Rozprawy doktorskie na temat „Physical properties of fault zones”

Rupture of the Chelungpu fault during the September 21, 1999, 7.6 Mwearthquake in Taiwan caused a 90-Jr,m-long surface rupture with variable displacement along strike. Analysis of core from two holes drilled through the fault zone, combined with geologic mapping and detailed investigation from three outcrops, define the fault geometry and physical properties of the Chelungpu fault in its northern and southern regions. In the northern region, the fault dips 45-60° east parallel to bedding and consists of a narrow (1-20 cm) core of dark-gray, sheared clay gouge at the base of a 30-50 m zone of increased fracture density that is confined asymmetrically to the hanging wall. Microstructural analysis of the fault gouge indicates the presence of extremely narrow clay zones (50-300 μm thick) that are interpreted as the fault rupture surfaces. Few shear indicators are observed outside of the fault gouge, which implies that slip was localized in the gouge in the northern region. Slip localization along a bed-parallel surface resulted in less high-frequency ground motion and larger displacements during the earthquake than in the southern region. Observations from the southern region indicate that the fault dips 20-30° at the surface and consists of a wide (20- 70 m-thick) zone of sheared, foliated shale with numerous gouge zones. A footwall-ramp geometry juxtaposes 2000-3000 m of flat-lying Quaternary Toukoshan Formation in the footwall with Pliocene and Miocene, east-dipping siltstone and muds tone in the hanging wall. The wide, diffuse fault zone contributed to the lower displacement and higher frequency ground motion in the southern region during the 1999 earthquake. The structure in the northern region is the result of the fault being a very young (<50 >ka) fault segment in the hanging wall of an older segment of the Chelungpu fault, buried in the Taichung basin. The fault in the southern region is located on an older (~1 Ma) fault trace. The contrasting fault properties in the different regions are responsible for the variability in strong-motion and displacement observed during the 1999 earthquake.

Les systèmes de failles décrochantes sont constitués d’une variété de complexités géométriques telles que des branchements de failles, des plis et des zones de relais. En particulier, la présence d’une structure de relais peut fortement déterminer la taille finale de la rupture sismique. Ainsi, comprendre la dynamique d’une rupture à travers une telle complexité est crucial pour l’évaluation des risques sismiques. Quelques études ont examiné cette question dans le contexte d’un milieu élastique linéaire. Cependant, lors d’un séisme, des zones d’endommagement sont générées, notamment aux extrémités d’une faille, ce qui modifie considérablement la dynamique globale d’une rupture. En utilisant un modèle micromécanique prenant en compte la croissance et l’ouverture de fissures et leur impact sur l’évolution dynamique des modules élastiques, nous évaluons comment l’endommagement dynamique peut affecter la capacité d’une rupture à se propager au travers des structures de relais. Nous montrons que, parfois, en tenant compte de cette dispersion de l’énergie sur les microstructures formées, les zones endommagées suppriment la capacité de la rupture à passer d’une faille à une autre. Mais, dans certains cas spécifiques, la zone de faible vitesse créée dynamiquement peut au contraire aider la rupture à sauter sur la deuxième faille. En combinant cette étude numérique avec une approche analytique, nous établissons les contours d’une approche systématique utile pour l’évaluation des risques sismiques
Strike-slip fault systems consist of a variety of geometrical complexities like branches, kinks and step-overs. Especially, the presence of a step-over structure can strongly determine the final size of the earthquake rupture. Thus understanding the dynamics of a rupture through such a complexity is crucial for seismic hazard assessment. A few studies have looked at this question within the context of a linear elastic medium. However, during an earthquake off-fault damage is generated, especially at the ends of a fault, which significantly changes the overall dynamics of a rupture. Using a micromechanical model, that accounts for crack growth and opening and its impact on the dynamic evolution of elastic moduli, we evaluate how dynamic off-fault damage can affect the capability of a rupture to navigate through step-over fault structures. We show that, sometimes, accounting for this energy sink, off-damage suppresses the ability of the rupture to jump from one fault to another. Whereas, in some specific cases, the dynamically created low-velocity zone may aid the rupture to jump on the secondary fault. Combing this numerical study with an analytical analysis we set the contours for a systematic approach useful for earthquake hazard assessments

Les zones de failles concentrent la migration de fluides et la déformation dans la croûte supérieure. Les propriétés hydrauliques des formations argileuses en font des excellents sites de stockage et des roches mères performants. Les zones de failles peuvent jouer deux rôles contraires dans la circulation de fluides, soit elles s’expriment sous forme de drains, soit elles constituent une barrière, et souvent les deux rôles sont combinés au sein d’une même zone de failles. Les processus de migration des fluides dans les zones de failles affectant les argiles sont peu connus. Cette étude s’est focalisée sur la structure, les paléo-circulations, les circulations actuelles lors de tests d’injection et les propriétés pétro-physiques de la zone de failles présente dans le laboratoire de recherche souterrain de Tournemire dans les argilites Toarciennes. La structure de la zone de failles a été caractérisée par des forages et reconstituée en 3D par modélisation numérique, permettant de définir des faciès de déformation. L’architecture de la zone de failles se caractérise par une imbrication de facies de déformations plus ou moins intenses sans claire organisation en cœur et zone endommagée comme observée dans les roches plus dures. Les zones intactes, fracturées et les brèches sont respectivement caractérisées par des porosités matricielles comprises entre 9.5-13.5, 10-15 et 13-21%. La circulation de fluide se concentrant aux limites de la brèche et au niveau des zones de failles «immatures» ou secondaires comprises dans les zones fracturées. Lors de son activité, la zone de failles a déjà été affectée par au moins deux phases de circulations de fluides
Fault zones concentrate fluids migration and deformations in the upper crust. The shale hydraulic properties make them excellent storage sites and hydrocarbon reservoirs/source rocks. Fault zones can play two roles in the fluid circulation; drains or barriers, in general, both roles are combined within the same fault zone. What are the conditions that promote the fluid circulation along the fault zones in shales and what are the fault zone impacts on the formation properties are relatively poorly explored key questions. This study focused on characterizing the relationships between fault architecture, paleo-fluid as well as current fluid circulations through the analysis of fault calcite mineralization, injection tests and petrophysical properties conducted on a fault zone outcropping underground in the Tournemire research laboratory nested in the Toarcian shale. The fault zone structure was characterized using boreholes data and reconstructed in 3D through modeling to define different deformation facies. No clear facies organization is observed, a fault core and a fault damage zone being difficult to define as it is in hard rocks. The intact, fractured and breccia facies are characterized by a porosity of 9.5-13.5, 10-15 and 13-21%. Large fluid flowrate concentrated along a few “channels” located at the breccia boundaries and in the secondary fault zones that displayed fractured facies and limited breccia fillings. Detailed microstructural and geochemical analysis at the breccia/fractured zones interface revealed that fluids circulated out of the main shear zones, in micro-more or less inherited fractures highlighting a decoupling between fault slip and fluid migrations

