Drill string axial vibration attenuator

Abstract

The drill string axial vibration attenuator ( 10 ) is installed in the bottom hole assembly (BHA) of a drill string to attenuate axial and torsional vibrations of the drill string. The vibration attenuator ( 10 ) includes a massive elongate stabilizer ( 14 ) installed in a sealed chamber ( 12 ) that is, in turn, rigidly installed within the BHA of the drill string. Clearance between the inner wall of the chamber ( 12 ) and the stabilizer ( 14 ) is provided to preclude frictional interference therebetween. The stabilizer mass ( 14 ) is supported from below by a compression spring ( 18 ) and a shock absorber or damper ( 24 ) at the top to allow movement of the mass ( 14 ). The stabilizer ( 14 ) substantially reduces or eliminates axial and coupled torsional vibration of the drill string when the mass of the stabilizer ( 14 ), the rate of the spring, and the damper stiffness are properly configured.

We claim: 
     
         1 . A drill string axial vibration attenuator, comprising:
 an elongate sealed chamber adapted for being immovably affixed within a pipe of a drill string; and   an elongate stabilizer mass resiliently supported within the sealed chamber.   
     
     
         2 . The drill string axial vibration attenuator according to  claim 1 , wherein:
 the chamber is adapted for being disposed concentrically within one of the pipes of the drill string, the chamber having an outer surface and an inner surface, the chamber outer surface and the inner surface of the pipe defining a toroidal passage therebetween; and   the stabilizer mass is disposed concentrically within the sealed chamber, the stabilizer mass having an outer surface, the stabilizer mass outer surface and the chamber inner surface defining a toroidal stabilizer mass clearance volume therebetween, the stabilizer mass being free of contact with the inner surface of the chamber.   
     
     
         3 . The drill string axial vibration attenuator according to  claim 1 , wherein the chamber has a lower end and an upper end opposite the lower end and the stabilizer mass has a lower end and an upper end opposite the lower end, the attenuator further comprising:
 a compression spring disposed between the lower end of the chamber and the lower end of the stabilizer mass; and   a damper disposed between the upper end of the chamber and the upper end of the stabilizer mass.   
     
     
         4 . The drill string axial vibration attenuator according to  claim 3 , wherein the compression spring is selected from the group consisting of springs having linear spring rates and springs having nonlinear spring rates. 
     
     
         5 . The drill string axial vibration attenuator according to  claim 3 , wherein the damper is selected from the group consisting of dampers having linear damper rates and dampers having nonlinear damper rates. 
     
     
         6 . The drill string axial vibration attenuator according to  claim 1 , wherein the stabilizer mass is rotationally stationary relative to the chamber. 
     
     
         7 . The drill string axial vibration attenuator according to  claim 1 , further comprising a motor communicating with the stabilizer mass, the motor selectively rotating the stabilizer mass. 
     
     
         8 . A drill string axial vibration attenuator, comprising:
 an elongate sealed chamber adapted for being disposed concentrically within a pipe of a drill string, the chamber having an outer surface and an inner surface, the chamber outer surface and the inner surface of the pipe defining a toroidal passage therebetween, the chamber having an upper end and a lower end;   a first resilient member extending downward within the chamber from the upper end;   a second resilient member extending upward within the chamber from the lower end; and   an elongate stabilizer mass disposed concentrically within the sealed chamber, the stabilizer mass being attached to and suspended between the first and second resilient members, the stabilizer mass having an outer surface, the stabilizer mass outer surface and the chamber inner surface defining a toroidal stabilizer clearance volume therebetween, the stabilizer being free of contact with the inner surface of the chamber.   
     
     
         9 . The drill string axial vibration attenuator according to  claim 8 , wherein:
 the chamber is immovably affixed within one of the pipes of the drill string; and   the stabilizer mass is resiliently supported within the sealed chamber.   
     
     
         10 . The drill string axial vibration attenuator according to  claim 8 , wherein the stabilizer mass has a lower end and an upper end opposite the lower end, the attenuator further comprising;
 a compression spring disposed between the lower end of the chamber and the lower end of the stabilizer mass; and   a damper disposed between the upper end of the chamber and the upper end of the stabilizer mass.   
     
     
         11 . The drill string axial vibration attenuator according to  claim 10 , wherein the compression spring is selected from the group consisting of springs having linear spring rates and springs having nonlinear spring rates. 
     
     
         12 . The drill string axial vibration attenuator according to  claim 10 , wherein the damper is selected from the group consisting of dampers having linear damper rates and dampers having nonlinear damper rates. 
     
     
         13 . The drill string axial vibration attenuator according to  claim 8 , wherein the stabilizer mass is rotationally stationary relative to the chamber. 
     
     
         14 . The drill string axial vibration attenuator according to  claim 8 , further comprising a motor communicating with the stabilizer mass, the motor selectively rotating the stabilizer mass. 
     
     
         15 . A drill string with axial vibration attenuation, comprising:
 a plurality of elongate pipes connected end-to-end to define a drill string, the drill string having an upper end and a lower end;   a drill bit mounted on the lower end of the drill string;   a bottom hole assembly located in the lower end of the drill string; and   at least one attenuator mounted in the bottom hole assembly, the attenuator having:
 an elongate sealed chamber mounted coaxially within the bottom hole assembly, the chamber being annularly spaced from the bottom hole assembly, the chamber having an upper end and a lower end; 
 a vibration damper mounted at the upper end of the chamber; 
 a spring mounted at the lower end of the chamber; and 
 an elongate mass having an upper end attached to the damper and a lower end attached to the spring, the elongate mass being annularly spaced from the chamber and resiliently move upward and downward to counteract axial forces occurring during drilling operations, thereby preventing and reducing axial vibration of the drill string. 
   
     
     
         16 . The drill string with axial vibration attenuation according to  claim 15 , wherein the chamber is immovably affixed within one of the pipes of the drill string. 
     
     
         17 . The drill string with axial vibration attenuation according to  claim 15 , wherein:
 the chamber has an outer surface and an inner surface, the chamber outer surface and the inner surface of the pipe defining a toroidal passage therebetween; and   the elongate mass is disposed concentrically within the chamber, the elongate mass having an outer surface, the elongate mass outer surface and the chamber inner surface defining a toroidal stabilizer clearance volume therebetween, the elongate mass being free of contact with the inner surface of the chamber.   
     
     
         18 . The drill string with axial vibration attenuation according to  claim 15 , wherein:
 the spring is selected from the group consisting of springs having linear spring rates and spring having nonlinear spring rates; and   the vibration damper is selected from the group consisting of vibration dampers having linear damper rates and vibration dampers having nonlinear damper rates.   
     
     
         19 . The drill string with axial vibration attenuation according to  claim 15 , wherein the elongate mass is rotationally stationary relative to the chamber. 
     
     
         20 . The drill string with axial vibration attenuation according to  claim 15 , further comprising a motor communicating with the elongate mass, the motor selectively rotating the elongate mass.