Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INJECTION DEVICE
FIELD OF THE INVENTION
The present invention relates to an injection device for injecting a fluid to
a
target location, such as into a down hole location.
BACKGROUND TO THE INVENTION
Many industries require fluids to be delivered, or injected, from a source to
a
target location. For example, in the oil and gas industry many well
completions include
a means of injecting chemicals into the wellbore at a point in the completion
for the
purposes of corrosion reduction, scale reduction, hydrate reduction, well
stimulation, a
variety of optimisation strategies or the like. It is highly desirable to be
able to control
the rate of injection, and in typical applications the preference is to permit
a relatively
constant rate of injection to be achieved, irrespective of and pressure
fluctuations
within the system. Injection may also be required at other locations, such as
into the
wellbore, associated formation, annulus and the like. Injection could also be
required
at a subsea location, such as at a Christmas tree, flow line, jumper,
manifold, wing line
or the like. Some other examples of injection in the oil and gas industry
include
downhole injection of a fluid to assist production.
A typical wellbore completion installation with injection capabilities is
diagrammatically illustrated in Figure 1. The wellbore, generally identified
by reference
numeral 10, comprises a casing string 12 located within a drilled bore 14
which extends
from surface 16 to intercept a hydrocarbon bearing formation 18. A lower
annulus area
20 defined between the casing 12 and bore 14 may be filled with cement 22 for
purposes of support and sealing. A production tubing string 24 extends into
the casing
12 from a wellhead 26 and production tree 28. A lower end of the production
tubing
string 24 is sealed against the casing 12 with a production packer 30 to
isolate a
producing zone 32. A number of perforations 34 are established through the
casing 12
and cement 22 to establish fluid communication between the casing 12 and the
formation 18. Hydrocarbons may then be permitted to flow into the casing 12 at
the
producing zone 32 and then into the production tubing 24 via inlet 36 to be
produced to
surface. Artificial lift equipment, such as an electric submersible pump (ESP)
37 may
optionally be installed inline with the production tubing 24 as part of the
completion to
assist production to surface. The production tree 28 may provide the necessary
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pressure barriers and provides a production outlet 38 from which produced
hydrocarbons may be delivered to a production facility (not shown), for
example.
A small bore injection line or conduit 40, which is often referred to as a
capillary
line, runs alongside the production tubing 24 from a surface located injection
fluid
source 42 to a downhole target location, which in the illustrated example is a
lower end
of the production tubing 24, below the ESP 37. The production tubing 24 may
include
an optional injection mandrel 44. An injection pump 46 is located at a topside
location
to facilitate injection of the injection fluid 42.
An injection valve 48 is located in a lower region of the injection line 40
and
functions to permit fluid injection into the production tubing 24, in some
cases
preferentially at a constant injection rate, while preventing reverse flow
back into the
injection line 40. Known valves for such purposes include an injection check
valve,
such as illustrated in Figure 2. In this example the check valve 48 includes a
housing
50 with an inlet 52 for communicating with the injection line 40 and an outlet
54 for
communicating with the production tubing 24. A poppet member 56 (other similar
members such as pistons and balls are also known) is mounted in the housing 50
and
is biased by a spring 58 towards a closed position in which the poppet 56
sealingly
engages a seat 60 to prevent flow through the housing 50. To permit injection
the fluid
pressure at the inlet 52 must establish a downward force on the poppet 56
which
exceeds the combined force of the spring 58 and the pressure at the outlet 54,
which
act in the opposing direction. Accordingly, in normal flow conditions the
inlet pressure
will be a fixed differential above the outlet pressure by a magnitude dictated
primarily
by the force of the spring 58, and also by any back-pressure created at the
inlet by the
effect of the poppet 56 and seat defining a flow restriction. An exemplary
graphical
representation of the effects of varying the inlet or outlet pressures is
provided in Figure
3. As shown, irrespective of pressure fluctuations at the outlet 54, the inlet
pressure 62
will always be a fixed value above the outlet pressure 64 by a differential 66
which is
defined primarily by the spring 58.
In chemical injection there is always a hydrostatic pressure gradient present
in
the injection line 40. This pressure gradient is a function of the density of
the fluid and
the true vertical height of the well known as the TVD (True Vertical Depth).
As depth
increases, the hydrostatic pressure will linearly increase, such that the
maximum
hydrostatic pressure will act at the inlet 52 of the injection valve 48. This
hydrostatic
pressure will act in a direction to open the valve poppet member 56 against
the
combined resistance of the spring 58 and the pressure at the valve outlet 54,
which will
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be largely equal to the pressure within the production tubing 24 at the point
of injection.
There may be circumstances where the hydrostatic pressure force acting at the
valve
inlet 52 exceeds the resistance provided by the valve outlet pressure and the
spring 58,
for example where large hydrostatic pressures exist in deeper wells, and/or
where
relatively low wellbore pressures exist, for example due to operation of the
ESP 37. In
such circumstances the result can be the undesirable flow or cascading of
injection
fluid into the target location. This effect may be termed "hydrostatic fall-
through".
If unchecked such hydrostatic fall-through will occur until the hydrostatic
pressure within the injection line 40 is in equilibrium with the target
location pressure
and the resistance provided by the valve spring 58. If the injection fluid is
not
continuously replenished, or not replenished as quickly as the injection fluid
cascades
through the valve 48, then the result will be the creation of low, vacuum or
near
vacuum pressures in the upper region of the injection line 40. Such a vacuum
may
present the injection line 40 to adverse mechanical forces and stresses, such
as radial
collapse forces. Furthermore, the established vacuum may be defined by a
pressure
which is lower than the vapour pressure of the injection fluid, thus causing
the injection
fluid to boil. This may be compounded by the effect of the increased
temperatures
associated with wellbore environments. The consequence of vacuum occurrence in
chemical injection lines is that the original fluid may not be able to retain
its intended
state and the fluid carrier will boil off. This has the potential of many
adverse effects,
such as solid depositing, viscosity change, crystal formation, waxing, partial
or full
solidification, and generally changes within the fluid causing loss of
effectiveness of the
injection chemical, and the like.
To provide a numerical example, for an injection line which has a TVD of 1420
meters with an injection fluid having a density of 1050 kg/m3, the hydrostatic
pressure
(calculated by the product of fluid density, gravity and TVD) acting at the
inlet 52 of the
valve 48 will be in the region of 146 bar. If the pressure in the production
tubing 24 at
the point of injection is 95 bar, and assuming that the valve spring 58 and
other flow
resistance is equivalent to providing 2 bar of pressure resistance, then this
creates a
pressure differential across the valve of 49 bar. Accordingly, due to the
tendency for
the system to seek equilibrium the injection fluid within the injection line
40 will cascade
through the valve 48 until the height of injection fluid establishes a
hydrostatic pressure
at the valve inlet 52 which is in equilibrium with the pressure in the
production tubing
plus other resistance, which in the present example will be 97 bar. Thus, a
hydrostatic
pressure of 97 bar at the valve inlet 52 will require the injection fluid to
cascade to
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define a height of around 942 metres. This will therefore leave the upper 478
meters of
the injection line 40 under vacuum conditions, which is graphically
illustrated in Figure
4.
Such hydrostatic fall-through may be addressed by increasing the spring force
rating of the spring 58. This will function to increase the resistance to flow
through the
valve 48, such that a greater pressure differential between valve inlet 52 and
outlet 54
can be accommodated before the onset of hydrostatic fall-through. A graphical
example of the use of a more powerful valve spring is illustrated in Figure 5.
As in the
previous graphical example of Figure 3, the effect of the spring is such that
irrespective
of pressure fluctuations at the valve outlet 54, the inlet pressure 70 will
always be a
fixed value above the outlet pressure 72 by the differential 68. In this
exemplary case a
differential of around 80 bar is established by a more powerful spring, and
such a
spring would prevent the occurrence of hydrostatic fall-through in the
specific numerical
example provided above.
However, the size of a valve spring may be limited by the size of the
injection
valve and available space to accommodate deployment and installation of such a
valve. Further, in circumstances where very large pressure differentials
exist, the
required size of a valve spring may be impossible to accommodate within the
valve.
In addition to establishing a desired pressure differential across a valve
using a
spring, it is also known in the art to utilise the effect of a flow
restriction within a valve to
establish a desired backpressure within the injection line 40. Also, such a
flow
restriction may be variable to ensure a consistent injection flow rate can be
achieved
irrespective of the pressure differential.
As described above, in known injection valves a fixed differential between
valve
inlet and outlet is provided. Thus, the expectation and desire is that the
valve inlet
pressure will track any variations in the outlet pressure by the fixed
differential. The
intention of this is to prevent hydrostatic fall-through, and to facilitate a
relatively
constant injection rate. However, in certain circumstances, for example where
the
outlet pressure should drop, for example due to activation of an ESP, it has
been
observed that there is an unexpected sudden rush of injection fluid through
the valve.
This is contrary to expectation, which is that a substantially continuous
injection rate
should be achieved by self-adjustment of the valve to maintain the fixed
pressure
differential between inlet and outlet. Further, such a sudden rush of
injection fluid
through the valve may cause damage to the valve.
