Veranstaltungsprogramm

Im Rahmen des europäischen Forschungsverbundvorhabens HEATSTORE wurde innerhalb dieser Arbeit zusammen mit der Fraunhofer Einrichtung für Energieinfrastrukturen und Geothermie (IEG) am Standort Bochum das Potential einer ehemaligen Kleinzeche als Speicher für saisonale Überschusswärme untersucht.

Obschon die Idee, Grubenwasser stillgelegter Bergwerke thermisch zu nutzen, nicht neu ist, gibt es derzeit weltweit nur wenige Dutzend Anlagen, in denen Grubenwasser gehoben und dessen vorhandene Erdwärme über Wärmetauscher entzogen wird. Insbesondere gibt es in Deutschland keine bestehenden Anlagen, welche die im Untergrund vorhandenen, durch Bergbau hinterlassenen Hohlräume, als Speicher von saisonal anfallender Überschusswärme nutzen.

Aus diesem Anlass begleitete diese Arbeit eine aktuelle Forschung des Fraunhofer IEG, wie die Sektoren der Solar- und Geothermie miteinander gekoppelt werden können, um zukünftig Wärmenetze nachhaltig und umweltfreundlich zu versorgen. Ein möglicher Schlüsselparameter hierfür sind dezentrale Niedertemperaturnetze mit Möglichkeiten der Speicherung solarthermisch erzeugter Überschüsse.

Um dies näher zu untersuchen, wurden die 1. sowie 4. Fördersohle einer ehemaligen und nicht mehr zugänglichen Kleinzeche unterhalb des Fraunhofer IEG durch drei Bohrungen erschlossen. Im Zuge der Masterarbeit wurde nach Abteufen der Bohrungen in die ehemalige Kleinzeche und Durchführung von Geländearbeiten das Verständnis des Untergrundes für eine geothermische Speicherung vertieft. Hieraus wurde eine grundsätzliche Machbarkeit bezüglich Errichtung einer Pilotanlage zur obertägigen Wärmegewinnung aus Solarthermie und untertägigen Wärmespeicherung unterhalb des Fraunhofer IEG abgeleitet.

Aus einem anschließenden ersten Speicherbetriebstest innerhalb der ehemaligen 4. Fördersohle in 63 m unterhalb des Fraunhofer IEG wurden neue Erkenntnisse hinsichtlich Effizienz und Funktionsweise des Grubenwärmespeichers gewonnen. Innerhalb dieser Arbeit wurde ein erster Langzeitspeichernutzungsgrad nach einer einwöchigen Beladung von ca. 3,5 % ermittelt.

Anhand der erhobenen Untergrunddaten wurden allgemeingültige geologische Eignungskriterien entwickelt und Möglichkeiten zur Steigerung des Langzeit-Speichernutzungsgrades diskutiert, um im Zuge der Dekarbonisierung von fossilen Energieträgern hin zu erneuerbaren Energiequellen durch eine Speicherung solarer Überschusswärme ein mögliches Konzept zur künftigen Ausspeicherung von geothermisch gespeicherter Wärme aus stillgelegten Bergwerken in ein städtisches Wärmenetz vorzustellen.

Thermische Aquiferspeicherung (ATES) kann zu Veränderungen der geochemischen Eigenschaften der Speichergesteine führen, wenn es z.B. zu Temperatur-gesteuerten mineralischen Ausfällungen im Speichergestein kommt. Aktuell werden in Berlin zwei ATES Forschungsprojekte, an zwei unterschiedlichen Standorten durchgeführt:

Im Berliner Westen sind die Rüdersdorfer Schaumkalke durch zahlreiche Bohrungen des ehemaligen Berliner Erdgasspeichers zwischen 500 und 600 m u GOK erschlossen. Diese werden durch die seit dem Sommer 2020 stattfinden hydraulischen Bohrlochtests im Hinblick auf die geothermische Nutzung untersucht. Hierbei konnten auch erstmals vollständige hydrochemische Daten des Formationsfluids gewonnen werden. Die mesozoischen Sandsteinaquifere im Liegenden des Rupeltons sind bisher nur vereinzelt im Berliner Raum mit Bohrungen erschlossen worden. Mit den salinen Sandsteinaquiferen als Zielformation in Teufen zwischen 300 und 600 m u GOK soll noch im Sommer 2021 die Forschungsbohrung in Berlin Adlershof abgeteuft werden. Nach dem Ausbau der Bohrung werden auch hier hydraulische Tests inkl. hydrochemischen Monitoring durchgeführt. Die gesammelten Daten dieser Feldversuche ergänzen die Ergebnisse aus Laborversuchen zu Wasser-Gesteins-Wechselwirkungen zwischen Reservoir Gestein und synthetischem Formationsfluid. Somit soll die thermische Beeinflussung des Untergrundes auf die chemischen Reaktionen aufgezeigt werden, damit potentielle Speicherschädigungen präventiv erfasst und durch geeignete Gegenmaßnahmen verhindert werden.

