An HPC-Based Hydrothermal Finite Element Simulator for Modeling Underground Response to Community-Scale Geothermal Energy Production

Geothermal heat, as renewable energy, shows great advantage with respect to its environmental impact due to its significantly lower CO2 emissions than conventional fossil fuel. Open and closed-loop geothermal heat pumps, which utilize shallow geothermal systems, are an efficient technology for cooling and heating buildings, especially in urban areas. Integrated use of geothermal energy technologies for district heating, cooling, and thermal energy storage can be applied to optimize the subsurface for communities to provide them with multiple sustainable energy and community resilience benefits. The utilization of the subsurface resources may lead to a variation in the underground environment, which might further impact local environmental conditions. However, very few simulators can handle such a highly complex set of coupled computations on a regional or city scale. We have developed high-performance computing (HPC) based hydrothermal finite element (FE) simulator that can simulate the subsurface and its hydrothermal conditions at a scale of tens of km. The HPC simulator enables us to investigate the subsurface thermal and hydrologic response to the built underground environment (such as basements and subways) at the community scale. In this study, a coupled hydrothermal simulator is developed based on the open-source finite element library deal.II. The HPC simulator was validated by comparing the results of a benchmark case study against COMSOL Multiphysics, in which Aquifer Thermal Energy Storage (ATES) is modeled and a process of heat injection into ATES is simulated. The use of an energy pile system at the Treasure Island redevelopment site (San Francisco, CA, USA) was selected as a case study to demonstrate the HPC capability of the developed simulator. The simulator is capable of modeling multiple city-scale geothermal scenarios in a reasonable amount of time.Comment: 46th Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 15-17, 202

GIS platform for management of shallow geothermal resources

Premi extraordinari doctorat UPC curs 2015-2016, àmbit d’Enginyeria CivilThis thesis promotes an efficient use of shallow geothermal energy by means of an integrated management system to organize its exploitation. Shallow geothermal energy is a renewable resource based on thermal energy exchange with the ground. Due to the growth in demand for this energy, the development of management techniques to organize the exploitation of this resource is mandatory to protect both groundwater and the users' rights. Shallow geothermal performance of underground is closely related to groundwater behavior, so it is necessary to understand and improve the knowledge about it. Thus, an integrated methodology is proposed for the 3D visualization of underground resources related to groundwater. A set of tools named HEROS3D was developed in a GIS environment to support the generation of 3D entities representing geological, hydrogeological, hydrochemical and geothermal features. The GIS technology also gives a wide-ranging support to environmental modeling, either conceptual or numerical, especially to groundwater modeling. However, there is a scarcity of tools to implement the conceptual model in numerical modeling platforms. This transition needs of specific methodologies to adapt the geometries and alpha-numerical data from the conceptual model to the numerical model to get optimal numerical results. Although most necessities can be satisfied with inherent GIS tools, there are particular steps in the implementation of hydrogeological conceptual model into the numerical modeling software that have not been solved yet. To overcome this gap, a set of tools is presented, named ArcArAz. It focuses on the configuration of geometry and parameterization for groundwater numerical models. Once both the hydrogeological conceptual model and the numerical model are defined, a solid basis for management of Shallow Geothermal energy is available. This thesis proposes two methodologies for the management of this energy resource at two different scales: for a regional scale and for a metropolitan scale. The first GIS methodology provides a response to the need for a regional quantification of the geothermal potential that can be extracted by Boreholes Heat Exchangers and its associated environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are considered in the regional estimation of the variables of interest. A sensitivity analysis leads to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated. To deepen the management of Shallow Geothermal Energy, this thesis proposes to establish a market of shallow geothermal energy use rights which would allow managing this resource at a metropolitan scale. This methodology is based on a GIS framework and is composed of a geospatial database to store the main information required to manage the installations and a set of GIS tools used to define, implant and control this use rights market. Thermal impacts derived from the exploitation of this resource can also be registered geographically, by taking into account the groundwater flow direction and adjusting the thermal impact to the available plot.Esta tesis promueve el uso eficiente de la geotermia somera a través de un sistema integrado de gestión de este recurso. La geotermia somera es un recurso renovable que se basa en el intercambio de energía con el suelo. Los Intercambiadores de calor, o Borehole Heat Exchangers (BHEs) se están popularizando como sistema para explotarla. Debido al crecimiento en la demanda de geotermia somera, es imprescindible establecer una gestión integrada de este recurso para organizar su explotación y proteger tanto a las aguas subterráneas como a los beneficiarios de esta energía renovable. Debido a que la geotermia somera está íntimamente relacionada con el comportamiento de las aguas subterráneas, es imprescindible ahondar y mejorar su conocimiento. Para ello, se propone una metodología para la visualización tridimensional de los recursos subterráneos relacionados con la hidrogeología. Se ha desarrollado un conjunto de herramientas, llamado HEROS3D, en un entorno SIG. Estas herramientas facilitan la creación de entidades tridimensionales que representan datos geológicos, hidrogeológicos, hidrogeoquímicos y geotermales. Están relacionadas con una base de datos donde tanto la información bruta como la interpretada se encuentran almacenadas. La tecnología SIG también da soporte, no sólo a la modelación conceptual, sino también a la numérica, especialmente en el caso de la hidrogeología. Para facilitar la implementación de los modelos conceptuales en las plataformas de modelación numérica, esta tesis presenta un segundo conjunto de herramientas llamado ArcArAz. Estas herramientas ofrecen soluciones a los problemas más comunes relacionados con la configuración de la geometría de entrada al modelo numérico, así como su parametrización. Las bases para una gestión eficiente de la geotermia somera se establecen llamado ArcArAz. Estas herramientas ofrecen soluciones a los problemas más comunes relacionados con la configuración de la geometría de entrada al modelo numérico, así como su parametrización. Las bases para una gestión eficiente de la geotermia somera se establecen una vez que hemos definido y están disponibles tanto el modelo hidrogeológico conceptual como el modelo numérico. En relación a este aspecto, en esta tesis se proponen dos metodologías de gestión enfocadas a escalas diferentes: escala regional y escala metropolitana o local. La primera metodología SIG ofrece una respuesta a la necesidad de una cuantificación regional del potencial geotérmico somero que puede extraerse con intercambiadores de calor o Borehole Heat Exchangers, así como sus impactos térmicos asociados. Por primera vez pueden tenerse en cuenta en la estimación regional de las variables de interés la advección y dispersión de calor, como mecanismos de transporte de calor, así como la evolución temporal desde el inicio de la explotación. Un análisis de sensibilidad demuestra que la consideración de los efectos de dispersión así como el régimen temporal de la explotación supone diferencias de hasta 2.5 veces el potencial extraído y hasta de varios ordenes de magnitud en los impactos térmicos generados. Para profundizar en la gestión de la geotermia somera a escala local, esta tesis propone establecer un mercado de derechos de uso de este recurso. Esta metodología se ha implementado en un ambiente SIG y está compuesta de una base de datos donde se almacena la información principal necesaria para gestionar las instalaciones y de un conjunto de herramientas para definir, implantar y controlar este mercado de derechos de uso de geotermia somera. Los impactos térmicos derivados de la explotación de este recurso pueden quedar registrados geográficamente, teniendo en cuenta la dirección de flujo de las aguas subterráneas y ajustando estos impactos a la superficie de la parcela disponible una vez que hemos definido y están disponibles tanto el modelo hidrogeológico conceptual como el modelo numérico. En relación a este aspecto, en esta tesis se proponen dos metodologías de gestión enfocadas a escalas diferentes: escala regional y escala metropolitana o local. La primera metodología SIG ofrece una respuesta a la necesidad de una cuantificación regional del potencial geotérmico somero que puede extraerse con intercambiadores de calor o Borehole Heat Exchangers, así como sus impactos térmicos asociados. Por primera vez pueden tenerse en cuenta en la estimación regional de las variables de interés la advección y dispersión de calor, como mecanismos de transporte de calor, así como la evolución temporal desde el inicio de la explotación. Un análisis de sensibilidad demuestra que la consideración de los efectos de dispersión así como el régimen temporal de la explotación supone diferencias de hasta 2.5 veces el potencial extraído y hasta de varios ordenes de magnitud en los impactos térmicos generados. Para profundizar en la gestión de la geotermia somera a escala local, esta tesis propone establecer un mercado de derechos de uso de este recurso. Esta metodología se ha implementado en un ambiente SIG y está compuesta de una base de datos donde se almacena la información principal necesaria para gestionar las instalaciones y de un conjunto de herramientas para definir, implantar y controlar este mercado de derechos de uso de geotermia somera. Los impactos térmicos derivados de la explotación de este recurso pueden quedar registrados geográficamente, teniendo en cuenta la dirección de flujo de las aguas subterráneas y ajustando estos impactos a la superficie de la parcela disponibleAward-winningPostprint (published version

