WASHPIPE STABILISATION

STABILISATION DE TUBE DE SURFORAGE

English Abstract

The invention relates to washpipe assemblies for use in well bores and
provides a washpipe assembly (2) comprising a washover shoe (10) attached to a
washpipe (18), wherein a washpipe stabiliser (22) is provided on the washpipe
(18) so that, when in use, deflection of the washover shoe (10) from a desired
position is substantially prevented. The washpipe assembly of the present
invention has the advantage over the prior art assemblies of providing means
for supporting the washpipe off the wall of a well bore or well bore casing
(52), and thereby reducing the torque required to rotate the washover string
and the tendency of the washover shoe (10) to deviate from its preferred path
down the well bore.

French Abstract

La présente invention concerne des ensembles tubes de surforage utilisés dans les puits de forage; elle comprend un ensemble tube de surforage (2) muni d'une couronne de surforage (10) fixée à un tube de surforage (18), et un dispositif stabilisateur (22) de tube de surforage qui est placé sur le tube de surforage (18) de manière à empêcher dans une large mesure la couronne de surforage (10) de s'écarter d'une position désirée lors de l'utilisation. Par rapport aux ensembles de l'état antérieur de la technique, l'ensemble tube de surforage de la présente invention présente l'avantage de constituer un moyen qui permet de maintenir le tube de surforage éloigné de la paroi d'un puits de forage ou du tubage (52) d'un puits de forage et, par conséquent, de réduire la force de torsion nécessaire pour faire tourner la colonne de tubage et de restreindre la tendance de la couronne de surforage (10) à dévier d'un parcours préféré de descente le long du puits de forage.

Claims

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CLAIMS:
1. A washpipe assembly (2) for use in a well bore, the
washpipe assembly (2) comprising a washover shoe (10) attached to a
washpipe (18), the washover shoe (10) and washpipe (18) being cylinders
defining a bore of the washpipe assembly (2) adapted to receive
equipment located within the well bore, characterised in that, a washpipe
stabiliser (22) is provided on the washpipe (18) so that, when in use,
deflection of the washover shoe (10) from a desired position is
substantially prevented.
2. A washpipe assembly (2) as claimed in claim 1, wherein the
cylinder of the washover shoe (10) is provided with cutting members
mounted on the lower end portion (44) thereof.
3. A washpipe assembly (2) as claimed in claim 1 or 2. wherein
the stabiliser (22) is provided as a plurality of blade members (24)
projecting from an exterior surface of the washpipe (18).
4. A washpipe assembly (2) as claimed in claim 3, wherein
each blade member (24) is arranged in a helix about the washpipe (18).
5. A washpipe assembly (2) as claimed in claim 3 or 4, wherein
the stabiliser (22) incorporates five blade members (24).
6. A washpipe assembly (2) as claimed in any of claims 3 to 5,
wherein the blade members (24) are provided with a cutting edge.
7. A washpipe assembly (2) as claimed in any of the preceding

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claims, wherein the stabiliser (22) is provided on a portion of the
washpipe (18) adjacent the washover shoe (10).
8. A washpipe assembly (2) as claimed in any of the preceding
claims, wherein the stabiliser (22) is an integral part of the washpipe
(18).

Description

CA 022~37~3 1998-11-06
WO 97/~3517 PCT/GB97/01219
WASHPIPE STABILISATIQN
The invention relates to washpipe assemblies for use in well bores.
It is common in the oil and gas drilling industry for equipment to
become trapped in a well bore so that access to the region of well bore
downhole of the e~uipment is restricted or prevented. Equipment
becomes trapped for a variety of reasons. For example, sediment may
settle about the equipment, the formation surrounding the equipment may
collapse or the equipment may even be dellberately cemented. In order to
remove equipment trapped under these circumstances, it is necessary to
remove the external material retaining the equipment within the well
bore. It is well known that this may be achieved by means of a washover
string. This type of string cuts the external material from the trapped
equipment and transfers the cut material to the surface by means of well
bore fluid flow passing uphole through the annulus.
A conventional washover string typically incorporates a washover
shoe, a washpipe, a drive sub (collectively referred to as the washpipe
assembly) and a drive shaft linking the drive sub to drive equipment
located at the surface. The washover shoe is rigidly connected to the
washpipe and has the function of cutting the external material preventing
the trapped equipment from being removed. Cutting elements, such as
tungsten inserts, are provided for this purpose. Both the washover shoe
and the washpipe are typically of a cylindrical shape having large inner
and outer diameters. The large inner diameters define a bore which is
capable of receiving the trapped equipment as the washover shoe cuts
through the external material and moves downhole. The washpipe is
rigidly connected to the drive sub which provides a connection between
the washpipe and the drive shaft. The washover string is rotated by
means of the drive equipment located at the surface and is pressed onto

