Significance of mechanical behavior and stress heterogeneity in a deep geothermal reservoir

The goal of this thesis is an improved quality of the mechanical characterization and stress distribution of the deep crystalline reservoir in Soultz-sous-Forêts (France). Four major studies, i.e. mechanical properties, in-situ stress field, hydraulic stimulation and numerical modeling were performed. The finding of the lithological and petrographical controls on wellbore stability and induced seismicity in granitic rock is crucial for the future development of the Enhaced Geothermal System

New non-destructive method for testing the strength of cement mortar material based on vibration frequency of steel bar: Theory and experiment

Timely and accurately obtaining the strength of pouring material, e.g., concrete, cement mortar, is of great significance for engineering construction. In this paper, a non-destructive, economical and accurate strength detection method that suites for on-site using is proposed for the steel bar cement mortar material. The method based on the relationship between the vibration frequency of the steel bar and the properties of the mortar material, which is obtained by solving the Euler-Bernoulli beam problem. Both Particle Flow Code (PFC) software simulation (calibrated) and Split Hopkinson pressure Bar experiment on test samples of cement mortar and steel bar were performed to verify the theoretically obtained relationship. Studies on samples of various aggregate ratio further confirmed such correspondence. Results show that the dynamic stiffness of the cement mortar material dominates the calculation of the vibration frequency of steel bar, while the combined effect of the density, length, elastic modulus, inertia moment of the steel bar can be safely ignored. A single-valued mapping relation exists in between the dynamic stiffness coefficient and the Uniaxial Compressive Strength (UCS) of the cement mortar sample, i.e., increased dynamic stiffness coefficient with increasing UCS. Both experimental and predicted results showed a linear relationship between the vibration frequency of the steel bar and the strength of the mortar material. Fitted linear relations were proposed with coefficients depending on sample size and aggregate ratio and might serve as a good indicator for the strength of the mortar material. Further studies on the effect of internal defects of the mortar materials as well as on samples of more size and aggregate ratio are required to make the proposed method a practical too

Constraining the Spatial Extent of Strain Localization at the Base of the Seismogenic Zone: A Case Study from the Sandhill Corner Shear Zone, Maine, USA

Knowledge of the structure and processes of strain localization at the base of the seismogenic zone can provide constraints on the rheologic evolution of shear zones at depth and the spatial extent that seismicity influences the surrounding rock. Such knowledge is hindered by limitations of borehole measurements from such depths and a lack of structural/mineralogical preservation of original rock fabric. The Sandhill Corner Shear Zone, Maine, USA provides an opportunity to study well-preserved structures relating to strain localization along major faults exhumed from seismogenic depths. In south-central Maine, this shear zone juxtaposes two rock types: the Cape Elizabeth Formation and the Crummett Mountain Formation. This work focuses on the less-studied Crummett Mountain Formation. Measurements of strain markers (quartz vein thickness, linear fracture density and aspect ratio in garnet) delimit strain gradients reflecting portions of the strain localization history in the field area. Optical and electron microscope observations of microstructures along the gradient provide context for changing deformation conditions reflected by changes in the slope of the strain gradients. Our results show that localization occurred initially at high temperatures (400-500oC) in a 90m-wide zone. The onset of seismicity narrowed the zone of localization, producing a 7m-wide zone of high-strain, containing a ~1.7m-wide core that preserves structures related to seismicity at the frictional-to-viscous transition. The results of this study refine previous observations on the structure of the Crummett Mountain Formation, provide minimum estimates of finite shear strain and displacement along the Sandhill Corner Shear Zone, and provide insight on the role that earthquake mechanics play in strain localization at the base of the seismogenic zone

The Mechanical Behavior of Salt X

Rock salt formations have long been recognized as a valuable resource - not only for salt mining but for construction of oil and gas storage caverns and for isolation of radioactive and other hazardous wastes. Current interest is fast expanding towards construction and re-use of solution-mined caverns for storage of renewable energy in the form of hydrogen, compressed air and other gases. Evaluating the long term performance and safety of such systems demands an understanding of the coupled mechanical behavior and transport properties of salt. This volume presents a collection of 60 research papers defining the state-of-the-art in the field. Topics range from fundamental work on deformation mechanisms and damage of rock salt to compaction of engineered salt backfill. The latest constitutive models are applied in computational studies addressing the evolution and integrity of storage caverns, repositories, salt mines and entire salt formations, while field studies document ground truth at multiple scales. The volume is structured into seven themes: Microphysical processes and creep models Laboratory testing Geological isolation systems and geotechnical barriers Analytical and numerical modelling Monitoring and site-specific studies Cavern and borehole abandonment and integrity Energy storage in salt caverns The Mechanical Behavior of Salt X will appeal to graduate students, academics, engineers and professionals working in the fields of salt mechanics, salt mining and geological storage of energy and wastes, but also to researchers in rock physics in general

