Geothermal Energy最新文献

Large-scale ground source heat pump (GSHP) systems are increasingly used for space heating and cooling. In comparison with smaller ones, large GSHP systems are often coupled with much more borehole heat exchangers (BHEs). Because of the intense thermal interactions between BHEs, they are more susceptible to significant ground temperature changes. Meanwhile, they possess the advantage that their operational strategies can be applied with a high degree of freedom, which presents chances to alleviate intense thermal interactions. In this study, we used a new performance indicator to access the effectiveness of GSHP operational strategies on alleviating thermal anomalies. The Daxing Airport GSHP system, contains 10,497 BHEs and is the largest in the world; therefore, it was selected as the test case for performance enhancement through operational strategies. We established a 2D model to predict ground temperature changes during the 50-year operation of the BHEs. First, it was revealed that the most severe thermal anomalies in the study area mainly occurred both within and between the BHE arrays, which should be mitigated. To alleviate the thermal anomalies caused by the thermal interactions of BHEs, operational strategies were applied by adjusting the cooling/heating starting sequence, setting time-dependent thermal loads, and reallocating thermal loads according to the position of the BHEs. Our study demonstrates that only the operation strategy that adjusts the cooling/heating starting sequence is beneficial for different BHE layouts, while the operational strategy that reallocates the thermal loads depending on BHEs position may be only effective for specific BHE layouts. In addition, our new performance indicator can be used to evaluate the effectiveness of the operational strategies and determine the spacing of adjacent BHE arrays. Therefore, it benefits the operation management of BHE array and design of BHE layout, and further guarantees the sustainable operation of the GSHP system.

The heat transfer along horizontal connection pipes in geothermal bore fields can have significant effects and should not be neglected. As practical and design-related applications require simple and efficient models, we investigate suitability of different models for the first time within this context. Three ground and three pipe models of different complexity are studied. All model combinations are coupled with a fixed ground load boundary condition on one side and a borehole heat exchanger (BHE) model on the other side. Models are tested under a variety of realistic conditions to evaluate performance. The investigations show that all investigated pipe models are equally suitable for the application. For the ground models, the horizontal finite line source model and the numerical 2D model produce identical results for homogeneous ground properties. The soil resistance model neglects the temperature accumulation in the ground and thus leads to considerable deviations and should be avoided. Based on the findings, we propose a computationally efficient approach using a novel combination of established simple steady-state models for the BHE and connection pipes. In the selected example scenario, the consideration of a 30 m connection pipe attached to the BHE leads to an increase in the BHE load by 40% for the heating case and a reduction in the BHE load by 5% for the cooling case.

The Tell Atlas of Algeria has a huge potential for hydrothermal energy from over 240 thermal springs with temperatures up to (98^circ) C in the Guelma area. The most exciting region is situated in the northeastern part which is known to have the hottest hydrothermal systems. In this work, we use a high-resolution gravity study to identify the location and origin of the hot water, and how it reaches the surface. Gravimetric data analysis shows the shapes of the anomalies arising due to structures at different subsurface depths. The calculation of the energy spectrum for the data also showcases the depths of the bodies causing anomalies. 3D-Euler deconvolution is applied to estimate the depths of preexisting tectonic structures (faults). These preprocessing steps assist with assessing signal attenuation that impacts the Bouguer anomaly map. The residual anomaly is used in a three-dimensional inversion to provide a subsurface density distribution model that illustrates the locations of the origin of the dominant subsurface thermal systems. Overall, the combination of these standard processing steps applied to the measurements of gravity data at the surface provides new insights about the sources of the hydrothermal systems in the Hammam Debagh and Hammam Ouled Ali regions. Faults that are key to the water infiltrating from depth to the surface are also identified. These represent the pathway of the hot water in the study area.

The Thrace Basin in northwestern Turkey is a deep Eocene–Oligocene hydrocarbon-bearing sedimentary basin. The basin has potential for geothermal energy utilization in the future due to its favorable geological conditions. In this study, we combined the available bottom hole temperature (BHT) data from 70 points with the thermal conductivity and radiogenic heat productions of the basin formations, and generated a detailed thermal model of the northern part of the basin. For heat flow determinations from the BHT data, we applied Bullard’s thermal resistance method on formation thermal conductivities and thicknesses. The results give an average surface heat flow of 65.8 ± 11.3 mW/m². We obtained high heat flow values (75–80 mW/m²) in the eastern and western sides, and the central part of the study area. These relatively high heat flow values can be explained by the combined effect of basement topography and the variations in the radiogenic heat production of the basement rocks. The calculated subsurface temperatures in selected hydrocarbon fields vary in the range of 45–64 °C at 1 km depth, 99–136 °C at 3 km depth, and 155–208 °C at 5 km depth as a result of local variations of the surface heat flow and formation thermal resistances. These variations in subsurface temperatures can have significant effects on the cost of geothermal energy production in future.

