@phdthesis{Cherubini2013,
  author    = {Cherubini, Yvonne},
  title     = {Influence of faults on the 3D coupled fluid and heat transport},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69755},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Da geologische St{\"o}rungen k{\"o}nnen als Grundwasserleiter, -Barrieren oder als gemischte leitende /stauende Fluidsysteme wirken. Aufgrund dessen k{\"o}nnen St{\"o}rungen maßgeblich den Grundwasserfluss im Untergrund beeinflussen, welcher deutliche Ver{\"a}nderungen des tiefen thermischen Feldes bewirken kann. Grundwasserdynamik und Temperaturver{\"a}nderungen sind wiederum entscheidende Faktoren f{\"u}r die Exploration geothermischer Energie. Diese Studie untersuchte den Einfluss von St{\"o}rungen auf das Fluidsystem und das thermische Feld im Untergrund. Sie erforschte die physikalischen Prozesse, welche das Fluidverhalten und die Temperaturverteilung in St{\"o}rungen und in den umgebenden Gesteinen. Dazu wurden 3D Finite Elemente Simulationen des gekoppelten Fluid und W{\"a}rmetransports f{\"u}r synthetische sowie reale Modelszenarien auf unterschiedlichen Skalen durchgef{\"u}hrt. Um den Einfluss einer schr{\"a}g einfallenden St{\"o}rung systematisch durch die schrittweise Ver{\"a}nderung der hydraulischen {\"O}ffnungsweite und der Permeabilit{\"a}t, zu untersuchen, wurde ein klein-skaliges synthetisches Modell entwickelt. Ein inverser linearer Zusammenhang wurde festgestellt, welcher zeigt, dass sich die Fluidgeschwindigkeit in der St{\"o}rung jeweils um ~1e-01 m/s verringert, wenn die {\"O}ffnungsweite der St{\"o}rung um jeweils eine Magnitude vergr{\"o}ßert wird. Ein hoher Permeabilit{\"a}tskontrast zwischen St{\"o}rung und umgebender Matrix beg{\"u}nstigt die Fluidadvektion hin zur St{\"o}rung und f{\"u}hrt zu ausgepr{\"a}gten Druck- und Temperaturver{\"a}nderungen innerhalb und um die St{\"o}rung herum. Bei geringem Permeabilit{\"a}tskontrast zwischen St{\"o}rung und umgebendem Gestein findet hingegen kein Fluidfluss in der St{\"o}rung statt, wobei das hydrostatische Druck- sowie das Temperaturfeld unver{\"a}ndert bleiben. Auf Grundlage der synthetischen Modellierungsergebnisse wurde der Einfluss von St{\"o}rungen auf einer gr{\"o}ßeren Skala anhand eines komplexeren (realen) geologischen Systems analysiert. Dabei handelt es sich um ein 3D Modell des Geothermiestandortes Groß Sch{\"o}nebeck, der ca. 40 km n{\"o}rdlich von Berlin liegt. Die Integration von einer permeablen und drei impermeablen Hauptst{\"o}rungen, zeigte unterschiedlich starke Einfl{\"u}sse auf Fluidzirkulation, Temperatur - und Druckfeld. Die modellierte konvektive Zirkulation in der permeablen St{\"o}rung ver{\"a}ndert das thermische Feld stark (bis zu 15 K). In den gering durchl{\"a}ssigen St{\"o}rungen wird die W{\"a}rme ausschließlich durch Diffusion geleitet. Der konduktive W{\"a}rmetransport beeinflusst das thermische Feld nicht, bewirkt jedoch lokale Ver{\"a}nderungen des hydrostatischen Druckfeldes. Um den Einfluss großer St{\"o}rungszonen mit kilometerweitem vertikalen Versatz auf das geothermische Feld der Beckenskala zu untersuchen, wurden gekoppelte Fluid- und W{\"a}rmetransportsimulationen f{\"u}r ein 3D Strukturmodell des Gebietes Brandenburg durchgef{\"u}hrt (Noack et al. 2010; 2013). Bez{\"u}glich der St{\"o}rungspermeabilit{\"a}t wurden verschiedene geologische Szenarien modelliert, von denen zwei Endgliedermodelle ausgewertet wurden. Die Ergebnisse zeigten, dass die undurchl{\"a}ssigen St{\"o}rungen den Fluidfluss nur lokal beeinflussen. Da sie als hydraulische Barrieren wirken, wird der Fluidfluss mir sehr geringen Geschwindigkeiten entlang der St{\"o}rungen innerhalb eines Bereichs von ~ 1 km auf jeder Seite umgelenkt. Die modellierten lokalen Ver{\"a}nderungen des Grundwasserzirkulationssystems haben keinen beobachtbaren Effekt auf das Temperaturfeld. Hingegen erzeugen permeable St{\"o}rungszonen eine ausgepr{\"a}gte thermische Signatur innerhalb eines Einflussbereichs von ~ 2.4-8.8 km in -1000 m Tiefe und ~6-12 km in -3000 m Tiefe. Diese thermische Signatur, in der sich k{\"a}ltere und w{\"a}rmere Temperaturbereiche abwechseln, wird durch auf- und abw{\"a}rts gerichteten Fluidfluss innerhalb der St{\"o}rung verursacht, der grunds{\"a}tzlich durch existierende Gradienten in der hydraulischen Druckh{\"o}he angetrieben wird. Alle Studien haben gezeigt, dass St{\"o}rungen einen beachtlichen Einfluss auf den Fluid-, und W{\"a}rmefluss haben. Es stellte sich heraus, dass die Permeabilit{\"a}t in der St{\"o}rung und in den umgebenden geologischen Schichten so wie der spezifische geologische Rahmen entscheidende Faktoren in der Ausbildung verschiedener