Conference Agenda

The Groß Schönebeck deep geothermal research platform was initiated with the idea of reusing an abandoned gas exploration well to demonstrate electricity production from the Rotliegend formation in the North German Basin via a matrix-dominated Enhanced Geothermal System (EGS). In this study, we propose as an alternative the concept of a fracture-dominated EGS to develop the Rotliegend formation in the North German Basin and demonstrate it numerically for the Groß Schönebeck site. This concept is based on 1) lessons learned from Groß Schönebeck and other recent EGS sites as well as 2) history matching of multiple well tests and 2.5 years of circulation tests in the previous matrix-dominated EGS. The simulations were performed using the commercial finite difference reservoir simulator CMG STARS. The fracture-dominated development concept includes re-using the existing wells by drilling a horizontal sidetrack from the current production well Gt GrSk 4/05 and using it as future injection well, re-using the current injection well E GrSk 3/90 as monitoring well and drilling a new horizontal well as future production well.

Enhanced geothermal systems (EGS) have the potential to bring a breakthrough in the utilization of geothermal energy by making the use of underground thermal energy possible outside hydrothermal reservoirs. However, many pilot EGS projects met an early end during the hydraulic stimulation phase due to lack of control over fluid injection induced seismicity. One of the halted projects is the GEOVEN project near Vendenheim, Upper Rhine Graben (France), which was suspended after a M_lv 3.6 event occurred in the vicinity of the well-doublet. Prior to the M_Lv 3.6 event, a M_Lv 3.0 event with a hypocentre 5 km to the south of the injection site was detected. A M_lv 3.9 event originated near the wells 6 months after the cessation of the project and the shut-in of the wells.

To understand the controlling mechanisms behind the seismicity at the site, we performed large-scale coupled thermo-hydro-mechanical (THM) numerical simulations. We demonstrate that the steady-state in-situ stress conditions and the geometry of the Robertsau fault together result in a higher slip tendency at a larger patch on the fault, approximately 5 km to the south from the doublet. Based on steady-state conditions, we simulate the 6 months long hydraulic stimulation campaign preceding the Mw 3.0 event on the southern seismic cluster. Compared with studies on earthquake aftershock-triggering, our modelling results indicate that the injected 100,000 m³ of water over a 6-month long period could potentially elevate the pore pressure on the critically stressed patch of the simulated fault enough to trigger seismicity.

Injection-induced shear stimulation, known as ‘hydro-shearing,’ is frequently utilized in Enhanced Geothermal Systems (EGS) to improve reservoir permeability. Hydro-shearing occurs when a pre-existing fracture or fault, already stressed by in-situ stresses, slips due to increased pressure. This slip can cause the fracture to open and potentially remain open due to self-propping asperities on the fracture surface. However, the reliability of permeability enhancement through hydro-shearing is not always assured, as the geological and operational conditions necessary for effective enhancement are not well understood.

This study investigates the conditions under which hydro-shearing enhances permeability, as well as those leading to permeability reduction, and examines how these conditions influence injection-induced shear slip and seismicity. Utilizing an MTS 815 frame, six cylindrical samples of Weschnitz Granodiorite, each with a diameter of 50 mm, were subjected to triaxial shear flow experiments. The samples included two induced shear fractures, two induced tensile fractures, and two saw-cut fractures. A stepwise injection scheme was employed under constant piston displacement control to investigate changes in permeability and slip characteristics of the fracture surfaces. Permeability was measured under a steady-state flow regime in accordance with Darcy’s law.

By focusing on the behavior of these various fracture types during shear flow tests, this study provides novel insights into how injection impacts slip and permeability in shear fractures. Comparisons with induced tensile and saw-cut fractures further enhance our understanding of fracture dynamics in EGS. The findings offer valuable information for optimizing conditions to achieve effective permeability enhancement through hydro-shearing in geothermal reservoirs.

The application of hydraulic stimulation to improve permeability in geothermal systems is a possible approach to optimize heat extraction efficiency. However, an undesired consequence can be potentially damaging induced seismicity, which is currently a challenge to mitigate. The aim of this study is to investigate the effects of injection parameters and fracture properties on fracture response in terms of stability and permeability in order to develop safe and efficient injection protocols, giving guidance on how to enhance the permeability in geothermal systems while mitigating seismic hazards. In a first step, we used finite element models of laboratory experiments to validate our simulation approach and explore injection criteria. Next, we include criteria on which injection parameters are automatically adapted, allowing a feedback-controlled injection. Subsequently, we will apply the gained insights from laboratory scale models to field scale simulations of the Balmatt geothermal site in Belgium to assess the feasibility of feedback-controlled injection schemes to better balance induced seismicity and permeability.c

Climate change and political measures are forcing energy users and suppliers to significantly reduce their CO₂ emissions. One sustainable, year-round available source providing heat, cooling and seasonal energy storage is geothermal energy. However, improvements in productivity, efficiency and monitoring of geothermal systems are much needed. Such reservoir enhancement is often being done now using intensified water via coiled tubing based micro jetting, milling or drilling technologies such as radial jetting, micro turbines etc. These methods are commonly self-propelling, uncontrolled, and their results are often uncertain. Currently there is no possibility to survey the process or its results (e.g. boreholes) during or post run.

