@book{MientusKlempinNowaketal.2023, author = {Mientus, Lukas and Klempin, Christiane and Nowak, Anna and Wyss, Corinne and Aufschnaiter, Claudia von and Faix, Ann-Christin and te Poel, Kathrin and Wahbe, Nadia and Pieper, Martin and H{\"o}ller, Katharina and Kallenbach, Lea and F{\"o}rster, Magdalena and Redecker, Anke and Dick, Mirjam and Holle, J{\"o}rg and Schneider, Edina and Rehfeldt, Daniel and Brauns, Sarah and Abels, Simone and Ferencik-Lehmkuhl, Daria and Fr{\"a}nkel, Silvia and Frohn, Julia and Liebsch, Ann-Catherine and Pech, Detlef and Schreier, Pascal and Jessen, Moiken and Großmann, Uta and Skintey, Lesya and Voerkel, Paul and Vaz Ferreira, Mergenfel A. and Zimmermann, Jan-Simon and Buddeberg, Magdalena and Henke, Vanessa and Hornberg, Sabine and V{\"o}lschow, Yvette and Warrelmann, Julia-Nadine and Malek, Jennifer and Tinnefeld, Anja and Schmidt, Peggy and Bauer, Tobias and J{\"a}nisch, Christopher and Spitzer, Lisa and Franken, Nadine and Degeling, Maria and Preisfeld, Angelika and Meier, Jana and K{\"u}th, Simon and Scholl, Daniel and Vogelsang, Christoph and Watson, Christina and Weißbach, Anna and Kulgemeyer, Christoph and Oetken, Mandy and Gorski, Sebastian and Kubsch, Marcus and Sorge, Stefan and Wulff, Peter and Fellenz, Carolin D. and Schnell, Susanne and Larisch, Cathleen and Kaiser, Franz and Knott, Christina and Reimer, Stefanie and Stegm{\"u}ller, Nathalie and Boukray{\^a}a Trabelsi, Kathrin and Schißlbauer, Franziska and Lemberger, Lukas and Barth, Ulrike and Wiehl, Angelika and Rogge, Tim and B{\"o}hnke, Anja and Dietz, Dennis and Großmann, Leroy and Wienmeister, Annett and Zoppke, Till and Jiang, Lisa and Gr{\"u}nbauer, Stephanie and Ostersehlt, D{\"o}rte and Peukert, Sophia and Sch{\"a}fer, Christoph and L{\"o}big, Anna and Br{\"o}ll, Leena and Brandt, Birgit and Breuer, Meike and Dausend, Henriette and Krelle, Michael and Andersen, Gesine and Falke, Sascha and Kindermann-G{\"u}zel, Kristin and K{\"o}rner, Katrina and Lottermoser, Lisa-Marie and P{\"u}gner, Kati and Sonnenburg, Nadine and Akarsu, Selim and Rechl, Friederike and Gadinger, Laureen and Heinze, Lena and Wittmann, Eveline and Franke, Manuela and Lachmund, Anne-Marie and B{\"o}ttger, Julia and Hannover, Bettina and Behrendt, Renata and Conty, Valentina and Grundmann, Stephanie and Ghassemi, Novid and Opitz, Ben and Br{\"a}mer, Martin and Gasparjan, David and Sambanis, Michaela and K{\"o}ster, Hilde and L{\"u}cke, Martin and Nordmeier, Volkhard and Schaal, Sonja and Haberbosch, Maximilian and Meissner, Maren and Schaal, Steffen and Br{\"u}chner, Melanie and Riehle, Tamara and Leopold, Bengta Marie and Gerlach, Susanne and Rau-Patschke, Sarah and Skorsetz, Nina and Weber, Nadine and Damk{\"o}hler, Jens and Elsholz, Markus and Trefzger, Thomas and Lewek, Tobias and Borowski, Andreas}, title = {Reflexion in der Lehrkr{\"a}ftebildung}, series = {Potsdamer Beitr{\"a}ge f{\"u}r Lehrkr{\"a}ftebildung und Bildungsforschung}, journal = {Potsdamer Beitr{\"a}ge f{\"u}r Lehrkr{\"a}ftebildung und Bildungsforschung}, number = {4}, editor = {Mientus, Lukas and Klempin, Christiane and Nowak, Anna}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, isbn = {978-3-86956-566-8}, issn = {2626-3556}, doi = {10.25932/publishup-59171}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-591717}, publisher = {Universit{\"a}t Potsdam}, pages = {452}, year = {2023}, abstract = {Reflexion ist eine Schl{\"u}sselkategorie f{\"u}r die professionelle Entwicklung von Lehrkr{\"a}ften, welche als Ausbildungsziel in den Bildungsstandards f{\"u}r die Lehrkr{\"a}ftebildung verankert ist. Eine Verstetigung universit{\"a}r gepr{\"a}gter Forschung und Modellierung in der praxisnahen Anwendung im schulischen Kontext bietet Potentiale nachhaltiger Professionalisierung. Die St{\"a}rkung reflexionsbezogener Kompetenzen durch Empirie und Anwendung scheint eine phasen{\"u}bergreifende