CA 022S37S3 1998-11-06
.
the external material until sufficient material has been cut to release the
trapped equipment.
In order to guide the movement of the washover string as the
washover shoe cuts through the external material, stabilising means is
generally provided on the drive shaft. The centralisation of the washover
shoe within the well bore is critical to the efficient and effective use of a
washover string. However, centralisation of the washover shoe is often
hindered when the direction of travel of the washover string is capable of
being influenced by the external profile of the trapped equipment. In
these circumstances, the portion of the washover string below the
stabilising means tends to bend allowing the washover shoe to deviate
from its preferred course.
Prior art document US 3,747,674 discloses a washover pipe
spear apparatus for engaging and washing over a pipe stuck within a well
bore. The apparatus includes a washpipe, a retrieving assembly within
the washpipe, and releasable latch means joining the retrieving assembly
and the washover pipe. The retrieving assembly includes a slip assembly
and a releasable clutch which is operated by vertical manipulations of the
supporting tubing string to selectively control the setting of the slip
assembly. A stuck pipe may be thereby engaged by the retrieving
assembly and removed from the well bore.
It is an objection of the present invention to provide a
washpipe assembly which does not tend to deviate from its preferred
course when the washover shoe engages the trapped equipment to be
washed over.
The present invention provides a washpipe assembly for use
in a well bore, the washpipe assembly comprising a washover shoe
attached to a washpipe, the washover shoe and washpipe being cylinders
defining a bore of the washpipe assembly adapted to receive equipment
A~lENDED SHEE~

CA 022S37S3 1998-11-06
located within the well bore, characterised in that, a washpipe stabiliser is
provided on the washpipe so that, when in use, deflection of the washover
shoe from a desired position is substantially prevented.
The distance between the stabiliser and washover shoe in the
washpipe assembly of the present invention is considerably less than in
traditional washpipe assemblies. The close proximity of the stabiliser to
the washover shoe reduces the degree of bend in the washover string
between the washover shoe and the stabiliser. Consequently, the
tendency of the washover shoe to deviate from the preferred path down
the well bore is reduced.
It is preferable for the cylinder of the washover shoe to be
provided with cutting members located on the lower end portion thereof.
Thus, as the washover shoe cuts external material surrounding trapped
equipment and subsequently progresses down the well bore, the trapped
equipment may be received within the bore of the washpipe assembly.
The stabiliser is preferably provided as a plurality of blade
members projecting from an exterior surface of the washpipe. The
stabiliser preferably incorporates five blade members and each blade
member is preferably arranged in a helix about the washpipe.
Furthermore, each blade member is preferably provided with a cutting
edge. It is also desirable for the stabiliser to be provided on a portion of
the washpipe adjacent the washover shoe.
The washpipe assembly of the present invention has the
advantage over the prior art assemblies of providing means for supporting
the washpipe off the wall of the well bore or well bore casing, and
thereby reducing the torque required to rotate the washover string and the
tendency of the washover shoe to deviate from its preferred path down the
well bore.
A specific embodiment of the present invention will now be
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CA 022.737.73 1998 - 1 1 - 06
described with reference to the accompanying drawings, in which:
Figure 1 is a cross-section view of a washpipe assembly
according to the present invention;
Figure 2 is a side view of the stabiliser shown in Figure l;
Figure 3 is an end view of the stabiliser shown in Figure 2;
and
Figure 4 is a cross-section view of the washpipe assembly of
Figure 1 located within a well l)ore above trapped equipment.
The washpipe assembly 2 shown in Figure 1 incorporates a
number of components rigidly attached to one another by means of
threaded connections 4,6,8. The components include a washover shoe 10,
a lower washpipe 12, an upper washpipe 14 and a drive sub 16. The
lower washpipe 12 is rigidly attached to the upper washpipe 14 by means
of threaded connection 6 and thereby provides a complete washpipe 18
of the desired length. The lower end of the washpipe 18 is rigidly
attached to the washover shoe 10 by means of threaded connection 4.
The upper end of the washpipe 18 is rigidly attached to the drive sub 16
by means of threaded connection 8. When in use, the drive sub 16 is
threadedly connected to a drive shaft 20 (shown in Figure 4).
The washpipe 18 is provided with a stabiliser 22
incorporating five bl;3de members 24 arranged in a helix about the lower
washpipe 12. The blade members 24 are formed as an integral part of the
lower washpipe 12 and may be provided by machining, welding or any
other suitable manufacturing techniques. A detailed view of the
washpipe 18 is provided by Figures 2 and 3. The washpipe assembly 2
has dimensions suitable for a 244 mm (9.625 inch) well bore casing
having an inner diameter of 220 mm (8.681 inches). The outer diameter
26 of the washpipe is 206 mm (8.125 inches) and the outer diameter 28 of
the blade members 24 is 216 mm (8.500 inches). The washpipe 18
AA~IENDED SHEET