W{\"a}rmetransportmechanismen sind, die sich in St{\"o}rungen entwickeln k{\"o}nnen. Die von permeablen St{\"o}rungen verursachten Temperaturver{\"a}nderungen k{\"o}nnen lokal, jedoch groß sein, genauso wie die durch hydraulisch leitende und nichtleitende St{\"o}rungen hervorgerufenen Ver{\"a}nderungen des Fluidystems. Letztlich haben die Simulationen f{\"u}r die unterschiedlich skalierten Modelle gezeigt, dass die Ergebnisse sich nicht aufeinander {\"u}bertragen lassen und dass es notwendig ist, jeden geologischen Rahmen hinsichtlich Konfiguration und Gr{\"o}ßenskala gesondert zu betrachten. Abschließend hat diese Studie demonstriert, dass die Betrachtung von St{\"o}rungen in 3D Finiten Elementen Modellen f{\"u}r die Simulation von gekoppeltem Fluid- und W{\"a}rmetransport auf unterschiedlichen Skalen m{\"o}glich ist. Da diese Art von numerischen Simulationen sowohl die geologische Struktur des Untergrunds sowie die im Erdinnern ablaufenden physikalischen Prozesse integriert, k{\"o}nnen sie einen wertvollen Beitrag leisten, indem sie Feld- und Laborgest{\"u}tzte Untersuchungen vervollst{\"a}ndigen.},
  language  = {de}
}
@phdthesis{Schintgen2016,
  author    = {Schintgen, Tom Vincent},
  title     = {The geothermal potential of Luxembourg},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87110},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XXII, 313},
  year      = {2016},
  abstract  = {The aim of this work is the evaluation of the geothermal potential of Luxembourg. The approach consists in a joint interpretation of different types of information necessary for a first rather qualitative assessment of deep geothermal reservoirs in Luxembourg and the adjoining regions in the surrounding countries of Belgium, France and Germany. For the identification of geothermal reservoirs by exploration, geological, thermal, hydrogeological and structural data are necessary. Until recently, however, reliable information about the thermal field and the regional geology, and thus about potential geothermal reservoirs, was lacking. Before a proper evaluation of the geothermal potential can be performed, a comprehensive survey of the geology and an assessment of the thermal field are required. As a first step, the geology and basin structure of the Mesozoic Trier-Luxembourg Basin (TLB) is reviewed and updated using recently published information on the geology and structures as well as borehole data available in Luxembourg and the adjoining regions. A Bouguer map is used to get insight in the depth, morphology and structures in the Variscan basement buried beneath the Trier-Luxembourg Basin. The geological section of the old Cessange borehole is reinterpreted and provides, in combination with the available borehole data, consistent information for the production of isopach maps. The latter visualize the synsedimentary evolution of the Trier-Luxembourg Basin. Complementary, basin-wide cross sections illustrate the evolution and structure of the Trier-Luxembourg Basin. The knowledge gained does not support the old concept of the Weilerbach Mulde. The basin-wide cross sections, as well as the structural and sedimentological observations in the Trier-Luxembourg Basin suggest that the latter probably formed above a zone of weakness related to a buried Rotliegend graben. The inferred graben structure designated by SE-Luxembourg Graben (SELG) is located in direct southwestern continuation of the Wittlicher Rotliegend-Senke. The lack of deep boreholes and subsurface temperature prognosis at depth is circumnavigated by using thermal modelling for inferring the geothermal resource at depth. For this approach, profound structural, geological and petrophysical input data are required. Conceptual geological cross sections encompassing the entire crust are constructed and further simplified and extended to lithospheric scale for their utilization as thermal models. The 2-D steady state and conductive models are parameterized by means of measured petrophysical properties including thermal conductivity, radiogenic heat production and density. A surface heat flow of 75 ∓ 7 (2δ) mW m-2 for verification of the thermal models could be determined in the area. The models are further constrained by the geophysically-estimated depth of the lithosphere-asthenosphere boundary (LAB) defined by the 1300 °C isotherm. A LAB depth of 100 km, as seismically derived for the Ardennes, provides the best fit with the measured surface heat flow. The resulting mantle heat flow amounts to ∼40 mW m-2. Modelled temperatures are in the range of 120-125 °C at 5 km depth and of 600-650 °C at the crust/mantle discontinuity (Moho). Possible thermal