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Furthermore, in the exemplary completion system shown in Figure 1 an optional
ESP 37 is provided, wherein the injection fluid is injected upstream, or on
the inlet side
of the ESP 37. The injection fluid may function to inhibit scale and the like
within the
ESP 37, to condition the production fluids to permit more efficient pumping,
for example
5 by reducing the viscosity of the production fluids, and the like. In this
respect, when the
ESP 37 is activated the pressure at the pump inlet, and thus at the injection
location
will fall. As described above, the injection valve 48 should permit this fall
in pressure to
be accommodated and ensure that the injection line pressure is maintained at a
fixed
differential above the target location pressure, and self-adjusts to ensure a
consistent
flow rate of injection fluid.
Expected, and indeed desired pressure profiles at the inlet and outlet of the
ESP 37, and at the inlet 52 of the valve 48 is graphically illustrated in
Figure 6. In this
respect, as the ESP 37 is activated the pump inlet pressure 74 should fall,
and the
pump outlet pressure 76 should rise, until a steady state running condition is
preferably
achieved. In view of the fixed pressure differential provided by the valve 48,
illustrated
by line 78 in Figure 6, the inlet pressure 80 of the valve 48 will be
maintained at a fixed
value above the inlet pressure 74 of the pump 37, and will thus define a
substantially
equivalent pressure profile, albeit at a fixed differential higher.
However, despite the expectation and desire for the pump inlet and outlet
pressures to reach a steady state shortly after activation of the ESP 37, the
present
inventor has observed that in practice this may not be the case. For example,
during
fluid injection, such as injection of a diluent to modify the viscosity of the
production
fluids, the pressure profiles observed may be more accurately depicted in
Figure 7 - it
should be noted that Figure 7 represents a generalisation of the observations
made by
the applicant. In this respect, when the ESP 37 is activated the pump inlet
pressure 82
falls, and the pump outlet pressure 84 rises, with the inlet pressure 86
tracking above
the pump inlet pressure 82 by the magnitude of the fixed differential 88, as
expected.
However, it has been observed that the pump inlet and outlet pressures 82, 84
may not
achieve the expected and desired steady state, and as illustrated in Figure 7
these
pressures may fluctuate for an extended period following activation of the ESP
37. In
this respect the observation is that pump inlet pressure 82 may fall while
outlet
pressure 84 rises, followed by an increase in inlet pressure 82 and
corresponding fall in
outlet pressure 84, with the cycle repeating. Further, as the valve inlet
pressure 86
tracks above the pump inlet pressure 82 by the fixed differential 88 then this
also
fluctuates, and as a consequence so, too, does the injection fluid pressure 90
at the
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surface. Such pressure fluctuations can cyclically load the completion
equipment, such
as the ESP 37, surface pump 46, injection line 40 and the like, which may have
a
detrimental effect, for example by fatiguing the equipment, by establishing
greatly
interrupted and irregular production, reducing the lifetime of the completion
equipment
requiring more frequent workover and servicing, requiring a greater monitoring
and
reducing the understanding about the effectiveness of the fluid being
injected, perhaps
leading to increased fluid injection in attempts to counter the effects of
this observation
of pressure fluctuations.
A greater understanding of the causes of such observations, and any solutions
to address such causes, is desired.
SUMMARY OF THE INVENTION
Aspects of the present invention relate to an injection device for use in
injecting
a fluid into a target location. Such an injection device may include a housing
having an
inlet for communication with an injection line or source of injection fluid,
an outlet for
communication with a target injection location, and a reference pressure port
for
communicating with a source of reference pressure, wherein the reference
pressure
port is isolated from the outlet. A valve member may be mounted within the
housing.
The injection device may be configured such that fluid pressures at the inlet
and
reference pressure port act to cause said valve member to move within the
housing to
vary flow between the inlet and the outlet. In some embodiments the injection
device
may include a sealing arrangement which permits pressures at the inlet and
reference
pressure port to move the valve member. Such a sealing arrangement may
optionally
function to control the effect of fluid pressure at the outlet acting on the
valve member.
In some embodiments the sealing arrangement may optionally function to
substantially
eliminate the effect of fluid pressure at the outlet acting on the valve
member.
Aspects of the present invention also relate to a method for injecting a fluid
into
a target location. Such a method may comprise communicating an inlet of an
injection
device to a source of injection fluid, and communicating an outlet of the
injection device
to a target location. The method may further comprise permitting a valve
member
mounted within the injection device to be moved by action of pressure at the
inlet of the
device and by pressure acting at a reference port of the device which is
isolated form
the outlet. Such movement of the valve member may function to vary flow
between the
inlet and the outlet.
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Such an injection device and method seeks to address certain unforeseen
problems and observations which are contrary to expectation in injection
processes. In
this respect, through diligent investigations and research the present
inventor has
discovered certain reasons for such observations and problems. For example, in
some
cases problems in known injection valves may be attributed to the fact that
such valves
function to modify valve inlet pressure based almost exclusively on the valve
outlet
pressure, which is understood to be largely equal to the pressure at the
injection
location, which in certain cases may be subject to large variations. Such
problems may
be mitigated in the present invention by permitting the valve member of the
injection
device to be moved by action of a fluid pressure provided at a reference
pressure port
which is isolated from the outlet of the housing. In certain embodiments the
effect of
outlet pressure may be substantially eliminated in the present invention.
As noted above, previously known injection valves principally operate by
modifying valve inlet pressure based on valve outlet pressure. As such, in the
event of
a variation in outlet pressure, inlet pressure should be varied accordingly.
However, in
some instances an unexpected surge of flow through the valve occurs when the
outlet
pressure varies. The
present inventor has attributed this observation to the
compressibility of the fluid being injected, and in particular to the
requirement for a
volumetric change in a fluid to occur in the event of a pressure change.
More specifically, fluids are often considered to be incompressible. This,
however, is only true to a limited extent and when high pressures are applied
to fluids
they do compress. Therefore if the pressure of an injection fluid at the inlet
of a valve
is required to fall, for example, a volume of fluid must be dissipated in
order for this to
occur. The valve inlet will be coupled to a source of injection fluid, and in
some cases
extremely long injection conduits will be utilised for this purpose, for
example in
downhole applications. As such, the volume of the injection fluid within an
injection
conduit may be significant, such that the volume of fluid to be dissipated in
order to
permit the pressure fall may also be significant. This fluid can only be
dissipated
through the injection valve. No matter how efficient the injection valve is at
maintaining
a differential pressure and tracking a change in outlet pressures, the valve
will have to
dissipate this volume of fluid to accommodate the fall in inlet pressure. It
has been
found the volumes of fluid that require dissipation due to pressure fall, for
example, as
may be found as a pump, such as an electric submersible pump (ESP), is
activated to
reduce pressure presented to an injection valve or device outlet, are more
than is often
thought.
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Conversely, it has been observed that following the dissipation of fluid in
the
injection line, as ESP inlet pressure falls, the ESP inlet pressure may then
be seen to
rise. In order to facilitate a continuing delivery of chemical through the
injection valve,
its inlet pressure must be increased. As fluid is delivered to increase inject
line
pressure flow is consumed by the fluid compressibility and enlargement of the
injection
line, thus causing a cessation or reduction of fluid flow through the
injection valve.
Thus creating a fall in flow following a surge of flow. This can lead to a
cyclic repetition
of a rise and surge of flow followed by a fall and loss of flow.
Although a general situation has been suggested above in which pressure
variations occur at a target location by use of an ESP, this may not always be
the case,
and such pressure variations may occur due to many reasons.
In addition to the compressibility of the fluid, any associated injection
conduit
may enlarge under internal pressure. This means its internal volume will
increase thus
requiring more fluid to be introduced in order to reach a required pressure.
Therefore
in order for the injection conduit to fall in pressure the volume of fluid
entrained at its
starting pressure must be fully dissipated in order to reach a lower pressure.
This fluid
volume dissipation therefore results in a significant rise, or surge of flow
through the
injection valve as the inlet pressure falls.
According to a first aspect of the present invention there is provided an
injection
device for use in injecting a fluid into a target location, comprising:
a housing defining an inlet for communicating with a source of injection
fluid, an
outlet for communicating with a target injection location, and a separate
reference port
for communicating with a reference pressure source;
a first valve member mounted within the housing;
a second valve member mounted within the housing and defining a flow path
therethrough to facilitate fluid communication between the inlet and outlet of
the
housing; and
a sealing arrangement provided between the second valve member and the
housing and configured such that fluid pressure at the housing inlet and
housing
reference port apply a force on the second valve member to cause said second
valve
member to move relative to the first valve member and vary flow between the
inlet and
the outlet.
In use, the effect of the reference pressure acting on the sealing arrangement
may contribute to movement of the second valve member. As such, the effect of
the
reference pressure may function to control movement of the second valve member
and
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thus control flow through the valve. Such an arrangement may permit the second
valve
member to be controlled without reliance, or with a reduced reliance, on
pressure at the
housing outlet, which may be substantially equivalent to pressure at the
target injection
location, as is the case in prior art devices.
The sealing arrangement may be configured to substantially confine any flow
between the inlet and the outlet to the flow path of the second valve member.
That is,
the sealing arrangement may be such that flow between the inlet and outlet of
the
housing may only be achieved through the flow path of the second valve member.
For the purposes of clarity, pressure acting at the inlet of the housing may
be
defined as inlet pressure, pressure acting at the outlet of the housing may be
defined
as outlet pressure, and pressure acting at the reference pressure port may be
defined
as reference pressure.
The sealing arrangement may be directly mounted between the second valve
member and the housing. For example, the sealing arrangement may directly
engage
the second valve member and the housing.
