TY - JOUR A1 - Wilke, Franziska Daniela Helena A1 - Schettler, Georg A1 - Vieth-Hillebrand, Andrea A1 - Kühn, Michael A1 - Rothe, Heike T1 - Activity concentrations of U-238 and Ra-226 in two European black shales and their experimentally-derived leachates JF - Journal of Environmental Radioactivity N2 - We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bomholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 mu g/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 mu g/g U. Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of U-238 is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of U-238, the Ra-226 activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released. KW - Unconventional gas production KW - Black shales KW - Flowback KW - Radioactivity KW - NOR KW - Batch experiments Y1 - 2018 U6 - https://doi.org/10.1016/j.jenvrad.2018.05.005 SN - 0265-931X SN - 1879-1700 VL - 190 SP - 122 EP - 129 PB - Elsevier CY - Oxford ER - TY - GEN A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Predicting macroscopic elastic rock properties requires detailed information on microstructure T2 - Energy procedia N2 - Predicting variations in macroscopic mechanical rock behaviour due to microstructural changes, driven by mineral precipitation and dissolution is necessary to couple chemo-mechanical processes in geological subsurface simulations. We apply 3D numerical homogenization models to estimate Young’s moduli for five synthetic microstructures, and successfully validate our results for comparable geometries with the analytical Mori-Tanaka approach. Further, we demonstrate that considering specific rock microstructures is of paramount importance, since calculated elastic properties may deviate by up to 230 % for the same mineral composition. Moreover, agreement between simulated and experimentally determined Young’s moduli is significantly improved, when detailed spatial information are employed. KW - digital rock physics KW - effective elastic properties KW - numerical Y1 - 2017 U6 - https://doi.org/10.1016/j.egypro.2017.08.195 SN - 1876-6102 VL - 125 SP - 561 EP - 570 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Hydraulic and mechanical impacts of pore space alterations within a sandstone quantified by a flow velocity-dependent precipitation approach JF - Materials N2 - Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny-Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface. KW - Bentheim sandstone KW - digital rock physics KW - micro-CT KW - elastic properties KW - permeability KW - precipitation Y1 - 2020 U6 - https://doi.org/10.3390/ma13143100 SN - 1996-1944 VL - 13 IS - 14 PB - MDPI CY - Basel ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Quantifying rock weakening due to decreasing calcite mineral content by numerical simulations JF - Materials N2 - The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution. KW - digital rock physics KW - micro-CT KW - elastic properties KW - numerical simulation KW - chemical-mechanical interaction KW - Code_Aster KW - composite properties Y1 - 2018 U6 - https://doi.org/10.3390/ma11040542 SN - 1996-1944 VL - 11 IS - 4 PB - MDPI CY - Basel ER - TY - GEN A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Quantifying rock weakening due to decreasing calcite mineral content by numerical simulations T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1092 KW - digital rock physics KW - micro-CT KW - elastic properties KW - numerical simulation KW - chemical-mechanical interaction KW - Code_Aster KW - composite properties Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-473089 SN - 1866-8372 IS - 1092 ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Diagenetic trends of synthetic reservoir sandstone properties assessed by digital rock physics JF - Minerals N2 - Quantifying interactions and dependencies among geometric, hydraulic and mechanical properties of reservoir sandstones is of particular importance for the exploration and utilisation of the geological subsurface and can be assessed by synthetic sandstones comprising the microstructural complexity of natural rocks. In the present study, three highly resolved samples of the Fontainebleau, Berea and Bentheim sandstones are generated by means of a process-based approach, which combines the gravity-driven deposition of irregularly shaped grains and their diagenetic cementation by three different schemes. The resulting evolution in porosity, permeability and rock stiffness is examined and compared to the respective micro-computer tomographic (micro-CT) scans. The grain contact-preferential scheme implies a progressive clogging of small throats and consequently produces considerably less connected and stiffer samples than the two other schemes. By contrast, uniform quartz overgrowth continuously alters the pore space and leads to the lowest elastic properties. The proposed stress-dependent cementation scheme combines both approaches of contact-cement and quartz overgrowth, resulting in granulometric, hydraulic and elastic properties equivalent to those of the respective micro-CT scans, where bulk moduli slightly deviate by 0.8%, 4.9% and 2.5% for the Fontainebleau, Berea and Bentheim sandstone, respectively. The synthetic samples