• Energy Research

The campus of the Karlsruhe Institute of Technology (KIT) contains several waste heat streams. In an effort to reduce greenhouse gas emissions by optimizing thermal power consumption on the campus, researchers at the KIT are proposing a ‘DeepStor’ project, which will sequester waste heat from these streams in an underground reservoir during the summer months, when the heat is not required. The stored heat will then be reproduced in the winter, when the campus’s thermal power demand is much higher. This paper contains a preliminary geochemical risk assessment for the operation of this subsurface, seasonal geothermal energy storage system. We used equilibrium thermodynamics to determine the potential phases and extent of mineral scale formation in the plant’s surface infrastructure, and to identify possible precipitation, dissolution, and ion exchange reactions that may lead to formation damage in the reservoir. The reservoir in question is the Meletta Beds of the Upper Rhein Graben’s Froidefontaine Formation. We modeled scale- and formation damage-causing reactions during six months of injecting 140 °C fluid into the reservoir during the summer thermal storage season and six months of injecting 80 °C fluid during the winter thermal consumption season. Overall, we ran the models for 5 years. Anhydrite and calcite are expected mineral scales during the thermal storage season (summer). Quartz is the predicted scale-forming mineral during the thermal consumption period (winter). Within ~20 m of the wellbores, magnesium and iron are leached from biotite; calcium and magnesium are leached from dolomite; and sodium, aluminum, and silica are leached from albite. These reactions lead to a net increase in both porosity and permeability in the wellbore adjacent region. At a distance of ~20–75 m from the wellbores, the leached ions recombine with the reservoir rocks to form a variety of clays, i.e., saponite, minnesotaite, and daphnite. These alteration products lead to a net loss in porosity and permeability in this zone. After each thermal storage and production cycle, the reservoir shows a net retention of heat, suggesting that the operation of the proposed DeepStor project could successfully store heat, if the geochemical risks described in this paper can managed.

With the amendment to the German Climate Change Act in 2021, the Federal Government of Germany has set the target to become greenhouse gas neutral by 2045. Reaching this ambitious target requires multisectoral efforts, which in turn calls for interdisciplinary collaboration: the Net-Zero-2050 project of the Helmholtz Climate Initiative serves as an example of successful, interdisciplinary collaboration with the aim of producing valuable recommendations for action to achieve net-zero CO2 emissions in Germany. To this end, we applied an interdisciplinary approach to combining comprehensive research results from ten German national research centers in the context of carbon neutrality in Germany. In this paper, we present our approach and the method behind the interdisciplinary storylines development, which enabled us to create a common framework between different carbon dioxide removal and avoidance methods and the bigger carbon neutrality context. Thus, the research findings are aggregated into narratives: the two complementary storylines focus on technologies for net-zero CO2 emissions and on different framing conditions for implementing net-zero CO2 measures. Moreover, we outline the Net-Zero-2050 results emerging from the two storylines by presenting the resulting narratives in the context of carbon neutrality in Germany. Aiming at creating insights into how complementary and related expertise can be combined in teams across disciplines, we conclude with the project’s lessons learned. This paper sheds light on how to facilitate cooperation between different science disciplines with the purpose of preparing joint research results that can be communicated to a specific audience. Additionally, it provides further evidence that interdisciplinary and diverse research teams are an essential factor for defining solution spaces for complex, interdisciplinary problems.

AbstractHigh-temperature aquifer thermal energy storage (HT-ATES) systems are designed for seasonal storage of large amounts of thermal energy to meet the demand of industrial processes or district heating systems at high temperatures (> 100 °C). The resulting high injection temperatures or pressures induce thermo- and poroelastic stress changes around the injection well. This study estimates the impact of stress changes in the reservoir on ground surface deformation and evaluates the corresponding risk. Using a simplified coupled thermo-hydraulic-mechanical (THM) model of the planned DeepStor demonstrator in the depleted Leopoldshafen oil field (Upper Rhine Graben, Germany), we show that reservoir heating is associated with stress changes of up to 6 MPa, which can cause vertical displacements at reservoir depth in the order of 10–3 m in the immediate vicinity of the hot injection well. Both the stress changes and the resulting displacements in the reservoir are dominated by thermoelasticity, which is responsible for up to 90% of the latter. Uplift at the surface, on the contrary, is primarily controlled by poroelasticity with by two orders of magnitude attenuated displacements of << 10–3 m. Our calculations further show that the reservoir depth, elastic modulus, and injection/production rates are the dominant controlling parameters for the uplift, showing variations of up to two order of magnitudes between shallower reservoirs with low elastic moduli and deeper and more competent reservoirs. In addition, our findings demonstrate that the cyclic operation of HT-ATES systems reduces the potential for uplift compared to the continuous injection and production of conventional geothermal doublets, hydrocarbon production, or CO2 storage. Consequently, at realistic production and injection rates and targeting reservoirs at depths of at least several hundred meters, the risk of ground surface movement associated with HT-ATES operations in depleted oil fields in, e.g., the Upper Rhine Graben is negligible.