Fault zone properties at depth are often inferred from seismic properties such as seismic velocities and attenuation. An understanding of how fault zone properties and processes influence seismic measurements is required for successful interpretations to be made. As fault zones are heavily fractured and often fluid-rich areas, a knowledge of the influences of cracking and fluid content on seismic measurements is needed. This will allow better interpretation of fault zone properties and how they may change at the time of an earthquake. Research presented in this thesis is concentrated on two regions of strike-slip faulting: the Parkfield area of the San Andreas fault and the exhumed Carboneras fault zone region of SE Spain. Well-preserved exhumed faults allow observation of fault structure at seismogenic depths. The structure of the exhumed Carboneras fault has previously been suggested as an analogue for the Parkfield area at depth. Laboratory measurements can help us to determine what processes occur at seismogenic depths in active faults. They can also aid in interpretation of seismic studies. In this thesis laboratory and seismic studies are brought together in order to gain a greater understanding of fault zone seismic properties at depth and how to interpret them. In order to characterise the properties of the Carboneras fault, laboratory experiments of velocities through fault gouge and fault zone rocks are performed. The influences of fracture damage and local geological fabric on velocities are investigated. Gouge velocities are measured to be less than those of the mica schist rock through which the fault cuts. Velocity changes due to variations in crack damage in cyclic loading experiments are less than 5% of the original rock velocity. Strong velocity anisotropy is observed in the mica schist, with velocities of the order of 30% less when measured perpendicular to the strong foliation present in the rock. The consequences in terms of seismically imaging the fault zone are discussed. The effects of this strong velocity anisotropy need to be considered for specific source-receiver geometries and the local geological fabric in the locations of seismic experiments. Surface wave tomography and ambient noise analysis of the Carboneras fault zone region shows that faults are imaged as low velocity features at depth. Results suggest that velocities are reduced by approximately 10% at depths close to 3 km. The strong anisotropy observed in laboratory experiments of mica schist may also have implications for seismic imaging of this region as this rock crops out widely. This is discussed in terms of a potentially strong crustal component to shear-wave splitting observations in the region. In the second part of the thesis, temporal changes in seismic attenuation at the time of the 2004 M6.0 Parkfield earthquake are investigated. Seismic attenuation can give indications of fracture damage and healing. Spectral ratios between earthquakes within repeating clusters are calculated. A sharp increase in attenuation is observed immediately after the earthquake, which then decays over the next 2 years. The postseismic decay is fit by a logarithmic function. The timescale of the decay is found to be similar to that in GPS data and ambient seismic noise velocities following the 2004 M6.0 Parkfield earthquake. The amplitude of the attenuation change corresponds to a decrease of approximately 10% in QP at the time of the earthquake. The greatest changes are recorded to the northeast of the fault trace, consistent with preferential damage in the extensional quadrant behind a north-westerly propagating rupture tip. Our analysis suggests that significant changes in seismic attenuation and hence fracture dilatancy during co-seismic rupture are limited to depths of less than about 5 km.

Quantification of the fluid flow properties of the Earth's crust is an essential precursor to the understanding of a wide range of geological processes, including earthquake generation and crustal strength, and the recovery of natural resources. Faults playa key role in the migration of fluids around the ;Earth's crust, and therefore the fluid flow properties of fractured rocks and how these properties evolve with time are of major importance. This thesis aims to improve our understanding of the hydraulic transport properties of large fault zones by presenting a large dataset of detailed field and microstructural observations and results from a suite of laboratory experiments to provide a basis for studying the distribution, and fluid flow properties, of damage surrounding large natural fault zones. Damage surrounding the core of faults is represented by both microfracturing of the rock matrix and by macroscopic fracture networks. Microfracture and macrofracture densities and orientations have been analysed on strike slip faults with displacements ranging over 3 orders of magnitude (~O.l2 m - 5000 m). These faults cut crystalline rock within the excellently exposed Atacama Fault Zone, Northern Chile. All faults consist of a fault core and associated damage zone. Damage zone width as defined by macrofractures and microfractures scale with displacement and fault length. Both microfractures (specifically fluid inclusion planes) and macrofractures within the damage zone show a log-linear .decrease in fracture density with perpendicular distance from the fault core. An empirical equation for microfracture density distribution based on the evolution of displacement has been derived for these faults. Preferred microfracture orientations in the damage zone suggest that this damage may predominantly be due to early processes related to enhanced stress at fault tips, in addition to cumulative wear processes from the juxtaposition of geometrical irregularities on the fault plane and damage from dynamic rupture. Fault core widths scale with displacement, with the largest displacement fault showing a wide multiple core zone. Detailed experimental studies of the development of permeability of crustal rock during deformation are essential in helping to understand fault mechanics and constrain larger scale models that predict bulk fluid flow within the crust. The strength, permeability and pore fluid volume evolution of initially intact crystalline rock under increasing differential load leading to macroscopic failure has been determined at water pore pressures of 50 MPa and varying effective pressures from 10 to 50 MPa. Permeability is seen to increase by, up to, and over two orders of magnitude prior to macroscopic failure, with the greatest increase seen at lowest effective pressures. Post-failure permeability is shown to be over three orders of magnitude higher than initial intact permeabilities and approaches the lower the limit of measurements of in situ bulk crustal permeabilities. Increasing amplitude cyclic loading tests show permeabilitystress hysteresis with high permeabilities maintained as differential stress is reduced and the greatest permeability increases are seen between 90-99% of the failure stress. Under hydrothermal conditions without further loading, it is suggested that much of this permeability can be recovered by healing and sealing, and pre-macroscopic failure fracture damage may heal relatively faster than post-failure macroscopic fractures. Pre-failure permeabilities are nearly seven to nine orders of magnitude lower than that predicted by some high pressure diffusive models suggesting that microfracture matrix flow cannot dominate, and agrees with inferences that bulk fluid flow and dilatancy must be dominated by larger scale structures, such as macrofractures. It is suggested that the permeability of a highly stressed fault tip process zone in low-permeability crystalline rocks could increase by more than 2 orders of magnitude, while stress drops related to fracture propagation close damage zone cracks, and some permeability is maintained due to hysteresis from permanent microfracture damage. Future work should aim to quantify experimentally-induced microfractures and. associated permeability measurements, and by relating the fracture densities surrounding natural fault zones with densities seen in experimental deformed samples with known permeabilities, modelling techniques can then be applied to gain estimates of bulk fluid flow of the fracture networks. This will provide a basis for predicting the influence of pore fluid pressures on important geological issues, such as crustal strength.

