Note: Descriptions are shown in the official language in which they were submitted.
CA 02675194 2009-08-11
Rotary Drill Bit
This invention relates to a drill bit, and in particular to an earth boring
rotary drill
bit for use in the formation of boreholes, for example for subsequent use in
the
extraction of oil and/or natural gas. The invention relates, in particular, to
a drill bit
having a gauge region provided with an abrasion resistant gauge surface.
One common form of rotary drill bit is shown in Figure 1 and comprises a bit
body
having a plurality of blades formed integrally therewith. Each blade is
provided
with a series of cutting elements which, in use, scrape, abrade or otherwise
remove
formation material upon rotation of the drill bit whilst a weight on bit
loading is
applied thereto. A range of cutting elements are known, one common form of
cutting element comprising a substrate of, for example, tungsten carbide to
which a
layer of polycrystalline diamond is integrally mounted. The cutting elements
are,
for example, brazed or shrink fitted to the bit body.
The bit body includes a gauge region which bears, in use, against the wall of
the
hole drilled by the drill bit. The bit body is typically formed of a
relatively soft
material, for example steel, and it will be appreciated that the gauge region
is
subject to significant levels of wear, for example resulting from abrasion as
the
surface of the gauge region engages and rubs against the wall. As replacing a
drill
bit involves halting the drilling process for a considerable period of time,
it is
desirable to protect the drill bit against such wear, thereby reducing the
regularity
with which the drill bit requires replacement. It is known to provide the
gauge
CA 02675194 2009-08-11
2
surface with a wear resistant arrangement in order to control wear of the
gauge
region and thereby extend the working life of the drill bit. For example, a
series of
tungsten carbide inserts or blocks and a hardfacing material layer may be
provided
upon the gauge region to enhance the wear resistance thereof. Alternatively,
elements including, for example, a surface of polycrystalline diamond may be
mounted upon the bit body with the polycrystalline diamond surface arranged to
bear against the wall of the hole, in use. A further alternative is to mount
rollers on
the gauge region. However, a number of other wear reducing techniques are
known.
Although such techniques serve to reduce wear of the gauge region, it has been
found that, after having been used for some time, there is a tendency for the
wear
reducing material to separate from the gauge region, thereby reducing its wear
reducing properties, or even causing damage to the drill bit. For example,
where a
hard facing material layer is used, there is a tendency for the layer to peel
away
from the gauge region. This effect is particularly apparent on bits of the
type in
which the gauge region is not continuous around the entire bit body, but
rather is of
segmental form. Obviously, such separation is undesirable.
It is an object of the invention to provide a drill bit in which the
disadvantages
described hereinbefore are overcome or are of reduced effect.
According to the present invention there is provided a drill bit comprising a
bit body
including a gauge region of discontinuous form, a wear reducing arrangement
CA 02675194 2009-08-11
3
applied to at least part of the gauge region, and a guard arrangement
protecting at
least part of a leading edge, in the direction of rotation of the drill bit,
in use, of the
wear reducing arrangement, the guard arrangement comprising an element of
tungsten carbide secured to the gauge region.
The element of tungsten carbide is preferably of generally cylindrical form,
and is
preferably arranged such that its axis extends substantially parallel to the
axis of
rotation of the drill bit.
Such an arrangement is advantageous in that the leading edge of the wear
reducing
arrangement is protected from at least some abrasion and impact damage,
thereby
reducing the risk of damage and separation thereof from the bit body.
The element is preferably of multi-part form, for example comprising a
plurality of
cylindrical components stacked one upon another. The use of a plurality of
components in this manner is advantageous in that if an individual component
is
damaged, the risk of cracks propagating along the element to an adjacent
component
is reduced.
The cylindrical components may have polycrystalline diamond layers formed
thereon, for example comprising used or reject cutters unsuitable for use as
cutting
elements on the drill bit.
CA 02675194 2009-08-11
4
The bit body is preferably formed with a locating groove in which the element
is
mounted. The locating groove may be designed such that the element, or
individual
components thereof, where appropriate, are inserted therein from an end of the
groove, and held captive by the groove. However, this need not be the case and
the
invention is also applicable to arrangements in which the element is secured
in other
ways, for example it is currently envisaged that the elements will be brazed
in
position on the bit body. Of course, these securing techniques may be used in
combination.
The invention will further be described, by way of example, with reference to
the
accompanying drawings, in which:
Figure 1 is a view illustrating, diagrammatically, a known, prior art form of
drill bit;
Figure 2 is a view similar to Figure 1 but illustrating a drill bit in
accordance with
one embodiment of the invention; and
Figure 3 is an enlarged, diagrammatic view illustrating part of the guard
element of
the bit illustrated in Figure 2.
Referring firstly to Figure 1 there is illustrated a drill bit comprising a
bit body 10 of
cast steel form. Although the body 10 is of cast form, the invention is also
applicable to matrix bodied bits. The bit body 10 includes a mounting region
12
whereby it can be secured to a drill string for rotation about an axis of
rotation 14.
CA 02675194 2009-08-11
The bit body includes a series of upstanding integral blades 16, each of which
includes a leading edge 18 provided with a series of cutting elements 20. The
cutting elements 20 each comprise a substrate 22 of tungsten carbide to which
is
bonded a layer of polycrystalline diamond 24. In the arrangement illustrated,
the
5 cutting elements 20 are each of substantially cylindrical form, but this
need not be
the case and arrangements are known in which the cutting elements have, for
example, domed or other shaped working surfaces. The cutting elements 20 are
brazed, shrink fitted or otherwise secured in position on the bit body 10.
