Enhanced anisotropy analysis with multicomponent dipole sonic data

A method for processing anisotropy comprising:

• disposing an acoustic logging tool in a wellbore, wherein the acoustic logging tool comprises a transmitter and a receiver;
• emitting a flexural wave from the transmitter;
• recording a four component dipole waveform with the receiver, wherein the four component dipole waveform comprises XX, XY, YX, and YY components;
• identifying a fast wave azimuth and slow wave azimuth corresponding to a middle point between the transmitter and the receiver;
• rotating the four component dipole waveform using Alford rotation to produce rotated waveform components, wherein the rotated waveform components comprise XXΘ, XYΘ, YXΘ, and YYΘ components;
• transforming the rotated waveform components into a frequency domain using a Fourier transform;
• determining a slowness difference between the fast wave azimuth and slow wave azimuth in the frequency domain;
• preparing an anisotropy model from a frequency dependent anisotropy curve;
• fitting the anisotropy model to a difference measurement;
• and
• determining a shear anisotropy from at least the anisotropy model.

A well measurement system comprising:

• an acoustic logging tool, wherein the acoustic logging tool comprises:
• at least one receiver;
• and
• at least one transmitter;
• a conveyance, wherein the conveyance is attached to the acoustic logging tool;
• and
• a computing device, wherein the computing device is configured to compute a high resolution-shear wave slowness, prepare an anisotropy model from the frequency dependent anisotropy curve, and determine a shear anisotropy from at least the anisotropy model.

A method comprising:

• disposing an acoustic logging tool in a wellbore, wherein the acoustic logging tool comprises a transmitter and a receiver;
• emitting a flexural wave from the transmitter;
• recording a four component dipole waveform with the receiver, wherein the four component dipole waveform comprises XX, XY, YX, and YY components;
• rotating the four component dipole waveform using Alford rotation to produce rotated waveform components, wherein the rotated waveform components comprise XXΘ, XYΘ, YXΘ, and YYΘ components;
• comparing a travel time of XXΘ and YYΘ components to identify a fast wave and a slow wave from the rotated waveform components wherein comparing the travel time comprises matching travel times in a specified time window using the following equation:
• min(Σ|XXθ(t+Δt)−YYθ(t)|)
• where XXΘ(t+Δt) and YYΘ(t) are rotated waveform components at the specified time and Δt is a time difference in arrival between the XX component and the YY component;
• processing the fast wave and the slow wave using high-resolution data-driven processing to obtain a fast wave flexural dispersion curve and a slow wave flexural dispersion curve;
• determining a frequency dependent anisotropy curve using the fast wave flexural dispersion curve and the slow wave flexural dispersion curve;
• and
• determining a shear anisotropy.

A method comprising:

• disposing an acoustic logging tool in a wellbore, wherein the acoustic logging tool comprises a transmitter and a receiver;
• emitting a flexural wave from the transmitter;
• recording a four component dipole waveform with the receiver, wherein the four component dipole waveform comprises XX, XY, YX, and YY components;
• rotating the four component dipole waveform using Alford rotation to produce rotated waveform components, wherein the rotated waveform components comprise XXΘ, XYΘ, YXΘ, and YYΘ components;
• comparing a travel time of XXΘ and YYΘ components to identify a fast wave and a slow wave from the rotated waveform components;
• applying a smoothing function, wherein the smoothing function comprises:
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• where {circumflex over (θ)} represents a mean value of an estimate of fast shear azimuth and θth represents a threshold of determination;
• processing the fast wave and the slow wave using high-resolution data-driven processing to obtain a fast wave flexural dispersion curve and a slow wave flexural dispersion curve;
• determining a frequency dependent anisotropy curve using the fast wave flexural dispersion curve and the slow wave flexural dispersion curve;
• and
• determining shear anisotropy.

A method comprising:

• disposing an acoustic logging tool in a wellbore, wherein the acoustic logging tool comprises a transmitter and a receiver;
• emitting a flexural wave from the transmitter;
• recording a four component dipole waveform with the receiver, wherein the four component dipole waveform comprises XX, XY, YX, and YY components;
• rotating the four component dipole waveform using Alford rotation to produce rotated waveform components, wherein the rotated waveform components comprise XXΘ, XYΘ, YXΘ, and YYΘ components;
• comparing a travel time of XXΘ and YYΘ components to identify a fast wave and a slow wave from the rotated waveform components;
• processing the fast wave and the slow wave using high-resolution data-driven processing to obtain a fast wave flexural dispersion curve and a slow wave flexural dispersion curve;
• determining a frequency dependent anisotropy curve using the fast wave flexural dispersion curve and the slow wave flexural dispersion curve wherein determining a frequency dependent anisotropy curve comprises solving the following equation:
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• where SFLs is flexural dispersion estimates for the slow wave, SFLf is flexural dispersion estimates for the fast wave, sens(f) is flexural sensitivity of shear wave slowness, and Ani(f) is a low-frequency asymptote;
• and
• determining a shear anisotropy.

A method comprising:

• disposing an acoustic logging tool in a wellbore, wherein the acoustic logging tool comprises a transmitter and a receiver;
• emitting a flexural wave from the transmitter;
• recording a four component dipole waveform with the receiver, wherein the four component dipole waveform comprises XX, XY, YX, and YY components;
• rotating the four component dipole waveform using Alford rotation to produce rotated waveform components, wherein the rotated waveform components comprise XXΘ, XYΘ, YXΘ, and YYΘ components;
• comparing a travel time of XXΘ and YYΘ components to identify a fast wave and a slow wave from the rotated waveform components;
• processing the fast wave and the slow wave using high-resolution data-driven processing to obtain a fast wave flexural dispersion curve and a slow wave flexural dispersion curve;
• determining a frequency dependent anisotropy curve using the fast wave flexural dispersion curve and the slow wave flexural dispersion curve;
• and
• determining a shear anisotropy wherein determining the shear anisotropy comprises:
• preparing an anisotropy model from the frequency dependent anisotropy curve;
• fitting the anisotropy model to a difference measurement wherein fitting the anisotropy model comprises determining:
• Δsmodel(f)=[Δs0+sFLAVG(af)*b]−sFLAVG(f)
• where Δsmodel(f) is the difference between the anisotropy model and the difference measurement, Δs0 is a variable, a is a variable, b is a variable, and sFLAVG(f) is an average value of the anisotropy model for a fast wave at a specified frequency;
• and
• determining an anisotropy specified by a distance resolution between transmitter and receiver.