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.

In view of the increasing scarcity of energy resources, wells are being drilled to progressively greater depths for the production of liquid and gaseous hydrocarbons. Consequently, the drilling equipment is being subjected to higher temperatures and pressures. Economical exploitation of the reservoir is possible only with the application of drilling and completion methods which do not damage the formation. The damage potential of drilling fluids and treatment fluids is assessed on the basis of return permeability tests. For obtaining more conclusive results from return permeability tests and for increasing the reliability of their interpretation in the future, systematic investigations on the reproducibility of the results were of special importance. In the course of this third project phase, several return permeability tests were performed on each of two different model cores under constant conditions in the circulation system constructed at the institute. On the one hand, Obernkirchen sandstone was employed as model material; on the other hand, a synthetic material consisting of sintered borosilicate glass was used for the other model core. At least five tests were performed on the model core of each material, in order to evaluate the results for their reproducibility. A further important task was the selection of a suitable core material for future tests.