Boring or penetrating the earth – With tool shaft detail – Shaft carried guide or protector
Patent
1996-05-06
1998-02-10
Bagnell, David J.
Boring or penetrating the earth
With tool shaft detail
Shaft carried guide or protector
175323, E21B 1710
Patent
active
057158983
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to downhole apparatus for use in drill strings as employed in the drilling of oil and gas wells, and in particular to apparatus for facilitating both rotational movement of a drill string in the well bore and running the drill string into or out of the well.
BACKGROUND OF THE INVENTION
Downhole stabilisers are tools which are coupled into a drill string to bear against the wall of the drilled bore, or the casing lining the bore, and thus centralise the drill string in the bore. One known form of downhole stabiliser is described in EP-A-0333450 and comprises a generally cylindrical body having a throughbore and presenting a number of bearing balls projecting from pockets formed in the stabiliser for engagement with the wall of the well bore. The bearing balls are carried in individual bearing elements. The pockets in which the bearing elements and balls are mounted are cylindrical and are formed at the radially outer periphery of radially extending blades formed on the body. The blades extend along the axial length of the body and have gaps between adjacent blades allowing passage of fluid past the exterior of the body.
Other arrangements for reducing friction between a drill string and a bore well are described in GB-A-271839, U.S. Pat. Nos. 1,699,087, 1,801,294, 1,517,027, 3,907,048 and 4,372,622.
Stabilisers of this general form have been known and used for a number of years, however manufacturers have had difficulties in producing such a stabiliser with bearing elements which will provide satisfactory omni-directional movement, that is to facilitate movement of the drill string as it is rotated in the well bore and also to facilitate running of the string through the bore, while possessing the desired robustness and reliability.
SUMMARY OF THE INVENTION
The present invention provides a downhole apparatus having rotary bearing members in the form of bearing balls which are each mounted for omni-directional movement in a bearing assembly mounted on the body of the apparatus, each bearing assembly comprising a housing containing a plurality of recirculating balls confined to the interior of the housing and forming a supporting bed for the bearing ball.
By virtue of the bearing assembly each bearing ball is completely omni-directionally movable and is therefore in rotatable engagement with the wall of the well bore when the apparatus is functioning as, for example, a stabiliser in rotational movement or is being run into or out of the well. Thus, the apparatus may be provided in the form of a stabiliser or incorporated in any other downhole tool in which it is desired to reduce torque or drag created by contact with the bore wall such as, for example, a downhole mud motor.
Preferably, each bearing assembly housing contains a load-bearing table which defines a seat for the bearing ball, the recirculating balls forming an inter-layer between the bearing ball and the load-bearing table.
Preferably also, each housing incorporates a retaining cap which retains the bearing ball and includes an annular seal element in engagement with the bearing ball.
Preferably also, each load bearing table defines a concave surface, for the recirculating balls to be directed and circulated around the respective main ball, and a convex surface over which the recirculating balls circulate, the housing defining a corresponding opposing concave surface.
Preferably also, each bearing assembly is removably mounted on a pocket in the body of the apparatus, permitting removal of the assembly to facilitate, for example, replacement of worn or damaged bearing balls. The housing of each bearing assembly may include means for engaging a retaining member. Conveniently, the retaining member is releaseable from the exterior of the body. In a preferred embodiment each bearing assembly housing includes a retaining groove for engagement with one or more retaining bolts.
Preferably also, each bearing assembly housing includes means for forming a seal between the housing and the body pocket wall,
REFERENCES:
patent: 1517027 (1924-11-01), Smith
patent: 4372622 (1983-02-01), Cheek
patent: 4440241 (1984-04-01), Anders
patent: 4548284 (1985-10-01), Shinn et al.
patent: 5522467 (1996-06-01), Stevens et al.
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