Note: Descriptions are shown in the official language in which they were submitted.
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WO 97/45620 PCTIGB97/01417
STABLISER FOR BOREHOLE DRLLING APPARATUS
This invention relates to stabilisers for borehole
drilling apparatus and more particularly to a drill
string stabiliser having fixed blade arms provided with
replaceable wear elements.
Drill string stabilisers, sometimes referred to as
drill collar stabilisers, or as drill stem stabilisers,
are used in earth boring operations to centralise the
drill stem in a borehole during drilling operations,
especially in the drill collar section of the drill
string, for example, at distances of from 0-300 metres
above the drill bit. The drill string stabiliser has a
variety of functions as follows:
(i) to control the hole angle direction;
20(ii) to prevent the bit from drifting laterally;
and
(iii) to improve the cutting performance of the bit
by keeping it rotating centrally about its
25axis so as to provide a substantially equal
force loading on all three drill bit cones.
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In addition, where the surrounding rock formation is
not too hard, the stabiliser may also provide a re~ming
function for undersized or irregularly shaped boreholes.
This invention is particularly concerned with
rotatable stabilisers of the kind which rotate together
with the drill string.
The wall-contacting members of a rotatable
stabiliser are subject to the various forces attendant on
the entire drill string, which may include thrust forces,
fretting forces, and the forces resulting from drill
string manipulations, the conditions of the borehole, and
the fluid conditions internal and external to the drill
string.
In the rotary system of drilling, employing a liquid
circulating through the drill string and through the
annulus between the drill string and the borehole, it is
necessary that the stabiliser includes not only fluid
passage means therethrough to form part of the drill
string flow passage, but also fluid passage means to form
part of the annulus fluid passage. The annular fluid
passage means are provided at the outer periphery of the
stabiliser, with the result that the wall-contacting
portion of the stabiliser is not continuous around the
circumference thereof, but instead consists of a number
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of blades azimuthally spaced apart by the fluid passage
means.
It is known to provide fixed blade arms,
incorporating wear elements, which are welded to the
stabiliser, or to a sleeve surrounding the stabiliser,
and such "welded-blade" stabilisers are disclosed in GB
2096210, US 2288124, and US 3268274.
10It is also known to provide rotatable stabilisers
with devices for connecting wear elements to fixed blade
arms, enabling the wear elements to be detached and
replaced. Such mechanisms include various slot and
groove connections, cap screw connections, tapering
wedging connections and combinations of these. Typical
arrangements are shown in US 3680647 and US 3818999. US
4662461 discloses a stabiliser having a plurality of
fixed blade arms with replaceable wear elements.
20Whilst all the above patents are concerned with
stabilisers in which the blades lie parallel to the axis
of the drill string, there is another class of
stabilisers, known as spiral blade stabilisers, for which
no solution to the problem of providing replaceable wear
elements has yet been found.
According to the present invention, there is
provided a drill string stabiliser for borehole drilling
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apparatus, which comprises a plurality of fixed blade
arms provided with replaceable wear elements,
characterised in that the blade arms are spiral and
provided with shoulders defining longitudinal grooves or
recesses in the external faces of the blade arms; in that
replaceable wear elements are provided with seating
portions which are located in the longitudinal grooves or
recesses; and in that the shoulders and the seating
portions of the wear elements are provided with holes
which, when a wear element is located in its groove or
recess, are aligned, such that a connecting means can be
inserted into the holes to secure the wear element to the
blade arm.
The stabiliser may be provided with any suitable
number of spiral blade arms, but usually two or three are
sufficient for most purposes. A larger number of blade
arms can, however, be used if appropriate.
The wear elements can comprise silicon carbide, or
similar hard materials. Preferably, each spiral blade
arm is provided with a single wear element, curved to
form a segment of a spiral or helix, which extends for
the full length of the working surface of the blade arm.
The wear element preferably has a surface which is proud
of the blade arm, and can, for example, extend to a
radial distance of from 10 to 500 mm from the blade arm.
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Examples of spiral blade stabilisers provided with
replaceable wear elements in accordance with the
invention will now be described with reference to the
accompanying Drawings in which:
Figure 1 shows a side elevation of a prior art
spiral blade stabiliser;
Figure 2 shows a side elevation of a first
embodiment of a spiral blade stabiliser according to the
invention;
Figure 3 shows a perspective view from the side and
one end of a wear element suitable for use in a
stabiliser of the present invention;
Figure 4 shows a sectional end elevation of a spiral
blade stabiliser according to the invention, illustrating
three different types of seating for the wear element;
and
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Figures 5(a) to (e) illustrate various securing
devices by which the wear element can be secured to the
spiral blade arm.