can be further altered to examine the impact of mineral dissolution or precipitation as well as fracturing on various petrophysical correlations, which is of particular relevance for numerous aspects of a sustainable subsurface utilisation. KW - digital core reconstruction KW - micro-CT scan KW - pore-scale KW - cementation KW - permeability-porosity relationship KW - elastic rock properties KW - numerical KW - simulation Y1 - 2021 U6 - https://doi.org/10.3390/min11020151 SN - 2075-163X VL - 11 IS - 2 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tranter, Morgan Alan A1 - De Lucia, Marco A1 - Wolfgramm, Markus A1 - Kühn, Michael T1 - Barite scale formation and injectivity loss models for geothermal systems JF - Water N2 - Barite scales in geothermal installations are a highly unwanted effect of circulating deep saline fluids. They build up in the reservoir if supersaturated fluids are re-injected, leading to irreversible loss of injectivity. A model is presented for calculating the total expected barite precipitation. To determine the related injectivity decline over time, the spatial precipitation distribution in the subsurface near the injection well is assessed by modelling barite growth kinetics in a radially diverging Darcy flow domain. Flow and reservoir properties as well as fluid chemistry are chosen to represent reservoirs subject to geothermal exploration located in the North German Basin (NGB) and the Upper Rhine Graben (URG) in Germany. Fluids encountered at similar depths are hotter in the URG, while they are more saline in the NGB. The associated scaling amount normalised to flow rate is similar for both regions. The predicted injectivity decline after 10 years, on the other hand, is far greater for the NGB (64%) compared to the URG (24%), due to the temperature- and salinity-dependent precipitation rate. The systems in the NGB are at higher risk. Finally, a lightweight score is developed for approximating the injectivity loss using the Damkohler number, flow rate and total barite scaling potential. This formula can be easily applied to geothermal installations without running complex reactive transport simulations. KW - reactive transport KW - radial flow KW - geothermal energy KW - scaling KW - phreeqc KW - formation damage Y1 - 2020 U6 - https://doi.org/10.3390/w12113078 SN - 2073-4441 VL - 12 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tranter, Morgan Alan A1 - De Lucia, Marco A1 - Kühn, Michael T1 - Numerical investigation of barite scaling kinetics in fractures JF - Geothermics : an international journal of geothermal research and its applications N2 - Barite stands out as one of the most ubiquitous scaling agents in deep geothermal systems, responsible for irreversible efficiency loss. Due to complex parameter interplay, it is imperative to utilise numerical simulations to investigate temporal and spatial precipitation effects. A one-dimensional reactive transport model is set up with heterogeneous nucleation and crystal growth kinetics. In line with geothermal systems in the North German Basin, the following parameters are considered in a sensitivity analysis: temperature (25 to 150 degrees C), pore pressure (10 to 50 MPa), fracture aperture (10(-4) to 10(-2) m), flow velocity (10(-3) to 10(0) m s(-1)), molar volume (50.3 to 55.6 cm(3) mol(-1)), contact angle for heterogeneous nucleation (0 degrees to 180 degrees), interfacial tension (0.07 to 0.134 J m(-2)), salinity (0.1 to 1.5 mol kgw(-1) NaCl), pH (5 to 7), and supersaturation ratio (1 to 30). Nucleation and consequently crystal growth can only begin if the threshold supersaturation is exceeded, therefore contact angle and interfacial tension are the most sensitive in terms of precipitation kinetics. If nucleation has occurred, crystal growth becomes the dominant process, which is mainly controlled by fracture aperture. Results show that fracture sealing takes place within months (median 33 days) and the affected range can be on the order of tens of metres (median 10 m). The presented models suggest that barite scaling must be recognised as a serious threat if the supersaturation threshold is exceeded, in which case, large fracture apertures could help to minimise kinetic rates. The models further are of use for adjusting the fluid injection temperature. KW - Geothermal KW - Fracture sealing KW - Reactive transport KW - Geochemical modelling KW - Crystal nucleation KW - PHREEQC Y1 - 2021 SN - 0375-6505 SN - 1879-3576 VL - 91 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Tranter, Morgan Alan A1 - De Lucia, Marco A1 - Kühn, Michael T1 - Barite scaling potential modelled for fractured-porous geothermal reservoirs JF - Minerals N2 - Barite scalings are a common cause of permanent formation damage to deep geothermal reservoirs. Well injectivity can be impaired because the ooling of saline fluids reduces the solubility of barite, and the continuous re-injection of supersaturated fluids forces barite to precipitate in the host rock. Stimulated reservoirs in the Upper Rhine Graben often have multiple relevant flow paths in the porous matrix and fracture zones, sometimes spanning multiple stratigraphical units to achieve the economically necessary injectivity. While the influence