Herausforderung der Lehrkr{\"a}ftebildung zu sein, die es zu bew{\"a}ltigen gilt. Ziele des Tagungsbandes Reflexion in der Lehrkr{\"a}ftebildung sind eine theoretische Sch{\"a}rfung des Konzeptes „Reflexive Professionalisierung" und der Austausch {\"u}ber Fragen der Einbettung wirksamer reflexionsbezogener Lerngelegenheiten in die Lehrkr{\"a}ftebildung. Forschende und Lehrende der‚ drei Phasen (Studium, Referendariat sowie Fort- und Weiterbildung) der Lehrkr{\"a}ftebildung stellen Lehrkonzepte und Forschungsprojekte zum Thema Reflexion in der Lehrkr{\"a}ftebildung vor und diskutieren diese. Gemeinsam mit Teilnehmenden aller Phasen und von verschiedenen Standorten der Lehrkr{\"a}ftebildung werden zuk{\"u}nftige Herausforderungen identifiziert und L{\"o}sungsans{\"a}tze herausgearbeitet.}, language = {de} } @phdthesis{Meier2017, author = {Meier, Tobias}, title = {Borehole Breakouts in Transversely Isotropic Posidonia Shale}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400019}, school = {Universit{\"a}t Potsdam}, pages = {xviii, 133}, year = {2017}, abstract = {Borehole instabilities are frequently encountered when drilling through finely laminated, organic rich shales ({\O}kland and Cook, 1998; Ottesen, 2010; etc.); such instabilities should be avoided to assure a successful exploitation and safe production of the contained unconventional hydrocarbons. Borehole instabilities, such as borehole breakouts or drilling induced tensile fractures, may lead to poor cementing of the borehole annulus, difficulties with recording and interpretation of geophysical logs, low directional control and in the worst case the loss of the well. If these problems are not recognized and expertly remedied, pollution of the groundwater or the emission of gases into the atmosphere can occur since the migration paths of the hydrocarbons in the subsurface are not yet fully understood (e.g., Davies et al., 2014; Zoback et al., 2010). In addition, it is often mentioned that the drilling problems encountered and the resulting downtimes of the wellbore system in finely laminated shales significantly increase drilling costs (Fjaer et al., 2008; Aadnoy and Ong, 2003). In order to understand and reduce the borehole instabilities during drilling in unconventional shales, we investigate stress-induced irregular extensions of the borehole diameter, which are also referred to as borehole breakouts. For this purpose, experiments with different borehole diameters, bedding plane angles and stress boundary conditions were performed on finely laminated Posidonia shales. The Lower Jurassic Posidonia shale is one of the most productive source rocks for conventional reservoirs in Europe and has the greatest potential for unconventional oil and gas in Europe (Littke et al., 2011). In this work, Posidonia shale specimens from the North (PN) and South (PS) German basins were selected and characterized petrophysically and mechanically. The composition of the two shales is dominated by calcite (47-56\%) followed by clays (23-28\%) and quartz (16-17\%). The remaining components are mainly pyrite and organic matter. The porosity of the shales varies considerably and is up to 10\% for PS and 1\% for PN, which is due to a larger deposition depth of PN. Both shales show marked elasticity and strength anisotropy, which can be attributed to a macroscopic distribution and orientation of soft and hard minerals. Under load the hard minerals form a load-bearing, supporting structure, while the soft minerals compensate the deformation. Therefore, if loaded parallel to the bedding, the Posidonia shale is more brittle than loaded normal to the bedding. The resulting elastic anisotropy, which can be defined by the ratio of the modulus of elasticity parallel and normal to the bedding, is about 50\%, while the strength anisotropy (i.e., the ratio of uniaxial compressive