In many seismically active areas (e.g. Italy, Greece) earthquakes, sometimes destructive, nucleate within (aftershocks surely do) and propagate through carbonates in the upper crust (e.g. L’Aquila earthquake, 2009, Mw 6.1). Seismology, geophysics and geodesy furnish key parameters related to the earthquake source (e.g. seismic moment, static stress drop, radiated energy) but lack sufficient resolution to constrain detailed three-dimensional fault zone geometry and coseismic on- and off-fault deformation processes at scales relevant to earthquake physics. In this thesis it is proposed to study the internal structure and mechanics of fault zones hosted in carbonate rocks using a multidisciplinary approach, complementary to the seismological-based one. This includes detailed structural survey to quantify the architecture of exhumed fault zones in carbonates both by field and remote sensed methods (e.g. use of a drone to get high-resolution aerial images), rock deformation experiments under conditions relevant to the seismic cycle (e.g. use of rotary shear apparatus, uniaxial press, Split Hopkinson Pressure Bar), microstructural-mineralogical characterization (optical and scanning electron microscopy, electron microprobe analyses, X-ray powder diffraction, cathodoluminescence, X-ray microtomography, white light interferometry, image analysis) of natural and experimental fault rocks to infer the physico-chemical processes occurring during earthquakes. Two fault zones cutting dolostones exhumed from < 3 km depth in the Italian Southern Alps were described: the Borcola Pass Fault Zone (BPFZ) and the Foiana Fault Zone (FFZ). In both cases the internal structure of the two fault zones was strongly influenced by the reactivation of preexisting anisotropies such as regional-scale joint sets and bedding surfaces. The BPFZ is a secondary strike-slip branch of the regional Schio-Vicenza Line that developed in a fluid-rich upper crustal environment. The microstructural characteristics of the principal and secondary slip zones of the BPFZ, including detailed analysis of the clast size distribution of injected cataclasites, suggested coseismic fluidization processes during faulting, most likely related to the propagation of ancient seismic ruptures in to the shallow crust. The FFZ is a major sinistral transpressive fault zone that developed in a fluid-poor upper crustal setting. Systematic along-strike and down-dip changes in the structure of the FFZ were recognized, allowing a comparison to be made between field observations and the predictions of three-dimensional earthquake rupture simulations. A noteworthy characteristic of the FFZ is the presence of thick belts (hundreds of meters) of in-situ shattered dolostones cut by discrete mirror-like fault surfaces. The origin of mirror-like fault surfaces and in-situ shattered dolostones in the FFZ was investigated using, respectively, low- to high-velocity (0.0001-1 m/s) rotary shear friction experiments on dolostone gouges and low- to high-strain rate (quasi-static 10-3 s-1, dynamic > 50 s-1) uniaxial compression tests on dolostone rock cylinders. At applied normal stresses and displacements consistent with those estimated for the FFZ, experimental mirror-like fault surfaces comparable to the natural examples (e.g. clast truncation along fault surfaces, similar surface roughness) were formed in rotary-shear experiments only at seismic slip rates (v ≥ 0.1 m/s). I suggest therefore that small-displacement mirror-like fault surfaces developed in dolostone gouge layers represent markers of seismic slip. In-situ shattered dolostones similar to those found within the FFZ (i.e. rock fragments up to a few millimeters in size elongated in the stress wave loading direction, incipient zones of microfracturing down to the micrometer scale) were formed during uniaxial compression tests only above strain rates of ~ 200 s-1. The association of in-situ shattered dolostones cut by discrete mirror-like fault surfaces is interpreted to record the propagation of multiple earthquake ruptures within the shallow crustal portions of the FFZ. Lastly, the structural complexity of the studied fault zones in terms of three-dimensional geometry of the fault-fracture network, fault rock spatial distribution, fault orientation and kinematics, compares favorably to the predicted damage distribution in three-dimensional earthquake rupture simulations, as well as the structure of active seismic sources hosted in carbonate rocks as illuminated by seismological techniques
In molte regioni sismiche dell’area Mediterranea, tra cui l’Italia e la Grecia, gran parte dei terremoti, anche distruttivi, enucleano e propagano in sequenze di rocce carbonatiche della crosta superiore (terremoto dell’Aquila, 2009, Mw 6.1). Questo è vero soprattutto per le sequenze di foreshock e aftershock. Le indagini sismologiche, geofisiche e geodetiche forniscono dei parametri fondamentali per la caratterizzazione delle sorgenti sismiche (momento sismico, caduta di sforzo statico, energia elastica irradiata) ma non hanno risoluzione spaziale sufficiente per descrivere in maniera dettagliata la geometria delle sorgenti sismiche e i processi chimico-fisici attivi nelle zone di faglia durante un terremoto. Questi aspetti limitano fortemente la nostra conoscenza della fisica dei terremoti. In questa tesi la struttura interna e le proprietà meccaniche di zone di faglia sismogenetiche in rocce carbonatiche sono state studiate utilizzando un approccio multidisciplinare e complementare rispetto a quello classico basato su dati sismologici principalmente ricavati dall’inversione delle onde sismiche. I metodi utilizzati sono: (i) il rilevamento strutturale di dettaglio di zone di faglia esumate in carbonati con tecniche di terreno e di telerilevamento (ad es. utilizzo di un drone per ottenere immagini ad alta risoluzione di grandi affioramenti), (ii) la realizzazione di prove meccaniche su roccia (e polveri di roccia) in condizioni di deformazione rilevanti per il ciclo sismico (utilizzo di apparati di tipo rotary, pressa uniassiale e Split Hopkinson Pressure Bar), (iii) lo studio mineralogico-microstrutturale (microscopia ottica e a scansione elettronica, microsonda elettronica, diffrazione a raggi X su polveri, catodoluminescenza, microtomografia a raggi X, interferometria in luce bianca, analisi di immagine) di rocce di faglia naturali e sperimentali per vincolare i processi chimico-fisici attivi in carbonati durante un terremoto. Sono state selezionate due zone di faglia in dolomie: la zona di faglia del Passo della Borcola (BPFZ) e la zona di faglia di Foiana (FFZ). Entrambe le zone di faglia sono esumate da profondità < 3 km e affiorano nel settore delle Alpi Meridionali (Italia). L’architettura interna delle due zone di faglia è fortemente controllata dalla riattivazione di strutture ereditate come sistemi di giunti a scala regionale e superfici di strato. La BPFZ è una faglia secondaria trascorrente appartenente al sistema della Linea Schio-Vicenza. La presenza all’interno della BPFZ di zone di scivolamento estremamente localizzate e spesso organizzate in livelli cataclastici ed ultracataclastici con bordi irregolari (a lobi e cuspidi), iniettati lungo fratture estensionali e caratterizzati da una forte selezione granulometrica ha suggerito l’attivazione di fenomeni di fluidizzazione durante la propagazione di rotture sismiche in un ambiente ricco in fluidi. La FFZ è una faglia transpressiva sinistra a scala regionale che presenta sistematiche variazioni nella propria struttura interna (e.g. spessore della zona di faglia, orientazione e cinematica delle faglie minori) lungo la direzione e l’immersione della faglia. La zona di faglia esposta è caratterizzata dalla presenza di dolomie frantumate senza evidenze significative di deformazione per taglio (dolomie frantumate in-situ) associate a faglie con piccoli rigetti (< 0.5 m) e superfici a specchio con clasti troncati. L’assenza di vene o fratture sigillate indica che la fagliazione è avvenuta in un ambiente povero in fluidi. L’origine delle faglie con superfici a specchio e delle dolomie frantumate in-situ della FFZ è stata investigata attraverso esperimenti eseguiti (1) con un apparato di tipo rotary imponendo basse ed alte velocità (0.0001-1 m/s) di scivolamento su polveri di dolomia e (2) con un pressa uniassiale e una Split Hopkinson Pressure Bar imponendo basse ed alte velocità di deformazione (quasi-statiche 10-3 s-1, dinamiche > 50 s-1) su cilindri di dolomia. Applicando le condizioni di sforzo normale e rigetto stimate per le faglie della FFZ, superfici a specchio simili a quelle naturali in termini di rugosità delle superfici e di microstrutture (presenza di clasti troncati lungo le superfici di faglia), sono state prodotte negli esperimenti di tipo rotary solo a velocità di scivolamento cosismiche (v ≥ 0.1 m/s). Inoltre dolomie frantumate in-situ con microstrutture simili a quelle descritte lungo la FFZ (frammenti di roccia con dimensioni fino a qualche millimetro allungati nella direzione di applicazione del carico e zone di microfratturazione incipiente) sono state prodotte negli esperimenti con la Split Hopkinson Pressure Bar solo a ratei di deformazione > 200 s-1 : tali ratei di deformazione sono in genere associati alle perturbazioni di sforzo dovute al passaggio di una rottura sismica. Pertanto l’associazione di dolomie frantumate in-situ tagliate da faglie discrete con superfici a specchio è stata interpretata come il risultato della propagazione di rotture sismiche nelle porzioni superficiali della FFZ. Infine, a livello qualitativo, la complessità strutturale delle due zone di faglia studiate in termini di geometria del network di faglie e fratture, distribuzione spaziale delle rocce di faglia, orientazione e cinematica delle faglie, è confrontabile sia con la distribuzione del danneggiamento di faglia predetta da simulazioni di rotture sismiche, sia con la struttura di sorgenti sismogenetiche attuali in carbonati desunta da osservazioni sismologiche

