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Deep crystalline rock formations of low permeability have been identified as a possible geological medium for high-level radioactive waste disposal. In order for the safe disposal of radioactive waste, a site characterization must be performed. A comparison of site characterization methods found out-diffusion methods to be the most viable technique for pore fluid extraction. Crush and leach, chemical and isotopic analyses such as, Cl-, 37Cl, 18O, 2H and 87Sr were valuable in characterizing the signature/origin of the pore fluids. Variations in the signatures of the pore fluids were observed and attributed to small differences in heterogeneity within the host rock and water to rock interactions. Estimates of the rate of effective diffusivity (De) were evaluated experimentally and with an analytical solution. Modelled De values were much greater than those determined experimentally, suggesting that the analytical solution provides a more conservative estimate of De for assessing radionuclide migration.

Deep crystalline rock formations of low permeability have been identified as a possible geological medium for high-level radioactive waste disposal. In order for the safe disposal of radioactive waste, a site characterization must be performed. A comparison of site characterization methods found out-diffusion methods to be the most viable technique for pore fluid extraction. Crush and leach, chemical and isotopic analyses such as, Cl-, 37Cl, 18O, 2H and 87Sr were valuable in characterizing the signature/origin of the pore fluids. Variations in the signatures of the pore fluids were observed and attributed to small differences in heterogeneity within the host rock and water to rock interactions. Estimates of the rate of effective diffusivity (De) were evaluated experimentally and with an analytical solution. Modelled De values were much greater than those determined experimentally, suggesting that the analytical solution provides a more conservative estimate of De for assessing radionuclide migration.

Salt tectonics is a key player in the evolution of many worldwide sedimentary basins on rifted continental margins. For more than a century, the evolving structures have been studied; but focus remained primarily on the onshore and shallow-water regions. The evolution of the poorly studied deep-water salt-tectonic structures is the focus of this thesis. Investigations are performed using 2D numerical models that comprise a viscous salt layer overlain by a frictional-plastic passive margin sedimentary sequence from shelf to deep water. This thesis addresses multiple salt-tectonic processes (gravity spreading, evolution of fold belts and salt canopies, diapirism) in a general context but with special focus on the structural evolution of the northwestern Gulf of Mexico (GoM). Here, multiple phases of gravity-spreading induced salt mobilization and thin-skinned deformation occurred throughout the Cenozoic. During the latest, late Oligocene-Miocene phase, the Perdido Fold Belt (PFB) formed from a 4.5km thick pre-kinematic section as a prominent salt-cored deep-water structure above the pinch-out of the autochthonous salt. It is here demonstrated with analytical as well as numerical calculations that the folding of the PFB can have formed by gravity spreading alone without basement tectonics. A requirement for this deformation is very high pore-fluid pressure in the sediments, which effectively reduces the sediments' mechanical strength. These values are refined using numerical models that couple compaction-induced fluid pressure to mechanical deformation. It is shown that very high fluid pressure is only necessary at the landward base of the deforming system; fluid pressure in other regions may remain moderate. This study shows, for the first time, the regional and dynamic evolution of pore-fluid pressure in a continental margin sedimentary system above salt. Additionally, the contribution of `lateral compaction' during fold-belt evolution is addressed. Landward of the PFB, a large-scale canopy developed during the Eocene. Its evolution is studied by investigating three different concepts of canopy evolution that have been proposed in the scientific literature. A canopy evolving via the mechanism of squeezed diapirs is most similar to the Eocene canopy of the northwestern GoM. A canopy evolving via the mechanism of breached anticlines is similar to that observed above the landward end of the PFB. Dynamic diapir growth is addressed in a neutral stress regime under uneven sedimentation employing a new mechanism of diapir initiation and evolution.

