LANDWER, WILLIAM R., Neidell and Associates, Houston, TX
To interpret conventionally processed seismic data in general one assumes a "near-zero" minimum phase display and/or reverse polarity with respect to recording tape conventions. Such phase relationships based on seismic and well log data tying only in time/depth is however largely not achieved at least initially. In fact, interpretive judgements often prove misleading without first performing a constant phase rotation back to "log-normal" thru interaction between seismic data processor and interpreter using synergistic exploration criteria for reconciling differing data sets, their event character, and in particular for applying color inversion. As we try to identify prospective data characteristics with other proven field analogs, or seismically modelled geologic constructs that pres mably represent an appropriate subsurface, the composite seismic wave form arising from multi-layer interference patterns also plays a variable role affecting our selection of true zero phase.
Evident phase distortions post "state-of-the-art" reprocessing commonly range to 270 degrees in the real world as noted by our examples, and the data should therefore be corrected by some constant phase rotation after appropriate considerations of geological criteria made both by the processor and interpreter. Reservoir sand imaging in the Gulf Coast tertiary illustrates this point as shown here for three distinct reflectivity Zones (I, II & III) regarding wet sand impedances versus their contemporary shale counterparts. These also serve to illustrate how seismic interpretation can be enhanced by achieving the proper seismic phase relation with available well logs and other known subsurface criteria for the purpose of reducing exploration risk.
AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.