AVO Response of a Visco-Elastic Porous Layer

Sumana Basu
Indian Institute of Technology Roorkee
[email protected]

Determination of fluid characteristics in a petroleum reservoir from its seismic response is an interesting problem. For this purpose the amplitude-versus-offset (AVO) response of an oil-bearing formation must be computed. Amplitudes of seismic waves and reflection coefficients must be computed when seismic waves propagate in a viscoelastic porous medium. The existence of a slow P-wave, in addition to a normal-travelling P-wave and S-wave, in a porous medium that depends on such characteristics like fluid viscosity and permeability, has been predicted on theoretical grounds. Seismic waves suffer different degrees of attenuation while propagating through the Earth’s layers, especially in the presence of fluids in the pore spaces. The attenuation of waves makes it imperative to consider all such media as visco-elastic, whether porous or non porous. A numerical experiment has been carried out to generate the synthetic AVO response of a porous viscoelastic formation underlying a porous elastic medium. The boundary problem has been solved, and the theoretical results have been cast into a form resembling Zoepprtiz’s equations for computation of reflection and transmission coefficients. The nature of reflection pulses associated with the slow P-wave have been investigated for fluids of different properties (density and viscosity). The objective is to be able to detect the type of fluid from some attribute of the pulse shapes and its variation with offset.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain