Method and apparatus for determining earth formation shear-wave transverse isotropy from borehole stoneley-wave measurements

A method of using an acoustic logging tool conveyed in a borehole in a formation for determining a characteristic of the formation, said logging tool having at least one source and a plurality of receivers, the method comprising:

• (a) obtaining an effective tool modulus of said logging tool;
• (b) measuring a Stoneley-wave slowness from array Stoneley-wave data;
• (c) calculating a horizontal formation shear velocity, Vsh, as a function of said measured Stoneley-wave slowness and an estimated Stoneley-wave slowness, said estimated Stoneley-wave slowness computed using said effective tool modulus of said logging tool;
• and
• (d) calculating a transverse isotropy for said formation.

A method of using an acoustic logging tool conveyed in a borehole in a formation for determining a characteristic of the formation, said logging tool having at least one source and a plurality of receivers, the method comprising:

• (a) measuring a Stoneley-wave velocity, {overscore (S)}ST, from acquired array Stoneley-wave data;
• (b) computing a spectrum A(ω) over a selected frequency range from said array Stoneley-wave data;
• (c) integrating ω2A2(ω) to obtain a denominator value;
• (d) selecting an initial horizontal shear velocity, Vsh, associated with said array Stoneley-wave data;
• (e) calculating a dispersion curve SST(ω,Vsh) for said initial horizontal shear velocity wherein SST(ω, Vsh) is a function including an effective tool modulus of said logging tool;
• (f) integrating SST(ω,Vsh) over the frequency range of said spectrum A(ω) wherein SST(ω, Vsh) is weighted by ω2A2 (ω), and dividing by said denominator value to obtain an estimated {overscore (S)}ST;
• (g) obtaining a measure of difference between said average {overscore (S)}ST and said estimated {overscore (S)}ST obtained from said Stoneley-wave data;
• (h) repeating steps (d)-(g) until said difference attains a predetermined minimum;
• and
• (i) outputting said selected Vsh as the formation horizontal shear-wave velocity.