Improved Seismic Stratigraphic Interpretation with VSPs and Well Logs

Carl K. Poster

The addition of Vertical Seismic Profiles (VSPs) and well logs to coinciding surface seismic data improves resolution and interpretation away from the well, of formations encountered at the well. The positioning of further delineation wells, the interpretation of stratigraphy between wells, and the interpretation of stratigraphic changes near a well, benefit from the rigorous use of these data.

The VSP, when parallel-processed with the surface seismic data, accurately indicates the location in time of the well on the seismic section, both laterally and vertically. The VSP also permits the time-scaling of the log data to match the seismic data. Thorough interpretation of these logs produces formational models, which include in situ lithology, porosity, hydrocarbon distribution, and the zoned reflectivity corresponding to formation boundaries. This reflectivity is used to estimate a wavelet filter from the seismic data, which, combined with the log's reflectivity and the measured relationship of acoustic impedance to porosity, permits accurate modeling of stratigraphic changes away from the well.

The wavelet can also be used to compute zero-phase filters for improving the resolution of seismic reflections near the well. The use and interpretation of complex trace attributes, envelope and instantaneous phase, is seen to be improved after zero-phasing.

Examples from major reservoirs in the Middle East, including the Mishrif reefs and other carbonate formations, illustrate the reconciliation of log and seismic data and improved stratigraphic interpretation between wells.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.