Seismic Data Processing for Amplitude-Versus-Offset Analysis
Jeffrey R. Resnick
Analysis of how seismic reflection amplitude varies with source-to-receiver offset or with reflection angle often can yield information about lithology or fluid content. The objectives of data processing are to faithfully extract such information and simultaneously to attenuate noise, ground roll, or other interfering energy. Data processing for amplitude-vs.-offset (AVO) or amplitude-vs.-angle (AVA) analysis requires a delicate balance between two extremes. If data are insufficiently processed, the results suffer from excessive noise contamination; if data are overprocessed, noise may be attenuated at the cost of damaging or distorting the desired signal.
A land data example illustrates how that balance has been struck in a particular case. The target zone in the example is a bright spot located in a sand-shale environment at a two-way traveltime of 2.0 sec. A well drilled after the data were processed encountered gas at the target level. The processing flow included geometric spreading correction, f-k filtering of shot records, surface-consistent deconvolution, surface-consistent statics removal, normal-moveout correction, trip statics adjustment, residual amplitude compensation, bandpass filter application, and conversion from offset to angle. Data viewed both before and after stack at several intermediate stages of processing reveal a step-by-step improvement in signal-to-noise ratio. After processing, the amplitude of seismic refle tions at the target location increases with offset, and the amplitude of reflections adjacent to the target zone exhibit a gradual decay with offset. Other lines may require additional or different processing steps. Nevertheless, this example illustrates the merits of a relatively straightforward flow in preserving signal and attenuating noise.
AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.