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In simultaneous source acquisition, seismic data can be recorded with a temporal overlap between the shots. Better sampled data in terms of source spacing, azimuth and/or offset distributions can be obtained in a much more efficient way. These potential benefits can only be realized if the recorded data, with interfering energy from multiple sources, can be handled properly. Common practice is to apply randomized time-delays to the sources during the acquisition of the data. As a result of using randomized firing schemes, coherency measures can be utilized to actively separate the recorded data over the individual sources. In this paper an inversion-based source separation method is utilized to a shallow water data set which may have specific challenges compared to deeper water applications. We will focus a bit more on the randomized firing schemes. It is shown that optimizing these firing schemes, introducing “pseudo randomization”, instead of using random time-delays, can benefit the performance of the source separation.
The separation method is illustrated using a controlled simultaneous source experiment where a shallow water field data set is used to mimic simultaneous recorded data where two sources were located with only a small cross line distance between them (simultaneous FLIP/FLOP acquisition). Results demonstrate that it is advised to utilize “pseudo randomization” of the firing delay-times. The controlled shallow water field data example shows that good separation results are obtained.
This paper illustrates an inversion approach based on matrix rank reduction that separates simultaneous source data. The algorithm operates on each common receiver gather of a multidimensional data set. We propose to minimize the misfit between the observed data and blended predicted data subject to a low-rank constraint that is applied to the data in the frequencyspace domain. The low rank constraint can be implemented via the classical truncated Singular Valued Decomposition (tSVD) or via a new randomized QR decomposition (rQRd) method. Compared to the tSVD, rQRd significantly improves the computational efficiency of the method. In addition, the rQRd algorithm is less stringent on the selection of the rank of the data. This is important as we often have no precise knowledge of the optimal rank that is required to represent the data. We adopt a synthetic 3D VSP data set to test the performance of the proposed deblending algorithm. Through tests under different survey time ratios, we show that the proposed algorithm can effectively eliminate interferences caused by simultaneous shooting.
Simultaneous source acquisition, or blended acquisition, has been attracting a great deal of attention because of the economic potential it brings to seismic data acquisition (Beasley et al., 1998; Berkhout, 2008). The technique aims at improving the acquisition efficiency by allowing continuous recording of overlapping shots. In simultaneous source acquisition, instead of firing one shot each time and waiting for its seismic response, several shots are fired with at close time intervals. In land acquisition, different phase-encoding schemes have been utilized to distinguish the signal from different Vibroseis (Bagaini, 2006). In marine acquisition, simultaneous shooting relies on the randomization of the firing time delays. This is because random time delays would preserve the coherency of desired signal while perturbing the interference in common receiver, offset and midpoint domains (Stefani et al., 2007). The latter is important as it allows separation of simultaneous source data via a coherent-pass constraint (Abma et al., 2010).
Various techniques have been developed for deblending simultaneous source data. Methods that exploit the low-rank property of the unblended data are of special interest to this paper. Maraschini et al. (2012) utilized the SSA low-rank filter, or equivalently the Cadzow filter, in an iterative manner to suppress the incoherent interference in common offset domain. Cheng and Sacchi (2013) posed deblending as a rank constrained inverse problem and solved it via the gradient projection method.
Much research and testing has been done with simultaneous sources in recent years because of its potential cost savings in acquisition. Similarly, broadband acquisition is gaining in popularity because of its potential to increase the frequency bandwidth of the acquired data. Both acquisition methods pose challenges in seismic imaging. Here, we simulate a simultaneous source experiment with a real variable-depth streamer NAZ survey acquired in Brazil and apply an iterative separation flow using a hybrid of median and f-x projection filters for deblending. The results show little leakage after deblending in both near and far offsets while preserving the AVO characteristics. We also perform Kirchhoff migration in order to examine the residual cross-talk in common image gathers after deblending. The results reveal little leakage, and the quality of the common image gathers is adequate for velocity model building. We also study how the existence of spatial aliasing when shots are coarsely sampled degrades the deblending quality. Last, we investigate the impact of firing multiple sources simultaneously to improve shot sampling.
Zarkhidze, Alexander (WesternGeco) | Salinas, Luis Arechiga (WesternGeco) | Le Diagon, Franck (WesternGeco) | Thompson, Jeff (WesternGeco) | Ortin, Marcela (WesternGeco) | Barnes, Penelope (WesternGeco) | Moore, Ian (WesternGeco) | Juárez C., Miguel (Pemex) | Diaz M., Arnulfo (Pemex) | Esquivel, Oscar G. (Pemex) | Nava, Horacio M. (Pemex)
Acquiring seismic data with simultaneous sources, already an established technique for land data, is gaining acceptance for towed-streamer marine data, and is fast becoming the norm for ocean-bottom data. Simultaneous-source acquisition is especially attractive because it can potentially improve both acquisition efficiency and data quality. The average shot time interval is reduced, often dramatically, and vessel and crew productivity are correspondingly increased. This, together with the improved ability to handle interference, also reduces and relaxes time-share requirements. Multiple source vessels increase flexibility in the acquisition geometry, allowing recording longer offsets and richer azimuth distributions. These benefits can materialize if we are able to separate the simultaneously acquired shots, preserving the primary shot energy whilst attenuating the interference from other shots. We achieve this through detailed survey design based on modelled data. This procedure allows us to determine the most efficient design consistent with our understanding of the geology and the objectives of the survey.
We focus on an ongoing ocean-bottom cable (OBC) survey from the southern part of the Gulf of Mexico. The shallow-water data are acquired using multicomponent point-source point-receiver technology over an area of 2,500 km2.
The project covers multiples provinces and has a very complex geological structure. On one side of the project we have the fold belt province, with salt-cored anticlines, folded diapirs, and structures associated with salt expulsion through faults. On the other side, we have Mesozoic structures associated with the autochthonous salt, with canopies and allochthonous bodies placed in the Neocene.
Presentation Date: Wednesday, October 17, 2018
Start Time: 1:50:00 PM
Location: 210C (Anaheim Convention Center)
Presentation Type: Oral