Über 50 % der deutschen CO₂-Emissionen werden durch die Bereitstellung von Gebäude- und Prozesswärme verursacht. Aufgrund saisonaler Bedarfsschwankungen, insbesondere in der Gebäudeversorgung, kommt der Möglichkeit lokaler Speicherung von überschüssiger Wärme im Sommer, die im Winter aus dem Speicher entnommen werden kann, eine immer größere Bedeutung zu. Bedeutende Mengen an Wärme können bei derzeitigem Stand der Technologie und absehbaren Entwicklungen nur im Untergrund unter Ausnutzung der dort verfügbaren großen Volumina gespeichert werden. Im Unterschied zu oberflächennahen Aquiferspeichern (ATES: Aquifer Thermal Energy Storage) können in tiefen Wärmespeichern wesentlich größere thermische Energien aufgrund deutlich höherer Einspeisetemperaturen gespeichert werden.

Basierend auf generischen thermohydraulischen Modellierungen zeigte eine frühere Studie das hohe generelle Potential ehemaliger Kohlenwasserstoffreservoire im Oberrheingraben für Hochtemperatur-Wärmespeicherung. Für eine vollständigere Bewertung des Potentials müssen allerdings alle gekoppelten physikalischen Prozesse berücksichtigt werden. Anhand des Fallbeispiels DeepStor, einem Pilotprojekt am Campus Nord des Karlsruher Institut für Technologie, befasst sich die vorliegende Studie mit gekoppelten thermo-hydraulisch-mechanischen Prozessen und deren Einfluss auf die Effizienz von Hochtemperatur-Wärmespeichern. Insbesondere betrachten wir den Einfluss von zyklischen poro- und thermoelastischen Spannungsänderungen auf die kritischen Reservoirparameter Porosität und Permeabilität.

Even though 99.9% of the Earth is hotter than 100 ℃, only a fraction of its heat can be utilized in practice. Thermal exploitation is bound to areas characterized by favorable conditions and suitable exploration methods. This is particularly evident in passive geothermal plays, that host low to medium enthalpy resources and are determined by conductive heat transfer. The northern margin of the Rhenish Massif, which is bordering the densely populated Ruhr Area represents such a passive geothermal play with a relatively low predicted geothermal gradient, but a well-developed infrastructure and a high demand for energy and, hence, development potential.

The stratigraphy of the subsurface of the city of Hagen that represents that region consists of several kilometer thick marine and continental deposits, including fluvial siliciclastics, marine carbonates, muds, and evaporites that have accumulated over a period of more than 380 million years. Geothermal research in the area has, in particular, focused on the Devonian carbonates that were shown to have favorable hydraulic transport properties. Both laboratory and field-based studies indicate a highly fractured reservoir at depths. The depth of which is believed to be in the range of 2600m and 4100m, according to seismic measurements and stratigraphic profiles. At the surface, in the northern part of Hagen, the Kabel Premium Pulp & Paper mill intends to utilize the heat stored within the hydrothermal waters of the target formation. However, despite its development potential, no thermal model exists at present that describes the temperature distribution in the subsurface, as deep borehole data are scarce. An alternative to geostatistical data that may overcome this obstacle is provided by physical models that compute the temperature distribution in terms of heat fluxes and thermal conductivities. This requires knowledge of the distribution of thermal conductivities in the subsurface and appropriate boundary conditions, the latter of which can be constrained with lithospheric scale models. Here we present such a lithospheric scale model in 1D for two selected sites, the cities of Münster and Hagen, which enables us to determine the temperature and its variation at one point. These data provide constraints for regional or local temperature analyses, its distribution in space, and its uncertainties in a second, future step. The model is based on the 1D public domain model of Limberger et al. (2017). It adopts a steady-state conductive thermal model, solved for fixed temperature boundary conditions at the surface and at the lithosphere-asthenosphere boundary at which the temperature corresponds to 10 ℃ and 1200 ℃, respectively. Moreover, the model accounts for different basin settings, crustal geometries, radioactive heat production, thermo-tectonic ages, erosion, and variable thermal conductivities that are both, temperature and pressure-dependent. For the calculation, geological data were collected in terms of crustal, sedimentary, and lithospheric composition and thickness in order to constrain its effect on the resulting temperature profile. The results of this study are calibrated against measured temperature data obtained from the Münsterland 1 well for a depth of up to 5956 m and show to be in excellent agreement. Our data demonstrate the impact of deep structures on shallow heat and predicts temperature values of 120 ℃ -160℃ for the Devonian target formation in Hagen. Future studies will focus on the spatial distribution of the formation and its volumetric heat content, based on the evaluated boundary conditions from this study.