Referring firstly to Figure l, there is illustrated
a prior art spiral blade stabiliser 1 having a body 2
provided with spiral blade arms 3 having wear surfaces 4.
Spiral channels 5 are provided between adjacent blade
arms to permit drilling fluid, carrying debris from the
borehole, to pass therealong.
Figure 2 illustrates a first embodiment of a spiral
blade stabiliser according to the invention, in which the
stabiliser lO has blade arms 11 having wear elements 12
seated in grooves 13 in the blade working surfaces 14.
Figure 3 shows a novel wear element for use in a
stabiliser according to the invention. The wear element
20, which is curved in two directions in order to conform
to the external surface of a spiral blade, has a working
surface 21, and a wedge-shaped seating portion 22.
The location of the wear element 20 on a spiral
blade arm is shown in figure 4, top right hand side. The
spiral blade arm 30 is provided with shoulders 31
defining a wedge-shaped groove 32 in the external surface
of the blade arm 30. The wear element 20 is seated on
the blade arm 30 such that the wedge-shaped seating
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portion 22 of the wear element fits tightly into the
groove 32. Although the seating faces 33, 34 are shown
as straight, they need not be straight, or symmetrical,
and any suitable curved shape can be used as appropriate.
The wear element 20 is seated proud of the blade arm 30
as shown.
Figure 4 also illustrates an alternative seating
arrangement. At the bottom right hand side there is
shown blade arm 40 having shoulders 41 defining a wedge-
shaped groove 42 with rounded bottom corners 43. The
wear element 44 is seated with its wedge-shaped seating
portion 45 in the ~loo~e 42, and is held tightly by the
sides thereof such that it extends proud of the blade 40.
Again, the sides do not have to be straight or
symmetrical.
Figure S shows various alternative arrangements for
mounting and securing the wear elements to the blade arms
of a stabiliser. In figure 5(a), the stabiliser blade
arm 50 has shoulders 51 having aligned, transversely
directed holes 52 therein. The flanged wear element 53
has a seating portion 54 in which there is a transverse
hole 55 which is aligned with the holes 52 to provide a
through passage. A tapered pin 56, which is a tight fit
in the passage formed by the holes 52 and 54, is inserted
therein to secure the wear element 53 in place.
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Figure 5(b) shows a second arrangement in which the
blade arm 60 is provided with shoulders 61 having a
passage 62 drilled transversely therethrough. The wear
element 63 has a corresponding recess 64 drilled therein
so as not to provide an obstruction to the passage 62
when the wear element is seated on the blade arm 60. A
barrel nut 65 is positioned in the passage 62 and aligned
such that its central threaded hole 66 is immediately
beneath a bolt hole 67 in the wear element 63. The
bolthole 67 is countersunk to accept a bolt 68 such that
the head of the bolt 69 is below the working surface of
the wear element 63.
In Figure 5(c) there is shown a further mounting
lS arrangement which is similar to that of Figure 5(a)
except that the tapered pin 56 is replaced by a roll pin
70 and the shoulders 71 of the blade arm 72 have straight
sides and curved corners to accommodate a similarly
shaped seating portion 73 of wear element 74.
Figure 5(d) shows a similar arrangement to that of
Figure 5(c) except that in this case the groove 80 in the
blade arm 81 is wedge-shaped to accommodate a wedge-
shaped seating portion 82 of the wear element.
Finally, Figure 5(e) shows a still further
arrangement which is similar to that of Figure 5(c)
except that the roll pin is replaced by a bent or cranked
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pin 90 fixed at one end to a locking plate 91 carrying a
locking screw 92. Locking plate 91 and screw 92 fit
within a recess 93 of the blade arm 94 and the locking
screw is secured to the blade arm 94 via a screw threaded
hole 95. The bent or cranked pin provides a radial force
to maintain the flanged wear element 96 firmly secured to
the blade arm 94 and its orientation is maintained by the
locking plate and screw arrangement 91, 92.
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stated otherwise, each feature disclosed is one example
only of a generic series of equivalent or similar
features.
The invention is not restricted to the details of
the foregoing embodiment(s). This invention extends to
any novel one, or any novel combination, of the features
disclosed in this specification (including any
A~.r.Dmpanying claims, abstract and drawings), or to any
novel one, or any novel combination, of the steps of any
method or process so disclosed.
. . .