Conventional orientation and positioning technologies from today’s directional drilling industry are not suitable for logging such small-caliber micro boreholes due to their geometric dimensions. Therefore, Fraunhofer IEG is developing new micro size logging tools for such applications. These probes use innovative measurement physics to precisely measure e.g. position, deviation and borehole run and quality of any small-caliber borehole or lateral. These miniaturized systems help improve efficiency, provide QA and QC and thus, minimize risk when using above mentioned geothermal reservoir enhancement micro drilling intervention methods. They also serve as 1^st step for possibly implementing MWD systems for such micro directional drilling technologies in general. Initial lab tests demonstrate their functionality and reliability, also for use in “directional” micro drilling and geothermal energy.

It is of great importance to have an understanding of the underground temperature distribution in order to evaluate the geothermal potential and to ensure the long-term safety of heat-producing waste in repositories. As there are few temperature observations in the subsurface, numerical modelling is utilized to make predictions of the subsurface temperature distribution for exploration and risk assessment. In contrast to statistical models, numerical physical approaches can account for local heterogeneities in thermal properties, given well informed structural and parametrical models of the subsurface.

Previous research, conducted primarily in Northern Europe and Canada, has demonstrated that the Pleistocene glaciations have an additive effect, resulting in a cooling of several degrees Celsius at depths of up to two kilometers. Recent studies indicate that the Last Glacial Period and the recent warming have the greatest paleoclimatic impact on the subsurface temperatures in Germany. However, a systematic study in sedimentary regions in Germany has only been conducted on a regional scale and with coarse spatial resolution.

Consequently, transient numerical simulations are required to account for the temporal and spatial changes in ground surface temperatures (GST). However, only a limited number of GST histories since the last glacial maximum are available, either from rare transient climate simulations or from ground surface temperature reconstructions using borehole climatology. Analyzing continuous, high-precision temperature profiles and geophysical well logs to derive the thermophysical subsurface characterization, we identify boreholes suitable for investigating the paleoclimatic effects of the Pleistocene and Holocene on Germany’s subsurface temperature distribution.

Distributed Acoustic Sensing (DAS) technology on the existing telecommunication networks can convert the fiber cable into arrays of receivers. Moreover, the seismic waves generated by human activities recorded on these networks can be used to seismically image the urban subsurface at high resolution with a small footprint. This capability can help in the assessment of the urban subsurface's potential for safe utilization in the geothermal development of an area. However, extracting coherent seismic signals from the complex urban seismic noise remains challenging.

We present the analysis of 15 days of anthropogenic seismic noise (mostly traffic noise) recorded on a pre-existing cable (dark fibers) running along an ~11 km long major urban road in Berlin, Germany. Our workflow comprises a standard interferometric approach based on the cross-correlation to retrieve coherent seismic phases for each hour of recording (Virtual Shot Gathers, VSGs) and Multichannel Analysis of Surface Waves (MASW) to derive 1D velocity models along consecutive portions of the array. The individual 1D velocity models are then merged into a 2D velocity model of the subsurface. Our final results are improved by incorporating a selection scheme for the immediately resulting VSGs using unsupervised machine-learning-based clustering along with a coherence-based enhancement approach that increases achievable investigation depth.

The resulting 1D velocity models, delineating the boundary of the Rupelian Layer, correspond well with available lithographic information. Our enhanced workflow yields high-quality results requiring less data than conventional processing schemes, thus opening the opportunity for reduced acquisition costs, which could be applied to geothermal exploration.

Geothermal energy in the North German Basin (NGB) shows significant untapped potential. This study aims to map the distribution of the underexplored Upper Maastrichtian Arenites (Reitbrook Formation), analyse their geological properties, and evaluate their geothermal potential using borehole and 3D seismic data.

In well logs, a consistent marly layer is identified over extensive distances, serving as the base for the overlying Arenite, which is subdivided into Upper and Lower parts by another thinner marly layer.A vertical trend shows increasing grain size with depth, emphasizing the Upper Arenite as the main exploration target. Additionally, a facies transition from arenites in the north to glauconitic sands in the south, which enhances porosity and permeability, can be noted. Observations indicate Maastrichtian stratigraphy eroded to varying depths below the Paleogene transgression, with underlying Arenites showing thickness and depth variations. Inversion tectonics during the Upper Cretaceous period and associated subsidence near inverted areas are believed to significantly contribute to the widespread distribution and preservation of the Arenites. Additionally, halokinesis exerts a significant overwhelming influence. Thick arenite deposits are likely in marginal troughs that developed parallel to the deposition. In contrast, on top of salt structures, there is little or no arenite present.

Global sea level changes, regional tectonic development, and local halokinesis have formed a complex synsedimentary reservoir, which represents a potentially suitable reservoir for medium-depth geothermal energy. Future efforts will involve conducting numerical simulations using a parameterized 3D model to comprehensively characterize the geothermal potential of arenites at a large scale.

