Towards a method for attenuation inversion from reservoir-scale ambient noise OBS recordings

Abstract

We analyze ambient seismic and acoustic noise from a broadband passive OBS survey acquired over an oil reservoir in the norwegian North Sea. We analyze the data with respect to azimuthal variation of the incident wavefield in order to find directions of possible dominant sources to evaluate the validity of the assumption of a diffuse wavefield. Whitening of the spectra yields the most clear Green's functions for higher frequencies more important, gives us the complex coherency. Following the approach of Prieto et al. 2009 we are able to determine the phase velocities by fitting Bessel functions to the real part of the complex coherencies. Fitting the distance-dependent coherency to a Bessel function, we are able to estimate the surface-wave slowness of the area; an important strength of this method is that it will ultimately allow us to evaluate the quality factor Q as well.