CA 022S37S3 1998-11-06
.. . ~ ~ .
defines a washpipe bore 30 having a diameter 32 of 185 mm (7.285
inches). The bore 30 and the length of the washpipe 18 are of sufficient
magnitude to receive trapped equinment when the washpipe assembly 2 is
in use. An appropriate length of washpipe 18 may be arranged prior to
use by selecting suitable lengths of lower and upper washpipe sections
12,14 or by using a suitable number of standard length washpipe sections.
Each blade member 24 of the stabiliser 22 has a helix angle 34 of 5.2~ and
has a width 36 at 90~ to the helix of 67 mm (2.G25 inches). Furthermore,
each blade member 24 is provided with a cutting edge 25.
The washover shoe 10 has substantially the same outer
diameter as the washpipe 18 and is provided with a bore 38 having
substantially the same diameter as the washpipe bore 30. The bores 30,38
of the washpipe 18 and the washover shoe 10 are in fluid communication
with one another and with a bore 40 provided in the drive sub 16. When
in use, the bores 30,38,40 of the washpipe assembly 2 are in fluid
communication with the surface via a bore 42 provided in the drive shaft
20 (see Figure 4).
The lower end portion 44 of the washover shoe 10 has a
smaller internal diameter and a larger external diameter than the main
body of the washover shoe 10. Tungsten inserts (not shown) are provided
on the external surface 46, the lower surface 48 and the internal surface
50 of the lower end portion 44 so as to provide means for cutting external
material from equipment trapped within a well bore. The lower end
portion 44 has an external diameter equal in magnitude to that of the
outer diameter 28 of the blade members 24. The external diameter of the
lower end portion 44 may alternatively have a greater magnitude than the
outer diameter 28, but should not have a magnitude less than the outer
diameter 28 since this would prevent the passage of the stabiliser 22
passed the trapped equipment during the washover operation. The lower
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CA 022~37~3 1998-11-06
- 6 --
surface 48 of the washover shoe lO is provided with fluid courses (not
shown~ which allow the flow of well bore fluid passed the external
material being cut, thereby cooling the washover shoe 10 and removing
cut portions of the external material.
The washover operation of the washpipe assembly 2 is
shown in Figure 4 of the accompanying drawings. The washpipe
assembly 2 is attached to a drive shaft 20 and run down a well bore 52
until the washover shoe 10 abuts external material 54 preventing removal
of trapped equipment 56. The external material 54 is removed by rotating
the drive shaft 20 and the washpipe assembly 2 by means of the drive
equipment located at the surface. External material 54 cut fiom the
trapped equipment 56 is removed by a flow of well bore fluid passing
downhole through the bores 42,40,30,38 of the washover stri~ through
the fluid courses and uphole through the annulus 58. The direction of
flow of the well bore fluid is indicated by arrows A, B and C.
As the washover shoe 10 cuts away the external material 54,
the washover strin~ is pushed downhole. As the washover shoe 10
progresses down the well bore 52, the trapped equipment 56 is received
within the bores 38,30 of the washover shoe 10 and the washpipe 18. The
tendency of the washover shoe 10 to be deflected from a central position
within the well bore 52 is reduced by the guiding effect of the stabiliser
22. The washpipe assembly 2 is moved down the well bore 52 so that the
washover shoe lO cuts away the external material 54 located both above
the trapped equipment 56 and between the trapped equipment 56 and the
well bore 52. Movement of the washpipe assembly 2 down the well bore
52 is continued until the stabiliser 22 passes the trapped equipment 56.
The blade members 24 of the stabiliser 22 not only guide the washover
shoe 10, but also act as a milling tool and clean the interior surface of the
well bore 52 in the region of the trapped equipment 56.
A~JlENDED SHEET

CA 02253753 1998-11-06
The present invention is not limited to the specific
embodiment described above. Alternative arrangements and suitable
materials will be apparent to a reader skilled in the art.
AMENDED SHEET

Representative Drawing