Use of VSP to Enhance Surface Seismic Processing
T. J. O'Rourke
Many exploratory successes in Mediterranean basins have been guided by the seismic location of structures. Continued exploration (and delineation) efforts must search for smaller, more subtle indications which may be obscured on seismic data by the effects of multiples, attenuation, and velocity errors. By introducing vertical seismic profiles (VSP) and well-log information, the processing of existing seismic data can be fine tuned, often improving resolution and correlation.
With VSP measurements, velocities used in the stacking process can be verified. When events are dipping, the potential errors in converting stacking velocities to interval velocities for migration are avoided by using directly measured VSP interval velocities. This may affect fault positioning and closure. Frequency-dependent propagation effects are removed with an inverse Q-filter, computed from the VSP data. This compensation often boosts resolution.
The response from surface seismic, VSP, and logs should be the same around a well. Differences are often due to variations in the source wavelet, which can be reconciled by matching both the frequency and phase of the wavelets or converting all results to zero phase. Sections of different vintages can be matched with the same method. After matching, inversion is constrained to match the VSP and logs at the well. This provides low-frequency control and gives a sensible correlation with formations. Introducing VSP and well-log information while reprocessing existing surface seismic data can often provide a cost-effective solution to the problems encountered in stratigraphic or development geophysics.
AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.