Boring or penetrating the earth – With tool shaft detail – Shaft carried guide or protector
Patent
1996-12-02
1999-02-09
Bagnell, David J.
Boring or penetrating the earth
With tool shaft detail
Shaft carried guide or protector
175401, E21B 1710, E21B 1722
Patent
active
058682120
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a stabiliser tool for stabilising operation of a drill string in borehole drilling through the earth's surface.
BACKGROUND OF THE INVENTION
Boreholes are frequently drilled as vertical holes, and prior art provides sufficient technology to frequently achieve continued alignment along a single axis, both when the drilling string penetrates the ground and upon withdrawal.
However difficulties are encountered when boreholes are drilled firstly vertically downwardly, and then curve to an inclined or horizontal direction, and maintaining of complete control is very important but very difficult to achieve. A borehole drill may, for example, comprise three cutters which are circumferentially spaced from one another, and when the drill bit is inclined to the original axis, the space between the cutters can cause erratic or irregular operation in negotiating a curve. This is slightly improved by the use of rotary roller reamers, and the most relevant prior art to this invention known to the Applicant is disclosed in its own two previous inventions, respectively Australian Patent 594885 and Application PM 2305 (PCT/AU94/00691). The former Application disclosed a reamer having a plurality of hard inserts projecting therefrom (or continuous with the outer surface of the reamer in some instances), and the reamer was carried in respective end blocks in a recess in a reamer body. The arrangement for retention of the blocks utilising wedge surfaces was an important aspect of that invention. However even with the improvements which have been disclosed in the above specifications, difficulty is still encountered when the drill bit is required to traverse a curve, particularly upon withdrawal, when the string tends to straighten. The tendency to straighten sometimes causes the drill string to lock into the borehole, whereupon abandonment is unavoidable. This sometimes occurs even when a curve is not intentionally traversed. Since the cost of a drill string is very high, it is the main object of this invention to provide improvements which will make it easier to control a drill string when in a curved portion of a borehole.
BRIEF SUMMARY OF THE INVENTION
In one aspect of this invention, a borehole drill string stabiliser tool has a circular body with recesses containing projecting pad assemblies arranged in a spaced helical configuration, each pad assembly having at least one projecting wear block retained in abutment with an undercut recess surface by a wedge block, the outer wear surfaces of the blocks being of relatively hard material.
In an aforesaid Patent 594885, the bearings for roller reamers were in end blocks in the reamer bodies, and each retention was by means of a wedge block which, on one side, abutted a recess surface spaced from but parallel to a radial plane which contained the axis of rotation of the roller, and on the other side abutted a sloping wall of the end block. While the same arrangement can be used for the stabiliser of this invention, it is much preferred to utilise two projecting wear blocks flanking a central wedge block, opposite side surfaces of each projecting wear block diverging radially inwardly and on one side abutting opposite inwardly converging side surfaces of the central wedge block and on the other side abutting an inwardly diverging wall in the body recess. It will be appreciated that immense forces may be imposed on the projecting wear blocks and these are transmitted to the inwardly diverging recess surfaces, the sloping surfaces locking the blocks in their recesses and resisting tendency for the wear blocks to be removed by compressive forces, turning moments, or both.
Further in the invention, there may be provided hard tipped cutters (for example polycrystallised diamond cutters) projecting outwardly from the projecting wear blocks, and if these are located towards the top end of the stabiliser and above the reamers of a drill string, the wall of a small bore hole will be enlarged upon withdrawal, thereby reducing likelihood of the drill string
REFERENCES:
patent: 2956781 (1960-10-01), Eastman
patent: 3454308 (1969-07-01), Kennedy
patent: 4254839 (1981-03-01), Schpok et al.
patent: 4765417 (1988-08-01), Perkin et al.
patent: 4792000 (1988-12-01), Perkin et al.
patent: 4986375 (1991-01-01), Maher
Bagnell David J.
Gearhart Australia Ltd
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