Note: Descriptions are shown in the official language in which they were submitted.
CA 02592918 2008-08-13
52941-6(S)
SYSTEM AND METHOD FOR BLEEDING OFF PRESSURE FOLLOWING
SERVICING OF A WELL
BACKGROUND OF THE INVENTION
[0001] A variety of well treatments are conducted when
servicing wells to improve productivity. For example, well
fracturing treatments are conducted in which fracturing
fluid is pumped downhole under pressure. Upon completion of
the well treatment, the fluid is removed from the well.
However, the fluid still may be under substantial pressure
which must be bled off. In some applications, flare pits or
testers can be used to bleed off the trapped pressure. In
other environments and applications, however, iio flare pits
nr tPsters are available.
[0002] In the latter scenario, a vacuum truck typically is
connected to the high pressure iron, e.g. surface treating
lines, and the trapped pressure is allowed to slowly bleed
off. However, the vacuum truck and vacuum hoses do not
provide optimal control over release of this excess
pressure.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the present invention,
there is provided a system to bleed off pressure,
comprising: a tubing deployed in a wellbore; a vacuum truck
to remove fluid from the wellbore during cleaning of the
wellbore following a well treatment; a fluid transfer
conduit to transfer fluid from the tubing in the wellbore to
the vacuum truck; and a bleed-off mechanism coupled to the
fluid transfer conduit, the bleed-off mechanism comprising a
vent open to atmosphere to relieve pressure and a separator
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52941-6(S)
body able to prevent loss of liquid during venting of
pressure from the fluid transfer conduit.
According to another aspect of the present
invention, there is provided a method of bleeding off
pressure, comprising: mounting a bleed-off mechanism in
fluid communication with the flow path between a wellhead
and a vacuum truck; applying suction with the vacuum truck;
opening a valve of the bleed-off mechanism to enable venting
of fluid under excess pressure through the bleed-off
mechanism; containing any liquid escaping to the bleed-off
mechanism; and cleaning out fluid from the flow path via the
vacuum truck.
According to another aspect of the present
invention, there is provided a method, comprising:
connecting a vacuum truck to a well via a bleed-off
mechanism; removing excess pressure from the well via the
bleed-off mechanism connected in line with a fluid flow path
from the well to the vacuum truck; and drawing fluid from
the well into the vacuum truck without exposing the vacuum
truck to the excess pressure.
According to another aspect of the present
invention, there is provided a system, comprising: a well
having a wellhead valve; a fluid transfer conduit located at
a surface location and coupled in fluid communication with
the wellhead valve; a manifold connected to the fluid
transfer conduit; and a bleed-off mechanism coupled to the
manifold to relieve excess pressure from the fluid transfer
conduit prior to cleanout of fluid with a vacuum truck.
[0003] In general, some embodiments of the present
invention provides a system and a method for providing a
bleed-off mechanism in fluid communication with a flow path
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CA 02592918 2008-08-13
52941-6 (S)
extending from the wellbore and designed for connection with
a vacuum truck. The bleed-off inechanism can be opened to
enable release of pressure by venting fluid that is under
excess pressure within the wellbore and/or flow path. The
bleed-off mechanism is also designed to contain any liquid
that escapes to the bleed-off inechanism. Once the trapped
pressure is relieved, the well service fluid in the wellbore
and/or flow path can be cleaned out via the vacuum truck.
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CA 02592918 2007-07-20
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Certain embodiments of the invention will hereafter be described with
reference to the accompanying drawings, wherein like reference numerals denote
like
elements, and:
[0005] Figure 1 is a flow chart illustrating a method for breaking the
containment
between a high pressure wellbore and/or flow path and a low pressure vacuum
truck,
according to an embodiment of the present invention;
[0006] Figure 2 is a schematic illustration of a system utilizing a bleed-off
mechanism, according to an embodiment of the present invention; and
[0007] Figure 3 is an enlarged view of the bleed-off mechanism illustrated in
Figure 2, according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] In the following description, numerous details are set forth to provide
an
understanding of the present invention. However, it will be understood by
those of
ordinary skill in the art that the present invention may be practiced without
these details
and that numerous variations or modifications from the described embodiments
may be
possible.
