Summary
The hydrocarbon deposits are often associated with higher than usual values of attenuation, which is generally ignored during amplitude-versus-offset (AVO) analysis. The moduli of standard linear solid model was chosen to substitute into the Zoeppritz equation to analyze the influence of attenuation and dispersion. A new forword modeling method on seismic reflectivity is developed to convolute reflection coefficients and wavelets in frequency domain. This method can obtain angle gathers with the attenuation informantion and have high efficiency. On the basis of reflection coefficients in viscoelastic media, we use frequency decomposition convolutional model (FCDM) to illustrate the impact of attenuation on prestack seismic angle gathers. It allow us to consider the viscoelasticity on seismic gathers and have the potential to applied AVA/AVF analysis to the real data.
Introduction
In the past decades, low-frequency seismic anomalies associated with the presence of hydrocarbon have been investigated by many researchers(Taner et al. (1979);Castagna et al. (2003); Korneev et al. (2004);Chapman et al. (2006)) The hydrocarbonsaturated reservoir zones often cause significant velocity dispersion characteristics (Castagna et al. (2003)), which are also confirmed by laboratory measurement in the seismic frequency range (Batzle et al. (2006)).
Regarding the velocity dispersion and attenuation, many physical mechanisms have been proposed and modeled in rocks, such as viscous fluids (Biot (2005a),Biot (2005b)), local flow or squirt mechanisms (Mavko and Nur (1975), Mavko and Nur (1979),Budiansky and O’connell (1976), and O’Connell and Budiansky (1977)), pachy-saturation model (White (1975)), double-porosity model (Pride and Berryman (2003a), Pride and Berryman (2003b), Pride et al. (2004)) et al. In spite of these distinctive mechanisms, we use viscoelasticity theory here, especially standard linear solid model, to describe velocity attenuation and dispersion by the low and high limiting moduli and a characteristic frequency. Our intent is not to discuss the interior mechanisms of poroelasticity but to present the concise way to depict dispersion.
Most studies are focused on the poroelastic mechanism of velocity dispersion and attenutaion, however, the plane-wave reflection coefficients in attenuative media are not fully discussed. A weak-contrast and weak-attenuation approximation of reflection and transmition coefficients in a thinly layered viscoelastic isotropic medium is proposed in Ursin and Stovas (2002). Ren et al. (2009) have investigated characteristics of the normal-incident reflection coefficient as a function of frequency at an interface between a nondispersive medium and a patchy-saturated dispersive medium. Innanen (2011) studies the problem of determining earth properties from the frequency signatures of anelastic AVF and AVA. Zhao (2014) developed a zoeppritz-style equation in Effective Biot Media.
