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We investigated how current least-squares reverse time migration (LSRTM) methods perform on subsalt images. First, we compared the formulation of data-domain vs. image-domain least-squares migration (LSM), as well as methods using single-iteration approximation vs. iterative inversion. Next, we examined the resulting subsalt images of several LSRTM methods applied on both synthetic and field data. Among our tests, we found image-domain single-iteration LSRTM methods, including an extension from Guitton’s (2004) method in the curvelet domain, not only compensated for amplitude loss due to poor illumination caused by complex salt bodies, but also produced subsalt images with fewer migration artifacts (i.e., noise) in the field data. By contrast, an iterative inversion method showed its potential for broadening bandwidth in the subsalt, but was less effective in reducing noise. Based on our understanding, we will summarize the current state of LSRTM for subsalt imaging, especially between single-iteration and iterative LSRTM methods.

The importance of inverting jointly velocity and density parameters in full waveform inversion (FWI) is well established. In a former work we had proposed an innovative preserved amplitude FWI allowing improving the convergence rate of FWI. It was derived from preserved amplitude reverse time migration (RTM), involved a deconvolution imaging condition and was limited to the estimation of velocity perturbation from reflection data. We extend here the approach to a joint velocity and density preserved amplitude FWI. We present the theoretical derivation of the improved common shot FWI gradients and show how we can decouple the two parameters. We validate our approach on the Marmousi II synthetic model which shows that we can efficiently reconstruct the two parameters, and on a real data showing that we significantly reduce the data residual with the joint inversion.

Spectral broadening of migrated and stacked seismic images is a common method to enhance interpretability of reflection data. In this paper we propose a prestack AVA compliant spectral broadening approach based on non-stationary wavelet deconvolution. The algorithm employs AVA coupling in the prestack domain to shape the spectra of all traces in angle gathers simultaneously. Using synthetic and real data we show that the characteristics of all AVA classes are preserved and that the spectra of all angles are enhanced and better balanced.

Posing migration as an inverse or a least-squares problem can improve the quality of imaging. This class of techniques can resolve illumination issues and improve focusing. Standard iterative least-squares imaging can be expensive and results are often compromised. We present a procedure using matching filters operating in data-space rather than image space. Effective inversion results are demonstrated on synthetic and real data.

Interbed multiples cause artifacts in subsurface images because they are incorrectly migrated when using standard primary-based migration algorithms. While surface-related-multiple-elimination has been well established as a standard step in seismic processing, the usage of interbed multiple attenuation (IMA) remains low due to various practical challenges such as inaccuracy in prediction, difficulty in subtraction, and prohibitively high compute cost. We propose a workflow with a few strategies to improve the applicability of IMA. Using a 3D field data example, we demonstrate the effectiveness of our workflow in predicting and attenuating interbed multiples. We also illustrate how the removal of interbed multiples can help with accurate interpretation of subsurface geology.

Geophysical imaging in the foothills environment is typically hampered by complex structure, and the high cost of data acquisition in poorly accessible, rugged topography. Seismic imaging is particularly difficult due to poor signal penetration, steeply dipping structures and irregular data coverage. The use of magnetotellurics (MT) has become a successful complementary tool, due to good sensitivity to the deep resistive targets typically encountered below folded sequences of more conductive units. Due to non-uniqueness and resolution limitations, MT 3D inversion requires additional constraints in order to recover a reliable image. These usually come from geological interpretation of available seismic and well data, however it is often the case that several competing structural models can be derived. In this abstract we propose a workflow that employs magnetotelluric inversion to assess the validity of such structural models, by examining whether they are compatible with the electromagnetic observations. We further apply 3D non-linear uncertainty estimation to address the reliability of the inversion results, obtaining a bounding envelope of the resistive anomaly.

Direct wave arrivals are the most robust signals to determine velocity and consequently they have been used for almost a century in hydrocarbon exploration. The reason is simple as the arrival time is explicitly available. In order to acquire these direct arrivals in a seismic experimental setting it is necessary that these waves turns back to the surface after having been sent into the Earth. As is well known it is possible to turn waves back up if they encounter faster propagation velocities than have been previously experienced. Using these simple concepts we show how it is possible to design a seismic acquisition to measure subsalt velocities when the salt cover is very thick and potentially not homogeneous. Until now (in marine seismic surveying) the physical limitations of the Earth have meant that use of direct wave arrivals have been restricted to relatively shallow depths of investigation, linked to streamer length. In this paper we describe how a new and novel application of node technology has been combined with a well established physical phenomena to support the acquisition of a world first exploration-scale Ocean Bottom Node (OBN) survey.

Exploring the Middle East’s energy landscape in an exclusive chat with CGG’s Ramez Refaat

We propose a more accurate alternative to Gassmann's equation for the modeling of the undrained bulk compressibility of a reservoir rock with moderate to high crack density. The new model combines the Vernik-Kachanov model and Brown-Korringa's equation. A practical quantification of the applicability of Gassmann's equation dependent on the rock stress dependency is also suggested.