Stadtwerke Göttingen AG aims to develop medium-deep geothermal systems in various potential target horizons. To support this, field and experimental analogue studies were conducted to parameterize better the geological input data necessary for economic feasibility studies. Variscan metasedimentary rocks in the Göttingen region of Germany are overlain by up to 1500 m of Permo-Mesozoic rocks. Zechstein layers, up to 500 meters thick, consist of rock salt, potash salt, gypsum, and carbonates, and are overlain by up to 1000 meters of Mesozoic sandstones (Buntsandstein), carbonates (Muschelkalk), and clay-rich Keuper layers. The sedimentary cover is structurally affected by the N-S trending Cenozoic Leinetal Graben.

Sixteen samples from the Zechstein, Buntsandstein, and Muschelkalk formations were collected from local natural exposures and quarries. Parameter measurements show porosities of 4 to 20% for the sandstones, 0.2 to 22% for carbonates, and 2.4 to 16.4% for dolomitic rocks. Respective density values are 2.0 g/cm³, 2.1 to 2.7 g/cm³, and 2.4 to 2.7 g/cm³. Permeability values range from 4.3 mD for the carbonates to 210 mD for the sandstones. Thermal conductivity values are 1.4 to 3.0 W/(m·K) for sandstones, 1.7 to 2.6 W/(m·K) for carbonates and 4.3 to 5.4 W/(m·K) for dolomites.

Samples from the Middle Bunter sandstone, with their high porosities and permeabilities, indicate significant geothermal potential when considering primary matrix permeability. Secondary permeability, such as through joints and faults, could greatly enhance reservoir quality. Therefore, this parameter needs further study.

Understanding subsurface rock properties is crucial for various applications, however conventional methods often fall short in providing detailed information. Conventional exploration methods such as seismic tomography and gravimetry have multiple limitations resulting in a need for novel/innovative technologies that can provide complementary information about the subsurface density structure.

Muography is a technique that measures the absorption of cosmic muons created by cosmic rays interactions with atmospheric atoms which offers a promising complementing technological solution to the limitations of the conventional technologies. By performing measurements at various subsurface locations, e.g. along boreholes, muography can provide a 3D density distribution of rock formations surrounding the wellbore. There are multiple options to design an optimal muography sensor, tailored towards specific tasks requiring various sensor sensitivities, sensor types, and layouts.

To assist the planning of a muography project, a simulation tool based on Geant4 is currently under development for conducting comprehensive feasibility studies. The tool considers the surrounding geology and detector layout to evaluate expected performance and measurement settings for a given exploration target. The software package also allows for studying the resolution and sensitivity to detect subsurface density variations. This allows users to easily optimize their sensor design before construction, thus reducing overall exploration or monitoring costs. This poster presents a case study demonstrating muography capabilities in mapping subsurface density variations.

This study focuses on the monitoring of low-enthalpy geothermal resources in the southern area of the San Juan province, northwestern Argentina. This region, characterized by extremely arid conditions and a pronounced water deficit, comprises the Tulum oasis, which supplies water and soils to the city of San Juan and surrounding areas. To carry out groundwater temperature monitoring, four types of data logger sensors have been installed in soils and aquifer wells distributed throughout the study area. These devices record temperature, absolute pressure and electrical conductivity over time. For their strategic location and to apply barometric corrections, the database reported by the Instituto Nacional del Agua (INA-CRAS) and the Servicio Agrometeorológico Estación Experimental San Juan (EEA-INTA) were consulted. From July to the present, there are 10 active sensors in the Tulum oasis and surrounding areas, set with a measurement interval time of 10-minute. In addition, water samples have been collected for in situ measurement of temperature, conductivity and pH; as well as for hydrochemical and isotopic analysis carried out at the Ruhr-Universität Bochum (RUB), Germany. Preliminary results indicate that groundwater temperature increases southward, reaching 32°C and showing a correlation with geological structures. First-order structures could act as pathways for the ascent of higher temperature fluids. On the other hand, the piezometric levels exhibit a negative trend of up to 3 meters in the measured period. All the information collected in this study will provide the basis for assessing the geothermal potential of the region and for monitoring the water resource.

This work presents the first results from Distributed Dynamic Strain Sensing (DDSS or DAS) measurements within a deep geothermal well doublet. The sensing technology's high spatio-temporal resolution enables us to monitor seismic activity, strain, and temperature changes along the sensing cable.
We measured a 3.7 km and an approximately 4.0 km long fiber optic cable in a production and an injection well, each reaching into the reservoir. Distributed sensing was accomplished with a commercial DDSS acquisition system measuring the boreholes at a 1 m spatial sampling and 2000 Hz.
This work focuses on the DDSS recordings from the initial production and injection phase and shows various phenomena along the cable. Low- and high-frequency strain variations were quantified by applying a cascading decimation routine and calculating a proxy for the vibrational energy content. The results reveal various processes related to the reservoir properties and well integrity.
We present the initial results of our monitoring campaign, acquired in the framework of the GFK-Monitor project. These results demonstrate the potential of DDSS to image subsurface processes in geothermal environments. Our research can advance downhole monitoring technologies to better understand subsurface processes and optimize geothermal energy provision.

