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Die vorliegende Erfindung betrifft ein System zur Gewinnung geothermischer Energie, umfassend a.) ein druckdichtes Kühlungsreservoir und einen tiefer gelegenen druckdichten Gesteinshohlraum als Wärmereservoir, wobei im Wärmereservoir gegenüber dem Kühlungsreservoir eine erhöhte Temperatur und optional ein erhöhter Druck vorliegt, b.) eine Injektionsleitung, über die ein im Kühlungsreservoir vorliegendes flüssiges Energietauschermedium dem Wärmereservoir zugeführt werden kann, c.) eine Steigleitung, über die das in seinen flüssigen oder überkritischen Aggregatzustand übergegangene Energietauschermedium aus dem Wärmereservoir in das Kühlungsreservoir zurückgeführt werden kann, wobei die Steigleitung eine Vorrichtung zur Energieumwandlung umfasst. Zudem wird ein Verfahren zur Gewinnung geothermischer Energie beansprucht.

This very young thesis is so simple that it is hard to imagine that it is new and that no one had this idea before. The thesis applies to the Green Karst only. It promises to be an essential addition to the understanding of karstification. NERO assumes that CO2 not only participates passively in the water cycle, but also has an independent, in‐depth mobility (Greek: nerochytis = sink). NERO could be highly relevant to karstification. CO2 has a higher specific density than air. Carbonated water has a higher specific density than non‐carbonated water. Overall, CO2 has an in‐depth mobility vector. The NERO thesis means turning the focus away from only the water cycle and towards both, water cycle and cave‐air CO2 mobility. There are stations and transitions: the soil, the gaseous transition from the soil to the vadose zone, the vadose zone with cave‐air ventilation, density‐driven dissolution at the karst water level, the phreatic zone and the karst spring. The NERO thesis offers a new approach to understanding cave formation in the Green Karst: At the karst water level, water is enriched with additional CO2 from the cave air. In the following new solubility arises. Subterranean waterways with their typically round, phreatic wall and ceiling shapes can be understood as a result of that process. Perhaps even giant halls can be explained by this process (SCHERZER et al. 2017, 2020).

We present a dataset of in-situ measurements in the marginal area of a CO2- and brine-rich cavernous structure in an underground salt mine. The data were collected within the framework of the BMBF-project ProSalz. One aim was to reveal the sources and dynamics of fluid movement as well as temporal and spatial distribution of fluids in a potentially weakened cavern rim. Over a period of three years pressure and gas monitoring was carried out along a transect from a cavernous structure to undisturbed rock salt. In addition, temperature and relative humidity data from the underground gallery were recorded. The gas inflow into isolated borehole sections provided an insight into short- and long-term changes of gas migration patterns in rock salt. Pressure increases of up to 4kPa/day and CO2 concentrations of up to 1.2%, especially at the start of the campaign were measured. The gas migration is coupled to discrete fractures and was limited spatially and temporary. Overall, gas occurrences were not correlated to their distance to the cavern, suggesting no wide-ranging fluid-rock interaction within the rim of the investigated natural cavernous structure in rock salt.

Data of the "density-driven dissolution of CO2 in karst water" column experiment. A laboratory column was filled with tapwater (water level 5,55 m) and exposed it to an elevated gaseous CO2-concentration, roughly 50 times the current atmospheric concentration (20000 +/- 5000 ppm). After stripping the water with ambient air, it was initially in equilibrium with atmospheric conditions. Then, the concentration of dissolved CO2 was measured over a time period of 60 days in two different depths in the column. Measuring points are in the column air, 1 m below water level and 0,15 m above ground. CO2-air concentration was provided using an air-membrane pump (KNF N86 KTE) and a 100 l TEDLAR bag (for more detailed information look into the related publication Class 2021 et al.)