[0009] The present invention relates to a system and method for breaking the
containment between high pressure iron, e.g. surface treating lines, and a low
pressure
vacuum truck when removing well treatment fluid from a wellbore. Following a
well
treatment process, such as a fracturing process, well treatment fluids remain
in the
surface treating lines and must be removed. In many well treatment operations,
however,
the well treatment fluid is delivered downhole under substantial pressure and
this
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CA 02592918 2007-07-20
pressure may be retained. The present system and method enables the bleeding
off of this
retained pressure to atmosphere via a bleed-off mechanism. Simultaneously, the
bleed-
off mechanism can be used to contain any liquids expelled while venting the
excess
pressure to atmosphere. The contained liquid is removed to an appropriate
containment
vessel, such as a vacuum truck. Once the excess pressure is relieved, the
vacuum truck
can be used to complete the removal of well treatment fluid from the surface
treating
lines. By way of example, the vacuum truck can be coupled to a manifold
positioned in
the flow path along which fluid flows from the well to the vacuum truck.
[0010] One approach for breaking the containment between the well and the
vacuum truck by venting any excess pressure is illustrated by the flow chart
of Figure 1.
As illustrated, a flow path is provided from the well to a vacuum truck or
other
containment vessel, as illustrated by block 20. The flow path may be created
by surface
piping that is coupled to the high pressure tubing within the wellbore. The
high pressure
tubing within the wellbore may comprise coiled tubing, jointed tubing, casing,
or other
types of tubing deployed in the wellbore and used to conduct fluid flow for a
given well
servicing operation.
[0011] The method also comprises connecting a bleed-off mechanism in fluid
communication with the flow path, as illustrated by block 22. As discussed in
greater
detail below, the bleed-off mechanism can be connected in line with the flow
path by
coupling the mechanism to the surface piping via an appropriate manifold. Use
of the
manifold is one way of enabling selective collection of liquid by the vacuum
truck during
both the venting process and the process of removing the remaining fluid from
the
wellbore and/or flow path following the venting process. As illustrated in
block 24, any
excess pressure within the surface treating lines can be vented through the
bleed-off
mechanism in a controlled manner.
[0012] Simultaneously, the bleed-off mechanism can be used to fully contain
any
liquid escaping during the venting process, as illustrated by block 26. For
example, the
release of excess pressure from the surface treating lines can result in the
expulsion of
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CA 02592918 2007-07-20
both gas and liquid through the surface piping and into the bleed-off
mechanism. The
liquid expelled under high pressure often has substantial velocity and energy
which is
dissipated by the bleed-off mechanism while the liquid is contained by the
bleed-off
mechanism once the energy is dissipated.
[0013] The contained liquid can be removed from the bleed-off mechanism and
delivered to an appropriate containment vessel, as illustrated by block 28.
The
containment vessel can be the vacuum truck utilized in removing fluid from the
wellbore.
For example, the vacuum truck can be connected to the bleed-off mechanism, and
vacuum can be applied to remove the liquid expelled into the bleed-off
mechanism
during the venting process.
100141 Upon venting of the excess pressure from the surface treating lines,
the
vacuum truck is connected in a manner that enables the cleaning out of fluid
from the
well and/or surface treating lines, as illustrated by block 30. In one
example, the bleed-
off mechanism is closed off from the surface piping, and the surface piping is
used to
direct the flow of fluid to the vacuum truck. Although this procedure can be
accomplished in a variety of ways, one method involves closing off the bleed-
off
mechanism with a valve and moving a vacuum hose from the bleed-off mechanism
to an
appropriate port on the manifold. The vacuum truck can then be used to apply a
vacuum
via the vacuum hose and to remove the well servicing fluid from the wellbore
and/or
surface piping.
