Processamento, imageamento, interpretação e predição de pressão de dados sísmicos na bacia sedimentar do Jequitinhonha

Abstract

This present work aimed to compose a seismic-stratigraphical framework for part of Jequitinhonha basin (marine east part of the State of Bahia), with data released for funded academic projects in progress. The study aims at the exploration of oil and gas, and corresponds to a proposal for for sedimentary basin revaluation. For this, the methodology is composed of velocity analysis, CRS stacking, migration, culminating in pressure prediction for the subsurface, where the aim is to map low (reservoir) and high (generator) pressure zones that act as natural pumps for fluid accumulation. The seismic data used in this study was provided by PETROBRAS for the Postgraduate Course in Geophysics (CPGF), of the Institute of Geosciences of the Federal University of Pará. The data were acquired by the PETROBRAS seismic team 214 in the offshore part or the basin. The available lines used in this study were the L214-266, L214-268, L214-270 and L214-297. Being able to separate them into two groups, we have three lines in the NE-SW directions (L214-266, L214-268, L214-270) and one in the direction NW-SE (L214-297). The velocity distributions used for the seismic sections were based on petrophysical information and empirical models, instead of using the subjective event picking in common-midpoint, stack or migration sections. The methodology presents as the first part the application of techniques based on the theory of the common reflection surface stack (CRS), which aims to generate seismic images of good quality for the interpretation of real data, and related to geologically complex media. The seismic-stratigraphic interpretation were performed using as a basis the geological information, making a correlation between the main reflectors (interfaces of higher impedance) and the stratigraphic units of the area. In this way, we constructed an empirical model for the velocity distribution (𝑣𝑅 and 𝑣𝑆) and density (𝜌) for the sections of the studied block. A higher study project aims to predict stress in sedimentary basins, as a contribution to the methods and techniques of geology and oil and gas engineering exploration. This subject is based on the knowledge of the compressional (𝑣𝑃 ) and shear (𝑣𝑆) velocities, and densities (𝜌), in order to locate areas low and high pressure zones in the subsurface, which serve as natural suction pumps for gas and oil accumulation. The theory is based on the elastodynamic equations, where the gravitational weight of the overload is responsible for the effects of strain-stress deformation in the subsurface. Therefore, to organize this problem requires the generalized Hooke’s law of linear elasticity. We presented details of the theoretical model, and an example to show how the pressure varies in the subsurface, where we highlight that pressure prediction does not necessarily increase linearly, but in a complex way that requires specific numerical formulas to be able to see important details. The applied theoretical model poses as pressure agent the vertical gravity load of the geological formations, and does not take into account the effects of curvatures, faulting and diagenesis. Also, the complex lateral tectonic events are not accounted for. The prediction of pressure and tension is an important issue for the analysis of sedimentary basins, aiming at mapping and extending potentially oil and gas productive areas. But an accurate prediction needs a 3D model for a significantly complete practical application.