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Multicomponent OBS And VC Acquisition For Wavefield Reconstruction
Amundsen, Lasse (Statoil Research Center, and NTNU) | Westerdahl, Harald (Statoil Research Center, and NTNU) | Thompson, Mark (Statoil Research Center, and NTNU) | Haugen, Jon A. (Statoil Research Center, and NTNU) | Reitan, Arne A. (Statoil Research Center, and NTNU) | Landrø, Martin A. (Statoil Research Center, and NTNU) | Ursin, Bjørn A. (Statoil Research Center, and NTNU)
SUMMARY In ocean-bottom seismic (OBS) and vertical-cable (VC) surveying, receiver stations are stationary on the sea floor while a source vessel shoots on a predetermined x-y grid on the sea surface. To reduce exploration cost, the shot point interval often is so coarse that the data recorded at a given receiver station are undersampled and thus irrecoverably aliased. However, when the pressure field and its x- and y-derivatives are measured in the water column, the non-aliased pressure field can be reconstructed by interpolation. Likewise, if the vertical component of the particle velocity (or acceleration) and its xand y-derivatives are measured, then also this component can be reconstructed by interpolation. The interpolation scheme can be any scheme that reconstructs the field from its sampled values and sampled derivatives. In the case that the two field’s first-order derivatives are recorded the number of components are six. When also their second-order derivatives are measured, the number of components is ten. The properly interpolated measurements of pressure and vertical component of particle velocity from the multicomponent measurements allow proper up/down wavefield decomposition, or deghosting. New wavefield reconstruction methods as those suggested here are of significant interest since, presently, the seismic industry is in the process of developing multicomponent cables or streamers, and is in the process of carrying out research on new multicomponent sensors. INTRODUCTION To reduce 3-D marine seismic acquisition cost the receiver spacing is often made larger than desirable. As a consequence, the recorded wavefield is spatially aliased. Specifically, in towed streamer acquisition, the sampling challenge is the large streamer separation, typically 50-100 m. In ocean-bottom seismic (OBS) or vertical cable (VC) acquisition, where data can be processed as common-receiver gathers, it is the coarse shot interval spacing, typically chosen 50 m by 50 m or more, that leads to undersampling. Here, OBS refers to acquisition with either nodes or cables. The undersampling of the wavefield causes challenges for 3-D up/down decomposition or deghosting of the recorded wavefield, which is one of the data preprocessing steps applied before seismic imaging. In this paper we introduce the concept of multicomponent (multi- C) wavefield measurements in the water column while the source vessel, just like in OBS and VC surveying, traverses the surface shooting on a predetermined grid. Six wavefield components — the pressure and the vertical component of the particle velocity and their horizontal first-order derivatives in xand y-directions — are required for proper reconstruction of the undersampled pressure and vertical component of particle velocity. When the second-order derivatives are recorded, the number of components is ten. This reconstruction allows the step of 3-D up/down decomposition or deghosting of common receiver station recordings to be achieved in the frequencywavenumber domain (Amundsen, 1993). New wavefield reconstruction methods as those presented in the present paper are of interest since, presently, the seismic industry is in the process of developing multicomponent cables or streamers (Robertsson, 2006; Singh el al., 2009). Further, the industry is actively carrying out research on and testing new multicomponent sensors.
ABSTRACT In 3D Ocean Bottom seismic surveys (3D-OBS) both pressure and vertical particle velocity is recorded. This presents the opportunity to decompose the recorded wavefields in up- and downgoing components and apply to 3D common receivers gathers a designature/demultiple algorithm to attenuate free surface multiples. This single processing step replaces several steps in conventional processing usually encompassing tau-p predictive deconvolution and Radon demultiple. Using a 3D-OBS data set from the Gullfaks Sør field in the North Sea, the new 3D designature/demultiple approach, together with 3D common receiver depth migration, is shown to result in seismic images of better quality than by the traditional processing sequence.
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 50 > Block 34/10 > Gullfaks Sør Field > Statfjord Group (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 50 > Block 34/10 > Gullfaks Sør Field > Lunde Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 50 > Block 34/10 > Gullfaks Sør Field > Lista Formation (0.99)
- (12 more...)
