Estimating a shear modulus of a transversely isotropic rock

A method of estimating c₆₆, one of the shear moduli of a transversely isotropic rock, using a guided wave generated during acoustic logging is described. The symmetry axis of the anisotropy is assumed to be parallel to the borehole. The inversion for c₆₆ is based on a cost function which has three terms: a measure of the misfit between the observed and predicted wavenumbers of the guided wave (tube wave), a measure of the misfit between the current estimate for c₆₆ and its most-likely value, and penalty functions which constrain the estimate for c₆₆ to physically acceptable values. Estimates for c₆₆ from synthetic data are almost always within 1% of their correct value. Estimates for c₆₆ from field data collected in a formation with a high clay content are typical of transversely isotropic rocks