Technical Paper: 3D Surface Related Multiple Elimination in the Presence of a Complex Water Bottom Geometry – A Case Study from offshore Nigeria

Society: SEG
Paper Number:
Presentation Date: 2009

In this case study, we look at some practical aspects of predicting and attenuating surface related multiples from a 3D dataset, acquired offshore Nigeria. The water bottom dips in a cross line direction giving multiples whose raypaths lie outside the acquisition line direction requiring a 3D surface-related multiple elimination (SRME) scheme. In common with 2D SRME schemes 3D SRME is performed in two phases: the first phase involves creating a multiple model for each target trace, the second phase involves adaptively subtracting the multiple model from the input data, usually using filters derived using a leastsquares approach. The first phase (multiple prediction) was performed using a new approach to 3D SRME described by Bisley, Moore and Dragoset (2005). The method, ‘3D General Surface Multiple Prediction’ (3D GSMP), enables a high quality 3D multiple prediction for surveys acquired in areas of complex geology and with irregular acquisition geometry. An important feature of this method is its ability to predict multiples at true azimuth, taking the true raypath of the multiple through the water layer into account, the sensitivity of multiple prediction to azimuth and other issues relating to 3DSRME are discussed by Moore and Bisley (2005). A more detailed description of the method is discussed by Moore and Dragoset (2008). Unlike other implementations of 3D SRME, minimal preprocessing was required, and the input data was not regularised, extrapolated to zero offset, or interpolated to harmonise the shot and receiver sampling intervals. The key parameters required for 3D GSMP include selection of aperture, and spatial sampling, which have an impact on effectiveness of the multiple prediction and the cost.

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