Resistivity Logs for Seismic Calibration in Gulf Coast Frio Trend

J. Dennis Loren

Seismic interpretation is enhanced by generating log-based synthetic seismograms representative of actual and modeled conditions throughout an exploration project area. However, since acoustic transit time and bulk density logs are often unavailable, incomplete, or inaccurate, the resultant synthetic seismograms may correlate poorly with the observed seismic. The Frio trend along the middle Texas coast is one area where relatively few acoustic and density logs are readily available, in spite of numerous prolific fields and well penetrations. Accurate synthetic acoustic and density logs are derived from resistivity and sand fraction logs and are then used to generate (1) synthetic seismograms representative of actual and modeled conditions, (2) time/depth relationships, an (3) rock property and reflection coefficient trend curves with water, oil, and gas in the reservoir rocks.

Key steps in the synthetic log generation process include the creation of a sand fraction curve and the use of a learning set of quality logs representative of local conditions. The general algorithms, which have been developed and successfully applied to a wide range of Gulf Coast rocks, are calibrated to Frio rocks within a five-county area by means of the learning set. The application of the algorithms to additional control wells demonstrates the favorable comparison between the synthetic logs and the measured logs and enables the procedure to be applied with confidence to wells where acoustic and/or density logs are unavailable. The explorationist may then routinely use commonly available resistivity logs for seismic time/depth and amplitude calibration based upon actual or modele conditions.

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