Limberger, J., Bonte, D., de Vicente, G., Beekman, F., Cloetingh, S., & Van Wees, J. D. (2017). A public domain model for 1D temperature and rheology construction in basement-sedimentary geothermal exploration: an application to the Spanish Central System and adjacent basins. Acta Geodaetica et Geophysica, 52(2), 269-282

For the economic exploitation, geothermal systems need to be improved to increase the profitability of the investment. One aspect to support this aim is the reservoir productivity, a key parameter, which depends on the hydraulic and mechanical properties of the reservoir formation. In order to develop possible improvement strategies for the profitability enhancement of geothermal reservoirs and/or nuclear waste repositories, hydraulic and mechanical properties of artificial generated fractures were investigated. The importance of the fracture geometry yields the fracture network of the geothermal system. As a result, the influence of stress exerted on single fractures was exploited. Hereby, the fracture aperture represents a key parameter for several other parameters such as the fracture permeability and fracture stiffness. Therefore, experiments of progressive and constant cyclic loading were performed to analyze the fluid flow inside of fractured rock samples from geothermal reservoirs. The specimens analyzed in this research project are the Odenwald Granodiorite which was extracted from the Bergstrasse in Heppenheim, Germany, and the Cornwall Granite from the St. Austell pluton in Cornwall, England. The progressive cyclic loading test (PCL) was performed with confining pressure maxima of 15 MPa, 30 MPa, 45 MPa, and 60 MPa. Within the constant cyclic loading test (CCL), the maximum pressure was raised up to 60 MPa to ensure reproducibility. Axial and lateral strain deformation were measured with LVDT extensometers to calculate the fracture and matrix deformation. Fracture stiffness, -permeability, and -closure were evaluated from the collected dataset. Moreover, the fracture geometry was taken into account by 3D surface scans to display fracture aperture distribution and to model the change in surface structure and its impact on the fracture behavior. The fracture stiffness visualized for both granitoids is similar in terms of values and behavior, despite their different origin and, respectively, their petrographical composition. Moreover, the PCL displayed a linear trend of the fracture stiffness in the 1^st cycle and before exceeding the previous stress maximum. This feature transformed into a non-linear trend when exceeding the previous stress level. The transition seems to be related to a stress-memory effect and the behavior of the ‘Kaiser effect’ for acoustic emissions. Both features were additionally detected in the fracture permeability results. The outcome of a similar research by Kluge et al. (2020) with the Flechtingen Sandstone shows the same characteristics in a different domain for the fracture stiffness, -permeability, and –closure values. Last but not least, the fracture permeability reduction turned out very similar in the PCL and the CCL test, a result that contrasts the outcome of Kluge et al. (2020). Experimental and theoretical results on single fractured rock specimens are discussed and display the importance of fracture stiffness on geothermal systems.

The interaction of CO₂-rich waters with reservoir rocks and fluids from Nesjavellir (Iceland) and Kizildere (Turkey) geothermal fields was studied in a series of batch reactor experiments in order to improve predictions on alteration reactions upon CO₂ injection. Experiments were carried out over a period of at least 30 days with one basaltic sample from Iceland and three metamorphic samples from Turkey. Experiments were performed at the corresponding T-P reservoir conditions respectively of 8MPa and 260 °C for the Icelandic sample and 17 MPa and 105 °C for the Turkish samples. The mineralogy of each sample was determined and analysed by using optical microscopy, XRD and SEM. SEM analyses were conducted before and after the batch experiments to observe the occurrence and effects of precipitation and dissolution reactions. The results were correlated with changes in fluid chemistry. The fluid was monitored throughout the experiments by periodic sampling.

