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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.

Several methods have been proposed to improve the signal-to-noise ratio by attenuating incoherent noise, including prediction error filtering (Canales 1984), projection filtering (Soubaras 1995), and more recently rank reduction filtering. In this last category, we can differentiate eigenimage filtering (Trickett 2003), Cadzow / Singular Spectrum Analysis (SSA) filtering (Trickett 2009, Sacchi 2009) and tensor methods (Kreimer and Sacchi 2012, Trickett 2013, Da Silva and Herrmann 2014). Also, these latter methods have been extended to robust noise attenuation to deal with erratic noise, or data interpolation for binned data within a defined grid (Trickett et al. 2010, 2012, Oropeza and Sacchi 2011, Chen and Sacchi 2013). Here, we propose a systematic formulation of the simultaneous random plus erratic noise attenuation and data interpolation problem as a convex optimization program, which can be solved efficiently. We model the coherent signal via its low-rank trajectory matrix in the spirit of Cadzow/SSA filtering, and the erratic noise as a sparse component of the input data. The signal component is recovered by solving a Joint Low-Rank and Sparse Inversion (JLRSI) thanks to a joint minimization of the nuclear and L1 norms of the low-rank and sparse components respectively.

One way to address the problem of weak subsalt illumination is through angle gather illumination weighting (AGILW). In this technique, synthetic data mimicking the field data are generated and migrated the same way as the field data. Illumination weighting scalars are obtained by measuring coherent amplitude on the synthetic migration gather. This weighting scalar can be applied to field data to enhance signal and attenuate noise. In this paper, we propose a refinement of this approach: shot patch-based angle gather illumination weighting, based on RTM 3D angle gathers. Instead of using the traditional approach of migrating all shots in a survey to form one set of angle gathers, we partition the input shots from both field and synthetic data into smaller shot patches and keep the migration gathers separate for each shot patch. This new approach can limit crosstalk between signal and noise from different shot patches, and can more effectively attenuate noise and improve subsalt images. We demonstrate the effectiveness of our method with both 2D synthetic data and 3D field data.

The test showed that, in the central North Sea, with appropriate denoising, we were able to successfully remove SI from all azimuths down to a vessel separation of less than 25 km. By adjusting vessel speeds to make sure that SI did not arrive at the same time from shot to shot, even better denoising results were achieved.

We present an input data selection workflow based on 3D ray-tracing to improve the RTM image in areas of poor illumination and low signal-to-noise ratio. It is effective for imaging subsalt three-way closure with weak subsalt primaries and strong noise levels. The workflow can be applied on any type of survey, but it is most suitable for full azimuth geometries. We focus on data selection using 3D ray-tracing, but this workflow can be easily adapted to use finite-difference wave-equation modelling. The data selection information can either be used to scale up the weak primary signal before migration or to be migrated separately and merged into a full migration result in the post-migration stage.

Serial processing of PP and PS waves leads to depth inconsistencies between the PP and PS migrated images. The link between P- and S-velocity model is the Vp/Vs ratio, whose estimation is an important task in multicomponent analysis because of its applications to lithology and fluid discrimination. We show the advantages of using the Vp/Vs ratio estimated with dynamic image warping as a volumetric constraint for nonlinear slope tomography. Our approach does not require repeated shift estimation between PP and PS events during inversion and does not depend on picked horizons thus reducing human interaction and uncertainty associated with interpretation.d PS events during inversion and does not depend on picked horizons thus reducing human interaction and uncertainty associated with interpretation.