Note: Descriptions are shown in the official language in which they were submitted.
CA 02494229 2005-O1-25
ADJUSTABLE DOWNHOLE TOOL
This invention relates to adjustable down-hole tools employed in the oil and
gas drilling industry.
WO-A-0053886 discloses an adjustable down-hole tool comprising a body
having a through bore; a mandrel axially movable in the body, the mandrel
being
movable by fluid pressure in the tool against the action of a first return
spring between a
first, deactivated position and a second activated position; a sleeve limiting
movement of
l0 said mandrel between said positions; at least two sets of castellations,
one set on the
sleeve and the other set on a facing edge so that, when the castellations are
in phase, the
mandrel is prevented from travelling from said first to second position and
when they are
out of phase they interdigitate and the mandrel is not prevented from
travelling from said
first to second position; and means to rotate the sleeve relative to the
facing edge between
15 said in-phase and out-of phase positions; characterised in that said means
comprises a
control piston slidable in or on the mandrel and in the body and being movable
by fluid
pressure in the tool against the action of a second return spring.
In the specific embodiments disclosed in that application, the control piston
20 slides sealingly against the bore of the body, and also against the bore,
or around the
outside of, the mandrel, also sealingly. Both embodiments disclosed are
satisfactory, but
the present invention relates to a modification of the tool disclosed in that
application.
The reason for the modification is that, in the previously described
arrangement, the
control piston seals against two components, the body and mandrel, that are
not fixed
25 with respect to one another. Consequently, there could be leakage past the
respective
seals if the tolerance in manufacture of the body and mandrel is not very
tight and there is
excessive play between them. Also, since the piston must seal to both the body
and
mandrel, it inevitably extends beyond the end of the mandrel, increasing its
overall
length. It is an object of the invention to overcome these disadvantages.
In accordance with the present invention, there is provided an adjustable
down-hole tool comprising a body having a through bore; a mandrel having a
through
bore axially movable in the body, the mandrel being movable by fluid pressure
in the tool
CA 02494229 2005-O1-25
against the action of a first return spring between a first, deactivated
position and a
second activated position; a sleeve between the body and mandrel limiting
movement of
said mandrel between said positions; at least two sets of castellations, one
set on the
sleeve and the other set on a facing edge of the body or mandrel so that, when
the
castellations are in phase, the mandrel is prevented from travelling from said
first to
second position and, when they are out of phase, they interdigitate and the
mandrel is not
prevented from travelling from said first to second position; and a control
piston to rotate
the sleeve relative to said facing edge between said in-phase and out-of phase
positions,
the piston being movable by fluid pressure in the tool against the action of a
second
1 o return spring; characterised in that said control piston is slidable in
the mandrel, the
mandrel carrying rotation transmitters that are in contact with both the
piston and sleeve,
whereby rotation of the piston relative to the mandrel rotates the sleeve
relative to the
mandrel.
Preferably, said rotation transmitters are carried by the mandrel intermediate
its ends. Preferably, they are between axially spaced seals of the piston
against the bore
of the mandrel. Said transmitters may comprise a gear rotationally journalled
in the
mandrel about an axis parallel the throughbores. Both the piston and sleeve
may have a
rack engaged with the gear. A plurality of gears may be disposed around the
2o circumference of the mandrel.
Drill string stabilisers, under reamers and fishing tools are some of the down
hole tools that require activation when they are in a given position down hole
to make
them operative, and deactivation when they are to be withdrawn, or
repositioned or
indeed simply to go into a different operating condition.
Taking stabilisers as an example, these tools centralise drill strings with
respect to the hole drilled. They normally comprise a sub assembly in the
drill string.
The stabiliser has a plurality of blades, (usually three and usually spirally
arranged),
3o whose edges are adapted to bear against the bore-hole. The blades are not
complete
around a circumference of the drill string so that the return route for
drilling mud pumped
down the bore of the drill string is not blocked. In order to control the
direction of drill
bits, it is sometimes required that the stabiliser has variable diameter.
Pistons in the
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blades are extendable to give the stabiliser a maximum diameter, which ensures
that the
drill string is central in the bore-hole. The drill bit, assuming the
stabiliser is close
behind the drill bit, is thus kept straight. However, if the pistons are
withdrawn, then
gravity can deflect the drill string so that it alters the inclination of the
hole.
Preferably, said mandrel is rotationally fixed with respect to the body.
