Vertical Seismic Profiling (VSP) Survey Optimization for Imaging Fracture Zones over Geothermal Areas

A primary focus of geothermal seismic imaging is to map dipping faults and fracture zones that control the permeability and fluid flow. We simulated and processed acoustic synthetic data to optimize VSP survey layouts for mapping moderately to steeply dipping fracture zones over geothermal reservoirs. The geophysical models were based on the geothermal site at Soultz-sous-Forêts (France). It was found that fracture zones located at a borehole offset distance of about 300 m can be imaged accurately for a range of the different dips. Only 8 to 12 source positions were required for obtaining very good results. Adding further sources did not necessarily improve the results, but rather resulted in image distortions. Generally, large offsets between sources and the borehole are required for imaging steeply dipping interfaces. When such features cross-cut the borehole, they are particularly difficult to image.