[0015] Referring generally to Figure 2, one example of a well servicing system
32
is illustrated. In this embodiment, a we1134 is serviced by pumping a well
service fluid
downhole into a wellbore 36. The fluid is pumped downhole by a suitable pump
38 that
may be positioned at a surface location to deliver the fluid through a conduit
40, e.g.
piping, and a wellhead valve 41 in the direction indicated by arrows 42. By
way of
example, the well service fluid may comprise a fracturing fluid pumped
downhole under
pressure via a tubing 44 to fracture a surrounding formation 45. Tubing 44 may
comprise
a service string used to deliver the fracturing fluid to a desired region
within wellbore 36.
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However, a variety of other well servicing operations can be performed, and
other types
of fluid may be pumped downhole to facilitate a particular well servicing
operation. The
pressure of the well servicing fluid may be measured by one or more pressure
sensors 46.
[0016] Upon completion of the fracturing or other well servicing operation,
the
well service fluid is removed into a vacuum truck 48. However, before exposing
vacuum
truck 48 to the potential pressures of the well servicing fluid utilized in
wellbore 36, the
excess pressure is vented. As illustrated by arrows 50, a flow path is created
between the
wellhead valve 41, which is normally closed to isolate tubing 44, and vacuum
truck 48.
In this example, conduit 40 can be used, at least in part, to create flow path
50 with fluid
flow moving in a direction opposite to the flow of fluid through conduit 40
during the
fracturing or other well servicing operation.
[0017] A bleed-off mechanism 52 is connected in fluid communication with flow
path 50. For example, bleed-off mechanism 52 may be connected to conduit 40
via a
manifold 54. However, other types of flow conduits and connection mechanisms
can be
utilized in coupling bleed-off mechanism 52 in line with flow path 50. Bleed-
off
mechanism 52 is able to relieve excess pressure within conduit 40, tubing 44,
and
wellbore 36 by venting the excess pressure to atmosphere while containing any
liquid
that moves into bleed-off mechanism 52 during the venting process. Although it
is not
intended to routinely bleed off wellbore pressure, it is possible to do so
with the
equipment of the present invention. The liquid that moves into bleed-off
mechanism 52
can be removed to an appropriate containment vessel 56. In the example
illustrated,
containment vessel 56 is vacuum truck 48 connected to bleed-off mechanism 52
by, for
example, an appropriate vacuum hose 58. Once the venting operation is
completed, the
vacuum hose 58 can be reconnected at an appropriate location, e.g. manifold
54, to
continue the removal of fluid from conduit 40 and, if desired, tubing 44 and
wellbore 36.
The repositioned vacuum hose 58 is illustrated as a dashed line in Figure 2.
[0018] With additional reference to the enlarged view found in Figure 3, one
embodiment of the bleed-off mechanism 52 is illustrated. In this embodiment,
bleed-off
CA 02592918 2007-07-20
mechanism 52 comprises a connection region 60 by which bleed-off mechanism 52
and
manifold 54 may be connected. The flow of fluid into bleed-off mechanism 52
during
venting of pressure from conduit 40 and, potentially, tubing 44 and wellbore
36, may be
controlled via one or more bleed valves 61 that control flow along a conduit
62 that leads
to a vent 64. In the example illustrated, conduit 62 comprises a pipe, and
vent 64
comprises one or more openings formed through a side wall of the pipe 62.
Conduit or
pipe 62 is terminated at a cap 66 that blocks further flow along conduit 62 to
thereby
direct the flow of fluid and release of pressure through the vent 64.
[0019] The energy and velocity of the fluid exiting vent 64 is dissipated by a
blocking member 68. In the embodiment illustrated, blocking member 68
comprises a
shroud 70 positioned around the region of conduit 62 having vent openings 64.
