Sibylle Mayr Livres

In the frame of the DGMK-Project 741-2 we contribute to the understanding of the stress dependency of anisotropic seismic velocity as background for seismic forward modeling (e. g. constuction of macro model for imaging) and the interpretation of seismic data with respect to pore pressure, effective stress tensor and lithology. We use the physically based porosity deformation approach for description of compliances in dry or drained anisotropic rocks. We improved the predictability of velocities by e. g. accounting for stiff porosity next to compliant porosity. We include the description of non-diagonal elements using the assumption of anellipticity and of an isotropic piezosensitivity tensor. We performed and explained supporting experiments under uniaxial loading conditions using various types of room dry sedimentary rocks with VTI and originally HTI symmetry. Furthermore we investigated the impacts of pore fluids in a sandstone and a fine grained posidonian limestone. The main effects are the Gassmann effect and local fluid flow. We conclusively explained our measurements in the fully saturated sandstone by combining velocity predictions by means of the porosity deformation approach in drained rocks with classical poroelastic models. Additionally measurements in shales under hydrostatic and triaxial loading conditions have been performed in cooperation with an external company and subsequently evaluated.

The project aimed to describe the dependency of seismic velocity in anisotropic siliclastic rocks as background for interpretation of seismic data with respect to effective stress and lithology. We use the tensorial porosity-deformation approach for anisotropic rocks (originally piezo-sensitivity theory, Shapiro 2003; Shapiro and Kaselow 2005) and give an adapted formulation for vertical and horizontal transverse isotropic rocks under uniaxial and triaxial loading conditions. By using the porosity-deformation approach the number of free parameters is reduced compared to phenomenological fitting of data. With this theory we explain literature data of compliances measured in a shale sample during a multistage pseudo triaxial experiment. The obtained model parameters from fitting the hydrostatic part are used for the prediction of the compliances describing the S-waves in the triaxial part of data. Furthermore, we developed further an experimental setup and are now able to measure complete sets of velocity for the description of transverse isotropic and orthorhombic rocks. The new data reveal new aspects of the stress dependency of anisotropy parameter. The applicability of the theory on the new data and on previously obtained incomplete datasets is shown, including the reconstruction of velocities.