Inversion of Borehole Guided Wave Amplitudes for Formation Shear Wave Attenuation Values

Abstract

A linear least squares inversion, based on analytic partition coefficient expressions, is developed to estimate the fluid and formation shear wave Q values from spectral ratio measurements-of the guided wave arrivals of full waveform acoustic logs recorded in open boreholes. The method provides excellent results when applied to synthetic data. Real data applications provide useful results, but noise reduces the resolution and increases the variance of the estimates. Permeability related losses and transmission losses (if interfaces are present) can have large effects on the estimated values. A similar procedure is developed for cased hole geometries. In this situation, the guided wave measurements are used to provide estimates of the fluid, formation shear wave, and cement shear wave Q values. Application of the method to synthetic data indicates that the formation shear Q estimate is extremely sensitive to the pseudo-Rayleigh wave data quality very close to the cutoff frequency.