Enhanced Velocity Modeling for a Geothermal Project in the Southern Vienna Basin – A Stacking Velocity Approach

Abstract

Velocity models can be build based solely on or from a combination of checkshots, VSPs, sonic logs or seismic stacking velocities. Depending on the information available, the method of building a velocity model can vary (using interval velocities, average velocities, layer cake model, V0-K method, models based on geostatistical methods ...). The advantages and disadvantages of these methods have been described by numerous authors. In the course of a geothermal project in the southern Vienna Basin, the problem of a time to depth conversion arose. In the area of interest, only six wells with checkshot-information were available and, therefore, the usage of a simple V0-K method or layer cake method was not suitable. Hence, the application of available seismic stacking velocities for velocity modeling was tested. The stacking velocities were converted into interval and average velocities using the Dix equation. These velocity values were then sampled into a geo-grid and spatially distributed in the grid using geostatistical methods. The stacking velocities were compared where checkshots or sonic logs were available. The result of this velocity modeling procedure was a 3D velocity cube that can be used to depth convert the seismic profiles and the interpretation from the time domain.