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Tsvankin I.,Colorado School of Mines | Gaiser J.,Geokinetics | Grechka V.,Royal Dutch Shell | Van der Baan M.,University of Alberta | Thomsen L.,Delta Geophysics

Recent advances in parameter estimation and seismic processing have allowed incorporation of anisotropic models into a wide range of seismic methods. In particular, vertical and tilted transverse isotropy are currently treated as an integral part of velocity fields employed in prestack depth migration algorithms, especially those based on the wave equation. We briefly review the state of the art in modeling, processing, and inversion of seismic data for anisotropic media. Topics include optimal parameterization, body-wave modeling methods, P-wave velocity analysis and imaging, processing in the τ-p domain, anisotropy estimation from vertical-seismic-profiling (VSP) surveys, moveout inversion of wide-azimuth data, amplitude-variation-with-offset (AVO) analysis, processing and applications of shear and mode-converted waves, and fracture characterization. When outlining future trends in anisotropy studies, we emphasize that continued progress in data-acquisition technology is likely to spur transition from transverse isotropy to lower anisotropic symmetries (e.g., orthorhombic). Further development of inversion and processing methods for such realistic anisotropic models should facilitate effective application of anisotropy parameters in lithology discrimination, fracture detection, and time-lapse seismology. Source

Vigner A.K.,PGS | Deighton M.,PGS | Swift C.,Geokinetics
72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010

Seismic absorption along the propagation path of a seismic wave has a considerable impact on amplitude and phase of recorded signal wavelets. It has been demonstrated that the knowledge of the absorption parameter (known as Q) is highly desirable when extracting lithological information. In this paper, we discuss the estimation of Q using different spectral ratio methodologies. We show that the choice of the reference wavelet is determinant in the accurate estimation of Q. Finally it is demonstrated that Q estimation takes great advantage from the broader bandwidth provided by dual-sensor (pressure and velocity) acquisition system compared to the conventional (pressure only) system © 2010, European Association of Geoscientists and Engineers. Source

Permian coal beds at 2400-2900 m depth in Cooper Basin, Australia have normal-incident reflection coefficient values as large as ±0.6. If internal multiples are included in synthetic seismograms, excellent correlations exist between the synthetic seismogram and seismic, even when more than 50 coal beds are present. However, neither the synthetic seismogram nor the seismic tie the well-log lithologic boundaries because the incident wavefield that strikes a lithologic boundary and returns to the surface contains a signal wavelet followed by high-amplitude noise, which are interbed multiple reflections. Because the spectra of the signal and noise coda at a given two-way time normally do not overlap, time-varying Gaussian filters applied to the near-offset stack enhance the signal and suppress the noise coda. After filtering, the apparent time delay of reflections introduced by the coal beds is removed with variable time shifts (time compression), based on the estimated time-varying signal wavelets. The two-step process of low-pass filtering and compression yields seismic events that successfully tie the lithologic boundaries in the borehole, although with limited resolution. Our preliminary tests on a seismic line indicate that the horizon event associated with the base of a 500-m-thick coal sequence is more coherently imaged with our processing than with conventional processing. © 2014 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved. Source

Olofsson B.,Seabird Exploration | Mitchell P.,Chevron | Doychev R.,Geokinetics
Leading Edge

A fundamental challenge for exploration is pushing seismic imaging to open new frontiers. Typical of these frontiers is complex overburden with varying lithologies and structure that give rise to strong lateral changes in velocity and anisotropy. Two examples are subsalt and subvolcanic imaging. It is widely recognized that rich- or full-azimuth data can provide superior imaging results in such complex areas, besides providing other additional information (e.g., through fracture characterization). Typical ocean-bottom node (OBN) seismic surveys are acquired with a regular grid of sparse node and dense shots, providing full-azimuth/offset data with uniform sampling in the azimuth/offset domain. Figure 1 illustrates this point, showing the trace distribution for one CMP bin for the OBN survey used in this test; it features uniformly spaced nodes and a dense shot carpet. Every CMP bin in the survey receives contributions of exactly one trace in each azimuth /offset sub-bin (grid cells drawn in Figure 1). This means that (a) there is no redundant fold, and (b) the full-azimuth/offset space is uniformly sampled, points previously discussed by Vermeer (e.g., 1994, 2010, and other publications). We note that the theoretical CMP (= surface) illumination does not necessarily translate into the same subsurface illumination depending on the complexity of the overburden geology and the asymmetric source-receiver depth. © 2012 Society of Exploration Geophysicists. Source

Wei Z.,INOVA Geophysical Equipment Ltd | Hall M.A.,Geokinetics
Leading Edge (Tulsa, OK)

The vibroseis method has, for half a century, achieved great success in land seismic exploration. However, some practical issues still arise that have remained theoretically unexplained. For example, on soft ground, the vibrator produces subharmonics and ultra-subharmonics in addition to main harmonics; whereas on hard ground, the vibrator generates harmonics only. Geophones on soft ground also behave abnormally while geophones on hard ground behave normally. This paper analyzes these phenomena and demonstrates that the softness of the ground's top layer is responsible for subharmonics and ultra-subharmonics. This soft ground layer causes the geophone abnormality as well. Unfortunately, quantification for this behavior has not been achieved. © 2011 Society of Exploration Geophysicists. Source

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