The relevance of CO2 emissions from geological sources to the atmospheric carbon budget is becoming increasingly recognized. Although geogenic gas migration along faults and in volcanic zones is generally well studied, short-term dynamics of diffusive geogenic CO2 emissions are mostly unknown. While geogenic CO2 is considered a challenging threat for underground mining operations, mines provide an extraordinary opportunity to observe geogenic degassing and dynamics close to its source. Stable carbon isotope monitoring of CO2 allows partitioning geogenic from anthropogenic contributions. High temporal-resolution enables the recognition of temporal and interdependent dynamics, easily missed by discrete sampling. Here, data is presented from an active underground salt mine in central Germany, collected on-site utilizing a field-deployed laser isotope spectrometer. Throughout the 34-day measurement period, total CO2 concentrations varied between 805 ppmV (5th percentile) and 1370 ppmV (95th percentile). With a 400-ppm atmospheric background concentration, an isotope mixing model allows the separation of geogenic (16–27%) from highly dynamic anthropogenic combustion-related contributions (21–54%). The geogenic fraction is inversely correlated to established CO2 concentrations that were driven by anthropogenic CO2 emissions within the mine. The described approach is applicable to other environments, including different types of underground mines, natural caves, and soils.

The toxicity of the copper oxide nanoparticles (CuO NP) has been attributed to the so-called “Trojan horse”-type mechanism, relying on the particle uptake and extensive intracellular release of copper ions, due to acidic pH in the lysosomes. Nevertheless, a clear distinction between extra- and intracellular-mediated effects is still missing. Therefore, the impact of the endocytosis inhibitor hydroxy-dynasore (OH-dyn), as well as bafilomycin A1 (bafA1), inhibiting the vacuolar type H+-ATPase (V-ATPase), on the cellular toxicity of nano- and microsized CuO particles, was investigated in BEAS 2 B cells. Selected endpoints were cytotoxicity, copper uptake, glutathione (GSH) levels, and the transcriptional DNA damage and (oxidative) stress response using the high-throughput reverse transcription quantitative polymerase chain reaction (RT-qPCR). OH-dyn markedly reduced intracellular copper accumulation in the cases of CuO NP and CuO MP; the modulation of gene expression, induced by both particle types affecting especially HMOX1, HSPA1A, MT1X, SCL30A1, IL8 and GADD45A, were completely abolished. BafA1 lowered the intracellular copper concentration in case of CuO NP and strongly reduced transcriptional changes, while any CuO MP-mediated effects were not affected by bafA1. In conclusion, the toxicity of CuO NP depended almost exclusively upon dynamin-dependent endocytosis and the intracellular release of redox-active copper ions due to lysosomal acidification, while particle interactions with cellular membranes appeared to be not relevant.

In eastern Hesse and western Thuringia, Germany hosts significant potassium-bearing salt deposits industrially excavated in the Werra-Fulda mining district. The salt belongs to the upper Permian (Zechstein) and was deposited around 258 to 252.5 Ma ago. In the Werra-Fulda mining district, the halite rocks (Werra-Rocksalt, z1NA) contain two minable potash seams, potash Seam Thüringen (z1KTh) and potash Seam Hessen (z1KHe), with an average thickness between 2 m and 3 m (Figure 1). To investigate the chemical and isotopic composition of the gas phase of Seam Hessen, gaseous samples were collected from five, 2-meter deep, horizontal boreholes drilled in the potash horizon which is mined at a depth of 540 m. About 4 weeks in advance of the gas sampling, the packer-closed boreholes were evacuated to about 3kPa and the pressure gradient inside the holes was continuously monitored in the boreholes D1 to D5. Selected gas samples were analyzed for their noble gas isotopic composition and the δ13C values of CO2 and CH4. The noble gas isotopic compositions were determined using a VG 5400 noble gas mass spectrometer after purification in a preparation line. The carbon isotope compositions were analysed with a GC-IRMS, comprising a GC 6890N connected to a GC-C/TC III combustion device and coupled to a MAT 253 mass spectrometer. The standard deviation of the δ13C values (in ‰ vs. VPDB) is ± 0.5 ‰.

