Downhole Tool Centralizing Pistons

Abstract

The present disclosure is directed to setting pistons designed to centralize downhole tools within a wellbore. In one embodiment, a downhole tool includes a probe extendable to engage a wall of a wellbore and a setting piston extendable towards the wall of the wellbore. A roller is coupled to the setting piston and designed to roll circumferentially along the wall to pivot the downhole tool within the wellbore.

What is claimed is: 
     
         1 . A downhole tool comprising:
 a probe extendable to engage a wall of a wellbore;   a setting piston extendable towards the wall of the wellbore; and   a roller coupled to the setting piston and configured to roll circumferentially along the wall to pivot the downhole tool within the wellbore.   
     
     
         2 . The downhole tool of  claim 1 , wherein the probe comprises a packer to sealingly engage the wall and an inlet to direct formation fluid into the downhole tool. 
     
     
         3 . The downhole tool of  claim 1 , wherein the roller comprises an outer diameter greater than and an outer diameter of the setting piston. 
     
     
         4 . The downhole tool of  claim 1 , wherein the roller comprises a grooved wheel. 
     
     
         5 . The downhole tool of  claim 1 , wherein the roller comprises a plurality of hemispheres coupled to the setting piston by a bearing extending between the plurality of hemispheres. 
     
     
         6 . The downhole tool of  claim 1 , wherein the roller is configured to pivot the downhole tool about a contact point between the probe and the wall. 
     
     
         7 . The downhole tool of  claim 1 , wherein the setting piston is disposed radially opposite from the probe. 
     
     
         8 . The downhole tool of  claim 1 , wherein the roller comprises a single wheel disposed in a housing coupled to an end of the setting piston. 
     
     
         9 . The downhole tool of  claim 1 , wherein the roller is configured to centralize the downhole tool along a longitudinal axis of the wellbore. 
     
     
         10 . A method for centralizing a downhole tool comprising:
 extending a probe of the downhole tool to engage a wall of a wellbore;   extending a setting piston of the downhole tool such that a roller coupled to the setting piston engages the wall; and   rolling the roller circumferentially along the wall to pivot the downhole tool within the wellbore.   
     
     
         11 . The method of  claim 10 , wherein extending a probe and extending a setting piston occur simultaneously. 
     
     
         12 . The method of  claim 10 , wherein rolling the roller comprises rolling a plurality of hemispheres along the wall. 
     
     
         13 . The method of  claim 10 , wherein extending a probe comprises disposing a packer against the wall. 
     
     
         14 . The method of  claim 10 , comprising locking the roller to inhibit movement of the roller along the wall. 
     
     
         15 . A downhole tool comprising:
 a probe extendable from a housing of the downhole tool to engage a wall of a wellbore;   a setting piston extendable from the housing at a location radially opposite the probe; and   a roller coupled to the setting piston and configured to roll circumferentially along the wall to pivot the downhole tool within the wellbore.   
     
     
         16 . The downhole tool of  claim 15  comprising an additional setting piston extendable from the housing at another location radially opposite the probe. 
     
     
         17 . The downhole tool of  claim 15 , wherein the housing comprises a recess that houses the setting piston in a retracted position. 
     
     
         18 . The downhole tool of  claim 15 , comprising one or more standoffs coupled to the housing and radially aligned with the setting piston. 
     
     
         19 . The downhole tool of  claim 18  wherein the one or more standoffs project from the housing such that the one or more standoffs radially extend beyond the roller when the setting piston is retracted. 
     
     
         20 . The downhole tool of  claim 15  comprising a pair of standoffs coupled to the housing and each radially aligned with the setting piston.