Jorge Fiori Fernandes Sobreira

Geotechnical characterization based on seismic data approaches applied in Campos Basin, southeastern Brazilian Margin

Accurately characterizing the nature and geotechnical behavior of the marine near surface (up to 50–100 m below seafloor) is essential when new E&P infrastructure is installed offshore where seabed conditions are frequently chaotic and highly variable.

Ultra-deepwater 4-C offshore Brazil

This paper is the case history of an ultra-deepwater 4-C seismic program, recently acquired in the Campos and Santos basins, offshore Brazil. All aspects of the program will be discussed, including the feasibility study which first indicated the potential value of multicomponent technology to this region, to the survey objectives, to the illumination analysis used in designing the survey, to the field operations, to the fully processed results. Acquisition was completed on 19 April 2005, and the fully processed data were delivered in early November 2005.

Simultaneous Seismic Inversion Applied To Geotechnical Analysis Of Near Seabed Sediments

This paper describes a near seabed geotechnical characterization study in Campos Basin, offshore Southeastern Brazil, including the analysis of elastic moduli distribution such as shear modulus and Lame’s c oefficient ( μ and λ , respectively). These two moduli were calculated from rock physics properties such as acoustic (P) and shear (S) impedances and density, derived through and as results of a prestack simultaneous AVO seismic inversion which algorithm uses a global optimization procedure including simulated annealing. Inverted 3D cubes allowed near seabed mapping of the elastic parameters that showed acceptable qualitative correlation with direct geotechnical measurements. This study will be applicable to improve understanding of subbottom sediments stiffness for engineering purposes, like future subsurface installation of oil platforms foundations.

Comparing P-S conversion point location in isotropic and anisotropic media

The determination of the exact position of the P-S conversion point (CP) is an important issue in converted-wave seismology. Frequently, this issue is approached considering that the rock formation is isotropic. This simple approach may lead to significant errors due to the anisotropic features of the subsurface. This paper presents a comparison between the position of the CP obtained from the isotropic solution and the position of the CP considering two types of anisotropy: the transversely isotropic medium with vertical axis of symmetry, the so-called VTI, and an orthorhombic medium. In order to determine the location of the CP, the modeling program ANRAY, based on ray tracing method, was used. It is shown that for the VTI case the discrepancy between the true position of the CP and the one found by assuming isotropy can be in the order of hundreds of meters, even for offset/depth ratio, (X/Z), less than 2. On the other hand, for some particular values of Thomsens parameters I and d, it can be demonstrated that, the position of the CP practically coincides with the isotropic case. For orthorhombic symmetry (azimuthal anisotropy), the CP, in general, is no longer located in the vertical plane defined by the source-receiver positions, i.e., the discrepancy between CP locations is expressed by an inline and an offline components. The offline component value depends on the anisotropic nature of the medium. This observation is not valid only for orthorhombic models since similar discrepancies can also be observed in cases where the anisotropy is induced by cross-dipping structures or in models with lower anisotropic symmetries.