I conducted an amplitude vs. offset (AVO) analysis on newly acquired 3D seismic reflection data to detect elevated pore fluid content and pore fluid pressure along the Costa Rica convergent margin to address dewatering processes of subduction zone sediments. These data provide the highest quality 3D seismic data acquired to date along a convergent margin for detailed analysis of geophysical properties along the plate boundary fault interface. In 2011, a 55 km by 11 km 3D seismic reflection survey was completed using the R/V Marcus G. Langseth offshore western Costa Rica at the convergent margin of the Cocos and Caribbean plates. We applied pre-stack Kirchhoff time migration to a subset of these data across the frontal prism where amplitude versus offset (AVO) attributes were extracted along the decollement. When pore fluid pressure, l , exceeds 0.7, the pressure at which Poisson’s ratio begins to approach that of water, the AVO response of a fluid-filled, clay-rich decollement requires a high Poisson’s ratio and an excessively low seismic P-wave and S-wave velocity. Acute wedge taper, undercompacted subducted hemipelagic and pelagic sediments, and a smooth decollement in the northwest half of the survey correspond with decollement AVO response of relatively high values of Poisson’s ratio. These findings suggest increased pore fluid content and vertical containment of near-lithostatic pore fluid pressures within the decollement. In contrast, increased wedge taper angles, thin hemipelagic and pelagic sediments, and a rugose decollement beneath the southeastern frontal prism produce an AVO response interpreted as due to lower pore fluid contents and pressures. We propose that large-offset subducting basement normal faults in this area, as close as 20 m from the decollement, induce vertical fractures within the decollement that allow for fluid expulsion into the frontal prism and lower fluid pressure. Lateral variability of overpressure within the decollement shear zone of subduction margins is important in understanding the evolution of frontal prism strain accumulation and seismogenic rupture. / text

Natural gas hydrates occur on most continental margins in organic-rich sediments at water depths >450 m (in polar regions >150 m). Gas hydrate distribution and abundance, however, varies significantly from margin to margin and with tectonic environment. The National Gas Hydrate Program (NGHP) Expedition 01 cored 10 sites in the Krishna-Godawari (K-G) basin, located on the southeastern passive margin of India. The drilling at the K-G basin was comprehensive, providing an ideal location to address questions regarding processes that lead to variations in gas hydrate concentration and distribution in marine sediments. Pore fluids recovered from both pressurized and non-pressurized cores were analyzed for salinity, Cl-, SO4 2-, alkalinity, Ca2+, Mg2+, Sr2+, Ba2+, Na+, and Li+ concentrations, as well as 􀀂13C-DIC, 􀀂18O, and 87/86Sr isotope ratios. This comprehensive suite of pore fluid concentration and isotopic profiles places important constraints on the fluid/gas sources, transport pathways, and CH4 fluxes, and their impact on gas hydrate concentration and distribution. Based on the Cl- and 􀀂18􀀁 depth profiles, catwalk infrared images, pressure core CH4 concentrations, and direct gas hydrate sampling, we show that the occurrence and concentration of gas hydrate varies considerably between sites. Gas hydrate was detected at all 10 sites, and occurs between 50 mbsf and the base of the gas hydrate stability zone (BGHSZ). In all but three sites cored, gas hydrate is mainly disseminated within the pore space with typical pore space occupancies being 􀀁2%. Massive occurrences of gas hydrate are controlled by high-angle fractures in clay/silt sediments at three sites, and locally by lithology (sand/silt) at the more “diffuse” sites with a maximum pore space occupancy of ~67%. Though a majority of the sites cored contained sand/silt horizons, little gas hydrate was observed in most of these intervals. At two sites in the K-G basin, we observe higher than seawater Cl- concentrations between the sulfate-methane transition (SMT) and ~80 mbsf, suggesting active gas hydrate formation at rates faster than Cl- diffusion and pore fluid advection. The fluids sampled within this depth range are chemically distinct from the fluids sampled below, and likely have been advected from a different source depth. These geochemical results provide the framework for a regional gas hydrate reservoir model that links the geology, geochemistry, and subsurface hydrology of the basin, with implications for the lateral heterogeneity of gas hydrate occurrence in continental margins.

