Fast inversion of formation permeability from Stoneley wave logs using a simplified Biot‐Rosenbaum model

This paper describes a fast algorithm for estimating formation permeability from Stoneley wave logs. The procedure uses a simplified Biot-Rosenbaum model formulation. The input to the inversion is the Stoneley-wave spectral amplitudes at each receiver position, the bore-hole fluid properties (velocity and density), the borehole caliper log, the formation density and porosity (from log data), and the compressional and shear velocities for the interval of interest. The model uses the borehole caliper and elastic properties to compute the Stoneley wave excitation (that is, predicted amplitude without permeability effects) as a function of frequency, and the porosity and permeability to compute the fluid flow amplitude reduction. This method also uses a reference depth of known permeability and compares amplitude variations at other depths relative to the reference depth. The permeability value obtained from the inversion represents the best fit over all receivers and all relevant frequencies. A processing example is shown to demonstrate the ability of this technique to extract formation permeability from Stoneley wave logs.