Note: Descriptions are shown in the official language in which they were submitted.
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VALVE APPARATUS
The present invention relates to methods and apparatus for use in wells and
fluid
pipes, and to safety valves and apparatus, and in particular to apparatus
comprising safety
valves for use in wells and pipes, and still more particularly for wells used
to obtain
hydrocarbons.
Multiple stage centrifugal pumps driven by submersible electric motors are an
established means of producing hydrocarbons from wells that have insufficient
pressure in
the hydrocarbon reservoir for the fluids to flow to surface naturally.
Traditionally electric submersible pumps (ESPs) have been deployed into wells
attached to the end of a string of jointed pipe (production tubing) with the
cable supplying
power to the motor being clamped to the outside of the tubing string, whilst
the
hydrocarbon fluids discharged from the pump flow up the inside of the tubing
string.
One disadvantage of these ESP systems is that the equipment will inevitably
wear
and degrade over time and eventually fail necessitating its replacement. In
order to replace
a failed ESP system the tubing must be recovered from the well to bring the
failed
equipment back to surface. The recovery of the tubing from a well requires the
use of a rig
which adds considerably to the time and cost involved in replacing the failed
equipment.
Often the rig intervention costs are considerably higher than the cost of the
actual failed
pump equipment.
Unsurprisingly alternatives to this method of deploying ESPs have been sought,
and
two main alternative methods exist, namely coiled tubing deployed ESPs and
cable
deployed ESPs.
In coiled tubing deployed ESP systems, the pump is attached to the end of a
continuous coil of small diameter tubing with the cable either housed inside
the tubing or
clamped to the outside in the same way as for jointed pipe deployed pumps.
Being a
continuous length of pipe coiled tubing can be deployed and recovered directly
onto a reel
and so the time and cost required to replace an ESP may be reduced.
In cable deployed ESP systems, the pump is deployed into the well on a cable
and
variously latched into or onto a permanent supporting arrangement designed to
receive it.
The cable may be an electromechanical cable that remains in the well during
operation to
supply power to the pump or a purely mechanical cable that is only used to
deploy and
recover the pump with a separate permanent electrical cable used to provide
electrical
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power.
Irrespective whether the pump is deployed using coiled tubing or cable
(mechanical
cable or electromechanical cable) the fact that the pump must pass through
either the
tubing or casing 1 to latch into or onto some receptacle precludes the
provision of a
conventional subsurface safety valve (SSV). Known safety valves complicate the
otherwise simple process of deploying the ESP system, due to the need to form
a reliable
seal between the coil or cable deploying the pump and the valve.
It is possible to provide a retrievable SSV in the case of mechanical cable
deployed
pumps, by providing a profile in the casing 1 or tubing above the pump, into
which the
valve can be latched in a separate operation after the pump has been deployed.
However
this adds to the number of operations and the time required replacing the pump
system.
Aspects and examples of the disclosure address at least a part of the above
described
technical problem.
In an aspect of the disclosure there is provided a subsurface flow control
apparatus
comprising:
a fluid flow passage configured to engage a packer in a well bore, the fluid
flow
passage being capable of permitting fluids to flow through the packer, wherein
the fluid
flow passage comprises a pump intake coupling adapted to couple to an intake
of a pump
for drawing fluid from the fluid flow passage into said pump intake and out of
a pump
discharge of the pump;
a control valve arranged to control the flow of fluid through the fluid flow
passage;
and
a controller arranged to control the control valve based on the fluid
pressure, P2, in
the fluid flow passage between the control valve and the pump intake coupling,
and based
on the fluid pressure, Pl, at said pump discharge.
The controller can be arranged to receive a first pressure input corresponding
to the
fluid pressure, P2, in the fluid flow passage between the control valve and
the pump intake
coupling and a second pressure input corresponding to the fluid pressure, Pl,
at said pump
discharge.
The controller can be configured so that in the event that the fluid pressure,
Pl, at
said pump discharge is equal to the fluid pressure, P2, in the flow passage
between the
control valve and the pump intake coupling, the controller is arranged to
inhibit fluid from
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flowing through the control valve unless the pressure, P2, in the flow passage
is greater
than the pressure, P3, on the other side of the control valve from the pump
intake coupling
by more than a selected threshold pressure.
It can be seen that the present invention is arranged such that, in use, it
can permit
fluid to flow to the surface of a well only when a pump is operating.
The controller can comprise at least one pressure feedback, separate from the
flow
passage, adapted to communicate pressure at least partially across the packer
for
controlling the control valve.
