Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE TOOL CONTROL
FIELD OF THE INVENTION
This invention relates to the control of a downhole tool or device, utilising
fluid
pressure or flow.
BACKGROUND OF THE INVENTION
In the oil and gas industry it is well known to utilise variations in flow
though a
drill string to actuate or control actuation of downhole tools or devices.
Flow through
a restriction in a spring-loaded sleeve may be utilised to create a pressure
differential
across the sleeve, the pressure differential moving the sleeve downwards from
a first
or no-flow position, against the action of the spring, to a second or flow
position
associated with activation or actuation of an associated device. The movement
of
the sleeve may be controlled by means of a cam arrangement, such as a J-slot
or
cam track and cam follower pin. The cam track may be configured to provide for
two
or more flow positions. One flow configuration may be associated with
actuation of
an associated device, and in another flow configuration the device may remain
inactive. The operator may achieve these positions simply by cycling the
surface
pumps on and off. However, if the pumps are cycled for other reasons, such as
to
make a connection at surface, the operator may have to cycle the pumps a
number
of times to achieve or regain the desired configuration. There is also a risk
that the
operator will have a mistaken belief that a tool is in a certain configuration
when it is
not, which may have significant operational and safety implications.
In other arrangements the cam track may define alternative paths. US Patent
No 6,289,999 describes a fluid flow control device in which an operator may
select a
path associated with a flow-through mode or a path associated with a valve
control
mode. The selection is made by the operator remotely tracking the movement of
a
lug along a ratchet path following the actuation of fluid pumps. At a certain
relative
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position of the lug on the ratchet path, shutting off the fluid pumps causes
the lug to
track back along the ratchet path, a corner in the ratchet path then
deflecting the lug
from a first operational mode path into a second path. The relative position
of the lug
on the ratchet path where shutting off the pumps will result in the change of
mode
path is described as the "window of opportunity" and is signalled to the
operator on
surface by fluid pulse signals created by an external flange on an inner
piston
aligning with flanges on an outer housing as the piston translates relative to
the
housing. Such an argument requires the operator to actively monitor a pressure
gauge and recognise the appropriate fluid pulse signals.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of operating a
downhole tool, the method comprising:
providing a downhole tool in a no-flow configuration in which an axially
movable tubular piston and a flow-restriction cooperate to substantially
occlude a tool
throughbore;
reconfiguring the tool to an intermediate configuration by flowing fluid
through
the tool at an intermediate flow-rate lower than an operating flow-rate and
axially
translating the piston to an intermediate position in which the piston and
flow-
restriction cooperate to define an intermediate flow area, wherein axial
translation of
the piston between a no-flow position and the intermediate position comprises
an
occlusional stage of a first axial extent during which the piston and the flow-
restriction
substantially occlude the tool throughbore and a transitional stage of a
second axial
extent during which the piston and the flow-restriction cooperate to provide a
step-
change in flow area;
holding the tool in the intermediate configuration by flowing fluid through
the
tool at the intermediate flow-rate; and
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reconfiguring the tool to an operating configuration by flowing fluid through
the
tool at the operating flow-rate and axially translating the piston to an
operating
position in which the tool defines an operating flow area.
The tool may be reconfigured between the different configurations in any
appropriate order or sequence.
For example, the tool may be provided in the no-flow configuration and then
reconfigured to the intermediate configuration by activating surface pumps to
circulate fluid through the tool at the intermediate flow-rate and axially
translate the
piston from the no-flow position to the intermediate position. In this
sequence, the
axial translation of the piston will comprise an initial occlusional stage and
a
secondary transitional stage. The flow-rate may subsequently be reduced to
zero to
return the tool to the no-flow configuration, or alternatively the flow-rate
may be
increased to the operating flow-rate to reconfigure the tool to the operating
configuration.
Alternatively, or in addition, the tool may be provided in the operating
configuration and then reconfigured to the intermediate configuration by
reducing the
flow-rate through the tool from the operating flow-rate to the intermediate
flow-rate
and permitting the piston to assume the intermediate position.
Alternatively, or in addition, the tool may be directly reconfigured from the
no-
flow configuration to the operating configuration by increasing the flow-rate
directly
from zero to the operating flow-rate without seeking to maintain the flow-rate
at an
intermediate level and thus attain and then maintain the intermediate
configuration.
Similarly, decreasing the flow-rate directly from the operating flow-rate to
zero may
directly reconfigure the tool from the operating configuration to the no-flow
configuration.
