Jones I.,ION Geophysical
75th EAGE Conference and Exhibition Incorporating SPE EUROPEC 2013 | Year: 2013
The physical behaviour of most earth materials is fairly straightforward, both in terms of their deposition and subsequent deformation. Consequently, the geometries to be imaged and interpreted are likewise usually well understood. Salts, however, do not conform to the usual behaviours of earth materials due to the ductile nature of the material. Consequently, in both imaging and interpretation of salt province data, special care needs to be taken. In this work, we review various considerations for velocity model building, migration, and subsequent interpretation of complex salt bodies.
Leveille J.P.,ION Geophysical |
Jones I.F.,ION GX Technology |
Zhou Z.-Z.,ION GX Technology |
Wang B.,TGS Inc |
Liu F.,Hess Corporation
Geophysics | Year: 2011
The field of subsalt imaging has evolved rapidly in the last decade, thanks in part to the availability of low cost massive computing infrastructure, and also to the development of new seismic acquisition techniques that try to mitigate the problems caused by the presence of salt. This paper serves as an introduction to the special Geophysics section on Subsalt Imaging for E&P. The purpose of the special section is to bring together practitioners of subsalt imaging in the wider sense, i.e., not only algorithm developers, but also the interpretation community that utilizes the latest technology to carry out subsalt exploration and development. The purpose of the paper is in many ways pedagogical and historical. We address the question of what subsalt imaging is and discuss the physics of the subsalt imaging problem, especially the illumination issue. After a discussion of the problem, we then give a review of the main algorithms that have been developed and implemented within the last decade, namely Kirchhoff and Beam imaging, one-way wavefield extrapolation methods and the full two-way reverse time migration. This review is not meant to be exhaustive, and is qualitative to make it accessible to a wide audience. For each method and algorithm we highlight the benefits and the weaknesses. We then address the imaging conditions that are a fundamental part of each imaging algorithm. While we dive into more technical detail, the section should still be accessible to a wide audience. Gathers of various sorts are introduced and their usage explained. Model building and velocity update strategies and tools are presented next. Finally, the last section shows a few results from specific algorithms. The latest techniques such as waveform inversion or the "dirty salt" techniques will not be covered, as they will be elaborated upon by other authors in the special section. With the massive effort that the industry has devoted to this field, much remains to be done to give interpreters the accurate detailed images of the subsurface that are needed. In that sense the salt is still winning, although the next decade will most likely change this situation. © 2011 Society of Exploration Geophysicists.
Jones I.F.,ION Geophysical
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014
Conventional seismic data processing, whether it be pre-stack data conditioning or migration, is designed with the theory of P-wave reflected energy in-mind, for travel paths involving only a single reflection. Any energy propagating with other modes or travel paths will not be dealt with appropriately during conventional seismic data processing. It is primarily for this reason that we spend so much time preconditioning seismic data, so as to meet the assumptions of the subsequent migration. In this study, looking at shallow-water marine data from high velocity-contrast environments (such as found with basalt or carbonates), I assess the behaviour of some other classes seismic energy, when subjected to conventional processing, so as to better understand the anomalous events appearing in migrated CRP gathers and images, due to contamination of the data with remnant refraction and mode-converted energy.
Liu F.,Hess Corporation |
Zhang G.,CAS Academy of Mathematics and Systems Science |
Morton S.A.,Hess Corporation |
Leveille J.P.,ION Geophysical
Geophysics | Year: 2011
Reverse-time migration (RTM) exhibits great superiority over other imaging algorithms in handling steeply dipping structures and complicated velocity models. However, low-frequency, high-amplitude noises commonly seen in a typical RTM image have been one of the major concerns because they can seriously contaminate the signals in the image if they are not handled properly. We propose a new imaging condition to effectively and efficiently eliminate these specific noises from the image. The method works by first decomposing the source and receiver wavefields to their one-way propagation components, followed by applying a correlation-based imaging condition to the appropriate combinations of the decomposed wavefields. We first give the physical explanation of the principle of such noises in the conventional RTM image. Then we provide the detailed mathematical theory for the new imaging condition. Finally, we propose an efficient scheme for its numerical implementation. It replaces the computationally intensive decomposition with the cost-effective Hilbert transform, which significantly improves the efficiency of the imaging condition. Applications to various synthetic and real data sets demonstrate that this new imaging condition can effectively remove the undesired low-frequency noises in the image. © 2011 Society of Exploration Geophysicists.
Vasconcelos I.,University of Edinburgh |
Sava P.,Colorado School of Mines |
Douma H.,ION Geophysical
Geophysics | Year: 2010
Wave-equation, finite-frequency imaging and inversion still face many challenges in addressing the inversion of highly complex velocity models as well as in dealing with nonlinear imaging (e.g., migration of multiples, amplitude-preserving migration). Extended images (EIs) are particularly important for designing image-domain objective functions aimed at addressing standing issues in seismic imaging, such as two-way migration velocity inversion or imaging/inversion using multiples. General one- and two-way representations for scattered wavefields can describe and analyze EIs obtained in wave-equation imaging. We have developed a formulation that explicitly connects the wavefield correlations done in seismic imaging with the theory and practice of seismic interferometry. In light of this connection, we define EIs as locally scattered fields reconstructed by model-dependent, image-domain interferometry. Because they incorporate the same one- and two-way scattering representations usedfor seismic interferometry, the reciprocity-based EIs can in principle account for all possible nonlinear effects in the imaging process, i.e., migration of multiples and amplitude corrections. In this case, the practice of two-way imaging departs considerably from the one-way approach. We have studied the differences between these approaches in the context of nonlinear imaging, analyzing the differences in the wavefield extrapolation steps as well as in imposing the extended imaging conditions. When invoking single-scattering effects and ignoring amplitude effects in generating EIs, the one- and two-way approaches become essentially the same as those used in today's migration practice, with the straightforward addition of space and time lags in the correlation-based imaging condition. Our formal description of the EIs and the insight that they are scattered fields in the image domain may be useful in further development of imaging and inversion methods in the context of linear, migration-based velocity inversion or in more sophisticated image-domain nonlinear inverse scattering approaches. © 2010 Society of Exploration Geophysicists.