of barite scaling on injectivity has been investigated for purely porous media, the role of fractures within reservoirs consisting of both fractured and porous sections is still not well understood. Here, we present hydro-chemical simulations of a dual-layer geothermal reservoir to study the long-term impact of barite scale formation on well injectivity. Our results show that, compared to purely porous reservoirs, fractured porous reservoirs have a significantly reduced scaling risk by up to 50%, depending on the flow rate ratio of fractures. Injectivity loss is doubled, however, if the amount of active fractures is increased by one order of magnitude, while the mean fracture aperture is decreased, provided the fractured aquifer dictates the injection rate. We conclude that fractured, and especially hydraulically stimulated, reservoirs are generally less affected by barite scaling and that large, but few, fractures are favourable. We present a scaling score for fractured-porous reservoirs, which is composed of easily derivable quantities such as the radial equilibrium length and precipitation potential. This score is suggested for use approximating the scaling potential and its impact on injectivity of a fractured-porous reservoir for geothermal exploitation. KW - reactive transport KW - radial flow KW - geothermal energy KW - injectivity KW - phreeqc KW - formation damage Y1 - 2021 U6 - https://doi.org/10.3390/min11111198 SN - 2075-163X VL - 11 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tillner, Elena A1 - Langer, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinisation in subsurface storage JF - Hydrology and earth system sciences : HESS N2 - Injection of fluids into deep saline aquifers causes a pore pressure increase in the storage formation, and thus displacement of resident brine. Via hydraulically conductive faults, brine may migrate upwards into shallower aquifers and lead to unwanted salinisation of potable groundwater resources. In the present study, we investigated different scenarios for a potential storage site in the Northeast German Basin using a three-dimensional (3-D) regional-scale model that includes four major fault zones. The focus was on assessing the impact of fault length and the effect of a secondary reservoir above the storage formation, as well as model boundary conditions and initial salinity distribution on the potential salinisation of shallow groundwater resources. We employed numerical simulations of brine injection as a representative fluid. Our simulation results demonstrate that the lateral model boundary settings and the effective fault damage zone volume have the greatest influence on pressure build-up and development within the reservoir, and thus intensity and duration of fluid flow through the faults. Higher vertical pressure gradients for short fault segments or a small effective fault damage zone volume result in the highest salinisation potential due to a larger vertical fault height affected by fluid displacement. Consequently, it has a strong impact on the degree of shallow aquifer salinisation, whether a gradient in salinity exists or the saltwater-freshwater interface lies below the fluid displacement depth in the faults. A small effective fault damage zone volume or low fault permeability further extend the duration of fluid flow, which can persist for several tens to hundreds of years, if the reservoir is laterally confined. Laterally open reservoir boundaries, large effective fault damage zone volumes and intermediate reservoirs significantly reduce vertical brine migration and the potential of freshwater salinisation because the origin depth of displaced brine is located only a few decametres below the shallow aquifer in maximum. The present study demonstrates that the existence of hydraulically conductive faults is not necessarily an exclusion criterion for potential injection sites, because salinisation of shallower aquifers strongly depends on initial salinity distribution, location of hydraulically conductive faults and their effective damage zone volumes as well as geological boundary conditions. Y1 - 2016 U6 - https://doi.org/10.5194/hess-20-1049-2016 SN - 1027-5606 SN - 1607-7938 VL - 20 SP - 1049 EP - 1067 PB - Copernicus CY - Göttingen ER - TY - GEN A1 - Tillner, Elena A1 - Langer, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinisation in subsurface storage T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Injection of fluids into deep saline aquifers causes a pore pressure increase in the storage formation, and thus displacement of resident brine. Via hydraulically conductive faults, brine may migrate upwards into shallower aquifers and lead to unwanted salinisation of potable groundwater resources. In the present study, we investigated different scenarios for a potential storage site in the Northeast German Basin using a three-dimensional (3-D) regional-scale model that includes four major fault zones. The focus was on assessing the impact of fault length and the effect of a secondary reservoir above the storage formation, as well as model boundary conditions and initial salinity distribution on the potential salinisation of shallow groundwater resources. We employed numerical