Bien que les zones de failles représentent un très petit volume de la croute terrestre, elles influencent grandement ses propriétés hydromécaniques. Ce travail compare des analyses multidisciplinaires, de hautes précisions, de deux zones de failles aux propriétés contrastées : l’une est une zone de failles mature de plusieurs kilomètres de long, l’autre s’étend seulement sur quelques centaines de mètres. Leurs propriétés architecturales, hydromécaniques et de résistance mécanique ont été caractérisées dans le but d’améliorer la compréhension des couplages entre l’évolution de leurs propriétés hydromécaniques et leur potentiel de réactivation. Un protocole de caractérisation in-situ des propriétés hydrauliques et mécaniques a été mis au point. Il intègre des analyses microstructurales, des descriptions détaillées des propriétés pétrophysiques à plusieurs échelles. Les deux zones de failles étudiées montrent toutes deux des relations entre leurs histoires diagénétiques, les propriétés initiales des formations sédimentaires et leurs propriétés actuelles hydromécaniques. Il a été mis en évidence que le paramètre le plus important gouvernant le comportement hydromécanique des zones de failles est la continuité de sa zone d’endommagement. Une zone de failles mature aura une zone d’endommagement relativement continue alors qu’une zone de failles non-mature aura une zone d’endommagement hétérogène caractérisée par une alternance de niveaux fracturés et non-fracturés. Ces contrastes architecturaux dépendent des propriétés initiales de la roche intacte. Au sein de la série sédimentaire, les variations de la résistance à la compression (σc) de la roche intacte induisent différents mécanismes d’accommodations des déformations. Il en résulte une architecture de zone de failles présentant de fortes variations d’épaisseur, caractérisée par une alternance de niveaux très perméables et très déformables avec des niveaux imperméables et peu déformables
Although fault zones represent a very small volume of the crust, they highly influence the crust’s mechanical and fluid flows properties. This work compares high definition trans-disciplinary analyses of two fault zones with highly contrasted properties. One is a mature fault zone of plurikilometer length, and the other is a small fault zone of a few hundred meters length. We have characterized the architectural, hydromechanical and strength properties of these faults to improve the understanding of the coupling between fault zones hydromechanical properties and their potential activation. A protocol to characterize in the field (on outcropping segments) the faults hydraulic and mechanical properties has been conducted through the coupling of micro-structural analyses, detailed rock physical descriptions at the rock mass several scales. The two studied fault zones despite their different sizes display some similarities. Both show a strong coupling between the fault zone diagenetic history, the initial properties of the sedimentary layers and the fault zone current hydraulic and mechanical properties. We show that the most important parameter governing the hydromechanical behaviors of fault zones is the continuity of the damage zones. A mature fault zone will have a relatively continuous damage zone while a small fault zone will contain a more heterogeneous damage zone characterized by an alternation of fractured and un-fractured layers. These architectural contrasts of damage zones also depend on the initial intact rock properties of the sedimentary series. Contrasted initial intact rock strengths (σc) induce contrasted strain accommodation mechanisms in the fault zone compartments, and an associated fault zone architecture that displays large thickness variations, characterized by alternate high-permeable-low-stiff and low-permeable-high-stiff layers in the damage zone