Résumé Les processus hydrothermaux affectent l'ensemble des domaines océaniques et contrôlent efficacement leur régime thermique. Cependant, les études de flux de chaleur à l'échelle globale conduisent à des interprétations parfois en contradiction avec les études locales. Il est donc essentiel de comparer les effets de l'hydrothermalisme dans différents contextes régionaux. Dans cette optique, nous avons étudié le rôle de l'hydrothermalisme sur le régime thermique d'un domaine océanique jeune (en Atlantique) et d'une marge continentale jeune (Sud Baléares). Pour cela, nous avons quantifié les transferts et pertes de chaleur et de matière en utilisant des traceurs thermiques (mesures du flux de chaleur) et des traceurs chimiques (analyse des fluides interstitiels). Le domaine océanique jeune se situe dans l'océan Atlantique sur le premier segment au sud de la faille transformante Oceanographer. Les faibles valeurs du flux de chaleur indiquent que les circulations hydrothermales, induites par les nombreux affleurements, extraient d'importantes quantités de chaleur de la croûte. La composition de l'eau interstitielle est similaire à l'eau de mer, indiquant un temps de résidence faible de l'eau dans le socle. Nous avons identifié que la rugosité du plancher océanique est un des paramètres majeurs qui contrôlent l'efficacité de ces circulations de fluides. Ce relief à petite échelle a été comparé à d'autres régions où l'efficacité des processus hydrothermaux avait préalablement été discutée. Nous en avons déduis une relation empirique qui relie la fraction du flux de chaleur à ce relief. Sur la marge Sud des Baléares, les processus hydrothermaux semblent plus restreints car leur impact thermique est plus local. Sur la pente continentale, des contrastes importants du flux de chaleur ont été mis en évidence. Ils suggèrent des circulations hydrothermales controlées par la présence de nombreux monts volcaniques. Cependant, la chimie des fluides reste proche de celle de l’eau de mer et ne permet pas de confirmer ces observations. En revanche, les processus hydrothermaux sont limités dans le bassin par les épais dépôts de sédiments. La chimie des fluides indique la présence de saumures résiduelles et leur simple diffusion vers la surface. Les valeurs du flux de chaleur sont perturbées par les contrastes de conductivité thermique induits par la présence de diapirs de sel ou du socle. Dans les deux zones d’étude, les circulations de fluides sont liées à la présence de structures basaltiques fracturées dont la perméabilité est supérieure de plusieurs ordres de grandeur à celle des sédiments alentours. La rugosité initiale du plancher océanique et le taux de sédimentation contrôlent la tranche d’âge durant laquelle la croûte reste connectée à l’océan. En revanche, les circulations sont rapidement inhibées sur les marges par les apports importants de sédiments venant du continent proche. Cette conclusion est contrebalancée par d’autres événements pouvant survenir sur les marges telles que le volcanisme ou la tectonique active. / Hydrothermal processes affect all oceanic domains therby controlling their thermal regime. At global scale, heat flow studies may lead to different interpretations than local studies. Comparing hydrothermal effects in different local contexts is essential to overcome this scale- issues. To do so, we studied the hydrothermal impact on the thermal regimes of a young oceanic domain (Atlantic Ocean) and a young margin (South Balearic). We quantified heat and matter transfers and heat losses with heat flow measurements and pore water chemical analyses. The young oceanic domain is situated on the first segment south of Oceanographer transform fault in the Atlantic Ocean. The low heat flow values indicate that hydrothermal circulations, conveyed by numerous outcrops, extract a lot of crustal heat. The composition of water in pores is similar to that of seawater. This points to a short residence time of water in the basement. We identified that the ruggedness of the seabed is one of the key parameters that control the fluid circulation efficiency. This small scale relief was compared to others regions where hydrothermal processes have already been debated. We deduced an empirical relation which links the fraction of the conductive heat flow to this relief. On the Southern Balearic margin, hydrothermal processes appear to be more limited because of their more local thermal impact. On the continental slope, great heat flow contrasts are highlighted. They suggest that hydrothermal circulation is controlled by numerous volcanic mounts. On one hand, pore fluid chemistry remains close to seawater composition and does not allow confirming these observations. On the other hand, hydrothermal processes in the basin are limited by thick sediment deposits and pore fluid chemistry indicates residual brines and their diffusion towards the surface. Heat flow values along the Southern Balearic margins are perturbed by thermal conductivity contrasts induced by salt diapirs or basement topography. In both study areas, fluid circulations are linked to fractured basaltic structures with a much larger permeability than the surrounding sediments. The seabed’s initial ruggedness and the sedimentation rate control the age range during which the crust is connected to ocean. Nevertheless, fluid circulations cease quickly due to important sediment flows from the nearby continent. This conclusion is partially offset by other events that may occur on the margins such as volcanism or active tectonic.

