Thomas Vienken

Geothermal energy systems: research perspective for domestic energy provision

This article is focused on research demand for the environmental and economic sustainable utilization of geothermal reservoirs for base load supply of heat and electricity by Enhanced Geothermal Systems; additional emphasis is placed on the promotion of the underground storage of thermal energy. Solutions for minimizing the mining risk and for addressing challenges related to the successful development and to the safe operation of geothermal systems are proposed. This includes the development of new technology approaches and concepts for scientific monitoring of operational and environmental processes related to geothermal systems. These research and development efforts require large research facilities and infrastructures. In addition to thermal energy extraction from the subsurface, shallow and deep geothermal reservoirs can also serve as underground thermal energy storage systems. The large potential for medium and high temperature underground thermal energy storage systems remains to be further investigated and developed.

Sustainable Intensive Thermal Use of the Shallow Subsurface-A Critical View on the Status Quo

Thermal use of the shallow subsurface for heat generation, cooling, and thermal energy storage is increasingly gaining importance in reconsideration of future energy supplies. Shallow geothermal energy use is often promoted as being of little or no costs during operation, while simultaneously being environmentally friendly. Hence, the number of installed systems has rapidly risen over the last few decades, especially among newly built houses. While the carbon dioxide reduction potential of this method remains undoubted, concerns about sustainability and potential negative effects on the soil and groundwater due to an intensified use have been raised-even as far back as 25 years ago. Nevertheless, consistent regulation and management schemes for the intensified thermal use of the shallow subsurface are still missing-mainly due to a lack of system understanding and process knowledge. In the meantime, large geothermal applications, for example, residential neighborhoods that are entirely dependent up on shallow geothermal energy use or low enthalpy aquifer heat storage, have been developed throughout Europe. Potential negative effects on the soil and groundwater due to an intensive thermal use of the shallow subsurface as well as the extent of potential system interaction still remain unknown.

High resolution aquifer characterization using crosshole GPR full‐waveform tomography: Comparison with direct‐push and tracer test data

Limited knowledge about the spatial distribution of aquifer properties typically constrains our ability to predict subsurface flow and transport. Here we investigate the value of using high resolution full-waveform inversion of cross-borehole ground penetrating radar (GPR) data for aquifer characterization. By stitching together GPR tomograms from multiple adjacent crosshole planes, we are able to image, with a decimeter scale resolution, the dielectric permittivity and electrical conductivity of an alluvial aquifer along cross sections of 50 m length and 10 m depth. A logistic regression model is employed to predict the spatial distribution of lithological facies on the basis of the GPR results. Vertical profiles of porosity and hydraulic conductivity from direct-push, flowmeter and grain size data suggest that the GPR predicted facies classification is meaningful with regard to porosity and hydraulic conductivity, even though the distributions of individual facies show some overlap and the absolute hydraulic conductivities from the different methods (direct-push, flowmeter, grain size) differ up to approximately one order of magnitude. Comparison of the GPR predicted facies architecture with tracer test data suggests that the plume splitting observed in a tracer experiment was caused by a hydraulically low-conductive sand layer with a thickness of only a few decimeters. Because this sand layer is identified by GPR full-waveform inversion but not by conventional GPR ray-based inversion we conclude that the improvement in spatial resolution due to full-waveform inversion is crucial to detect small-scale aquifer structures that are highly relevant for solute transport.

Auswirkungen von Messunsicherheiten bei der Korngrößenanalyse auf die Berechnung des Durchlässigkeitsbeiwertes

