Schlumberger

General Deterministic Water-Layer Demultiple (GDWD)

Overview Library

Effective attenuation of shallow-water-layer multiples

Data-driven demultiple approaches such as surface-related multiple elimination (SRME) are negatively affected by lack of near-offset information and the limitations of first-order approximation, resulting in poor predictions of strong water-layer reverberations.

Improving clarity of North Sea data - before multiple attenuationImproving clarity of North Sea data - after multiple attenuation

Move the slider to see how the subtraction of surface multiple energy predicted by GDWD and 3D GSMP general surface multiple prediction methods has significantly improved the clarity of this North Sea data. (Data example courtesy of Statoil).

General deterministic water-layer demultiple (GDWD) is a model-driven method that provides a solution and offers numerous advantages. Although primarily used in shallow-water marine environments (typically <200 m deep), where it is difficult to interpolate the near-offset traces needed for the 3D GSMP general surface multiple prediction workflow, the technique can also be used in transition and deep water.

  • It accurately predicts water-layer multiples for all complexities of bathymetry and subsurface structure. Only the seafloor map is required to compute multiples generated in the water layer.
  • It provides true-azimuth predictions.
  • The method is applicable for all marine geometries, including wide-tow and undershoot data.
  • The flexible workflow can be applied in conjunction with other multiple prediction techniques and algorithms that are based on multiple periodicity and apparent velocity discrimination, such as deconvolution- and Radon-transform-based methods.
  • It effectively attenuates water-layer peg-leg multiples while reducing the risk of primary attenuation compared with deconvolution-based methods.
  • The technique overcomes the limitations of first-order approximation methods (such as SRME) when predicting higher-order water-layer multiples.

Built-in flexibility for wider scope of applications

GDWD is able to model complex water-bottom multiples and water-layer peg legs accurately in a single application. Separation of the recorded multiples from the seismic data is simpler and less aggressive than conventional data- and model-driven methods. GDWD can be combined with other tools to predict and attenuate all modes of surface multiples. It is often combined with 3D GSMP general surface multiple prediction, eliminating both water-layer-related and other surface multiples.

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