Note: Descriptions are shown in the official language in which they were submitted.
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GUIDE APPARATUS
The present invention relates to an active downhole cutting
tool guide device for use in a hole with sides between which a
hole-cutting tool provided with said apparatus may be
disposed.
There is a need for guiding of downhole cutting tools for
various purposes including inter alia lateral or kick-off hole
cutting, directional drilling, as well as to stabilise an
existing cutting tool advance direction against unwanted
deviation therefrom. Existing solutions to such problems are
generally cumbersome to use and/or unsuitable for use with
coiled tubing.
There is a need for cutting windows in oil/gas well casings
used to line the sides of well holes. Well casing is however
normally very tough, thick walled steel pipe which is placed
inside a borehole of a well as a lining to secure the borehole
and prevent the walls thereof from collapsing. Casing -
sometimes referred to as casing tubing - may be seamless,
spiral welded or seam welded and may, for example, be
fabricated from various API grades of steel such as H40, J55,
N80 or P110. Sizes typically vary from around 4 inches
(101.6mm) OD to 30 inches (762mm)OD, while weights typically
range from around 11 lb/ft to 200 lb/ft (16.4 kg/m to 298 kg/m
approximately) depending on diameter, thickness and grade. It
has also been known to employ glass fibre reinforced plastic
casing.
It is known that the cutting of windows in oil well casing, as
required for side tracking, is a complicated process, normally
requiring the use of a large number of tools not directly
related to the cutting of the window itself, such as
whipstocks, packers etc. The normal procedure is the setting
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of cement plug on top of a packer above which a so-called
"whipstock" is placed. The whipstock basically consists of a
hard metal wedge which guides a window milling drill bit
gradually into the casing thus cutting a slot in the casing.
As the slope of the whipstock is of a low value the pinching
action on the drill bit is very severe therefore requiring
extremely high torque and yet a low rate of progress is
achieved due to the high friction losses of the drill bit
against the whipstock which have to be subtracted from the
total energy available for the cutting of the window.
Furthermore once the window has been cut the whipstock and
packer require to be retrieved which is often a difficult and
tedious process. To date the duration of an average window
milling job is three to four days and often much longer.
There is also a need for stabilising drilling tools used to
clear well holes which have become obstructed to a greater or
lesser degree as a result of deposits on the sides thereof,
and/or as a result of deformation of a well hole casing as a
result of movement of the surrounding strata. Conventional
near bit stabilisers are essentially passive devices,
typically comprising a heavy duty ring with four angularly
distributed wings which more or less closely approach the hole
sides thereby limiting the amount of deviation of the cutting
tool possible. With such stabilisers though the resistance to
deviation remains substantially constant throughout use of the
device i.e. during travel of the cutting tool along clear
sections of the hole when ease of travel is desired and
stabilisation is not required, as well as during cutting
through obstructions, so that in practice the degree of
stabilisation available when it is required is substantially
insufficient for proper stabilisation.
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It is an object of the present invention to obviate or
mitigate at least some of the aforementioned problems and
disadvantages in the prior art.
It is a further object of the present invention to provide a
cutting tool guide apparatus which may be used with coiled
tubing with its inherently shorter positioning and retrieval
times against the use of jointed oil field tubing.
It is another object of the invention to provide a cutting
tool guide apparatus suitable for down-hole use in a hole with
sides between which a hole-cutting tool provided with said
device may be disposed, whereby in use of the device at least
one of the angle, the orientation and the lateral offset of a
hole-cutting tool relative to the longitudinal axis of the
hole in which said tool is disposed, may be controlled.
The present invention provides a down-hole tool guide
apparatus suitable for use in controlling the path of the
cutting tool of a down-hole cutting apparatus provided with a
pressurised working fluid supply in a borehole, said apparatus
comprising: a body having a chamber in which is slidably
mounted a piston, said body being formed and arranged for
connection of a high pressure end of said chamber to the
pressurized working fluid supply in use of the apparatus for
supplying pressurized working fluid to a high pressure side of
said piston, said body being further formed and arranged for
connecting a low pressure end of said chamber with the outside
of said guide apparatus, said low pressure end of said chamber
being provided with a resilient biasing device formed and
arranged for applying a biasing force to said piston
corresponding to a predetermined threshold pressure of the
pressurised fluid supply at the high pressure side of said
piston, so as to urge said piston towards the high pressure
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end of the chamber, said body mounting at least one shoe, each
said shoe having a radially outwardly facing longitudinally
extending engagement face, said piston being operatively
coupled to a shoe displacement mechanism formed and arranged
so that said shoe is held in a stowed position when said
piston is urged towards the high pressure end of said chamber
by the resilient biasing means, and said shoe is displaced
outwardly so that said engagement face projects outwardly of
the body when said piston is displaced towards the low
pressure end of the chamber by supply of pressurised working
fluid at a pressure higher than said threshold pressure.
