ABSTRACT:

The coda of seismic waves is the signal after the directly arriving phases. Small changes in the medium, which may have no detectable influence on the first arrivals, are amplified by the repeated sampling and may thus be detectable in the coda. In this paper numerical simulations of wave propagation in elastic and poroelastic media, in a 4D seismic application, were based upon the spectral element method (SEM) with implementation of elastic and poroelastic formulations. The properties for base synthetic seismic acquisition were based on a field from the North Sea; for monitor acquisition, the shear modulus and bulk modulus of the frame were altered in order to change Vp and Vs by 1% and 2%. The corresponding values were also the input for elastic simulations. Coda wave interferometry (CWI) analysis detected the small changes in velocity in all simulations. The time lags are very sensitive to the velocity changes. Therefore, our studies suggest that coda-wave interferometry analysis could be used to detect small time-lapse reservoir changes, as long as the 4D seismic effects are larger than the measurable signal-to-noise ratio.

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