Preferably, a circumferential barrel cam is defined in one of said piston and
mandrel, a
cam follower being disposed in the other thereof, the follower being within
the barrel
cam so that axial movement of the piston with respect to the mandrel results
in
1 o corresponding rotation of the piston with respect to the mandrel. In this
case, the barrel
cam may be shaped so that movement of the piston in one axial stroke and
return thereof
results in rotation of the sleeve from a said in-phase position to a said out-
of phase
position or vice versa. Said castellations are preferably angularly spaced by
a phase angle
and said stroke and return of the piston results in rotation of the sleeve by
said phase
15 angle. Instead of the piston rotating in its entirety in the mandrel, a
separate component
thereof may be rotationally freely, but axially fixedly, mounted in the
piston, which
component carries said barrel cam or follower. In this event, said separate
component
drives said rotation transmitters on rotation of said component in response to
axial
movement of the piston in said mandrel. This arrangement avoids the necessity
to rotate
2o the piston with respect to the mandrel. Thus the barrel cam does not need
to overcome
the resistance of the piston's frictional contact with the mandrel through its
seals thereto
and other parts in contact therewith.
When said mandrel is in said deactivated position, a rise in hydraulic
pressure
25 in the tool preferably results in movement of the piston before movement of
the mandrel.
Said first return spring may be sufficiently stronger than said second return
spring to
ensure that, when said mandrel is in said deactivated position, a rise in
hydraulic pressure
in the tool results in movement of the piston before movement of the mandrel.
Alternatively, or in addition, a spring loaded detent may be provided between
said
3o mandrel and body to retain the mandrel in said deactivated position until a
threshold
hydraulic pressure has been exceeded, which pressure is greater than that
required to
move said piston. Said detent may comprise a plunger in a radial bore of the
mandrel or
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body, spring biased against a lip of the body or mandrel, respectively. Said
lip may be of
a circumferential groove around the body or mandrel.
Preferably, the plunger has a through bore connecting the space between the
mandrel and body with a space behind the plunger so that hydraulic effects are
substantially eliminated. Moreover, there are preferably a plurality of said
detents
arranged around the circumference of the mandrel. This reduces any moment on
the
mandrel relative to the body.
1 o The mandrel is preferably sealed to the body about first and second
circumferences, the first being a larger circumference upstream, in terms of
fluid flow
through the tool, of the second, smaller circumference. Thus hydraulic forces
act on the
mandrel relative to the body urging the mandrel in a downstream direction.
References to
upstream and downstream are purely for convenience, of course. The direction
of
15 movement of the components in question is dependent only on hydraulic
pressure, not on
direction of flow.
The piston preferably also has a through bore and is sealed to the mandrel
about third and fourth circumferences, the third being a larger circumference
upstream, in
2o terms of fluid flow through the tool, of the fourth, smaller circumference.
Thus hydraulic
forces likewise act on the piston relative to the mandrel, also urging the
piston in a
downstream direction.
In said activated position, the bore of the mandrel preferably engages a
throat
25 in the bore of the body to create a flow restriction and consequent back
pressure
detectable to indicate the position of the tool.
Said tool can be a drill-string stabiliser, in which case said mandrel has
wedge surfaces to engage corresponding surfaces on radially disposed pistons
slidable in
3o the body, whereby, when the mandrel moves from said deactivated to said
activated
position, the pistons extend from the body increasing the working diameter of
the
stabiliser.
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An embodiment of the invention is further described hereinafter, by way of
example, with reference to the accompanying drawings, in which:-
Figures 1 a, b and c are part side sections through different parts
(downstream, middle and upstream sections) of a stabiliser in accordance with
the present
5 invention;
Figure 2 is a section on the line II-II in Figure lb;
Figure 3 is a side view of a control piston of the tool of Figure 1;
Figure 4 is a view in the direction of arrow A in Figure 3;
Figure 5 is a side view of the facing castellations of the sleeve and mandrel
of
I o the stabiliser of Figures 1 a to c;
Figure 6 is a view similar to Figure 5, but of an alternative embodiment of
the
present invention; and
Figure 7 is a partial side section of a variation of the embodiment shown in
Figures 1 a, b and c.
IS
In the drawings, a stabiliser 10 comprises a body 12 connectable to a drill
string 13 by means of male and female connectors 14 at either end thereof. A
bore 16
extends from one end of the body 12 to the other, to permit flow of mud to
lubricate the
drill bit (not shown) at the end of the string. Slidable in the bore 16 is a
mandrel 18
2o which is rotationally fixed therein by virtue of a stud 20 in the body 12
which extends
into a slot 22 in the mandrel 18. The slot 22 extends axially of the mandrel
18 permitting
axial movement thereof within the body 12.