Thus, embodiments of the invention permit an operator to reliably attain and
hold an intermediate configuration of the downhole tool, increasing the
activation
options available when compared to a conventional flow-activated tool, which
is likely
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to be only reliably maintained in a no-flow configuration and an operating
flow
configuration. This degree of control may be achieved merely by selecting an
appropriate flow-rate of fluid through the tool, typically by control of
surface pumps
used to circulate fluid through a downhole tubing string incorporating the
tool.
The provision of the occlusional stage of axial translation of the piston
between the no-flow configuration and the intermediate position may provide
the
operator with assurance that the piston has moved to the intermediate position
and
achieved the desired function, for example a tool activation or setting
associated with
the intermediate tool configuration. In certain embodiments, even a relatively
small
flow-rate will ensure that the intermediate configuration is achieved.
Further, in
certain embodiments an intermediate flow-rate within a relatively broad range
will
achieve the desired intermediate configuration. The interaction of the flow-
restriction
and the piston serves to facilitate attaining the intermediate configuration
from the
operating configuration, the step-change in flow area at the transitional
stage tending
to maintain the tool in the intermediate configuration over a range of flow-
rates below
the operating flow-rate.
The second axial extent of the transitional stage may be less than the first
axial extent of the occlusional stage.
The reconfiguration of the tool to the operating configuration may involve a
degree of translation of the piston from the no-flow configuration greater
than the
degree of translation of the piston from the no-flow position to the
intermediate
position.
The method may comprise removing the flow-restriction from the tool, moving
the restriction out of cooperating engagement with the piston, or otherwise
reconfiguring the restriction, to improve access to the tool throughbore below
the
restriction location or to increase the flow area through the tool. For
example, a flow-
restricting member provided in the body may be retrievable or otherwise
removable.
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The order or sequence of reconfiguration of the tool may be controlled or
guided, for example a cam or J-slot arrangement may be provided between the
piston and a tool body. In one embodiment one element of the tool may define a
cam track and another element may define a cam follower, such as a pin. The
cam
track may define alternative or multiple paths or branches and the path
followed may
be operator-determined by selecting a particular sequence of configurations.
In one embodiment the method may be utilised to allow selection of a first
operating configuration and a second operating configuration, the method
comprising:
flowing fluid through the tool at the operating flow-rate and with the tool in
a
first operating configuration;
reducing the flow through the tool to the intermediate flow-rate and
reconfiguring the tool to the intermediate configuration; and
increasing the flow through the tool from the intermediate flow-rate to the
operating flow-rate and reconfiguring the device from the intermediate
configuration
to a second operating configuration.
In an alternative operating sequence, if the flow-rate is reduced directly
from
the operating flow-rate to zero the tool may be reconfigured directly from the
first
operating configuration to the no-flow configuration, and if the flow rate is
then
increased directly from zero to the operating flow-rate the tool may be
reconfigured to
the first operating configuration. Thus, for example, in normal operations in
which the
flow-rate is varied directly between zero and the operating flow-rate as the
surface
pumps are switched on and off, the tool may be cycled between the no-flow
configuration and the first operating configuration. Only if the operator
selects to
operate the surface pumps to provide a particular sequence of flow-rates, for
example reducing the flow-rate to the intermediate flow-rate and then
increasing the
flow-rate to the operating flow-rate, will the tool assume the second
operating
configuration.
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The second operating configuration may be associated with a branch or path
of a cam track distinct from a branch or track associated with the first
operating
configuration.
The method may further comprise:
ceasing fluid flow through the tool and reconfiguring the tool from the
second operating configuration to the no-flow configuration, or
ceasing fluid flow through the tool and reconfiguring the tool from the
first operating configuration to the no-flow configuration.
According to another aspect of the present invention there is provided a
downhole tool having utility in an operator-selectable intermediate
configuration and
in an operating configuration, the tool comprising:
a tubular body;
a tubular piston axially movably mounted in the body and defining a through
bore, the piston being movable between a no-flow position, an intermediate
position
and an operating position; and
a flow-restriction cooperating with the piston to vary the flow area of the
through bore;
in the no-flow position the piston and flow-restriction cooperating to
substantially occlude the through bore;
in the intermediate position the piston and flow-restriction cooperating to
define an intermediate flow area, axial translation of the piston between the
no-flow
position and the intermediate position comprising an occlusional stage of a
first axial
extent during which the piston and the flow-restriction cooperate to
substantially
occlude the through bore and a transitional stage of a second axial extent
during
which the piston and the flow-restriction cooperate to provide a step-change
in flow
area; and
with the piston in the operating position the tool defining an operating flow
area.