Fluid inclusions are voids enclosed in the rock matrix and contain, depending on their origin and development, various amounts of gaseous, liquid or solid phases. Depending on their occurrence within the crystalline structure or in healed micro-fractures, primary and secondary inclusions can be distinguished. Their characteristics are utilized in various geological settings to reconstruct rock history and fluid involvement. Fluid inclusions could also be considered to be small equivalents to large cavities. As salt is regarded a favorable host rock for the storage of natural gas and other materials in artificial caverns, knowledge on gas migration and retention is crucial. Here, we present results of a fluid inclusion study in various salt rocks using Raman spectroscopy in addition to conventional microscopic characterization and gas analysis on whole rock samples. This approach allows for a better understanding of fluid generation and migration in different salt lithologies over geological times. Various salt minerals (halite, sylvite, kieserite and carnallite) from an area of potential overprint of CO2-dominated gas migration were investigated. Numerous fluid inclusions exhibit chevron structure and are small sized. Large single- or two-phased inclusions are observed with irregular shapes, often indicative for leakage or necking down. Interestingly, although the CO2 concentrations in whole rock samples were high, fluid inclusions were dominated by an aqueous phase and often contain numerous daughter minerals. This suggests that CO2-rich gas is stored along distinct fractures or grain boundaries within an otherwise intact rock.

Natural gas hydrates occur at all active and passive continental margins and are supposed to contain tremendous amounts of methane, which makes them attractive as a potential source of energy. During the last two decades several methods have been developed and tested to produce methane from gas hydrates in lab experiments and field trials. In principle, three different approaches, namely depressurization, thermal stimulation and chemical stimulation have been tested. The injection of CO2 into hydrate-bearing sediments as a variant of a chemical stimulation appears to be particularly favorable because it combines the production of methane from the hydrate phase with the storage of CO2 as a solid clathrate. Despite the fact that numerous experimental and modelling studies have been conducted worldwide in order to understand the process on different scales and to evaluate its efficiency, some issues remain pending. We obtained laboratory data from micro-scale experiments using analytical methods such as Raman spectroscopy and X-ray diffraction providing information about the structural changes of the hydrate phase and the gas exchange processes on a molecular scale. The results indicate that the processes related to the exchange of the guest molecules are quite complex. It is generally accepted that the driving force for the release of methane from the hydrate lattice and the incorporation of CO2 into the hydrate structure is the chemical potential gradient between the hydrocarbon hydrate phase and the injected CO2 phase. Raman spectroscopic and X-ray diffraction measurements indicate that this process correlates with a (partial) decomposition or opening of the hydrate cavities. In case of mixed hydrocarbon hydrates with structure II the exchange of the guest molecules with CO2 also induces a change of the hydrate structure (sII to sI). In general, the exchange of the guest molecules results in the formation of a secondary mixed hydrate phase containing CO2 besides methane and other hydrocarbons depending on the composition of the surrounding gas phase. We also obtained laboratory data from large-scale experiments providing information about the methane recovery and fluid migration, hydrate dissociation rates and the formation of a secondary hydrate phase, heat and mass transfer. The experimental results show a wide variation indicating that the recovery rate of methane strongly depends on the experimental conditions such as the volume of the sample, hydrate saturation and thus permeability of the hydrate bearing sediment, hydrate morphology as well as pressure and temperature of the injected CO2 phase. To avoid clogging due to the formation of a CO2 hydrate in the vicinity of the injection area we used gas mixtures containing N2 besides CO2 which also has an impact on the recovery rate of methane and the potential formation of a secondary hydrate phase. In any case, the injection of CO2 results in the production of a gas mixture rather than the extraction of pure methane because the injected CO2 forms a mixed hydrate with a certain amount of methane remaining in the hydrate phase. In addition, the long-term stability of the secondary formed CO2-rich hydrate phase also depends on the potential changes of the chemical environment which may result in the release of CO2 due to a re-exchange of the hydrate bonded gas molecules or dissociation of the hydrate phase. Maybe these results make the approach of methane production from natural gas hydrate deposits via CO2 injection less attractive with regard to efficiency and safe CO2 sequestration than originally expected. This contribution will present the experimental results of our investigations on various scales using different analytical methods and the overarching interpretation and conclusions based on these data.