Spiral blades 24 are defined on the surface of the body 12 and bear against
the
25 surface of the bore hole (not shown) being drilled to guide the drill bit.
The blades permit
the return passage of drilling mud by being spaced around the body 12. The
blades 24
have radial bores 26 defined in spaced relation along each blade 24. Within
each bore 26
is a piston 28 urged radially inwards by springs 29. The base of each piston
is formed
with a wedge surface 30 against which a wedge 31 of the mandrel 18 acts. Thus,
if the
3o mandrel moves rightwardly in the drawings, the pistons 28 are thrust
radially outwardly
projecting beyond the circumference of the stabiliser 10 defined by the blades
24. In this
way, the working diameter of the stabiliser increases with the faces of the
pistons 28
bearing against the wall of the bore hole.
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At its upstream end 33, the mandrel receives a control piston 36. The control
piston is slidable in a bore 38 of the mandrel which extends from its upstream
end 33 to
its downstream end 32. The control piston carries seals 46,48a which seal the
piston with
respect to the mandrel 18. The mandrel is sealed to the body at its upstream
end 33 by
seal 34, and at its downstream end 32 by seal 48b.
As far as the body 12 is concerned, the mandrel and piston are a single unit,
and it can be seen that the circumference of the seal 34 in the body 12 is
much larger than
1 o the circumference of the seal 48b. Consequently, hydraulic pressure of the
mud in the
tool 10 results in a larger downward force acting at the end 33 of the mandrel
18, via the
seal sleeve 34, than acting in the reverse direction through the seal 48b.
A spring 44 acts between a shoulder 42 in the body 12 and the mandrel 18,
15 urging the mandrel in the upstream direction. Should the pressure
differential be such
that the force acting on the mandrel exceeds the return force of the spring
44, the mandrel
will move rightwardly in the drawing.
Likewise, hydraulic pressure acting on the control piston 36 across the
20 circumference of its seals 46,48a to the mandrel result in a downward force
on the piston
36 because the circumference of the seal 48a is smaller than seal
circumference 46.
Again, a spring 50 (not shown) acts between shoulder 52 in the mandrel 18 and
shoulder
54 on the piston 36 to urge the piston in an upstream direction. Again, should
the
hydraulic pressure be such that the force of the spring 50 is overcome, the
piston 36 will
25 move rightwardly in the drawings.
The piston has a barrel cam 56 defined in its surface (see Figure 3). Pins 58
in the mandrel are received within the confines of the barrel cam 56 so that
movement of
one relative to the other forces the piston to follow a course defined by the
barrel cam 56.
30 If the mandrel is considered, for the moment, to be stationary, then, as
hydraulic pressure
increases in the bore 38 of the mandrel 18, the piston 36 begins movement from
left to
right (with reference to Figure 1). Suppose the pins 58 start at position 58a,
for example
(see Figure 4), where they lie at the base of a first notch 56a of the barrel
cam. They will
CA 02494229 2005-O1-25
thus move, relatively to the barrel cam 56, until they contact the opposite
wall thereof at
56b. Further axial movement of the piston 36 then only occurs when the piston
rotates
through a small angle al, so that the pin 58 effectively moves to position 58b
in notch
56c on the opposite side of the barrel cam 56 from notch 56a.
Should the hydraulic pressure be released, return spring 50 forces the piston
36 leftwardly in the drawing (Figure 1). The pin 58 is obliged to follow a
course from
position 58b in notch 56c of the barrel cam 56, axially until the opposite
wall of the
barrel cam 56d is contacted. Thereafter, further axial movement of the piston
can only
occur on further rotation of the piston. In this event, the pin moves to the
base of notch
56e on the same side of the barrel cam 56 as notch 56a. In this movement, the
piston has
rotated through a further angle a2, which is not necessarily the same as a~ .
Nevertheless
the sum (al + a2) is equal to 2a, the angle of rotation of the piston 36 on
one complete
return stroke thereof in relation to the mandrel 18.
A subsidiary feature of the barrel cam 56 and pins 58 is that the pins 58 have
a large diameter section 58' and a small diameter end 58". The barrel cam has
a
correspondingly wide slot 56' and a deeper, narrow slot 56", so that the wide
slot 56'
accommodates the large diameter section 58' of the pin 58, while the narrow
slot 56"
2o accommodates the thin pin end 58". The purpose of this is that a wide slot
is inevitably
somewhat coarse compared with a narrow slot, which can be precise. On the
other hand,
a wide slot with a large diameter pin significantly reduces point loads, both
on the pin
and cam surface it is following. Given that the control piston is spring
loaded, it
inevitably resists rotation due to frictional forces, although these can be
alleviated, for
example, by employing a thrust bearing between the spring 50 and piston 36.