ABSTRACTAn indirect electromagnetic geothermometer is used for deep temperature estimations in the Soultz‐sous‐Forêts geothermal area (France) using magnetotelluric sounding data. Validation of temperature assessment carried out by comparison of the forecast temperature profile with temperature log from the deepest borehole has resulted in the relative extrapolation accuracy of less than 2%. It is found that the resistivity’s uncertainty caused by magnetotelluric inversion errors and by possible effects of external factors very weakly affects the resulting temperature, with the latter being influenced mainly by the ratio between the borehole length and the extrapolation depth. The temperature cross‐section constructed up to the depth 5000 m manifests local temperature maxima at large depths beneath the wells GPK2 and RT1/RT3. The analysis of the temperature profile in GPK2 location beneath 5000 m indicates that its behaviour continues to be of the conductive type (as in the depth range of 3700 m–5000 m) up to the depth 6000 m, while manifesting convective type below this depth. Finally, application of the indirect electromagnetic geothermometer for the deep temperature forecasting in the Rittershoffen site enabled us to constrain the location for future drilling.

Abstract The technical feasibility of Enhanced Geothermal Systems (EGS) has been demonstrated for the first time in fractured crystalline basement rocks at the Soultz-sous Forets project (France), thus creating a unique and vast data base. At this EGS reference site, different hydraulic and chemical stimulation procedures and experiments were performed in four wells at three different reservoir levels located between 2 and 5 km depth. These measures enhanced significantly the hydraulic yield of the three reservoirs, in some instances by about two orders of magnitude. In this compilation of hydraulic data, we summarize the achievements at Soultz during the development of three reservoirs by more than 15 major stimulations over a 20-year period between 1988 and 2007. We evaluate the efficiency of the different injection schemes used and provide details on the performance history and testing conditions. In addition to the 52 experiments described for the testing phase, this compilation includes nine tests under operational conditions conducted over the 2008–2013 period. The evolution of hydraulic yield resulting from various injection, production, and circulation experiments is a major achievement of the Soultz reservoir development. This experience points to two important results: 1) the amount of total volume circulated between wells has a very significant effect on reservoir performance and 2) given the large flow rate variation a common linear trend of pressure increase at higher fluid flow rates develops that manifests over all three reservoirs. A strong focus is on the well tests in the intermediate reservoir allowing for a characterization of productivity and injectivity indices. Our analysis showed that initial hydraulic conditions from single-well injection tests are comparable to each other in the three reservoirs, but individual fault zones may determine the stimulation behaviour. We identify progressive cyclic injection in combination with circulation between wells reaching high hydraulic yields at comparatively low pressure. The Soultz data suggest how to maximize injection and minimize induced seismicity. This unique data base illustrates the learning curve achieved in Soultz and provides a strong basis for further conceptual model developments.

The growing demand for energy, natural resources and urban expansion during the last two centuries increased human interference with the geosphere far beyond geothermal usage. The increasing number of large-scale projects intervening the area of life of communities raised public concerns related to their environmental and social impact. Integration of public concerns into such projects should therefore go beyond outreach and communication measures. It requires an open approach to inclusive governance structures with respect to designing research and development processes and to modify technological options. Geoethical concepts emphasize that geoscientific knowledge may assist society in decision making as well as in dealing with risks, user conflicts and environmental threats on local, regional and global scale in order to support more sustainable practices at the intersection of human beings and the geosphere. In the present article, we analyse the social response to recent geothermal development and identify the precondition for public acceptability of geothermal projects. On this basis, the potential contribution of a GeoLaB, a Geothermal Laboratory in the crystalline Basement, to a geoethic approach in geothermal research and technology development is discussed. The underground research laboratory is planned as an infrastructure to answer scientific challenges and to offer the necessary transparency to interact with the public. The GeoLaB approach aims on transparent, tangible science and can serve to enhance mutual understanding of stakeholder groups. It may increase public awareness on geothermal research and potentially enhance the opportunity for public approval of planned activities. As a generic site, GeoLaB can develop scientific-technological solutions for a responsible exploitation of geothermal energy accompanied by sociological studies. The underground research laboratory will serve as a platform for science communication, participation and dialogue of stakeholders from industry, politics, administration and society. This complies with the comprehension of responsible research in a geoethical sense.

AbstractAs estimated by the International Energy Agency, geothermal power can contribute to 3.5 % of worldwide power and 3.9 % to heat production by 2050. This includes the development of enhanced geothermal systems (EGSs) in low‐enthalpy systems. EGS technology is still in an early stage of development. Pushing EGS technologies towards market maturity requires a long‐term strategic approach and massive investments in research and development. Comprehensive multidisciplinary research programs that combine fundamental and applied concepts to tackle technological, economic, ecological, and safety challenges along the EGS process chain are needed. The Karlsruhe Institute of Technology (KIT) has defined a broad research program on EGS technology development following the necessity of a transdisciplinary approach. The research concept is embedded in the national research program of the Helmholtz Association and is structured in four clusters: reservoir characterization and engineering, thermal water circuit, materials and geoprocesses, and power plant operation. The proximity to industry, closely interlinked with fundamental research, forms the basis of a target‐orientated concept. The present paper aims to give an overview of geothermal research at KIT and emphasizes the need for concerted research efforts at the international level to accelerate technological breakthrough of EGS as an essential part of a future sustainable energy system.