Acoustic logging-while-drilling tools having a hexapole source configuration and associated logging methods

An acoustic logging-while-drilling (LWD) tool, comprising:

• a tool body having a generally cylindrical surface;
• an array of six acoustic sources, wherein the acoustic sources in the array are evenly-spaced azimuthally on the surface of the tool body;
• and
• a plurality of receiver arrays axially spaced on the surface of the tool body from the source array, wherein each receiver array is configured to detect hexapole acoustic waves.

An acoustic logging-while-drilling (LWD) method that comprises:

• generating multipole acoustic waves in a fluid-filled borehole using an excitation pattern with a cutoff frequency greater than about 3 kHz;
• selectively detecting acoustic waves that propagate with said excitation pattern;
• and
• determining an acoustic shear wave slowness for a formation penetrated by the borehole.

A method for obtaining information for a subsurface earth formation using acoustic logging-while-drilling (LWD) techniques in a borehole formed in said subsurface earth formation, comprising:

• selecting a multipole excitation pattern having a cutoff frequency greater than about 3 kHz;
• disposing, in said borehole, a drill string having an array of transmitters and an array of at least one receiver coupled thereto;
• generating acoustic data having said multipole excitation pattern using said array of transmitters;
• acquiring, with said array of receivers, data from which said information for said subsurface earth formation may be determined;
• and
• said multipole excitation pattern selected to maximize signal to noise ratio (SNR) between said generated acoustic waves having said multipole excitation pattern and drilling noise generated by operation of said drill string.