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The flow restriction may take any appropriate form. In one embodiment the
flow restriction may include an elongate flow-restricting member mounted in
the
body. The flow-restricting member may be coaxial with the piston. The flow-
restricting member may be received within the piston. The flow-restricting
member
may be axially movable relative to the piston.
In one embodiment the flow-restricting member may include a substantially
cylindrical portion which cooperates with a complementary passage or
restriction in
the piston when the tool is in the no-flow configuration and during the
occlusional
stage of translation between the no-flow position and the intermediate
position. The
transitional stage of translation occurs when the cylindrical portion of the
flow-
restricting member and the complementary passage or restriction separate to
provide
a step-change in flow area. Of course other configurations of flow-restricting
member
and piston may be utilised to achieve a similar effect, such as a flow-
restricting
member with a stepped profile which provides the step change in area.
Alternatively, or in addition, the flow restriction may include an elongate
flow
restriction or probe mounted on the piston which cooperates with a
complementary
passage or restriction in the body.
The piston may define a flow restriction, for example a nozzle, such that
increasing flow through the piston creates an increasing axial fluid pressure
force on
the piston. If the piston is biased towards the no-flow position, increasing
flow may
tend to increase the distance of the piston from the no-flow position. In some
embodiments the piston flow restriction may cooperate with a body-mounted flow-
restricting member. In other embodiments the piston and body may cooperate to
define a differential piston, wherein an area of the piston is exposed to
internal tool
pressure, which may be drill string pressure, and an oppositely directed area
of the
piston is exposed to external tool pressure, which may be annulus pressure.
Accordingly, a higher internal pressure may be utilised to urge the piston
towards the
operating position.
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According to an aspect of the present invention there is provided a method of
reconfiguring a downhole device between a no-flow configuration, a first flow
configuration and a second flow configuration, the method comprising:
providing a downhole device in a no-flow configuration;
flowing fluid through the downhole device at an operating flow-rate and
reconfiguring the device to a first flow configuration;
maintaining fluid flow through the downhole device at the operating flow-rate
and maintaining the device in the first flow configuration;
reducing the fluid flow through the downhole device from the operating flow-
rate to an intermediate flow-rate lower than the operating flow-rate and
reconfiguring
the device to an intermediate flow configuration between the no-flow
configuration
and the first flow configuration; and
increasing the fluid flow through the downhole device from the intermediate
flow-rate to the operating flow-rate and reconfiguring the device from the
intermediate
configuration to a second flow configuration.
The method may further comprise:
stopping fluid flow through the downhole device and reconfiguring the
device from the second flow configuration to the no-flow configuration, or
stopping fluid flow through the downhole device and reconfiguring the
device from the first flow configuration to the no-flow configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
Figures la, 1 b, lc and Id are schematic illustrations of a tool in accordance
with a first embodiment of the present invention;
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Figures 2a, 2b and 2c are schematic illustrations of a tool in accordance with
a second embodiment of the present invention;
Figure 3 is a schematic illustration of a cam track of a tool in accordance
with
an embodiment of the present invention;
Figures 4a, 4b and 4c are schematic illustrations of a tool in accordance with
another embodiment of the present invention; and
Figure 5 is a schematic illustration of a tool in accordance with a further
embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Reference is first made to Figures 1 a, lb and lc of the drawings, which are
schematic illustrations of a tool 10 in accordance with a first embodiment of
the
present invention. The tool 10 is intended to form part of a downhole tubular
string,
such as a drill string, tool string, or the like. Accordingly, the tool 10
includes a
cylindrical body 12 having appropriate end connections (not shown) for
incorporation
in the associated string. Mounted within the body 12 is a tubular piston 14
including
an internal flow restriction in the form of a nozzle 16, such that circulation
or flow of
fluid in the normal direction, that is from surface towards the distal end of
the string,
creates a fluid pressure force across the piston 14, tending to translate the
piston
downwards, against the action of a compression spring 18.
A cylindrical flow restriction in the form of a probe 20 is mounted to the
body
12 and, with the piston 14 in the raised position (Fig 1c), the probe 20
extends into
the piston 14 and through the nozzle 16. The probe 20 is coaxial with the
piston 14
and has an outer diameter only slightly smaller than the internal diameter of
the
nozzle 16. Accordingly, while the probe 20 is located within the nozzle 16 the
tool
body is substantially occluded.