The pressure feedback may comprise at least one of a fluid line or a rigid
mechanical
coupling. In an embodiment, the pressure feedback comprises at least one port
arranged to
communicate the fluid pressure, Pl, at said pump discharge to an actuator. The
port may
extend through a wall of the fluid flow passage.
In one embodiment, the apparatus may comprise a sealed bladder, filter, or
labyrinth
chamber coupled to the fluid line of the pressure feedback to inhibit solids
from clogging
the fluid line.
The controller may comprise a pressure driven actuator coupled to control the
control
valve based on the fluid pressure, P2, in the flow passage between the control
valve and the
pump intake coupling, and based on the fluid pressure, P1, at said pump
discharge.
The control valve can be biased into a closed configuration. In an embodiment,
the
controller comprises a pressure chamber arranged so that the pressure in the
chamber acts
against the bias to open the control valve.
The pressure feedback can comprise a fluid line coupled to communicate the
fluid
pressure, P1, at said pump discharge to the chamber.
A pump may be provided which is couplable to the pump intake coupling for
drawing fluid through the flow passage. With this arrangement, the controller
is arranged
to open the control valve in response to operation of the pump.
The controller is preferably arranged to open the control valve in the event
that the
pressure difference across the packer is greater than the selected threshold
pressure. The
threshold can be selected so that the difference between the intake pressure
and discharge
pressure of the pump is sufficient to open the control valve.
The pump may be one which allows fluid to be forced back through the pump from
the discharge to the intake.
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In an embodiment of the invention, the apparatus further includes an
equalisation
valve operable separately from the control valve to enable fluid to flow
through the flow
passage. This equalisation valve is typically biased closed. The equalisation
valve is
preferably arranged so that any pressure difference across the equalisation
valve does not
act against the bias to open the equalisation valve. Optionally, the
equalisation valve
comprises a sliding sleeve valve.
The apparatus may comprise a latch for engaging with a tool to enable the
apparatus
to be removed from a well bore wherein the equalisation valve is configured to
be actuated
by a tool engaged with the latch.
The control valve may comprise a sliding sleeve valve. In this case, the
sliding
sleeve valve can comprise a sleeve and a piston arranged inside the sleeve,
and the side
wall of the piston and the sidewall of the sleeve may each comprise a port
arranged so that
sliding the piston relative to the sleeve throttles the flow of fluid through
the port to control
the flow of fluid through the sliding sleeve valve.
According to a second aspect of the invention, a subsurface flow control
apparatus
comprises:
a fluid flow passage adapted to enable fluids to flow between a first pressure
zone
and a second pressure zone in a well;
an outflow control valve for controlling the flow of fluid from the first
pressure
zone, through the fluid flow passage to the second pressure zone, wherein the
outflow
control valve is configured to remain closed unless a pressure in the fluid
flow passage
(that is, the pressure in the fluid flow passage on the side of the control
valve facing the
second pressure zone) is less than the pressure in the second pressure zone by
more than a
first selected threshold pressure; and
an inflow control valve operable to allow fluid to flow from the second
pressure
zone, through the fluid flow passage to the first pressure zone, when the
pressure inside the
fluid flow passage is greater than the pressure in the first pressure zone by
more than a
second selected threshold pressure. The first pressure zone is typically the
section of
wellbore below a packer and the second pressure zone is typically the section
of wellbore
above the packer.
Typically, a pump having a pump intake and a pump discharge is coupled to the
fluid
flow passage for drawing fluid from the fluid flow passage and pumping the
fluid into the
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second pressure zone.
The first selected threshold pressure can be selected based on the pressure
difference
between the pump intake and the pump discharge so that operating the pump
opens the
outflow control valve.
5 A controller may be provided, which is adapted to control the outflow
control valve
based on said pressure difference between the pump intake and the pump
discharge. The
controller can comprise a pressure driven actuator comprising a pressure
driven sleeve
coupled to actuate the outflow control valve.
The inflow control valve can comprise a second pressure driven sleeve arranged
so
that, when the pressure in the first pressure zone is greater than the
pressure in the fluid
flow passage, the second pressure driven sleeve is driven to close the inflow
control valve.
Generally, at least one of the inflow control valve and the outflow control
valve is
biased into a closed configuration that inhibits flow through said at least
one valve. The
biasing may be provided by a spring.
According to another aspect of the invention, a coiled tubing deployed
electric
submersible pump apparatus can comprise the subsurface flow control apparatus
described
in the above embodiments.
In a further aspect of the invention, a cable deployed electric submersible
pump
apparatus can comprise the subsurface flow control apparatus described in the
above
embodiments.