simulations of brine injection as a representative fluid. Our simulation results demonstrate that the lateral model boundary settings and the effective fault damage zone volume have the greatest influence on pressure build-up and development within the reservoir, and thus intensity and duration of fluid flow through the faults. Higher vertical pressure gradients for short fault segments or a small effective fault damage zone volume result in the highest salinisation potential due to a larger vertical fault height affected by fluid displacement. Consequently, it has a strong impact on the degree of shallow aquifer salinisation, whether a gradient in salinity exists or the saltwater-freshwater interface lies below the fluid displacement depth in the faults. A small effective fault damage zone volume or low fault permeability further extend the duration of fluid flow, which can persist for several tens to hundreds of years, if the reservoir is laterally confined. Laterally open reservoir boundaries, large effective fault damage zone volumes and intermediate reservoirs significantly reduce vertical brine migration and the potential of freshwater salinisation because the origin depth of displaced brine is located only a few decametres below the shallow aquifer in maximum. The present study demonstrates that the existence of hydraulically conductive faults is not necessarily an exclusion criterion for potential injection sites, because salinisation of shallower aquifers strongly depends on initial salinity distribution, location of hydraulically conductive faults and their effective damage zone volumes as well as geological boundary conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 548 KW - geological CO2 storage KW - brine migration KW - fluid-flow KW - pressure management KW - dynamic flow KW - permeability KW - sequestration KW - simulations KW - injection KW - leakage Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-411854 SN - 1866-8372 IS - 548 ER - TY - JOUR A1 - Steding, Svenja A1 - Kempka, Thomas A1 - Zirkler, Axel A1 - Kühn, Michael T1 - Spatial and temporal evolution of leaching zones within potash seams reproduced by reactive transport simulations JF - Water / Molecular Diversity Preservation International (MDPI) N2 - Leaching zones within potash seams generally represent a significant risk to subsurface mining operations and the construction of technical caverns in salt rocks, but their temporal and spatial formation has been investigated only rudimentarily to date. To the knowledge of the authors, current reactive transport simulation implementations are not capable to address hydraulic-chemical interactions within potash salt. For this reason, a reactive transport model has been developed and complemented by an innovative approach to calculate the interchange of minerals and solution at the water-rock interface. Using this model, a scenario analysis was carried out based on a carnallite-bearing potash seam. The results show that the evolution of leaching zones depends on the mineral composition and dissolution rate of the original salt rock, and that the formation can be classified by the dimensionless parameters of Peclet (Pe) and Damkohler (Da). For Pe > 2 and Da > 1, a funnel-shaped leaching zone is formed, otherwise the dissolution front is planar. Additionally, Da > 1 results in the formation of a sylvinitic zone and a flow barrier. Most scenarios represent hybrid forms of these cases. The simulated shapes and mineralogies are confirmed by literature data and can be used to assess the hazard potential. KW - carnallite KW - water rock interaction KW - density-driven flow KW - PHREEQC KW - Pitzer KW - equations Y1 - 2021 U6 - https://doi.org/10.3390/w13020168 SN - 2073-4441 VL - 13 IS - 2 PB - Molecular Diversity Preservation International CY - Basel ER - TY - JOUR A1 - Steding, Svenja A1 - Kempka, Thomas A1 - Kühn, Michael T1 - How insoluble inclusions and intersecting layers affect the leaching process within potash seams JF - Applied Sciences : open access journal N2 - Potash seams are a valuable resource containing several economically interesting, but also highly soluble minerals. In the presence of water, uncontrolled leaching can occur, endangering subsurface mining operations. In the present study, the influence of insoluble inclusions and intersecting layers on leaching zone evolution was examined by means of a reactive transport model. For that purpose, a scenario analysis was carried out, considering different rock distributions within a carnallite-bearing potash seam. The results show that reaction-dominated systems are not affected by heterogeneities at all, whereas transport-dominated systems exhibit a faster advance in homogeneous rock compositions. In return, the ratio of permeated rock in vertical direction is higher in heterogeneous systems. Literature data indicate that most natural potash systems are transport-dominated. Accordingly, insoluble inclusions and intersecting layers can usually be seen as beneficial with regard to reducing hazard potential as long as the mechanical stability of leaching zones is maintained. Thereby, the distribution of insoluble areas is of minor impact unless an inclined, intersecting layer occurs that