In the field of high temperature Aquifer Thermal Energy Storage, numerous studies have shown that temperature increases can induce changes in permeability and mobilize contaminants in the aquifer. Such transformations are primarily facilitated by a number of processes: precipitation and migration of fine particles on the one hand, and dissolution, desorption, and ion exchange on the other. The occurrence and intensity of these processes are influenced by the properties of the fluid and, in particular, by the properties of the solid phase. These include ferrous mineral phases, carbonates and clay minerals. The aim of this study was the geochemical comparison and characterization of X-ray fluorescence data of six aquifers explored via an exploration well in Berlin. 200 m of core samples were analyzed on site immediately after drilling using a handheld X-ray fluorescence spectrometer. Many elements and oxides were qualitatively and semi-quantitatively determined despite the high moisture content and the influence of drilling fluid. The detection of heavy elements was found to be only slightly affected by water content, while measurements of lighter elements were significantly disturbed. Ca, Fe and Mn concentrations provide insight into the reactive phases within the aquifers. Aluminum and, more significantly, Rb concentration indicate clay content of the formation and heterogeneities of the aquifer matrix. In conclusion, the handheld XRF can be used as a screening tool at drilling sites to detect geochemical anomalies, reactive phases and heterogeneities to assist geologists in their decision-making process, such as the selection of the filter section in the borehole.

In response to climate change and resource shortages, the EU prioritizes domestic sourcing of Critical Raw Materials (CRM) and “clean” energy. This study, part of the EU-funded CRM-Geothermal project (ID 101058163), aims at investigating the long-term sustainability of lithium and heat coproduction from the low-saline geothermal fluids circulating at relatively shallow depths within the fractured crystalline rocks at United Downs, southwest England. This research combines traditional fieldwork, laboratory measurements, and data analysis with advanced numerical methods. The fieldwork conducted in June and July 2023 includes hydrogeological testing, chemical-physical fluid monitoring, and sampling of fluids and solids from two boreholes operated by Cornish Lithium Ltd. These boreholes access the crystalline reservoir and target two major fracture zones known to be highly permeable to the lithium-enriched fluids circulating within the formation. The results of sample processing and data analysis are used to characterize the geothermal system and build the numerical models of the study site. Using PHREEQC for sequential thermo-dynamic equilibrium modelling, this study investigates potential scaling processes during geothermal operation. A finite-element model (MOOSE/GOLEM) simulates coupled thermal, hydraulic, and conservative mass transport processes within the fractured geothermal system. This model is used to evaluate the system's thermo-hydraulic and chemical evolution under various long-term (10 years) production scenarios. The modelling results indicate the reservoir being suitable for long-term heat and mineral extraction. Nonetheless, scaling and associated radioactivity issues may require careful management – particularly in case of high discharge rates during operation and the oxidation of produced fluids at the surface.

In ehemaligen Bergbauregionen, wie dem Erzgebirge oder dem Ruhrgebiet, bietet Grubenwassergeothermie ein großes Potenzial zur Bereitstellung von regenerativer Wärme und Kälte. Ein aktueller Investitionsvorbehalt besteht in der Prognose der Wirtschaftlichkeit solcher Anlagen. Aus diesem Grund wurde ein Tool entwickelt, mit dem anhand von verschiedenen Eingangsparametern (z.B. Bohrteufe, Volllaststunden, Temperaturdifferenz Grubenwasser) die Investitionskosten, Kapitalwert und Amortisationsdauer berechnet werden können. Dabei können neben einer Einzelversorgung auch verschiedene Konzepte zur netzgebundenen Versorgung ausgewählt werden. Zur Abschätzung der Wirtschaftlichkeit unter den volatilen Gegebenheiten des Energiemarktes wurde die Option geschaffen, durch die Variation von z.B. Gaspreis oder CO₂-Steuer die Robustheit der Anlage zu evaluieren, indem dargestellt wird, bei welchem Anstieg oder Abfall des jeweiligen Parameters die Anlage nicht mehr wirtschaftlich ist.

Die Erprobung des Werkzeugs am Standort Ehrenfriedersdorf (Sachsen) zeigte, dass sich eine Anlage mit ca. 13 GWh Jahresheizwärmebedarf (Investitionskosten: 5,4 Mio. €) unter den aktuellen Rahmenbedingungen nach knapp 8 Jahren amortisieren würde. Durch die Verbindung mit verschiedenen Förderoptionen wäre eine Reduktion der Amortisationsdauer auf bis zu 5,5 Jahre möglich. Um mögliche zukünftige Preisentwicklungen abbilden zu können, kann innerhalb der Sensitivitätsanalyse eine Änderung des Strom- bzw. Gaspreises modelliert werden. So wäre die Anlage z.B. bis zu einer Reduktion des Gaspreises um 26 % trotzdem noch wirtschaftlich.

Im Rahmen einer Folgenutzung von Bergwerken ermöglicht eine geothermische Nutzung von Grubenwasser eine emissionsarme und nachhaltige Bereitstellung von regenerativer Wärme und/oder Kälte an ehemaligen Bergbaustandorten. Die Eignung eines ehemaligen Bergbaustandortes für eine geothermische Grubenwassernutzung ist im Rahmen einer standortspezifischen Potentialanalyse zu evaluieren, wobei insbesondere die Beschaffenheit von Bergwerk und Grubenwasser zu berücksichtigen ist.