The experiment with the basaltic rock produced an extensive secondary mineral assemblage consisting of clay, chlorite, anhydrite and various types of zeolites. In contrast, experiments with three metamorphic quartz-mica shists from Turkey showed considerably less to no secondary mineral formation. The most reactive sample contained Fe-Mg-Ca-carbonate, which was susceptible for dissolution as indicated by changes in the fluid chemistry and measured carbonate composition before and after the experiment. Iron-rich smectites were precipitated on pyrite accumulations. The other two Turkish rock samples did not contain any carbonates or pyrite but essentially consisted of quartz and micas. Secondary precipitates were not observed on these samples.

It was concluded that for the Turkish samples the dissolution rates and associated element liberation were too low to allow significant precipitation of secondary minerals under the considered experimental conditions. For the experiment with the basaltic rock from Iceland the results indicate that the assemblage of mineral precipitates after 30 days was significantly controlled by the initial solution composition.

In a fault-related deep granitic reservoir located in Redruth, Cornwall (UK), a geothermal doublet-system (United Downs Deep Geothermal Power Project, UDDGP) was completed in June 2019. The development of the geothermal resource of the high-heat-producing granites beneath SW England (Cotton et al., 2020), is the major goal of UDDGP. In the production well UD-1 with a depth of 5275 m (MD), up to 190°C have been measured. The doublet-system (UD-1 and the injection well UD-2 with a depth of 2393 m MD) is aligned vertically, so that both wells penetrate the large-scale Porthtowan Fault Zone (PTF), acting as the geothermal reservoir linking the wells. The PTF is located in the Carnmenellis Granite, the largest onshore pluton of the Cornubian Batholith. A complete understanding of the geothermal reservoir is needed to create a basis for reservoir modelling and to allow for an adequate configuration and dimensioning of the geothermal system including the geothermal power plant. Within the scope of the EU funded MEET project (EU-H2020, GA no. 792037), which aims to support and develop new technologies, approaches and potentials for exploration and exploitation of enhanced geothermal systems (EGS), 20 side wall cores (SWCs) were obtained in UD-1 at selected depths between 4200 m MD and 4900 m MD to petrographically and petrophysically analyze the granitic reservoir rock.

The rock characterization laboratory workflow includes petrophysical measurements followed by a mineralogical and geochemical analysis to define and characterize the properties and composition of the relevant granite types and fracture and fault zones. The cores were analyzed for particle and bulk density, porosity, permeability, thermal conductivity, thermal diffusivity including calculated heat capacity and ultra-sonic wave velocities. Thin sections were analyzed for mineralogical composition and interconnection, intensity of hydrothermal alteration, fractures and the general condition of the rock. Further, XRD, ESEM, XRF and ICP-MS analyses were performed on the samples to provide information about the mineral assemblage, bulk geochemistry and the resulting radiogenic heat production. For the preparation of a reservoir-scale chemical stimulation, acidification experiments under in-situ conditions (150°C and 17.5 MPa) were conducted by Core Flooding Tests (CFTs) on seven selected SWCs using customized acid systems for stimulation of granitic rocks (Lummer et al., 2018). The CFTs resemble the planned chemical stimulation of the reservoir and thus is an experiment for the evaluation of the effectiveness of a potential chemical treatment of the reservoir rock to reach sufficiently high flow rates to allow for an economic productivity. The SWCs consist to major parts of hydrothermally-altered granite, so that the results of the experiments can be transferred to altered faults zones and fractures of the PTF. According to the XRD results, the Carnmenellis granite can be classified as monzogranite, while the altered SWCs are plotting as quartz-rich granitoides, monzogranites, granodiorites, and even as tonalities and quartz diorites/ -gabbros/ -anorthosites (according to Streckeisen) for the highly altered samples. The XRF results suggest a more uniform composition so that the samples plot in the granite, granodiorite, quartz monzonite and only one highly altered sample in foid monzodiorite field of the TAS diagram. The CFT results show a high efficiency of the customized acid system with resulting permeability enhancement factors between 2 and up to >100, depending on the initial permeability of the specimens and dissolution of secondary minerals during the experiments.

Geothermal energy is one of the most viable sources of renewable heat. However, the potential risk of induced seismicity associated to geothermal operations may slow down the growth of the geothermal sector. The potential for induced seismicity is related to the potential for fault reactivation, which is controlled by the ratio of the resolved shear stress and effective normal stress on the fault surface. Previous research has led to significant progress in understanding fluid-injection-induced seismicity in geothermal reservoirs. However, an in-depth assessment of temperature effects on the seismic risk is often missing. This study aims to investigate the relative influence of temperature and key geological and operational parameters on the slip tendency of pre-existing faults through a coupled thermo-hydro-mechanical simulation of the injection and production processes in a synthetic geothermal reservoir model of the Slochteren Sandstone formation in the Netherlands. The non-linear initial-boundary value problem was solved using GOLEM- an open-source finite element based application.

