Flow retarder for bearing assembly of downhole drilling motor

Abstract

A flow retarder is provided for use in the bearing assembly of a downhole drilling motor. The bearing assembly comprises an inner tubular mandrel and an outer tubular housing. The flow retarder comprises: an inner carbide sleeve connected to the rotating mandrel by a resilient elastomer layer bonded to a driver ring which is locked on the rotating mandrel; an outer carbide sleeve affixed to the stationary tubular housing; the sleeves forming a narrow annular clearance or metering gap between them; a secondary port extending through the mandrel side wall directly above the carbide sleeves; and a housing port extending through the housing side wall below the flow retarder sleeves. Drilling fluid leaks down from the adapter/adjustable housing clearance and passes through the metering gap to lubricate the carbide sleeves. Part of this fluid returns through the secondary port to the main bore of the mandrel. By providing the elastomer layer, the transmission of radial loads from the inner sleeve to the outer sleeve is reduced.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A flow retarder for use in a downhole drilling motor bearing assembly used in a well borehole, said bearing assembly comprising a main clearance through which drilling fluid can move, an inner rotatable tubular mandrel having a side wall forming a longitudinal bore, an outer stationary tubular housing having a side wall, an annular pressure balancing chamber formed between the housing and mandrel side walls and an annular floating piston seal closing the bottom end of the chamber, the flow retarder comprising: 
 an erosion-resistant inner sleeve mounted on a driver ring connected to rotate with the mandrel, said inner sleeve being secured to the driver ring by a layer of resilient elastomer positioned between the sleeve and the driver ring;    an erosion-resistant outer sleeve fixed to the inside surface of the housing side wall;    the inner sleeve being positioned within the outer sleeve, said sleeves forming a narrow annular metering gap between them, the sleeves being positioned in the upper end of the chamber and extending there across;    the housing side wall forming a housing port extending therethrough below the sleeves to connect the pressure balancing chamber and the lower end of the metering gap with the borehole.    
     
     
         2 . The flow retarder as set forth in  claim 1  wherein: 
 the mandrel side wall forms a secondary mandrel port at the upper end of the metering gap for connecting the lower end of the main clearance with the mandrel bore.  
 
     
     
         3 . The flow retarder as set forth in  claim 2  comprising: 
 the mandrel having an outwardly protruding shoulder;  
 the driver ring being seated on the shoulder and having a frictional engagement with the mandrel so as to rotate therewith;  
 the elastomer layer being bonded to the driver ring and the inner sleeve so that the inner sleeve rotates with the mandrel.  
 
     
     
         4 . The flow retarder as set forth in  claim 3  comprising: 
 means for resiliently pressing the driver ring against the mandrel shoulder.  
 
     
     
         5 . The flow retarder of  claim 1 ,  2 ,  3  or  4  wherein: 
 the inner sleeve has a plurality of circumferential grooves formed in its outer surface at spaced intervals along its length.