strength normal and parallel to the bedding) is up to 66\%. Based on the petrophysical characterization of the two rocks, a transverse isotropy (TVI) was derived. In general, PS is softer and weaker than PN, which is due to the stronger compaction of the material due to the higher burial depth. Conventional triaxial borehole breakout experiments on specimens with different borehole diameters showed that, when the diameter of the borehole is increased, the stress required to initiate borehole breakout decreases to a constant value. This value can be expressed as the ratio of the tangential stress and the uniaxial compressive strength of the rock. The ratio increases exponentially with decreasing borehole diameter from about 2.5 for a 10 mm diameter hole to ~ 7 for a 1 mm borehole (increase of initiation stress by 280\%) and can be described by a fracture mechanic based criterion. The reduction in borehole diameter is therefore a considerable aspect in reducing the risk of breakouts. New drilling techniques with significantly reduced borehole diameters, such as "fish-bone" holes, are already underway and are currently being tested (e.g., Xing et al., 2012). The observed strength anisotropy and the TVI material behavior are also reflected in the observed breakout processes at the borehole wall. Drill holes normal to the bedding develop breakouts in a plane of isotropy and are not affected by the strength or elasticity anisotropy. The observed breakouts are point-symmetric and form compressive shear failure planes, which can be predicted by a Mohr-Coulomb failure approach. If the shear failure planes intersect, conjugate breakouts can be described as "dog-eared" breakouts. While the initiation of breakouts for wells oriented normal to the stratification has been triggered by random local defects, reduced strengths parallel to bedding planes are the starting point for breakouts for wells parallel to the bedding. In the case of a deflected borehole trajectory, therefore, the observed failure type changes from shear-induced failure surfaces to buckling failure of individual layer packages. In addition, the breakout depths and widths increased, resulting in a stress-induced enlargement of the borehole cross-section and an increased output of rock material into the borehole. With the transition from shear to buckling failure and changing bedding plane angle with respect to the borehole axis, the stress required for inducing wellbore breakouts drops by 65\%. These observations under conventional triaxial stress boundary conditions could also be confirmed under true triaxial stress conditions. Here breakouts grew into the rock as a result of buckling failure, too. In this process, the broken layer packs rotate into the pressure-free drill hole and detach themselves from the surrounding rock by tensile cracking. The final breakout shape in Posidonia shale can be described as trapezoidal when the bedding planes are parallel to the greatest horizontal stress and to the borehole axis. In the event that the largest horizontal stress is normal to the stratification, breakouts were formed entirely by shear fractures between the stratification and required higher stresses to initiate similar to breakouts in conventional triaxial experiments with boreholes oriented normal to the bedding. In the content of this work, a fracture mechanics-based failure criterion for conventional triaxial loading conditions in isotropic rocks (Dresen et al., 2010) has been successfully extended to true triaxial loading conditions in the transverse isotropic rock to predict the initiation of borehole breakouts. The criterion was successfully verified on the experiments carried out. The extended failure criterion and the conclusions from the laboratory and numerical work may help to reduce the risk of borehole breakouts in unconventional shales.}, language = {en} }