The sealing arrangement may be indirectly mounted between the second valve
member and the housing. For example, the sealing arrangement may indirectly
engage at least one of the second valve member and the housing. In one
embodiment
an intermediate component may be provided between the sealing arrangement and
at
least one of the second valve member and the housing.
A portion of the sealing arrangement may be in communication with the inlet of
the housing such that inlet pressure may establish a force on the second valve
member
in a first direction. A portion of the sealing arrangement may be in
communication with
the reference pressure port of the housing such that reference pressure may
establish
a force on the second valve member in a second direction. The second direction
may
be opposite to the first direction. In such an arrangement the forces
generated by the
effect of pressures at the inlet and reference pressure port may result in a
net
movement of the second valve member to thus vary flow between the inlet and
the
outlet.
The sealing arrangement may be configured such that movement of the second
valve member is achieved in accordance with a pressure differential between
inlet and
reference pressures. The sealing arrangement may be configured to establish a
preferential bias of forces applied by action of inlet and reference
pressures.
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The sealing arrangement may define a sealing area between the second valve
member and the housing. The sealing area may determine the magnitude of a
force
applied on the second valve member upon exposure to various pressures.
In one embodiment the sealing arrangement may define an inlet sealing area
5 configured to be exposed to inlet pressure, and a reference sealing area
configured to
be exposed to reference pressure. A ratio of the inlet and reference sealing
areas may
affect a net force generated on the second valve member by the inlet and
reference
pressures.
The inlet and reference sealing areas may be substantially equal. In such an
10 arrangement a net force applied on the second valve member may be a
function of a
pressure differential between the inlet and reference pressures.
The inlet and reference sealing areas may by different. In such an arrangement
a force bias on the second valve member may be applied by the sealing
arrangement
by action of the inlet and reference pressures. That is, a net force applied
on the
second valve member may be a function of both a differential of inlet and
reference
sealing areas and a differential between the inlet and reference pressures.
The injection device may be configured such that inlet pressure establishes a
force on the valve member to cause said valve member to move in a direction to
increase flow, for example initiate flow, between the inlet and the outlet of
the housing.
The injection device may be configured such that reference pressure
establishes a
force on the valve member to cause said valve member to move in a direction to
decrease flow, for example to prevent flow, between the inlet and the outlet
of the
housing.
A portion of the sealing arrangement may be in communication with the outlet
of
the housing. The sealing arrangement may be configured to control the effect
of the
outlet pressure on the second valve member.
In one embodiment the sealing arrangement may be configured to substantially
eliminate the effect of outlet pressure on the valve member. In such an
embodiment
the sealing arrangement may be configured such that the effect of outlet
pressure does
not establish or significantly minimises any net force on the second valve
member.
Such an arrangement may remove or eliminate any reliance on outlet pressure to
control movement of the second valve member. This may contribute to addressing
problems associated with prior art devices where variations in outlet pressure
may
have a detrimental effect on operation of the injection device.
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The sealing arrangement may be configured such that outlet pressure may
establish first and second substantially equal and opposite forces on the
second valve
member, such that any net force is substantially minimised.
The sealing arrangement may be configured such to permit the outlet pressure
to provide a desired bias force on the second valve member. In such an
arrangement
any effect of outlet pressure may be utilised in a desired way, for example to
bias the
second valve member to move in a desired direction.
The sealing arrangement may define first and second outlet sealing areas
between the second valve member and the housing, wherein each of the first and
second outlet sealing areas is configured to be exposed to outlet pressure.
The first
and second sealing areas may be configured to permit outlet pressure to
generate a
force on the second valve member in opposite directions.
In one embodiment the first and second outlet sealing areas may be
substantially equal. In such an arrangement the effect of outlet pressure
acting on the
first and second outlet areas may be cancelled out, such that no or minimal
net force is
applied on the second valve member by outlet pressure.
In one embodiment the first and second outlet sealing areas may be different.
In such an arrangement the effect of the same outlet pressure acting on the
first and
second outlet areas may present a net force acting in one direction, and thus
the outlet
pressure may act to apply this bias force on the second valve member in this
one
direction.
The sealing arrangement may comprise one or more seal members. The
sealing arrangement may comprise one or more of sliding seal members, o-rings,
bellows seals, diaphragm seals piston rings or the like.
The sealing arrangement may include first and second seal assemblies which
extend between the second valve member and the housing.
The first seal assembly may comprise one or more seal members.
The second seal assembly may comprise one or more seal members.
The first seal assembly may be configured to isolate the housing inlet from
the
housing outlet, such that fluid communication between the inlet and the outlet
is
permitted only through the flow path in the second valve member.
The second seal assembly may be configured to isolate the housing outlet from
the housing reference port.
The first seal assembly may define an inlet sealing area configured to be
exposed to inlet pressure.
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The first seal assembly may define a first outlet sealing area configured to
be
exposed to outlet pressure.
The second seal assembly may define a reference sealing area configured to
be exposed to reference pressure.
The second seal assembly may define a second outlet sealing area configured
to be exposed to outlet pressure.
The inlet, reference and first and second outlet sealing areas may be as
defined
above.
The device may comprise a biasing arrangement configured to bias the second
valve member in a desired direction. The biasing arrangement may be configured
to
bias the second valve member to move in a direction to decrease flow between
the
inlet and the outlet, for example to close the injection device. The biasing
arrangement
may be selected to provide a desired biasing force.
The second valve member may be configured to be actuated to move in a
direction to decrease flow by a combination of biasing force from a biasing
arrangement and the action of reference pressure. The second valve member may
be
configured to be actuated to move in a direction to increase flow by the
action of inlet
pressure.
The biasing arrangement may be configured to establish a force on the second
valve member to permit a desired pressure differential within the injection
device to be
achieved. For example, the biasing arrangement may permit or require the
injection
pressure to be maintained at a fixed pressure differential above the reference
pressure,
by a magnitude associated with the force applied by the biasing arrangement.
The biasing arrangement may comprise one or more springs, such as a coil
spring, wave spring, flat spring, disk spring, Belleville spring or the like.
The biasing
arrangement may comprise a deformable member capable of elastic recovery, such
as
an elastic body subject to deformation, for example compression.
The biasing arrangement may be adjustable.
The second valve member may comprise a profile to permit engagement with
the biasing arrangement, such as an annular rib, one or more pins, or the
like. The
biasing arrangement may directly engage the second valve member. The biasing
arrangement may indirectly engage the second valve member, for example via an
intermediate component such as a plate member or the like.
The injection device may be configured for use in any application, such as in
any application where a fluid is required to be injected into a target
location, such as in
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the oil and gas industry, chemical processing industry, manufacturing industry
or the
like.
The injection device may be configured for use in injection into a wellbore
target
location. The target location may be associated with wellbore equipment or
infrastructure. The target location may be associated with downhole tubing or
equipment, such as production tubing, casing or liner tubing, drill pipe,
coiled tubing or
the like.
The injection device may be configured for use in injection into a separate
flow
line. Such a separate flowline may include a pressure varying device, such as
a pump
assembly, for example an electric submersible pump (ESP) assembly. In one
embodiment the injection device may be configured for use in injection of a
fluid into a
flow line at a location which is upstream of a pressure varying device. In
such an
arrangement the target injection location may be located on an inlet side of
such a
pressure varying device, and as such the target location may be subject to
pressure
variations established by operation of the pressure varying device. Thus, the
injection
device of the present invention may assist to minimise any detrimental effect
by virtue
of the variations at the target injection location.
The inlet fluid pressure at the inlet of the housing may be at least partially
defined by fluid pressure within an associated injection line and/or an
associated
source of injection fluid. The outlet fluid pressure may be at least partially
defined by
fluid pressure at an associated target location.
The reference pressure may be selected to be any desired pressure. In some
embodiments the reference pressure may be selected to be lower than the inlet
pressure.
The reference pressure may be configured to define a minimal pressure, such
as atmospheric or less than atmospheric. Such an arrangement may minimise the
effect of the reference pressure of applying a force on the second valve
member. This
arrangement may be selected when, for example, the effect of the outlet
pressure is
minimised or negated by the form of the sealing arrangement, such that
variation in
flow through the injection device is controlled largely by inlet pressure, and
the
presence of any associated biasing arrangement acting on the second valve
member.
The reference pressure port may be configured for communication with any
desired source of reference pressure. The source of reference pressure may
exclude
the target location. Such exclusion of the target location may minimise
reliance on the
outlet pressure or target location pressure on operation of the device. This
may assist
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to minimise any effects of volumetric expansion, or even contraction, of fluid
positioned
on the inlet side of the housing, for example within an associated injection
line.
The reference pressure port may be configured for communication with a local
source of reference pressure. In one embodiment the reference pressure port
may be
configured for communication with a source of reference pressure which is
incorporated within the injection device, for example formed within the
housing of the
injection device. Such a local source of reference pressure may be configured
to
provide a fixed reference pressure. In some embodiments a local source of
reference
pressure may be variable.
The reference pressure port may be configured for communication with a
source of reference pressure at a remote location. In some embodiments where
the
injection device is utilised for injection into a downhole target location,
the source of
reference pressure may be provided at surface level and/or at a separate
downhole
location.
In one embodiment the outlet of the housing is configured to communicate with
a target location which is positioned on one side of a pressure varying
device, and the
reference pressure port is configured to communicate with a location which is
positioned on an opposite side of the pressure varying device. The pressure
varying
device may comprise a pump, such as an ESP. The pressure varying device may
comprise a choke.