Embodiments of the disclosure will now be described, by way of example only,
with
reference to the accompanying drawings, in which:
Figure 1 shows a schematic illustration of an electric submersible pump
assembly
and a flow control valve apparatus in a well bore;
Figure 2 shows a schematic illustration of a section through a flow control
valve
apparatus according to an embodiment of the invention;
Figure 3 shows a schematic illustration of a section through a flow control
valve
apparatus according to another embodiment of the invention; and
Figure 4 (comprising Figures 4a and 4b) shows a schematic illustration of a
section
through a flow control valve apparatus according to a further embodiment of
the invention.
In general, embodiments of the disclosure provide a flow control apparatus for
controlling fluid flow in a well bore. The apparatus comprises a control valve
and is
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coupled to a packer so that the control valve closes the tail pipe of a pump
seated above the
packer for pumping fluids out of the well. Packers are well known in the field
of oil and
gas production, and provide a seal between the interior surface of an outer
conduit, such as
the wellbore or well casing, and an exterior surface of an inner tubular, such
as a section of
production tubing.
A pressure feedback communicates the pump discharge pressure to the control
valve,
such that the differential pressure developed across the pump when it is
operating is
applied to control the control valve. The control valve is biased closed so
that it operates as
a deadman's switch. In the absence of a signal holding the control valve open,
the control
valve closes. Accordingly, when the pump fails, or the feedback line is broken
or damaged,
the control valve closes to provide a system that "fails safe closed". In this
way, the
control apparatus can operate as a subsurface safety valve.
Embodiments of the disclosure permit fluids to be forced, or "bullheaded",
into a
closed well through the control valve to displace hydrocarbons back into the
formation,
prior to a workover and further inhibit the unwanted production of fluids from
the well.
Figure 1 shows an apparatus according to an embodiment of the invention inside
the
production casing 1 in a well bore. A packer 2 is disposed in the casing 1.
The packer 2 is
annular in shape, and the outer edge of the annulus engages with the casing 1
to provide a
seal so that fluid flow in the casing 1 flows through the annular packer 2.
The packer 2 has a first side, for facing into the well, and a second side for
facing out
of the well. A fluid flow passage 8 extends through the annular packer 2 from
the first side
to the second side to permit fluid to flow out of the well.
In the arrangement illustrated in Figure 1, a pump 10 is seated on the second
side of
the packer 2. The intake 20 of the pump 10 is in communication with the flow
passage so
that it can draw fluid through the flow passage 8. The pump discharge port 22
is
positioned in the production casing above the packer 2 for pumping the fluid
up the
production casing, out of the well.
A control valve 4 is coupled to the fluid flow passage 8 and arranged to
control the
flow of fluid along the fluid flow passage 8 so that closing the control valve
4 closes the
fluid flow passage 8 and shuts the pump intake 20 off from the well bore below
the packer.
The control valve 4 is biased into a closed state, so that as a default it
prevents fluid from
flowing through the flow passage 8.
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The packer 2 has a pressure feedback line 9 extending through it, separate
from the
flow passage 8. The pressure feedback line 9 communicates fluid pressure P1
above the
packer 2 (e.g. the pressure on the second side of the packer 2) back through
the packer 2 to
the control valve 4 beneath the packer 2 (the first side of the packer 2).
The flow control apparatus comprises a coupling 36 to which the pressure
feedback
line 9 is coupled. The coupling 36 may include known means capable of
connecting the
pressure feedback line 9 to a port through a sidewall of the fluid flow
passage 8. The port
puts the pressure feedback line 9 in pressure communication with a chamber 34
(discussed
below) which can control the actuation of the control valve 4.
The flow control apparatus is configured so that, if the differential pressure
between
the chamber 34 and the pump intake 20 is greater than a threshold pressure,
the control
valve 4 will open. In the example of Figure 1, where the apparatus comprises a
pump 10,
the biasing of the control valve 4 can be selected based on the difference
between the pump
discharge and pump intake pressures so that the pressure difference generated
when the
pump is turned on is sufficient to overcome the biasing and cause the control
valve 4 to
open.
In operation, in the event that the pump 10 is not pumping, and the pressure
P3 in the
wellbore beneath the packer 2 is greater than or equal to the pressure P1 in
the wellbore
above the packer 2, the control valve 4 is held in its default, closed, state.
In the event that
the pressure P1 above the packer 2 is greater than the pressure P3 below the
packer 2 by
more than the threshold pressure of the control valve 4, the control valve 4
opens to permit
fluid to flow back through the flow passage 8 into the well. This can permit
"bullheading"
fluid into a well.
In the event that the pump 10 begins pumping, the operation of the pump 10
reduces
the pressure P2 at the pump intake 20 and also therefore in the flow passage
8. The pump
discharge pressure P1 above the packer 2 increases and is communicated back
through the
pressure feedback line 9 to the chamber 34 to open the control valve 4. Whilst
the pump 10
is pumping, the pressure difference between the pump discharge 22 and the pump
intake
20 is maintained and the control valve 4 is held open.
In the event that the pump 10 fails and stops pumping, the pump discharge
pressure
P1 reduces and the pressure difference across the pump is no longer sufficient
to maintain
the valve in the open position. Consequently, the control valve 4 closes and
inhibits fluid
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flowing through the flow passage 8. The pump intake 20 is then sealed from the
wellbore
below the packer 2. The control valve 4 therefore prevents well fluids flowing
up the well.
Figure 2 shows an example of one type of apparatus according to that
illustrated in
Figure 1.
Figure 2 shows a packer 2 and a flow passage 8 through the packer 2. A
pressure
feedback line 9, which is separate from the flow passage 8, extends through
the packer 2.
A pump 10 is arranged to draw fluid from a first side of the packer 2, and to
discharge it to
the second side of the packer 2.
A control valve 4 is arranged on a first side of the packer 2 to control the
flow of
fluid through the flow passage 8 of the packer 2 into the pump intake 20. The
control valve
4 comprises a throttle 26,28 through which fluid can pass. A coupling 36
couples the
pressure feedback line 9 to a chamber 34 which can actuate movement of the
valve 4 so as
to open and close the throttle based on the pressure applied to the chamber
34.
The control valve 4 illustrated in Figure 2 comprises a sleeve valve. In the
example
shown in Figure 2, the sleeve valve includes a hollow cylindrical piston 5
surrounded by a
sleeve 7 so that the piston 5 can slide axially along the sleeve 7. A first
end of the sleeve 7
is open to the wellbore below the packer 2, and the second end of the sleeve 7
is in fluid
communication with the pump intake 20. The first end of the piston 5 is
closed, and, inside
the sleeve 7, the second end of the piston 5 is in fluid communication with
the pump intake
20.
In this example, the sleeve 7 forms an integral part of the fluid flow passage
8.
Accordingly, the control valve 4 is located at one end of the fluid flow
passage 8 and the
other end of the fluid flow passage 8 is coupled to the pump intake 20.
Alternatively,
rather than being integral, the sleeve 7 may be connected to a first end of
the fluid flow
passage 8 which passes through the packer 2.
In another example, the sleeve 7 may be connected directly to one side of the
packer
2. In turn, the pump intake 20 can be connected directly to the other side of
the packer 2.
Other mechanical constructions will be apparent to the skilled reader, for
putting the
control valve 4 in fluid communication with the intake 20 of the pump.
The piston 5 and the sleeve 7 both comprise throttle ports 26,28 in their
sidewalls.
When the throttle ports are aligned, fluid can flow between the outside of the
sleeve 7 and
the pump intake 20 via the inside of the piston 5. When the throttle ports 26,
28 are not
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aligned, the throttle port 28 on the piston 5 is closed by the sidewall of the
sleeve 7 and
vice versa, which closes the control valve 4. As described further below, the
control valve
4 is biased closed, in which case the ports 26,28 are misaligned. When the
piston 5 slides
axially along the sleeve against this bias, the ports 26,28 can be brought
into alignment.
The interior surface of the sleeve 7 comprises a waist 17 that is narrower in
interior
diameter than the rest of the sleeve 7. The second, open, end of the piston 5
fits through the
waist 17 and comprises a flange 18 that extends radially outwards from the
piston 5 to
engage with the internal surface of the sleeve 7 above the waist 17. This
provides an
annular gap 21 between the exterior surface of the piston 5, and the interior
surface of the
sleeve 7. A coil spring 30 is disposed in this annular gap 21 surrounding the
piston 5 so
that one end of the spring 30 abuts the waist 17 of the sleeve 7 and the other
end of the
spring abuts the flange 18 of the piston 5. Thus, the spring lies between the
sidewalls of the
piston 5 and the sleeve 7, and can be compressed by pushing the flange towards
the waist
17 to extend the piston 5 towards and/or out of the first, open, end of the
sleeve 7 away
from the packer 2. The fluid pressure inside the piston 5 is coupled to this
annular gap by
vents 32.
Towards the first, closed, end of the piston 5 there is a shoulder 19 that is
wider than
the waist 17 and lies on the other side of the waist 17 from the flange 18 so
that the flange
18, waist 17 and shoulder 19 cooperate to limit the range of motion of the
valve piston 5
and retain the piston 5 in the sleeve 7.
