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  4. The In Situ Stress State, its Variability, and Implications for Conventional and Unconventional Geothermal Reservoirs
 
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2023
Doctoral Thesis
Title

The In Situ Stress State, its Variability, and Implications for Conventional and Unconventional Geothermal Reservoirs

Abstract
Characterisation of the present-day in situ stress state is an integral part of the safe de velopment of geothermal resources regardless of geographic location. The state of stress allows quantification of seismic hazard, which is one of the main factors, besides eco nomical reasons, hindering the wider use of deep geothermal energy sources worldwide. Although the state of stress is considered of high importance in deep geothermal projects, which often benefit from high permeabilities of fault zones and/or fracture networks, stress data records are either highly uncertain, scant, or, in the worst case, non-existent. This may eventually lead to questionable assumptions and, therefore, unreliable statements on the pre-existing seismic hazard potential. The geothermal industry urgently needs ways to better characterise the in situ stress state and its anthropogenic disturbance resulting from subsurface operations. The following doctoral dissertation presents both classical and advanced workflows of characterisation and modelling of the in situ stress state as well as its perturbation in both conventional and unconventional geothermal reservoirs. The thesis starts with two studies, i.e., first in a geothermal greenfield and second in a geothermal brownfield, estimating the in situ stress state of unconventional geothermal systems. In these studies, due to the significant data availability limitations, several different estimation methods and data sources were applied to constrain the in situ stress tensor. With the "stress picture" being derived, implications for the development of geothermal resources in the two discussed geothermal fields were addressed. The third study addresses the implications of the in situ stress state on the permeability anisotropy, and subsequent utilisation of geothermal resources in the Ruhr region. The fourth study presents an approach to simulate the three-dimensional in situ state of stress of the Ruhr region. Using physics-based numerical simulation and a comprehensive set of validation data, this study presents a reliable picture of the state of stress in the region and allows the quantification of seismic hazard resulting from the reactivation of major faults. The fifth study tackles the problem of simulating the spatio-temporal evolution of stress and seismicity caused by long-term geothermal fluid circulation within a geothermal doublet system utilising numerical approaches. It emphasises the significance of the thermally-induced stresses over the pore pressure perturbance during long-term fluid circulation in a geothermal system. Finally, in the last study, a database of in situ stress magnitudes and orientations, quality-rated accordingly to the World Stress Map quality standards, created for the greater Ruhr region is presented. This study benefits from the vast amount of in situ stress data, which had just recently been made public, and should serve as a template for other regions worldwide aiming at better in situ stress characterisation in terms of both stress orientations and magnitudes.
Thesis Note
Bochum, Univ., Diss., 2023
Author(s)
Kruszewski, Michal  
Fraunhofer-Einrichtung für Energieinfrastrukturen und Geothermie IEG  
Advisor(s)
Backers, Tobias
sl-0
Saenger, Erik  orcid-logo
Fraunhofer-Einrichtung für Energieinfrastrukturen und Geothermie IEG  
DOI
10.13154/294-10450
Language
English
Fraunhofer-Einrichtung für Energieinfrastrukturen und Geothermie IEG  
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