In dieser Masterarbeit wurde umfassend das Potential für eine thermische Grubenwassernutzung am Standort der 1956 stillgelegten Steinkohlebergwerke in Barsinghausen (Niedersachsen) evaluiert.

Durch die Analyse des historischen Risswerkes wurde die räumliche Struktur des Grubengeböudes und die potenziellen Fließwege des Grubenwassers untersucht. Um die Genese und Dynamik des Grubenwassers nachzuvollziehen, wurden Druck- und Temperaturdaten eines am Schacht IV verbauten Sensors aus einem mehrjährigen Beobachtungszeitraum ausgewertet und mit lokalen Grundwasserständen sowie Niederschlagsmengen verglichen. Zur hydrochemischen Charakterisierung wurden Grubenwasserproben laboranalytisch untersucht sowie In-situ-Messungen durchgeführt.

Die Ergebnisse zeigen ein ganzjährig erhöhtes Grubenwasser-Temperaturniveau von durchschnittlich 20,8 ± 0,2 °C sowie saisonal abhängige Austrittsraten am Schacht IV. Das Grubenwasser ist hydrochemisch ein erdalkalisches, sulfatiges Wasser mit einer elektrischen Leitfähigkeit von ca. 1600 μS/cm. Das Grubenwasser fließt, aus Grund- und Sickerwasser gespeist und dem Gefälle des Grubengebäudes folgend, zum tiefsten Bereich des Grubengebäudes, wo es über den offenen Schacht IV an der Tagesoberfläche austritt.

Zusammenfassend zeigt die Potentialanalyse, dass das Grubenwasser des ehemaligen Steinkohlebergwerks Barsinghausen mit seinem ganzjährig hohen Temperaturniveau von über 20 °C, signifikanten Austrittsraten und dem natürlichen Auslauf ein nutzbares Potential unter günstigen wirtschaftlichen und technischen Bedingungen darstellt. Eine detailliertere Betrachtung des Standortes durch Folgeuntersuchungen wird folglich als sinnvoll erachtet.

Im Rahmen der Entwicklung einer nachhaltigen Energieversorgung eines Neubaus der Universitätsmedizin in Göttingen wurden für die Erschließung eines oberflächennahen Geothermiefeldes drei 200 m tiefe Pilotbohrungen in Gesteinen des Keupers, die im Einflussbereich eines Sulfatauslaugungsbereichs liegen, durchgeführt. Ziel dieser Arbeit war es, über eine detaillierte Bohrkleinanalyse, ein Gamma-Ray- sowie ein Fokuselektro-Log eine genaue stratigraphische Zuordnung und damit eine Integration in ein bestehendes geologisches 3D-Modell zu ermöglichen. Zudem sollte eine quantitative Aussage zum Sulfatgesteinsgehalt, d.h. insbesondere zum Anhydritgehalt, ermöglicht werden, was insbesondere für die Teufenauslegung des Geothermiefeldes und damit der Wärmeentzugsleistung, eine planerische Entscheidungskenngröße und eine Risikoeinordnung bietet.

Die durchteuften Schichten bestehen zunächst aus quartärem Lockermaterial, welches innerhalb der obersten 36 m in die Festgesteine des Keupers übergeht. Stratigraphisch kann das darunter folgende Festgestein der Grabfeld-, Stuttgart- und Weser-Formation des Mittleren Keupers zugeordnet werden. Damit konnten die neuen Bohrungen, sowie Profilschnitte von fünf bereits im Jahr 1975 durchgeführten Bohrungen, in das bereits bestehende geologische 3D-Modell integriert werden. Vorkommen von Anhydrit wurden nicht beobachtet. Geringe Mengen von Gips konnten ab einer Tiefe von 160 m nachgewiesen werden. Insgesamt können die Risiken einer Hebung oder eines Absenkens des Untergrundes aufgrund von Lösungs- und Quellprozessen von Gips bzw. Anhydrit, bei der Realisierung oberflächennaher Geothermie in dem Arbeitsgebiet unter Berücksichtigung der in dieser Arbeit gesammelten Daten als gering eingeschätzt werden. Eine Teufenauslegung des Sondenfeldes bis mindestens 160 m ist möglich, was die ursprüngliche Modellauslegung von 60 m deutlich erweitert und damit eine Effizienzsteigerung erlaubt.

Fluid flow can significantly modify the background conductive thermal field in sedimentary basins. In the North German Basin (NGB), permeable Permian to Quaternary reservoirs, structural dips, and locally eroded seals create favorable conditions for high Darcy flux and, hence, for advective heat transport. At depths of tens to first hundreds of meters, groundwater flow is further mediated by recharge and surface water level fluctuations.

We present results from transient thermal-hydraulic models beneath the Berlin-Brandenburg region in the NGB that rely on a data-constrained 3D geological model, which has been converted into a finite-element mesh with effective properties assigned to 14 sedimentary units and top boundary conditions based on a 70-year long hydrometeorological record.