consequences of the 10-20 Ma old Eifel plume, which apparently caused upwelling of the asthenospheric mantle to 50-60 km depth, were modelled in a steady-state thermal scenario resulting in a surface heat flow of at least 91 mW m-2 (for the plume top at 60 km) in the Eifel region. Available surface heat-flow values are significantly lower (65-80 mW m-2) and indicate that the plume-related heating has not yet entirely reached the surface. Once conceptual geological models are established and the thermal regime is assessed, the geothermal potential of Luxembourg and the surrounding areas is evaluated by additional consideration of the hydrogeology, the stress field and tectonically active regions. On the one hand, low-enthalpy hydrothermal reservoirs in Mesozoic reservoirs in the Trier-Luxembourg Embayment (TLE) are considered. On the other hand, petrothermal reservoirs in the Lower Devonian basement of the Ardennes and Eifel regions are considered for exploitation by Enhanced/Engineered Geothermal Systems (EGS). Among the Mesozoic aquifers, the Buntsandstein aquifer characterized by temperatures of up to 50 °C is a suitable hydrothermal reservoir that may be exploited by means of heat pumps or provide direct heat for various applications. The most promising area is the zone of the SE-Luxembourg Graben. The aquifer is warmest underneath the upper Alzette River valley and the limestone plateau in Lorraine, where the Buntsandstein aquifer lies below a thick Mesozoic cover. At the base of an inferred Rotliegend graben in the same area, temperatures of up to 75 °C are expected. However, geological and hydraulic conditions are uncertain. In the Lower Devonian basement, thick sandstone-/quartzite-rich formations with temperatures >90 °C are expected at depths >3.5 km and likely offer the possibility of direct heat use. The setting of the S{\"u}deifel (South Eifel) region, including the M{\"u}llerthal region near Echternach, as a tectonically active zone may offer the possibility of deep hydrothermal reservoirs in the fractured Lower Devonian basement. Based on the recent findings about the structure of the Trier-Luxembourg Basin, the new concept presents the M{\"u}llerthal-S{\"u}deifel Depression (MSD) as a Cenozoic structure that remains tectonically active and subsiding, and therefore is relevant for geothermal exploration. Beyond direct use of geothermal heat, the expected modest temperatures at 5 km depth (about 120 °C) and increased permeability by EGS in the quartzite-rich Lochkovian could prospectively enable combined geothermal heat production and power generation in Luxembourg and the western realm of the Eifel region.},
  language  = {en}
}
@phdthesis{Ziegler2017,
  author    = {Ziegler, Moritz O.},
  title     = {The 3D in-situ stress field and its changes in geothermal reservoirs},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-403838},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 110, XV},
  year      = {2017},
  abstract  = {Information on the contemporary in-situ stress state of the earth's crust is essential for geotechnical applications and physics-based seismic hazard assessment. Yet, stress data records for a data point are incomplete and their availability is usually not dense enough to allow conclusive statements. This demands a thorough examination of the in-situ stress field which is achieved by 3D geomechanicalnumerical models. However, the models spatial resolution is limited and the resulting local stress state is subject to large uncertainties that confine the significance of the findings. In addition, temporal variations of the in-situ stress field are naturally or anthropogenically induced. In my thesis I address these challenges in three manuscripts that investigate (1) the current crustal stress field orientation, (2) the 3D geomechanical-numerical modelling of the in-situ stress state, and (3) the phenomenon of injection induced temporal stress tensor rotations. In the first manuscript I present the first comprehensive stress data compilation of Iceland with 495 data records. Therefore, I analysed image logs from 57 boreholes in Iceland for indicators of the orientation of the maximum horizontal stress component. The study is the first stress survey from different kinds of stress indicators in a geologically very young and tectonically active area of an onshore spreading ridge. It reveals a distinct stress field with a depth independent stress orientation even very close to the spreading centre. In the second manuscript I present a calibrated 3D geomechanical-numerical modelling approach of the in-situ stress state of the Bavarian Molasse Basin that