The study suggests that the changes in the slip tendency of a fault can largely be attributed to thermoelastic effects. While the direct pore pressure effect on slip tendency does not change after a new equilibrium is reached in a doublet system, the cold water front continues to grow around the injection well. A significant increase in the slip tendency was observed when this low temperature front reached the fault zone. The distance between an injection well and a pre-existing fault thus plays a pivotal role in determining the mechanical stability of the fault. Careful selection of a suitable target formation and operational parameters is also crucial to mitigate the risk of induced seismicity. Besides the obvious importance of stress field and local fault geometry, rock mechanical properties and operating conditions have a major influence on induced stress changes and the related fault activation potential triggered by geothermal operations.

Study on seismic activity in the Rhine-Ruhr region with considering the rapid growth of geothermal exploration in this densely populated region is important. For this purpose, a slip tendency analysis which is used to assess a seismic reactivation potential based on shear to effective normal stress ratio plays a crucial role. In order to qualify the reactivation potential, critical pore pressure needed for fault reactivation, and the sensitivity of individual parameters influencing the reactivation potential we applied the Monte-Carlo simulation approach. This statistical method gives valuable information on the uncertainty of the critical fault structures based on a normal distribution of each input parameter. In this study, we investigated 8896 faults located in the Rhine-Ruhr region and determined their reactivation potential and critical pore pressures at depth of 5000 meters, which we assumed to be a future reservoir level.

In crystalline reservoirs, fault zones play a first-order role in permeability, having a controlling influence on the migration of hydrothermal fluids. In this type of system, geophysical prospection involving different physical properties, complemented with a multiscale fracture characterization, allow a better understanding of the fluid circulation along the damage zone.

The studied area is located in the Catalan Coastal Ranges, where a major crustal fault, the Vallès normal fault, controls the main extensional basin. This normal fault and its related damage zone have been previously identified as the reservoir and the main path for the hot fluids in the La Garriga-Samalús geothermal system. The presence of other hot springs in similar structural locations suggests an important relationship between these geothermal evidences and the regional structural setup.

This study presents an integration of the previous 2D geophysical data (Mitjanas et al., 2021) with a multiscale analysis of the fractures which outcrop in the La Garriga-Samalús geothermal system. The previous 2D geophysical data involves a gravity map, a magnetotelluric and an ambient seismic noise profile. The fractures characterization combines the analysis of lineaments from satellite pictures, field fracture data collection, and petrographic description of field and borehole samples.

New results have allowed a better identification of the damage zone along the Vallès fault, characterized by permeable fractured granodiorites with thermal fluid circulation evidence. By contrast, the different fault cores identified are characterized mainly by protocataclasites and catalaclasites which seal the reservoir.

Along the Vallès fault trace, intersecting damage zones caused by perpendicular minor faults, together with the presence of relay ramps, explain the variation of the fracture density and the location of hot springs. The fracture density degree conditions the permeability, and therefore, its characterization allows a better understanding of the fluid flow circulation and the creation of a 3D conceptual model.

New 3D gravity and magnetotelluric models are currently undertaken in order to confirm the final conceptual model.

Mitjanas, G., Ledo, J., Macau, A., Alías, G., Queralt, P., Bellmunt, F., Rivero, L., Gabàs, A., Marcuello, A., Benjumea, B., Martí, A., & Figueras, S. (2021). Integrated seismic ambient noise, magnetotellurics and gravity data for the 2D interpretation of the Vallès basin structure in the geothermal system of La Garriga-Samalús (NE Spain). Geothermics, 93.

