How Seismic Ray Trace Modeling Can Enhance the Interpretation of Seismic Data from Complex Subsurface Structures: An Example from the Wichita Mountains Frontal Zone, Southern Oklahoma

Jan M. Dodson, Roger A. Young, and Kevin J. Smart
School of Geology & Geophysics, University of Oklahoma, Norman, OK

The Wichita Mountain Front (WMF) is part of the linear trend in southern Oklahoma that extends from the Arbuckle Mountains in south central Oklahoma through the Wichita Mountains to the buried Amarillo Mountains in the Texas Panhandle. Intense subsurface deformation exists along the WMF, including overturned beds and crystalline basement rocks thrust over Paleozoic sedimentary rocks. Dipmeter data indicate 180^o changes in dip direction. Correct migrations of seismic data are vital to accurate interpretations, but they cannot be achieved without well-defined velocity models. Velocity models are in turn based on interpretations of the data. Seismic ray tracing can confirm or discredit an interpretation. Accurate interpretations are a prerequisite to improving exploration successes.

A synthetic seismic data set paralleling an actual seismic line was created with ray-tracing software by building a viable cross section using all available data, including well data and seismic data. X, Z horizon coordinates, layer velocities, and ray propagation parameters (such as attenuation coefficient, and generation of shear or compressional rays) are specified. Ray paths were calculated and analyzed to determine where reflections occurred in the subsurface and their corresponding CMP location. Arrival times and reflection amplitudes were convolved with a wavelet to produce synthetic traces for comparison to actual seismic data.

Two alternate velocity models were constructed to demonstrate that a lack of data, or an inaccurate interpretation produce ambiguous results. The synthetic data set was migrated with the exact velocity grid used to create the data and then the data set was migrated with the alternate velocity models. Comparing the three resulting migrations to the actual seismic data confirmed that the more accurate migration velocity model produced the clearest result. The most accurate migration, however, still does not accurately position all reflection events.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas