Acoustic Anisotropy and Imaging by Means of High Resolution Azimuthal Sampling

Abstract

In an acoustic logging system utilizing one or more acoustic sources, each with a specified radiation pattern around a source orientation, an acoustic signal is transmitted into a formation with a source oriented in a first source orientation. An acoustic waveform is received in response with a receiver oriented in a first direction. The slowness of the formation in the first direction is calculated using the received acoustic waveform.

1 - 20 . (canceled) 
     
     
         21 . A method, comprising:
 rotating an acoustic logging while drilling tool in a borehole, the tool comprising at least one acoustic transmitter and an array of receivers longitudinally spaced apart from the transmitter;   determining an acoustic wave slowness of the formation at multiple azimuthal angles while rotating the tool;   determining a maximum and minimum slowness of the formation; and   using the maximum slowness and the minimum slowness to determine the acoustic anisotropy of the formation.   
     
     
         22 . The method as defined in  claim 21 , wherein determining the acoustic wave slowness comprises calculating acoustic wave slowness at three or more azimuthal angles. 
     
     
         23 . The method as defined in  claim 21 , wherein determining the acoustic wave slowness comprises measuring an azimuthal angle corresponding to each of the acoustic wave slowness calculations. 
     
     
         24 . The method as defined in  claim 21 , wherein determining the acoustic wave slowness comprises:
 firing the at least one acoustic transmitter to transmit an acoustic waveform into the formation; receiving acoustic waveforms at each of the receivers in the array;   processing the received waveforms to obtain the acoustic wave slownesses; and   measuring an azimuthal angle at substantially a same time as firing the at least one acoustic transmitter.   
     
     
         25 . The method as defined in  claim 21 , wherein determining the acoustic wave slowness comprises calculating at least one of compressional wave slownesses, shear wave slownesses, and stoneley wave slownesses. 
     
     
         26 . A method for determining an acoustic anisotropy of a geological formation, the method comprising:
 rotating an acoustic logging while drilling tool in a borehole, the tool comprising at least one acoustic transmitter and an array of receivers longitudinally spaced apart from the transmitter;   calculating an acoustic wave slowness of the formation at multiple azimuthal angles while rotating the tool;   utilizing a mathematical model to obtain a maximum and minimum slowness; and   processing the maximum slowness and the minimum slowness to determine the acoustic anisotropy of the formation.   
     
     
         27 . The method as defined in  claim 26 , wherein calculating the acoustic wave slowness comprises calculating acoustic wave slowness at eight or more azimuthal angles. 
     
     
         28 . The method as defined in  claim 26 , wherein calculating the acoustic wave slowness comprises measuring an azimuthal angle corresponding to each of the acoustic wave slowness calculations. 
     
     
         29 . The method as defined in  claim 26 , wherein calculating the acoustic wave slowness comprises:
 firing the at least one acoustic transmitter to transmit an acoustic waveform into the formation;   receiving acoustic waveforms at each of the receivers in the array;   processing the received waveforms to obtain the acoustic wave slownesses; and   measuring an azimuthal angle at substantially a same time as firing the at least one acoustic transmitter.   
     
     
         30 . The method as defined in  claim 26 , wherein calculating the acoustic wave slowness comprises calculating at least one of compressional wave slownesses, shear wave slownesses, and stoneley wave slownesses.