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ABSTRACT. We have presented alternative solutions for the displacement and stress fields outside and inside of a 3D right rectangular prism under constant pressure. These solutions are obtained by integrating the well-known nucleus-of-strain solution over the volume of the prism. They are based on the similarity between the gravitational potential yielded by a volume source under a density variation and the thermoelastic displacement potential yielded by a volume source in a half-space under a pressure variation. This similarity enables the use of closed expressions of the gravitational potential and its derivatives. We use our solution for approximating the displacement and stress fields due to a reservoir with arbitrary shape and under arbitrary pressure changes. We discretized the reservoir as a grid of 3D right rectangular prisms juxtaposed in the horizontal and vertical directions. Each prism has homogeneous pressure; however, pressure variations among different prisms are allowed. This parametrization of the reservoir yields a piecewise constant distribution of pressure in the subsurface. We validate the resultant displacement and stress fields due to the reservoir by numerical simulations including a reservoir with arbitrary geometry and under arbitrary pressure distribution, based on a production oil field in offshore Brazil.

ABSTRACT. The pre-salt reservoirs in Santos Basin are known for being overlaid by thick evaporitic layers, which degrade the quality of seismic imaging and, hence, impacts reservoir studies. Better seismic characterization of this section can then improve decision making in E&P (Exploration and Production) projects. Seismic inversion - particularly with adequate low-frequency initial models – is currently the best approach to build good velocity models, leading to increased seismic resolution, more reliable amplitude response, and to attributes that can be quantitatively connected to well data. We discuss here a few considerations about inverting seismic data for the evaporitic section, and address procedures to improve reservoir characterization when using this methodology. The results show that we can obtain more realistic seismic images, better predicting both the reservoir positioning and its amplitude. Keywords: evaporitic section, seismic imaging, seismic inversion, reservoir characterization, seismic resolution.RESUMO. Os reservatórios do pré-sal da Bacia de Santos são conhecidos por estarem abaixo de uma espessa camada de evaporitos, que degradam a qualidade das imagens sísmicas e impactam os estudos de reservatórios. Melhores caracterizações desta seção podem, então, melhorar o processo de tomada de decisão em projetos de E&P (Exploração e Produção). Inversão sísmica – particularmente com modelos de baixa frequência inicial adequados – é correntemente a melhor abordagem para se construir modelos de velocidades, auxiliando no aumento de resolução sísmica, obtendo-se respostas de amplitude mais coerentes, e tendo seus atributos quantitativamente conectados com as informações de dados de poços. Aqui discutiremos algumas considerações sobre inversões sísmicas para seção evaporítica, e indicaremos procedimentos para melhorar a caracterização de reservatórios quando utilizando esta metodologia. Os resultados mostram que podemos obter imagens sísmicas mais realistas, com melhores predições tanto em termos de posicionamento quanto de sua amplitude.Palavras-chave: seção evaporítica, imagem sísmica, inversão sísmica, caracterização de reservatórios, resolução sísmica.