ZusammenfassungKorngrößenanalysen werden häufig für die hochauflösende Charakterisierung der räumlichen Variabilität von kf-Werten genutzt und sind somit Grundlage vieler hydrogeologischer Modellierungen. In Anbetracht der Vielzahl von Formeln zur Berechnung von kf-Werten auf Grundlage von Korngrößenanalysen existiert ein breites Spektrum an Literatur zur Evaluierung dieser Formeln, allerdings wurden bislang weder der Grad der Reproduzierbarkeit, noch die Auswirkungen der in der Praxis unvermeidbaren Messunsicherheit bei der Korngrößenanalyse auf die errechneten kf-Werte kritisch betrachtet.Die Auswertung verschiedener Ringanalysen in dieser Studie zeigt, dass die Messunsicherheit bei der Korngrößenanalyse zu deutlichen Unterschieden in den abgeleiteten wirksamen Korndurchmessern und in der Folge zu deutlichen Unterschieden in den berechneten kf-Werten führte, wobei sich die Messunterschiede in Abhängigkeit von der Zusammensetzung der analysierten Proben und dem gewählten wirksamen Korndurchmesser verschieden stark auswirken. Jedoch zeigte sich im direkten Vergleich hierzu, dass die Auswahl der Berechnungsgrundlage die auf Grundlage von Korngrößenanalysen berechneten kf-Werte deutlich stärker beeinflusst.AbstractGrain size analyses are often used for the high-resolution characterization of hydraulic conductivity (K) and its variation in space. Resulting K values are then frequently used in hydrogeological modeling. In consideration of the variety of formulas to determine K from grain size data, several publications exist that evaluate the performance of these formulas. However, neither the degree of reproducibility nor the effects of measuring inaccuracy on the determination of K from grain size data has yet been evaluated. In this study, data from several ring analyses show that measuring inaccuracies during grain size analyses lead to strong differences in effective grain size diameters and hence, calculated K values. The effects depend on the sample composition and the approach to determine the effective grain size diameter. However, a direct comparison between methods indicated that the variability of K is mainly influenced by strong differences of K estimates between formulas.

On the importance of a coordinated site characterization for the sustainable intensive thermal use of the shallow subsurface in urban areas: a case study

Shallow geothermal applications have become standard solutions for heating and cooling in many newly built or redeveloped residential neighborhoods, but current urban development practices do not yet consider the new demands that result from the intensive thermal use of the shallow subsurface. A coordinated site characterization is of great importance as a sound basis for an optimized planning of geothermal systems that brings together user requirements (heating, cooling, and/or seasonal energy storage) and (hydro)geological subsurface conditions. The aim of this study is to raise awareness and to demonstrate the relevance of a coordinated site characterization. Therefore, this study quantifies the advantages of a site-specific over a desktop-based site characterization in reducing uncertainty for calculation of borehole heat exchanger length and predicted induced temperature changes in the subsurface for a newly developed residential neighborhood in the city of Taucha, Germany. Results show that savings of over EUR 1850 per house (EUR 98,050 for the entire neighborhood) can be achieved by a coordinated exploration and prediction accuracy of temperature plume development was substantially improved. Although being more cost intensive, exploration costs for this case study are <3% of the assumed individual geothermal system costs of EUR 16,000 if divided equally among geothermal users. Three different options are presented to implement coordinated exploration concepts into site development practice.

Energiewende braucht Wärmewende – Chancen und Limitierungen der intensiven thermischen Nutzung des oberflächennahen Untergrundes in urbanen Gebieten vor dem Hintergrund der aktuellen Energiedebatte in Deutschland

als ein Drittel des Primärenergiebedarfes wird durch Wärmebereitstellung inkl. Warmwasseraufbereitung verursacht (BMWi 2015a). Ein konsequenter Wechsel von Heizanlagen, die statt fossiler Brennstoffe regenerative Energieträger nutzen, birgt daher ein erhebliches CO2-Einsparpotenzial (Saner et al. 2010; VDI 2001). Ein in der Praxis zunehmend etabliertes Verfahren zur Nutzung erneuerbarer Energien für die Wärmebereitstellung ist die Nutzung oberflächennaher Geothermie. So liegt die geschätzte Gesamtanzahl verbauter Systeme zur Nutzung oberflächennaher Geothermie in Deutschland bei rund 316.000 (Bundesverband Geothermie 2015) mit einer Wärmebereitstellung von 9,6 Mrd. kWh im Jahr 2014 (oberflächennahe Geothermie und Umweltwärme). Zum Vergleich hierzu lag die Stromund Wärmebereitstellung durch tiefe Geothermie bei 0,2 Mrd. kWh bzw. 0,9 Mrd. kWh (BMWi 2015b). Gegenüber der tiefen Geothermie steht die Nutzung oberflächennaher Geothermie allerdings deutlich weniger im Forschungsfokus, obwohl dieses Thema hinsichtlich räumlicher Koordination quantitativ von großer Bedeutung ist (Schmid 2015). Die Vorteile der Nutzung der Geothermie liegen darin, dass das Wärmedargebot im Untergrund in großen Teilen Deutschlands mittels oberflächennaher Geothermie nutzbar und ständig verfügbar ist. Darüber hinaus sind oberflächennahe Geothermiesysteme neben dem Wärmeentzug im Untergrund zu Heizzwecken auch häufig für die Gebäudekühlung durch Ableiten der Gebäudewärme in den Boden und/oder das Grundwasser nutzbar. Insbesondere hierbei besteht ein erhebliches CO2-Einsparpotenzial gegenüber rein strombasierten Kühlsystemen. Der Anwendungsbereich der oberflächennahen Geothermie ist häufig bis Tiefen von 400 m definiert (Stober & Bucher 2012), in der Praxis sind allerdings Installationstiefen bis zu 100 m Tiefe bei Einund Mehrfamilienhäusern üblich. Bei der Nutzung oberflächennaher Geothermie stehen verschiedene thermische Systeme Einführung

