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The scope of this paper is to illustrate how surface-consistent deconvolution operators can help to image the shallow subsurface on land data. Two case studies from modern, dense, wide-azimuth surveys recently acquired in Oman are presented. The predictive deconvolution operators were computed from an advanced simultaneous inversion of surface consistent scalars and autocorrelations. Source and receiver operator volumes were compared to the migrated stack of primary reflections. A significant improvement in the imaging of the shallow layers was achieved. Some structures that were almost invisible on the migrated stack were revealed and the shallow reflectivity was recovered in undershoot areas. These high resolution reflectivity volumes can be used as a guide for velocity model building of the shallow subsurface or as an input to internal or surface multiple modelling.

Anisotropic parameter estimation is very challenging for new exploration areas where there are no wells. In an offshore survey of over 3000 km2 in the west of Africa, we used surface seismic data in a non-linear tomographic inversion to simultaneously estimate migration velocity and anellipticity. Although a blank model of anisotropic parameters was used as input model, the joint tomography created an anellipticity model which followed the geological structures. It was one of the first projects where the non-linear tomography achieved to build an anisotropic model which was geologically consistent and minimized residual moveout.

Reverse Time Migration of Multiples (RTMM) adapted for OBN data with examples from deepwater Gulf of Mexico.

Standard joint AVO inversion of PP and PS seismic data rely on a registration process beforehand to align PP and PS data in a common time domain. This is a difficult step prone to error that may deteriorate the inversion results. We present a new method to jointly invert PP and PS data without prior registration by integrating the travel times as well as the amplitudes in a model-based inversion. Including the travel times brings extra constraints on the VP/VS ratio and therefore helps the inversion converge. This new method is demonstrated on a shale gas data example and shows better results than PP inversion and standard joint inversion.

The high costs associated with hydrocarbon exploration in deepwater have led to an increased business demand for acquisition and processing of high-resolution broadband seismic data. In this paper, we review our experience of working on the Shell Sandman 3D survey, which was acquired using variable-depth streamers and synchronized multi-level sources. We focus on the key factors that influence the surface seismic temporal resolution and the technologies that provide solutions to these challenges: (1) source deghosting using source designature with near-field hydrophone data; (2) receiver deghosting using the 3D deghosting algorithm; and (3) compensation for the Earth absorption using centroid frequency shift Q tomography (FS-QTOMO) and QPSDM. The extra-wide bandwidth obtained from these processes provides a final image with detailed resolution that enhances quantitative characterization, not only for shallow geo-hazards but also for resolving relatively thin reservoirs in the deep section. Therefore, we can conclude that broadband seismic methodologies coupled with advanced seismic processing techniques, provide an effective solution for generating high-resolution seismic images, especially in challenging areas.

We present a two-step sequence to estimate uncertainties in lateral positioning of fault planes on 3D PSDM seismic images. The first step provides an approximate evaluation of what causes the uncertainties, how uncertainties are distributed in 3D space and what to expect within our target zones. In the second step we focus on a single fault of practical interest and assess how far the velocity changes can move the image of the fault and still satisfy the available seismic data. We use a real multi-azimuth 3D seismic dataset from the North-West Australian shelf to illustrate this sequence.

Conventional imaging does not deal adequately with absorption, especially in the case of strong anomalies. Over recent years, many authors have proposed to compensate the absorption loss effects inside of the migration through the use of an attenuation model. Q tomography has been developed for estimating this attenuation model but is generally limited to estimating attenuation in predefined anomalies. In this paper, we explain how we developed a high-resolution volumetric Q tomography to attain an accurate volumetric estimation of the attenuation model. A key component of our workflow is the estimation of effective attenuation in the pre-stack data domain through accurate picking of the frequency peak. Finally we present a case study where our approach has been used to reveal shallow gas pockets and compensate for absorption in the migration.

The importance of anisotropy in seismic imaging has been recognized for several decades. In recent years, a growing number of anisotropic applications of reverse time migration (RTM) and full waveform inversion (FWI) have attempted to account for anisotropic effects of the real-world subsurface physics. In anisotropic media the P-wave, SV wave and SH wave are intrinsically coupled, therefore the media are elastic in nature. But the elastic anisotropic wave equation is computationally very demanding and requires S-wave velocity models, for which in practice we often have little information. Consequently, the acoustic assumption is widely-used in seeking anisotropic wave equations. Stable acoustic anisotropic wave equations may create apparent pseudo S-waves during wave simulation. These S-waves then show up as artifacts in migrated images from RTM and in velocity perturbations from FWI. We propose the model taper method to eliminate the source generated S-wave, and derive a series of approximate formulae that allow accurate and efficient attenuation of pseudo S-waves after acoustic anisotropic wave propagation, as a supplementary routine. Synthetic data and real data examples are shown to verify the proposed prescription in complex media.

In shallow water environments, water-layer related multiples (WLRMs) typically dominate other classes of multiple, and achieving effective attenuation of WLRMs is of significant interest. When combined with an appropriate adaptive subtraction, Model-based Water-layer Demultiple (MWD) has been found to be highly effective in attenuating WLRMs. In this paper we demonstrate a limitation of the conventional implementation of MWD, and propose an extension to the method to account for this limitation. We demonstrate the effectiveness of our approach on simple 1D synthetics, and real-world 3D seismic data from towed-streamer acquisition in the North Sea.