We have been able to identify areas with negative thermal anomalies, which we could relate to strong groundwater recharge and high hydraulic gradients, and to map depths below which stable temperatures occur on decadal or annual scales.

The results obtained from the model also indicate a widespread increase in groundwater temperatures at the water table of ~1.2°C, in response to climate variability. This trend is in agreement with measured temperatures from the state monitoring network. An additional positive anomaly is associated with the urban heat island beneath Berlin, a major city in the study area.

We finally discuss how our modelling workflow can be used for projecting shallow aquifer responses to global warming, and, in the context of geothermal exploration, for estimating the incremental accumulated thermal energy that can be targeted by shallow geothermal systems.

Die Masterarbeit untersucht die Machbarkeit des Ausbaus der nicht-fündigen Hydrothermal-Geothermiebohrung LAVEY-1 zu einer koaxialen Tiefen-Erdwärmesonde. Die Studie wird am Lehrstuhl für Hydrogeologie der Technischen Universität München in Kooperation mit der Firma Erdwerk GmbH durchgeführt und voraussichtlich Ende September 2024 abgeschlossen.

Im Fokus der Arbeit steht die Analyse technischer und wirtschaftlicher Aspekte, um die bestehende Bohrung LAVEY-1 in der Schweiz für die Nutzung als Tiefen-Erdwärmesonde zu adaptieren. Dazu werden geologische, hydrogeologische und thermische Daten ausgewertet und verschiedene Ausbauvarianten hinsichtlich ihrer Effizienz und Wirtschaftlichkeit bewertet. Ein zentrales Element der Untersuchung ist die Verwendung des Programms FEFLOW, mit dem die thermische Leistung der Erdwärmesonde abgeschätzt wird. In Abgrenzung zu bisherigen Arbeiten wird die abgelenkte Bohrung in einem 3D unstrukturierten Netz repräsentiert, was eine präzisere Modellierung und genauere Ergebnisse ermöglichen soll.

Die Ergebnisse der Studie sollen nicht nur Aufschluss über das spezifische Potenzial der Bohrung LAVEY-1 geben, sondern auch als Referenz für ähnliche Projekte dienen, bei denen Kohlenwasserstoff- oder nicht-fündige Geothermiebohrungen in Tiefe Erdwärmesonden umgewandelt werden.

Die Vorstellung dieser Arbeit im Rahmen der Science Bar des DGK 2024 soll Fachleute und Interessierte gleichermaßen ansprechen und den Diskurs zur Nutzungsmöglichkeit bestehender Kohlenwasserstoff- sowie nicht-fündiger Geothermiebohrungen als Tiefen Erdwärmesonden fördern.

Am Standort des Fraunhofer IEG in Bochum wurde in zwei aufeinander folgenden Forschungsprojekten zunächst ein Bergwerk thermisch erschlossen und mit Parabolrinnenkollektoren beladen, um dieses System dann in einem weiteren Forschungsprojekt mit einer zweistufigen Hochtemperaturwärmepumpe an das vor Ort befindliche Fernwärmenetz der unique Wärme anzukoppeln. Die Wärmepumpe ist in der Lage, das Fernwärmenetz mit Temperaturen von 70°C - 120°C zu versorgen, die sie von Quelltemperaturen von mindestens 10°C zunächst mit der ersten Stufe R717 (Ammoniak) auf ca. 55°C und dann mit der zweiten Stufe R600 (Butan) auf die erforderliche Temperatur des Fernwärmenetzes anhebt.

Da das bestehende Konzept jedoch aufgrund der begrenzten Quellenleistung keinen Ganzjahresbetrieb gewährleisten kann, werden in dieser Arbeit verschiedene Untersuchungsvarianten für die Strom- und Umweltwärmeversorgung entwickelt. Die Analyse der Stromversorgung umfasst den Vergleich des Netzstrompreises mit der Stromerzeugung durch Photovoltaik. Für die Bewertung der Wärmeversorgung werden zwei Varianten untersucht: Die erste Variante beinhaltet Solarthermie in Kombination mit einem saisonalen Grubenwasserwärmespeicher. Die zweite Variante analysiert eine Luftwärmepumpe.

Der Variantenvergleich zeigt, dass die Luftwärmepumpe mit einer Jahresarbeitszahl von 2,7 für das Gesamtkonzept die kostengünstigste Lösung ist, um eine ganzjährige Vollauslastung der Anlage zu gewährleisten und einen nachhaltigen Betrieb sicherzustellen.

Für die Potenzialeinschätzung der Nutzung von oberflächennaher Geothermie im Untersuchungsgebiet Berlin wurde im Rahmen dieser Arbeit eine webbasierte Applikation entwickelt, die es ermöglicht, in Echtzeit für jedes beliebige Flurstück in Berlin das geothermische Potenzial einzuschätzen. Dabei werden alle gesetzlichen Abstandsregeln, die lokale Vegetation sowie Tiefenbegrenzungen berücksichtigt. Zudem ist eine algorithmische Modellierung einer potenziellen Sondenverteilung für das gewählte Flurstück möglich, welche Aufschluss über sondengenaue Entzugsleistungen gibt.

