Seismic interpretation when short-period internal multiples are present

Abstract

Seismic waves propagating in sedimentary sequences that include thin beds with large acoustic-impedance variations develop a distinct signature called stratigraphic filtering (SF). The source wavelet transforms into a low-frequency bell-shaped signal at the front end followed by a high-frequency noise coda. These effects produce low-frequency reflections that are delayed and exhibit poor continuity — a consequence of the short-period internal multiples. Applying a high-cut filter to the seismic and multiple synthetics removes noise coda and improves their correlation. Now, the need for multiple suppression of long-period internal multiples is evaluated. Multiple generators are easily identified for the multiple suppression process with synthetics morphing from primary only to primary plus multiples. Likewise, the stretch produced by SF is easily determined by inverting the primary and multiple synthetics for impedance correlation. The reduction in frequency is not desirable in the final product, so the high signal-to-noise low-frequency portion is extended to high frequency in the time-frequency domain. These principles are part of an interpretation workflow applied in Cooper Basin, Australia, which has as many as 50 coal beds of Permian age. By suppressing the SF effects from the Permian coal beds, the quality of fault and stratigraphic interpretation increases for units within the older Warburton Basin below the coal beds.