4D Processing for OBS
Repeatability is fundamental to time-lapse processing and depends on a robust processing workflow. Two PGS proprietary techniques, Complete Wavefield Imaging and SWIM, are ideal for full azimuth, wide aperture, broad bandwidth OBS datasets.
Repeatability is fundamental to successful time-lapse or 4D processing. An important component in this is a robust 4D compliant processing workflow that establishes confidence in the observed 4D signatures.
Essential key processing steps to ensure a high level of repeatability include advanced statics, 4D binning, and matching filter solutions.
The interplay of optical sensor technology, accurate acquisition and advanced processing solutions mean PGS Optoseis® installations achieve lower than 3% normalized RMS difference (NRMS). This level of repeatability enables the detection of weak 4D signals in complex reservoirs over short time-lapse repeat cycles, all in pursuit of providing critical reservoir information in time for making development decisions.
The following key steps are essential to ensure a high level of repeatability:
- Statics are caused by changes in the water column between time-lapse surveys. PGS corrects static shifts between the various surveys with a combination of proprietary tools and methodologies.
- 4D Binning: Time-lapse surveys can be binned simultaneously to ensure geometric repeatability by matching the source positions and offset distribution. Several binning attributes can be used, such as azimuth, offset, signal to noise ratio, quality factor from regularization and metrics such as seismic similarity found by minimizing NMRSD between pairs of traces, or by maximizing their cross-correlation.
- Matching: PGS designs matching filters using smoothed and stabilized spectral division in either the frequency or time domain. This offers flexibility in terms of spectral smoothing and multiple global filter options. When facing significant variations of the signal to noise ratio between surveys, we can perform signal-only matching.
Complete Wavefield Imaging (CWI) is a proprietary PGS technique that integrates advanced velocity model building and depth imaging, utilizing primaries, multiples, and refractions. It is ideal for full azimuth, wide aperture, broad bandwidth PRM datasets.
Separated wavefield imaging (SWIM) using higher-order multiples recorded with multi-component ocean-bottom receivers in deep water can significantly increase the footprint of the seismic image from a PRM array.