However,
even with this measure, if only a coarse cam surface 56' and large pin 58' is
employed,
then, in moving from notch 56a to contact surface 56b, a rotational drift back
in the
direction of Arrow X in Figure 4 of only 1 ° can be permitted. Any
greater drift, which
would generally be caused by the spring having been "wound up" by previous
3o movements, would cause contact of the pin 58' with point 56f of the cam
56', such that
secure guidance of the pin to notch 56c could not be guaranteed. Because slot
56" can be
more precise, however, the permitted angle of drift can be much greater, such
as 15° (see
Arrow Y in Figure 4), while still ensuring that the pin is guided correctly
and rotation of
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the piston 36 in the correct direction is guaranteed. At the same time,
however, it is only
during these extreme situations that loading only occurs through the narrow
slot 56" and
thin pin end 58". Most of the time, and indeed mostly all the time when thrust
bearings
are employed, both surfaces 56' and 56" are contacted by both pin parts 58'
and 58", so
that wear on the pin 58 and slot 56 is minimised, even though accurate
guidance is
ensured.
As shown in Figure 3, the piston 36 has a splined section 60a which is
engaged with a plurality of gears 61 disposed in pockets formed in the mandrel
18. The
1o gears 61 axe journalled for rotation in the mandrel pockets about axes 63
that are parallel
the length of the stabiliser 10. The gears 61 mesh with a splined rack 64a
disposed
internally of a castellated sleeve 66. Consequently, since the mandrel is held
rotationally
fixed by stud 20 engaged with slot 22, when the piston rotates through angle
2a on one
complete return stroke thereof, the sleeve likewise rotates relative to the
mandrel about
15 the same angle 2a, albeit in the opposite direction.
The sleeve 66 is received between a shoulder 68 of the body 12 (in fact, on an
end of compensation collar 25) and shoulder 69 of the mandrel 18. The sleeve
is axially
fixed on the mandrel 18 by a retention ring 67, but it is freely rotatable on
the mandrel.
2o The shoulder 68 is castellated having fingers 18a and slots 18b. The end
569 of the
sleeve 66 is likewise castellated having fingers 69a and slots 69b. When the
fingers
18a,69a of the body and sleeve are in phase with one another (as shown in
Figure 5), then
rightward movement of the mandrel 18 (in Figure lb of the drawings -
leftwardly in
Figure 5), is limited, with the fingers 18a,69a abutting one another and the
other end 70
25 of the sleeve 66 abutting shoulder 69 of the mandrel 18.
On the other hand, however, when the sleeve 66 is out of phase with respect
to the body 12, (as shown in Figure 2) fingers 18a face slots 69b and fingers
69a face
slots 18b so that, when the mandrel 18 moves rightwardly in the drawings, the
3o castellations on the body and sleeve interdigitate, so that further
rightward movement of
the mandrel 18 is possible than when the castellations are in phase. The
angular
separation of the fingers and slots in the mandrel and sleeve is arranged to
be the same
angle 2a (or multiples thereof), as described above.
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Consequently, when the piston makes a complete return stroke serving to
rotate the sleeve 66 through the angle 2a, the sleeve 66 moves from an in-
phase position
to an out-of phase position, or vice versa.
Turning now to Figure 6, an alternative arrangement is shown to that
described above with reference to Figure 5. Here, the sleeve 66' has alternate
slots 69b'
which have different depths (shallow, 69b'~ and deep, 69b'2). Similarly, the
body 12' has
alternate fingers 18a' which are correspondingly short, 18a'z and long 18a'2.
Such an
to arrangement necessitates, of course, an even number of fingers and slots
around the
sleeve 66' and body 12', which has a consequent effect on the barrel cam 56.
In the
previous embodiment, there were three fingers/slots around the periphery (as
shown in
Figure 2), meaning that angle 2a was 120° of rotation. Here, there are
preferably six
fingers/slots, so that angle 2a is 60°.
