Time domain stacking of acoustic dipole LWD measurements

An acoustic logging while drilling tool comprising:

• a logging while drilling tool body;
• an acoustic transmitter deployed in the logging while drilling tool body;
• a directional acoustic receiver including a plurality of circumferentially spaced receiver arrays deployed in the logging while drilling tool body axially spaced from the acoustic transmitter;
• a controller deployed in the logging tool body and configured to:
• cause the acoustic transmitter and the direction acoustic receiver to make a plurality of directional sonic logging measurements while the logging while drilling tool rotates in a wellbore;
• identify a plurality of orthogonal pairs of measurements among the plurality of directional sonic logging measurements, wherein each of the plurality of orthogonal pairs includes a first measurement and a second measurement, wherein a measured angle of a transmitter firing direction of the first measurement is orthogonal with a measured angle of a transmitter firing direction of the second measurement within a predetermined tolerance;
• compile 4C component waveforms for each of the identified plurality of orthogonal pairs of measurements;
• rotate the compiled 4C component waveforms to align with predefined axes;
• and
• stack selected ones of the rotated 4C component waveforms in the time domain.

A method for acoustic logging a wellbore, the method comprising:

• rotating a logging tool in a wellbore penetrating a subterranean formation, the logging tool including an acoustic transmitter and a directional acoustic receiver including a plurality of circumferentially spaced receiver arrays;
• making a plurality of directional sonic logging measurements while rotating the logging tool in the wellbore;
• identifying a plurality of orthogonal pairs of measurements among the plurality of directional sonic logging measurements, wherein each of the plurality of orthogonal pairs includes a first measurement and a second measurement, wherein a measured angle of a transmitter firing direction of the first measurement is orthogonal with a measured angle of a transmitter firing direction of the second measurement within a predetermined tolerance;
• compiling 4C component waveforms for each of the identified plurality of orthogonal pairs of measurements;
• rotating the compiled 4C component waveforms to align with predefined axes;
• stacking selected ones of the rotated 4C component waveforms in the time domain;
• estimating an anisotropy angle of the formation from the stacked waveforms;
• using the anisotropy angle of the formation to set new predefined axes;
• and
• repeating the making, the identifying, the compiling, the rotating, and the stacking using the new predefined axes.