The added value of the joint pre‐stack inversion of PP (incident P‐wave and reflected P‐wave) and PS (incident P‐wave and reflected S‐wave) seismic data for the time‐lapse application is shown. We focus on the application of this technique to the time‐lapse (four‐dimensional) multicomponent Jubarte field permanent reservoir monitoring seismic data. The joint inversion results are less sensitive to noise in the input data and show a better match with the rock physics models calibrated for the field. Further, joint inversion improves S‐impedance estimates and provides a more robust quantitative interpretation, allowing enhanced differentiation between pore pressure and fluid saturation changes, which will be extremely useful for reservoir management. Small changes in reservoir properties are expected in the short time between the time‐lapse seismic acquisitions used in the Jubarte project (only 1 year apart). The attempt to recover subtle fourth‐dimensional effects via elastic inversion is recurrent in reservoir characterization projects, either due to the small sensitivity of the reservoirs to fluid and pressure changes or the short interval between the acquisitions. Therefore, looking for methodologies that minimize the uncertainty of fourth‐dimensional inversion outputs is of fundamental importance. Here, we also show the differences between PP only and joint PP–PS inversion workflows and parameterizations that can be applied in other projects. We show the impact of using multicomponent data as input for elastic seismic inversions in the analysis of the time‐lapse differences of the elastic properties. The larger investment in the acquisition and processing of multicomponent seismic data is shown to be justified by the improved results from the fourth‐dimensional joint inversion.
We show that time-lapse (4D) time-shifts from PS-wave data are valuable as they are very sensitive to pressure changes, whereas 4D time-shifts from PP-wave data are sensitive to both pressure and saturation changes. This gives another opportunity from using 4D amplitudes alone to understand and discriminate areas of pressure changes from areas of saturation changes in field data. 4D PS time-shifts sense transmission related changes taking into consideration propagation through the altered medium, whereas amplitude changes are reflection or backscattered signals from the boundary. Therefore, these two attributes will be complimentary in 4D interpretation. Rock-physics-based time-shift cross-plots are generated to analyse how pressure and saturation changes in a reservoir impact PP-and PS-wave time-shifts. The developments of 4D time-shifts are shown fixing the reservoir properties and varying reservoir layer thickness. Synthetic seismic data from a wedge is modelled to understand differences between 4D amplitude and time-shift changes and the value of PS time-shifts. Cases with pressure changes only and saturation changes only are also analysed with the wedge model. The method is next applied to two 4D field data sets. One is in the North Sea and the other offshore Brazil. In these field data sets, with different levels of noise in the 4D data, we see interpretable results from PS-wave time-shifts that can help in 4D signal understanding and improve reservoir characterization and monitoring practices. We believe that with modern acquisition and processing, this technology is realizable and provides quantitative and accurate 4D interpretations. It is shown that the use of PS-wave data can lead to a larger chance of success in placing development wells.
The identification of clay-rich layers is crucial for development of pre-salt reservoirs. They represent flow barriers and compromise the return of investment of the project if the thickness is misvalued. This issue becomes more relevant for thin clay-rich layers. The solution for the characterization of thin beds is classic: increase of the frequency bandwidth in seismic data. Here, we present a new methodology to derive high-frequency impedance volume. The approach starts with the recovery of low and high-frequency components in seismic data by the application of interactive deconvolution (iterdec). The extended bandwidth data is employed as an input amplitude data to the sparse-spike inversion. The outcome is a high-frequency acoustic impedance volume, which improves the interpretation of thin clay-rich layers. We present a study case of a presalt reservoir to demonstrate that this technique mitigated the location risk of an injection well and helped to maximize the oil swept of its vicinity. Furthermore, we discuss the required adaptations in the sparse-spike inversion workflow, and present the advantages of this approach when compared with conventional inversion results.Keywords: Inversion, resolution, broadband, pre-salt. RESUMOA identificação de camadas argilosas é crucial para o desenvolvimento de reservatórios do pre-sal. Elas atuam como barreira para o fluxo dos fluidos, comprometendo o retorno do investimento no projeto, caso sua espessura seja subavaliada. Esta questão se torna mais relevante no caso the camadas argilosas de pequena espessura. A solução para a caracterização de camadas finas é clássica: torna-se necessário aumentar a banda espectral do dado sísmico. O presente trabalho apresenta a metodologia e os primeiros resultados da incorporação de uma nova metodologia para geração de volumes de impedância de alta resolução. Nesta abordagem, os componentes de baixa e alta frequência do dado sísmico são recuperados através da aplicação de um processo de deconvolução iterativa (iterdec). Em seguida, este dado com banda espectral expandida é utilizado como entrada para uma inversão esparsa, resultando num volume de impedância acústica, que reduz as incertezas na interpretação de camadas argilosas de pouca espessura. Apresenta-se o estudo de caso de um reservatório do pre-sal para demonstrar a efetividade desta técnica na mitigação de risco associado ao posicionamento de um poço injetor, resultando na maximização da varredura de óleo em torno do poço. São apresentadas e discutidas as adaptações necessárias ao fluxo tradicional de inversão e condicionamento de dados sísmicos, bem como as vantagens da aplicação dessa metodologia sobre os resultados da inversão.Palavras-chave: Inversão, resolução, banda-larga, pre-sal.
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