Monopole acoustic transmitter ring comprising piezoelectric material

Abstract

A monopole acoustic transmitter for logging-while-drilling comprising as a ring that comprises one or more piezoelectric arc segments. The ring is oriented in a plane whose normal is essentially coincident with the major axis of a logging tool in which it is disposed. The ring disposed within a recess on the outer surface of a short, cylindrical insert. The insert is inserted into a drill collar, rather than into the wall of the collar. The ring can comprise a continuous ring of piezoelectric material, or alternately arc segments or active ring segments of piezoelectric ceramic bonded to segments of other materials such as alumina to increase the frequency or heavy metals such as tungsten to reduce the frequency. The material and dimensions of the material used in-between the piezoelectric segments is chosen to alter the frequency of the ring.

1 . A LWD logging tool acoustic transmitter comprising:
 (a) a transmitter ring comprising at least one arc segment of piezoelectric material; wherein   (b) said ring is disposed within a drill collar of said logging tool;   (c) the normal of said ring is essentially coincident with the major axis of said logging tool; and   (d) said at least one arc segments of said piezoelectric material is polarized and configured electrically to emit a pressure pulse perpendicular to said normal upon application of a voltage to said at least one arc segment of piezoelectric material.   
     
     
         2 . The transmitter of  claim 1  wherein said ring comprises a single arc segment of piezoelectric material forming a continuous ring. 
     
     
         3 . The transmitter of  claim 1  wherein said ring comprises a plurality of said sections of piezoelectric material alternately bonded to arc segments of non piezoelectric material. 
     
     
         4 . The transmitter of  claim 1  wherein said ring comprises a single arc segment of piezoelectric material upon which bands of electrode material have been applied to the surface of said single arc segment of piezoelectric material. 
     
     
         5 . The transmitter of  claim 1  further comprising a transmitter ring assembly comprising a ring pressure compensation housing in which said ring is disposed. 
     
     
         6 . The transmitter of  claim 5  further comprising:
 (a) an insert with a flow conduit therein along a major insert axis of said insert: wherein   (b) said transmitter ring assembly is disposed within a recess in an outer surface of said insert; and   (c) said normal is essentially coincident with said insert major axis.   
     
     
         7 . The transmitter of  claim 6  wherein:
 (a) said insert is disposed within said collar with said insert major axis essentially coincident with the major axis of said collar; and   (b) said ring is axially aligned with at least one opening in said collar.   
     
     
         8 . The transmitter of  claim 7  wherein:
 (a) said ring comprises a plurality of said segments of piezoelectric material alternately bonded to arc segments of non piezoelectric material or active arc segments of piezoelectric material polarized by said bands of electrode material; and   (b) at least one said segment of piezoelectric material is azimuthally aligned with at least one said opening in said collar.   
     
     
         9 . The transmitter of  claim 1  wherein:
 (a) the outer diameter of said ring is about 3 to 4 inches;   (b) the output frequency of said transmitter is about 8 to 15 KHz; and   (c) the pressure output of said transmitter is about 2 to 4 KiloPascals (KPa) at about 40 inches when said ring is excited with about 1000 volt pulse.   
     
     
         10 . A method emitting a pressure pulses into a borehole from a LWD logging tool, the method comprising:
 (a) disposing within said borehole a transmitter ring comprising at least one arc segment of piezoelectric material; wherein   (b) said ring is disposed within a drill collar of said logging tool;   (c) the normal of said ring is essentially coincident with the major axis of said logging tool; and   (d) said at least one arc segments of said piezoelectric material is polarized and configured electrically to emit a pressure pulse perpendicular to said normal upon application of a voltage to said at least one arc segment of piezoelectric material.   
     
     
         11 . The method of  claim 10  wherein said ring comprises a single arc segment of piezoelectric material forming a continuous ring. 
     
     
         12 . The method of  claim 10  wherein said ring comprises a plurality of said segments of piezoelectric material alternately bonded to arc segments of non piezoelectric material. 
     
     
         13 . The method of  claim 10  wherein said ring comprises a single arc segment of piezoelectric material upon which bands of electrode material have been applied to the surface of said single arc segment of piezoelectric material. 
     
     
         14 . The method of  claim 10  further comprising disposing said ring within a transmitter ring assembly comprising a ring pressure compensation housing. 
     
     
         15 . The method of  claim 14  further comprising:
 (a) providing an insert with a flow conduit therein along a major insert axis of said insert; and   (b) disposing said transmitter ring assembly within a recess in an outer surface of said insert; wherein said normal is essentially coincident with said insert major axis.   
     
     
         16 . The method of  claim 15  further comprising:
 (a) disposing said insert within said collar with said insert major axis essentially coincident with the major axis of said collar; and   (b) axially aligning said ring with at least one opening in said collar.   
     
     
         17 . The method of  claim 16  wherein:
 (a) said ring comprises a plurality of said segments of piezoelectric material alternately bonded to arc segments of non piezoelectric material or active arc segments of piezoelectric material polarized by said bands of electrode material; and   (b) at least one said segment of piezoelectric material is azimuthally aligned with at least one said opening in said collar.   
     
     
         18 . The method of  claim 10  further comprising: wherein:
 (a) fabricating said ring with an outside diameter of about 3 to 4 inches;   (b) operating said transmitter at an output frequency of about 8 to 15 KHz; and   (c) providing a pressure output of said transmitter of about 2 to 4 KiloPascals (KPa) at about 40 inches when said ring is excited with about 1000 volt pulse.   
     
     
         19 . A LWD logging tool acoustic transmitter comprising:
 (a) a transmitter ring comprising at least one arc segment of piezoelectric material; wherein said ring is disposed within a transmitter ring assembly comprising a ring pressure compensation housing containing high dielectric oil and a pressure compensator;   (b) an insert with a flow conduit therein along a major insert axis of said insert: wherein   said transmitter ring assembly is disposed within a recess in an outer surface of said insert; and   the normal of said ring is essentially coincident with said insert major axis; wherein   (c) said insert is disposed within a drill collar of a logging tool with said normal of said ring essentially coincident with the major axis of said logging tool;   (d) said at least one arc segments of said piezoelectric material is polarized and configured electrically to emit a pressure pulse perpendicular to said normal upon application of a voltage to said at least one arc segment of piezoelectric material;   (e) said ring is axially aligned with at least one opening in said collar; and   (f) at least one said segment of piezoelectric material is azimuthally aligned with at least one said opening in said collar.