accelerates leaching zone growth in one direction. Moreover, it is found that the saturation dependency of dissolution rates increases the growth rate in the long term, and therefore must be considered in risk assessments. KW - salt dissolution KW - reactive transport KW - heterogeneity KW - density-driven KW - convection KW - PHREEQC KW - porous media Y1 - 2021 U6 - https://doi.org/10.3390/app11199314 SN - 2076-3417 VL - 11 IS - 19 PB - MDPI CY - Basel ER - TY - GEN A1 - Martens, Sonja A1 - Juhlin, Christopher A1 - Bruckman, Viktor J. A1 - Mitchell, Kristen A1 - Griffiths, Luke A1 - Kühn, Michael T1 - Editorial: energy, resources and the environment BT - interdisciplinary answers to approach the sustainable energy and resources conundrum T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - Every year, the European Geosciences Union (EGU) brings together experts from all over the world at its General Assembly, covering all disciplines of the Earth, planetary and space sciences. The EGU Division on Energy, Resources and the Environment (ERE) is concerned with one of the humankind's most challenging goals – providing affordable, reliable and sustainable energy and other georesources. A collection of contributions from the ERE Division at the EGU General Assembly 2018 is assembled within the present special issue in Advances in Geosciences. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 834 Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-427880 SN - 1866-8372 IS - 834 ER - TY - JOUR A1 - Ma, Jianli A1 - Li, Qi A1 - Kühn, Michael A1 - Nakaten, Natalie Christine T1 - Power-to-gas based subsurface energy storage BT - a review JF - Renewable and Sustainable Energy Reviews N2 - The Renewable energy power generation capacity has been rapidly increasing in China recently. Meanwhile, the contradiction between power supply and demand is becoming increasingly more prominent due to the intermittence of renewable energies. On the other hand, on the mitigation of carbon dioxide (CO2) emissions in China needs immediate attention. Power-to-Gas (PtG), a chemical energy storage technology, can convert surplus electricity into combustible gases. Subsurface energy storage can meet the requirements of long term storage with its large capacity. This paper provides a discussion of the entire PtG energy storage technology process and the current research progress. Based on the comparative study of different geological storage schemes for synthetic methane, their respective research progress and limitations are noted. In addition, a full investigation of the distribution and implementation of global PtG and CO2 capture and storage (CCS) demonstration projects is performed. Subsequently, the opportunities and challenges of the development of this technology in China are discussed based on techno-economic and ecological effects analysis. While PtG is expected to be a revolutionary technology that will replace traditional power systems, the main issues of site selection, energy efficiency and the economy still need to be adequately addressed. Additionally, based on the comprehensive discussion of the results of the analysis, power-to-gas and subsurface energy storage implementation strategies, as well as outlook in China are presented. KW - Renewable energy KW - Power-to-Gas KW - Subsurface energy storage KW - Underground gas storage KW - Carbon dioxide KW - Methane Y1 - 2018 U6 - https://doi.org/10.1016/j.rser.2018.08.056 SN - 1364-0321 VL - 97 SP - 478 EP - 496 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Ma, Jianli A1 - Li, Qi A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Hydromechanical response and impact of gas mixing behavior in subsurface CH4 storage with CO2-based cushion gas JF - Energy & fuels N2 - Power-to-gas (PtG) stores chemical energy by converting excess electrical energy from renewable sources into an energy-dense gas. Due to its higher available capacity compared to surface-based storage technologies, subsurface storage in geological systems is the most promising approach for efficient and economic realization of the PtG system’s storage component. For this purpose, methane (CH4) produced by methanation by means of hydrogen (H2) and carbon dioxide (CO2) is stored in a geological reservoir until required for further use. In this context, CO2 is used as the cushion gas to maintain reservoir pressure and limiting working gas, i.e., (CH4) losses during withdrawal periods. Consequently, mixing of both gases in the reservoir is inevitable. Therefore, it is necessary to minimize the gas mixing region to optimize the efficiency of the PtG system’s storage component. In the present study, the physical properties of CH4, CO2 and their mixtures are reviewed. Then, a multicomponent flow model is implemented and validated against published data. Next, a hydromechanically coupled model is established, considering fluid flow through porous media and effective stresses to investigate the mixing behavior of both gases and the mechanical reservoir stability. The simulation results show that, with increasing reservoir thickness and dip angle, the mixing region is reduced during gas injection if CO2 is employed as the cushion gas. In addition, the degree of mixing is