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Caractérisation et modélisation des écoulements fluides en milieu fissuré.
Relation avec les altérations hydrothermales et quantification des paléocontraintes.

Abstract : In all materials (rocks, concretes, ceramics, ...), the presence of fractures at different scales implies high permeability and often oriented fluid flows. These fluid circulations in fractures induce more or less intense fluid-rock interactions with mineral crystallisation and/or dissolution. These phenomena directly depend on the nature of the fluids and the rocks, the physical and chemical properties of the media and the rate of fluid renewal (permeabilities).
Usually, the development of such alterations leads to a massive sealing of the fractures (vein alterations) and of the fissures (fluid inclusion planes and microcracks, pervasive alteration). Therefore, their study brings us precious indications for the understanding of the mechanisms of fluid migrations in fossil systems.
A geometrical study of the fracture systems at micro or macroscopic scales, based on the spatial distribution of sealing minerals, is applied to two different granites: the Soultz-sous-Forêt granite (Bas - Rhin, France) and the Brézouard granite (Vosges, France). At the macroscopic scale, a new graphical method is proposed in order to study drilling data (Soultz granite). It allows to identify the presence of three independent mineral associations (quartz - illite, calcite-chlorite and hematite) in independent fracture systems characterised by a specific 3D geometry and hydraulic properties. These three types of vein alteration correspond to distinct and non contemporaneous fluid percolations.
At the microscopic scale, the reconstitution of crack opening - fluid percolation – crack sealing stages is delicate. However, the study of their geometrical characteristics (orientations, radius, volumic densities) and thereby the quantification of their porosities, exchange surfaces and permeabilities, allow to identify their respective roles in the fluid propagation. These microstructures, which are very numerous in granites, imply high but variable matrix permeabilities. This has been confirmed by the modelisation of the space-time evolution of the Brézouard granite crack permeability during fluid-rock interactions.
The two used permeability models (geometrical or statistical) remain very dependent on the definition of the characteristic opening of fracture or fissure. Real fractures in a rocky mass are characterised by non parallel, flat and thus overlapped walls. The study of these natural fracture surfaces at micro and macroscopic scale is completed by a theoretical modelisation of their hydro-mechanical behaviour. This work indicates the influence of the surface roughness on the fluid flow as well as the propagation of the alteration.
These fractures were formed and percolated under a particular tectonic regime that controls their orientation. Numerous quartz veins in the Soultz granite are opened and sealed during the Oligocene extension. The characteristic fluid pressure of these opening - sealing stages are quantified thanks to fluid inclusion studies. These inclusions are located in secondary quartz which seal the veins. A new method of paleostress quantification is proposed, based on the knowledge of this fluid pressure. It takes i) the geometrical distribution of the vein poles, ii) some empirical considerations of rupture criteria, and iii) the fluid pressures into account.
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https://tel.archives-ouvertes.fr/tel-00011716
Contributor : Judith Sausse <>
Submitted on : Thursday, March 2, 2006 - 5:35:30 PM
Last modification on : Wednesday, November 4, 2020 - 1:56:02 PM
Long-term archiving on: : Saturday, April 3, 2010 - 8:55:38 PM

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  • HAL Id : tel-00011716, version 1

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Judith Sausse. Caractérisation et modélisation des écoulements fluides en milieu fissuré.
Relation avec les altérations hydrothermales et quantification des paléocontraintes.. Géologie appliquée. Université Henri Poincaré - Nancy I, 1998. Français. ⟨tel-00011716⟩

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