Ali Özbek

On the use of multicomponent streamer recordings for reconstruction of pressure wavefields in the crossline direction

Three-component measurements of particle motion would bring significant benefits to towed-marine seismic data if processed in conjunction with the pressure data. We show that particle velocity measurements can increase the effective Nyquist wavenumber by a factor of two or three, depending on how they are used. A true multicomponent streamer would enable accurate data reconstruction in the crossline direction with cable separations for which pressure-only data would be irrecoverably aliased. We also show that conventional workflows aimed at reducing these aliasing effects, such as moveout correction applied before interpolation, are compatible with multicomponent measurements. Some benefits of velocity measurements for deghosting data are well known. We outline how the new measurements might be used to address some long-standing deghosting challenges of particular interest. Specifically, we propose methods for recovering de-ghosted data between streamers and for 3D deghosting of seismic data at the stream...

Crossline wavefield reconstruction from multicomponent streamer data: Part 2 — Joint interpolation and 3D up/down separation by generalized matching pursuit

Computation of the 3D upgoing/downgoing separated wavefield at any desired position within a marine streamer spread is enabled by multicomponent streamers that can measure the crossline and vertical components of water-particle motion in addition to the pressure. We introduce the concept of simultaneous interpolation and deghosting and describe a new technique, generalized matching pursuit (GMP), to achieve this. This method is based on the matching-pursuit technique and iteratively reconstructs the signal as a combination of optimal basis functions. In the GMP method, the basis functions describing the unknown 3D upgoing wavefield are filtered by appropriate forward ghost operators before being matched to the multicomponent measurements. As a data-dependent method, GMP can operate on data samples that are highly aliased in the crossline direction without relying on assumptions about seismic events such as linearity. The technique is naturally suitable for data with only a small number of samples that may be irregularly spaced. We demonstrate the efficacy and robustness of the GMP method on several synthetic data sets of increasing complexity and in the presence of noise.

Crossline wavefield reconstruction from multicomponent streamer data: Part 1 — Multichannel interpolation by matching pursuit (MIMAP) using pressure and its crossline gradient

We introduce a technique that uses multicomponent seismic measurements to reconstruct the seismic wavefield at any desired crossline position between towed streamers. This method, called multichannel interpolation by matching pursuit (MIMAP), operates on pressure and crossline particle-motion measurements. It is based on the matching-pursuit technique and iteratively reconstructs the signal as a combination of optimal basis functions. Being a data-dependent technique, MIMAP can interpolate severely aliased data without assumptions about seismic events such as linearity or the model related to the seismic wavefield. MIMAP has the capability to perform well in the presence of irregular sampling and is robust when only a small number of samples are available. Using synthetic data examples, we show that the new method has the potential to interpolate signals that are sampled at realistic crossline streamer spacing and in the presence of noise.

Optimized deghosting of over/under towed-streamer data in the presence of noise

Seismic exploration is widely used to locate geologic formations for hydrocarbon accumulations. In a typical marine seismic survey, one or more marine seismic streamers are towed behind a survey vessel. As the streamers are towed, acoustic signals, commonly referred to as “shots,” are produced by the seismic source. These travel down through the water column into strata beneath the water bottom surface, where they are reflected from the various geologic formations and travel back to the sea surface. One well-known marine seismic problem is that these upgoing waves are then reflected with inverted polarity at the sea surface because of the air/water interface. Hence, the sensors in the seismic streamer cable record not only the desired wavefield (i.e., the upgoing wave-reflected signal from various subterranean geologic formations), but also their reflections from the sea surface (the downgoing wave). The undesired downgoing reflected signal is known as the “receiver ghost.” Depending on the incidence angl...