Figure la illustrates the relative positions of the tool elements in a typical
operating configuration, with fluid being pumped through the tool 10 and the
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associated string at a normal operational rate such as required during, for
example, a
drilling operation. In this situation the fluid pressure differential created
across the
nozzle 16 is sufficient to move the piston 14 to its lowermost position in the
body 12.
It will be observed that the upper end of the piston 14 is spaced from and
clear of the
probe 20.
Figure lb illustrates the relative positions of the tool elements when the
flow-
rate of the fluid flowing through the string has been reduced to a relatively
low
intermediate rate such that there is a minimal if any fluid pressure force
created
across the nozzle 16 and the upwards spring force on the piston 14 is greater
than
the opposing downwards forces; the piston 14 thus moves upwards under the
influence of the spring 18. However, as the upper end of the piston 14
approaches
the lower end of the probe 20, the piston 14 and probe 20 cooperate to create
a rapid
or step-change restriction in the fluid flow area, the pressure drop resulting
from the
flow restriction creating a fluid pressure force which maintains the piston 14
in the
illustrated intermediate position.
The piston 14 will remain in this intermediate position until the flow-rate is
increased to generate a sufficient fluid pressure force across the nozzle 16
to
overcome the action of the spring 18 and move the piston 14 downwards towards
the
operating position as illustrated in Figure 1a, or until the flow-rate is
reduced to a
negligible level and the piston 14 translates upwards towards the no-flow
configuration as illustrated in Figure 1c.
The configuration of the tool 10 is such that the operator may hold or retain
the piston 14 in the intermediate position over a range of flow-rates, and it
is not
necessary for the operator to achieve a precise flow-rate to cause the piston
14 to
hover in the intermediate position, as would be the case in the absence of the
interaction between the piston 14 and the probe 20; the step-change in flow
area
created as the piston 14 and probe 20 move from the intermediate configuration
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towards the no-flow configuration tends to retain the intermediate
configuration over
a wider range of flow-rates.
As noted above, with negligible or no flow, the piston 14 moves upwards such
that the probe 20 extends into and through the piston nozzle 16.
To return the tool from the no-flow configuration to the intermediate
configuration, the operator initiates flow through the string, typically by
activating the
surface pumps. The intermediate configuration is likely to be achieved simply
by
turning the pumps up sufficiently to circulate fluid through the string; the
occlusion of
the tool 10 by the interaction of the piston 14 and the probe 20 causes the
piston 14
to move beyond the end of the probe 20 and thus permit a degree of fluid flow.
At
very low flow-rates the tool 10 may experience a degree of chatter, as the
piston 14
moves between a just-open and just-closed position, however this may be
avoided
by a small increase in flow-rate.
Alternatively, if the surface pumps are simply restored to the normal
operating
flow-rate the piston 14 will move directly to the operating position, passing
through
but not remaining in the intermediate position. Similarly, simply shutting the
pumps
down directly from the normal operating level will cause the tool to move
directly from
the operating configuration to the no-flow configuration, passing through but
not
remaining in the intermediate position.
Reference is now made to Figures 2a, 2b and 2c of the drawings, these
Figures being schematic illustrations of a tool 110 in accordance with a
second
embodiment of the present invention. The tool 110 operates in a generally
similar
manner to the tool 10 described above, but includes a number of different
features,
as will be described.
The tool 110 includes a cylindrical body 112 and mounted within the body 112
is a tubular piston 114 having a cylindrical inner flow surface 115. A stepped-
profile
cylindrical flow probe 120 is mounted to the body 112 and, with the tool 110
in the
no-flow configuration and the piston 114 in the raised position (Fig 2c),
extends into
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the piston 114. The probe 120 is coaxial with the piston 114 and has an upper
portion 120a with an outer diameter only very slightly smaller than the
internal
diameter of the inner flow surface 115 and a lower portion 120b at the probe
free end
with an outer diameter significantly smaller than the internal diameter of the
surface
115. Accordingly, while the probe upper portion 120a is located within the
piston 114
the tool body is substantially occluded, and while the probe lower portion
120b is
located within the piston 114 fluid may flow through the tool 110.
Figure 2a illustrates the relative positions of the tool elements in a typical
operating configuration, with fluid being pumped through the tool 110 and the
associated string at a normal operational rate such as required during, for
example, a
drilling operation. In this situation the fluid pressure differential created
across the
piston 114 and the restriction 130a resulting from the interaction between the
piston
inner flow surface 115 and the probe lower portion 120b is sufficient to move
the
piston 114 to its lowermost position in the body 112, and fully compress the
spring
118. It will be observed that the upper end of the piston 114 is spaced from
and clear
of the probe upper portion 120a.
