Elastic impedance estimation for inversion of far offset seismic sections

摘要

A computer-implemented method, and system implementing the method, of performing impedance inversion of seismic survey data are disclosed. Sonic and density well logs are used to generate an elastic impedance model, at selected angles of incidence or offset range, using an expression for elastic impedance that depends upon the measured or estimated compressional velocity, shear velocity, and density of the subsurface layers in the survey region. The elastic impedance expression also includes a reference density value, and is dependent upon the ray parameter (or angle of incidence). This elastic impedance model is used, for example by way of a pseudo-density log, in estimating the input wavelet, and in carrying out an impedance inversion of the seismic survey over the entire survey region, for at least two angles of incidence. Low- frequency components of the elastic impedance, at the selected angles of incidence, are merged with the corresponding impedance inversion sections, to produce a merged impedance model at the selected angles of incidence. Rock properties, such as Poisson's ratio, are then retrieved from a comparison, such as a ratio, of the impedance traces at the varying angles of incidence for common midpoints.