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 180o 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