Multiphysics coupling in exploitation and utilization of geo-energy: State-of-the-art and future perspectives

Natural gas hydrates and geothermal energy are potential sources of low-carbon geo-energy that are crucial in achieving a sustainable energy future for human society. The exploitation and utilization of these sources inherently involve thermal-hydraulic-mechanical-chemical coupling processes, and these complex coupling processes need to be numerically simulated for exploitation and utilization technology developments. This paper provides a brief overview of the current status and future challenges of numerical simulations for these coupling processes in the context of exploiting and utilizing natural gas hydrates, shallow and deep geothermal energy. It also presents perspectives on how to address these challenges, aiming to advance the development of numerical coupling technology within the geo-energy exploitation and utilization communities.Document Type: PerspectiveCited as: Wan, Y., Yuan, Y., Zhou, C., Liu, L. Multiphysics coupling in exploitation and utilization of geo-energy: State-of-the-art and future perspectives. Advances in Geo-Energy Research, 2023, 10(1): 7-13. https://doi.org/10.46690/ager.2023.10.0

Sequential coupled numerical simulations of an air/ground-source heat pump: Validation of the model and results of yearly simulations

Numerical simulations are important tools for the assessment of exploiting geothermal energy in heat pump applications. They can be used to evaluate the performance of the system, the long-term production scenarios and the sustainability of the geothermal reservoir. The present work introduces and describes a numerical model, in which a dedicated Matlab script has been realized to allow sequentially coupled simulations of a shallow geothermal reservoir and of a heat pump system. A mathematical model of a dual-source heat pump, working alternatively with the ground or the air as heat source/sink, has been developed in Matlab environment. The heat exchangers of the heat pump have been modelled considering the equations that govern the physical phenomena. The dynamic numerical simulator FEFLOW, based on the finite element method, has been used to simulate the behaviour of the geothermal reservoir, subjected to heat extraction/reinjection by a closed loop vertical heat exchangers field. This methodological approach is useful to evaluate the performance of the coupled system in the long term, and it is important for understanding the advantages and limits of the dual-source heat pump in assuring sustainability over time avoiding the depletion of geothermal resources. The models and their coupling have been calibrated and validated with experimental data from a shallow geothermal plant located in Tribano (Padova, IT). It consists of eight coaxial borehole heat exchangers 30 m deep, connected to a 16 kW dual-source heat pump prototype. The heat pump system provides heating and cooling to an office area. The coupled model has been used to compare the performance of the heat pump when working in air-mode only or in ground-mode only. This allowed the development of a switching control strategy between the two thermal sources. Yearly simulations with the switching strategy have shown that the seasonal performance factor of the dual-source heat pump during the heating mode can be 13.8 % higher compared to the one obtained with a conventional air source heat pump and 3.8 % higher with respect to a ground source heat pump

Electromagnetic imaging and deep learning for transition to renewable energies: a technology review

