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- ItemEvaluation of Expert Reports to Quantify the Exploration Risk for Geothermal Projects in Germany(Amsterdam [u.a.] : Elsevier, 2015) Ganz, Britta; Ask, Maria; Hangx, Suzanne; Bruckman, Viktor; Kühn, MichaelThe development of deep geothermal energy sources in Germany still faces many uncertainties and high upfront investment costs. Methodical approaches to assess the exploration risk are thus of major importance for geothermal project development. Since 2002, expert reports to quantify the exploration risk for geothermal projects in Germany were carried out. These reports served as a basis for insurance contracts covering the exploration risk. Using data from wells drilled in the meantime, the reports were evaluated and the stated probabilities compared with values actually reached.
- ItemDeep Geothermal Energy for Lower Saxony (North Germany) – Combined Investigations of Geothermal Reservoir Characteristics(Amsterdam [u.a.] : Elsevier, 2014) Hahne, Barbara; Thomas, Rüdiger; Bruckman, Viktor J.; Hangx, Suzanne; Ask, MariaFor the economic success of a geothermal project the hydraulic properties and temperature of the geothermal reservoir are crucial. New methodologies in seismics, geoelectrics and reservoir geology are tested within the frame of the collaborative research programme “Geothermal Energy and High-Performance Drilling” (gebo). Within nine geoscientific projects, tools were developed that help in the evaluation and interpretation of acquired data. Special emphasis is placed on the investigation of rock properties, on the development of early reservoir assessment even during drilling, and on the interaction between the drilling devices and the reservoir formation. The propagation of fractures and the transport of fluid and heat within the regional stress field are investigated using different approaches (field studies, seismic monitoring, multi-parameter modelling). Geologic structural models have been created for simulation of the local stress field and hydromechanical processes. Furthermore, a comprehensive dataset of hydrogeochemical environments was collected allowing characterisation and hydrogeochemical modelling of the reservoir.
- ItemModelling the Surface Heat Flow Distribution in the Area of Brandenburg (Northern Germany)(Amsterdam [u.a.] : Elsevier, 2013) Cacace, Mauro; Scheck-Wenderoth, Magdalena; Noack, Vera; Cherubini, Yvonne; Schellschmidt, Rüdiger; Kühn, Michael; Juhlin, Christopher; Held, Hermann; Bruckman, Viktor; Tambach, Tim; Kempka, ThomasA lithosphere scale geological model has been used to determine the surface heat flow component due to conductive heat transport for the area of Brandenburg. The modelling results have been constrained by a direct comparison with available heat flow measurements. The calculated heat flow captures the regional trend in the surface heat flow distribution which can be related to existing thermal conductivity variations between the different sedimentary units. An additional advective component due to topography induced regional flow and focused flow within major fault zones should be considered to explain the spatial variation observed in the surface heat flow.
- ItemDeep Geothermal Energy Production in Germany(Basel : MDPI, 2014) Agemar, Thorsten; Weber, Josef; Schulz, RüdigerGermany uses its low enthalpy hydrothermal resources predominantly for balneological applications, space and district heating, but also for power production. The German Federal government supports the development of geothermal energy in terms of project funding, market incentives and credit offers, as well as a feed-in tariff for geothermal electricity. Although new projects for district heating take on average six years, geothermal energy utilisation is growing rapidly, especially in southern Germany. From 2003 to 2013, the annual production of geothermal district heating stations increased from 60 GWh to 530 GWh. In the same time, the annual power production increased from 0 GWh to 36 GWh. Currently, almost 200 geothermal facilities are in operation or under construction in Germany. A feasibility study including detailed geological site assessment is still essential when planning a new geothermal facility. As part of this assessment, a lot of geological data, hydraulic data, and subsurface temperatures can be retrieved from the geothermal information system GeotIS, which can be accessed online [1].
