Seismic Gather Conditioning
Most academic data in processed to optimize image quality for structural and stratigraphic interpretation, with little regard the preserving characteristic essential for successful seismic reservoir characterization. No matter how sophisticated the inversion logarithm, use of inadequately processed seismic data will severely impact the quality of the final interpretation.
As a consequence, seismic data con rarely be used «as is» for seismic reservoir characterization without substantial pre-conditioning. RSI use our Seismic Gather Conditioning toolkit to provide a complete suite of seismic data conditioning steps to optimize the quality of pre-stack and post-stack seismic data prior to use in impedance, AVO and seismic facies inversion application.Â
Similarly, Geophysical Well Log Analysis GWLA is used to condition well-logs used for seismic modeling and Well Tie analysis.Â
RSI Gather Conditioning may be applied to pre or post-stack seismic data and is composed of several interlinked steps:
Spectral Normalization with Offset
Gabor-Moriet Joint Time-Frequency Analysis (JTPA) is used to separate the frequency spectra of each gather trace into a specific number of sub-band. The sub-band are calculated using a running Gaussian form window which gives a slowly varying amplitude profile of each sub-band. Then each sub-band spectro is balanced against the corresponding sub-band of a user specified pilot trace within the gather. The primary advantage of this approach
two-fold:
- Â the Bandwidth of the gather at each time sample is determined by the pilot trace, and
- the total energy contained in each reflector a held constant by computing its energy envelope and requiring that the energy of all sub-band (after scaling) sum to the original energy envelope amplitude. This ensure that AVO character la not altered in this process.
Edge Preserving Smoothing
 This program performs «edge-preserving smoothing» in 3D, which is a methodology to enhance S/N by means of noise reduction. It works in the affect domain by resorting the pre-stack seismic volume into offset volumes. This acts to preserve AVO effect because smoothing do not take place between adjacent offset withing the gather. It considers spatial dip of coherent reflection so that frequency and continuity are preserved. The «edge-preserving» characteristics result from user-defined semblance cutoff so that summation and filtering do not occur across traces with different reflector characteristic (i.e. faults, angular unconformity, channel/ boundaries, etc.).
ALIGN – Prestack Data Alignment – different
A fundamental assumption made in AVO Inversion is that primary reflection event are horizontally aligned (flat) across each CDP gather. The presence of residual moveout, non-hyperbolic moveout, random noise, multiples, tuning effects, etc.  will violate this assumption and introduce noise (uncertainty) into the AVO results. The ALIGN moduleÂ
correct for various residual move out effect, resulting in a much improved AVO signature.
ALIGN flatters gathers based on a conditional minimization of a reflector’s least-square fit error by determining local statics shift on each gather trace. The «condition» that is minimized can be either semblance or AVO fit. Semblance is the most robust but it is only applicable for AVO Class 2 and III anomalies. AVO Class II phase rotations (especially those that are not full phase reversal) present a special problem that require great core in addressing. For this case, we minimize the fit error to either a Z-term Shuey or S-term Aki & Richards equation. These least-square solutions are less stable but are required where AVO Class Il anomalies are present or suspected.