Tapered Transitional Radial Support for Drilling Tools

Abstract

A bearing assembly for a downhole mud motor has a transitional radial support in the form of a transitionally tapered bearing mandrel. The new radial support includes a generally cylindrical bearing housing having an upper end facing upstream in the direction of the drill string and a lower end, an outer cylindrical surface and an inner cylindrical surface, and wherein a portion of the inner cylindrical surface surrounds and contains a plurality of axial bearings. The bearing mandrel underlies the bearing housing and has an outer surface which defines a lower bearing region. The lower bearing region including a series of stepped outer diameter regions that also define a transitional reduction in cross-section area for the lower bearing region of the mandrel which, in turn, allows the bearing mandrel to have a progressive reduction in bending strength and to become a more active element in bending strength of the mud motor, instead of relying primarily upon the bearing housing.

What is claimed is: 
     
         1 . A tapered, transitional lower radial support for a bearing section of a mud motor, where the mud motor has a top sub at one end for connection to a drill string and a bottom sub at an opposite end for connection to a downhole tool such as a drill bit, the mud motor also having a power section, a transmission section and a bearing section which transfers rotational power from the power section to the drill bit, the radial support comprising:
 a generally cylindrical bearing housing having an upper end facing upstream in the direction of the drill string and a lower end, an outer generally cylindrical surface and an inner generally cylindrical surface, and wherein a portion of the inner generally cylindrical surface surrounds and contains a plurality of axial bearings;   a bearing mandrel, a portion of which underlies the axial bearings and the bearing housing, the bearing mandrel having an upper end for connection with upstream components of the mud motor , a lower end for connection to the drill bit and an open bore therethrough, the bearing mandrel having an outer surface defined between the upper and lower ends thereof which defines a lower bearing region for the bearing mandrel, the lower bearing region including a series of stepped outer diameter regions that also define a transitional reduction in cross-section area for the lower bearing region of the mandrel which, in turn, allows the bearing mandrel to become a more active element in bending strength of the mud motor, instead of relying primarily upon the bearing housing.   
     
     
         2 . The lower radial support for the bearing section of a mud motor of  claim 1 , wherein there are multiple regions of transitional reduction in cross-section area in the lower bearing region of the bearing mandrel, each of which carries a spaced-apart lower male radial bearing, the transitional reduction in cross-sectional area allowing for the use of larger diameter bearings, providing an increased friction surface and reducing surface pressure on the bearings, providing more uniform bearing wear. 
     
     
         3 . The radial support for the bearing section of a mud motor of  claim 1 , wherein the bearing mandrel has a given overall length which can be divided into an upper half and a lower half, and wherein there are multiple regions of transitional reduction in cross-sectional area in the lower half of the bearing mandrel. 
     
     
         4 . The radial support for the bearing section of a mud motor of  claim 3 , wherein the lower bearing region of the bearing mandrel includes a lower female bearing with both a lower male bearing and a spaced-apart intermediate male bearing being received within the lower female bearing. 
     
     
         5 . The radial support for the bearing section of a mud motor of  claim 4 , wherein there is a first region of stepped outer diameter on the bearing mandrel which is located above a second region of stepped outer diameter, the first region allowing a progressive reduction in diameter to the second region. 
     
     
         6 . The radial support for the bearing section of a mud motor of  claim 5 , wherein the second region of stepped outer diameter may or may not continue as a generally constant region of cross-sectional diameter to the upper end of the bearing mandrel. 
     
     
         7 . The radial support for the bearing section of a mud motor of  claim 1 , wherein the bearing assembly includes a lower female bearing which threadedly engages a lower end of the bearing housing, the lower female bearing being designed with a relatively constant wall thickness to accommodate oversize radial bearings following an outer profile dictated by the lower female bearing's outer profile. 
     
     
         8 . The radial support for the bearing section of a mud motor of  claim 7 , wherein the lower female bearing is a ring-shaped body with a first cylindrically shaped outer region which steps down to a second outer cylindrical threaded region. 
     
     
         9 . The radial support for the bearing section of a mud motor of  claim 8 , wherein the modified shape of the lower female bearing is designed with an internal diameter which takes advantage of the increase in diameter of the bearing mandrel, which allows a more uniform spread of load across the length of the entire lower female bearing. 
     
     
         10 . The radial support for the bearing section of a mud motor of  claim 9 , wherein the first cylindrically shaped outer region of the lower female bearing overlies a lower male bearing and the second outer cylindrical threaded region overlies an intermediate male bearing. 
     