The space between the waist 17 of the sleeve 7 and the shoulder 19 of the
piston 5
provides the chamber 34 that can be expanded by sliding the piston 5 to move
the shoulder
19 away from the waist 17, compressing the spring. The feedback line 9 is
coupled to
provide fluid pressure to the chamber 34 by the coupling 36. It can be seen,
therefore, that
the valve can be actuated by movement of the piston 5 and that movement of the
piston is
controlled based on the difference in pressure between the pump discharge
(which is
communicated to the chamber 34) and the pump intake.
It will be appreciated that the following parameters contribute to the force
on the
control valve piston 5:
= the fluid pressure, P1, in the feedback line 9 and chamber 34;
= the fluid pressure, P2, inside the control valve piston 5;
= the exterior (bottomhole) fluid pressure, P3, acting on the piston 5;
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= the geometry of the piston 5 and sleeve 7;
= the geometry of the chamber 34; and
= the bias force exerted by the spring 30.
In the event that the exterior (bottomhole) fluid pressure, P3, acting on the
piston 5 is
5 greater than the fluid pressure P2 inside the piston 5, the piston 5 is
pushed into the sleeve
7 so that the piston's shoulder 19 moves towards the sleeve's waist 17. This
causes the two
throttle ports 26, 28 to be misaligned to close the control valve 4.
In the event that the bottomhole pressure, P3, is less than the pressure, P2,
in the
piston 5, the control valve 4 still remains closed until the pressure
difference between the
10 pressure P2 in the piston 5 and the bottomhole pressure P3 exceeds a
threshold pressure
difference. This threshold pressure difference is determined by the geometry
of the piston
5, sleeve 7 and chamber 34, and the bias force applied by the spring 30. This
threshold
pressure difference can be selected by choosing the geometry and spring
constant so that
the control valve 4 can be configured to support a specific threshold back
pressure. For
example, this threshold pressure difference might be selected to be large
enough to support
a hydrostatic head associated with the depth at which the control valve 4 is
to be deployed.
This can enable the control valve 4 to inhibit the inadvertent flow of fluid
and solids back
down through the pump and into the well. The threshold pressure difference can
also be
selected to be small enough to enable the control valve 4 to be opened by
pumping fluid
back into the well to increase the pressure P1 above the packer 2 to overcome
the
threshold, for example as part of a "bullhead kill" process. When this pumping
is stopped
and the increased pressure above the packer 2 is relieved, the control valve 4
will close
again under the bias of the spring 30, keeping the kill fluid in place above
the control valve
4. Accordingly, in the absence of a pump, or when the pump 10 is inoperative,
the
apparatus operates as a sub-surface controlled safety control valve 4 which
"fails safe
closed" to close off the well.
When the pump 10 is operated, there is an increase in the pressure in the
chamber 34
associated with the discharge pressure P1 of the pump 10, and a reduction in
the pressure,
P2, associated with the intake pressure of the pump 10. The parameters listed
above are
selected so that these pressure changes are sufficient to open the control
valve 4. Once the
control valve 4 is opened, the hydrostatic pressure on either side of the flow
ports 26, 28
are equalised, and so the pressures above, P2, and below, P3, the control
valve 4 are equal.
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Accordingly, the spring constant of the spring 30 and the geometry of the
chamber 34 can
be selected for the pump 10 so that the differential pressure evolved by the
pump 10 (the
difference between its discharge pressure, P1, and its intake pressure, P2) is
sufficient to
hold the control valve 4 open whilst the pump 10 is operating.
It is possible that the pressure in the wellbore beneath the packer 2 (i.e.
bottomhole
pressure, P3) may be so great that the pressure, Pl, generated by the pump 10
is
insufficient to open the control valve 4. This may occur in the case of a well
that is shut in,
wherein the bottomhole pressure, P3, can increase during the shut-in period.
In this
situation, before the pump is switched on, fluid can be pumped down into the
well to
increase the pressures P1 and P2 (since P1 is equal to P2 at this point) to
balance out the
high bottomhole pressure, P3. Then, when the pump is switched on, the
pressure, Pl,
generated by the pump 10 can overcome the bottomhole pressure, P3, and open
the control
valve 4. Similarly the flow out of the top of the well may be choked back to
maintain P1 at
a sufficiently high pressure to hold the valve open until the bottomhole
pressure P3
reduces.
Figure 3 illustrates another sleeve valve suitable for use as a control valve
4 in the
apparatus described with reference to Figure 1 and Figure 2.
