Patent ID: 7764572

Claim:
A method for processing sonic waveforms acquired in a borehole traversing a subterranean formation, comprising: (a) generating a plurality of model dispersion curves from mud slowness parameter and formation slowness parameter; (b) generating a measured dispersion curve from the acquired waveforms; (c) determining a difference between the model dispersion curves and the measured dispersion curve to compute a cost function; (d) determining, with a processor, a formation velocity from a model dispersion curve that produces the minimal cost function or reduces the cost function to below a selected value, wherein the determining comprises iteratively adjusting values of the mid slowness parameter and formation slowness parameter to produce the minimal cost function or reduce the cost function between the model dispersion curves and the measured dispersion curve to below the selected value; and (e) outputting, with the processor, at least a portion of a set of borehole-formation parameters wherein the subterranean formation comprises a fast formation and the formation velocity is determined without prior knowledge of a mud velocity.