Carbonate reservoirs contain approximately two-thirds of the world's oil and gas reserves (Al-Anzi et al., 2003). Carbonates often pose a significant problem when it comes to understanding their reservoir quality because of their heterogeneous nature, which is caused by both the variety of processes occurring depositionally and their high susceptibility to diagenetic alterations. In order to fully characterise the behaviour of carbonate rocks in the subsurface is it important to understand their textural heterogeneity and also how faulting can modify their textures. Deformation in fault zones causes the petrophysical properties (e.g. porosity, permeability and velocity) to alter from the background values. For example, fracturing in damage zones surrounding faults increase the permeability, creating conduits to fluids, conversely, fault cores often act as barriers, created by pore occluding processes. However, faulting in carbonate rocks is often complicated by their textural variations, leading to a variety of deformation microstructures, and each will create different petrophysical properties. This thesis aims to understand how faulting effects different carbonate rocks and analyse the controls on any alterations to the petrophysical properties (porosity, permeability and velocity) into the fault zones. Alterations to the permeability are important to unravel in order to assess the fluid flow potential and hydraulic properties of a rock. Understanding the alterations to the velocity can help to better image faults at depth and to provide information on their microstructures.

Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第12119号
理博第3013号
新制||理||1449(附属図書館)
23955
UT51-2006-J114
京都大学大学院理学研究科地球惑星科学専攻
(主査)教授 嶋本 利彦, 助教授 田上 高広, 教授 平島 崇男
学位規則第4条第1項該当

Les zones de failles ont un impact important sur les réservoirs carbonatés car elles peuvent agir comme des drains ou des barrières en fonction de leurs propriétés structurales et diagénétiques. Il est important de bien comprendre ces propriétés pour déterminer les caractéristiques hydrauliques des zones de failles. Pour cela, l'approche multidisciplinaire de cette thèse combinant l’analyse structurale, diagénétique et géochimique vise à (1) contraindre l'évolution structurale et diagénétique des zones de failles dans les carbonates, (2) établir des règles et des concepts géométriques permettant de construire des modèles géologiques cohérents, et (3) permettre une meilleure compréhension de la réponse dynamique hydraulique des zones de failles dans les carbonates à travers leurs évolutions. Nous avons étudié 3 zones de failles (Castellas, D19) affectant les carbonates de plate-forme du Barrémien inférieur (faciès Urgonien) situées dans l'anticlinal de La Fare et dans celui de la Nerthe (Provence - SE France). Ces travaux ont permis de restaurer les séquences diagénétiques des zones de failles avec des analyses de ciment sous catholuminescence et des mesures des isotopes 13C et 18O. L'analyse structurale a permis de compléter l'évolution diagénétique en déterminant les caractéristiques architecturales liées à chaque activité de faille et en discriminant l'effet des structures préexistantes sur le développement ultérieur de ces dernières. Enfin, cette étude a permis d'améliorer notre compréhension du comportement hydraulique des zones de failles dans les carbonates au cours temps
Fault zones strongly impact carbonates reservoir properties as they can act as drains or barriers depending of their structural and diagenetic properties. Hence, it is important to have an integrativecomprehension of these properties that affect the fault zones hydraulic properties. To this end, the multidisciplinary approach of this thesis combining structural, diagenetic and geochemical approaches aims to (1) constrain the structural and diagenetic evolution of fault zones in carbonates (2) draw rules and geometrical concepts allowing building of coherent geological models, and (3) allow a better understanding of the hydraulic dynamic response of fault zones in carbonates through their evolutions. We studied 3 fault zones (Castellas, D19) affecting lower Barremian platform carbonates (Urgonian facies) located in La Fare and Nerthe anticlines (Provence – SE France). This work allowed the restoration of fault zones diagenetic sequences with cement analyses under catholuminescence and 13C and 18O isotopes. The structural analysis completed the diagenetic evolution by determining the architectural characteristics related to each fault activity and discriminating the effect of pre-existing structures on subsequent fault development. Finally, this study improved our understanding of fault zones hydraulic behaviour in carbonates through times

