Downhole drag reduction apparatus

Abstract

A downhole drag reducing apparatus 18 comprises a mandrel 20 and a bearing sleeve 24 mounted on the mandrel 20, such that the mandrel 20 and bearing sleeve 24 are rotatable relative to each other. The bearing sleeve 24 defines a bore wall engaging surface. The apparatus 18 comprises a reciprocating piston 23 mounted within a piston housing 25 to define a piston chamber 27. The apparatus 18 further comprises a rotary valve assembly 29 operated by relative rotation between the mandrel 20 and the bearing sleeve 24 to cyclically pressurise and depressurise the piston chamber 27 to provide reciprocating movement of the reciprocating piston 23 and the generation of vibration within the apparatus 18.

1 . A downhole drag reducing apparatus, comprising:
 a mandrel;   a bearing sleeve mounted on the mandrel such that the mandrel and bearing sleeve are rotatable relative to each other, the bearing sleeve defining a bore wall engaging surface;   a reciprocating piston mounted within a piston housing to define a piston chamber; and   a rotary valve assembly operated by relative rotation between the mandrel and the bearing sleeve to cyclically pressurise and depressurise the piston chamber to provide reciprocating movement of the reciprocating piston and the generation of vibration within the apparatus.   
     
     
         2 . The downhole apparatus of  claim 1 , wherein the rotary valve assembly comprises a valve inlet and a valve exhaust, wherein the rotary valve assembly is operated between a pressure configuration and an exhaust configuration, wherein in the pressure configuration, the piston chamber is in pressure communication with the valve inlet and isolated from the valve exhaust, and in the exhaust configuration, the piston chamber is isolated from the valve inlet and in pressure communication with the valve exhaust. 
     
     
         3 . (canceled) 
     
     
         4 . The downhole apparatus of  claim 2 , comprising a rotary valve member operatively associated with the valve inlet and the valve exhaust, wherein the rotary valve member is configured to provide selective communication between at least one of the valve inlet and valve exhaust and the pressure chamber. 
     
     
         5 . (canceled) 
     
     
         6 . The downhole apparatus of  claim 4 , wherein the rotary valve member is rotatably fixed with respect to the bearing sleeve and comprises one or more flow passageways. 
     
     
         7 . The downhole apparatus of  claim 2 , wherein the mandrel comprises the valve inlet and valve exhaust, and wherein the valve inlet and the valve exhaust are rotatable with respect to the one or more flow passageways. 
     
     
         8 . The downhole apparatus of  claim 4 , wherein the rotary valve member is configured to selectively block or obturate at least one the valve inlet and valve exhaust. 
     
     
         9 . The downhole apparatus of  claim 7 , wherein the mandrel comprises one or more flow passages extending through a wall thereof, the flow passages defining or communicating with the valve inlet. 
     
     
         10 . The downhole apparatus of  claim 7 , wherein the mandrel comprises one or more flow channels defining or communicating with the valve exhaust. 
     
     
         11 . The downhole apparatus of  claim 1 , comprising a retaining shoulder rotabably fixed with respect to the mandrel and located axially between the rotary valve assembly and the piston chamber. 
     
     
         12 . The downhole apparatus of  claim 11 , wherein the retaining shoulder comprises one or more flow paths permitting pressure communication between at least one of the valve inlet and valve exhaust and the pressure chamber. 
     
     
         13 . The downhole apparatus of  claim 12 , wherein the one or more flow paths comprises a plurality of flow paths, and the plurality of flow paths are circumferentially distributed. 
     
     
         14 . The downhole apparatus of  claim 1 , wherein the reciprocating piston travels in a first axial direction and a second axial direction within the piston chamber, and the apparatus comprises a biasing arrangement biasing the reciprocating piston in the second axial direction, wherein pressurisation of the piston chamber urges the reciprocating piston to move in the first axial direction. 
     
     
         15 . (canceled) 
     
     
         16 . The downhole apparatus of  claim 14 , wherein the biasing arrangement acts on the reciprocating piston with a force sufficient to move the reciprocating piston in the second axial direction to depressurise the piston chamber. 
     
     
         17 . The downhole apparatus of  claim 14 , wherein the biasing arrangement comprises one or more springs circumferentially arranged with respect to the reciprocating piston. 
     
     
         18 . (canceled) 
     
     
         19 . The downhole apparatus of  claim 11 , wherein the reciprocating piston comprises a first impact surface for impacting a second impact surface formed on an impact shoulder provided on or formed with the mandrel, and the reciprocating piston comprises a third impact surface for impacting a fourth impact surface formed on the retaining shoulder, and wherein impact of the first and third impact surfaces and/or impact of the second and fourth impact surfaces generates vibration within the apparatus. 
     
     
         20 . The downhole apparatus of  claim 19 , wherein the first and third impact surfaces and/or the second and fourth impact surfaces do not impact one another, the reciprocating movement of the reciprocating piston being sufficient to generate vibration within the apparatus. 
     
     
         21 . (canceled) 
     
     
         22 . The downhole apparatus of  claim 1 , wherein the mandrel defines a circumferentially continuous inner bearing race, and wherein the bearing sleeve defines a circumferentially continuous outer bearing race, the bearing sleeve being mounted on the mandrel such that the outer bearing race of the bearing sleeve circumscribes the inner bearing race of the mandrel. 
     
     
         23 . The downhole apparatus of  claim 22 , comprising a rolling bearing arrangement radially interposed between the inner bearing race of the mandrel and the outer bearing race of the bearing sleeve to permit the bearing sleeve and the mandrel to be rotatable relative to each other. 
     
     
         24 . The downhole apparatus of  claim 22 , wherein at least one of the outer bearing race and inner bearing race comprises a bearing raceway for axially captivating the rolling bearing arrangement. 
     
     
         25 . The downhole apparatus of  claim 1 , wherein the bearing sleeve comprises a varying outer diameter and includes a central region which defines an outer gauge diameter of the downhole drag reducing apparatus defining the bore wall engaging surface, and axial end regions which define a smaller diameter than the central region. 
     
     
         26 . (canceled) 
     
     
         27 . The downhole apparatus of  claim 25 , wherein the bearing sleeve comprises an extended section extending from the axial end region located adjacent the first axial shoulder, the extended section defining the piston housing. 
     
     
         28 . A method for performing a wellbore operation, comprising
 engaging a bore wall with a bore wall engaging surface of a bearing sleeve, wherein the bearing sleeve is mounted on a mandrel;   rotating the mandrel relative to the bearing sleeve while the bearing sleeve is engaged with the bore wall;   operating a rotary valve assembly by relative rotation between the mandrel and the bearing sleeve to cyclically pressurise and depressurise a piston chamber to provide reciprocating movement of a reciprocating piston mounted within a piston housing defining the piston chamber; and   generating vibration within the apparatus by the reciprocating movement of the reciprocating piston.