In one embodiment the outlet of the housing is configured to communicate with
an inlet of a pump assembly, and the reference pressure port is configured to
communicate with an outlet of the same pump assembly. Such an arrangement may
be utilised where the pump assembly is used within a wellbore, such as to
provide
artificial lift to produced fluid, to pressurise fluids for injection into a
surrounding
formation or the like. In such an arrangement, the effect of any significant
pressure
variation, in particular a significant pressure decrease, experienced at the
reference
pressure port (i.e., the pump outlet) is minimised, and as such the effect of
possible
volumetric expansion or the like within fluid located on the inlet side of the
injection
device is also minimised.
The reference pressure applied at the reference pressure port may be user
variable. Such an arrangement may permit a user to tune or vary the use of the
injection device to accommodate particular operation conditions, such as the
density of
the fluid being injected and the like.
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The first and second valve members may cooperate to define a restriction to
flow. This may establish a back pressure in the inlet side assisting to
maintain the inlet
pressure above the outlet pressure. This arrangement may assist to prevent
hydrostatic fall-through of an injection fluid. The degree of separation
between the first
5 and
second valve members may be adjustable to adjust the restriction to flow. The
degree of separation may be adjusted automatically to maintain the inlet
pressure
above outlet pressure. Such automatic adjustment may be achieved by the desire
for
the injection device to continuously satisfy force equilibrium. In such a case
force
equilibrium may permit the desired pressure differential to be maintained.
10 The first
and second valve members may be engageable. Such engagement
may permit the first valve member to seal the flow path in the second valve
member.
The second valve member may be moveable within the housing to become separated
form the first valve member, to thus permit flow through the flow path. The
degree of
separation between the first and second valve members may define a restriction
to flow
15 through
the injection device, which may function to define a back-pressure within the
inlet side of the injection device.
The first valve member may be fixed relative to the housing, such that
movement of the second valve member is required to vary flow.
The first valve member may be defined by an integral part of the housing.
The first valve member may be defined by a component which is separate from
the housing. The first valve member may be permitted to move within the
housing.
Permitting both the first and second valve members to move within the housing
may
provide advantages in terms of improving sealing between the first and second
valve
members when engaged. For example, when engaged the first valve member may be
biased against the second member by inlet fluid pressure to assist sealing
therebetween.
The use of inlet pressure to assist sealing may permit improved sealing to be
achieved upon engagement of the first and second valve members minimising the
risk
of leakage therebetween. This in turn may, in some applications, minimise the
possibility of an associated injection line in communication with the housing
inlet being
exposed to vacuum or negative pressure conditions, for example due to
hydrostatic
fall-through.
The second valve member may be configured to support the first valve member
when engaged therewith. In such an arrangement movement of the second valve
member when engaged with the first valve member will result in movement of
both
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members. This arrangement may permit the valve members to retain the flow path
in
the second valve member closed in the event of such collective movement of the
valve
members. This may assist to regulate or minimise the effects of spurious or
undesired
pressure fluctuations which may otherwise cause inadvertent disengagement of
the
members. Such undesired pressure fluctuations may be transitory or fleeting
and not
intended to represent operational pressure fluctuations. For
example, transitory
pressure fluctuations may be created by flow surges.
The first valve member may be located on the inlet side of the second valve
member.
Each valve member may define an engagement surface configured to be
mutually engaged to prevent flow through the injection device. Each engagement
surface may define a sealing surface.
The first and second valve members may define a seal area at the region of
engagement. When the first and second valve members are engaged inlet fluid
pressure may act on one side, which may be defined as an upstream side of the
seal
area. The bias force acting on the first valve member may therefore be a
function of
the seal area and the inlet pressure. Outlet fluid pressure may act on an
opposite side
of the seal area, which may be defined as a downstream side. The outlet
pressure
may define a force acting on the first valve member which is a function of the
seal area
and the outlet pressure. In this arrangement the first valve assembly may be
biased by
the effect of a pressure differential between inlet and outlet pressures.
The apparatus may comprise a limiting arrangement configured to limit or
restrict movement of the first valve member. The limiting arrangement may be
configured to limit movement of the first valve member during opening of the
valve
assembly. The limiting arrangement may be arranged to limit movement of the
first
valve member at a point of limitation and permit the second valve member to
move
beyond the point of limitation and to become disengaged from the first valve
member.
The limiting arrangement may be fixed relative to the housing.
The limiting arrangement may comprise a tether.
The limiting arrangement may comprise a land region configured to be engaged
by the first valve member when at a point of limitation.
The limiting arrangement may comprise a no-go. The limiting arrangement may
comprise a shoulder arrangement. The limiting arrangement may comprise an
elongate member. The elongate member may extend through the second valve
member.
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The first valve member may be biased by a biasing arrangement in a desired
direction. The biasing arrangement associated with the first valve member may
be
configured to bias said member in a direction towards engagement with the
second
valve member. Such a biasing arrangement may assist sealing between the valve
members when engaged. The biasing arrangement associated with the first valve
member may comprise one or more springs, such as a coil spring, wave spring,
flat
spring or the like. The biasing arrangement may comprise a deformable member
capable of elastic recovery, such as an elastic body subject to deformation,
for
example compression.
One of the first and second valve members may define a valve seat member
and the other of the first and second members may define a valve body member.
The
valve seat member may define a valve seat which is engaged by the valve body
member.
The valve body member may comprise a pin. The valve body member may
comprise a ball. The valve body member may comprise a disk, plug, plunger or
the
like.
The injection device may comprise a pressure rated frangible arrangement
configured to rupture upon exposure to a predetermined pressure. The frangible
arrangement may be located within the housing. The frangible arrangement may
be
located on the inlet or upstream side of the second valve member. The
frangible
arrangement may be configured to isolate at least the second valve member from
inlet
pressure until required. The frangible arrangement may comprise a burst disk
arrangement, rupture cartridge or the like.
The injection device may comprise a surge protection arrangement configured
to provide protection against surging flow within or through the housing. Such
surging
flow may be caused by a particular pump duty cycle, rupturing of a frangible
arrangement or the like. The surge protection arrangement may be configured to
provide protection to the valve assembly. The surge protection arrangement may
be
located within the housing. The surge protection arrangement may be located on
the
inlet or upstream side of the second valve member.
The surge protection arrangement may comprise a component defining a flow
path, wherein the flow path is restricted in the event of surging flow. The
flow path may
be restricted by being partially or fully closed. The surge protection
arrangement may
be biased towards a condition in which the flow path is open, and moved
against said
bias during surging flow. The magnitude of the bias may define the surge
rating of the
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surge protection arrangement. The surge protection arrangement may comprise a
spring configured to bias the surge protection arrangement towards a condition
in
which the flow path is open.
The injection device may comprise a filter arrangement configured to filter
injection fluid. The filter arrangement may be mounted within the housing. The
filter
arrangement may be located on the inlet or upstream side of the second valve
member.
The injection device may comprise at least one check valve configured to
prevent flow through the injection device in a direction from the outlet to
the inlet. Such
an arrangement may eliminate the risk of flow reversal, for example in the
event of
outlet pressure exceeding inlet pressure. At least one check valve may be
located on
an outlet or downstream side of the second valve member. At least one check
valve
may be located on an inlet or upstream side of the second valve member. At
least one
check valve may be located within the second valve member, for example within
the
flow path of the second valve member. At least one check valve may be mounted
within the housing of the injection device. At least one check valve may be
provided
separately and secured to the housing of the injection device, for example via
a
suitable conduit or the like.
The housing may be defined by a unitary component. The housing may be
defined by multiple components coupled together.
The inlet and outlets of the housing may be arranged in-line with each other.
The inlet may be arranged on one end location of the housing and the outlet
may be arranged on one side of the housing.
The injection device may form part of an injection system. The injection
system
may comprise multiple injection devices. At least one of the multiple
injection devices
may be provided in accordance with any aspect of the present invention. An
injection
device according to any aspect of the present invention may be used in
combination
with any other injection device. In one embodiment the injection device may be
used in
series with a further injection device. For example, two or more injection
devices may
be arranged in series within a common injection line.
At least an injection device which is arranged to communicate directly with a
target location may be provided in accordance with the present invention. Such
an
injection device may be considered to be a final stage injection device. Other
associated injection devices which are located upstream of a final stage
injection
device may or may not be provided in accordance with the present invention.
For
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example, an injection device located upstream of a final stage injection
device may
modify inlet pressure to said upstream injection device based on outlet
pressure of said
injection device.
Where multiple injection devices are arranged in series within an injection
line,
the devices may operate to divide any required pressure differential between
the
injection line and ultimate injection location into stages. This may reduce
the required
pressure drop across an individual injection device, which may provide
advantages.
For example, in some cases an injection fluid may have behavioural problems
when
passed over an injection device at a high differential pressure. Such problems
may
include cavitation, depositing of solids or a change in the state of the
injection fluid,
which may lead to reduced effectiveness, such as chemical effectiveness, of
the
injection fluid. Accordingly, by use of multiple injection devices arranged in
series, the
differential pressure presented across each device may be restricted or
reduced, and in
particular to levels which are advantageously lower than any threshold where
problems
may occur within the injection fluid. Such an advantageous use of more than
one
injection valve in series may also be achieved while still providing the
effect of avoiding
low, vacuum or near vacuum pressures within the injection line.