Electromagnetic imaging is a technique that has been employed and perfected to investigate the Earth subsurface over the past three decades. Besides the traditional geophysical surveys (e.g., hydrocarbon exploration, geological mapping), several new applications have appeared (e.g., characterization of geothermal energy reservoirs, capture and storage of carbon dioxide, water prospecting, and monitoring of hazardous-waste deposits). The development of new numerical schemes, algorithms, and easy access to supercomputers have supported innovation throughout the geo-electromagnetic community. In particular, deep learning solutions have taken electromagnetic imaging technology to a different level. These emerging deep learning tools have significantly contributed to data processing for enhanced electromagnetic imaging of the Earth. Herein, we review innovative electromagnetic imaging technologies and deep learning solutions and their role in better understanding useful resources for the energy transition path. To better understand this landscape, we describe the physics behind electromagnetic imaging, current trends in its numerical modeling, development of computational tools (traditional approaches and emerging deep learning schemes), and discuss some key applications for the energy transition. We focus on the need to explore all the alternatives of technologies and expertise transfer to propel the energy landscape forward. We hope this review may be useful for the entire geo-electromagnetic community and inspire and drive the further development of innovative electromagnetic imaging technologies to power a safer future based on energy sources.This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 955606 (DEEP-SEA) and No. 777778 (MATHROCKS). Furthermore, the research leading of this study has received funding from the Ministerio de Educación y Ciencia (Spain) under Project TED2021-131882B-C42.Peer ReviewedPostprint (published version

On the efficient and sustainable utilisation of shallow geothermal energy by using borehole heat exchangers

In the context of energy transition, geothermics play an important role for the heating and cooling supply of both residential and commercial buildings. Thereby, the increasingly and intensive utilisation of shallow geothermal resources bears the risk of over-exploitation and thus poses a future challenge to ensure the sustainability and safety of such systems. Particularly, the well-established technology of borehole heat exchanger-coupled ground source heat pumps is applied for the thermal exploitation of the shallow subsurface. Due to the complexity of the involved physical processes, numerical modelling proves to be a powerful tool to enhance process understanding as well as to aid the planning and design processes. Simulations can also support the management of thermal subsurface resources, planning and decision-making on city and regional scales. In this work, the so-called dual-continuum approach was adopted and enhanced to develop a coupled numerical model considering flow and heat transport processes in both the subsurface and borehole heat exchangers as well as the heat pumps’ performance characteristics, and including the relevant phenomena influencing the underlying processes. Beside the temperature fields, the efficiency and thus the consumption of electrical energy by the heat pump is computed, allowing for the quantification of operational costs and equivalent carbon-dioxide emissions. The model is validated and applied to a number of numerical studies. First, a comprehensive sensitivity analysis on the efficiency and sustainability of such systems is performed. Second, a method for the quantification of technically extractable shallow geothermal energy is proposed. This procedure is demonstrated by means of a case study for the city of Cologne, Germany and its implications are discussed.Im Rahmen der Energiewende nimmt die Geothermie eine besondere Rolle in der thermische Gebäudeversorgung ein. Die zunehmende, intensive Nutzung oberflächennaher geothermischer Ressourcen erhöht die Gefahr der übermäßigen thermischen Ausbeutung des Untergrundes und stellt damit eine wachsende Herausforderung für die Nachhaltigkeit und Sicherheit solcher Systeme dar. Zur Erschließung oberflächennaher geothermischer Energie wird insbesondere die etablierte Technologie Erdwärmesonden-gekoppelter Wärmepumpen eingesetzt. Aufgrund der daran beteiligten komplexen physikalischen Prozesse erweisen sich numerische Modelle als leistungsfähiges Werkzeug zur Erweiterung des Prozessverständnisses und Unterstützung des Planungs- und Auslegungsprozesses. Zudem können Simulationen zum Management thermischer Ressourcen im Untergrund sowie zur Planung und politischen Entscheidungsfindung auf städtischen und regionalen Maßstäben beitragen. Im Rahmen dieser Arbeit wurde, basierend auf dem sogenannten ”dual-continuum approach” und unter Berücksichtigung des Einflusses der Wärmepumpe, ein erweitertes gekoppeltes numerisches Modell zur Abbildung der in Erdwärmesonden und dem Untergrund stattfindenden Strömungs- und Wärmetransportprozesse entwickelt. Das Modell ist in der Lage, alle relevanten Einflussfaktoren zu berücksichtigen. Neben den Temperaturfeldern im Untergrund und der Erdwärmesonde werden die Effizienz und damit der Stromverbrauch der Wärmepumpe simuliert. Damit können sowohl die Betriebskosten als auch der äquivalente CO 2 -Ausstoß abgeschätzt werden. Das Modell wurde validiert und in einer Reihe numerischer Studien eingesetzt. Zuerst wurde eine umfassende Sensitivitätsanalyse zur Effizienz und Nachhaltigkeit entsprechender Anlagen durchgeführt. Weiterhin wird ein Verfahren zur Quantifizierung des technisch nutzbaren, oberflächennahen geothermischen Potentials vorgestellt und anhand einer Fallstudie für die Stadt Köln demonstriert, gefolgt von einer Diskussion der Ergebnisse