Thus with an apparatus of the present invention, it is
possible to apply a guiding force to a down-hole cutting tool
as and when required, simply by increasing the flow of working
fluid. In general the guide apparatus of the present
invention is intended for use with a pressurised fluid
operated cutting tool apparatus wherein is employed a fluid
operated motor such as a turbine or positive displacement
motor and pressurised fluid is also supplied to the cutting
tool for lubrication thereof, carrying away cuttings etc.
Typically the guide apparatus would be mounted between the
motor and the cutting tool, the latter normally being
supported on a thrust bearing unit. With such a cutting tool
apparatus the pressurised fluid pressure applied to the high
pressure side of the cylinders) can be simply increased by
increasing the flow rate of the pressurised fluid supply
delivered down the drill string. The pressurised fluid supply
is generally provided, downstream of the cylinder , with a
flow restrictive nozzle in order to increase the backpressure
thereat and the pressure differential obtained for a given
pressurized fluid flow rate. By suitable choice of the
diameter of the flow restriction nozzle, it is possible to
adjust the pressure differential obtained for a given flow
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rate. This has the advantage of simultaneously increasing the
motor torque and/or speed and the fluid supply to the cutting
tool which is exactly what is required when kicking-off or
cutting through an asymmetric hole obstruction. Conversely
when kicking-off or cutting through an obstruction, the
guiding apparatus is automatically brought into operation by
the working fluid pressure increase which occurs with such
operations.
In one form of the invention there may be used a single shoe.
In this case displacement of the shoe into engagement with the
hole sidewall to one side of the drill string will force the
cutting tool against the hole sidewall to the other side of
the drill string. This is useful in cutting windows in well
casings by driving the cutting tool, conveniently a milling
tool, laterally through the casing to cut a window
therethrough. The window may then be elongated longitudinally
of the well by driving the drill string forwards. In this
type of arrangement, the angular directioning or orientation
of the cutting tool (around the well) may be conveniently
effected by means of a so-called indexing means (which is a
well known remotely operable device used to set the angular
orientation of a tool on drill string) to control the angular
orientation of the guide device and hence of the shoe around
the well prior to operation of the actuator means so that the
cutting tool is forced against the well casing at a desired
side of the well.
In another form of the invention at least two angularly
distributed, e.g. two diametrically opposed, or three, four or
more, symmetrically distributed, shoes may be used. These may
be displaced together by a single piston common thereto, or
alternatively there may be used two or more separate pistons
for the various shoes. In this case when the cylinders) is
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(are) displaced, the existing drill string direction is
stabilised against deviation, for example by asymmetrical
obstruction to the cutting tool. This is particularly useful
when re-boring holes which have become obstructed to a greater
or lesser degree e.g. by the formation of deposits therein, or
by deformation of the casing which could have arisen, for
example, as a result of shifts in the surrounding strata.
Where it is merely desired to provide stabilisation of an
existing drill string direction, then control of the angular
orientation of the guide apparatus with its shoes will not
normally be required. Nevertheless if desired the guide
apparatus could be used in conjunction with an indexing
device.
It will be appreciated that by varying the preloading of the
resilient biasing means it is possible to adjust the fluid
pressure threshold required to activate the guide device by
displacement of the piston. Typically there could be used a
threshold pressure in the region of from 5 to 20 Bar, for
example, about 10 Bar, when a positive displacement motor is
used. Furthermore by choice of a suitable spring rate, which
may moreover be linear or non-linear, it is possible to modify
the rate of extension of the shoes) with increasing fluid
pressure, for example, in order to control the force applied
to the cutting tool.
Any convenient kind of shoe displacement mechanism may be used
in accordance with the present invention. Thus, for example,
there could be used a cam mechanism, in which a cam is rotated
to deploy the shoe(s).
Conveniently there is used a linkage mechanism captively
secured to the piston and comprising a plurality of pivotally
connected links. If used as a stabilizer form of guide
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apparatus of the invention, the shoes will be maintained
parallel to the drill string. With the kick-off tool form of
guide apparatus the shoe may lie at a slight angle to the
drill string as the tool is pushed over to one side of the
tube and the tool bends.
The tool guide apparatus may be connected to the pressurised
working fluid supply in any suitable manner. In general the
tool guide apparatus will have a working fluid conduit
extending axially through its centre which can be coupled to
the working fluid conduits) exiting the motor stage and
running through the thrust bearing assembly to the cutting
tool. In such cases there is conveniently employed a
perforated connector for coupling the working fluid conduit
extending through the guide apparatus to that of the thrust
bearing, for tapping off working fluid pressure directly or
indirectly into the high pressure end of the guide apparatus
chamber. By varying the cross sectional area of the
perforation(s), the amount of pressure drawn off in this way
can be suitably adjusted.
