WO1999023346A1

WO1999023346A1 - Anti-whirl drilling improvement

Info

Publication number: WO1999023346A1
Application number: PCT/AU1998/000913
Authority: WO
Inventors: Derek Clauson
Original assignee: Gearhart Australia Ltd.
Priority date: 1997-11-04
Filing date: 1998-11-04
Publication date: 1999-05-14
Also published as: AUPP020497A0

Abstract

The present application is for a member for use with a drilling bit in a bore which is removably attached to the bit and is of a non-symmetrical bulbous configuration so that during rotation of the member it is caused to be unbalanced. The bulbous configuration causes the unbalancing of the member during rotation. Disposed within and extending from the bulbous member is at least one wear pad or roller that is thus caused to bear against the inside of the drill hole during rotation of the member. This then provides stability against bit whirl by causing the wear pad or roller to be biased against the inner surface of a drill hole.

Description

ANTI-WHIRL DRILLING IMPROVEMENT

This invention relates to an anti-whirl improvement for rotatabie drilling bits which have a cutting head including cutters.

BACKGROUND OF THE INVENTION

Typical drilling bits can include three cone bits, two cone bits, and polycrystalline diamond compact bits for down-the-hole rotation drilling. The problem to which this invention is directed is a problem that is conventionally referred to as "bit whirl" or it can otherwise be explained as "multiple centre rotation".

Bit whirl is known to be a major cause of bit degradation and failure. This phenomenon occurs when variations in cutter loading cause a bit to rotate about multiple centres. The problem is most severe with conventionally balanced bits when one or more cutters grab the formation and force the bits centre of rotation therefore to change. The result is that the bit then "whirls" about, with a result that the bit can be forced against the side of the hole with a random effect which can cause impacting and fracturing of the cutters against various portions of the thus resulting oversized hole. Bit whirl is experienced typically in harder formations or stringers, and often leads to rapidly accelerated bit wear as well as lower penetration rates. This can dramatically increase drilling costs and a loss of precious drilling time.

It is currently known to provide a bit which is intentionally unbalanced but which therefore has a wear pad at the outermost location of the bit in the vector direction of resultant force from the unbalanced part. The problem is that, as it is presently developed, such an arrangement integrated into the bit, requires substantial expertise and quite complex calculations involving the backrake, siderake, exposure and location of each individual element to ascertain loads on each cutter and net forces acting on the bit. This has meant that both the design and manufacture of the bit becomes very complex indeed and accordingly the cost is substantially increased as well. Typically, the cost of a bit having this technology is increased by a factor of five times in the current commercial environment. In addition, it is not always possible to obtain a bit having this technology which is otherwise appropriate for the actual cutting conditions required. Further, if a bit of this type is used, its life will also be dependent on the extent to which the wear pad can survive the wear demanded of it in the application. This can in some instances be a severely limiting factor in the effectiveness and economic value of such a bit.

The object of this invention is to provide an alternative to the current technology which however can provide an anti-whirl effect of value.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is proposed a member for use with a drilling bit in a bore which can be operatively attached to the bit but is therefore separable from the bit which can provide for an unbalance effect during rotation of said member and further provide for an engaging surface against a side of the bore.

In preference said member includes a sub which can be fitted between a main drill stem and drilling bit.

In preference said member has an outer surface in the vectored direction of the force caused by the unbalance effect during rotation of said member.

In preference disposed within said outer surface is at least one element engaging said side of bore.

In preference said element is a wear pad.

Preferably said element is a roller arranged to rotate about an axis that is substantially parallel to the axis of a drill stem to said member is to be attached.

In preference said member includes a non-symmetrical sub to thereby provide an off-balance effect during rotation of said member, and further including an inset within the shape of the outer surface of the sub, a roller or rollers positioned in said inset and having an outermost surface which protrudes further than other parts of the sub when measured from an axial alignment passing centrally through the sub and being aligned with the centre of a drill stem to which it is to be attached and any bit to which it is to be attached.

Preferably said member further has blocks having leading sloping surfaces adjacent each end of a roller.

In preference said sloping surfaces are faced with harder materials to provide for a wearing surface.

In preference said member further includes a central supply conduit extending through said member.

By separating the member providing the anti-whirl stabilisation from the bit itself, this allows for this to be attached to any style of rotary bit.

Further, because there is much more space when separate from the bit and it doesn't relate so directly to net the specific design of elements within the bit, it is substantially less complex to provide such technology separate from the bit and accordingly very much cheaper indeed.

