Dissertations / Theses on the topic 'Relationship between tectonics and relief'

Le Delta du Niger a été utilisé comme un cas d’étude pour les relations en offshore profond entre tectonique, surpression et migration verticale des fluides. L’intérêt a été porté sur la partie Est du Delta du Niger, couvrant le bloc OML130/OPL246, où le déplacement des niveaux de décollement donne des structures de type « toe-thrust ». L’approche utilisée intègre l’interprétation sismique, les analyses de surpression, l’analogue de terrain des grès d’Annot (dépôts turbiditiques marins profonds situés dans la partie externe de la chaîne alpine externe) et la modélisation structurale. Les indices de migration au niveau du fond marin du Delta du Niger ont été classifiés. Ils sont liés à des conduits structuraux et à des couches sédimentaires intermédiaires. La nature de ces fuites, leur apparition au toit d’horizons, ainsi que leur contenu géochimique ont permis une première datation de génération de surpression dans les réservoirs et dans les niveaux argileux très profonds. Avec les données de puits (pressions in-situ, températures, rivés de COT et Rock Eval de la roche mère) et avec les horizons interprétés sur les marqueurs sismiques régionaux, la modélisation du bassin a conduit à une mise en relation entre mouvements de raccourcissement tectonique, enfouissements, générations d’hydrocarbures, piégeages et des pertes éventuelles. Le modèle conceptuel « layer-by-layer » de dissipation de pression de fluides est proposé pour expliquer le rôle des failles chevauchantes dans les compartimentations verticales et latérales des surpressions, et pour comprendre comment les roches de couverture sont faillées par ces chevauchements puis plissées. La conséquence est deux types de fuites majeures à l’échelle régionale : à travers les failles chevauchantes ou à l’aplomb des anticlinaux. Le contrôle de rétention à l’échelle du réservoir se fait par les autres types de fuites le long des failles d’extrados, par capillarité ou par perméabilité. Les simulations en laboratoire de compaction et décompaction ont permis de mieux contraindre les variations de perméabilité en fonction des contraintes, et d’évaluer les mécanismes d’écoulement dans les zones de failles synsédimentaires affectant les réservoirs turbiditiques. Il a été montré, avec des cas pratiques, que le taux et la quantité d’écoulement des fluides à travers ces failles peuvent être modélisés. Cette étude montre que la tectonique gravitaire amène une création d’espace d’accommodation dans les synclinaux et la génération et la transmission de surpressions vers les flancs des anticlinaux, instaurant alors une migration verticale d’hydrocarbures. Ce constat a des conséquences sur le piégeage des hydrocarbures dans les « toe-thrusts », d’autant plus lorsque la tectonique est encore active et qu’elle se fait par épisodes. Ainsi, ce travail a conduit à une amélioration des méthodes d’évaluation de rétention des hydrocarbures, mettant en lumière l’inadaptabilité d’utilisation des contraintes régionales aux réservoirs locaux dans le cas de subsidences différentielles ou d’enfouissements inhomogènes. Cette amélioration est possible grâce à une méthode intégrée. Elle consiste à identifier et à prendre en compte (1) les types de scellements stratigraphiques et structuraux, (2) les types de systèmes dynamiques en raccourcissement contrôlés par les étapes de déformation : fuite à l’ouverture de failles pendant le chevauchement actif et surpression au niveau des anticlinaux à cause du scellement des failles inactives, (3) la chronologie des systèmes pétroliers entre la maturation de roche mère, la génération de surpression et le chargement des hydrocarbures par rapport au moment de la compartimentation/structuration du réservoir et (4) la combinaison des facteurs de perméabilité, de capillarité et de composition des zones de failles pour évaluer l’écoulement statique et dynamique dans les zones de failles à l’échelle de ces réservoirs. Cette méthode intégrée permet une meilleure prédiction des pièges d’hydrocarbures et limite le risque dans ces structures complexes de chevauchements en surpression dans le deep offshore<br>The Niger Delta was used as a case study in the investigation of the relationship between tectonics, consequent pressure build-up, and vertical fluid leakage in the deep offshore. The attention was focused on the eastern part of the Niger Delta, covering the OML130/OPL246 block, where the detachment translates to distal toe-thrusts. An integrated approach, using seismic interpretation, geopressure analyses, field analogue (The Annot Sandstone – external alpine deep marine turbiditic deposits) and structural modelling, was adopted. The seabed leakage features in the Niger Delta case study were classified and linked to structural conduits and intermediate sedimentary carrier bodies. The nature of the leakage types and their emplacement on ancient seabeds, as well as their geochemical content, helped in the preliminary analyses of the timing of overpressure generation in the reservoirs and deeper shaly levels. With present day well data (in-situ pressure, temperature, derived source rock TOC and Rock Eval), and with the horizons interpreted from seismic markers tied to the regional chronostratigraphy, further basin modelling related the tectonic shortening and burial to hydrocarbon generation, trapping and eventual leakages. A conceptual layer-by-layer fluid pressure dissipation model is proposed to explain the role of thrust faults in vertical and lateral geopressure compartmentalisation, and how major lithological seals are offset by these thrusts and later folded. This results in major up-thrust fault and anticlinal leakages, which are the major leakage processes at regional scale. Other types of leakages, including migration laterally along the crestal collapse faults, capillarity and permeability within fault zones, are emphasised for estimating the retention at reservoir scale. Laboratory simulation of compaction and decompaction was used to better constrain the permeability variation with changing stress conditions and the flow mechanisms in the syn-sedimentary fault zones affecting such turbiditic reservoirs. It has been shown, with practical cases, that the rate and amount of leakages through these faults can be modelled. The work has shown that the creation of local synclinal accommodation space, high overpressure generation and weak anticlinal uplift relate gravity controlled tectonics to vertical hydrocarbon leakage. This has a consequence on the hydrocarbon trapping at toe-thrusts, especially as the tectonic events are still active and episodic. A proper evaluation of these major thrusts and the secondary crestal collapse faults was carried out. This helped in the improvement of seal evaluation methods, highlighting the inadaptability of the use of regional stress trends for local reservoirs in cases of differential subsidence or inhomogeneous burial. The improvement was made possible by the use of an integrated evaluation approach. This identifies and takes into account (1) the stratigraphic and structural seal types, (2) the stage of deformation controlling the dynamic system: active thrust faults leaking due to fault opening and inactive faults where pressure may be building up within the related anticlines, which propagated above thrust tips, (3) timing of the petroleum system – source rock maturation, overpressure generation and hydrocarbon charging with respect to reservoir compartmentalisation/trap formation and (4) the combination of factors such as permeability, capillarity and fault zone composition in constraining static and dynamic fluid flow in fault zones affecting these reservoirs. This integrated approach was found to be better for predicting the nature of the hydrocarbon traps at the problematic overpressured toe-thrust prospects in this deep offshore zone