Further preferred features and advantages of the invention
will appear from the following detailed description given by
way of example of some preferred embodiments illustrated with
reference to the accompanying drawings in which:
Figs 1 and 2 are general side elevations of a bottom hole
assembly with a kick-off tool of the invention in its
retracted and deployed conditions;
Figs 3 and 4 are detailed sectional elevations of the kick-off
tool;
Fig 5 is a detail front elevation of the kick-off tool in its
retracted condition;
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Fig 6 is a transverse section of the kick-off tool in the
plane VI-VI in Fig.4;
Fig 7 is a sectional elevation of a centralizing tool of the
invention;
Figs 8 and 9 are schematic transverse sections through the
centralizing tool of Fig. 7 in its deployed and retracted
condition; and
Fig 10 is a longitudinal section of a cutting tool suitable
for use with a kick-off tool according to Figs 3 to 6 for
window milling.
Figs 1 and 2 show (schematically) a bottom hole assembly 1
suspended from a coiled tubing drill string 2 and comprising a
downhole motor 3 and drill bit 4 supported on a thrust bearing
unit 5 with a kick-off tool 6 of the invention mounted between
the thrust bearing 5 and the motor 3. In Fig 1 the kick-off
tool 6 is in its inactive or stowed condition, whilst in Fig 2
the kick-off tool is shown fully extended.
As shown in Figs 3 and 4 the kick-off tool 6 comprises a
generally tubular body 7 having a reduced internal diameter
upper portion 8 and a larger internal diameter lower portion
9. A fluid supply tube 10 extends along the central
longitudinal axis X-X of the body 7 closely fitting the
interior 11 of the upper body portion 8 and spaced from the
interior 12 of the lower body portion 9 so as to define an
annular chamber 13 therebetween. An annular piston 14 is
slidably mounted between the fluid supply tube 10 and the
interior 12 of the lower body portion 9. A central
intermediate diameter body portion 15 houses a helical spring
16 which engages the upper end 17 of the piston 14 for
resiliently biasing the piston 14 downwardly.
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The upper end 17 of the piston 14 has secured thereto a
connector 18 which is pivotally connected 19 to the lower end
20 of a shoe assembly 21, the upper end 22 of which is
pivotally connected 23 to part 24 of the upper body portion 8.
In more detail the shoe assembly 21 comprises an elongate shoe
member 25 having an outer engagement surface 26 with closely
spaced longitudinally extending ridges 27 for positive
engagement in use of the tool with the side of a hole or pipe
and stabilizing the tool against angular displacement whilst
permitting longitudinal displacement - for example, for window
milling (longitudinal hole elongation). The ends 25a,25b of
the shoe member 25 are connected by respective link members
28, 29 to the piston 14 and upper body portion 8, so that the
shoe assembly 21 is movable between a stowed radially
retracted configuration as shown in Fig 3 with the shoe member
25 and link members 28, 29 fully extended longitudinally, and
a deployed radially extended configuration as shown in Fig 4
with the shoe member 25 and link members 28, 29 partially
collapsed together longitudinally.
The working end portion 30 of the piston 14 has a reduced
diameter and is slidably received within a sleeve 31 mounted
within the annular chamber 13 in order to reduce the surface
area of the working end face 32 of the piston 14 thereby to
reduce the force exerted on the shoe assembly 21 for a given
differential fluid pressure exerted thereon.
The lower end 33 of the fluid supply tube 10 is connected via
a tubular coupling 34 (see Fig 4) to a further fluid supply
tube section 35 extending through a thrust bearing unit 5.
The tubular coupling 34 has a number of apertures 36 which
connect the interior 37 of the fluid supply tube 10 to the
high pressure end 13a of the annular chamber 13 below the
piston working end face 32 for supplying fluid pressure
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thereto. Inside the coupling 34 is provided a flow
restriction nozzle 38 for increasing the fluid pressure
diverted to the chamber 13. The back-pressure generated and
the pressure differential obtained for a given flow rate can
be adjusted by selecting a suitable flow restriction nozzle
diameter. The low pressure end 13b of the annular chamber 13
above the piston 14 is open to the outside of the guide
apparatus 6 around the shoe member 25 (see Figs 3 to 6).