Down-the-hole (DTH) hammer drilling technology has been used successfully for many years in the mining as well as oil and gas industry to access hydrocarbon reservoirs. Typical DTH hammers use a piston moved by hydraulic power or compressed air, applying alternating loads onto the drill bit to crush the rock at the borehole bottom and thus, eroding the rock. Due to this alternating movement of the piston this technology is called hammer drilling. The internal components of any DTH hammer are called percussion system and include mainly the piston itself and a valve system controlling its movement. Currently, most DTH hammer systems have a maximum operating temperature of 150 °C and are limited to use compressed air or clean water as drilling fluid. As a result, the wellbore control and cuttings transport are more difficult compared to conventional rotary drilling technologies using drill mud with tri-cone or PCD bits. Furthermore, the lifetime of hydraulic type DTH hammers depends much on the quality of the liquid being used, while the achievable rate of penetration (ROP) in hard rock formation is multiple times higher compared to other rotary drilling technologies. The more widespread use of DTH hammer technology towards geothermal reservoirs requires the use of more conventional type of drill mud with additvies, higher lifetime of the device and tool functionality at high-pressure and high-temperature (HPHT) conditions. Therefor, a novel DTH hammer for deep reservoir exploration is being developed using a fluidic switch, instead of a mechanical valve system, and advanced surface coatings to increase tool lifetime. The development of the novel prototype hammer is realized by experimental as well as numerical work (simulations), and iteratively optimizing each component of the percussion mechanism. For this purpose a numerical model of this mechanism is developed based on a mass-spring-damper approach. The model allows to evaluate the efficiency of numerous variations of the mechanism and, therefore, straightens the path of investigation.

Prediction and optimization of the drilling efficiency and the rate of penetration (ROP) in drilling operations have been the subject of numerous research projects over the past few years. While earlier scientific works in this field have focused mainly on analytical approaches for the calculation, prediction, and eventually optimization of the ROP, more recent attempts tend to rely on various data-driven approaches using algorithms based on the ideas of statistical analysis, pattern recognition, and Machine Learning (ML). Thanks to the advances that have been made in the computer science-related fields over the last years, the growing community, and the accessibility of advanced and easy to use frameworks, encouraging results could be in reach; however, there have been multiple obstacles preventing the success of such methods including lack of substantial deep geothermal formation drilling data, lack of computationally cost-effective algorithms, etc.

This paper focuses on developing, evaluating, and comparing different AI-based methods for solving the latter mentioned problems and enable prediction and optimization of the drilling rates efficiency using state of the art AI models with the focus on Deep Learning algorithms. Apart from the models developed, further aspects related to the development process will also be discussed, including the availability of technical deep geothermal drilling data for the training and evaluation of the DL models, requirements for the data, and the extraction and curation of data and their relevant features. Multiple novel methods for the curation, augmentation, and usage of such extensive numerical databases will be discussed, which eventually enables the possibility of using Deep Learning algorithms for historical drilling data.

Furthermore, the significance and influence of the process parameters used for the development of such models will be analyzed to determine the most influential process parameters to identify the drilling parameters which have the highest impact on the efficiency of deep geothermal drilling, which is crucial information used during the optimization of the drilling process.

Das Fündigkeitsrisiko für Geothermiebohrungen ist hoch, da aufgrund zu geringer Durchlässigkeiten der Gesteine in Förderhorizonten häufig nicht die erwünschten Schüttungsraten erzielt werden können. Aus der Öl- und Gasindustrie sind bereits Verfahren bekannt, die grundsätzlich zur Steigerung der Durchlässigkeit eines Reservoirs eingesetzt werden können. Dazu gehören druckwasserbasierte Verfahren (z.B. Radial Jet Drilling (RJD)), mit denen kleinkalibrige Ablenkbohrungen von der Hauptbohrung aus hergestellt werden, um umliegende Störzonen, vor allem Klüfte, hydraulisch an die Bohrung anzuschließen. Die bekannten Verfahren bieten Lösungsansätze für weiche, leicht mit konventionellen Methoden zu bohrende Speichergesteine. Diese für Öl- und Gaslagerstätten typischen Bedingungen lassen sich aber nicht einfach auf geothermische Reservoirs übertragen. Hierbei handelt es sich häufig um Formationen aus Hartgestein, bei denen die beim RJD-Verfahren eingesetzte Wasserstrahltechnik keine oder zu geringe Bohrleistungen aufweist.

Im Vorhaben Micro Turbine Drilling (MTD) am Fraunhofer IEG wird ein Verfahren entwickelt, mit dem die Durchlässigkeit auch in sehr harten Förderhorizonten von Geothermiebohrungen gesteigert werden kann. Die Lösungsidee baut grundsätzlich auf dem Prinzip des RJD auf. Es wird jedoch kein Düsenkopf verwendet, der den Gesteinsabtrag direkt durch einen austretenden Fluidstrahl generiert. Stattdessen wird eine Mikro-Bohrturbine eingesetzt, in der die hydraulische Energie des Fluids in mechanische Energie umgewandelt wird, um einen Bohrmeißel anzutreiben, mit dem der Gesteinsabtrag mechanisch generiert wird. Durchgeführte Voruntersuchungen mit Funktionsprototypen bestätigen die grundsätzliche Funktionsfähigkeit und damit das große Potential der Technologie.

