Direct Inversion Algorithm for Shear Velocity Profiling in Dipole Acoustic Borehole Measurements

Abstract

The evaluation of radial heterogeneities within formations plays an important role in oil and gas exploration and exploitation. Dipole acoustic well logging data are widely used to invert radial shear velocity profiles, for which efficient dispersion analysis algorithms and radial profile inversion algorithms constitute fundamental issues. A direct parametric inversion method is, therefore, proposed in this letter, and a phase-based dispersion method is employed to calculate the dispersion curves of measured dipole acoustic data. The accuracy and computational efficiency of the inversion can be simultaneously guaranteed by using the proposed dispersion analysis method. An exponential radial profile function with three parameters, namely, the relative change in the shear modulus, the decaying parameter of the exponential function, and the radial extent of the perturbation zone, is used to describe alterations in formation shear wave velocities. Formations with different alteration characteristics can be expressed effectively using this proposed exponential function. The cost function is then calculated in terms of the three exponential function parameters and the real data dispersion curve. After the three parameters are inverted by finding the minimum value of the cost function, the radial shear wave velocity profile can be expressed using the exponential function. Finally, processing results using synthetic data confirm the efficiency of the proposed algorithm.