lower at higher temperatures. Feasible injection rates and injection schedules can be derived from the integrated reservoir stability analysis. The methodology developed in the present study allows the determination of optimum strategies for storage reservoir selection and gas injection scheduling by minimizing the gas mixing region. Y1 - 2019 U6 - https://doi.org/10.1021/acs.energyfuels.9b00518 SN - 0887-0624 SN - 1520-5029 VL - 33 IS - 7 SP - 6527 EP - 6541 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Kühn, Michael A1 - Schöne, Tim T1 - Multivariate regression model from water level and production rate time series for the geothermal reservoir Waiwera (New Zealand) T2 - Energy procedia N2 - Water management tools are necessary to guarantee the preservation of natural resources while ensuring optimum utilization. Linear regression models are a simple and quick solution for creating prognostic capabilities. Multivariate models show higher precision than univariate models. In the case of Waiwera, implementation of individual production rates is more accurate than applying just the total production rate. A maximum of approximately 1,075 m3/day can be pumped to ensure a water level of at least 0.5 m a.s.l. in the monitoring well. The model should be renewed annually to implement new data and current water level trends to keep the quality. KW - geothermal reservoir KW - water management KW - data based model KW - multivariate regression KW - coefficient of determination KW - scenario analysis Y1 - 2017 U6 - https://doi.org/10.1016/j.egypro.2017.08.196 SN - 1876-6102 VL - 125 SP - 571 EP - 579 PB - Elsevier CY - Amsterdam ER - TY - GEN A1 - Kühn, Michael A1 - Li, Qi A1 - Nakaten, Natalie Christine A1 - Kempka, Thomas T1 - Integrated subsurface gas storage of CO2 and CH4 offers capacity and state-of-the-art technology for energy storage in China T2 - Energy procedia N2 - Integration and development of the energy supply in China and worldwide is a challenge for the years to come. The innovative idea presented here is based on an extension of the “power-to-gas-to-power” technology by establishing a closed carbon cycle. It is an implementation of a low-carbon energy system based on carbon dioxide capture and storage (CCS) to store and reuse wind and solar energy. The Chenjiacun storage project in China compares well with the German case study for the towns Potsdam and Brandenburg/Havel in the Federal State of Brandenburg based on the Ketzin pilot site for CCS. KW - gas storage KW - carbon dioxide KW - methane KW - hydrogen KW - renewable energy KW - carbon cycle Y1 - 2017 U6 - https://doi.org/10.1016/j.egypro.2017.08.039 SN - 1876-6102 VL - 125 SP - 14 EP - 18 PB - Elsevier CY - Amsterdam ER - TY - GEN A1 - Kühn, Michael A1 - Kempka, Thomas A1 - de Lucia, Marco A1 - Scheck-Wenderoth, Magdalena T1 - Dissolved CO2 storage in geological formations with low pressure, low risk and large capacities T2 - Energy procedia N2 - Geological CO2 storage is a mitigation technology to reduce CO2 emissions from fossil fuel combustion. However, major concerns are the pressure increase and saltwater displacement in the mainly targeted deep groundwater aquifers due to injection of supercritical CO2. The suggested solution is storage of CO2 exclusively in the dissolved state. In our exemplary regional case study of the North East German Basin based on a highly resolved temperature and pressure distribution model and a newly developed reactive transport coupling, we have quantified that 4.7 Gt of CO2 can be stored in solution compared to 1.5 Gt in the supercritical state. KW - carbon dioxide KW - dissolved KW - storage capacity KW - numerical simulation KW - saline aquifer KW - Buntsandstein Y1 - 2017 U6 - https://doi.org/10.1016/j.egypro.2017.03.1607 SN - 1876-6102 VL - 114 SP - 4722 EP - 4727 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kühn, Michael A1 - Altmannsberger, Charlotte A1 - Hens, Carmen T1 - Waiweras WarmwasserreservoirWelche Aussagekraft haben Modelle? JF - Grundwasser : Zeitschrift der Fachsektion Hydrogeologie in der Deutschen Gesellschaft für Geowissenschaften (FH-DGG) N2 - The warm water geothermal reservoir below the village of Waiwera in New Zealand has been known by the native Maori for centuries. Development by the European immigrants began in 1863. Until the year 1969, the warm water flowing from all drilled wells was artesian. Due to overproduction, water up to 50 A degrees C now needs to be pumped to surface. Further, between 1975 and 1976, all warm water seeps on the beach of Waiwera ran dry. Within the context of sustainable water management, hydrogeological models must be developed as part of a management plan. Approaches of varying complexity have been set-up and applied since the 1980s. However, none of the models directly provide all results required for optimal water management. Answers are given simply to parts of the questions, nonetheless improving resource management of the geothermal reservoir. KW - Groundwater KW - Geothermal water KW - Seawater intrusion KW - Simulation KW - Reservoir KW - Management Y1 - 2016 U6 - https://doi.org/10.1007/s00767-016-0323-2 SN - 1430-483X SN - 1432-1165 VL - 21 SP - 107 EP - 117 PB - Springer CY - Heidelberg ER -