The result of varying depth of fingers 18a' and slots 69b' is that mandrel 18
can have three positions instead of just two, that is to say an intermediate
position
between deactivation and full activation. 1n Figure 6 at its top, the mandrel
is shown in
its fully activated position 18'A, in which long fingers 18a'2 coincide with
deep slots
69b'2, so that this corresponds entirely with at activated position of the
previous
embodiment. At the bottom of Figure 6, the fingers 18a'Z coincide with the
fingers 69a of
the sleeve 66' (which fingers are all level, as in the embodiment described
with reference
to Figure 5), so that the mandrel is in its deactivated position 18'C, again
corresponding
with the deactivated position of the previous embodiment and as shown in
Figure 5.
However, in the middle of Figure 6, there is shown the intermediate position
18'B in
which long fingers 18a'2 coincide with shallow slots 69b'~, with the result
that the pistons
28 are only displaced radially outwardly to a lesser extent.
Returning to Figure 1 b, the body has on a collar 25 a series of pockets 90 in
3o which a plunger 92 is disposed. Springs 94 press the plunger radially
outwards, the
plungers being retained in the pockets 90 by threaded retainers(not shown).
The plunger
92 is adapted to be received within a circumferential groove 100 in the
mandrel 18. It is
therefore apparent that rightward movement of the mandrel in the body 12 is
only
CA 02494229 2005-O1-25
possible if the plungers 92 are first pressed radially inwardly and released
from the
groove 100. For this purpose groove 100 is provided with an angled cam surface
102.
Thus when the mandrel is pressed sufficiently strongly in the rightward
direction in the
drawings, the returning force of the springs 94 may be overcome and the
plungers 92 are
pressed radially inwardly so that they pass over the lip of the groove 100.
In operation of the stabiliser 10, therefore, a user at ground level who
wishes
to increase the working diameter of the stabiliser 10 increases the flow and
pressure of
drilling mud down the bore of the drill string so that hydraulic pressure
begins to act on
1 o the components within the stabiliser tool. Because of the detent
represented by the
plungers 92, the mandrel is at first prevented from moving. However, the
piston 36 has
no such detent and so commences to move rightwardly in Figure 1 aagainst the
pressure of
spring 50. Rightward movement of the piston 36 is thus accompanied by rotation
thereof
through the angle al which, for the sake of argument, rotates the sleeve 66,
via the gears
61, to the position shown in Figure 5 where the fingers 69a of the sleeve 66
are in phase
with the fingers 18a of the body 12. Thus, even if the pressure in the tool 10
should
continue to rise sufficient to release the detent plungers 92 from the slot
100, the mandrel
18 cannot move much further rightwardly by virtue of the fingers 18a
contacting the
fingers 69a of the sleeve 66. Indeed, such movement as there is merely takes
up the
2o clearance between the fingers 18a,69a, and between end 70 of the sleeve 66
and shoulder
69.
However, should it be desired by the user that the stabiliser operate in its
maximum working diameter, the operator reduces the pump pressure so that the
spring 44
returns the mandrel (to the extent that this is necessary) to its home
position. The spring
50 also returns the piston. In doing so, the piston rotates through the
further angle a2.
On the next occasion, therefore, that the hydraulic pressure is increased
again so that the
piston 36 moves once again, and it rotates the sleeve through a further angle
al, then, on
this occasion, the castellations on the body 12 and sleeve 66 will be out of
phase.
Consequently, once the hydraulic pressure rises sufficiently to force the
mandrel past the
detent plungers 92, the mandrel will move fully rightwards as shown in Figure
lb, with
the respective castellations on the mandrel and sleeve inter-digitating.
CA 02494229 2005-O1-25
Here, as shown in Figure lb, the pistons are pressed radially outwardly so
that
they stand proud of the surface of the blades 24 and increase the working
diameter of the
stabiliser 10.
Refernng again to Figure 4c, on rightward movement of the mandrel 18, the
detent plungers 92 move into a shallow groove 112 in the body 12, which has a
much less
steep return face 114. Consequently, springs 44, once hydraulic pressure has
been
released, have no problem in compressing plungers 92 to return them over lip
104.
t o Finally, Figure 7 shows an arrangement in which the barrel cam 56 and
splines 60a of the piston 36' are mounted on a separate component 361' carned
by the
piston 36'. The component 361' is mounted on the piston between bearings
362',364' to
axially fix the component with respect to the piston, but permit it to rotate
freely. This
has the effect of reducing the amount of work that the barrel cam arrangement
56,58 has
15 to do to rotate the sleeve 66. It removes the necessity to rotate the whole
piston, so
removing the resistance of frictional force between the seals 46,48a and the
mandrel 18,
as well as other contacts between the piston and mandrel.