Innovative strategies for high resolution site characterization: application to a flood plain@@@Strategie innovative per la caratterizzazione ad alta risoluzione: applicazione al caso di una pianura alluvionale

Solving complex hydrogeological problems often requires a thorough understanding of (hydro-) geological subsurface conditions. This is especially true for sedimentary deposits with complex architecture, where lithology and/or hydraulic properties can significantly vary over short horizontal and vertical distances. At these sites, a traditional, solely sample-based investigation approach is often not applicable due to limited data accuracy, resolution, and efficiency. Instead, an adapted investigation approach is required that combines exploration technologies of different resolution and investigation scales. This paper aims to demonstrate the feasibility of such a multi-scale approach for the characterization of a test site near the city of Lobnitz, Germany, that is comprised of heterogeneous alluvial deposits. Our focus is on site characterization in terms of lithology and hydraulic properties, as well as on the delineation and characterization of an aggradated oxbow as a typical example of a small scale geological structure.

Erwiderung zum Kommentar von Fuchs et al. zum Beitrag „Auswirkungen von Messunsicherheiten bei der Korngrößenanalyse auf die Berechnung des Durchlässigkeitsbeiwertes“ von Matthes et al. (2012) in Grundwasser 17(2), 105–111

Wir danken den Kollegen S. Fuchs, Dr.-Ing. P. Nillert und M. Ziesche (im Folgenden Fuchs et al.) für die kritische Auseinandersetzung mit unserem Beitrag Matthes et al. (2012) und möchten die Möglichkeit nutzen, einige unserer Ergebnisse und Schlussfolgerungen, die durch die Autoren Fuchs et al. nur unzureichend bewertet und interpretiert werden, genauer zu erläutern. Die Ergebnisse und Schlussfolgerungen unseres Artikels Matthes et al. (2012) lauteten wie im vorletzten und letzten Abschnitt des Artikels aufgeführt: • Die Messunsicherheit bei der Korngrößenanalyse kann zu einer deutlichen Unsicherheit bei der Berechnung von Durchlässigkeitsbeiwerten führen, jedoch ist die Auswahl der Berechnungsformel das wesentliche Element für Unsicherheiten bei der Ermittlung von Durchlässigkeitsbeiwerten aus Korngrößenanalysen. • Durch die Kombination aus dem Einfluss der Messunsicherheit während der Korngrößenanalyse und dem Ein-

Development of an in situ thermal conductivity measurement system for exploration of the shallow subsurface

In this study, we attempted to develop an in situ thermal conductivity measurement system that can be used for subsurface thermal exploration. A new thermal probe was developed for mapping both the spatial and temporal variability of thermal conductivity, via direct push methods in the unconsolidated shallow subsurface. A robust, hollow cylindrical probe was constructed and its performance was tested by carrying out thermal conductivity measurements on materials with known properties. The thermal conductivity of the investigated materials can be worked out by measuring the active power consumption (in alternating current system) and temperature of the probe over fixed time intervals. A calibration method was used to eliminate any undesired thermal effects regarding the size of the probe, based on mobile thermal analyzer thermal conductivity values. Using the hollow cylindrical probe, the thermal conductivity results obtained had an error of less than 2.5% for solid samples (such as Teflon, Agar Jelly and Nylatron).