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A numerical sensitivity study of how permeability, geological structure, and hydraulic gradient control the lifetime of a geothermal reservoir
No full textMultiphase, decoupled faulting in the southern German Molasse Basin – evidence from 3-D seismic data
No full textStructural synthesis of the Northern Calcareous Alps, TRANSALP segment
No full textThe Northern Calcareous Alps (NCA) are the site of very large top-to-north convergent movements during Cretaceous–Tertiary Alpine mountain building. To determine the amount of shortening, the depth of detachment and the style of deformation, we retro-deformed an approximately 40 × 40 km area comprising the Lechtal and Allgäu Nappes. On the basis of all available geological data and processed sections of the TRANSALP reflection seismic experiment, coherent 3D models were constructed by splining lines from N–S cross-sections. Integration of 3D kinematic modeling and field data shows the following. The structure of the Lechtal Nappe is controlled by the Triassic Hauptdolomit. Four main thrusts link to a detachment at 2–6 km depth below sea level. Shortening estimates vary, from 25% (east) to 42% (west). Additional contraction is accommodated by folding. In the east the subjacent Allgäu Nappe can be traced about 10 km down-plunge, and is shortened by about one third. In the western part the downplunge width is at least 15–20 km, with restorable shortening of one third. The triple (Inntal, Lechtal, Allgäu Nappes) NCA nappe system was moved uniformly N–S to produce laterally heterogeneus shortening of 40–90 km or 50–67%. We suggest that the NCA are underlain by substantial amounts of buried Molasse sediments and/or overthrust units of Helvetic and Rheno-Danubian Flysch, indicating post-Eocene N–S shortening of at least 55 km. Restored to an initial configuration, the basin topography of the NCA reveals strong E–W thickness variations of the Triassic Wettersteinkalk and Hauptdolomit platform carbonates. Such variations may pertain to N–S trending growth faults, which were important precursors to later Jurassic extension of the Austroalpine passive margin. Such structures are unlikely to be seen in the conventional N–S cross-sections, but form an essential geometrical and mechanical element in later, convergent mountain building
A numerical sensitivity study of how permeability, porosity, geological structure, and hydraulic gradient control the lifetime of a geothermal reservoir
Full text linkGeothermal energy is an important and sustainable resource that has more potential than is currently utilized. Whether or not a deep geothermal resource can be exploited, mostly depends on, besides temperature, the utilizable reservoir volume over time, which in turn largely depends on petrophysical parameters. We show, using over 1000 (n=1027) 4-D finite-element models of a simple geothermal doublet, that the lifetime of a reservoir is a complex function of its geological parameters, their heterogeneity, and the background hydraulic gradient (BHG). In our models, we test the effects of porosity, permeability, and BHG in an isotropic medium. Furthermore, we simulate the effect of permeability contrast and anisotropy induced by layering, fractures, and a fault. We quantify the lifetime of the reservoir by measuring the time to thermal breakthrough, i.e. how many years pass before the temperature of the produced fluid falls below the 100 ∘C threshold. The results of our sensitivity study attest to the positive effect of high porosity; however, high permeability and BHG can combine to outperform the former. Particular configurations of all the parameters can cause either early thermal breakthrough or extreme longevity of the reservoir. For example, the presence of high-permeability fractures, e.g. in a fault damage zone, can provide initially high yields, but it channels fluid flow and therefore dramatically restricts the exploitable reservoir volume. We demonstrate that the magnitude and orientation of the BHG, provided permeability is sufficiently high, are the prime parameters that affect the lifetime of a reservoir. Our numerical experiments show also that BHGs (low and high) can be outperformed by comparatively small variations in permeability contrast (103) and fracture-induced permeability anisotropy (101) that thus strongly affect the performance of geothermal reservoirs
Predictability of properties of a fractured geothermal reservoir: the opportunities and limitations of an outcrop analogue study
Full text linkAbstract Minimizing exploration risk in deep geothermics is of great economic importance. Especially, knowledge about temperature and permeability of the reservoir is essential. We test the potential of an outcrop analogue study to minimize uncertainties in prediction of the rock properties of a fractured reservoir in the Upper Rhine Graben. Our results show that although mineralogical composition, clay content, grain size, and fabric type are basically comparable, porosity and quartz cementation are not. Young’s modulus, as observed in the outcrop closest to the reservoir is about twice as high (~ 64 GPa) as observed in the reservoir (~ 34 GPa). Most importantly, however, the parameters that describe the fracture system, which are essential to predict reservoir permeability, differ significantly. While the outcrops are dominated by perpendicular fracture sets (striking NE–SW and NW–SE), two different conjugate fracture sets (striking NW–SE and N–S) occur in the reservoir. Fracture apertures, as reported from the FMI, are one order of magnitude wider than in the outcrop. We conclude that our outcrop analogue study fails to predict important properties of the reservoir (such as permeability and porosity). This must be in part because of the tectonically complex setting of the reservoir. We propose that analogue studies are important, but they must be treated with care when attempting to predict the controlling parameters of a fractured reservoir
Strukturgeologische 3D-Modellierung der Grabenrandstörung des Leinetals im östlichen Stadtgebiet von Göttingen
No full textIm Rahmen von verschiedenen Geothermie-Projekten wurden im östlichen Stadtgebiet von Göttingen Bohrungen beprobt, analysiert und beschrieben. Die Bohrung 2 (Tannenweg 20) durchteufte dabei die hier unter der Lias-Gruppe liegende, östliche Grabenrandstörung und traf auf Gipse des Mittleren Muschelkalkes. Für einen Aufstieg von Zechstein-Evaporiten entlang der Grabenrandstörung, so wie vormals vermutet, finden sich damit keine Belege. Unter Einbindung von weiteren Bohrungen und Fundstücken aus dem Museum des GZG sowie Fundangaben aus geologischen Kartierungen des frühen 19. Jahrhunderts hat sich der Verlauf der östlichen Grabenrandstörung gegenüber der publizierten Karte von Stille (1932) um etwa 100m in Richtung Osten verschoben. Weiterhin zeigte sich in der erstellten, geologischen Karte, dass eine dextrale Seitenverschiebung eine Umbiegung der Lias-Schichten im Norden und einen dextralen Versatz der östlichen Grabenrandstörung von etwa 70m verursacht. Das generierte, strukturgeologische 3D-Modell zeigt, dass die Basis der als Leithorizont genutzten Lias-γ-Kalksteinbank im n¨ordlichen Bereich einen ausgeprägten Knick aufweist und mit 30°steiler als der südliche Bereich einfällt. Ferner konnte anhand der 3D-Modellierung die Orientierung der östlichen Grabenrandstörung mit 289/55 ermittelt werden. Abstract— Within the context of various geothermal projects, wells were sampled, analysed and described from the eastern side of the city of G¨ ottingen. The well No. 2 (Tannenweg 20) encountered, in addition to the Lower Jurassic Lias Formation, the eastern Leinetal border fault and then gypsum layers of the Middle Muschelkalk. The previous assumption that Zechstein had risen along the border faults, could not be confirmed in this work. With the information from wells and finds from the museum of the GZG, and geological maps and their memoirs from the early 19th Century, the trace of the main eastern border fault was moved about 100 metres toward the east. From the resulting geological map it becomes apparent that a dextral strike-slip fault caused a bend in the Liassic strata to the north and a dextral displacement of the eastern border fault by ca. 70 metres. The generated 3D structural geological model indicates that the base of Lias γ horizon in the northern area has a pronounced bend and dips 30°steeper than the southern area. By the use of 3D modelling, it was possible to determine that the orientation of the eastern border fault in this area is 289/55
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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