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Habilitation à diriger des recherches

Contribution à l'étude thermomécanique des cavités réalisées par lessivage dans des formations géologiques salines

Abstract : Fruit of about thirty years of experience in the research field of salt caverns, this dissertation presents succinctly the industrial problem at the source of my research. Whatever the considered theme, salt production through the dissolution of rock salt or underground salt cavern storage, the industrial problem open the way for many research axises in different disciplines relating to the study of geomaterials with a particular thermo-mechanical coupling problem in elasto-viscoplastic material submitted to finite transformations. The part "Mechanical behaviour of rock salt" points out the basic concepts of solid material constitutive behaviour and highlights two ongoing difficulties regarding the specific rock salt behaviour. The first one deals with the end effects during the classical laboratory tests. This problem can distort the determination of constitutive laws that govern the rock damage and failure (non desirable stress heterogeneity phenomenon within the sample). An approach, already presented by the author,is used in order to demonstrate the fact that the same laboratory data concerning the rock salt dilatancy phenomenon can be interpreted with a rheological model which assume that damage can starts when one of the principal stresses is tensional. The second difficulty is related to the restricted character of the validity range of some classical behaviour laws that were proposed to describe the ductile behaviour of rock salt and in particular to the stress variations range (low deviatoric stress range). This phenomenon concerning the rock salt behaviour under small deviatoric stresses is already known. In this work, it will be illustrated by an original theoretical example. The Chapter "Modelling of underground structures", highlights the interest of 1D modelling approaches (although geometric simplifications) and draw the attention on the fact that a rheological model which represents badly the behaviour under small deviatoric stresses can lead to results well different from what happens in-situ. This problem was already known but deserved that one insists on it by presenting an example which can be declined under various alternatives. In the context of thermo-elasto-viscoplasticity, it is possible to explain the strong influence of small deviatoric stresses on the cavern volume variation. Furthermore, a simple methodology of taking into account the mechanical aspect during the cavern leaching phase is presented. We reconsider then the problem of the mobility of the cavern boundaries during the leaching phase in the chapter "Leaching phase modelling" but in this case with thermal aspect. Indeed, software which model the physico-chemical dissolution phenomenon need, as an input parameter, the cavern temperature with a good accuracy. For the moment, tackling the general thermal problem (2D or 3D) is relatively difficult. However, we can get round this difficulty by using a model that mix artfully 1D cylindrical approach around the well, 1D spherical approach around the cavern and 0D approach for the fluid within the cavern. An original method for the choice of the spherical model is described. Its use for a real gas storage cavern case is encouraging.
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Habilitation à diriger des recherches
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Submitted on : Friday, November 6, 2009 - 3:31:41 PM
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Michel Tijani. Contribution à l'étude thermomécanique des cavités réalisées par lessivage dans des formations géologiques salines. Planète et Univers [physics]. Université Pierre et Marie Curie - Paris VI, 2008. ⟨tel-00430361⟩

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