Formulation of a 1D finite element of heat exchanger for accurate modelling of the grouting behaviour: Application to cyclic thermal loading

This paper presents a comprehensive formulation of a finite element for the modelling of borehole heat exchangers. This work focuses on the accurate modelling of the grouting and the field of temperature near a single borehole. Therefore the grouting of the BHE is explicitly modelled. The purpose of this work is to provide tools necessary to the further modelling of thermo-mechanical couplings. The finite element discretises the classical governing equation of advection-diffusion of heat within a 1D pipe connected to ground nodes. Petrov-Galerkin weighting functions are used to avoid numerical disturbances. The formulation is able to capture highly transient and steady-state phenomena. The proposed finite element is validated with respect to analytical solutions. An example consisting of a 100 m depth U-pipe is finally simulated. A first continuous heating simulation highlights the nonsymmetric distribution of temperature inside and near the borehole. An estimation of the error on the results as a function of the resolution parameters is also carried out. Finally simulations of cyclic thermal loading exhibit the need to take into account all daily variations if the grouting behaviour must be modelled. This is true especially in case of freeze-thaw damaging risk.Geotherwa

Investigation on the heat extraction performance of deep closed-loop borehole heat exchanger system for building heating

In recent years, deep geothermal energy has been widely exploited through closed-loop borehole heat exchanger system for building heating. In order to precisely evaluate the sustainable heat extraction capacity and the impact of different designs and operating parameters, two heat transfer models are implemented in the open-source scientific software OpenGeoSys (OGS), with respect to the Deep Borehole Heat Exchanger (DBHE) and Enhanced U-tube Borehole Heat Exchanger (EUBHE) system. Besides, three types of boundary conditions are implemented, including the constant inflow temperature, the constant heat extraction rate, and constant building thermal power that integrates the ground source heat pump (GSHP) module. By applying the two BHE models, the influence of different designs and operating parameters on the GSHP system is evaluated. The sustainable heat extraction capacity and efficiency of a deep EUBHE system are predicted. Moreover, its performance and efficiency are further compared against the 2-DBHE array system that has the same total borehole length. It is found that the soil thermal conductivity is the most important parameter in the design of DBHE and EUBHE systems. The sustainable specific heat extraction rate of the EUBHE system is 86.5 W/m higher than an array with 2 DBHEs. Under the building thermal load of 1.225 MW, the total electricity consumed by the EUBHE system is approximately 27 % less than the 2-DBHE array over 10 years. The average Coefficient of System Performance (CSP) value of the EUBHE system is 1.66 higher over 10 heating seasons. The two numerical models implemented in the OpenGeoSys software can be used to predict and optimize the thermal characteristics of the closed-loop DBHE and EUBHE systems in real projects