Das Ergebnis dieses Projekts wird ein neues Bohrverfahren sein, mit dem es erstmals möglich ist kostengünstige, mindestens 50 m lange Ablenkbohrungen von einer bis zu 5 km tiefen, verrohrten Bohrung aus in bis zu 200 °C heiße Formationen aus Hartgestein herzustellen. Der entscheidende Vorteil gegenüber dem Stand der Technik ist, dass dieses Verfahren bei geringen Kosten auch für die Anwendung in der Geothermie sowie zahlreicher anderer Erschließungmaßnahmen im Untergrund geeignet ist.

Der Zielmarkt des neuen Bohrverfahrens ist der Fluidbergbau. Dabei steht insbesondere die Geothermie inkl. Untertägiger Speichertechnik im Fokus, aber auch die Öl- und Gasindustrie stellen einen potentiellen Abnehmer dar. Das Marktpotential des Verfahrens ist aufgrund des Alleinstellungsmerkmals und dem durch die Bundesregierung beschlossenen Ausbaus der Geothermie in den kommenden Jahren enorm groß. Eine Vielzahl von Anfragen aus der Industrie nach einem solchen Verfahren bestätigen dies.

Das Radial Jet Drilling (RJD) wird bereits seit den 1980er Jahren in der Öl- und Gasindustrie erfolgreich genutzt, um angrenzende Reservoire und Störzonen an unproduktive Bohrlöcher anzuschließen bzw. bei diesen die Produktion wieder zu erhöhen. Auch in der Geothermie findet die Technologie zunehmend an Bedeutung und Anwendung, siehe u.a. auch die Forschungsprojekte "SURE", "ZoDrEx" oder "CAGE".

Weiterentwicklungen in der Richtung sowie alternative Möglichkeiten zur Nutzung des RJD sind seit längerem Gegenstand aktueller Forschungsarbeiten am Fraunhofer IEG in Bochum.

Das Verfahren basiert auf Hochdruckwasserstrahlen („Jets“), um damit kleinkalibrige Horizontalbohrungen aus einer bestehenden Vertikalbohrung heraus zu erzeugen. Einerseits aufgrund der erschwerten (und engen downhole) Bedingungen sowie dem sehr einfachen, kostengünstigen Aufbau der Jetting-BHA („bottom hole assembly“), findet bisher keine aktive, insitu Überwachung oder gar Regelung des RJD in der Tiefe statt. Es ist meist sehr schwer nachzuvollziehen, ob und was dort in der Tiefe final nach einem RJD-run passiert ist.

Im Rahmen mehrerer Projekte wird die Automatisierung des RJD an diversen Versuchsständen am IEG untersucht und schrittweise entwickelt. Unter Reservoir ähnlichen Bedingungen können dort manuell jegliche Jetting- und Bohrsituationen durchgeführt werden. Mittels Sensorik ist es dabei möglich, die Steuerung der Antriebe anhand von ausgewählten Parametern zu regeln, und somit erstmals einen vollautomatischen RJD-Bohrprozess unter Reservoir ähnlichen Bedingungen zu realisieren. Dazu wurde die Datenerfassung direkt mit der Antriebssteuerung verknüpft und somit eine Regelung des RJD Prozesses insitu umgesetzt. Die vollautomatische Vorschubeinheit kann via Proportional-Integral-Differential-Regeltechnik sowie einem Zweipunktregler vielfältig variiert werden. Zur Validierung des ersten Prototyps solch einer Regeleinheit wurden im Anschluss umfangreiche Versuche durchgeführt und mit zuvor manuell durchgeführten Versuchen verglichen.

Compressive, shear or tensile wellbore failures occur when the stress exerted on a rock exceeds its strength. These failures, if left unattended, can cause wellbore instability, resulting in blowouts or lost circulations. Hence, Mechanical Earth Models (MEM) are established to help understanding how such failures are initiated and how they can be prevented. To construct these models, information about the in-situ principal stress magnitudes and orientations is required along with knowledge of the rock strength properties. This study aims at building 1D MEMs for various wells to avoid the onsets of failures in future wells drilled in the Ruhr area in western Germany, using wireline logging data. COMSOL® software is used to model the stress state around the wellbore and its potential failure. Thus, prompting better decision-making in measures that will improve wellbore stability. These measures include adjusting mud densities with depth, designing well paths that will minimize failure onsets, and deciding upon appropriate casing setting depths.

