Mag Magesan

De‐aliased, high‐resolution radon transforms

Multiple elimination methods based on the move-out discrimination between primaries and multiples rely heavily on the focusing of seismic events in the parabolic Radon domain. This focusing, however, is affected both by the finite spatial aperture and sampling of the data. As a consequence of the resulting smearing, multiple energy may be mapped into the primary model and conversely primary energy may be mapped into the multiple model. This leads to poor multiple removal and to the nonpreservation of the primary amplitudes. To overcome these pitfalls one has to make use of De-aliased, HighResolution Radon transforms. High-resolution Radon transforms have already been proposed by some authors. Here we present a novel approach that simultaneously tackles the aliasing and resolution issues in a non-iterative way.

3D surface-related multiple modeling

The shape of seismic reflected energy on shot or CMP gathers can be ex-tremely complicated in comparison with the actual geometry of geologic generators. A simple synclinal structure may produce a triplication in the zero-offset domain, and migration processing is needed to resolve this situation. By comparison, multiple generation “squares” (at least for first-order multiples) the degree of complexity of the reverberated reflected energy, and, in general, there is no domain, neither time, depth, nor pre- or postmigrated, where multiples and primaries can be simplified simultaneously.

Seismic interference noise attenuation

Summary Attenuation of seismic interference noise that overpowers seismic reflections can be achieved by making use of wellknown f-x prediction filters and the non-predictability of interfering noise from shot to shot.

Seismic processing for time-lapse study: Genesis Field, Gulf of Mexico

Extraction of the maximum resolution that the data will permit is the usual objective for optimal processing of a single seismic survey. Careful data analysis and appropriate choice of technology are key to achieve this goal. Processing for recovery of true time-lapse (TL) signal, where multiple data sets are involved, differs substantially from the usual approach. A TL study involves surveys acquired over a period of time. Careful preplanning is seldom undertaken in the design of the original surveys, resulting in data sets that resulted from different acquisition designs and technology. The acquisition geometry, signal, and noise contents and the resolution limits of the data sets can be very different. Unlike the single survey case, extraction of the true TL signal demands application of processes that restore common signal characteristics and identical S/N and resolution for the datasets.

Diffracted noise attenuation in shallow water 3D marine surveys

3D marine surveys occasionally suffer from scattering of source energy from sharp discontinuities at, or around, the sea bottom as the scattered energy gets recorded by the streamers. Nearby rigs, wellheads, shipwrecks, and, boulders at the sea bottom add to the problem. As the reflected energy from deep strata is weak and such scattered noise is much stronger than reflections, since it has traveled only in water, the position of these energy sources must be detected and the energy recorded on the seismic traces from such sources must be attenuated. Such strong energy interferes with many other pre-migration processes among which are prestack deconvolution and surface related multiple prediction, and therefore must be attenuated before reaching migration stage.

Processing Solutions For Wide Azimuth Data: Outcome From a WATS Field Experiment In Deep Water Gulf of Mexico

Wide Azimuth Towed Streamer (WATS) acquisition has already proved to be a key technique in improving seismic imaging, especially in complex areas such as sub-salt plays. In 2006, a WATS field experiment was conducted in a deep water area of the Gulf of Mexico. The main purpose was to challenge recently developed 3D processing algorithms and find the most suitable processing strategy for a wide azimuth dataset. The results indicate that a 3D shot based processing sequence is an effective solution that accommodates the effects related to the multi-pass acquisition method and realizes the full benefit of the recorded 3D wide azimuth wave field.

Fast Broadside Diffractors: A Case History.

Diffracted energy in 2D marine surveys is a source of problem especially if they are broadside. Strong energy radiated from the source travels to the scatterers at the water bottom and gets scattered. This energy travels back in the water and is received by the receivers on the streamer. 2D processes, including 2D migration, cannot properly address such events. On the other hand, 3D migration in 3D surveys provides a means for collapsing such energy properly. Neverthelesss, in deeper portions of the data diffracted noise is so high in energy and is so different in spectral content than the reflected energy that it might be desirable to attenuate such energy before some prestack processes if the number of such diffractors is so large to block the signal underneath.

Shot Based Pre-Processing Solutions for a WATS Survey – An Example from a Field Trial in Green Canyon – Gulf of Mexico

C014 Shot Based Pre-Processing Solutions for a WATS Survey – An Example from a Field Trial in Green Canyon – Gulf of Mexico M. Magesan (CGGVeritas) J.-C. Ferran* (CGGVeritas) S. Kaculini (CGGVeritas) C.J. Faulkner (CGGVeritas) P. Herrmann (CGGVeritas) A. Pica (CGGVeritas) G. Poole (CGGVeritas) & S. Le Roy (CGGVeritas) SUMMARY In July 2006 a 3D Wide Azimuth Towed Streamer (WATS) field trial was carried out in a deep water area of Green Canyon in the Gulf of Mexico. The purpose was to provide insight into the potential problems and complexities of such seismic datasets and to challenge conventional and newly