Constrained Migration Velocity Analysis - A Case Study in the German Molasse Basin

Abstract

Summary Seismic exploration of geothermal resources in the German Molasse Basin (GMB) requires a proper seismic imaging of deep productive horizons. Success of this process is heavily reliant on the correct estimation of seismic velocities by migration velocity analysis (MVA). However, the MVA has a high computational cost and, depending on the quality of seismic data and approach chosen for the analysis, it might produce erroneous results. In this work, we developed an MVA workflow that enables to create a velocity model that is consistent with seismic, geological and borehole data, despite the limitations inherent to the MVA. A 2D seismic data set acquired in the GMB was used to test the MVA. The results were evaluated based on four criteria: increase in seismic resolution, availability of good quality reflectors beneath velocity components, geological plausibility and consistency with borehole data. Such an interpretive approach to the initially purely processing procedure allowed to discriminate genuine velocity components from erroneous components. Our work shows that the MVA produces an accurate velocity model of the subsurface, if the data have good quality, sufficient cable length, and geological constraints in form of lithological and velocity logs from boreholes in the vicinity of a study area.