Resumo: O interesse pela exploração petrolífera em armadilhas associadas à halocinese motivou a realização deste trabalho, que teve como objetivo caracterizar e descrever a evolução halocinética da região centro-norte da Bacia de Santos. Dados sísmicos e de poços foram utilizados na determinação do arcabouço estrutural-estratigráfico e na evolução cinemática do sal, por meio de técnicas de restauração palinspática. O contexto geológico-estrutural estabelecido serviu de alicerce para análise da dinâmica do sal em experimentos físicos análogos em caixa de areia com silicone. A área foi palco de intensa atividade halocinética a partir do Albiano, em resposta à distensão provocada pela abertura do Atlântico Sul e pela sobrecarga sedimentar, especialmente durante o Senoniano, quando imensas cunhas clásticas progradantes adentraram a bacia e expulsaram a espessa camada de sal, resultando numa extensa zona de falhas antitéticas, cujo bloco baixo consiste numa cicatriz da halocinese. Concomitantemente, falhas lístricas sintéticas se desenvolveram na porção norte da área, coexistindo dois sistemas de cisalhamento que resultou na instalação da zona de acomodação da distensão. No Paleoceno-Eoceno, importante sedimentação adentrou na porção sul da área exercendo sobrecarga diferencial sobre os diápiros adjacentes às mini-bacias senonianas, resultando na remobilização do sal e na inversão das mini-bacias para anticlinal tipo casco de tartaruga
Abstract: The interest in petroleum traps associated to salt tectonics was the motivation to conduct this work. The objective of the thesis is to characterize and explain the halokinetic evolution of north-central region of Santos Basin. Seismic data and wells were used to construct the structural-stratigraphic framework leading to halokinetics evolution by using palinspatic restoration techniques. The structural geologic framework was the basis of salt dynamics analyses using silicone in sandbox analogues experiments. The studied area underwent intense halokinetic activities since Albian age in response to stretching associated to Atlantic South opening and sediment loading. During Senonian huge prograding clastics wedges entered the basin expelling thick layer of salt creating an extensive antithetic fault zone, known as Cabo Frio Fault Zone, where the hangingwall rests on a salt weld. Two sets of synthetic listric fault developed concomintantly in the northern portion of area, producing an accommodation zone. During Paleocene-Eocene an important sedimentation event estabilished in the southern area causing differential loading on diapirs adjacent to senonian mini basins, resulting in salt remobilization and inversion of mini basins to form turtle structures
Orientador: Chang Hung Kiang
Coorientador: Jean Letouzey
Banca: Claudio Ricomini
Banca: Mario Luis Assine
Banca: Sidnei Pires Rostirolla
Banca: Flavio Luis Fernandes
Doutor

Borehole breakouts provide valuable information with respect to the evaluation of the in-situ stress direction and magnitude, and also verification of any geomechanical models built for a specific field. Identifying the locations along a borehole where the breakouts form is therefore very important. On the other hand, the borehole geometry (defined as width and depth of breakouts), which is a critical factor in completion and production optimisation design, can also be estimated from the back analysis of breakout information. While breakout width has been widely used in obtaining an estimate of the maximum horizontal stress magnitude, few studies have been reported on the estimation of breakout depth and the information it may provide.Caliper and image logs are customarily used to identify and characterise borehole enlargement zones; in particular, the breakouts. However, these methods are limited in their applications in many instances. In addition, good quality image logs are not available in many wells including old wells. This leads to a need for the development of a new approach to identify the location of borehole enlargements along a wellbore.This research aims to understand the mechanisms under which breakouts form with respect to a rock’s physical and mechanical properties. Petrophysical logs, which are often acquired in most of the drilled wells, show correlations with mechanical properties of the rock. Therefore, this research attempts to develop an approach to identify the location of borehole enlargement zones using the information gained from petrophysical logs.This research introduces a new multi-variable approach based on various data processing techniques (including wavelet, classifiers, and neural networks) to extract rock properties from different petrophysical logs. This information was combined using a robust data fusion technique which determined the location of the enlarged borehole. The results demonstrated the accuracy of the location of the borehole enlargement identified along a borehole compared to that observed using calipers and image logs.In addition, there were correlations between breakout width and depth measurements when measurements taken from high quality acoustic image logs were used. Elastic and elastoplastic finite element numerical models also showed how breakout width and depth could change due to a change in different rock properties. The models were verified by comparing results of numerical analysis with real observations from field data.

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O interesse pela exploração petrolífera em armadilhas associadas à halocinese motivou a realização deste trabalho, que teve como objetivo caracterizar e descrever a evolução halocinética da região centro-norte da Bacia de Santos. Dados sísmicos e de poços foram utilizados na determinação do arcabouço estrutural-estratigráfico e na evolução cinemática do sal, por meio de técnicas de restauração palinspática. O contexto geológico-estrutural estabelecido serviu de alicerce para análise da dinâmica do sal em experimentos físicos análogos em caixa de areia com silicone. A área foi palco de intensa atividade halocinética a partir do Albiano, em resposta à distensão provocada pela abertura do Atlântico Sul e pela sobrecarga sedimentar, especialmente durante o Senoniano, quando imensas cunhas clásticas progradantes adentraram a bacia e expulsaram a espessa camada de sal, resultando numa extensa zona de falhas antitéticas, cujo bloco baixo consiste numa cicatriz da halocinese. Concomitantemente, falhas lístricas sintéticas se desenvolveram na porção norte da área, coexistindo dois sistemas de cisalhamento que resultou na instalação da zona de acomodação da distensão. No Paleoceno-Eoceno, importante sedimentação adentrou na porção sul da área exercendo sobrecarga diferencial sobre os diápiros adjacentes às mini-bacias senonianas, resultando na remobilização do sal e na inversão das mini-bacias para anticlinal tipo casco de tartaruga
The interest in petroleum traps associated to salt tectonics was the motivation to conduct this work. The objective of the thesis is to characterize and explain the halokinetic evolution of north-central region of Santos Basin. Seismic data and wells were used to construct the structural-stratigraphic framework leading to halokinetics evolution by using palinspatic restoration techniques. The structural geologic framework was the basis of salt dynamics analyses using silicone in sandbox analogues experiments. The studied area underwent intense halokinetic activities since Albian age in response to stretching associated to Atlantic South opening and sediment loading. During Senonian huge prograding clastics wedges entered the basin expelling thick layer of salt creating an extensive antithetic fault zone, known as Cabo Frio Fault Zone, where the hangingwall rests on a salt weld. Two sets of synthetic listric fault developed concomintantly in the northern portion of area, producing an accommodation zone. During Paleocene-Eocene an important sedimentation event estabilished in the southern area causing differential loading on diapirs adjacent to senonian mini basins, resulting in salt remobilization and inversion of mini basins to form turtle structures