Die Arbeit verfolgt damit zwei Ansätze. Zum einen wird gezeigt, wie ein zukünftiger technischer Ausbau die Nutzung oberflächennaher Geothermie erleichtern und in manchen Schritten auch automatisieren kann. Diese Arbeit bietet ein Beispiel dafür, wie öffentliche Geodaten aktiv genutzt werden können und soll einen ersten Ausblick darauf geben, wie eine deutschlandweite webbasierte geothermische Potenzialanalyse – speziell für Innenstädte und im Bestand - aussehen könnte. Dies könnte sowohl die Arbeiten für eine geothermischen Ersteinschätzung erleichtern als auch Laien das mögliche geothermische Potenzial für ihr Grundstück aufzeigen.

Der zweite Ansatz ist die wissenschaftliche Auswertung. Es wird aufgezeigt, dass etwa die Hälfte des gesamten Wärmebedarfs Berlins mithilfe oberflächennaher Geothermie – speziell durch Erdwärmesondenanlagen - gedeckt werden könnte. Dabei wird dargestellt, unter welchen Voraussetzungen dies möglich ist und welche gesetzlichen Regelungen dafür angepasst werden müssten. Es wird ebenfalls veranschaulicht, dass selbst ohne größere regulatorische Änderungen eine potenzielle Versorgung von knapp 30 % des gesamten Wärmebedarfs Berlins durch Erdwärmesondenanlagen bereits möglich ist. Im Verlauf dieser Untersuchungen wird nachgewiesen, welches Potenzial in öffentlichen Grünflächen steckt und was es für die Berliner Wärmeplanung bedeuten würde, öffentliche Flächen für die Geothermie-Sondensetzung benachbarter Grundstücke freizugeben.

Zur Dimensionierung von Erdwärmesonden (EWS)-feldern werden üblicherweise g-Funktionen verwendet, die die Wärmeaustauschfähigkeit (also die thermische Reaktion des Untergrunds auf den Entzug oder die Einbringung von Wärme) einer oder mehrerer EWS beschreiben. Mittels g-Funktionen ist eine recheneffiziente Modellierung der aus dem EWS-Feld kommenden Fluidtemperatur möglich. Um g-Funktionen zu erlangen, werden normalerweise physikalische Modelle, die die Wärmeaustauschprozesse im Untergrund simulieren, genutzt.

g-Funktionen können jedoch auch direkt aus Messdaten extrahiert werden. Dabei handelt es sich um eine neue Methode, die bisher erfolgreich auf TRT (thermal response test) Daten angewandt wurde. Hierbei wird ausgenutzt, dass sich die Rücklauftemperatur einer EWS aus der Konvolution einer g-Funktion mit dem Gebäude-Lastprofil ergibt. Der Vorteil dieser experimentellen g-Funktionen ist, dass sie, verglichen mit modellbasierten g-Funktionen, keine Vereinfachungen hinsichtlich der Komplexität der physikalischen Prozesse im Untergrund machen müssen, sondern alle Wärmeaustauschprozesse im Untergrund wiedergeben.

In diesem Beitrag stellen wir experimentelle g-Funktionen vor, die wir aus Monitoringdaten eines EWS-Feldes mit 40 Doppel-U-Rohr-Sonden à 100 m bestimmt haben. Zur Berechnung der 40 für die Sonden charakteristischen g-Funktionen verwenden wir Vor- und Rücklauftemperaturen und Volumenströme eines Monats, die an jeder Sonde gemessen werden. Die experimentellen g-Funktionen zeigen Unterschiede im Wärmeaustauschpotenzial der EWS. Um Gründe für diese Unterschiede zu identifizieren, vergleichen wir die experimentellen mit modellbasieren g-Funktionen, die mittels eines numerischen Modells berechnet wurden. Der Vergleich zeigt, dass die unterschiedliche Wärmeaustauschfähigkeit der Sonden neben der Länge der horizontalen Zuleitung wahrscheinlich auch durch unterschiedliche Bohrlochwiderstände verursacht wird. Eine Berücksichtigung dieser Faktoren hat das Potenzial, die Auslegung und den Betrieb von Erdwärmesondenfeldern zu verbessern.

The northern campus of the University of Göttingen comprises around 40 buildings with a heat demand of approximately 45 Gwh/a integrated into a larger natural gas-based heat supply infrastructure. A decoupling from the central district heating system and a transformation to a low-temperature subnet is proposed to achieve a fossil-free heat transformation of the northern campus. This includes the utilisation of waste heat and the integration of a “geothermal hub.” The hub aims to supply heat by combining shallow and medium-deep geothermal energy, along with heat storage and cooling. Beyond evaluating and implementing new heating systems, the accompanying infrastructural changes present an opportunity to comprehensively develop a sustainable campus. This work aims to gather and consolidate relevant infrastructure data and propose initial ideas for a holistic transition approach. Key data include buildings characteristics, traffic infrastructure, water protection zones, as well as the reserves for the critically endangered European hamster. Open space maps have been created to identify potential areas for implementing various geothermal systems during the construction and operation phases. This initiative provides the opportunity to develop a sustainable land-use plan, which has been based on the three ethical principles of permaculture design. These are “earth care”, “people care”, and “sharing of surplus” and aim to create mutual beneficial connections within the design elements. Coupled with a survey among students, this initiative results in recommendations for modifying traffic routes, designing a multi-functional parking layout, enhancing green area vegetation, and establishing more park-like spots for students to relax and interact.

