Modelagem e inversão de coeficientes de reflexão em meios fraturados usando algoritmo genetico

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

We present a method for the exact modeling and inversion of multi-azimutal qP-wave reflection coefficients at an interface separating two anisotropic media with at least one of its planes of symmetry paralIel to the interface, Le., monoclinic or higher symmetries. To illustrate the procedure, we compute qP-wave reflection coefficients at an interface separating an isotropic medium (representing a seal rock) from an anisotropic medium (representing a reservoir rock with vertical aligned fractures). Forward modeling of the qP reflection coefficients for alI possible azimuths and angles of incidence suggests that amplitude versus offset (AVO) effects, combined with amplitude versus azimuth (A V A) effects, can be indicate of fracture density orientation. Particularly, the difference in the offset ofthe critical angles arrivals for different azimuths is proportional to the fracture density: the higher the fracture density, the larger the difference. We also use a global optimization technique (genetic algorithm) to the invert wideangle (up to 45 degrees of incidence) AVO synthetic data, for three azimuths of the plane of the data acquisition. We found that configuration is the minimum number of acquisition planes and the minimum distance of the far offset needed to invert A VOI A V A data is forty-five degrees. The model space consists of the mass density and five elastic parameters of a transversely isotropic medium with a horizontal symmetry axis, which represents the fractured reservo ir rock. The parameters of the fractured rock are computed using real data from a oil reservoir. There are no prior information on the values of the model space parameters, except for reasonable value of wave velocities in crostal rocks and constraints of elastic stability of solid media. Mild anisotropy is also assumed, i.e., shear waves are slower than compressional waves for any direction of propagation and neither anomalous polarizations nor triplications occur. After inversion of the model space parameters, we compute statistics of the thirty better models and likelihood functions, which indicate the quality of the A VOI A V A inverse problem

ASSUNTO(S)

anisotropia prospecção sismica reservatorios algoritmos

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