The injection device may be configured for use in combination with one or more
other injection devices arranged in parallel. In such an arrangement multiple
injection
devices may be arranged for injection of a fluid from a common injection fluid
source
into multiple different locations.
The injection device may be configured to be coupled within fluid tubing. The
injection device may be configured to be located at a downhole location. The
injection
device may be configured to be located within downhole tubing. The injection
device
may be configured to be located in an annulus surrounding downhole tubing. The
injection device may be configured to be located within a pocket formed in
downhole
tubing. The injection device may be configured to be located at a subsea
location. The
injection device may be configured to be located at a surface location.
The injection device may be configured to be permanently installed within an
injection system. The injection device may be configured to be temporarily
installed
within an injection system. In one embodiment the injection device may be
configured
to be deployed and/or retrieved by an elongate member, such as by wireline,
coiled
tubing or the like.
The injection device may be for use with any suitable injection fluid. Such an
injection fluid may comprise a chemical. Such an injection fluid may comprise
any one
20
of, for example, a scale inhibitor, corrosion inhibitor, pH modified,
viscosity modified, diluent,
water, oil, acid or the like. It will be appreciated by those of skill in the
art that any injection
fluid may be utilised with the injection device of the present invention.
The injection device may be configured to inject a fluid into a subterranean
formation,
for example for sequestration of a fluid, to assist with production of fluids
from the formation,
to support the surrounding subterranean geology, or the like.
The injection device may be configured for use in injecting a fluid into any
location of
any flow line or flow process, such as at any location of a flow line
extending from a
subterranean formation to a surface location.
According to a second aspect of the present invention there is provided a
method for
injecting a fluid into a target location, comprising:
communicating an injection fluid to an inlet of a housing of an injection
device;
communicating an outlet of the housing to a target location;
communicating a reference port of the housing to a source of reference
pressure;
causing a second valve member to move relative to a first valve member by
exposure
to pressure at the inlet of the housing and pressure at the reference pressure
port of the
housing, wherein such movement permits flow through a flow path of the valve
member to be
adjusted.
According to a third aspect of the present invention there is provided a
pumping
system comprising:
a flow line;
a pump associated with the flow line and defining an inlet side and an outlet
side;
an injection device as described herein, wherein the outlet of the injection
device
housing is in communication with the flow line on an inlet side of the pump.
In one embodiment the reference pressure port of the injection device housing
may
be in communication with the flow line on an outlet side of the pump.
The reference pressure port may be in communication with a remote source of
reference pressure.
The reference pressure port may be in communication with a local source of
reference
pressure, for example provided by a pressure reservoir within the housing of
the injection
device.
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According to a fourth aspect of the present invention there is provided an
injection device for injecting a fluid into a target location, comprising:
a housing defining an inlet for communicating with a source of injection
fluid, an
outlet for communicating with a target injection location, and a separate
reference port
for communicating with a reference pressure source which excludes the target
injection
location;
a valve member mounted within the housing and defining a flow path
therethrough to facilitate fluid communication between the inlet and outlet of
the
housing, wherein the valve member is moveable within the housing by exposure
to fluid
pressure at the housing inlet and fluid pressure at the housing reference
pressure port
to vary flow between the inlet and the outlet.
According to a fifth aspect of the present invention there is provided an
injection device for use in injecting a fluid into a target location,
comprising:
a housing including an inlet chamber for communicating with an injection line,
an outlet chamber for communicating with a target location, and a reference
chamber
for communicating with a reference pressure source;
a valve member mounted within the housing and defining a valve flow path to
facilitate fluid communication between the inlet and outlet chambers;
a first seal assembly provided between the valve member and the housing and
isolating the inlet chamber from the outlet chamber such that a pressure
differential
between the inlet and outlet chambers acting over the first seal assembly will
establish
a force on the valve member; and
a second seal assembly provided between the valve member and the housing
and isolating the reference chamber from the outlet chamber such that a
pressure
differential between the reference chamber and the outlet chamber acting over
the
second seal assembly will establish a force on the valve member,
wherein the valve member is permitted to move within the housing in
accordance with the pressure forces applied via the first and second seal
assemblies to
vary flow through the valve flow path between the inlet and the outlet
chambers.
According to a sixth aspect of the present invention there is provided an
injection system for injecting a fluid into a target location, comprising:
an injection line in communication with a source of injection fluid;
an injection device coupled to the injection line and comprising:
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a housing defining an inlet coupled to the injection line, an outlet for
communicating with a target injection location, and a separate reference port
for
communicating with a reference pressure source;
a first valve member mounted within the housing;
a second valve member mounted within the housing and defining a flow
path therethrough to facilitate fluid communication between the inlet and
outlet
of the housing; and
a sealing arrangement provided between the second valve member and
the housing and configured such that fluid pressure at the housing inlet and
housing reference port apply a force on the second valve member to cause said
second valve member to move relative to the first valve member and vary flow
between the inlet and the outlet.
The injection device may define a first injection device and the injection
system
may comprise a second injection device located upstream of the first injection
device.
In such an arrangement the second injection device may comprise an outlet in
communication with the inlet of the first injection device.
The provision of a second injection device within the injection system may
permit a pressure differential between an injection line and a target location
to be
divided into stages, which may be advantageous in certain circumstances.
The second injection device may be configured similarly to the first injection
device. For example, the second injection device may permit movement of an
associated valve member by exposure to a reference pressure which is isolated
from
an outlet pressure.
The second injection device may be configured differently from the first
injection
device.
The second injection device may comprise a housing defining an inlet coupled
to the injection line and an outlet for communicating with the inlet of the
first injection
device. The second injection device may comprise a first valve member mounted
within the housing. The second injection device may comprise a second valve
member
mounted within the housing and defining a flow path therethrough to facilitate
fluid
communication between the inlet and outlet of the housing. The first and
second valve
members may move relative to each other to vary flow through the flow path of
the
second valve member, and thus also through the second injection device.
The second injection device may comprise a sealing arrangement provided
between the second valve member and the housing and configured such that fluid
23
pressure at the housing inlet and housing outlet may apply a force on the
second valve
member to cause said second valve member to move relative to the first valve
member and
vary flow between the inlet and the outlet.
According to a seventh aspect of the present invention there is provided a
method for
creating an injection system, comprising:
determining a required pressure differential between an injection line and a
target
injection location which maintains the injection line at a positive pressure;
determining an operational threshold pressure differential of an injection
fluid;
determining a required number of discrete pressure reduction stages within the
injection line
to provide the required pressure differential between the injection line and
target location
while maintaining each pressure reduction stage below the operational
threshold pressure
differential of the injection fluid; and
installing a number of injection devices within an injection line to
correspond to the
determined number of discrete pressure reduction stages.
In such an arrangement an injection line may be created which includes a
number of
injection devices to provide a required number of discrete pressure
differentials each below
the operational threshold pressure differential of an associated injection
fluid, yet which
collectively maintain the injection line in a positive pressure.
The injection devices may be located at any location along the length of the
injection
line.
The pressure within the injection line may be associated, at least partly,
with
hydrostatic pressure.
At least one injection device may be provided in accordance with any other
aspect.
According to an eighth aspect of the present invention there is provided an
injection
device for use in injecting a fluid into a target location, comprising:
a housing defining an inlet for communicating with a source of injection fluid
having a
variable flow rate, an outlet for communicating with a target injection
location, and a separate
reference port for communicating with a reference pressure source;
a first valve member mounted within the housing;
a second valve member mounted within the housing and defining a flow path
therethrough;
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23a
wherein the second valve member is moveably mounted within the housing between
an open position, wherein the first and second valve members are disengaged to
facilitate
fluid communication between the inlet and outlet of the housing through the
flow path, and a
closed position, wherein the first and second valve members are engaged,
thereby preventing
fluid communication between the inlet and outlet of the housing through the
flow path;
a biasing arrangement that acts upon the second valve member to bias the
second
valve member toward the closed position so as to decrease flow between the
inlet and the
outlet;
a sealing arrangement provided between the second valve member and the
housing,
the sealing arrangement including a first sealing assembly exposed to inlet
fluid pressure and
a second sealing assembly exposed to the reference pressure source, such that
fluid
pressure at the housing inlet and housing reference port apply a force on the
second valve
member to cause said second valve member to move relative to the first valve
member and
vary the flow rate of the injection fluid between the inlet and the outlet;
wherein, to facilitate movement between the second valve member and the first
valve
member, the fluid pressure at the housing inlet must exceed the combined force
of the
housing reference port pressure and the biasing arrangement, such that the
position of the
second valve member is achieved in accordance with a pressure differential
between inlet
and reference pressures, thereby establishing a consistent injection fluid
flow rate through
the flow path; and
wherein the first and second sealing assemblies define equivalent seal areas,
such
that the effect of the outlet pressure on the first and second sealing
assemblies will be
cancelled.
According to a ninth aspect of the present invention there is provided a
pumping
system comprising:
a flow line;
a pump associated with the flow line and defining an inlet side and an outlet
side; and
an injection device as described herein, wherein the outlet of the injection
device
housing is in communication with the flow line on an inlet side of the pump.
Other aspects of the present invention may relate to the use of the injection
device
according to any previous aspect, for example in a wellbore injection system,
in a downhole
pumping system, or the like.
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23b
Other aspects of the present invention may relate to a completion system for a
wellbore, such as a wellbore associated with the exploration and production of
hydrocarbons.
