resistivity planes were obtained. In combination with drilling verification and the analysis of geophysical logging data, the stratigraphic lithology and the range of potential geothermal reservoirs were largely clarified. The results show that using the magnetotelluric sounding method can well delineate the range of deep geothermal reservoirs in sedimentary basins and that the MT method is suitable for exploring buried geothermal resources in deep plains. The analytical results showed that the XZR-1 well yielded 1480 cubic meters of water per day, with the water temperature of the wellhead being approximately 78 °C, and combined with the results of this electromagnetic and drilling exploration, a geothermal geological model and genesis process of the west of the Taikang Uplift area was constructed. The water yield and temperature were higher than those of previous exploration results, which has important guiding significance for the future development and utilization of karst fissure heat reservoirs in the western Taikang Uplift. Full article

At present, there are relatively few studies on the exploitation of geothermal resources in depleted high-temperature gas reservoirs with carbon dioxide (CO₂) as the heat-carrying medium. Taking the high-temperature gas reservoir of the Huangliu Formation in the Yingqiong Basin as the research object, we construct an ideal thermal and storage coupling model of a CO₂ plume geothermal system using COMSOL6.2 software to conduct a sensitivity analysis of geological parameters in the operation of a CO₂ plume geothermal system. The simulation results show that, compared with medium- and low-temperature reservoirs, a high-temperature reservoir exhibits higher fluid temperature in the production well and a higher heat extraction rate owing to a higher initial reservoir temperature but has a shorter system operational lifetime; the influence of the thermal conductivity of a thermal reservoir on the CO₂ plume geothermal system is relatively minor, being basically negligible; and the thinner the thermal reservoir is, the faster the fluid temperature in the production well decreases and the shorter the thermal breakthrough time. These findings form a basis for selecting heat extraction areas for CO₂ plume geothermal systems and also provide a theoretical reference for future practical CO₂ plume geothermal system projects. Full article

As a renewable resource, geothermal energy plays an increasingly important role in global and regional energy structures. Influenced by regional tectonic activities, multi-stage thermal evolution, and continuous subsidence, the subsurface temperatures in the Yinggehai Basin has been consistently rising, resulting in the formation of multiple geothermal reservoirs. The Neogene Huangliu Formation, with its high geothermal gradients, suitable burial depths, considerable thickness, and wide distribution, provides excellent geological conditions for substantial geothermal resources. However, the thermal storage characteristics and geothermal resources of this formation have not been fully assessed, limiting their effective development. This study systematically collected and analyzed drilling, geological, and geophysical data to examine these reservoirs’ geometric structures, thermal properties, and physical characteristics. Further, we quantitatively evaluated the geothermal resource potential of the Huangliu Formation and its respective reservoirs through volumetric estimation and Monte Carlo simulations, pointing zones with high geothermal prospects and formulating targeted development strategies. The findings indicate: (1) The Yinggehai Basin exhibits an average geothermal gradient of 39.4 ± 4.7 °C/km and an average terrestrial heat flow of 77.4 ± 19.1 mW/m², demonstrating a favorable geothermal background; (2) The central depression of the Huangliu Formation harbors considerable geothermal resource potential, with an average reservoir temperature of 140.9 °C, and a total geothermal resource quantified at approximately 2.75 × 10²⁰ J, equivalent to 93.95 × 10⁸ tec. Monte Carlo projections estimate the maximum potential resource at about 3.10 × 10²⁰ J, approximately 105.9 ×10⁸ tec. (3) Additionally, the R14 and R23 reservoirs have been identified as possessing the highest potential for geothermal resource development. The study also proposes a comprehensive utilization model that integrates offshore geothermal power generation with multiple applications. These findings provide a method for the evaluation of geothermal resources in the Yinggehai Basin and lay a foundation for the sustainable development of resources. Full article

This study introduces a robust methodology utilizing Multi-Criteria Decision Analysis (MCDA) combined with an Analytic Hierarchy Process (AHP) to repurpose abandoned hydrocarbon fields for energy storage, supporting the transition to renewable energy sources. We use a geostatistical approach integrated with Python scripting to analyze reservoir parameters—including porosity, permeability, thickness, lithology, temperature, heat capacity, and thermal conductivity—from a decommissioned hydrocarbon field in Southeast Hungary. Our workflow leverages stochastic simulation data to identify potential zones for energy storage, categorizing them into high-, moderate-, and low-suitability scenarios. This innovative approach provides rapid and precise analysis, enabling effective decision-making for energy storage implementation in depleted fields. The key finding is the development of a methodology that can quickly and accurately assess the feasibility of repurposing abandoned hydrocarbon reservoirs for underground thermal energy storage, offering a practical solution for sustainable energy transition. Full article

The adsorption of CO₂ fracturing fluid into coal reservoirs causes the expansion of the coal matrix volume, resulting in changes in the fracture opening, which alters the permeability of the coal reservoir. However, it is not yet clear whether thermal expansion during CO₂ adsorption on coal is the main cause of coal adsorption expansion. Therefore, by testing the thermal properties, expansion coefficient, and adsorption heat of the three coal samples, the adsorption thermal expansion characteristics of coal and their impact on the permeability of coal reservoirs are clarified. The results reveal the following: (1) Under the same conditions, the adsorption heat increases with increasing pressure, while it decreases with increasing temperature. The relationship between adsorption heat and pressure conforms to the Langmuir equation before 40 °C, and it follows a second-order equation beyond 40 °C. At 100 °C, the adsorption heat of coal samples to CO₂ is primarily determined by temperature. (2) The maximum temperature variation in coal samples from Xinjiang, Liulin, and Zhaozhuang during CO₂ adsorption is 95.767 °C, 87.463 °C, and 97.8 °C, respectively. The maximum thermal expansion rates are 12.66%, 5.74%, and 14.37%, and the maximum permeability loss rates are 16.16%, 7.51%, and 18.24%, respectively, indicating that thermal expansion is the main reason for coal adsorption expansion. (3) This research can elucidate the impact of CO₂ fracturing fluid on coal reservoirs and its potential application value, thus providing theoretical support for coalbed methane development and CO₂ geological storage. Full article