Key Topics in Deep Geological Disposal : Conference Report (KIT Scientific Reports ; 7696)

The current state of knowledge of central aspects of radioactive waste repository research was presented in the course of the DAEF conference "Key topics in deep geological disposal". For the first time socio-economic and socio-technical issues played an important role within a conference focusing on the disposal of radioactive waste. Scientists from about 16 different countries presented their scientific work in 8 sessions and during a poster session

Modelling geomechanics of residual soils with DMT tests

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Universidade de Aveiro, Instituto Politécnico da Guarda. 200

Appraisal of the self-organization and evolutionary dynamics of seismicity based on (non-extensive) statistical physics and complexity science methods

Θεμελιώδης πρόκληση σε πολλά επιστημονικά πεδία αποτελεί ο καθορισμός κανονικοτήτων και νόμων ανωτέρας κλίμακας σε σχέση με την υπάρχουσα γνώση για φαινόμενα κατωτέρας κλίμακας. Είναι πλέον αποδεκτό ότι o ενεργός τεκτονικός ιστός αποτελεί ένα κρίσιμο πολύπλοκο σύστημα, αν και δεν έχει ακόμη οριστικοποιηθεί αν είναι στατικό, δυναμικό/εξελικτικό, ή ένας χρονικά εξαρτημένος συνδυασμός αμφοτέρων. Σε κάθε περίπτωση, τα κρίσιμα συστήματα χαρακτηρίζονται από μορφοκλασματική ή πολυ-μορφοκλασματική κατανομή των στοιχείων τους, ισχυρές αλληλεπιδράσεις μεταξύ των κοντινών και μακρινών γειτόνων και διακοπτόμενη (ασυνεχή) έκφρασή τους. Οι ιδιότητες αυτές μπορούν να μελετηθούν με όρους Μη Εκτατικής Στατιστικής Φυσικής (ΜΕΣΦ). Πέραν του ρυθμού έκλυσης ενέργειας που εκφράζεται μέσω του μεγέθους (Μ), μέτρο των πιθανών συσχετίσεων αποτελεί ο παρέλθων χρόνος (Δt) και η υποκεντρική απόσταση (Δd) μεταξύ αλλεπάλληλων σεισμών πάνω από ένα κατώφλι μεγέθους σε μια περιοχή. Πρόσφατες έρευνες έδειξαν ότι, εάν οι κατανομές μεγέθους (Μ), χρονικής (Δt) και χωρικής (Δd) εξάρτησης μεταξύ διαδοχικών σεισμών θεωρηθούν ανεξάρτητες έτσι ώστε η από κοινού πιθανότητα p(M, Δt, Δd) να παραγοντοποιείται σε p(MUΔtUΔd) = p(M) p(Δt) p(Δd), τότε η συχνότητα εμφάνισης ενός σεισμού εξαρτάται πολλαπλώς όχι μόνο από το μέγεθος όπως πρόβλεπει ο νόμος Gutenberg – Richter αλλά και από τη χρονική και χωρική εξάρτηση διαδοχικών σεισμών. Αυτό, με τη σειρά του, σημαίνει ότι η αυτο-οργάνωση της σεισμικότητας θα πρέπει να εκδηλώνεται μέσω μιας συγκεκριμένης στατιστικής συμπεριφοράς της χρονικής και χωρικής εξάρτησης της (κατανομές νόμων δύναμης). Στην παρούσα διατριβή θα επιχειρηθεί η περιγραφή της σεισμικότητας με όρους ΜΕΣΦ, σε σεισμογενετικά συστήματα κατά μήκος του ορίου πλακών του ΒΑ-Β Ειρηνικού και της Βορείου Αμερικής, καθώς και στο σεισμογενετικό σύστημα του ελλαδικού χώρου-Δυτικής Τουρκίας. Η ανάλυση πραγματοποιείται σε πλήρης και ομαδοποιημένους καταλόγους σεισμών, όπου οι μετασεισμοί έχουν αφαιρεθεί με τη στοχαστική μέθοδο απομαδοποίησης του Zhuang et al., (2002). Η στατιστική συμπεριφορά της σεισμικότητας υποδεικνύει ότι η επιφανειακή σεισμικότητα των συστημάτων που μελετώνται είναι υποεκτατική, χαρακτηρίζεται από μακράς εμβέλειας συσχετίσεις και για το λόγο αυτό είναι αυτο-οργανωμένη και πιθανόν κρίσιμη. Ο βαθμός της υπο-εκτακτικότητας δεν είναι ομοιόμορφος, ούτε σταθερός, αλλά διαφέρει δυναμικά από σύστημα σε σύστημα, ενίοτε διαφέρει στη χρονική εξέλιξη και μπορεί να παρουσιάζει κυκλικότητα. Το μόνο σύστημα βαθειάς δομής (σεισμικότητα σε μεγάλα εστιακά βάθη) που εξετάζεται εδώ - η Αλεούτια ζώνη υποβύθισης- φαίνεται να παρουσιάζει στατιστική που περιγράφεται με όρους κατανομής Poisson (απουσία συσχέτισης). Τα αποτελέσματα που προκύπτουν υποδεικνύουν ότι η ΜΕΣΦ αποτελεί ένα εξαιρετικό εργαλείο για την φυσική περιγραφή της σεισμικότητας σε διάφορα σεισμογενετικά περιβάλλοντα. Ο μη εκτατικός φορμαλισμός θεωρείται το κατάλληλο μεθοδολογικό εργαλείο για να περιγράψει φυσικά συστήματα που δε βρίσκονται σε ισορροπία και έχουν μεγάλη μεταβλητότητα και πολυκλασματική δομή όπως η σεισμικότητα.A fundamental challenge in many scientific fields is to define norms and laws of higher-order in relation to the existing knowledge about phenomena of lower-order. It has been long suggested that the active tectonic grain comprises a self-organized complex system, therefore its expression (seismicity) should be manifested in the