Abstract Four-component ocean bottom seismic (4C-OBS) surveying, in contrast to conventional towed streamer acquisition, records the complete seismic wavefield. When developing seismic processing tools for 4C-OBS data one therefore can liberate one's mind from the line of thought used in the development of seismic processing methodology for streamer seismic. In particular, using the complete wavefield source signature deconvolution and the troublesome problem of attenuation of sea-surface related multiples can be specially designed for 4C-OBS data. The attenuation of these events is an essential prerequisite for an accurate seismic imaging. In 2001, Amundsen et al. published a fully data-driven method that without any information transforms, during processing in a computer, the recorded 4C-OBS data with the sea surface present into those data that would be recorded in a hypothetical 4C-OBS experiment with the sea surface absent. Removing the sea surface is equivalent to removing all seasurface related multiples. Further, this method automatically designatures the 4C-OBS data. Under the model assumption of a layered earth, the designature/demultiple method reduces to deterministic deconvolution where the deconvolution operator is designed from the inverse of the downgoing acoustic field. This assumption, however, does not severly limit the method's practical use in attenuating free-surface related multiples even in geologically quite complex areas. Further, this designature/demultiple scheme is the only method in the class of free-surface demultiple methods that straightforwardly is implemented in 3D for removing free-surface multiples in today's geometries of 4C-OBS surveys. The method, which is numerically fast, is implemented by several seismic contractors. During the presentation we show results of designature/demultiple processing on half a dozen 4C-OBS deep-water and medium-water depth exploration lines. Introduction Soon after the introduction of four-component ocean bottom seismic (4C-OBS) technology (Berg et al., 1994a,b; Ikelle and Amundsen, 2004) efforts to develop 2D and 3D wave-equation prestack depth imaging intensified (Amundsen et al., 2000; Arntsen and Røsten, 2002). To obtain accurate and detailed imaging, however, attenuation of multiple energy while preserving the character of primaries is required. Through the 1990's till today one has seen many excellent developments of wave-equation based free-surface demultiple algorithms for 2D and 3D streamer seismic and land seismic data (see, e.g., Fokkema and van den Berg, 1990; Verschuur et al., 1992; Matson and Weglein, 1996; Matson, 1997; Weglein et al., 1997; Ziolkowski et al., 1999; Lokshtanov, 1999; Ikelle, 1999a,b; Ikelle et al., 2003; Kleemeyer et al., 2003; Hokstad and Sollie, 2003). The attractiveness of these methods is that they do not require any information about the subsurface. A possible disadvantage is that these methods require information of the source signature. Further, the streamerseismic demultiple methods can not straightforwardly be adapted to 4C-OBS data, in particular not for 3D ocean bottom seismic surveys. Amundsen (2001), Amundsen et al. (2001), and Holvik (2003) published an alternative way of removing free-surface multiples in the case that the complete wavefield is recorded in the seismic experiment. For streamer seismic, the complete wavefield on the streamer is the pressure field and the vertical component of the particle velocity (or vertical pressure gradient).
Summary Amundsen (2001) has presented a general wave-equation method for multidimensional signature deconvolution (“designature”) and elimination of free-surface related multiples (“demultiple”) from four-component ocean bottom seismic (OBS) data. Contrary to other free-surface multiple attenuation schemes, the method requires no information about the source signature. Here, we consider implementation and testing of the multidimensional multiple attenuation and designature scheme for general inhomogeneous media. The designature and demultiple algorithm may be divided into two major computational steps. First, a multidimensional “deconvolution operator”, being inversely proportional to the time derivative of the downgoing part of the normal component of the particle velocity just above the sea floor, is computed from the normal component of the particle velocity itself along with the pressure recording.
The analysis, which is based on decomposition of sea floor, respectively. The horizontal slowness the measured fields into up-and downgoing waves just is p and the vertical P-and S-wave slownesses below the sea floor, yields algorithms that efficiently and The filter can be expressed in terms of the attenuate these unwanted waves.
We in seismic data processing for extracting reliable derive algorithms for estimating signatures from measurements information of the earth's structure.
We assume that a marine survey employing a marine We here give an algorithm for decomposing multicomponent source in the water layer is conducted over a plane layered sea floor data generated by a marine source into upgoing medium.
We first have received little attention. To establish the pair of transformations consider the acoustic or elastic response of an explosive point is of interest for several reasons: apart from its intrinsic source in a horizontally layered medium. Then the response interest, the transformations may be used as amplitude of a point force in a horizontally layered elastic medium is pre-or postprocessing for some multistep seismic processing considered. Finally, we give a numerical example where we schemes, as well as to transform some two-dimensional wave apply the 2-D to 3-D transformation to an acoustic pressure propagation phenomena to their three-dimensional counterpart.
Estimation of Phase Velocities And Q-factors From VSP Data
Amundsen, Lasse (Statoil) | Mittet, Rune (IKU Norway)
We select a subset of rays from case where zero-offset VSP-data are acquired in a medium with these equations in our modeling algorithm. We extract the dl-horizontally plane layers.
An Improved Nonlinear Acoustic Inverse Algorithm
Arntsen, Borge (Continental Shelf and Petroleum Technology Research Institute A/S (IKU)) | Amundsen, Lasse (Continental Shelf and Petroleum Technology Research Institute A/S (IKU)) | Mittet, Rune (Continental Shelf and Petroleum Technology Research Institute A/S (IKU)) | Holberg, Olav (Informasjonskontroll A/S)
The algorithm will not and wave velocities) which minimizes the error between give correct results when using marine seismic data recorded synthetic seismic data and observed data.