It should be understood that the features defined in relation to one aspect
may be
applied to any other aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
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These and other aspects of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic illustration of a typical wellbore system which
includes injection capabilities;
Figure 2 is a diagrammatic representation of a known injection valve
arrangement;
Figure 3 is a diagrammatic illustration of inlet and outlet pressure profiles
of the
injection valve of Figure 2;
Figure 4 graphically represents the effects of hydrostatic fall-through within
a
capillary or injection line;
Figure 5 provides an illustration of inlet and outlet pressure profiles of the
injection device of Figure 2, with the use of a more powerful spring;
Figures 6 and 7 illustrate, respectively, expected and actual pressure
profiles of
the inlet and outlet pressures of a downhole pump, and of the inlet pressure
of an
associate injection valve;
Figure 8 is a cross-sectional view of an injection device in accordance with
one
embodiment of the present invention;
Figure 9 is a cross-sectional view of an injection device in accordance with
an
alternative embodiment of the present invention;
Figure 10 provides an exemplary pressure plot of the use of an injection
device
according to the present invention, in which a reference pressure from an
outlet of a
downhole pump is utilised;
Figure 11 provides an exemplary pressure plot of the use of an injection
device
according to the present invention, in which a reference pressure from a
remote
location, such as a surface location, is utilised;
Figure 12 is a cross-sectional view of an injection device according to an
alternative embodiment of the present invention;
Figure 13 is an exemplary pressure plot of the use of the injection device of
Figure 12;
Figures 14 to 18 are cross-sectional views of an injection device in
accordance
with respective alternative embodiments of the present invention;
Figure 19 is a diagrammatic representation of a downhole injection system in
accordance with an embodiment of the present invention; and
Figure 20 is an exemplary pressure plot of the injection system of Figure 19.
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DETAILED DESCRIPTION OF THE DRAWINGS
The present invention relates to an injection device which may be used in
multiple applications. However, for exemplary purposes some specific
embodiments of
an injection device have been illustrated in the drawings, and described
below, with a
5 potential application within a wellbore system, such as a wellbore system
for the
extraction of oil and/or gas form a subterranean reservoir.
Figure 1, which has also been described above, provides an illustration of a
wellbore completion installation, generally identified by reference numeral
10, with
injection capabilities via injection valve 48. A known injection valve 48 is
illustrated in
10 Figure 2, which has already been described above. Furthermore, it has
been
explained above that although with the use of such a known injection valve 48
the
expected pressure behaviour within an injection system, which is reflected in
Figure 6,
may not actually be achieved, and in fact a more accurate representation of
reality is
provided in Figure 7. In this particular example, which involves the use of a
downhole
15 pump, such as an ESP 37 (Figure 7), upon activation the pump 37, inlet
and outlet
pressures might continue to fluctuate for extended periods, and may not reach
a
desired steady state condition. It is believed by the present inventor that
such
extended periods of fluctuation is caused by unsteady rates of injection via
the injection
valve 48 which is initiated by a sudden rush of injection fluid through the
valve shortly
20 after initial activation of the pump 37. Through diligent investigation
and research
performed by the present inventor it is considered that such a rush of fluid
through the
valve is caused by the compressibility of the injection fluid, as described
below in detail.
However, in general terms, the present inventor believes that as known
injection valves
require the valve inlet pressure to track above valve outlet pressure, then in
the event
25 of a relatively quick pressure change at the valve outlet, for example
by activation of a
pump, then the fluid in the injection line acting at the valve inlet will
require to undergo
a volumetric change to accommodate the required change in pressure. This
volumetric
change will cause the rush through the valve, and destabilise the system.
A common injection or capillary control line size currently used for chemical
injection is 9.5 mm (3/8") OD tube. Also, many wells are completed with
"deviation"
where the well may be drilled off at progressive angles to increase its reach
from a
central commencement location. Therefore a well may possess a true vertical
depth of,
for example, 2000 metres but in fact be far more in its true deviated or
Measured Depth
(Md).
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The normal internal volume of such a control line can be summarised at varying
measured depths as follows:
Capillary Line Length - metre
Length - m 1000 2000 3000 4000
Volume - L 39.4 78.9 118.3 157.8
Fluids are often considered to be incompressible. This is only true to a
limited
extent and when high pressures are applied to fluids they do compress. This is
a fluid
property that is a function of the compressibility of the fluid which may also
change with
temperature and pressure.
Therefore if the capillary line 40 (Figure 1) is at a given pressure which
then is
required to fall, a volume of fluid must be dissipated in order for this to
occur. This fluid
can only be dissipated through the injection valve 48. No matter how efficient
the
injection valve 48 is at maintaining a differential pressure and tracks a
change in outlet
pressures, the valve will have to dissipate this volume of fluid to
accommodate a
change in capillary line pressure. It has been found the volumes of fluid that
require
dissipation are more than is often thought.
In addition to the compressibility of the fluid, the capillary line 40 itself
will
enlarge under internal pressure. This means its internal volume will increase
thus
requiring more fluid to be introduced in order to reach a required pressure.
Therefore,
in order for the capillary line 40 to fall in pressure the volume of fluid
entrained at its
starting pressure must be fully dissipated in order to reach a lower pressure.
This fluid
volume dissipation therefore results in a significant rise, or surge of flow
through the
injection valve 48 as the capillary line pressure falls.
This may occur as the ESP 37 is brought online causing the ESP inlet pressure
and therefore the valve outlet pressure to fall. As the injection valve 48
attempts to
maintain a fixed differential from its inlet to outlet it allows the increased
flow to occur
through itself. This rise in flow may be very significant and constitute a
flow surge
through the injection valve 48. This has another detrimental effect where the
injection
valve 48 can be overwhelmed and once the flow surge has passed the valve may
fall in
its resistance pressure and struggle to retrieve a fixed value above its
outlet pressure.
In doing this the capillary line 40 must gain in pressure before it can reach
a value to
overcome the valve resistance pressure and continue to flow again.
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The flow may therefore fluctuate, starting with a flow spike followed by a
fall in
flow, a stop in flow and then a slow recovery of flow until flow is normalised
again.
A significant consequence of this is that flow of chemical to the ESP 37 is
not of
a fixed value and is inconsistent. In this respect certain chemicals are used,
called
diluents, to reduce heavy oil viscosity or density to aid in production. A
surge of
chemical or diluent flow may overdose the chemical or diluent resulting in a
lighter fluid
for the ESP 37 to pump followed by a fall in chemical flow which increases
fluid weight
causing a reduction in ESP 37 pumping efficiency.
The ESP 37 therefore is seen to increase flow then suffer a reduction in
efficiency. This is generally illustrated in Figure 7 in which the ESP outlet
pressure 84
is seen to rise as its inlet 82 falls but then suffers a decrease in
efficiency where its
outlet 84 falls again as the inlet 82 rises while the injection valve pressure
86 is seen to
track the ESP inlet pressure 82. This is due to firstly the surge of chemical
or diluent
and then the fall in chemical or diluent flow.
Another effect of this variation in pressures due to the rise and fall of
valve
outlet pressure is that the surface injection pressure 90 (a fixed value above
the valve
outlet pressure by the valve resistance pressure minus the capillary line
hydrostatic
pressure) will also vary which could create loading on surface injection pump
equipment 42.
The consequences of this cycling of load on the ESP 37 is considered to be, as
a minimum, greatly interrupted and inconstant production, greater cycle load
on the
ESP 37 leading to reduced lifetime requiring the well be worked over to
service the
ESP 37, greater monitoring and a lack of understanding about the effectiveness
of the
chemical or diluent input leading to increased chemical or diluent input in
attempts to
counter the problem.
It is also possible that the surge effect through the injection valve 48 could
cause damage to its ability to provide a back pressure. This could lead to a
fall in
resistance ultimately allowing a vacuum to occur in the control line 40 which
itself
creates risk of blockage, corrosion etc.
In view of such issues identified by, the inventor as developed an injection
device which seeks to address these problems. An embodiment of such an
injection
device will now be described with reference to Figure 8.
The injection device, which is generally identified by reference numeral 100
includes a housing 102 defining an inlet 104, outlet 106 and a reference
pressure port
108. The inlet 104 is configured to be in communication with a source of
injection fluid
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110, for example via an injection line (not shown). The outlet 106 is
configured to be in
communication with a target location 112, such as a downhole location. The
reference
pressure port 108 is configured to be in communication with a source of
reference
pressure 114.
The device 100 further includes a first valve member 116 which in the present
embodiment is rigidly secured to the housing 102. A second valve member 118 is
moveably mounted within the housing 102 and defines a flow path 120 extending
therethrough to facilitate fluid communication between the inlet 104 and
outlet 106. As
will be described in further detail below, the second valve member 118 is
permitted to
move in accordance with inlet and reference pressures to vary flow between the
inlet
104 and outlet 106.
The first and second valve members 116, 118 are configured to be engaged
and define a sealed area 122 therebetween, such that when the first and second
valve
members 116, 118 are engaged flow through the flow path 120 is prevented.
However,
when the second valve member 118 is moved the valve members 116, 118 become
disengaged such that flow is permitted. Also, when the first and second valve
members 116, 118 are disengaged the gap defined therebetween may create a flow
restriction and movement of the second valve member 118 may vary this flow
restriction to assist to vary flow of injection fluid through the device 100.