Identifying tectonically active faults and quantifying rates of movement is a key challenge in the Earth Sciences, in addition to this the interactions between active faulting and the landscape, specifically involving the fluvial network, is a relatively new area of study. Previous work has highlighted the value of understanding how the fluvial network responds to active tectonics, showing that a comprehensive understanding of the dynamic relationship between fluvial geomorphology and active tectonics is an important next step in geological research. This study presents new information about the poorly constrained Quaternary tectonic history of the Gediz Graben, Turkey, providing the first quantification of rates of movement of the key fault array that presently controlling graben topography. The fluvial network has been investigated and the data has been used in order to add resolution to the tectonic history for the fault array, allowing for the quantification of post-linkage throw rates. The study then investigates the key controls on the behaviour of the fluvial network that cross the active topography building fault array in the Gediz Graben. This study shows that there has been a linkage event occurring between 0.6 – 1 Ma, involving the three segments of the graben bounding fault array. The pre- and post-linkage throw rates are then extrapolated using data derived from the fluvial network, showing a faulting enhancement factor of 3 at the centre of the fault array, with the throw rate at the centre of the array predicted to have increased from a pre-linkage rate of 0.6 ± 0.1 mm/yr to a rate of 2 ± 0.2 mm/yr. This research provides evidence that the fluvial network can be used in conjunction with other types of evidence to provide a greater resolution tectonic history. Using both digital data and field studies this research presents an examination of the factors that influence the behaviour of bedrock rivers undergoing perturbation due to tectonics. Factors such as drainage area, tectonic throw rates and lithology have been investigated and the complicated interactions of these variables with the fluvial system have been quantified. This study shows that the bedrock rivers are a significant source of information about tectonics, but further work is needed to resolve quantitatively how various factors influence how rivers adjust to tectonic perturbation, in a variety of tectonic situations, in order to enable river to be used as a primary tool for deriving information about tectonics.

The largest earthquakes on Earth take place on the megathrusts of subduction zones, but the slip behavior of megathrusts is variable. This thesis considers why by conducting local, regional and global studies of the interrelationships between the structure and seismogenic behavior of subduction zones. New marine geophysical data collected from the collision zone between the Louisville Ridge seamount chain with the Tonga-Kermadec trench constrain overthrusting and subducting plate structure. Mo'unga seamount is identified beneath the outer-forearc, which calibrates the association of residual bathymetric anomalies and subducting relief, implies an E-W geometry for the subducted ridge and suggests the 200 km wide Louisville seismic gap is modulated by the sediment filled flexural moat. Spectral averaging is then applied along the Tonga-Kermadec margin and along strike variations in overthrusting plate structure are verified by wide-angle seismic transects. The remnant Tonga-Ridge occupies the inner fore-arc and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5&deg;S), width (110&pm;20 km) and strike (~005&deg; south of 25&deg;S). Plate tectonic reconstructions suggest the Lau Ridge is unmodified by subduction related erosion, &lt;200 km of the Tonga Ridge has been eroded, and neither ridge ever occupied the southern Kermadec arc. Crustal thickness variations are thus inherited, reflecting the Cenozoic tectonic evolution of the Tonga-Kermadec-Hikurangi margin. Spectral averaging is finally applied to all subduction zones on Earth. Part one develops a global catalogue of subducting relief, which is compared with seismological and geodetic inferences of fault-slip behavior. Most seamounts are aseismic, relatively undeformed and observations are not consistent with mechanical models proposing full-decapitation. Aseismic ridges are also associated with megathrust complexity, but are of a larger wavelength and contrasting mode of isostatic compensation. Part two shows almost all intra-margin along-strike transitions in seismogenic behavior are related to pre-existing crustal structure. A paired forearc anomaly is interpreted consisting of a trench-parallel ridge landward of the deep-sea-terrace basin. The ridge crest correlates with the down-dip limit of coseismic slip and strong interplate coupling, the up- dip limit of tremor epicentres, and is interpreted as defining the boundary between the velocity-weakening and seismogenic portion of the subduction interface and the down-dip frictional transition zone. Paired anomalies may be attributed to unrecovered interseismic elastic strain, the preferential subduction erosion of the outer-forearc and/or underplating beneath the inner forearc.