In den Geowissenschaften gehört es zum Standard, internationale Netzwerke aufzubauen, um Zugang zu bestimmten Regionen zu erhalten oder auf lokales Wissen zuzugreifen. Die DFG-Arbeitsgruppe „Geowissenschaftlicher Nachwuchs“ hat Netzwerkbildung und Internationalisierung im Rahmen eines Rundgespräches analysiert. Ein berufliches Netzwerk ist Grundbest andteil wissenschaftlichen Arbeitens. Es erleichtert Kenntnisse über den state of the art und erlaubt, Ergebnisse zu erzielen, die Einzelkämpfer nicht erreichen. Drittmittelgeber fordern häufig die Etablierung oder Nutzung internationaler Kooperationen. Aktiver wissenschaftlicher Austausch, Einladungen zu Vorträgen oder Fachbeiträgen können als Form des Netzwerkens die eigene Sichtbarkeit erhöhen und Chancen auf dem Bewerbungsmarkt verbessern.

Methane (CH4) hydrates are considered as a player in the field of energy supply and – if applied as such – as a possible sink for the greenhouse gas carbon dioxide (CO2). Next to the more conventional production methods depressurization and thermal stimulation, an extraction of CH4 by means of CO2 injection is investigated. The method is based on the chemical potential gradient between the CH4 hydrate phase and the injected CO2 phase. Results from small-scale laboratory experiments on the replacement method indicate recovery ratios of up to 66% CH4 but also encounter major discrepancies in conversion rates. So far it has not been demonstrated with certainty that the process rates are sufficient for an energy and cost effective production of CH4 with a concurrent sequestration of CO2. In a co-operation of GFZ and GEOMAR we used LARS (Large Scale Reservoir Simulator) to investigate the CO2-CH4-replacement method combined with thermal stimulation. LARS accommodates a sample volume of 210 l and allows for the simulation of in situ conditions typically found in gas hydrate reservoirs. Based on the sample size, diverse transport mechanisms could be simulated, which are assumed to significantly alter process yields. Temperature and pressure data complemented by a high resolution electrical resistivity tomography (ERT), gas chromatography, and flow measurements serve to interpret the experiments. In two experiments 50 kg heated CO2 was injected into sediments with CH4 hydrate saturations of 50%. While in the first experiment the CO2 was injected discontinuously in a so called “huff’n puff” manner, the second experiment saw a continuous injection. Conditions within LARS were set to 13 MPa and 8°C, which allow for stability of pure CO2 and CH4 hydrates as well as mixed hydrates. The CO2 was heated and entered the sediment sample with temperatures of approximately 30° C. In this presentation we will discuss the results from the largescale experiments and compare them with data from small-scale experiments.

Natural gas hydrates occur at all active and passive continental margins, in permafrost regions, and deep lakes. Since they are supposed to contain enormous amounts of methane, gas hydrates are discussed as an energy resource. For the production of gas from hydrate bearing sediments, three different production methods were tested during the last decade: depressurization, thermal and chemical stimulation as well as combinations of these methods. In the framework of the SUGAR project we developed a Large Scale Reservoir Simulator (LARS) with a total volume of 425L to test these three methods in a pilot plant scale. For this purpose we formed hydrate from methane saturated brine in sediments under conditions close to natural gas hydrate deposits. The obtained hydrate saturations varied between 40-90%. Hydrate saturation and distribution were determined using electrical resistivity tomography (ERT). The volumes of the produced gas and water were determined and the gas phase was analyzed via gas chromatography. Multi-step depressurization, thermal stimulation applying in-situ combustion as well as chemical stimulation via the injection of CO2 and a CO2-N2-mixture were tested. Depressurization and thermal stimulation appear to be less complicated compared to the chemical stimulation. For the understanding of the macroscopically observed processes on a molecular level, we also performed experiments on a smaller scale using microscopic observation, Raman spectroscopy and X-ray diffraction. The results of these experiments are of particular importance for the understanding of the processes occurring during the CO2-CH4 swapping. Under the chosen experimental conditions the observations indicate a (partial) decomposition and reformation of the hydrate structure rather than a diffusion-controlled exchange of the molecules.