The device 100 further comprises a biasing spring 101, in this case a coil
spring, which acts on the second valve member 118 to bias this in an upward
direction
(relative to the orientation of Figure 8), towards engagement with the first
valve
member 116. Thus, spring 101 effectively operates to bias the second valve
member
118 towards a closed position.
The device 100 further comprises a sealing arrangement 122 which includes
first and second sealing assemblies 124, 126 extending between the second
valve
member 116 and the housing 102. The first sealing assembly 124 provides
isolation
between the inlet 104 and the outlet 106, such that flow between the inlet and
outlet
must be achieved via the flow path 120 in the second valve member 118.
Further, the
second sealing assembly 126 isolates the outlet 106 from the reference
pressure port
108.
The first sealing assembly 124 is exposed to inlet fluid pressure, such that
said
inlet fluid pressure will establish a force on the second valve member 118 in
a
downward direction (relative to the orientation of Figure 8). Further, the
second sealing
assembly 126 is exposed to reference pressure such that said reference
pressure will
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establish a force on the second valve member 118 in an upward direction
(again,
relative to the orientation of Figure 8). Accordingly, a net force will be
applied on the
second valve member 118 by the action of the inlet and reference pressures,
and in
particular in accordance with a pressure differential between the inlet and
outlet
pressures.
In the present embodiment the first and second sealing assemblies 124, 126
define equivalent seal areas, and as such there is no effect on any seal area
differential, although in other embodiments such a seal area differential may
be
provided.
Furthermore, both the first and second sealing assemblies 124, 126 are
exposed to outlet fluid pressure. Also, as the first and second sealing
assemblies 124,
126 define equivalent seal areas then the effect of the outlet pressure will
be cancelled,
and no net force will be created by outlet pressure. It should be noted,
however, that in
other alternative embodiments a seal area differential may be provided to
establish a
bias force generated by outlet pressure.
Accordingly, in the present embodiment the outlet pressure, which will largely
be defined by pressure at the target location 112, will not have any effect on
the
operation of the device 100. This may therefore avoid those problems
identified above
which stem from possible variations in outlet pressure resulting in a sudden
surge
through an injection device.
In use, for flow through the device 100 to be established, the force applied
on
the second valve member 118 by the inlet pressure must exceed to combined
force
applied by the reference pressure and the spring 101. In this way, the inlet
pressure
may be presented at a pressure which is greater than the reference pressure by
the
appropriate equivalent pressure generated by the spring 101, in addition to
any
backpressure created by the restriction to flow between the first and second
valve
members 116, 118.
The device 100 may be used in conjunction with any desired source of
reference pressure 114. In particular, the effects and advantages of the
present
invention may be achieved where the source of reference pressure 114 excludes
the
target location 112.
An alternative embodiment of an injection device, in this case generally
identified by reference numeral 200, is shown in Figure 9, reference to which
is now
made. Device 200 is similar to device 100 of Figure 8, and as such like
features share
like reference numerals, incremented by 100. Further, the operation of the
device 200
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is largely similar to device 100, and as such only the difference in structure
and
operation will be described with reference to device 200.
In this respect device 200 also includes a housing 202 defining an inlet 204,
outlet 206 and reference pressure port 208, with first and second valve
members 216,
5 218 mounted within the housing 202. A sealing arrangement 222 comprising
first and
second sealing assemblies 224, 226 is positioned between the second valve
member
218 and the housing, and functions, as before, to provide a desired force bias
on the
second valve member 218 by action of inlet and reference pressures.
In the present embodiment, however, the first valve member 216 is not rigidly
10 secured to the housing 202, but is instead also permitted to move within
the housing
202. In particular, the first valve member 216 is provided in the form of a
pin which is
mounted on a spring 130 which acts to bias said valve member 216 into
engagement
with the second valve member 218 to close the flow path 220 in said second
valve
member 218. Accordingly, when the first and second valve members 216, 218 are
15 engaged, movement of the second valve member 218, for example by action
of the
various pressures and the second valve member bias spring 201, will also cause
movement of the first valve member 216.
The housing 201 further comprises a limit arrangement in the form of an
annular lip 132, and the second valve member 216 includes a corresponding
20 circumferential rib 134. When the first and second valve members 216,
are engaged,
with the annular lip 132 and circumferential rib 134 disengaged, inlet fluid
pressure will
act over the seal area 222 between the engaged valve members 216, 218, which
will
have the effect of pressing said members together. This arrangement therefore
permits inlet pressure to be utilised to improve the seal between the valve
members
25 when engaged.
However, when the appropriate pressure forces applied at the inlet is
sufficient
to move the second valve member downwardly, the circumferential rib 134 of the
first
valve member 216 will eventually engage the annular lip 132, such that
continued
downward movement of the second valve member 218 will cause disengagement of
30 the valve members, thus establishing flow between the inlet 204 and
outlet 206.
Also shown in the present embodiment is a check valve assembly 136 located
at the outlet 206 of the housing, and which functions to prevent backflow from
the
target location 212 into the device. Although the check valve assembly 136 is
shown
mounted in an integrated part of the housing 202, a separate check valve
assembly
may instead be provided and secured relative to the outlet 206 of the housing
202.
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As defined above, it is possible to use any desired source of reference
pressure, perhaps with the exception of pressure at the target location. For
example,
in one exemplary use, the injection device may be used in the wellbore
completion
arrangement 10 first shown in Figure 1, reference to which is again made,
wherein the
injection valve 48 in Figure 1 may be replaced with the device according to
any
embodiment of the invention. In such an exemplary use the target location is
on the
inlet or suction side of an ESP 37. As noted above, problems have been
discovered in
prior art systems which also use this target location to vary the pressure
within the
associated injection line 40. However, in the present exemplary use the
reference
pressure may be provided from the outlet or delivery side of the ESP. A
graphical
representation of the various pressure profiles associated with such an
exemplary use
of the present invention is illustrated in Figure 10.
As illustrated, when a pump (where use) such as an ESP is activated the inlet
pressure 140 will fall, and the outlet pressure 141 will rise. As the device
utilises this
outlet pressure 141 as a reference pressure, this results in the inlet
pressure 143 of the
device defines the same pressure profile, albeit at a differential higher
provided by the
effect of the spring acting against the second valve member in addition to the
effect of
any back pressure created by flow through the device. As illustrated also in
Figure 10,
the pressure differential 146 between the inlet and outlet of the device is no
longer
fixed, which differs from the prior art. Also, the surface pressure 146
defines a similar
profile to that of the pump outlet pressure 142. As is clear from Figure 10,
the pump is
considered to reach a desired steady state condition, without any problems
occurring
due to cascading of fluid through the device.
In an alternative exemplary use, the device may be arranged such that the
reference pressure is provided from a source, for example at surface level,
which
permits the reference pressure to be varied. The associated pressure profiles
of an
associated ESP and of the device is illustrated in Figure 11. In this respect,
when the
pump is activated the inlet pressure 150 falls. At this stage the reference
pressure 151
is fixed at a first value, and as such the inlet pressure 152 of the device is
initially
constant at a first value, which will be a fixed differential above reference
pressure 151.
If at some point a change in reference pressure is required, for example due
to a
change in density of injection fluid, then this may be readily achieved,
irrespective of
the pump inlet pressure. In the exemplary embodiment the change involves an
increase in reference pressure 151 (initiated around time interval 6), such
that the inlet
pressure 152 is seen to increase to a second, higher level.
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A further alternative embodiment of an injection device, in this case
generally
identified by reference numeral 300, is shown in Figure 12. Device 300 is
similar to
device 200 shown in Figure 9, and as such like features share like reference
numerals,
incremented by 100. For brevity, only differences between the embodiments in
Figures
9 and 12 will be highlighted. In this respect, device 300 includes bellows
type first and
second sealing assemblies 324, 326 which form the sealing arrangement.
Further, the
device 300 comprises an integrated reference pressure reservoir 160 which
contains
an internal reference pressure which acts at the reference port 308. Thus, the
second
valve member 318 is affected by the pressure within this reservoir 160.
Further, the second valve member 318 includes a lower pin 142 which engages
a plate 144, which in turn is acted on by the bias spring 301, which in this
case is a disk
spring, mounted within the reservoir 160.
In this present embodiment the device 300 does not necessarily require the
presence of any external source of reference pressure, which may provide
significant
advantages in terms of permitting a simplified system to be utilised.
Furthermore, in
certain cases the pressure within the reservoir may define a minimal pressure,
such
that the effect of any active pressure is essentially negligible, such that
any force
applied to move the second valve member 318 upwardly is achieve primarily by
the
spring 301.
A pressure plot associated with the device 300 of Figure 12 is shown in Figure
13, in this case again assuming that the device is arranged to inject a fluid
into the inlet
side of an ESP, such as ESP 37 of Figure 1. Referring to Figure 13, as a pump
(where
used) such as an ESP is activated pump inlet pressure 162 falls. However, as
the
reference pressure within reservoir 160 is constant, a constant valve inlet
pressure 164
and surface pressure 166 will be achieved, with the pressure differential 168
between
the device inlet 304 and outlet 306 varying.
An injection device according to the present invention may be embodied in a
number of ways, and a selection of further example embodiments are presented
in
Figures 14 to 18, reference to which will now be made. For brevity only
particular
differences between the embodiments will be identified.
Injection device 400 of Figure 14 is generally similar to device 200 of Figure
9,
and as such like features share like reference numerals, incremented by 200.
