Simon Barnes

Enhanced demultiple by 3D SRME using dual-sensor measurements

In recent years, dual-sensor recording has been introduced to marine seismic acquisition with reported benefits such as the increased bandwidth of the acquired seismic signal, improved signal-to-noise ratios due to deep-tow streamers, and operational efficiency due to an increased weather window.

Data regularization for 3-D SRME: A comparison of methods

Summary This paper discusses and compares different strategies for data regularization prior to the application of 3-D SRME. It is shown that synthetic analysis can be utilized to determine whether azimuth corrections are needed during data regularization. It is shown that only in certain instances this is needed, depending on the azimuth between the dipping reflectors and the acquisition direction. Also, the reflector dips, offset ranges and the reflectors depths are important. For geometries where azimuth corrections are needed, a comparison is made between two well-known solutions: Forward DMO followed by inverse DMO (DMO-DMO -1 ) regularization, and Fourier regularization with azimuth correction. It is shown that the latter shows better performance in terms of amplitude fidelity, as well as dealing with practical issues such as irregular sampling due to feathering of the streamers. Application of the Fourier regularization method to a field data set shows that the method is very capable of predicting complex 3-D multiples in the presence of multiple diffractions.

Near Surface Issues In 4C-3D Data From The Middle East - A Case Study

Summary We discuss the effects of both geometry and sub-surface seismic properties on mode-converted, shallow reflections from a 4C-3D survey in the Middle East. We observe a particularly strong PS reflection event some 400m below the seafloor. Azimuthal analysis of this event, and those in its proximity, allow us to deduce that the shallow section is azimuthally anisotropic and that the principal axes are aligned approximately N135°/45°E.

Shallow Reverberation Prediction Methodology with SRME

It is well known that surface-related multiple elimination (SRME) breaks down when applied to shallow water datasets. The prediction is distorted at the reconstruction stage by the NMO stretch of the seabed, progressing to the loss of seabed information beyond the critical distance. Furthermore, the adaptive subtraction (multiple elimination) struggles when several orders of the predicted short period reverberation are present, within a given design window for minimization, as the predicted amplitude (and phase) between multiple orders from a single convolution of the data with itself are incorrect. This abstract describes a novel seabed modelled SRME approach with regards to predicting simultaneously and non-iteratively both the amplitude and phase of simple and pegleg source and receiver-side sea layer reverberation correctly with minimal distortion for moderately undulating shallow seabeds. Using a shallow water dataset from the Central North Sea, it is demonstrated that the 3D approach can replace more limited 1D τ-p shot-based deterministic multiple prediction techniques to form part of a multi-model multiple prediction strategy that includes iterative SRME where appropriate.

Dual-sensor Enhanced 3D Surface-related Multiple Elimination

In recent years dual-sensor recording has been introduced to marine seismic acquisition with reported benefits such as the increased band-width of the acquired seismic signal, improved signal-to-noise ratios due to deep-tow streamers, and operational efficiency due to an increased weather window. This abstract describes another advantage of dual-sensor measurements, namely the opportunity it provides to better predict and subtract surface-related multiples from marine seismic data compared to using conventional data acquisition. Using a dataset from offshore Greenland, it is demonstrated that dual-sensor acquisition leads to a more accurate set of predicted multiples with respect to phase and amplitudes. As a result, the adaptive subtraction of the multiples can be carried out in a more constrained and robust manner, leading to better multiple elimination and better primary preservation.

True-azimuth Versus Zero-azimuth 3-D Multiple Prediction – Two Case Studies

The paper discusses two different strategies for data-driven 3-D multiple prediction in marine seismic data processing. A comparison is made between methods that make use of zero-azimuth assumptions, where multiples are generated for source and receiver p

Better Ways to Image North Sea Central Graben Diapirs

The velocity regime of The North Sea is noted for its step like character between lithologic zones, in stark contrast to the gentle velocity gradient of the Gulf of Mexico where conventional DMO performs so well. One of the more pronounced North Sea steps is between the Tertiary and Cretaceous Chalk sequences and in such areas it has been shown that conventional DMO is seriously flawed. It has become quite common practice to attempt to circumvent the DMO’s failings by using various schemes that combine it with zero offset pre-stack time migration. We examine the validity of such schemes, comparing them with the theoretically sound Pre-Stack Depth Migration (PSDM) and a relatively new DMO that is able to comprehend any variations in the vertical velocity profile, HDDMO. It is well known that a vertical velocity variation requires the DMO operator to be three dimensional. For the linear velocity gradient of the Gulf of Mexico, the MZO saddle operator is considered appropriate. In the North Sea, however, the 3D DMO operator cannot be generalized so readily and is more complex. HDDMO computes the true 3D nature of the operator that is required and we illustrate its performance in a velocity environment of a typical Central Graben diapir.