Figure 2b illustrates the relative positions of the tool elements when the
flow-
rate of the fluid flowing through the string has been reduced to a relatively
low level
such that there is a minimal fluid pressure force created across the
restriction 130a.
The upwards spring force on the piston 114 is thus greater than the opposing
downwards forces and the piston 114 moves upwards under the influence of the
spring 118. However, as the upper end of the piston 114 approaches the step or
transition 120c between the upper and lower probe portions 120a, 120b, the
piston
114 and probe transition 120c cooperate to create a rapid or step-change
restriction
in the fluid flow area, the pressure drop resulting from the resulting
restriction 130b
creating a fluid pressure force which maintains the piston 114 in the
illustrated
intermediate position.
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The piston 114 will remain in this intermediate position until the flow-rate
is
increased to generate a sufficient fluid pressure force across the restriction
130b to
overcome the action of the spring 118 and move the piston 114 downwards, or
until
the flow-rate is reduced to a negligible level and the piston 114 translates
upwards
towards the no-flow configuration as illustrated in Figure 2c.
As with the tool 10 described above, the configuration of the tool 110 is such
that the operator may retain the piston 114 in the intermediate position over
a range
of flow-rates, and it is not necessary for the operator to achieve a precise
flow-rate to
cause the piston 114 to hover in the intermediate position, as would be the
case in
the absence of the interaction between the piston 114 and the probe transition
120c;
the step-change in flow area created as the piston 114 and probe 120 move from
the
intermediate configuration tends to retain the configuration over a wider
range of
flow-rates.
With negligible or no flow, the piston 114 moves upwards such that the entire
probe 120 extends into the piston 114 and the upper probe portion 120a
substantially
occludes the piston 114.
To return the tool 110 to the intermediate configuration as illustrated in
Figure
2b, the operator initiates flow through the string, typically by activating
the surface
pumps. The intermediate configuration is likely to be achieved simply by
turning the
pumps up sufficiently to circulate fluid through the string; the occlusion of
the tool 110
by the interaction of the piston 114 and the probe upper portion 120a causes
the
piston 114 to move beyond the end of the probe transition 120c in the presence
of a
relatively low flow rate.
The upper end of the probe 120 includes a wireline overshot profile 132 and a
probe-mounting spider 134 which secures the probe 120 to the body 112 via
shear
pins 136, thus permitting removal of the probe 120 from the tool 110 if
desired.
Retrieval of the probe 120 removes the bore restriction created by the probe
120 and
also provides unrestricted access to the string bore below the tool 110.
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Reference is now made to Figure 3 of the drawings, which is a schematic
illustration of a cam track 50 of a tool, such as one of the tools 10, 110 as
described
above, in accordance with an embodiment of the present invention. As will be
described, this embodiment permits an operator to configure the tool in two
distinct
operating configurations.
The cam track 50 is formed on the inner diameter of the tool body 12, and a
cam follower pin 52 extends radially outwards from the piston 14. In normal
flow
conditions the piston 14 is urged downwards with the interaction of the pin 52
and
track 50 holding the piston 14 in a first position 1 corresponding to a first
operating
configuration, for example as illustrated in Figure la. If the fluid flow is
then reduced
to the intermediate flow-rate the pin 52 moves up the track 50 to a second
position 2,
corresponding to the intermediate configuration, as illustrated in Figure lb
of the
drawings. If the flow is held at the intermediate flow-rate for a short
period, given the
manner in which the piston 14 and probe 20 interact, the operator can be
confident
that the intermediate configuration has been achieved. If the pumps are then
brought
up to normal flow, the pin 52 will travel back down the track 50 but will move
into a
blind track branch 50a and to a third position 3, which permits the piston 14
to be
translated further downwards to a second operating configuration, as
illustrated in
Figure Id of the drawings. This extra stroke may be utilised to perform a
desired tool
activation, for example to actuate or extend a cutting blade on a reaming
tool.
However, if the tool is in the first operating configuration, with the pin 52
in
position 1, and flow is stopped completely, the pin will move directly from
position 1
to a fourth position 4, corresponding to the no-flow configuration, as
illustrated in
Figure lc. If the pumps are then restarted the pin 52 will move to the next
position 1,
corresponding to the first operating configuration. Accordingly, if the pumps
are
stopped, for example to make a connection at surface, and then restarted, the
tool 10
will not be activated. If activation is required the flow-rate must be reduced
to and
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preferably held at the intermediate flow-rate and then increased again without
stopping the pumps.