The knowledge of the physical and geo-mechanical properties of hydrate-bearing sediments as a function of hydrate saturation is crucial for the estimation of the mechanical behavior during production. Since the formation of methane hydrate in sediments is a complex and time consuming process, tetrahydrofuran hydrate is commonly used as a substitute for methane hydrates in laboratory experiments. Tetrahydrofuran (C4H8O, hereafter THF) forms structure II hydrates at ambient pressure and temperatures below 277.5 K. In addition, THF is completely miscible in water and thus the formation of THF hydrate in sediments is fast and homogenous compared to the formation of methane hydrates. Depending on the THF concentration in water a certain hydrate volume fraction forms in coexistence with an aqueous phase. At equilibrium, the chemical potential has to be the same in both the THF hydrate phase and the coexisting aqueous phase. Thus, not all THF dissolved in the original aqueous phase can be transferred into THF hydrate. In this study we determined the formed hydrate volume fraction depending on the THF concentration in water, the remaining THF concentration in the coexisting aqueous phase and the lowest concentration of THF in water necessary for hydrate formation using Raman spectroscopy, calorimetry and X-ray diffraction. The results of Raman spectroscopic measurements indicate that about 5.5 wt% of THF remain in the aqueous phase coexisting with the hydrate phase. There was no clear coexistence of a hydrate phase and an aqueous phase observed for THF-H2O mixtures containing less THF in the aqueous phase. This is in agreement with calorimetric data. On the contrary, X-ray diffraction measurements indicate a coexistence of ice and THF hydrate for the complete THF-H2O solution series.

This study assesses the capability and limits of silicone tubes as tools to monitor the methane gas flux and it s distribution in the course of hydrate formation and dissociation. Also, their ability to serve as a suitable in situ gas extraction tool for methane released during hydrate decomposition has been examined. In the framework of the SUGAR Project, we simulate different methods (depressurization, thermal stimulation and distortion of the chemical equilibrium by CO2) for methane gas production from gas hydrates deposits in a LArge scale Reservoir Simulator LARS. Within this setup, thin - walled (0.8 mm) silicon tubes are utilized for in situ gas capture. They function as membranes for the extraction of methane gas, leaving sediment and brine behind. First tests show that, driven by the transmembrane pressure difference, the methane flux through these membranes is about 1 mL per minute per cm² membrane surface at a reservoir pressure of about 20 MPa. The operation of the membranes as a simple capture tool for the released methane from a hydrate deposit is therefore considered as feasible and, due to their robust nature, reliably applicable in remote and rough areas. Furthermore, the silicone tubes have been utilized for the monitoring of spatial and temporal gas distributions. For that, LARS has been equipped with silicone membranes at various locations to quantify free and dissolved gas volumes in the progress of hydrate formation and decomposition. The results show that inhomogeneous gas distributions within the reservoir are detectable and terminable.

The in situ dissociation of gas hydrate is prerequisite for the commercial recovery of natural gas from hydrate deposits. We examined different methods such as depressurization, thermal stimulation and distortion of the chemical equilibrium by carbon dioxide sequestration for methane gas production from hydrates within our Large Scale reservoir simulator LARS in a pilot plant scale. Within this setup, thin-walled (0.8 mm) silicon tubes are utilized for in situ gas capture. They function as membranes for the extraction of methane gas, leaving sediment and brine behind. The gas capture via silicone tube membranes is, due to their robust nature, reliably applicable in remote and rough areas. First tests show that, driven by the transmembrane pressure difference, the methane flux through these membranes is about 1 mL per minute per cm² membrane surface at a reservoir pressure of about 20 MPa. This is in good agreement with values reported in the literature [e.g. 2]. The operation of the membranes as a simple capture tool for the released methane from a hydrate deposit is therefore considered as feasible. Furthermore, silicone tube membranes are suitable for the quantification of free and dissolved gas volumes. For the monitoring of spatial and temporal gas distribution, LARS has been equipped with several silicone membranes at various locations. They have been utilized to monitor the progress of hydrate formation and decomposition and show that inhomogeneous gas distributions within the reservoir are detectable and terminable. The quantification of carbon dioxide/methane gas ratios during exchange experiments, however, is due to differences in water solubility and permeation rates of the gas species challenging. The study assesses the capability and limits of silicone tubes as membranes for gas extraction and as a tool to monitor gas distribution and composition in the course of hydrate dissociation experiments.