Methods for attenuating noise signals in a cement evaluation tool

Abstract

Systems and methods for evaluating cement in the annulus of a wellbore are provided. In one embodiment, the cement may be evaluated using a casing arrival measurement sensor that measures casing arrival signals resulting from firing a signal from a cement bond logging acoustic source. Signals other than casing arrival signals may be attenuated using grooves between the transmitter and receiver in the drill collar.

What is claimed is: 
     
         1 . A drilling tool comprising:
 a drill collar that comprises:
 a transmitter configured to apply cement bond logging pulses to casing within a wellbore; 
 a receiver configured to detect a casing arrival signal generated within the casing by the cement bond logging pulses; and 
 a plurality of grooves positioned between the transmitter and the receiver, and configured to attenuate acoustic waves propagating through the drill collar, wherein at least one of the plurality of grooves extends from an outer surface of the drill collar. 
   
     
     
         2 . The drilling tool of  claim 1 , wherein the transmitter and the receiver are separated by a distance of less than or equal to 1 meter. 
     
     
         3 . The drilling tool of  claim 1 , wherein each groove comprises a width between 50 mm and 100 mm. 
     
     
         4 . The drilling tool of  claim 1 , wherein each groove comprises a width and the plurality of grooves have uniform widths. 
     
     
         5 . The drilling tool of  claim 1 , wherein the grooves are spaced apart by a distance between 50 mm and 100 mm. 
     
     
         6 . The drilling tool of  claim 1 , wherein the grooves are spaced apart by a uniform distance. 
     
     
         7 . The drilling tool of  claim 1 , wherein the cement bond logging pulses are applied at a frequency between 20 kHz and 25 kHz. 
     
     
         8 . The drilling tool of  claim 1 , further comprising:
 a data processing system configured to determine a condition of cement disposed within a cement annulus of the wellbore using the casing arrival signal.   
     
     
         9 . The drilling tool of  claim 1 , further comprising an acoustic damping material disposed in the grooves. 
     
     
         10 . The drilling tool of  claim 9 , wherein the acoustic damping material includes at least one of a heavy oil, a drilling fluid, and a fiber glass. 
     
     
         11 . The drilling tool of  claim 1 , where the drilling tool is a logging-while-drilling tool. 
     
     
         12 . A method comprising:
 inserting a drilling tool into a wellbore that is at least partially cased and cemented, wherein the drilling tool comprises a transmitter, a receiver, and a drill collar;   using the transmitter to apply cement bond logging pulses to casing within the wellbore;   using the receiver to obtain an acoustic casing arrival signal generated within the casing by the cement bond logging pulses;   attenuating vibrations within the drill collar between the transmitter and the receiver using a plurality of grooves that extend into the drill collar from an outer surface of the drill collar; and   determining a condition of cement within a cement annulus of the wellbore using the acoustic casing arrival signal.   
     
     
         13 . The method of  claim 12 , wherein the condition of cement comprises a cement bond defect within the cement annulus. 
     
     
         14 . The method of  claim 13 , wherein the cement bond defect is a microannulus. 
     
     
         15 . The method of  claim 12 , wherein each groove comprises a width and the method further comprises:
 determining the width of the grooves based on (i) a material of the drill collar, (ii) inner and outer diameters of the drill collar, and (iii) a frequency of the cement bond logging pulses applied by the transmitter.   
     
     
         16 . The method of  claim 12 , wherein the transmitter and the receiver are separated by a distance of less than or equal to 1 meter. 
     
     
         17 . The method of  claim 12 , wherein each groove comprises a width between 50 mm and 100 mm. 
     
     
         18 . The method of  claim 12 , wherein each groove comprises a width and the plurality of grooves have uniform widths. 
     
     
         19 . The method of  claim 12 , wherein the grooves are spaced apart by a uniform distance. 
     
     
         20 . The method of  claim 12 , wherein the cement bond logging pulses are applied at a frequency between 20 kHz and 25 kHz.