In order to recover apparatus such as that shown in Figure 1 and Figure 2 from
a
well, it can be necessary to overcome significant forces exerted by the
hydrostatic pressure
above and below the apparatus. The flow control apparatus of Figure 3
comprises a
pressure equalisation valve configured to be mechanically actuated by a
pulling tool
latching on to the valve to retrieve it.
The flow control apparatus of Figure 3 is similar to the apparatus of Figure
2, and in
Figure 2 and Figure 3, like reference numerals are used to indicate like
elements. As in the
apparatus of Figure 2, the control valve 204 comprises a piston 205 disposed
in a sleeve 7.
Also, the piston 205 comprises a shoulder 19, and a flange 18, and there is a
waist 17 on
the interior surface of the sleeve 7. Also as in the example shown in Figure
2, the flange 18
and waist 17 hold a spring 30 between them that surrounds the piston 5. In
addition, the
shoulder 19 and waist 17 cooperate to provide a chamber 34 that is couplable
to a pressure
feedback line 9 (not shown in Figure 3) by a coupling 36.
The flow control apparatus shown in Figure 3 further comprises an equalisation
valve 206 that is operable to enable fluid to flow through the flow passage 8
even when the
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throttle ports 26, 28 of the control valve 204 are closed. The equalisation
valve 206 is
arranged so that the difference between the pressure, P2, inside the piston
205, and the
bottomhole pressure, P3, outside the piston 205, does not alter the force
required to operate
the equalisation valve 206. This enables the pressure in the well above the
control valve
204, and the bottomhole pressure in the well beneath the control valve 204 to
be equalised
without the need to displace the piston 205 to open the throttle ports 26,28
of the control
valve 204.
The equalisation valve 206 is biased closed, and arranged so that the pressure
differential across the control valve 204 does not act to open it. Therefore,
in the absence
of a positive opening force the equalisation valve 206 remains closed.
In Figure 3, the equalisation valve is arranged in the closed end of the
piston 5. The
equalisation valve comprises a body 220, having a recess 222 facing into the
valve piston
5. Seated in the recess is a cylinder 221 which can move axially within the
recess 222, and
behind the cylinder in the recess is a second spring 223.
The body 220 and the cylinder 221 comprise throttle ports 226, 228 which, when
aligned, provide fluid communication between the outside of the control valve
sleeve 7,
and the inside of the control valve piston 205. The throttle ports 226,228 of
the
equalisation valve 206 can be opened by sliding the cylinder 221 axially with
respect to the
body 220 to align them, and closed by sliding the cylinder axially to misalign
them. The
second spring 223 is arranged to bias the cylinder 221 against detents or some
other stop in
the body (not shown). This holds the cylinder in a position in which the ports
are
misaligned and the equalisation valve is closed.
The throttle ports 226,228 in the body 220 of the equalisation valve 206 are
also
arranged so that fluid pressure in the ports acts only radially on the
cylinder. Accordingly,
this fluid pressure does not alter the force required to open or close the
equalisation valve
206. The force required to open or close the equalisation valve 206 is which
is determined
by the second spring 223.
In operation, when it is desired to retrieve the apparatus from a well, a
pulling tool
can be lowered to engage the flow control apparatus, for example by coupling
with a latch
on the apparatus. The pulling tool can then push the cylinder 221 into the
body 220 of the
equalisation valve 206, against the force of the second spring 223 to open the
equalisation
valve, thereby enabling the flow control apparatus to be removed from the
well.
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The features of the embodiments described with reference to the drawings are
merely
exemplary, and many alternatives and variations will be apparent to the
skilled addressee
in the context of the present disclosure.
For example, although the control valve 4 has been described as a sliding
sleeve
valve, the same control may equally be applied to any type of controllable
valve for
example flapper valves, ball valves, needle valves and the like. For example,
a ball valve
may be substituted by simply allowing the sliding piston to bear upon a pin
offset from the
axis of rotation of the valve ball to allow the linear motion of the sleeve to
rotate the ball.
Similarly, other valve types may be actuated with suitable mechanisms derived
from an
actuator controlled by either the differential pressure across the entire
valve or the
differential pressure across a pump 10 coupled to the control valve 4 as
described with
reference to Figure 1 and Figure 2.
As another example, the pressure feedback line 9 through the packer 2 need not
comprise a fluid pipe, and may comprise a pressure sensor adjacent the pump
discharge 22
which communicates a control signal through the packer 2.
It will also be seen that the chamber 34 in the control valve 4 need not be
actuated
simply by fluid pressure, and a transducer, such as an electromechanical, or
auxiliary
powered hydraulic actuator may be provided to operate the control valve 4 in
response to a
control signal, or in response to pressure communicated by the feedback line
9. Each of
these two optional features may be used individually, or in combination.