Die Energiewende und der damit verbundene Bedarf an nichtenergetischen, mineralischen Rohstoffen haben die Bundesregierung veranlasst, die Forschungs- und Entwicklungsaktivitäten entlang der gesamten Wertschöpfungskette auszubauen. Es ist bekannt, dass die hochmineralisierten Thermalwässer, die bei der Gewinnung geothermischer Energie zirkulieren, zum Teil signifikante Anreicherungen an wirtschaftsstrategischen Elementen wie Lithium aufweisen. Die Gewinnung von mineralischen Rohstoffen aus Thermalwässern ist verfahrenstechnisch anspruchsvoll, aber neue nachhaltige Methoden ebnen den Weg für eine wirtschaftliche Gewinnung als Alternative zum konventionellen Bergbau.

In dem deutsch-chilenische Projekt BrineMine wird dieser Ansatz, Rohstoffe aus geothermischen Wässern zu gewinnen, erforscht. Mit Hilfe von Membrantechnologie soll die Wärme des Wassers verwendet werden, um in einem geschlossenen System, die mineralischen Rohstoffe und das Wasser durch einen technischen Prozess voneinander zu trennen. Ziel ist es so neben den Mineralen auch Frischwasser als wichtige Ressource zu gewinnen. Im Vergleich zu herkömmlichen Evaporationsverfahren beschleunigen die Membranverfahren die Aufkonzentration der Wässer, sodass eine rohstoffeffiziente und nachhaltige Alternative zum konventionellen Li-Bergbau aufgezeigt wird. Dafür wurde eine Demonstrationsanlage entwickelt, mit welcher erste Extraktions- und Aufkonzentrationsschritte im laufenden Betrieb eines Geothermiekraftwerks getestet werden konnten. Ein Augenmerk liegt hierbei auf der Vorbehandlung der Thermalwässer um Mineralablagerungen innerhalb der Membranmodule zu verhindern. Unkontrollierten Ausfällungen von Silikaten, welche in geothermalen Wässern häufig nahe der Sättigung sind, können die Produktivität der Anlage einschränken. Ein gezieltes Ausfällen gewährt die Prozessierbarkeit des Fluids und bietet weiterhin die Möglichkeit, das gefällte Silikat selbst als gefragten Rohstoff zu produzieren.

In dieser Studie soll die Entwicklung der Behandlungsstrategie anhand von Laborversuchen und numerischen Designrechnungen dargestellt werden. Weiterhin wird die erfolgreiche Implementierung der Pilotanlage im laufenden Kraftwerksprozess gezeigt sowie die Auswirkung auf das behandelte Wasser und entstandenen Fällungsprodukte.

In the context of the decarbonization of the energy system, shallow geothermal energy such as borehole heat exchangers (BHE) provide an efficient option to both heat and cool buildings in a sustainable manner. Since design and performance of BHE fields depend on the thermal properties of the subsurface, geothermal potential maps help both professional planners and homeowners to decide whether or not shallow geothermal energy is an economic option on a particular site. The creation of these maps requires knowledge of various geological and hydrogeological subsurface information. In common potential estimation workflows, they are usually assessed in accordance with the prevailing data situation in order to model the geothermal potential of a region.

Such manual workflows make it difficult to compare the geothermal potential between different regions, for example in Germany between the federal states. In addition, existing workflows do not account for the significant uncertainties that arise when interpolating between boreholes or assigning thermal properties. Consequently, BHE fields are often oversized and thus expensive.

To tackle these issues, we present a workflow for the calculation of the geothermal potential of BHE including its uncertainty and a corresponding web geoportal. The workflow is solely based on publicly available hydrogeological and geological data and enables the propagation of uncertainty into the outcome. For data processing, the geoportal provides standardized web-based data acquisition techniques of the Open Geospatial Consortium to request and transfer data from the data servers of the geological surveys using open web services (OWS). After selecting a user defined target area via a bounding box, required input data such as boreholes are requested via OWS Web Feature Service (WFS) and send to a Web Processing Service (WPS) server that executes the required calculations. Finally, the precise prediction of the geothermal potential and its uncertainty are provided as Web Map Service (WMS) for visualization within the geoportal. The described approach benefits from updates in the databases of the geological surveys, thus keeping the geothermal potential prediction always up-to-date.

Initially, we demonstrate the workflow and geoportal using data from the federal state of Hamburg. However, it can be applied to all federal states and even for all regions for which input data are publicly and standardized available.