temporal and spatial statistics of energy release rates, and exhibit memory due to long-range interactions in a fractal-like space-time. Such attributes can be properly understood in terms of Non-Extensive Statistical Physics (NESP) In addition to energy release rates expressed by the magnitude M, measures of the temporal and spatial interactions are the time (Δt) and hypocentral distance (Δd) between consecutive events. Recent work indicated that if the distributions of M, Δt and Δd are independent so that the joint probability p(M, Δt, Δd) factorizes into the probabilities of M, Δt and Δd, i.e. p(MUΔtUΔd) = p(M) p(Δt) p(Δd), then the frequency of earthquake occurrence is multiply related, not only to magnitude as the celebrated Gutenberg – Richter law predicts, but also to interevent time and distance by means of well-defined power-laws consistent with NESP. The present work applies these concepts to investigate the dynamics of seismogenetic systems along the NE – N boundary of the Pacific and North American plates and the seismogenic zones of Greece – Western Turkey. The analysis is conducted to full and declustered (reduced) catalogues where the aftreshocks are removed by the stochasting declustering method of Zhuang et al., 2002.The statistical behaviour of seismicity suggests that crustal seismogenetic systems along the Pacific–North American plate boundaries in California, the seismogenic zones of Greece – Western Turkey, Alaska and the Aleutian Arc are invariably sub-extensive; they exhibit prominent operative long-range interaction and long-term memory, therefore they are self-organized and possibly critical. The degree of sub-extensivity is neither uniform, nor stationary but varies dynamically between systems and may also vary with time, or in cycles. The only sub-crustal system studied herein (Aleutian Subduction) appears to be Poissonian. The results are consistent with simulations of small-world fault networks in which free boundary conditions at the edges, (i.e. at the surface) allow for self-organization and criticality to develop, and fixed boundary conditions within, (i.e. at depth), do not. The results indicate that NESP is an excellent natural descriptor of earthquake statistics and appears to apply to the seismicity observed in different seismogenetic environments. The NESP formalism, although far from having answered questions and debates on the statistical physics of earthquakes, appears to be an effective and insightful tool in the investigation of seismicity and its associated complexity

Water and Earthquakes

This open access book explores the interactions between water and earthquakes, including recent concerns about induced seismicity. It further highlights that a better understanding of the response of the water system to disturbances such as earthquakes is needed to safeguard water resources, to shield underground waste repositories, and to mitigate groundwater contamination. Although the effects of earthquakes on streams and groundwater have been reported for thousands of years, this field has only blossomed into an active area of research in the last twenty years after quantitative and continuous documentation of field data became available. This volume gathers the important advances that have been made in the field over the past decade, which to date have been scattered in the form of research articles in various scientific journals

Water and Earthquakes

This open access book explores the interactions between water and earthquakes, including recent concerns about induced seismicity. It further highlights that a better understanding of the response of the water system to disturbances such as earthquakes is needed to safeguard water resources, to shield underground waste repositories, and to mitigate groundwater contamination. Although the effects of earthquakes on streams and groundwater have been reported for thousands of years, this field has only blossomed into an active area of research in the last twenty years after quantitative and continuous documentation of field data became available. This volume gathers the important advances that have been made in the field over the past decade, which to date have been scattered in the form of research articles in various scientific journals