     
         11 . The radial support for the bearing section of a mud motor of  claim 10 , wherein the lower male bearing is of greater relative outer diameter than the outer diameter of the intermediate male bearing. 
     
     
         12 . A radial support for a bearing section of a mud motor, where the mud motor has a top sub at one end for connection to a drill string and a bottom sub for connection to a drill bit, a power section including a rotor and a stator, a transmission section where eccentric power from the rotor is converted and transmitted as concentric power and a bearing section which transfers rotational power from the transmission to the drill bit, the radial support comprising:
 a generally cylindrical bearing housing having an upper end facing upstream in the direction of the drill string and a lower end, an outer generally cylindrical surface and an inner generally cylindrical surface, and wherein a portion of the inner generally cylindrical surface surrounds and contains a plurality of axial bearings;   a bearing mandrel, a portion of which underlies the axial bearings and the bearing housing, the bearing mandrel having an upper end for connection with upstream components of the mud motor, a lower end for connection to the drill bit and an open bore therethrough, the bearing mandrel having an outer surface defined between the upper and lower ends thereof which defines a lower bearing region for the bearing mandrel, the lower bearing region including a series of stepped outer diameter regions that also define a transitional reduction in cross-section area for the lower bearing region of the mandrel which, in turn, allows the bearing mandrel to become a more active element in bending strength of the mud motor, instead of relying primarily upon the bearing housing;   wherein the outer surface of the bearing mandrel has a given overall length which can be divided into an upper half and a lower half, and wherein there are two stepped outer diameter regions of the outer surface of the bearing mandrel, both of which are located in the lower half of the outer surface of the bearing mandrel, wherein there is a first region of stepped outer diameter which is located above a second region of stepped outer diameter, the first region constituting a greater relative reduction in outer diameter than the second region; and   wherein a set of lower male bearings are carried within the lower bearing region on the respective stepped outer diameter regions.   
     
     
         13 . A radial support for a bearing section of a mud motor, where the mud motor has a top sub at one end for connection to a drill string and a bottom sub for connection to a drill bit, a power section including a rotor and a stator, a transmission section where eccentric power from the rotor is converted and transmitted as concentric power and a bearing section which transfers rotational power from the transmission to the drill bit, the radial support comprising:
 a generally cylindrical bearing housing having an upper end facing upstream in the direction of the drill string and a lower end, an outer cylindrical surface and an inner cylindrical surface, and wherein a portion of the inner cylindrical surface surrounds and contains a plurality of axial bearings;   a bearing mandrel, a portion of which underlies the axial bearings and the bearing housing, the bearing mandrel having an upper end for connection with upstream components of the mud motor , a lower end for connection to the drill bit and an open bore therethrough, the bearing mandrel having an outer surface defined between the upper and lower ends thereof which defines a lower bearing region for the bearing mandrel, the lower bearing region including a series of stepped outer diameter regions that also define a transitional reduction in cross-section area for the lower bearing region of the mandrel which, in turn, allows the bearing mandrel to become a more active element in bending strength of the mud motor, instead of relying primarily upon the bearing housing;   wherein the outer surface of the bearing mandrel has a given overall length which can be divided into an upper half and a lower half, and wherein there are stepped outer diameter regions of the outer surface of the bearing mandrel, all of which are located in the lower half of the outer surface of the bearing mandrel;   wherein a set of lower male bearings are carried within the lower bearing region on the respective stepped outer diameter regions; and   wherein the bearing assembly includes a lower female bearing which threadedly engages a lower end of the bearing housing, the lower female bearing being designed with a wall thickness designed to accommodate oversize radial bearings.   
     
     
         14 . The radial support for the bearing section of a mud motor of  claim 13 , wherein the lower female bearing is a ring-shaped body with a first cylindrically shaped outer region which steps down to a second outer cylindrical threaded region. 
     
     
         15 . The radial support for the bearing section of a mud motor of  claim 14 , wherein the modified shape of the lower female bearing is designed with an internal diameter which takes advantage of the increase in diameter of the bearing mandrel, which allows a more uniform spread of load across the length of the entire lower female bearing and a more uniform bending stress distribution on the mandrel. 
     
     
         16 . The radial support for the bearing section of a mud motor of  claim 15 , wherein the first cylindrically shaped outer region of the lower female bearing overlies a lower male bearing and the second outer cylindrical threaded region overlies an intermediate male bearing. 
     
     
         17 . The radial support for the bearing section of a mud motor of  claim 16 , wherein the lower male bearing is of greater relative outer diameter than the outer diameter of the intermediate male bearing.