In use of the kick-off tool of Figs 3 to 6, under normal
operating conditions, the shoe member 25 is held in its
retracted position by the spring 16. When the differential
fluid supply pressure exerted on the working end face 32 is
increased by increasing the flow rate of the pressurized
fluid, then the piston 14 is forced upwardly thereby partly
collapsing the shoe assembly 21 and forcing out the shoe
member 25 into a radially outwardly deployed position in
engagement with one side 40 of the hole or pipe 41 inside
which the bottom hole assembly 1 is disposed and forcing the
latter towards the other side 42 of the hole or pipe 41 in
order to, for example, bring a window cutting tool (not shown)
into engagement therewith, deviate the drilling direction etc.
Figs 7 to 9 show a centralizing tool 43 of the invention for
use in centralizing a bottom hole assembly 1 and stabilizing
it against unwanted deviations e.g. due to asymmetric
obstructions in the hole or pipe 41 or other asymmetric
resistance to the advance of the bottom hole assembly 1. The
centralizing tool 43 is of essentially similar construction to
the kick-off tool 6 of Figs 1 to 6 but with three
symmetrically angularly distributed shoe assemblies 21A, 21B,
21C instead of the one shoe assembly 21 of the kick-off tool
6, and similar components corresponding generally to those of
the latter are indicated by like reference numbers. In this
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case when the differential fluid supply pressure applied to
the piston working end face 32 is increased the shoe members
25 are brought into engagement with the sides 45 of the hole
or pipe 41 around the tool 43 so that the bottom hole assembly
1 is held firmly in the centre of the hole or pipe 41 against
unwanted deviations therefrom.
As may be seen in Fig.6, the side 46 of the kick-off tool 6
has a substantially larger radius of curvature (comparable to
that of the tool with the shoe assembly 21 in its deployed,
radially extended position) than that of the tool 6 in its
radially retracted condition. By this means the surface area
of the tool side 46 which is forced into engagement with the
pipe side 42 in which, for example, a hole is to be cut, is
maximized thereby spreading the load thereon, whilst at the
same time maximizing ease of movement of the tool 6 along the
pipe 41 when the shoe assembly 21 is in its radially retracted
condition.
Fig 10 is a longitudinal section of a cutting tool suitable
for use with a kick-off tool according to Figs 3 to 6 for
window milling. In more detail the cutting tool 47 has an
outer generally cylindrical cutting surface 48 which may have
carbide inserts or crushed carbide particles or similar
cutting materials brazed or attached on to it. This
cylindrical cutting surface 48 will cut during the initial
perforating operation as the kick-off tool 6 is actuated and
pushes laterally the milling tool 47 into the wall of the
tubing P (see Figs 1-2). The front end face 49 of the tool
has a central recess 50 made of a generally conical form.
This end face 49 will also be coated with an abrasive cutting
coating e.g. crushed carbide. Once the perforation has been
made and the BHA starts to advance down the well to elongate
axially the perforation to form a window in the tubing P, the
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end face 49 will be the cutting face. The conical recess 50
of the end face 49 is designed to stabilise the BHA so that it
does not drift back into the centre of the tube P, by tending
to centralise the cutting 47 in the wall of the tubing P. (If
a flat face or an external conical face is used, the tool
tends to push back in towards the centre of the tubing).
It will be appreciated that various modifications may be made
to the above described embodiment without departing from the
scope of the present invention. Thus, for example, although
in Figs. 3, 4 and 7, the piston-cylinder device 14, 13 is
shown connected to the lower end of the shoe assembly, the
piston-cylinder device could also be connected to the upper
end thereof. It is believed that in use a piston located
connected at the lower end could be advantageous as if the
tool becomes difficult to operate, e.g. because of
contaminants in the pressurized fluid causing a blockage, then
in the process of withdrawing the tool from the hole the
piston is pushed back by the force of the springs and the
lever action of the shoe without having to overcome the effect
of the blockage or debris above the piston. To encourage the
shoe to retract on pull out of the hole, the angle of the
links 28 and 29 at full extension should be less than 90° from
centreline of the body and preferably in the range from 30 to
60°.
Also, if it is desired to provide axial stabilization against
longitudinal displacement of the tool - for example in use as
a perforating tool, where a hole is to be made in the wall of
the casing/tubing but a window is not required, or in use as
an anchor, then, instead of longitudinally extending grooves
and ridges 27, there could be used part-annular grooves and
ridges. In use as an anchor the guide apparatus would be
positioned between the downhole motor 3 and the coiled
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tubing/drill string 2. As a stabiliser the guide apparatus
may be positioned between the downhole motor 3 and the coiled
tubing/drill string 2 or between the downhole motor 3 and the
bearing section 5.
To reduce the possible bending of the bottom hole assembly 1
between the drill bit 4 and the guide apparatus 6 it may be
advantageous to integrate the bearing section 5 and the guide
apparatus 6 into a single unit.