The bit body 10 further includes a gauge region 26 defining a gauge surface 28
of
generally cylindrical outer periphery, but of discontinuous form, being
interrupted
to defined flow channels 30 through which drilling fluid delivered from
nozzles 17
in the blades 16 can flow to carrying cuttings, etc, away from the blades 16
and
cutting elements 20. The gauge surface 28 is provided with a wear reducing
arrangement in the form of a plurality of blocks 32 tungsten carbide secured
to the
gauge region 26 and overlaid with a layer of a hard facing material. Although
the
use of a plurality of blocks 32 is illustrated, a number of other wear
reducing
techniques are also known for enhancing the wear or abrasion resistance of the
gauge surface 28, for example as described in EP 1036913.
In use, the drill bit is rotated about the axis 14 and a weight on bit loading
is applied
to the bit, with the result that the cutting elements 20 bear against the
formation
material being drilled, scraping, abrading or otherwise removing material
therefrom,
and thus extending the length of the hole drilled using the bit. The drilling
fluid
CA 02675194 2009-08-11
6
supplied to the nozzles 17 serves to clean and cool the cutting elements 20,
washing
the material through the flow channels 30 and away from the drill bit.
Abrasion andJor impact damage to the hard facing material can result in it
peeling
away of otherwise becoming separated, exposing the blocks 32 which in turn
will
wear at an increased rate, possibly also becoming dislodged or separating from
the
gauge region 26. It will be appreciated that these effects give rise to a
reduction in
the wear reducing capability of the wear reducing arrangement, and as a
result, the
gauge region 26 may be subject to increased, undesirable levels of wear, and
the
working life of the drill bit may be shortened.
Figure 2 illustrates a drill bit similar to that illustrated in Figure 1 but
modified, in
accordance with the invention, to include a series of guard arrangements 34.
In
other respects, the drill bit of Figure 2 is substantially the same as that
shown in
Figure 1 and so a further description of those parts of the drill bit is not
included
herein, and like reference numerals are used hereinafter to refer to parts
equivalent
to those described hereinbefore.
Each guard arrangement 34 comprises an element 36 of tungsten carbide which is
secured to the gauge region 26 at a position ahead of a leading edge 38 of the
wear
reducing arrangement, in the direction of rotation of the drill bit, to
protect the wear
reducing arrangement from at least some wear and/or impact damage, thereby
reducing the risk of peeling of the hard facing material thereof, or wear or
damage
to the blocks 32 or other components of the wear reducing arrangement causing
CA 02675194 2009-08-11
7
lifting or separation thereof from the gauge region 26, and thus reducing wear
and
extending the working life of the drill bit.
As can be seen in Figure 3, the element 36 is of generally cylindrical form
having a
longitudinal axis 40 extending substantially parallel to the axis of rotation
14 of the
drill bit, and arranged so that the part thereof most remote from the axis of
rotation
14 of the drill bit lies as substantially the same diameter as the gauge
diameter of the
bit. Conveniently, the element 36 is of substantially circular cross-sectional
shape,
as this may result in manufacturing advantages or simplifications, but this
need not
always be the case. The element 36 is, in this arrangement, of multi-part
form,
being made up of a series of individual components 42. One advantage of such
an
arrangement is that the propagation of damage along the element 36 is, reduced
compared to arrangements in which the element 36 is of one piece form. As a
result, damage to part of the element 36 is less likely to result in total
failure of the
element, but rather parts thereof will continue to function adequately despite
such
damage having occurred.
As illustrated, it is envisaged that one or more of the components 42 may
comprise
a cutter 44 including a substrate 46 of tungsten carbide to which a layer 48
of
polycrystalline diamond is bonded. For example, cutters which have been
rejected
as unsuitable for use in performing a cutting function may be used.
Alternatively,
used or worn cutters could be used. It will be appreciated that the cutters 44
used in
the element 36 do not perform a cutting function, their orientation and
positioning
on the drill bit being such that substantially no cutting is undertaken
thereby, in use.
CA 02675194 2009-08-11
8
However, although cutters 44 are illustrated as being used in the element 36,
it will
be appreciated that this need not be the case, and that the element 36 could
be
formed of a series of discs of tungsten carbide or the like.
The elements 36 are secured to the bit body 10 by being located within
locating
grooves 50 formed in the gauge region 26 adjacent the leading edges of the
wear
reducing arrangements. The grooves 50 are of substantially part cylindrical
form
and serve to locate the elements 36, the elements 36 being secured in position
by
brazing. However, other techniques could be used to secure the elements 36 in
position. For example, the grooves 50 may be shaped to hold the elements 36
captive, thereby providing a mechanical lock securing the elements 36 in
position.
Of course, these securing techniques may be used in combination, if desired.
As described hereinbefore, the arrangement of the invention has the advantage
that
peeling, lifting or other separation of the wear reducing arrangement is
reduced,
thereby reducing wear of the gauge region and extending the operating life of
the
drill bit.
A number of modifications and alterations may be made to the arrangement
described hereinbefore without departing from the scope of the invention.