Accordingly, the high pressure fluid exiting vent 64 is directed against the
inside surface
of shroud 70 which dissipates the energy and velocity of the fluid. Any liquid
exiting
vent 64 under sufficient pressure is blocked by shroud 70 and simply drops
into the
bottom of a separator body 72. In the example illustrated, separator body 72
is open to
atmosphere by virtue of, for example, an open top 74 that enables the venting
of conduit
40 and, potentially, well 34, to atmosphere without loss or spillage of any
liquid. The
separator body 72 also may comprise a sloped bottom 76 that is oriented to
have an
incline directing contained liquid to an appropriate fitting 78. Fitting 78 is
designed for
coupling with an appropriate conduit to deliver the collected liquid to a
proper
containment vessel. For example, fitting 78 may be designed for coupling with
vacuum
hose 58 such that vacuum truck 48 can be used to apply a vacuum and remove the
contained liquid from separator body 72. Accordingly, the flow path 50 extends
to bleed-
off mechanism 52, where any excess pressure is vented to atmosphere, and then
continues to vacuum truck 48.
[0020] When a well treatment is completed and it is necessary to remove
servicing fluid from the surface treating lines (conduit 40), the excess
pressure is initially
removed via bleed-off mechanism 52. In one operational embodiment, vacuum
truck 48
or another containment vessel is connected to the fitting 78. A vacuum is then
applied
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via, for example, vacuum truck 48 which creates suction at fitting 78. The
bleed valve or
valves 61 are then slowly opened to bleed any trapped pressure/fluid into
separator body
72. The fluid released into separator body 72 typically comprises a liquid/gas
mixture.
[0021] The trapped pressure is released upwardly through valves 61 along
conduit
62 until stopped by high pressure cap 66 which directs the pressure release
through vent
64. The high pressure gas and/or liquid is directed outwardly against blocking
member
68, e.g. shroud 70, which dissipates the velocity and thus the energy of the
high pressure
fluid. The fluid then drops downwardly from shroud 70 toward the bottom of
separator
body 72. The gas phase is vented to atmosphere as it moves out of the
separator body
through, for example, open top 74. The liquid phase drops to the bottom of
separator
body 72 and is directed by the force of gravity to fitting 78. The suction
applied to fitting
78 via vacuum hose 58 removes the liquid from the interior of separator body
72 and
directs it into the appropriate containment vessel 56.
[0022] Once the pressure is bled off and the liquid is removed from the bleed-
off
mechanism 52, the remaining fluid can be safely removed from conduit 40 and,
if
necessary, tubing 44 and wellbore 36. According to one embodiment, vacuum hose
58 is
simply moved from fitting 78 to an appropriate coupling on manifold 54 below
bleed
valves 61. Because the surface treating lines no longer contain excess
pressure, the well
servicing fluid can be cleaned out via vacuum truck 48. If all excess pressure
has been
removed from conduit 40, the bleed valves 61 can be returned to a closed
position. In
other embodiments, separate vacuum hoses 58 can be connected to an appropriate
valve
or manifold to eliminate the need to move a single vacuum hose from fitting 78
to
manifold 54. Additionally, other types of manifolds, conduits, valving, and
fluid flow
control structures can be utilized in removing liquid from bleed-off mechanism
52 and
from conduit 40 and wellbore 36.
[0023] Following removal of the well treatment fluid, the bleed-off mechanism
52 and manifold 54 can be reset to a pumping configuration to enable
performance of
another well treatment operation. Upon completion of the subsequent well
treatment
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operation, the bleed-off mechanism 52 can again be used to relieve excess
trapped
pressure before conducting a cleanout procedure. By utilizing bleed-off
mechanism 52,
all pressure is contained within conduits, e.g. piping, designed to withstand
the high
pressures that may be retained from the well treatment operation. Furthermore,
the
bleed-off mechanism 52 fully contains vented liquids to avoid any
environmental issues
without increasing the time associated with a given well treatment operation.
[0024] The system illustrated and described above can be utilized with a
variety
of well treatment operations and cleanout procedures. Additionally, the bleed-
off
mechanism can be constructed with additional or alternate components and with
components of different sizes depending on the environment and specific
application.
Furthermore, a variety of manifolds, vacuum sources, and containment vessels
can be
incorporated into the overall system and method.
[0025] Accordingly, although only a few embodiments of the present invention
have been described in detail above, those of ordinary skill in the art will
readily
appreciate that many modifications are possible without materially departing
from the
teachings of this invention. Such modifications are intended to be included
within the
scope of this invention as defined in the claims.
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