Role of Synthetic Seismograms in Exploration for Upper Ismay Algal Mounds, Paradox Basin

Jan A. McCutcheon

Synthetic seismograms have traditionally been used primarily to tie in a particular geologic top to a seismic section. If applied solely in this manner, the synthetic is underutilized, especially in basins where seismic stratigraphy is used extensively. In fact, with a little ingenuity, synthetic seismograms can give an interpreter insight into which seismic picks are consistent and suitable for mapping, the geologic significance of amplitude variations, and how to estimate reservoir quality and thickness from seismic sections. The key to this approach is to generate as many synthetics as possible, making them as consistent as possible, and then, integrating the geologic information, to analyze them as a package.

A synthetic study was undertaken in the Ismay fairway of the Paradox basin, southeastern Utah. Synthetics were generated for both producers and dry holes and were analyzed, as a group, for consistency of the geologic picks. The upper Ismay, lower Ismay, and Desert Creek picks were the most consistent, while the intervening Hovenweep and Gothic shales were the least consistent. Isochrons, based on consistent picks, were calculated from the synthetics and plotted against the corresponding isopach. Results indicate that a linear relationship exists, allowing for conversion of seismic data to isopach. Error analysis can quantify the significant contour interval. By highlighting producing wells from dry holes, it is apparent that there is a critical isochron value needed for production.

Further analysis indicates that amplitude can be used in estimating reservoir quality and that it is possible to estimate carbonate thickness from the isochron.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.