- ItemAssessment and Public Reporting of Geothermal Resources in Germany: Review and Outlook(Basel : MDPI, 2018) Agemar, Thorsten; Weber, Josef; Moeck, Inga S.Any geothermal resource assessment requires consistent and widely accepted terminology, methods, and reporting schemes that facilitate the comparison of geothermal resource estimates. This paper reviews common resource assessment methods, as well as reporting codes and terminology. Based on a rigorous analysis of the portrayed concepts and methods, it discusses the appropriateness of the existing reporting codes for sustainable utilization of geothermal resources in Germany. Since the last quantitative geothermal resource assessment in Germany was done 15 years ago, a revised report is overdue. Unlike fossil energy commodities, geothermal energy replenishes naturally and heat recuperation increases in created heat sinks. This replenishment process offers the opportunity for sustainable reservoir management in the case of moderate production rates or cyclic operation. Existing reporting codes, however, regard geothermal resources in a similar way to fossil resources or focus too much on field development rather than on the whole assessment process. In order to emphasize the renewability of geothermal energy, we propose the reporting of geothermal capacities (per doublet or per km2) instead of recoverable heat energy which depends very much on project lifetime and other factors. As a first step, a new classification scheme for geothermal resources and reserves is outlined.
- ItemS-wave seismic imaging of near-surface sediments using tailored processing strategies(Amsterdam [u.a.] : Elsevier Science, 2020) Burschil, Thomas; Buness, HermannReflection seismic imaging using horizontally-polarized S-waves (SH) can increase resolution and it could be cost-efficient compared to the common use of P-waves. However, since S-wave application often delivers varying data quality, appropriate processing schemes are required for particular imaging and interpretation purposes. In this paper, we present four tailored processing strategies that are applied to SH-wave data acquired in an overdeepened Quaternary basin in the Alpine foreland, the Tannwald Basin. The applied processing schemes consist of (1) processing using a short automatic gain control window that enhances structural details and highlights small-scale structures, (2) offset restriction indicating that relative small offsets are sufficient for adequate imaging, which offers reduced field operation costs, (3) coherency-enhancement that reveals large-scale structures for interpretation, and (4) adapted amplitude scaling that enables structural comparison of P-wave and S-wave seismic sections. With respect to P-wave data measured on the same profile, we demonstrate the benefits of the S-wave seismic reflection method. P-waves offer robust imaging results, but S-waves double the resolution, better depict shallow reflections, and may image reflectors in areas where the P-wave struggles. At least for the Tannwald Basin, S-wave imaging is also more cost-efficient than P-wave imaging. © 2020 The Authors
- ItemGeophysical investigation of a freshwater lens on the island of Langeoog, Germany – Insights from combined HEM, TEM and MRS data(Amsterdam [u.a.] : Elsevier Science, 2017) Costabel, Stephan; Siemon, Bernhard; Houben, Georg; Günther, ThomasA multi-method geophysical survey, including helicopter-borne electromagnetics (HEM), transient electromagnetics (TEM), and magnetic resonance sounding (MRS), was conducted to investigate a freshwater lens on the North Sea island of Langeoog, Germany. The HEM survey covers the entire island and gives an overview of the extent of three freshwater lenses that reach depths of up to 45 m. Ground-based TEM and MRS were conducted particularly on the managed western lens to verify the HEM results and to complement the lithological information from existing boreholes. The results of HEM and TEM are in good agreement. Salt- and freshwater-bearing sediments can, as expected, clearly be distinguished due to their individual resistivity ranges. In the resistivity data, a large transition zone between fresh- and saltwater with a thickness of up to 20 m is identified, the existence of which is verified by borehole logging and sampling. Regarding lithological characterisation of the subsurface, the MRS method provides more accurate and reliable results than HEM and TEM. Using a lithological index derived from MRS water content and relaxation time, thin aquitard structures as well as fine and coarse sand aquifers can be distinguished. Complementing the existing borehole data with the lithology information estimated from MRS, we generate a map showing the occurrence of aquitard structures, which significantly improves the hydrogeological model of the island. Moreover, we demonstrate that the estimates of groundwater conductivity in the sand aquifers from geophysical data are in agreement with the fluid conductivity measured in the boreholes.