Indeed, any kind
of controller may be used to control the control valve 4 based on the fluid
pressure, P2, in
the flow passage 8 between the control valve 4 and the pump intake 20, and
based on the
fluid pressure, P1, at said pump discharge 22.
It will also be appreciated that the control valve 4 need not be disposed
below the
packer 2, and may be arranged inside it, or even above the packer. In either
case, the
control valve 4 is arranged such that the second end of the piston is in fluid
communication
with the pump intake 20, the first, closed end of the piston is exposed to the
bottomhole
pressure P3, and the throttle ports 26,28 can allow or prevent fluid flow
between the
wellbore below the packer and the pump intake 20 when they are aligned or
misaligned
respectively. This could be achieved, for example, by positioning the control
valve inside
an outer conduit which extends through the packer. A seal is provided around
the control
valve between the outside surface of the control valve and the inner surface
of the conduit
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to prevent fluid travelling along the conduit around the outside of the
control valve. When
the throttle ports 26,28 are aligned fluid can flow between the conduit below
the control
valve and the inside of the control valve.
Although the control valve 4 and the equalisation valve 206 have been
described as
being biased closed by springs, any mechanical, electrical, hydraulic or
magnetic form of
biasing may be used. In addition, the control valve 4 has been described as
being opened
initially by a change in pressure associated with starting the pump 10. It
will be appreciated
that other means of opening the valve to initiate flow may additionally be
provided. For
example, a hydraulic line to the surface, or an electromechanical mechanism
may be used
to open the control valve 4 to equalise the pressures P2 and P3.
It has been noted that when the pump 10 is inactive or absent, the valve may
behave
as a pressure relieving non-return valve. By applying an overpressure in the
injection
direction, the valve can be opened to allow fluid flow into the well. In an
embodiment, this
allows the well to be killed by displacing well fluids through the valve.
Given the valve actuating mechanism, it is possible to select the spring to
ensure that
the valve opens at a selected over pressure. This also ensures a defined
overbalance
pressure above the valve to act as a second barrier to flow. However this
feature also
means that if it is ever required to remove or replace the flow control
apparatus, it could be
difficult to remove it as the force created by the differential hydrostatic
pressure would
have to be overcome in order to unseat the apparatus. The equalisation valve
described
with reference to Figure 3 provides one way to address this issue.
Additionally, when the valve is closed, the fluid column above the valve can
be
monitored to confirm that the well is static (no flow is entering or leaving
the fluid column
above the valve).
Figure 4 (split over Figures 4a and 4b) shows another example of a flow
control
apparatus adapted to be disposed inside a well bore, in accordance with the
present
invention.
The assembly shown in Figure 4 comprises a packer 100 configured to be
deployed
in a well bore, and a fluid flow passage 110 arranged to enable fluids to flow
through the
packer and adapted to be coupled to a pump intake of a pump (not shown in
Figure 4) for
drawing fluid through the fluid flow passage 110. The apparatus comprises an
inflow
control valve 120 and an outflow control valve 130. The outflow control valve
130 is
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arranged in the flow passage 110 beneath the packer 100 to control the flow of
fluid from
beneath the packer into the fluid flow passage and to the pump intake. The
inflow control
valve 120 is coupled in the flow passage 110 between the packer 100 and the
outflow
control valve 130, and can permit fluid to flow from above the packer to below
the packer,
5 for example for a "bullheading" operation.
The outflow control valve comprises a ball valve 130 which is controlled by a
controller 140. The controller 140 comprises a first pressure driven sleeve
144 and a
pressure driven actuator rod 142. A first end of the pressure driven actuator
rod 142 is
connected to the ball valve 130. The other end of the pressure driven actuator
rod 142 is
10 connected to the first pressure driven sleeve 144. The actuator rod is
arranged so that
longitudinal movement of the first pressure driven sleeve 144 opens and closes
the ball
valve to permit or inhibit fluid flow out from the wellbore below the packer
into the fluid
flow passage 110. The first pressure driven sleeve 144 is located in the fluid
flow passage
between the pump intake and the packer 100 and is biased by a first spring
146. The bias
15 of the first spring acts to close the ball valve 130.