This study explored the potential of low-medium enthalpy geothermal reservoirs for electricity production using ORC power plants. It analyzed various ORC configurations and efficiency improvement methods. The performance degradation of ORC power plant with an air-cooled condenser (ACC) with rising ambient temperature was investigated. Using reference data from ROM Technik and Turboden S.p.A., a proposed power plant's parameters were analyzed. Results showed a significant net plant output drop of 52.1% and cycle efficiency decrease of 45.4% at maximum ambient temperature (35°C) compared to design conditions (10°C). To address this, three alternative condenser designs employing low-temperature fluids – LNG, liquid CO2, and ammonia-water mixture – were proposed. The possibility of coupling a geothermal ORC powerplant with an LNG regasification plant, a geothermal ORC with a CO2 liquefaction plant, and a geothermal ORC plant with an ammonia-water-based absorption refrigeration system was conceived, and their thermodynamic and economic performance were evaluated during the study. All proposed systems outperformed the ORC with ACC. When subjected to same geothermal conditions, the maximum net power output achieved using LNG, ammonia-water, and liquid CO2 condensers were 6.97 MW, 6.85 MW, and 6.97 MW, respectively, compared to 4.85 MW for the reference case. Additionally, the study assessed the total investment cost and payback period for each plant configuration, revealing that the geothermal ORC coupled with absorption refrigeration had the shortest payback time, followed by LNG and liquid CO2.

The Ruhr region is undergoing a profound transformation toward renewable energy solutions with the ending of traditional coal mining and steel industry. To meet the increasing demand for sustainable energy supply, the successful implementation of renewable energy and energy storage concepts is necessary, such as deep geothermal or solar energy. Particularly in the Ruhr region with its long mining history, disused coal mines hold considerable geothermal potential and can serve as systems for seasonal heat storage, that is, mine thermal energy storage (MTES) systems. While MTES-systems allow the storage of surplus heat in waterfilled cavities in the subsurface for heating during winter, thermal stress caused by the injection of how water can result in local uplift or subsidence phenomena. Therefore, a complete condition monitoring of a MTES testing site is required to ensure a safe operation. As a result, the WINZER pilot study has been founded to observe and monitor the operation and the geological response of the local geology as a response to the operation of the MTES. As part of this pilot study, this dissertation aims to create a model of the mine reflecting the current geological situation as well as predicting the geological response over the entire lifespan of a MTES. To create the model in-situ tests and laboratory experiments are combined to generate a new state-of-the-art dataset used to simulate the current and future hydraulic-thermal-mechanical stress state surrounding the testing site. The model will be constantly validated with real-time data logged by various observational tools.

The integration of geothermal heat and storage within district heating networks represents a promising approach to enhance energy efficiency and sustainability in the heat supply of urban areas. In order to gain a comprehensive understanding of the dynamics of both geothermal and district heating systems, it is advisable to numerically couple both systems, or to co-simulate them. This approach enables the simultaneous analysis of thermo-hydraulic dynamics and network interactions and ensures the highest accuracy in both systems. This results in strategies for optimising the energy distribution, as well as operating scenarios for enhancing the overall efficiency and reliability of district heating networks. The aim of this thesis is to present a range of numerical modelling and coupling strategies for open-source and proprietary simulation software, with a focus on the development of calibrated models of existing systems, the planning of future networks, and the evaluation of integration scenarios for different types of geothermal systems. In order to achieve this, tools for importing and exporting simulations as co-simulation models using the standardised Functional Mock-Up Interface (FMI) are required. This will facilitate integrated analysis and optimisation of the system performance. The aim is to enable co-simulation of energy system models with finite element simulations of the subsurface, making them more accessible and easier to implement using standardised interfaces and formats.

Waste glass engenders unembellished environmental challenge, mainly due to the impulsiveness conditions in mass waste state. With snowballing environmental pollution, need to reduce solid waste to it is very important in order for the protection of future generations. Recycling of waste glass is one alternative measure to reduce the influx of solid waste into the environment. Out of the five hierarchies of waste management reduce, reuse, recycle, recover and landfilling; recycling is the best alternative measure by heating glass. Geothermal energy is clean, sustainable and renewable resources. Embracing and direct use of geothermal energy in Kenya is one way which will empower waste control to enhance environmental shield and improve the use of energy. In the study, geothermal energy on or after dormant wells was simulated using mathematical model to investigate experimental test to enhance waste oil in melting of waste glass. The broad objective of this study was to design a numerical model investigating experimental test verifying the potential of geothermal energy to enhance waste oil in recycling glass. Computer simulation was involved by application of mathematical relations applying different types of recycling parameters was formulated based on theories of recycling glass with proper assumptions. Finite difference method of numerical analysis was applied during the process to govern temperature in the glass recycling chamber. The data obtained was applied in testing and verification of the mathematical model developed and provide the exact temperature in the glass recycling process. This data collected was analyzed by use of MATLAB.