Patent ID: 7529152

Claim:
A method of estimating a shear modulus in an anisotropic formation surrounding a borehole, comprising: measuring Stoneley dispersion around a vertical borehole with an acoustic tool; calculating a horizontal shear modulus c 66 from the measured Stoneley dispersion; accounting for acoustic tool bias on the horizontal shear modulus c 66 calculation by replacing the acoustic tool structure with a resonance-impedance model that comprises an equivalent surface impedance placed concentrically with a substantially vertical X 3 - axis and simplifying the equivalent surface impedance to a column having frequency-dependent complex material properties and a surface impedance condition at an interface between the acoustic tool and a borehole fluid; introducing the equivalent surface impedance to an open hole and calculating fundamental eigenmodes associated with a lowest-order axi-symmetric Stoneley mode of the equivalent surface impedance using a mode-search routine; accounting for near-borehole alteration effects on horizontal shear slowness estimation; and storing an indication of the shear modulus.