3D Multiple Attenuation in the F-XY Domain: A Case History from Abu Dhabi

Abstract

Multiples are successfully removed from seismic data to increase the signal-to-noise ratio in a 3D land dataset acquired in Abu Dhabi. The process aims at removing in user specified spatial-temporal windows only that multiple energy (surface or inter-bed), interfering with particular primary seismic events. The anti-multiple is designed in the f-xy domain and applied prestack, on constant offset time migrated data volumes. Subtraction of the multiple events from the original seismic data is shown to produce an improved subsurface seismic image that is more suitable for interpretation and attribute analysis. The ability to remove multiple events without affecting the primary signal is a crucial issue in seismic processing, as spurious energy at a target level leads to suboptimal images and adds uncertainty to reservoir characterization. The state of the art in attenuating multiple arrivals involves a two steps process. First the multiples are predicted via a data driven technique. Then the predicted events are matched to the multiples actually present in the data and removed with some matching filter. The removal assumes that the kinematics of the multiple events are correctly derived and that the prediction locates them correctly in time and space. The technique applied on the Abu Dhabi dataset focuses on a particular family of reverberating events that invade the target area. This is a marked difference with respect to general techniques that try to predict the whole multiple wavefield. The technique requires the strong impedance contrast that generates the multiple (surface related or internal) to be reasonably flat. When this requirement is met the prediction of the multiple is simple and avoids all shortcomings of general techniques such as SRME with irregular acquisition geometries, poor signal to noise ratio or variable near surface effects. Moreover we believe that this requirement is often met in the Arabic Peninsula. Introduction The need for seismic processing to more effectively remove multiple energy noise while preserving at the same time the primary events is growing in important due to both structural interpretation and advance geophysical analyses that require higher quality seismic data. Multiples can corrupt the primary seismic events at the target and lead to incorrect seismic attributes and erroneous interpretations. Multiple attenuation as applied in this land seismic study was a two step process. In the first step the multiples, which include both surface and inter-bed related multiples are predicted using a data driven process that does not involve any prior information concerning the subsurface velocities. In the second step the predicted multiple events are matched to the multiple events present in the seismic data and removed using a derived matching filter. This approach assumes that the dominant multiple events in the zone of interest are correctly derived and that the prediction locates the multiples at their proper seismic time. The method is applied in a way that minimizes any possible interference between the primary seismic events and the multiples to preserve the primary seismic event amplitudes. Figure 1 compares a simple reflection, surface related multiple and interbed multiple to illustrate their differences. The seismic data used in this study has strong multiple energy that has similar moveout to the primary events and is difficult to remove without damaging the primaries. The multiple method used in this study did not require moveout differences between the primary and multiple events in order to be able to remove the multiples.