Simultaneous inversion of formation shear‐wave anisotropy parameters from cross‐dipole acoustic‐array waveform data

Abstract

This study presents an effective technique for obtaining formation azimuthal shear‐wave anisotropy parameters from four‐component dipole acoustic array waveform data. The proposed technique utilizes the splitting of fast and slow principal flexural waves in an anisotropic formation. First, the principal waves are computed from the four‐component data using the dipole source orientation with respect to the fast shear‐wave polarization azimuth. Then, the fast and slow principal waves are compared for all possible receiver combinations in the receiver array to suppress noise effects. This constructs an objective function to invert the waveform data for anisotropy estimates. Finally, the anisotropy and the fast shear azimuth are simultaneously determined by finding the global minimum of the objective function. The waveform inversion procedure provides a reliable and robust method for obtaining formation anisotropy from four‐component dipole acoustic logging. Field data examples are used to demonstrate the application and features of the proposed technique. A comparison study using the new and conventional techniques shows that the new technique not only reduces the ambiguity in the fast azimuth determination but also improves the accuracy of the anisotropy estimate. Some basic quality indicators of the new technique, along with the anisotropy analysis results, are presented to demonstrate the practical application of the inversion technique.

Crack‐Induced Shear‐Wave Orthorhombic Anisotropy: Modeling and Inversion of Shear‐Wave Borehole Measurements

“…It is interesting to note that shear‐wave logging with a four‐component (4C) dipole acoustic tool in a vertical borehole penetrating orthorhombic rock formations can determine both the background and azimuthal anisotropy parameters, such that the tasks of formation evaluation and fracture characterization can be performed in an efficient manner. For this evaluation, the shear‐wave VTI property is determined from borehole monopole Stoneley‐wave (Tang, 2003) and dipole flexural‐wave (Xu et al, 2017) measurements, while shear‐wave HTI property is determined from dipole flexural‐wave measurements (Tang & Chunduru, 1999; Walker et al, 2015; Zeng et al, 2018). In the following, we develop an inversion method for estimating the shear‐wave anisotropy parameters.…”

Mapping formation radial shear-wave velocity variation by a constrained inversion of borehole flexural-wave dispersion data

“…Processing the dipole data yields the radial variation along the direction. In particular, the 4C data can be rotated to the two principal directions of the anisotropy, which correspond, respectively, to the fast and slow shear-wave polarization directions, as obtained from crossed-dipole processing ͑e.g., Tang and Chunduru, 1999͒. Processing the dipole data for each direction yields the radial profiles of the two directions.…”

“…3͒ In the case of 1C dipole logging data, apply dispersion analysis ͑e.g., Tang and Cheng, 2004͒ to obtain dispersion-curve data for the frequency range of the data ͑normally 0.5-8 kHz͒. 4͒ In the case of 4C crossed-dipole data, apply anisotropy processing ͑e.g., Tang and Chunduru, 1999͒ to data to obtain fast and slow shear-wave polarization directions. Then rotate the 4C data to these two directions to yield fast and slow flexural-wave data.…”

Evaluating Hydraulic Fracturing in Cased Holes With Cross-Dipole Acoustic Technology

“…These data are processed with an array waveform inversion method. 2 This method computes the fast and slow dipole-shear waves from the four-component data and matches the fast and slow waves across the array to determine the magnitude and azimuth of the anisotropy simultaneously.…”