Device
400 includes bellows type sealing assemblies 424, 426 which form the sealing
arrangement 422.
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Injection device 500 of Figure 15 is generally similar to device 200 of Figure
9,
and as such like features share like reference numerals, incremented by 300.
Device
500 includes bellows sealing assemblies 524, 526 which form the sealing
arrangement
522. Further, the second valve member 516 includes an extension pin 170 which
is
engaged by a plate 172 which in turn is engaged by bias spring 501.
Injection device 600 of Figure 16 is generally similar to device 200 of Figure
9 ,
and as such like features share like reference numerals, incremented by 400.
Device
600 includes bellows sealing assemblies 624, 626 which form the sealing
arrangement
622. Further, the second valve member 616 includes an extension pin 174 which
is
engaged by a plate 176 which in turn is engaged by bias spring 601.
Furthermore, the second valve member 616 includes a ball member which
cooperates with the second valve member 618. A support stalk 178 extends
through
the flow path 620 of the second valve member 618 and functions to limit
movement of
the ball of the first valve member 616.
Injection device 700 of Figure 17 is generally similar to device 300 of Figure
12,
and as such like features share like reference numerals, incremented by 400.
In this
embodiment the first valve member 716 includes a profiled pin 180 which
extends
upwardly therefrom and is received within an annular chamber 182. the pin 180
and
chamber 182 cooperate to limit movement of the second valve member 716 to
permit
disengagement from the second valve member 718.
Injection device 800 of Figure 18 is generally similar to device 300 of Figure
12,
and as such like features share like reference numerals, incremented by 500.
In
device 800 the outlet 806 is provided inline with the inlet 804. This is
achieved by
providing a flow path 186 around the reservoir chamber 660. Further, device
800
includes a check valve assembly 190 in communication with the outlet 806.
In some cases the required differential resistance pressure required where an
ESP is set to a very high Total Vertical Depth (TVD) and the ESP will draw to
extremely
low pressures may be very high. This is by way of a capillary line hydrostatic
being
large due to the great depth (TVD) and the ESP drawing to an exceptionally low
pressure for the purposes of enhanced production, for example. In such cases
the fluid
being injected may have behavioural problems when passed over the injection
device
at a high differential pressure. Such problems may include cavitation,
depositing of
solids or a change in the state of the injection fluid which may lead to
reduced
effectiveness, such as chemical effectiveness.
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The present inventor therefore considers it to be desirable that in some
situations a differential pressure be reduced to levels that are under the
thresholds
where such issues may occur with the injection fluid. This reduction in
differential
pressure, however, may not be readily achieved in conventional prior art
systems as
the requirement still exists that the overall resistance within the injection
device must
be large enough to ensure there is no vacuum in the capillary injection line.
To address this, an injection device according to the present invention (such
as
in any embodiment described above) may be installed at a lower point of
injection but
in addition to this a second (or third etc.) injection valve may be installed
at a higher
point in the injection line, for example at any higher point in the injection
line. Such an
arrangement is illustrated in Figure 19, reference to which is now made. In
this
respect, Figure 19 provides a diagrammatic illustration of a wellbore system,
generally
identified by reference numeral 910, which includes injection capabilities and
is largely
similar to the system 10 of Figure 1. As such, like features share like
reference
numerals incremented by 900. Thus, wellbore system 910 includes a casing
string 912
located within a drilled bore 914 which extends from surface 916 to intercept
a
hydrocarbon bearing formation 918. A lower annulus area 920 may be filled with
cement 922 for purposes of support and sealing. A production tubing string 924
extends from a wellhead 926 and production tree 928. A lower end of the
production
tubing string 924 is sealed against the casing 912 with a production packer
930 to
isolate a producing zone 932. A number of perforations 934 are established
through
the casing 912 and cement 922 to establish fluid communication between the
casing
912 and the formation 918. Hydrocarbons may then be permitted to flow into the
casing 912 at the producing zone 932 and then into the production tubing 924
via inlet
936 to be produced to surface. Artificial lift equipment, such as an ESP 937
may
optionally be installed inline with the production tubing 924 as part of the
completion to
assist production to surface. The production tree 928 may provide the
necessary
pressure barriers and provides a production outlet 938 from which produced
hydrocarbons may be delivered to a production facility (not shown), for
example.
A small bore injection line or conduit 940, which is often referred to as a
capillary line, runs alongside the production tubing 924 from a surface
located injection
fluid source 942 to a downhole target location, which in the illustrated
example is a
lower end of the production tubing 924, below the ESP 937. The production
tubing 924
may include an optional injection mandrel 944. An injection pump 946 is
located at a
topside location to facilitate injection of the injection fluid 942.
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A first injection valve 948 is located at the lower end of the injection line
940 in
proximity to the location of injection. This injection valve 948 may be
provided in
accordance with any embodiment of the present invention. A second injection
valve
949 is coupled to the injection line 940 at a location which is upstream of
the first
5 injection
valve 948. The second injection valve 949 may be provided in accordance
with any embodiment of the present invention. The second injection valve 949
may be
provided in accordance with any known or conventional injection valve, such as
a
conventional backpressure injection valve which may modify its inlet pressure
based on
its outlet pressure.
10 With the
example arrangement shown in Figure 19, the overall required
differential pressure may be broken into two stages, thus ensuring that the
differential
pressure occurring at any one of the injection valves 948, 949 is reduced
ensuring the
injection fluid is not subjected to high shear rates through the device under
high
differential pressures.
15 This
installation mode may be generally illustrated in the below example where
a very high setting depth (TVD) is required for the ESP 937 which is intended
to run at
a very low intake pressure. The injection line 940 is installed with a
conventional back
pressure injection device (the second injection device 949) at approximately
50% of its
TVD and an injection device (the first injection device 948) at the ESP intake
depth (full
20 TVD). If
a single back pressure device is used it would be required to have a minimum
back pressure resistance of 314 bar. However, if we assume in the present
illustration
that the injection fluid has been found to suffer degradation of properties if
passed
through a differential of more than 180 bar, then this required pressure
differential of
314 bar will have an adverse effect on the injection fluid. Therefore two
stages are
25 employed with an upper device 949 and a lower device 948.
A process of designing or selecting the from of an appropriate injection
system
in the present illustration is set out in the table below:
35
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Total Vertical Capillary Line Height (TVD) ¨ metres 3050
Determine Capillary Hydrostatic Pressure
Specific Gravity of Injected Fluid 1.050
Density of Fluid - kg/m3 1050.00
TOTAL Capillary Line Hydrostatic pressure - bar 314.2
Identify Chemical Differential Limitations
Maximum Allowable Differential - bar 180.0
Is Allowable Dp greater than required Dp ? NO
Required Stages of Resistance 2
Determine Upper and Lower Stage Conditions
Minimum ESP Inlet Pressure ¨ bar 86.0
Lower Device Resistance Pressure - bar 150.0
Lower Device Inlet Pressure ¨ bar 236.0
Installation Depth of Upper Stage (TVD) - metre 1480.0
% of Overall TVD for Installation of Upper Stage - % 49%
Capillary line height from lower to upper stage (TVD) - m 1570.0
Hydrostatic Pressure in line from lower to upper Stage - bar 161.8
Upper Stage Device outlet Pressure - bar 74.2
Upper Device Resistance Pressure - bar 100.0
Upper Device Inlet Pressure ¨ bar 174.2
Hydrostatic Pressure in line from upper Stage to Surface - bar 152.5
Surface Injection Pressure - bar 21.8
Although in the example above the upper device is located at approximately
50% of the TVD, this is only exemplary, and any suitable depth may be
utilised. This is
illustrated in the further example below, in which the upper device is located
at an
further example depth of 71% of TVD.
Determine Upper and Lower Stage Conditions
Minimum ESP Inlet Pressure - bar 86.0
Lower Device Resistance Pressure - bar 150.0
Lower Device Inlet Pressure - bar 236.0
Installation Depth of Upper Stage (TVD) - metre 2180.0
% of Overall TVD for Installation of Upper Stage - % 71%
Capillary line height from lower to upper stage (TVD) - m 870.0
Hydrostatic Pressure in line from lower to upper Stage - bar 89.6
Upper Stage Device outlet Pressure - bar 146.4
Upper Device Resistance Pressure - bar 100.0
Upper Device Inlet Pressure - bar 246.4
Hydrostatic Pressure in line from upper Stage to Surface - bar 224.6
Surface Injection Pressure¨bar 21.8
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Therefore by using two stages (upper and lower) each with appropriate
differential settings of 100 and 150 bar respectively, the overall resistance
is provided
and the full injection line is maintained in a positive pressure thus avoiding
vacuum fall
out conditions and ensuring the injection fluid is passed through differential
pressures
beneath its property change threshold of 180 bar.
The first example provided above may be further illustrated in Figure 20,
which
is a pressure plot along the length of the injection line showing the
individual pressure
drop effect of the first and second injection devices 948, 949.
It should be understood that the embodiments described herein are merely
exemplary and that various modifications may be made thereto without departing
from
the scope of the invention. For example, various embodiments have been
described
above, and it should be recognised that further embodiments are possible in
which the
features of some of the illustrated embodiments may be applied to others.
Thus, any
combination of the illustrated features may be possible.
Further, in the example of Figure 19, any number of injection devices may be
utilised to provide the desired stages of pressure drop along the length of
the injection
line.
