Tony Curtis

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.

Efficient broadband marine acquisition and processing for improved resolution and deep imaging

Summary We present a new method for broadband marine acquisition and processing. A 3D shallow towed-streamer spread is deployed, designed to optimize the mid- and high-frequency parts of the bandwidth. In addition, data are simultaneously acquired from a small number of deeper towed streamers. The depth of these deeper streamers is optimized for the low frequencies such that the combined overall bandwidth is enhanced. Because the deep streamers will only provide the low-frequency part of the bandwidth, we can more sparsely sample these data enabling efficient acquisition scenarios as fewer streamers are required. The data are combined in processing, optimizing the signal-to-noise ratio over the entire bandwidth. The resulting data exhibit both high resolution and deep penetration, for subsalt and sub-basalt imaging, for example. In addition, inversion for acoustic impedance, imaging, and velocity model building, also benefit from the broadband result. Data acquired in this way are also more robust to poor weather conditions than conventionally acquired data. Data for a 3D case study using this new acquisition method were acquired off the NW Shelf of Australia. The streamer spread consisted of six shallow streamers towed at a depth of 6m and two deeper streamers (below shallow streamers 2 and 5) towed at a depth of 20m.

Acquisition of Highly Repeatable Seismic Data Using Active Streamer Steering

Summary At the 62nd meeting of the European Association of Geoscientists and Engineers, in Glasgow, a new system for marine seismic cable steering and control was described (Bittleston et al., 2000). In this paper, recent operational experience with this system is reported. Seismic data acquired using active streamer steering, to achieve repeat positioning, is demonstrated to be highly repeatable.

On the Role of Priors in Generalized Matching Pursuit to Reconstruct Wavefields from Multicomponent Streamer Data

In conventional single-component data acquisition, a common way to solve the problem of reconstructing aliased seismic data is to use priors that are computed at low frequencies and applied at high frequencies. In contrast, parametric matching pursuit methods such as Generalized Matching Pursuit applied on multicomponent data do not need priors in most conditions to achieve accurate reconstruction under aliasing. In this paper, we examine how and when soft priors can provide further robustness to multichannel matching pursuit algorithms. We illustrate our concepts on synthetic data generated by finite-difference modelling and on data acquired by a 3D-4C towed cable array. We find that multicomponent data allow matching pursuit algorithms to compute and use the priors in ways that are not possible with single-component data. For instance, the priors can be estimated by matching pursuit within an intermediate temporal frequency band, where the signal-to-noise ratios of all the components are high, while the data are already subject to spatial aliasing. The priors generated at these intermediate frequencies can then be used at higher frequencies where the aliasing is stronger, and also at lower frequencies, still aliased and affected by stronger noise.

Extending the bandwidth of marine seismic data

A long-term goal of the seismic industry has been to extend the spatial and temporal bandwidth of seismic data and thereby to improve the resolution of the resulting seismic image. In this paper we consider the limitations of systems used to acquire and process marine seismic data, in particular the effect of spatial arrays, and consider some techniques that might extend the bandwidth beyond that which is typically achieved.

Evaluating Fidelity and Repeatability of Wavefields Reconstructed from Multicomponent Streamer Data

In marine time-lapse (4D) seismic data processing, each wavefield snapshot is usually interpolated onto a common grid to compensate for differences in acquisition, especially receiver, geometry. Because crossline sampling is usually sparse compared to inline sampling, and most mispositioning results from poor crossline repeatability from variable feathering, crossline interpolation is often aliased and causes 4D errors that increase with interpolation distance. Recent developments in multicomponent wavefield reconstruction hold promise for good amplitude fidelity, even for data that are spatially aliased to high order. In this paper we examine repeated data acquired by an experimental 3D-4C towed-cable array. Data from six crossline samples are reconstructed 1:12 and placed on a rectangular grid uniformly sampled at 6.25 m inline and crossline. Wavefields are interpolated using pressure alone and compared with wavefields reconstructed from pressure, crossline gradient and vertical gradient. We find that 3C reconstruction has excellent fidelity, recapturing highly aliased diffractions which are lost by pressure-only interpolation. 3C reconstruction is also more repeatable, outperforming 1C reconstruction, where error correlates with midpoint mispositioning. Although the experimental 3D data have limited inline aperture, the level of repeatability achieved is extremely encouraging compared to full-aperture, pressure-only, 4D datasets at an equivalent stage of processing.

Increasing Spatial and Temporal Bandwidth with Multi-component Streamer Data

Increasing bandwidth is not only about temporal frequencies but also about spatial wavenumbers, in particular those which are poorly sampled in the cross-line direction with streamer separations of 16 to 24 times the inline sampling interval. In this talk, we present results from a test with a mini-3D array of prototype 4C marine streamers in which we use, in addition to the pressure, the vertical and crossline gradients of the pressure wavefield in order to reconstruct and 3D deghost the wavefield at arbitrary points within the aperture. From the experimental 3D survey, we show examples of spatial and temporal enhancement of wavefields reconstructed using a generalised matching pursuit algorithm, comparing pressure-only and multi-component reconstructions. We find that multicomponent reconstruction is able to de-alias high wavenumber diffractions, that are completely missed by a pressure-only matching pursuit algorithm with priors, and generate broad-band unmigrated timeslices with excellent resolution.