Boring or penetrating the earth – Means traveling with tool to constrain tool to bore along...
Patent
1994-06-01
1996-04-30
Dang, Hoang C.
Boring or penetrating the earth
Means traveling with tool to constrain tool to bore along...
1753252, E21B 708
Patent
active
055116272
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a drilling tool, and in particular to a downhole stabiliser for use in a drill string during directional drilling. The invention also relates to a method of directional drilling.
Boreholes, particularly gas and oil bores, are often drilled to extend downwardly and upwardly; this permits bores to, for example, fan outwardly over a wide area from a single, central drilling location and this arrangement is frequently utilised in offshore drilling operations. The drilling of such inclined bores is achieved through use of drilling tools generally known as stabilisers mounted on the drill string comparatively near the drill bit, such as described in European Patent Specification No. EP-A-0 251 543.
Conventional directional drilling techniques utilise stabilisers of different diameters of stabilisers with variable effective diameters: a maximum diameter equal to the bore will tend to centralise the drill string in a bore which maintains the straightness of the well being drilled, and a lesser diameter will allow at least part of the drill string to bow downwardly under its own weight and thus create an upward curvature of the well.
It is an object of the present invention to provide a drilling tool which further permits bores to be drilled in a desired lateral direction in addition to the choice of upward inclinations available using conventional stabilisers.
According to one aspect of the present invention there is provided a downhole stabiliser for use in a drill string adjacent the drill bit, the stabiliser comprising defines first, second and third angularly spaced protrusions the radially outer surfaces of which define a diameter which is marginally less than the diameter of the bore to be drilled, retractable spacer members which are interconnected so that radially outward movement of one member results in radially inward movement of the other member and vice versa, effectively to vary the radial length of the respective protrusions, between first and second positions, the control mandrel defining abutment means for limiting the inward movement of the spacer members, in the first position the mandrel permitting a greater degree of travel of one spacer member than the other, and in a second position the mandrel providing the opposite.
The arrangement is such that, in use, the stabiliser with the mandrel in its first position causes the drill bit to veer laterally about a generally vertical axis in a first direction and with the mandrel in its second position the drill bit is caused to veer laterally in the opposite direction.
In use, the stabiliser is utilised on an inclined drill string where bowing of the drill string under its own weight results in the tool being pushed into contact with a lower portion of the bore wall. Thus, with the control mandrel in its first position, once in each revolution of the stabiliser, one spacer member may be pushed inwardly by contact with the lower portion of the bore wall and the other spacer member is thus pushed outwardly to push against a side portion of the bore wall and thus push the stabiliser and adjacent drill bit towards the opposite side of the bore wall. This results in the drill bit tending to drill towards said opposite side of the bore wall to produce a bore which veers laterally to that side. With the control mandrel in the second position the opposite effect is produced to provide a bore hole which veers laterally to the other side of the hole.
To produce a bore which does not veer off in one direction the control mandrel is moved from one position to the other at predetermined intervals to maintain the bore hole substantially straight about a generally vertical axis.
Preferably, the spacer members are in the form of pistons each located in a respective protrusions. Preferably also, the third protrusion is of fixed radial length.
The control mandrel may be locked in the respective positions by appropriate means and is preferably locked in the first position relative to the body by a locking piston mounted in the fixed length prot
REFERENCES:
patent: 4307786 (1981-12-01), Evans
patent: 4388974 (1983-06-01), Jones, Jr. et al.
patent: 4416339 (1983-11-01), Baker et al.
patent: 4637479 (1987-01-01), Leising
patent: 4886130 (1989-12-01), Evans
patent: 4991667 (1991-02-01), Wilkes, Jr. et al.
patent: 5265682 (1993-11-01), Russell et al.
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