A supplementary pressure driven sleeve and supplementary pressure driven
actuator
rod (not shown) may be provided in series with the first pressure driven
sleeve 144 and
first pressure driven actuator rod 142. The supplementary sleeve and rod work
in tandem
with the first sleeve and rod to increase the force of the controller. The
supplementary
pressure driven sleeve and pressure driven actuator rod can be arranged
between the first
pressure driven sleeve 144 and pressure driven actuator rod 142 and the pump
The fluid pressure at the pump discharge (i.e. above the packer 100) is
communicated to the first pressure driven sleeve 144 through ports 148 in the
sidewall of
the fluid flow passage 110. An increase in pump discharge pressure acts, via
the ports 148,
against the bias of the first spring 146.
The inflow control valve 120 comprises a second pressure driven sleeve 122 and
a
second spring 126. The second spring 126 biases the second pressure driven
sleeve 122 to
cover vents 124 through the fluid flow passage 110. Accordingly, unless the
force of the
spring 126 is overcome by a difference in pressure between the inside of the
fluid flow
passage 110 and the annulus outside the fluid flow passage (i.e. the pump
discharge
pressure), the vents 124 remain closed.
In operation, the outflow control valve is controlled as follows. The
controller 140 is
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arranged to control the outflow control valve 130 based on the difference
between the fluid
pressure, Pl, in the annulus above the packer 100 and a pressure, P2, inside
the fluid flow
passage 110 at the pump intake. In the event that the fluid pressure, Pl, in
the annulus (e.g.
at the pump discharge above the packer) is greater than the fluid pressure,
P2, in the flow
passage 110 by more than a first selected threshold pressure, the controller
140 is arranged
to open the outflow control valve 130 to enable fluid to flow from the
wellbore below the
packer into the fluid flow passage 110 towards the pump intake. The threshold
pressure is
dictated by the spring.
In the event that the pump is not pumping, there is no pressure difference
across the
pump and so the outflow control valve 130 remains in its default, closed,
state.
As with the apparatus illustrated in Figure 1, in the event that the pump
begins
pumping, the operation of the pump reduces the pressure at the pump intake in
the fluid
flow passage. The difference between the pump discharge pressure and the pump
intake
pressure causes the first pressure driven sleeve 144 to move against the first
spring 146 and
to move the actuator rod 142. This in turn causes the outflow control valve
130 to open.
Whilst the pump is pumping, the pressure difference between the pump intake
and
the pump discharge is maintained and the outflow control valve 130 is held
open. In the
event that the pump fails, and stops pumping, the controller 140 closes the
outflow control
valve 130 to inhibit fluid flowing out of the well through the flow passage.
As regards the inflow control valve 120, the second pressure driven sleeve 122
is
arranged to open to permit fluid to flow back into the wellbore in the event
that the
pressure inside the fluid flow passage 110 is greater than the pressure in the
annulus
beneath the packer 100 by more than a second selected threshold pressure ¨
sufficient to
overcome the biasing force of the second spring 126. Accordingly, in
operation, fluid can
be forced (e.g. "bullheaded") back into the wellbore through the inflow
control valve 120
by applying sufficiently high back pressure in the wellbore above the valve.
In addition, the second pressure driven sleeve 122 is arranged so that, when
the
pressure in the annulus beneath the packer 100 is greater than the pressure in
the fluid flow
path, this pressure forces the sleeve to cover the vents 124. Accordingly, a
build up of
pressure beneath the packer helps to maintain the control valve closed.
It can be seen that, in contrast to the apparatus illustrated Figure 1, the
apparatus
illustrated in Figure 4 does not comprise a separate pressure feedback line
through the
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packer because the controller 140 comprises an actuator that is operated by
the annulus
pressure above the packer. In other respects, however, the mode of operation
is
unchanged.
Although the example of Figure 4 is illustrated as comprising a packer, the
packer
100 need not be part of the apparatus. For example, the apparatus may be
retrofitted to
existing packers in place in a well bore, or it may be provided as a kit of
parts with a
separate packer. In Figure 4, the controller 140 comprises an actuator rod
142, and a first
pressure driven sleeve 144 which operates to control the outflow valve
mechanically.
However, such direct mechanical coupling is not necessary, and in some
examples
electrical and/or electromechanical actuators can be used to provide the same
functionality.
In Figure 4, the outflow control valve 130 comprises a ball valve, however any
appropriate valve such as a sleeve valve may also be used. Similarly, the
inflow control
valve 120 of Figure 4 comprises a sleeve valve, but in some examples other
kinds of valve
may be used for this purpose.
The first pressure driven sleeve 144 and the second pressure driven sleeve 122
are
shown in Figure 4 as being biased by springs. However other means of biasing
may be
used, for example other mechanical biases, for example electromechanical
biases, for
example magnetic biases.
Other examples and variations will be apparent to the skilled addressee in the
context
of the present disclosure.
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