In order to compensate for the variable mismatch between heat demand and heat production from renewable sources or waste heat, high-temperature aquifer thermal energy storage (HT-ATES) is a promising option. A reliable prediction of the energetic performance as well as thermal and hydraulic impacts of a HT-ATES requires a suitable model parameterization regarding the subsurface properties. In order to identify the subsurface parameters on which investigation efforts should be focused, we carried out an extensive sensitivity analysis of the thermal and hydraulic parameters for a high-temperature heat injection test (HIT) using numerical modeling of the governing coupled thermo-hydraulic processes. The heat injection test was carried out in a quaternary shallow aquifer using injection temperatures of about 75 °C over 5 days, accompanied by an extensive temperature monitoring. The sensitivity analysis is conducted for parameter ranges based on literature values, based on site investigation at the HIT site and based on a model calibrated to the measured temperature distribution following the heat injection. Comparing the parameter ranges thus obtained in this three-step approach allows to identify those parameters, for which model prediction uncertainty decreased most, which are also the parameters, that strongly affect the thermal behavior. The highest sensitivity is found for vertical and horizontal hydraulic conductivity as well as for groundwater flow velocity, indicating that investigation efforts for HT-ATES projects should focus on these parameters. Heat capacity and thermal conductivity have a smaller impact on the temperature distribution. Our work thus yields a consistent approach to identifying the parameters which can be best restricted by field investigations and subsequent model calibration. Focusing on these during field investigations thus enable improved model predictions of both HT-ATES operation and induced impacts.

The expanding geothermal energy sector still faces performance issues due to scalings in pipes and surface level installations, which require elevated operation pressure levels and costly maintenance. For facilities in the North Alpine Foreland Basin, the precipitation of ({hbox {CaCO}}_{3}) is the main problem which is a consequence of the disruption of the lime-carbonic acid equilibrium during production. The formation of gas bubbles plays a key role in the scaling process. This work presents experiments in a bubble column to quantify the effects of gas stripping on carbonate precipitation and an extension of PhreeqC to include kinetic exchange between a gas phase and water for the simulation of the experimental results. With the same hybrid model not only precipitation of ({hbox {CaCO}}_{3}) but also the dissolution of scalings by the injection of ({hbox {CO}}_{2}) could be quantified. The bubble column was filled with tap water and brine. By varying the ionic strength of the solution, a wider range of geothermal waters was covered. Air and ({hbox {CO}}_{2}) were introduced at the bottom. The precipitates built on the column wall were analyzed with Raman spectroscopy: injecting air into tap water at low ionic strength led to the formation of aragonite with 59.8% of the precipitates remaining at the column wall and the rest as particles in dispersion. At moderate ionic strength the dominant polymorph was calcite and 81.5% of the crystals were attached to the wall. At high ionic strength precipitation was inhibited. The presence of crystallization nuclei reduced the time for precipitation, but not the amount of scalings formed. Injecting ({hbox {CO}}_{2}) into the solution completely removed the scalings from the column wall. The model and its experimental backup lay the foundation for a process-based prediction of the scales (not only) in geothermal systems.

Geothermal heat pumps are one of the most growing and cost-effective renewable energy technologies based on the temperature difference between the ground and the environment. In the cold seasons, the temperature inside the soil or water is higher than the ambient temperature. Therefore, the heat pump is used to extract the warm temperature of the ground into the house or any other controlled space. In the summer, the air temperature is higher than the temperature of the soil or water. This temperature difference is used again to cool the house or any other environment. This paper examines the energy and exergy assessments of a hybrid system in Shanghai, China, that employs a geothermal heat pump with an economizer for winter heating and a wind turbine to provide clean electricity. The complete set of procedures, as well as every component and every aspect of the hybrid system, have all been carefully examined. The heat pump's coefficient of performance is 3.916, its net power output is 22.03 kW, its overall energy efficiency is 77.2%, and its exergy efficiency is 25.49%.

Graphical Abstract

Open-loop borehole heat exchanger (OBHE) is a single well geothermal heat exchanger with an open-loop structure that can realize the geothermal energy extraction without mining the geothermal water. In this paper, a sandbox experiment is designed to simulate the convective heat transfer process in the reservoir area of OBHE. The mechanism of convective heat transfer in the reservoir area is studied, and the key factors that affect the convection heat transfer intensity are analyzed. The results show that the convection heat transfer of OBHE in the reservoir area is affected by both the driving effect of fluid flow inside the screen tube and the buoyancy effect. In the forward flow mode, the two effects have the opposite direction. While in the backward mode, the two effects have the same direction. The backward flow mode is more conducive to convective heat transfer. In addition, many factors influencing significantly the convective heat transfer of OBHE include inlet temperature, inlet flow rate, reservoir temperature, fluid flow direction and inner tube diameter.

Recent researches have proposed the use of enhanced geothermal system reservoirs consisting of dense networks of microfractures, created by hydraulic and/or thermal fracturing in superhot/supercritical geothermal environments, because of their suitability for thermal energy harvesting. During fracturing and energy extraction, the fracture networks are exposed to cooling due to the injection of cold fluid into the reservoirs. Previous studies showed such cooling enhanced reservoir permeability in conventional geothermal environments. However, the cooling may result in a higher risk of seismicity, owing to decreased normal stress on the fractures. Nevertheless, it is unclear whether cooling-induced permeability enhancement and a higher risk of seismicity occurs within networks of microfractures which consist of numerous interconnected microfractures at various orientations to the in situ triaxial stress. Thus, no dominant fractures have the possibility to cause permeability enhancement/induced seismicity. In this study, results are presented for borehole cooling experiments on a dense network of microfractures in granite, at 400 °C, under true triaxial stress. Permeability and acoustic emissions were measured with decreases in borehole temperature (up to ~ 90 °C). Results showed that permeability increased with increasing temperature drop at relatively low stress levels (15 and 20 MPa). The permeability enhancement occurred without intensive failure, and was reversible. However, permeability was almost constant at a higher stress level (65 MPa). Results showed that permeability enhancement required a thermal stress equivalent to the mean stress, so that the normal stress was reduced to near-zero, for a considerable amount of the microfractures. Additionally, the permeability of dense microfracture networks can be increased by cooling primarily through thermo-elastic deformation (without intensive failure), which may be useful to compensate for the reduction in injectivity due to cooling-induced fluid property changes.