Djalma Manoel Soares Filho

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.

A 3D Reverse Time Migration Scheme For Offshore Seismic Data

This work introduces a reverse time migration formulation specially designed for offshore data acquired with a single boat pulling one or two air-guns and some streamers of receivers. 3D depth migrations are performed using the concept of areal shot record, as introduced by Berkhout in 1992. In the proposed scheme, an areal shot record is computed through the sum of convolutions between the seismograms registered along a sail line and a synthesis operator, which is designed to form a specific wave front just above the target zone (controlled illumination). All extrapolations are performed solving the acoustic two-way wave equation without smooth the macro-velocity field. The method is illustrated with an application on the SEGEAGE Overthrust model. Except for some small artifacts, less than forty areal shot records were enough to image the main interfaces. The execution time was considerably less than that required to reserve time migrate all seismograms independently.

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.

On the Scaling of the Update Direction for Multi-parameter Full Waveform Inversion: Applications to 2D Acoustic and Elastic Cases

Full waveform inversion (FWI) is traditionally designed as an iterative non-linear optimization problem. Thus, it is subject to scaling problems due to inappropriate choice of model parametrization. It is well known that the conventional gradient-based direction update of the parameters, although widely reported and used, does not have the correct physical units; thus, it needs to be properly weighted to provide an adequate model update. The purpose of this work is to examine this issue and to provide an alternative computation to the update directions for the multi-parameter FWI by taking into account the transformation properties of the Hessian and its approximations, since the Hessian contains information related to parameter scaling. To put in evidence the benefits of this approach, we present applications to mono-parameter acoustic and multi-parameter elastic FWI using the 2D Marmousi-2 synthetic model. The proposed direction of update properly scales the estimated models and provides a much faster convergence rate.

Modelagem e migração em profundidade 2D em meios com simetria polar local

This paper shows a technique based on the phase-shift method (PSM) to implement pre-stack depth migration on locally transverse isotropic media (LTI), with the symmetry axis direction varies continually along the layers. For seismic modeling, a generalization of the finite differences method for the solution of the elastic wave equation was used. With this procedure, it was possible to accommodate seismic modeling on LTI media defined by six parameters at each grid point, i.e. , density, P and S wave propagation velocities along the local symmetry axis, Thomsen parameters and the direction of the local symmetry axis itself. In order to separate from the seismograms the qP and qSV wavefields, an algorithm based on the Christoffel equation was implemented. The migration for each common shot gather is implemented solely by phase-shift based algorithms, which means that not only the depropagation of the registered wavefield, but also the generation of the time matrices involved in the imaging condition were obtained in this manner for each set of parameters at each depth level. The migration results using qP-qP and qP-qSV reflections show that the horizons were located precisely, and that the process is stable in relation to the symmetry axis variations. The proposed method is for multicomponent seismic acquisitions and might be applied to marine seismic data using streamers, or Ocean Bottom Cables or vertical cables. Since the proposed method uses phase-shift algorithms, its parallel implementation can be highly efficient.

Phase-shift anisotropic depth migration using controlled illumination applied to a model of the San Alberto field - Bolivia.

Summary We introduce a new scheme for depth migration in elastic vertical transverse isotropic media (VTI), using the concept of controlled illumination. In the proposed method the areal shots obtained from multicomponent records are extrapolated using phase-shift techniques. Through the weighted addition of delayed shots we synthesize appropriate areal shots, which increases the accuracy of the seismic imaging in the area of interest. The computational cost of the present method is much lesser, when compared to the cost of migrating all the records, since only a few areal shots are necessary to image the area selected by the interpreters. The proposed method was tested on a typical numerical 2D model from the San Alberto field in Bolivia. It was possible to correct image an exploration target located underneath a thick highly tectonic deformed anisotropic shale layer, using only 3% of the computational time necessary to migrate all the shot records.

Phase-shift anisotropic depth migration using controlled illumination: Stability in relation to addition of random noise

The present work studies the stability of a depth migration for elastic vertical transverse isotropic media (VTI), using the concept of controlled illumination. In the proposed method the areal shots obtained from multicomponent records are extrapolated using phase-shift techniques. Through the weighted addition of delayed shots we synthesize appropriate areal shots, which increases the accuracy of the seismic imaging in the area of interest. The computational cost of the present method is much lesser, when compared to the cost of migrating all the records, since only a few areal shots are necessary to image the area selected by the interpreters. The proposed method was tested on a typical numerical 2D model from the San Alberto field in Bolivia exposed to noisy conditions created by a random noise generator. Even with lower signal to noise ratio (SNR) we can correctly migrate anticline structures under a thick anisotropic shale layer. Introduction One of the great challenges in the search for new oil and gas fields has to do with seismic imaging underneath intensively tectonic deformed areas. This includes areas underneath thick salt layers, such as the coastal basins in the east of South America and areas subjected to great compressional efforts, like some coastal basins in the west of South America. In this context, the wave equation migration based methods have played a fundamental role. In fact, its simplicity and the generality of their premises render its superiority in terms of accuracy when compared to asymptotic approximation based methods. On the other hand, wave equation depth migration usually demands a computational effort that is several times superior to the capacity of most computer centers, which turns many projects unfeasible. Many propositions aim at the wave equation migration optimization. Most of them are based in the concept of wave synthesis, as initially proposed by Taner (1976) and by Schultz and Claerbout, (1978). In these works, the synthesized waves were positioned near the surface, which in many instances, were very far from the exploration targets. Berkhout (1992) proposed a method in which the synthesized waves were positioned closer to the targets, that allowed to image the interested areas more precisely. Recently, among the several works in this area, we can cite Cunha (2002), who generalizes the concept of reverse time migration for areal sources, and Wang et al. (2001) who introduced the concept of multi controlled illumination. In the present work we test the stability, in relation to random noise addition, of an algorithm for areal shot migration scheme applied to multicomponent seismic data in VTI media (Cetale Santos, et al 2005). Areal shots from multicomponent data Once we have the field seismograms for the horizontal and vertical wavefield at the surface, derived from a multicomponent 2D survey, we compute the compressional wavefield seismograms by applying the divergent operator at a datum located near the surface (Sun and Wang, 1999). From the compressional wave seismograms, represented by P(kx,z0,ω;xj), where xj is j shotpoint position at the surface, we compute the areal shots through the weighted sum of delayed shots,