Device and method for attenuating acoustic signals

Abstract

Illustrative embodiments of the present disclosure are directed to methods and devices for attenuating acoustic signals traveling within bodies. A device includes a body and at least one acoustic attenuator disposed along the body. The attenuator includes a cavity and granular particles disposed within the cavity. A liquid is also disposed within the cavity. A restrictor applies a stress to the granular particles within the cavity.

What is claimed is: 
     
         1 . A device comprising:
 a body;   at least one acoustic attenuator disposed along the body, the attenuator comprising:
 a cavity; 
 a plurality of granular particles disposed within the cavity; 
 a liquid disposed within the cavity; and 
 a restrictor configured to apply a stress to the granular particles within the cavity. 
   
     
     
         2 . The device of  claim 1 , further comprising:
 a plurality of acoustic attenuators, wherein at least one attenuator applies a first stress to the granular particles and at least one other attenuator applies a second stress to the granular particles, the first stress and second stress having different values.   
     
     
         3 . The device of  claim 1 , wherein the restrictor is configured to apply a stress to the granular particles, within the cavity, in the range of 1 Pa to 5 MPa. 
     
     
         4 . The device of  claim 1 , wherein the liquid has a viscosity in the range of 2 to 1,000,000 cSt at room temperature. 
     
     
         5 . The device of  claim 1 , wherein a volume ratio within the cavity of the liquid to the granular particles is in the range of 0.001% to 5%. 
     
     
         6 . The device of  claim 5 , wherein a volume of the liquid in the cavity is configured so that the liquid coats the granular particles. 
     
     
         7 . The device of  claim 1 , wherein a particle size for the granular particles is in the range of 1 to 500 microns. 
     
     
         8 . The device of  claim 1 , further comprising:
 at least one acoustic transmitter disposed on the body; and   at least one acoustic receiver disposed on the body;   wherein the at least one acoustic attenuator is located between the at least one acoustic receiver and the at least one acoustic transmitter.   
     
     
         9 . The device of  claim 8 , further comprising
 a plurality of attenuators located between the at least one acoustic transmitter and the at least one acoustic receiver, the plurality of attenuators comprising a volume between 5% and 20% of a volume of the tool body between the at least one acoustic transmitter and the at least one acoustic receiver.   
     
     
         10 . The device of  claim 1 , wherein the device is a logging-while-drilling tool and the body is a drill collar. 
     
     
         11 . A logging tool for performing acoustic investigations of subsurface geological formations traversed by a borehole, the logging tool comprising:
 a tool body extending longitudinally;   at least one acoustic transmitter disposed at a first longitudinal location on the body;   at least one acoustic receiver disposed at a second longitudinal location on the body;   at least one acoustic attenuator located between the at least one acoustic transmitter and the at least one acoustic receiver, the attenuator comprising:
 a cavity within the tool body; 
   a plurality of granular particles disposed within the cavity;   a liquid disposed within the cavity and configured to coat the granular particles within the cavity; and
 a restrictor configured to apply a stress to the granular particles within the cavity. 
   
     
     
         12 . The logging tool of  claim 11 , wherein the restrictor includes a spring configured to apply a stress to the granular particles within the cavity. 
     
     
         13 . The logging tool of  claim 11 , further comprising:
 a plurality of attenuators located between the at least one acoustic transmitter and the granular particles and at least one other attenuator applies a second stress to the granular particles, the first stress and second stress having different values.   
     
     
         14 . The logging tool of  claim 11 , wherein the liquid has a viscosity in the range of 2 to 1,000,000 cSt at borehole temperatures. 
     
     
         15 . The logging tool of  claim 11 , wherein the restrictor is configured to apply a stress to the granular particles within the cavity in the range of 1 Pa to 5 MPa. 
     
     
         16 . The logging tool of  claim 11 , wherein a particle size for the granular particles is in the range of 1 to 500 microns. 
     
     
         17 . The logging tool of  claim 11 , further comprising:
 a plurality of attenuators located between the at least one acoustic transmitter and the at least one acoustic receiver, the plurality of attenuators comprising a volume between 5% and 20% of a volume of the tool body between the at least one acoustic transmitter and the at least one acoustic receiver.   
     
     
         18 . The logging tool of  claim 11 , wherein the logging tool is a logging-while-drilling tool and the tool body is a drill collar. 
     
     
         19 . A method for attenuating an acoustic signal passing through a body, the method comprising:
 disposing a plurality of granular particles within a cavity disposed along the body; and   applying a stress to the granular particles within the cavity.   
     
     
         20 . The method of  claim 19 , wherein the stress applied to the granular particles is tuned to attenuate particular frequencies of the acoustic signal.