Mud volcanoes constitute an important component of petroliferous basins and their understanding is essential for successful exploration and development of hydrocarbon fields. They occur in both extensional and compressive tectonic settings, along with passive and active continental margins. Although extensive research exists on the geochemistry, geomorphology and stratigraphic evolution of these localized fluid flow structures, little is known about their geomechanical characteristics. This research investigates the geomechanics of mud volcanoes from the South Caspian Basin and West Nile Delta. This is achieved by establishing a workflow for geomechanical assessment of mud volcanoes using a P-wave velocity dataset from across the mud volcano within the offshore South Caspian Basin. This objective is developed further with the availability of seismic and wellbore data from around the Giza mud volcano, offshore West Nile Delta. Preliminary results of this study from the South Caspian Basin enable confidence in estimating the realistic magnitudes of elastic rock properties, stresses and fluid pressures from empirical and analytical correlations. Moreover, analysis of the variations in fluid pressures allow the fluid flow models around the mud volcano to be constrained and their gradients provide preliminary estimates of the drilling window. Structural and stratigraphic analysis around the Giza mud volcano offers insight into the formation of the mud volcano during the Quaternary and how the fault networks on the hanging wall of the arcuate tectonic fault have acted as conduits for primarily the pre-Pliocene fluids exploiting the areas of weakness along the hanging wall of the fault by entraining the Pliocene sediments. Fluid pressure evaluation reveals small overpressures caused by disequilibrium compaction. Further analysis offers insight into the critical fluid pressures that control fault movement, the stresses responsible for rock deformation around the wellbore and the width of the drilling window constrained by the fracturing of the strata. Analysis presented here provides details on the geomechanical significance of mud volcano environments, with implications for engineering practices. Overall, findings contribute to a systematic understanding of mud volcano settings not only from a field exploration and development point of view, but also at a wider scale for basin analysis and relatively small scale for play analysis.

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Die Arbeit dient der numerischen Simulation der Spurbildung in Asphaltstraßen und der Herstellung widerstandsfähiger Asphaltmischungen. Zur Modellbildung musste die physikalisch-mechanische Ursache der bleibenden Verformungen bei hohen Temperaturen geklärt werden. Im Gegensatz zu bisher existierenden Stoffmodellen ist in dieser Arbeit das Verhalten teilgesättigter granulerer Stoffe unter zyklischer Belastung als die Grundlage der Untersuchung gewählt worden. Diese zeigen bei entsprechend hoher Sättigung der Hohlräume des mineralischen Korngerüsts unter zyklischer Scherbeanspruchung und bei gleichzeitigem Druck das Phänomen der „zyklischen Mobilität”. Die Erklärung dafür ist die Verdichtungsneigung des Korngerüstes und die Inkompressibilität des Porenfluids, wodurch Porenüberdrücke entstehen. Zyklische Mobilität bedeutet den Abfall der Steifigkeit. Durch die Zunahme der Dehnungsamplituden infolge zyklischer Scherbelastung und der Irreversibilität des granularen Materials verursacht dieses Verhalten die erhöhte Spurbildungsneigung. Die richtige Modellwahl konnte durch systematische experimentelle Ergebnisse belegt werden. Die monotonen triaxialen Kompressionsversuche beweisen die Barotropie und Pyknotropie der Steifigkeit, der Festigkeit und der Dilatanz des mineralischen Korngerüstes. Durch Kompression unter zyklischem Scheren wird die Existenz eines optimalen Bitumengehalts bewiesen, bei welchem die höchste Dichte des Kornegerüstes erreicht werden kann. Bei Mischungen über dem optimalen Bindemittelgehalt wird der Porenfluidüberdruck durch Druckmessungen im Mörtel nachgewiesen. Für den Strassenbauasphalt ist erstmalig zur numerischen Simulation das aus Karlsruhe stammende, mit der „intergranularen Dehnung” erweiterte hypoplastische Stoffgesetz herangezogen worden. Den Schwerpunkt der Arbeit bildet die Bestimmung der hypoplastischen Stoffparameter und die Überprüfung des gewählten Stoffgesetzes durch Nachrechnung von zyklischen Einfachscherversuchen und Triaxialversuchen. In einer selbstentwickelten Torsionszelle wird durch unmittelbare Messung gezeigt, dass der Bitumengehalt über dem Optimum die Schubsteifigkeit verringert. Die Triaxialversuche beweisen die Möglichkeit des Eintretens der zyklischen Mobilität und dadurch die extreme Neigung zur Spurbildung. Diese Messungen beweisen die praktische Bedeutung des optimalen Bitumengehaltes. Das positive Ergebnis der Überprüfung des genanntes Stoffgesetzes liefert die theoretische Unterstützung der experimentellen Ergebnisse. Diese können als Grundlage einer neuen Perspektive in der rechnerischen Prognose sowie beim Entwurf und bei der Herstellung von Asphaltmischungen dienen.