Reference is now made to Figures 4a, 4b and 4c of the drawings, schematic
illustrations of a tool 210 in accordance with another embodiment of the
present
invention. The tool 210 operates in a manner which is generally similar to the
tools
10, 110 described above but has some different constructional features, as
will be
described.
Mounted within the tool body 212 is a tubular piston 214 including an internal
nozzle 216, such that flow of fluid through the tool in the normal direction,
that is from
surface towards the distal end of the drill string incorporating the tool 210,
creates a
fluid pressure force across the piston 214, over seal area B, tending to
translate the
piston downwards, against the action of a compression spring 218. A
cylindrical
probe 220 is mounted on the upper end of the piston and cooperates with a
restriction 215 provided in the body 212 above the piston 214. With the piston
214 in
the raised position (Fig 4c), the probe 220 extends into the restriction 215.
The
probe 220 has an outer diameter only slightly smaller than the internal
diameter of
the restriction 215. Accordingly, while the probe 220 is located within the
restriction
215 the tool body is substantially occluded.
Figure 4a illustrates the relative positions of the tool elements in a typical
operating or drilling configuration, with fluid being pumped through the tool
210 at a
normal operational rate, for example while drilling. In this situation the
fluid pressure
differential created across the nozzle 216 is sufficient to move the piston
214 to its
lowermost position in the body 212 in which the lower end of the body
restriction 215
is spaced from and clear of the upper end of the piston probe 220. The
relatively
large seal area B minimises the pressure drop required across the nozzle 216,
thus
minimising the pump pressure required to maintain the piston in the operating
or
drilling position.
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Figure 4b illustrates the relative positions of the tool elements when the
flow-
rate of the fluid flowing through the string has been reduced to a relatively
low,
intermediate rate such that there is minimal if any fluid pressure force
created across
the nozzle 216 and the upwards spring force on the piston 214 is greater than
the
opposing downwards forces; the piston 214 thus moves upwards under the
influence
of the spring 218. As the upper end of the probe 220 approaches the lower end
of
the restriction 215, the probe 220 and the restriction 215 cooperate to create
a rapid
or step-change restriction in the fluid flow area. The fluid pressure force
now acting
over diameter A, corresponding to the diameter of the probe 220, maintains the
piston 214 in the illustrated intermediate position.
The piston 214 will remain in this intermediate position until the flow-rate
is
increased to generate a sufficient fluid pressure force across the nozzle 216
to
overcome the action of the spring 218 and move the piston 214 downwards
towards
the operating position as illustrated in Figure 4a, or until the flow-rate is
reduced to a
negligible level and the piston 214 translates upwards to the no-flow
configuration as
illustrated in Figure 4c.
Reference is now made to Figure 5 of the drawings, which illustrates a tool
310 in accordance with a further embodiment of the invention. The tool 310 is
illustrated in the intermediate or reduced flow position, with fluid pressure
acting over
area A, the area of the upper end of the piston probe 320. It will be noted
that the tool
310 is similar to the tool 210 described above in a number of respects.
However, the
piston 314 does not feature an internal nozzle. Rather, movement of the piston
314
to the operating position is achieved utilising differential pressure, as
described
below.
The piston 314 carries external seals B, C which engage the inner wall of the
body 312, the volume between the seals B,C being in communication with the
tool
exterior. Accordingly, in use, the volume will be in communication with the
annulus.
The upper seals B describe a larger diameter than the lower seals C.
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When flow through the string is increased to the normal operating rate the
pressure differential between the interior of the tool and the drill string,
at pressure
P1, and the annulus surrounding the drill string, at pressure P2, will
increase due to
drill bit pressure losses and the like. This pressure differential will act on
both seal
areas B and C, and because seal area B is larger than seal area C the piston
314 will
move down within the body 312 to the operating position. However, there is no
pressure drop in the fluid flowing through the piston 314 such that there is
no
increase in pump pressure required at the operating fluid flow rate.
It will be apparent to those of skill in the art that the above-described
embodiments are merely exemplary of the present invention.
It will also be apparent that the advantages provided by the various
embodiments of the present invention are applicable to many different tools
and
devices. For example, the ability to reliably achieve and maintain a fluid
flow or
pressure activated tool in an intermediate position or configuration provides
additional functionality to tools which previously offered only two
configurations (a no-
flow configuration and a flow configuration).
