11th International Congress of the Brazilian Geophysical Society

This paper presents a novel 3D seismic attribute classification technique based on a framework in which the interpreter defines the data partitioning required to generate the classified data volume by directly interacting with a multi-attribute visualisation system. The classification process utilises the latest advances in graphics processing unit (GPU) parallel computation technology, enabling the classification to be achieved in real time on standard (non-cluster) desktop workstations.
The ability to deliver classification results in real time enables interpreter driven feature definition and introduces a new paradigm in multi-attribute analysis techniques, that can be applied so quickly and easily that they can be incorporated simply into any standard 3D seismic interpretation workflow.

Neste trabalho estimamos a orientação estratigráfica de um intervalo de testemunho horizontal de rocha através da análise de anisotropia de velocidades sísmica (VelAn). Análises de tomografia computadorizada foram importantes para o controle de qualidade dos resultados. Os resultados obtidos concordam satisfatoriamente com a direção de orientação recuperada nos registros da sonda.

Receiver Functions (RF) in the frequency range 0.1 to 1 Hz have been extensively used to estimate crustal thicknesses. Here we show that high frequency RF (1 to 5 Hz) can be used to determine the thickness of sedimentary basins. However, the non-uniqueness of the RF inversion requires other information to be added in the inversion scheme. For example, different velocity profiles of the shallow (<100m) layers have a large effect in the inversion results for the deeper layers. We used a shallow seismic refraction survey to constrain the seismic velocities in the first 30m. Surface-wave group-velocity dispersion was used to constrain the average crustal S-wave velocity. Long-period RF was jointly inverted with high-frequency RF to estimate both the deep crustal and the sedimentary structure. Station CDSB is located in the northern part of the Paraná Basin, in the middle of a low-gravity anomaly, which has been attributed to a buried graben. Our inversion of the RFs suggests the graben could be about 7-8 km deep, consistent with gravity modeling, but has a thick basalt flood layer, perhaps related to the graben evolution.

Using the method introduced by Landro (2001), it has been possible to study the pressure and saturation changes induced by production in the Marlim field, figure 1. This methodology does not make any assumption about production, requiring only petrophysical and seismic data covering the field of interest. Maps representing pressure and saturation changes are presented and also a section over one well, showing how these anomalies can be compared with flow simulator prediction. The main result obtained is a better understanding of the mechanism by which water saturation and effective pressure changes are created during field production.

Geoelectric fields induced in the Earth during geomagnetic storms drive electric currents through the windings of power transformers and the transmission lines carrying electric power. These currents, known as GIC (Geomagnetically Induced Currents), flow in the entire electric power systems and cause deleterious effects. The well-known and documented GIC events of
13-14 March 1989 and 29-30 October 2003 inflicted considerable damages and power failures in the northern auroral regions. In Brazil, there is an on-going project to study GIC in a collaborative effort between the National Institute for Space Research-INPE and Furnas Centrais Elétricas S.A. We present here the already published results on calculated intensity of GIC flowing in the transmission lines near Itumbiara in central Brazil during the event of 7-11 November 2004 and the recent progress of the work. We established a linear relationship
between the rate of variation of the horizontal geomagnetic dH/dt and the calculated GIC flowing in the transmission lines near Itumbiara (Goiás). Although no significant geomagnetic storms have occurred after November 2004 we present here results from direct measurements of GIC on the neutral phase of the power transformer at the electric power substation at Itumbiara
and compare the measured GIC values to the deduced GIC values flowing in the transmission lines.

In heterogeneous media, standard one-way wave equations only describe the kinematic parts of oneway wave propagation correctly. For a correct description of amplitudes, the one-way wave equations must be modified. In vertically inhomogeneous media, the resulting true-amplitude one-way wave equations can be solved analytically. The corresponding amplitude modifications can be taken into account in split-step and Fourier finite difference migrations in such a way that they use these true amplitude oneway wave equations instead of the standard ones in order to implement a true amplitude wave equation migration for zero-offset data. Synthetic data examples demonstrate that the technique improves amplitude recovery in the migrated images.

Standard real-valued finite-difference (FD) and Fourier finite-difference (FFD) migrations cannot handle evanescent waves correctly, which can lead to numerical instabilities in the presence of strong velocity variations. A possible solution to these problems is the complex Pad´e approximation, which avoids problems with evanescent waves by a rotation of the branch cut of the complex square root. In this paper, we apply this approximation to the acoustic wave equation for vertical transversely anisotropic (VTI) media to derive more stable FD and hybrid FD/FFD migrations for such media. Our analysis of the dispersion relation of the new method indicates that it should provide more stable migration results with less artifacts and higher accuracy at steep dips. These studies lead to the conclusion that the rotation angle of the branch cut that should yield the most stable image is 60◦. This result is confirmed by the numerical
impulse responses and synthetic data examples.

This paper presents de results of a geophysical survey carried through to assist the studies of erosive processes and silting in area located at the city of Brotas-SP, Brazil. Surveys had been carried through in water-covered area (lake in silting process) using bathymetry and on land (area where there was an ancient lake that is entirely silted nowadays) by using GPR method.

Dual-sensor technology allows one to separate the upgoing and down-going wave fields, and ultimately remove the receiver ghost. This increases the spectral bandwidth of the recorded data and results in a final image that is improved for all depths. Application of this technology in offshore Guyana has resulted in an improved image of the subsurface as compared to what could be achieved with more conventional streamer technology.

In this paper we present the state of the art of Petrobras data management in national area. We start with a short historical retrospective of Petrobras experience with data management. We then present the main features of geological and geophysical data in Brazil and the implications of the production of a large amount of data in the huge territory that comprises Petrobras exploration area. Finally, we discuss the recent Petrobras data management approaches in order to organize legacy and incoming data.