It is widely recognised that inverted fault zones form economically significant structures for subsurface fluid exploration and production. Inverted fault zones are formed by the contractional reactivation and reversal of pre-existing extensional fault zones. Recognising the reverse-reactivation of normal faults in sedimentary basins is fundamental, as the reconfiguration of fault geometries has implications for overall basin geometry, sediment accommodation and supply, and fluid flow pathways. This is particularly important for understanding the modification or creation of petroleum system elements through time, which in turn allows for increased targeted exploration. Notwithstanding the broad economic relevance of inverted fault zones, integrated multi-scale (from micrometre-scale to outcrop-scale) studies on the structural, petrophysical, and geochemical properties of inverted fault zones within porous reservoir rocks are limited. This thesis characterises the structural, petrophysical, and geochemical properties of inverted fault zones from two localities, the Otway Basin (Australia) and Bristol Channel Basin (United Kingdom), in order to understand how inverted faults influence fluid flow at a range of scales. To address this, this thesis has two main topics of focus: (1) identify the influence of inverted faults on surrounding lithology by assessing the relationship between faults, damage zones around faults, and fractures related to fault growth; and (2) identify how subsurface fluids flow, interact, and modify their surrounds by assessing the geochemistry of fluids in fractures and thereby constraining the source, evolution, and migration of fluids preserved in fractures. An integrated, multi-scale approach is crucial for improving the prediction of subsurface fluid flow beyond the wellbore. In order to understand the influence of inverted faults on surrounding lithology, an inverted fault (Castle Cove Fault) in the Otway Basin, southeast Australia, is the focus of the first two chapters of this thesis. The geometries and relative chronologies of natural fractures adjacent to the Castle Cove Fault are investigated. Structural mapping in the hanging wall damage zone reveals three sets of shear fractures that are geometrically related to the Castle Cove Fault. Inversion of the Castle Cove Fault has resulted in the development of an extensive network of fractures and complex fold structures, and inversion would have subsequently improved the outcrop-scale permeability structure of the damage zone for fluid migration. At the micrometre-scale, the permeability structure has also been influenced by fault inversion. Petrophysical and petrographical analyses in the hanging wall damage zone show that microstructural changes due to faulting have enhanced the micrometre-scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore-lining chlorite morphology as a result of fault deformation. Consequently, inversion has subsequently improved the micrometre-scale permeability structure of the damage zone adjacent to the Castle Cove fault plane. Characterisation of the permeability structure adjacent to reverse-reactivated faults at a range of scales will aid with predicting fluid flow associated with inversion structures. Structural and geochemical analyses in the next two chapters of this thesis aim to understand how subsurface fluids flow and characterise the source, evolution, and migration pathways of fluids preserved in inverted fault zones. The geochemical evolution of fluids precipitated as calcite and siderite-cemented concretions and fractures throughout the eastern Otway Basin have been investigated. Pore fluids were sourced from both meteoric water and sea water during the deposition of the Eumeralla Formation and pore fluid evolution was strongly influenced by diagenetic reactions and increased temperature during burial. Using a similar analytical approach, the geochemical evolution of fluids precipitated as calcite and gypsum-cemented fractures throughout the eastern Bristol Channel Basin have vibeen investigated. The main source of fluids were connate pore waters, which were altered by diagenetic reactions within their host lithologies and subsequently redistributed through migration along faults and their associated damage zones. Knowledge of the source, evolution, and migration pathways of these fluids provides valuable insights for understanding the development of inverted sedimentary basins through time. Consequently, integrated studies on the multi-scaled permeability structure of inverted fault zones and the fluids preserved within them will ultimately improve fluid exploration and monitoring strategies in sedimentary basins.
Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum (ASP), 2019

博士
國立中央大學
地球物理研究所
98
The Taiwan Chelungpu-fault Drilling Project (TCDP) drilled a 2-km-deep research borehole in Dakeng, Taiwan. Geophysical logs of the TCDP were carried out over depths of 500–1900 m in two boreholes. In order to identify the shear zones, a shear zone at a depth of 1110 meters is interpreted to be the Chelungpu fault, located within the Chunshui shale. Stress-induced borehole breakouts were observed over nearly the entire length of the wellbore from image logs (FMI). These data show an overall stress direction (~N115°E) that is essentially parallel to the regional stress field and parallel to the tectonic stress direction. The Dipole Sonic logs (DSI) also analyzed in this study, the data shows that the most dislocation of fast shear azimuth is close to the depth 1110 meters and consistence with the borehole breakout rotation. The logging data show that near the fault, the azimuth of the maximum horizontal principal stress (SHMAX) changes by about 90o from the regional tectonic stress direction (N130oE). Hydraulic fracturing tests were used to determine the magnitude of the minimum principal stress (S3) at multiple depths. Through dislocation modeling, we simulated the abrupt stress rotation observed in the image logs at the depth of the Chelungpu Fault. In addition, the modeling indicates that the magnitudes of the minimum horizontal principal stress Shmin changed markedly during the earthquake. In order for the co-seismic stress changes to result in a ~90o stress rotation near the fault, the state of stress prior to the earthquake had to have been a reverse faulting stress regime (as expected), but with SHMAX ≈ Shmin >>Sv. The modeling in the stresses with low frictional coefficient and a near complete stressdrop after the earthquake suggests a weak Chelungpu fault, at least in the northern part of the fault.

