- Copyright © 2001 Society of Exploration Geophysicists
Historically, the Pennsylvanian Morrow Formation has been a challenging target for conventional, compressional wave (P-wave) seismic acquisition. A relatively small acoustic-impedance change associated with the thin, productive sand targets has rendered P-wave data a marginally useful, but not definitive, tool in these regions. To address this problem, three land 3-D/3-C surveys were acquired to investigate the use of modeconverted shear waves (PS waves) in defining and describing these sand channels. The three surveys, although located in different basins, represent a progression in our understanding of survey design, processing, and interpretation using multicomponent reflection seismic.
When applied to PS waves, conventional interpretation techniques such as amplitude or isochron mapping are often adequate to analyze the data. In some cases, however, more specialized tools may be required. Akey concern for all the surveys was the correct correlation of events between P-wave and PS-wave volumes. In some situations, the character of the geology was sufficient to make a good visual tie. In others, more subtle indicators were used to make the correlation. Correlation-based VP/VS analysis techniques can provide more detail and can highlight subtle features missed by subjective interpretation methods. The time-to-depth correlation difficulty also emphasizes the value of additional information such as P-wave and shear-wave (S-wave) sonic logs or VSP surveys, which were not generally available. Although interpretation results for these surveys are preliminary, each shows significant promise in the use of PS waves.
The three surveys in this study were recorded in southwestern Kansas, the Panhandle of Oklahoma, and south-eastern New Mexico (Figure 1). Although quite separate in location, they share a common target reservoir within the Morrow Formation. The Morrow is Pennsylvanian in age and primarily a shale unit with interspersed sand accumulations along with oolitic limestones and coals. Target …