- ItemNon-remote reference noise cancellation - using reference data in the presence of surface-NMR signals(Amsterdam [u.a.] : Elsevier Science, 2020) Müller-Petke, MikeSurface-NMR measurements commonly suffer from low signal-to-noise ratios. In recent years, with the introduction of multi-channel surface-NMR instruments, the technique of remote-reference noise cancellation (RNC) was developed and significantly improved the applicability of surface-NMR. The current formulation of RNC requires a reference loop to be placed a remote distance from the transmitter loop such that no NMR signal is recorded. Reference loops placed at non-remote distances have been envisaged to provide both improved noise cancellation performance and field efficiency; however, the concept has not been previously applied because the theoretical framework was missing. In this paper, the theoretical framework is presented. It is demonstrated that reference loops placed at non-remote distances provide superior noise cancellation performance. Considerations for placing the reference loop relative to the transmitter loop are provided, and the theoretical framework is evaluated based on a semi-synthetic example using real field noise and synthetic surface-NMR data. © 2020
- ItemEvaluation of spectral induced polarization field measurements in time and frequency domain(Amsterdam [u.a.] : Elsevier Science, 2020) Martin, Tina; Günther, Thomas; Orozco, Adrian Flores; Dahlin, TorleifSpectral induced polarization (SIP) measurements have been demonstrated to correlate with important parameters in hydrogeological and environmental investigations. Although SIP measurements were often collected in the frequency domain (FDIP), recent developments have demonstrated the capabilities to solve for the frequency-dependence of the complex conductivity through measurements collected in the time domain (TDIP). Therefore, the aim of our field investigations is a comparison of the measured frequency-dependence at a broad frequency range resolved through FDIP and TDIP. In contrast to previous studies, we conducted measurements with different instruments and measuring technologies for both FDIP and TDIP. This allows for investigating the robustness of different measurements and assessing various sources of errors, for the assessment of the advantages and drawbacks from different measuring techniques. Our results demonstrate that data collected through different instruments are consistent. Apparent resistivity measurements as well as the inversion results revealed quantitatively the same values for all instruments. The measurements of the IP effect are also comparable, particularly FDIP readings in the low frequencies (< 10 Hz) revealed to be quantitatively the same for different instruments. TDIP measurements are consistent for data collected with both devices. As expected, the spatial distribution of the values is also consistent for low frequency data (in FDIP) and late times measurements in TDIP (> 0.1 s). However, data quality for higher frequencies in FDIP (i.e., early times in TDIP) show larger variations, which reflects the differences between the instruments to deal with the electromagnetic contamination of the IP data. Concluded in general, the different instruments and measuring techniques can provide consistent responses for varying signal-to-noise ratio and measuring configurations. © 2020 The Authors
- ItemComparison of novel semi-airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from Schleiz, Germany(Amsterdam [u.a.] : Elsevier Science, 2020) Steuer, Annika; Smirnova, Maria; Becken, Michael; Schiffler, Markus; Günther, Thomas; Rochlitz, Raphael; Yogeshwar, Pritam; Mörbe, Wiebke; Siemon, Bernhard; Costabel, Stephan; Preugschat, Benedikt; Ibs-von Seht, Malte; Zampa, Luigi Sante; Müller, FranzIn the framework of the Deep Electromagnetic Sounding for Mineral EXploration (DESMEX) project, we carried out multiple geophysical surveys from regional to local scales in a former mining area in the state of Thuringia, Germany. We prove the applicability of newly developed semi-airborne electromagnetic (EM) systems for mineral exploration by cross-validating inversion results with those of established airborne and ground-based investigation techniques. In addition, supporting petrophysical and geological information to our geophysical measurements allowed the synthesis of all datasets over multiple scales. An initial regional-scale reconnaissance survey was performed with BGR's standard helicopter-borne geophysical system deployed with frequency-domain electromagnetic (HEM), magnetic and radiometric sensors. In addition to geological considerations, the HEM results served as base-line information for the selection of an optimal location for the intermediate-scale semi-airborne EM experiments. The semi-airborne surveys utilized long grounded transmitters and two independent airborne receiver instruments: induction coil magnetometers and SQUID sensors. Due to the limited investigation depth of the HEM method, local-scale electrical resistivity tomography (ERT) and long-offset transient electromagnetic (LOTEM) measurements were carried out on a reference profile, enabling the validation of inversion results at greater depths. The comparison of all inversion results provided a consistent overall resistivity distribution. It further confirmed that both semi-airborne receiver instruments achieve the bandwidth and sensitivity required for the investigation of the resistivity structure down to 1 km depth and therewith the detection of deeply seated earth resources. A 3D geological model, lithological and geophysical borehole logs as well as petrophysical investigations were integrated to interpret of the geophysical results. Distinct highly-conductive anomalies with resistivities of less than 10 Om were identified as alum shales over all scales. Apart from that, the petrophysical investigations exhibited that correlating geophysical and geological information using only one single parameter, such as the electrical resistivity, is hardly possible. Therefore, we developed a first approach based on clustering methods and self-organizing maps (SOMs) that allowed us to assign geological units at the surface to a given combination of geophysical and petrophysical parameters, obtained on different scales. © 2020 The Authors