investigates the regional (70x70x10km³) and local (10x10x10km³) stress state. To link these two models I develop a multi-stage modelling approach that provides a reliable and efficient method to derive from the larger scale model initial and boundary conditions for the smaller scale model. Furthermore, I quantify the uncertainties in the models results which are inherent to geomechanical-numerical modelling in general and the multi-stage approach in particular. I show that the significance of the models results is mainly reduced due to the uncertainties in the material properties and the low number of available stress magnitude data records for calibration. In the third manuscript I investigate the phenomenon of injection induced temporal stress tensor rotation and its controlling factors. I conduct a sensitivity study with a 3D generic thermo-hydro-mechanical model. I show that the key control factors for the stress tensor rotation are the permeability as the decisive factor, the injection rate, and the initial differential stress. In particular for enhanced geothermal systems with a low permeability large rotations of the stress tensor are indicated. According to these findings the estimation of the initial differential stress in a reservoir is possible provided the permeability is known and the angle of stress rotation is observed. I propose that the stress tensor rotations can be a key factor in terms of the potential for induced seismicity on pre-existing faults due to the reorientation of the stress field that changes the optimal orientation of faults.},
  language  = {en}
}
@phdthesis{Tranter2022,
  author    = {Tranter, Morgan Alan},
  title     = {Numerical quantification of barite reservoir scaling and the resulting injectivity loss in geothermal systems},
  doi       = {10.25932/publishup-56113},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-561139},
  school      = {Universit{\"a}t Potsdam},
  pages     = {131},
  year      = {2022},
  abstract  = {Due to the major role of greenhouse gas emissions in global climate change, the development of non-fossil energy technologies is essential. Deep geothermal energy represents such an alternative, which offers promising properties such as a high base load capability and a large untapped potential. The present work addresses barite precipitation within geothermal systems and the associated reduction in rock permeability, which is a major obstacle to maintaining high efficiency. In this context, hydro-geochemical models are essential to quantify and predict the effects of precipitation on the efficiency of a system. The objective of the present work is to quantify the induced injectivity loss using numerical and analytical reactive transport simulations. For the calculations, the fractured-porous reservoirs of the German geothermal regions North German Basin (NGB) and Upper Rhine Graben (URG) are considered. Similar depth-dependent precipitation potentials could be determined for both investigated regions (2.8-20.2 g/m3 fluid). However, the reservoir simulations indicate that the injectivity loss due to barite deposition in the NGB is significant (1.8\%-6.4\% per year) and the longevity of the system is affected as a result; this is especially true for deeper reservoirs (3000 m). In contrast, simulations of URG sites indicate a minor role of barite (< 0.1\%-1.2\% injectivity loss per year). The key differences between the investigated regions are reservoir thicknesses and the presence of fractures in the rock, as well as the ionic strength of the fluids. The URG generally has fractured-porous reservoirs with much higher thicknesses, resulting in a greater distribution of precipitates in the subsurface. Furthermore, ionic strengths are higher in the NGB, which accelerates barite precipitation, causing it to occur more concentrated around the wellbore. The more concentrated the precipitates occur around the wellbore, the higher the injectivity loss. In this work, a workflow was developed within which numerical and analytical models can be used to estimate and quantify the risk of barite precipitation within the reservoir of geothermal systems. A key element is a newly developed analytical scaling score that provides a reliable estimate of induced injectivity loss. The key advantage of the presented approach compared to fully coupled reservoir simulations is its simplicity, which makes it more accessible to plant operators and decision makers. Thus, in particular, the scaling score can find wide application within geothermal energy, e.g., in the search for potential plant sites and the estimation of long-term efficiency.},
  language  = {en}
}