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Linear inversion for source signatures from ministreamer data

Statoil, Trondheim, Norway

Corresponding author: lam@statoil.com

The first 20% of the full text of this article appears below.

Estimation of the source signature, an old and important problem in exploration seismology, is becoming even more important. Areas where this knowledge is potentially of great value are onboard source array QC, deconvolution, multiple attenuation, tying reflection data to wells, modeling and inversion, AVO analysis, reservoir monitoring, and analysis of marine multicomponent recordings.

In another article in this special section, Landrø discusses the motivation for recording data on a short streamer (typically 50 m) deployed below (typically 10–20 m) the source array to determine the far-field source signature. Landrø and Sollie (GEOPHYSICS, 1992) developed a nonlinear inversion method based on physical modeling of the bubble created by each air gun in the source array. At that time good numerical methods had been developed to model the pressure output in three dimensions from air guns. The modeling reproduced the main features in typical measured air-gun signatures.

"Ministreamer" data offer an attractive alternative solution to the source-signature estimation problem. Since these data are recorded outside the nonlinear, near-field zone of the source array, they allow a linear inversion of the acoustic wave equation for the effective source signature of each gun in the array (Amundsen, GEOPHYSICS, 1993). Thus, for an interacting array of air guns, the source array is treated as an equivalent array of independent, noninteracting monopole sources, each generating a spherical wave, as proposed by Ziolkowski et al. (GEOPHYSICS, 1992). Further, since the recording depth is 10–20 m below the source array, the relative motion between the bubbles emitted by the air guns and the hydrophones is insignificant in comparison with the source-ministreamer separation. The total source wavefield is simply the superposition of the pressure field from each gun, including the source ghosts from the air/water interface. The far-field signature of the source array . . . [Full Text of this Article]