Luiz Alberto Santos

Target oriented illumination analysis using wave equation

The proposed methodology requires considerably less resources, in terms of processing time and disk space, than the traditional procedure using wave equation. The traditional procedure compares depth images obtained by a migration scheme, after modeling the complete dataset for a certain acquisition geometry. Both methodologies are more accurate than the results based on ray tracing modeling in complex areas (due to the high frequency approximations involved in this scheme).

Application of Blended Seismic Data in Full Waveform Inversion

Summary In seismic imaging the Full Waveform Inversion (FWI) has recently gained much importance, mainly due to advances in computational power and seismic acquisition improvements, especially in areas with high geological complexities. In fact, it can provide higher seismic resolution compared to pre-stack depth migration, which may contribute to better seismic interpretation. However, for complex geological models the success of seismic imaging depends on the design of the seismic experiment. In fact, besides the necessity of a wide spectrum of frequencies, it is required to properly register the scattering wavefields associated to the geological targets. Otherwise, the imaging and inversion schemes are not effective. Acquiring the scattering wavefields as a 3D field may be cost prohibitive using conventional surveys, where consecutive shot records don’t have time superposition. In this work, we abandon this condition, and extend the inversion scheme called Contrast Source Inversion (CSI) to handle data in which shots are superposed randomly (Blended data). On the propose method, the deblending phase (separation the interference between shots) is not necessary. Numerical results applied on Marmousi model show how efficient, accurate, and stable this method is when compared to results obtained with traditional acquisition approaches. Even in very low signal to noise ratio cases, except for small artifacts, it was possible to recover all features present in the original model.

Tomographic Inversion Over Diffraction CFP Operators In Structurally Complex Areas

In the universe of tomographic techniques aiming to determine the subsurface velocity field, inversion over CFP Operators (CFPOs) reduces depth-velocity ambiguity. Its main drawback is the operator estimation for very complex areas, where conventional CFPO estimation is damaged by the non-continuity of events and diffractions. We overcome this problem using diffractions in Common Offset Gathers (COG) to estimate CFPOs. A synthetic example based on a geologic-geophysics model of the Santos Basin (offshore Brazil) is used to validate the idea. An overview of the inversion workflow is presented in which a Singular Value Decomposition (SVD) pseudo-inverse technique is explored.

Qualitative and quantitative illumination analyses using wave equation

The proposed methodology is based on solutions for the Acoustic Wave Equation obtained by FDM (Finite Difference Method). The first step involves a wavefield extrapolation from the target up to the surface, applying the Reciprocity Principle like Alves et al. (2008). Thus a lower computational cost is obtained when compared to conventional methods, which make one extrapolation for the source and another extrapolation for the receiver.

Numerical Experiments of Full Waveform Inversion on a Typical Pre-salt Model - Part 2 - Elastic Effects

We consider the elastic effects on an acoustic full waveform inversion generated by a synthetic pre-salt model of Santos basin, Brazil. We used P/S-velocity and density models to generate shot-gathers with acoustic, elastic (isotropic), constant and variable density modelling. The comparison of the amplitudes of the shot-gathers already provides a clue to the challenges acoustic FWI may face, as acoustic modelling is not able to provide the correct amplitude for the elastic data. This test is complemented with a constant-density acoustic FWI inversion, for all the different datasets, but with the same algorithm and parameterization. FWI with acoustic data was able to retrieve the correct information of high velocity sediments in the post/pre-salt environment and the stratification of the evaporitic sequence. On the other hand, the inversion of elastic data could not properly invert anything underneath the top of salt. The comparison of the inversion results indicates a direction in which algorithm and simplifications can be done to pursue an adequate property inversion.

Seismic Illumination with Incidence Angle Estimation

This paper presents a way to perform Seismic Illumination Studies with incidence angle estimation using Acoustic Wave Equation solved by Finite Difference Method. A target-oriented methodology to calculate illumination values using the maximum amplitude of the wavefields based on Alves et al. (2008, 2009) and Silva et al. (2011) was extended in order to considerer the incidence angle at the target in the studies. Applications are presented and analyzed on a modified version of the Hess model.

Contrast Source Inversion of Blended Data

Full waveform inversion has the potential of playing the central role in seismic imaging in the near future. In fact, its power of providing higher seismic resolution compared to pre-stack depth migration may contribute to seismic interpretation in areas which present high geological complexities. However, its success depends on the design of the seismic experiment. In fact, besides the necessity of a wide spectrum of frequencies, it is required to properly register the scattering wavefields associated to the geological targets. Otherwise, the inversion scheme is not effective. On the other hand, acquiring the scattering wavefields as a whole may be unfeasible using conventional surveys, where consecutive shot records don’t have time superposition. In this work, we abandon this condition, and extend the contrast source inversion method to handle data in which shots are superposed randomly. In our method, the deblending phase is not necessary. Applications on Marmousi model show how efficient, accurate, and stable this method is when compared to results obtained with traditional acquisition approaches. Even in very low signal to noise ratio cases, except for small artifacts, it was possible to recover all features present in the original model.