On data-independent multicomponent interpolators and the use of priors for optimal reconstruction and 3D up/down separation of pressure wavefields

In marine acquisition, the interference between the upgoing and downgoing wavefields introduces a receiver ghost which reduces the effective bandwidth of the seismic wavefield. A two-component streamer provides means for removing the receiver ghost by measuring pressure and vertical particle velocity. However, due to nonuniform and relatively sparse sampling in the crossline direction, the seismic data are usually severely aliased in the crossline direction and the deghosting may not be feasible in a true 3D sense. A true multicomponent streamer measures all components of the particle motion wavefield in addition to the pressure wavefield. This enables solving the 3D deghosting and crossline reconstruction problems simultaneously, without making assumptions on the wavefield or the subsurface. We havedeveloped two data-independent algorithms suited for multicomponent acquisition. The first algorithm reconstructs the total pressure wavefield in the crossline direction by using the pressure and the crossline...

Acquisition of marine point receiver seismic data with a towed streamer.

Summary A new concept for the acquisition of point receiver towed streamer data is introduced. Recording of point receiver data, rather than the analogue outputs of hardwired arrays, enables both dynamic group forming and enhanced attenuation of noise. Dynamic group forming allows better signal preservation and enhanced frequency recovery, particularly at far offsets. Data adaptive noise attenuation methods allows improved attenuation of the low frequency noise induced by water flow around the streamer, enabling the enhancement of the low frequency signal-to-noise ratio through avoidance of low cut filters. Point receiver marine seismic data will improve the dynamic range of the seismic signal and enhance the viability of time-lapse monitoring of reservoirs with towed streamer data.

3-D Filter Design on a Hexagonal Grid with Applications to Point-receiver Land Acquisition

Summary Recording seismic data through point receivers rather than analogue receiver arrays has several potential advantages. Design of optimal 3-D digital filters is important to realize this potential. Hexagonal (staggered) spatial sampling is more efficient than rectangular sampling for seismic signals, but requires development of special techniques for the design of 3-D filters. We present a method based on the APOCS (Alternating Projections onto Convex Sets) approach for designing optimal 3-D FIR (finite impulse response) filters for digital group-forming.

Mitigation of streamer noise impact in multicomponent streamer wavefield reconstruction

where ρ is the density of the medium. It is known (Linden, 1959) that the crossline component of the pressure gradient, Py, gives an important contribution in recovering from the cross-line aliasing, allowing the multi-channel reconstruction in the crossline direction of the seismic pressure. The MIMAP technique (Multichannel Interpolation by Matching Pursuit, Vassallo et al., 2010), has been proposed to exploit the anti-aliasing potential of two-component seismic data, P and Py, in realistic acquisition settings. It has also been discovered that the combined use of pressure, crossline and vertical component of the pressure gradient, P, Py and Pz, gives even more benefit, as it allows joint-interpolation and 3D deghosting of severely aliased data (Ozbek et al., 2010). Ozbek et al. (2010) introduced Generalized Matching Pursuit (GMP) as a technique to achieve this. Both MIMAP and GMP rely on the combination of measurements of different nature: in this paper we describe how this combination needs to take into account the differences between the signals and the noise characteristics that are observed on multicomponent marine measurements.

Anti-alias Optimal Interpolation with Priors

We introduce a new technique referred to as Optimal Interpolation with Priors, or OIP, for interpolation of irregularly sampled signals, using prior estimates of their spectral content, which is optimal in the least square sense. In this paper, after introducing this technique and describing its basic advantages with respect to other state of the art regularization techniques, we demonstrate its potential to interpolate signals that are spatially aliased, based on realistic prior information. We also propose an algorithm to obtain a reliable prior estimate of the signal spectrum. The combined use of this algorithm and OIP, referred to henceforth as Anti-Alias OIP (AA-OIP), can be applied to datasets irregularly sampled in multi-dimensional spaces.

Crossline Wavefield Reconstruction From Multi-component Streamer Data: Multichannel Interpolation By Matching Pursuit

We introduce a new technique that uses multicomponent seismic measurements that would be recorded by a true multicomponent streamer to reconstruct the seismic wavefield at any desired position between streamers. This method, called Multichannel Interpolation by Matching Pursuit (MIMAP), operates on pressure and crossline particle motion measurements. As a data-dependent technique, MIMAP can interpolate severely aliased data without any assumptions about seismic events such as linearity or the model related to the seismic wavefield. MIMAP has the capability to perform well in the presence of irregular sampling and is robust even when only a small number of samples are available.