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Filtrage géostatistique de données géophysiques en vue de la cartographie de l’impédance d’une formation argileuse : exemple du Callovo-Oxfordien de Meuse

Abstract : In the framework of researches carried out by ANDRA (the French agency for nuclear waste), which aim at evaluating the feasibility of creating a repository of radioactive waste in the Callovo Oxfordian clay formation. This thesis studies two key steps to obtain a 3D image of the formation: its geometry and its internal heterogeneity. The geometry of the sedimentary formation is determined from seismic time picking along profiles. These profiles are oriented along two main directions. At the intersections, the values registered by two profiles are different. The low number of intersections does not allow a precise study of the spatial behavior of these differences; they are analyzed via the pseudo-cross-variogram. The variography analysis allows the choice of a coherent model for all the profiles, from which an estimation of the corrected time is presented. The internal heterogeneity is performed through the study of the impedance, a variable linked to the intrinsic properties of the rock. Two types of measurements are available. On one hand, the seismic impedance resulting from the geophysical inversion of the amplitude recorded along seismic reflection profiles is densely distributed in the area of interest. On the other hand, the impedance log, resulting from the product of rock density and P wave velocity, is known at only few wells. Bivariate spatial behavior along the vertical direction has allowed the formulation of the following hypothesis: each impedance measurement can be decomposed into a sum of a variable Z (common to both measures) and a residual specific to each measure. Under certain supplementary hypotheses, it is possible to estimate the common component along the seismic sections. Some complements to these studies are mentioned, for example the correspondence between geophysical and geostatistical methods or the consideration of uncertainty in the amplitudes.
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Danitza Aburto Mardones. Filtrage géostatistique de données géophysiques en vue de la cartographie de l’impédance d’une formation argileuse : exemple du Callovo-Oxfordien de Meuse. Sciences de la Terre. Ecole Nationale Supérieure des Mines de Paris, 2012. Français. ⟨NNT : 2012ENMP0012⟩. ⟨pastel-00716232⟩

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