I present physical shear-box experiments investigating the relationship between geometrical properties of shear zones and mechanical properties of deformed rocks. Experimental methodology is also examined critically and new materials for analogue modelling of shear localization are presented. First, I tested experimentally whether meaningful rheological information can be deduced from finite geometrical shear zone data. The results predict characteristic geometrical responses for certain end-member materials. However, it will be difficult to constrain such responses in the field. In the second part physical controls on deformation in the shear box are analysed for Newtonian and power-law fluids and an elastoviscoplastic strain-softening material. Since models always represent simplifications of the natural problem, it is essential to understand fully the physics of a given simulation. I show that displacement boundary conditions, model geometry, and rheology control shear zone geometry. Practical applications of the shear box for modelling natural shear localization and limitations of isothermal physical models with displacement boundary conditions in general are discussed. In the third part, new data on the rheology of highly-filled silicone polymers are introduced. Since dynamic similarity must be satisfied in analogue models to permit scaled, quantitative simulations of deformation processes, the choice of suitable rock analogues is critical for physical experiments. In particular, we address the problem of designing power-law fluids to model rocks deforming by dislocation creep. We found that highly-filled polymers have complex rheologies. Hence, such materials must be used with care in analogue modelling and only for certain experimental stress-strain rate conditions. Finally, I investigated whether fault network geometry and topography of brittle strike-slip faults are influenced by the degree of compaction of the host rock. Analogue shear experiments with loose and dense sand imply that the degree of sediment compaction may be a governing factor in the evolution of fault network structure and topography along strike-slip faults in sedimentary basins. Therefore, models of strike-slip faults should consider potential volume changes of deformed rocks.

During the last decades, the study of seismic anisotropy has provided useful information for the interpretation and evaluation of the stress field and active crustal deformation. Seismic anisotropy can yield valuable information on upper crustal structure, fracture field, and presence of fluid-saturated rocks crossed by shear waves. Several studies worldwide demonstrate that seismic anisotropy is related to stress-aligned, filled-fluid micro-cracks (EDA model, Crampin et al., 1984b; Crampin, 1993). The seismic anisotropy is an almost ubiquitous property of the Earth and the Shear Wave Splitting is the most unambiguous indicator of anisotropy, but the automatic estimation of the splitting parameters is difficult because the effect of the anisotropy on a seismogram is a second order, not easily detectable effect. Different researchers developed automated techniques aimed to study the Shear Wave Splitting: in this study, the results of different codes are compared in order to evaluate the best method for automatic anisotropy evaluation. In the last three years, an automatic analysis code, “Anisomat+”, was developed, tested and improved to calculate the anisotropic parameters: fast polarization direction () and delay time (∂t). “Anisomat+” consists of a set of MatLab scripts able to retrieve automatically crustal anisotropy parameters from three-component seismic recordings of local earthquakes. It needs waveforms and hypocentral parameters in the format routinely archived by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The code uses horizontal component cross-correlation method: a mathematical algorithm aimed to measure the similarity of the pulse shape between two shear waves. Anisomat+ has been compared to other two automatic analysis codes (SPY and SHEBA) and tested on three zones of the Apennines (Val d’Agri, Tiber Valley and L’Aquila surroundings). It was observed that, if the number of measures is large enough, at each station the average values of the parameters (fast direction and delay time) are comparable. The main goal in developing of an automatic code was to have tool able to work on a big amount of data, in a short time, by reducing the errors due to the subjectivity. These two acquirements are very useful and are the basis to develop a quasi real-time monitoring of the anisotropic parameters. The anisotropic parameters, resulting from the automatic computation, have been interpreted to determine the fracture field geometries; for each area, I defined the dominant fast direction and the intensity of the anisotropy, interpreting these results in the light of the geological and structural setting and of two anisotropic interpretative models, proposed in the literature. In the first one, proposed by Zinke and Zoback (2000), the local stress field and cracks are aligned by tectonics phases and are not necessarily related to the presently active stress field. Therefore the anisotropic parameters variations are only space-dependent. In the second, EDA model (Crampin, 1993), and its development in the APE model (Zatsepin and Crampin, 1995) fluid-filled micro-cracks are aligned or ‘opened’ by the active stress field and the variation of the stress field might be related to the evolution of the pore pressure in time; therefore in this case the variation of the anisotropic parameters are both space- and time- dependent. I recognized that the average of fast directions, in the three selected areas, are oriented NW-SE, in agreement with the orientation of the active stress field, as suggested by the EDA model, proposed by Crampin (1993), but also, by the proposed by Zinke and Zoback model; in fact, NW-SE direction corresponds also to the strike of the main fault structures in the three study regions. The mean values of the magnitude of the normalized delay time range from 0.005 s/km to 0.007 s/km and to 0.009 s/km, respectively for the L'Aquila (AQU) area, the High Tiber Valley (ATF) and the Val d'Agri (VA), suggesting a 3-4% of crustal anisotropy (Piccinini et al., 2006). In each area are also examined the spatial and temporal distribution of anisotropic parameters, which lead to some innovative observations, listed below. o The higher values of normalized delay times have been observed in those zones where most of the seismic events occur. This aspect was further investigated, by evaluating the average seismic rate, in a time period, between years 2005 and 2010, longer than the lapse of time, analyzed in the anisotropic studies. This comparison has highlighted that the value of the normalised delay time is larger where the seismicity rate is higher. o In the Alto Tiberina Fault area the higher values of normalised delay time are not only related to the presence of a high seismicity rate but also to the presence of a tectonically doubled carbonate succession. Therefore, also the lithology, plays a important role in hosting and preserving the micro-fracture network responsible for the anisotropic field. o The observed temporal variations of anisotropic parameters, have been observed and related to the fluctuation of pore fluid pressure at depth possibly induced by different mechanisms in the different regions, for instance, changes in the water table level in Val D’Agri (Valoroso et al., GJI submitted), occurrence of the April 6th Mw=6.1 earthquake in L’Aquila (Lucente et al., 2010). Since these variations have been recognized, it is possible to affirm that the models that better fit my results, both in term of fast directions and of delay times, seems to be those proposed by Crampin (1993) and Zatsepin & Crampin (1995), respectively EDA and APE models.
Università degli studi di Perugia
Published
1.11. TTC - Osservazioni e monitoraggio macrosismico del territorio nazionale
3.1. Fisica dei terremoti
3.2. Tettonica attiva
3.8. Geofisica per l'ambiente
open