Further, because no longer is space at a premium, there can be a significant bearing surface provided which can therefore be provided by a roller rather than simply a wear pad and as such there can be much longer life achieved in any application.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of this invention it can now be described with the assistance of drawings and in relation to a preferred embodiment wherein:

FIG. 1 is a perspective view of a sub in accord with the invention;

FIG. 2 is a side elevation of an assembly including a sub as in FIG 1 , attached to a lowermost tricone type bit and its upper end attached to the end of a drill string; and

FIG. 3 is a cross sectional view along the lines A-A in FIG 2. DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in detail, the problem is to provide stability against forced multicentre rotation of the bit and to this end therefore there is provided a sub 10 which is constructed so as to have a non-symmetrical shape which is achieved by having a bulbous part 12 which is a radial extension through an arc approximately 105 degrees from the otherwise circular body of the sub.

The shape is achieved then by having a tangential edge at for instance 14 and 16 extending to a greater diameter which is larger than the diameter of the remainder of the body sub 10 which does not extend to the full diameter of the drilled hole 18. The shape then results in the bulbous part of the sub having a greater weight.

The effect of this asymmetry in the weight distribution is to provide for a centrifugal force outwardly in the direction of the weight and there is provided thereby a roller 20 the axis of rotation of which is parallel to an axis 22 of the main body of the sub 10 but offset to this so that an outermost surface at 24 of the roller 20 will be positioned to bear directly against the inner surface of the hole 18.

This has then the effect of stabilising the sub and through this the attached drill 26 specifically when this is subject to off-centre forces.

The roller in this case is supported by blocks 28 in the one case and 30 in the other and the position of the roller 20 as well as its diameter is chosen so as to allow for sufficient room in the sub for a central supply conduit 32.

The nature of the roller 20 is such that this has smooth sides and can be of a sufficient length so as to provide sufficient bearing surface over the inside of the hole 18 so as to provide sufficient stability for the purpose.

The amount of material in the bulbous part of the sub 10 is chosen so as to provide a selected amount of pressure against the side so as to resist reasonable expected off rotational forces against the bit 26.

This however depends upon the rotational speed of the drill stem and of course the bit and this can vary but to illustrate the typical size and forces involved, where the hole overall has a 6 inch diameter then with the proportions shown in the drawings, the side centrifugal forces at 75 rpm is calculated to be at 4.07 pounds, at 120 rpm, 7.24 pounds and at 130 rpm, 12.23 pounds.

It is to be clear that this concept of providing an asymmetrical loading separate from a rotary bit can apply to other configurations which may not specifically include or comprise a sub.

Further, the invention has been described in the embodiment in connection with a smooth roller, but it is possible to simply use a wear pad in this position and it is also possible to provide a plurality of rollers either in adjacent arrangement or longitudinally spaced apart with the purpose in each case simply to provide for reduced friction and therefore wear in connection with the application.

In trials conducted so far, the invention has shown to provide very significant advantages over that which has gone before in that it is very economic to provide such an arrangement rather than integrating asymmetrical or otherwise unbalanced forces within the drill bit itself and of course integrate with the complexities of design and attendant cost, wear pads into the total complex structure of the drill bit whether this be of a tricone character or otherwise.

Throughout this specification the purpose has been to illustrate the invention and not to limit this.

Claims

1. A member for use with a drilling bit in a bore which can be operatively attached to the bit but is therefore separable from the bit which can provide for an unbalance effect during rotation of said member and further provide for an engaging surface against a side of the bore.

2. A member as in claim 1 including a sub which can be fitted between a main drill stem and drilling bit.

3. A member as in claim 1 or 2 having an outer surface in the vectored direction of the force caused by the unbalance effect during rotation of said member.

4. A member as in claim 3 wherein disposed within said outer surface is at least one element engaging said side of bore.

5. A member as in claim 4 wherein said element is a wear pad.

6. A member as in claim 4 wherein said element is a roller arranged to rotate about an axis that is substantially parallel to the axis of a drill stem to said member is to be attached.

7. A member as in claim 1 including a non-symmetrical sub to thereby provide an off-balance effect during rotation of said member, and further including an inset within the shape of the outer surface of the sub, a roller or rollers positioned in said inset and having an outermost surface which protrudes further than other parts of the sub when measured from an axial alignment passing centrally through the sub and being aligned with the centre of a drill stem to which it is to be attached and any bit to which it is to be attached.

8. A member as in any one of claims 5 to 7 further having blocks having leading sloping surfaces adjacent each end of a roller.

9. A member as in claim 8 wherein said sloping surfaces are faced with harder materials to provide for a wearing surface.

10. A member as in any one of the preceding claims further including a central supply conduit extending through said member.