FOLDS AND TENSION FRACTURES IN STRATIFIED ROCKS

Abstract : The first objective of this thesis is to contribute to the development of quantitative tools for an objective interpretation, based on mechanical equilibrium and material strength, of kink-folds and fault-related folds which are potential oil reservoirs. The second objective is to improve the prediction of fracture distributions in layered sequenceswhich control the permeability. Experiments and analytical results are presented on the onset, the development and the arrest of kink-folds and fault-propagation folds. The experiments, with a sequence of paraffin layers under compression, show the relation between the fracture distribution, the formation of damaged hinges and the development of kink-folds. The analytical results are obtained by combining simple geometrical rules with the application of the maximum strength theorem (limit analysis). It is shown how compaction bands, reverse faults and kinks are competing at the onset of a kink fold, depending on the initial dip of the layered structure and the burial depth. The same methodology is applied to the development of the fault-propagation fold which is shown to be potentially interrupted by thrusting, depending on the frictional properties of the various hinges. The second part presents experimental, numerical and analytical results on the extension of a block, composed of an analogue material (compacted gypsum), resulting from the stretching of its foundation. A linear relation between the bed thickness and the fracture spacing is observed at saturation. Saturation is linked to the delamination of the interface between the block and its foundation. The finite-elements calculations, based on plasticity theory, to produce strain localisation, confirms the competition between the delamination and the fracture process. The analytical approach, based again on the maximum strength theorem, provides a simple criterion to decide on the dominant mode of failure as well as a new relation for the fracture spacing. The last part of this thesis presents a new experimental device to create bending fractures. It is shown that layer thickness does not influence the fracture spacing under bending. To the contrary, this influence is remarkable if a combination of bending and stretching is applied.
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Theses
Mechanics. Ecole Normale Supérieure de Paris - ENS Paris, 2010. English


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Submitted on : Wednesday, February 9, 2011 - 11:01:57 AM
Last modification on : Wednesday, February 9, 2011 - 6:44:06 PM

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Günther Kampfer. FOLDS AND TENSION FRACTURES IN STRATIFIED ROCKS. Mechanics. Ecole Normale Supérieure de Paris - ENS Paris, 2010. English. <tel-00564546>

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