Note: Descriptions are shown in the official language in which they were submitted.
CA 02736736 2011-04-08
DOWNHOLE SEPARATOR
FIELD OF THE INVENTION
The present invention relates to a downhole tool used to separate sand and
similar solid particles
from a fluid stream before the fluid is pumped to the surface. This invention
may also involve a gas
separator to separate gas from liquids.
BACKGROUND OF THE INVENTION
Various types of pumping systems have been devised to pump fluid from a
downhole formation
to the surface. Solid particles, such as sand, and/or gas bubbles may
significantly detract from the
efficiency of the pump, and may lead to pump damage. Various types of
desanders and gas separators
have been devised for removing sand or gas from downhole fluids before
entering the pump.
U.S. Pat. No. 6,234,248 discloses well production apparatus which includes a
gas fluid separator
in the casing of the well. A fluids composition sensor and transmitter are
also provided. U.S. Pat. No.
6,723,158 discloses another type of gas separator with a single large gas exit
port and a single large fluid
inlet. U.S. Pat. No. 6,322,331 discloses a system with a centrifugal pump
driven by a motor. The bypass
tube is used for workovers and does not require pulling the tubing. U.S. Pat.
No. 6,277,286 discloses a
system for separating lower density fluids from a higher density fluid. The
separated fluids are removed
through separate outlets. U.S. Pat. No. 5,314,018 discloses a desander which
includes a spiral guide such
that helical motion is imparted to the well fluids and solid particles settle
downwardly within the vortex
chamber.
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The disadvantages of the prior art are overcome by the present invention,
which discloses an
improved downhole desander and method of operating a desander. An improved gas
separator and
method of operating a gas separator are also disclosed.
SUMMARY OF THE INVENTION
In one embodiment, a desander for positioning downhole to separate fluid from
other components
prior to pumping the fluid to the surface includes a generally tubular
desander body for connection to a
production tubing string, with the desander body having one or more fluid
inlets positioned
circumferentially about the desander body. The generally sleeve-shaped vortex
body is positioned within
a desander body, with the vortex body extending from above the plurality of
fluid inlets to below the
plurality of fluid inlets. The vortex body has one or more tangential inlet
ports spaced circumferentially
about the vortex body for imparting a vortex flow to the fluid entering the
vortex body. The vortex body
extends axially from above the inlet ports to a generally conical vortex body
interior surface with a
reduced cross-sectional flow area compared to a cross-sectional flow area
adjacent the inlet ports. A lower
end of the vortex body has a discharge port, such that solid particles pass
through the discharge port in the
lower end of the vortex body. The formation fluids flow upward through an
upper end of the vortex body
and into the production tubing string. In one embodiment, a seal supported on
the desander body seals
between an exterior surface of the desander body and an interior surface of a
downhole casing. Multiple
vortex bodies may be positioned in parallel within the tubular desander body.
In another embodiment, a downhole gas separator is provided for separating gas
from downhole
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formation fluids prior to pumping the formation fluids down to the desander
then up to the surface. The
gas separator includes a generally tubular body having a fluid inlet. In one
embodiment, an elongate tube
has a lower end in fluid communication with the annulus below the seal and an
upper end for exhausting
gas to a reduced pressure region less than pressure at the lower end of the
tube.
These and further features and advantages of the present invention will become
apparent from the
following detailed description, wherein reference is made to the figures in
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates one embodiment of a desander.
FIG. 2 is a pictorial view of the inner vortex body generally shown in FIG. 1.
FIG. 3 is a cross-sectional view through tangential inlet ports in the vortex
body.
FIG. 4 illustrates another embodiment of a desander with a inlet strainer and
a mud anchor.
FIG. 5 is a pictorial view of another embodiment of a desander with a seal for
sealing with a casing.
FIG. 6 illustrates yet another embodiment of the invention with a gas
separator positioned above a
desander.
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FIG. 7 illustrates another embodiment of the gas separator and desander.
FIG. 8 illustrates a desander with multiple vortex tubes positioned within an
outer body.
FIG. 9 is a cross-sectional view illustrating the position of the vortex tubes
shown in FIG. 8.
FIG. 10 depicts another embodiment of a desander below an ESP.
FIG. 11 depicts a desander with the ESP positioned within a shroud.
FIG. 12 depicts a desander with a lower perforated nipple.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates a desander 10 which comprises outer desander body 16 and
coupling 14 for
interconnecting a pup joint with the desander body 16 and an inner vortex body
39. The desander body 16
includes the plurality of circumferentially spaced fluid inlets 18. The upper
end of the desander body is
adapted for connection to the pup joint, or may be directly connected to a
production tubing string.
Body 16 is threaded at its upper end for interconnection with the coupling 14,
and is threaded at
its lower end for interconnection with coupling 22. An annular gap 34 exists
between an interior of the
body 16 and exterior of the vortex body 39. Flow enters through fluid inlets
18 and flows upward through
the one or more ports 36 in the vortex body 39. End port 36 may have a
generally rectilinear configuration
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for high flow rates and sound structural integrity for the vortex body. Solids
are forced radially outward
within the vortex body and fall into the mud anchor, while liquids flow upward
and through upper port
29. The body 39 has a frustoconical inner surface 40, which when combined with
the tangential ports 36,
produces a vortex flow in the vortex body. Threaded member 30 has a central
fluid outlet 31, and is
threaded to the lower end of the body 16. Solid particles pass through the
discharge port 31, and
formation fluids flow upward through the port 29 and into the production
tubing string. The vortex body
39 may be centered in the body 38 by lower flange 38, which may engage an
interior surface of body 16.
An upper retainer 37 with port 29 therein similarly centers the upper portion
of vortex body 39 within the
tubular outer body 16.
For the embodiment shown in FIGS. 1, 2, and 3, the inlet ports 18 in the
desander body may pass
fluid inwardly from the casing annulus into the vortex body in substantially a
radial direction. FIG. 2 is a
pictorial view of the vortex body shown in FIG. 1. As shown in FIG. 3, each of
the plurality of fluid inlets
36 in the vortex body 39 has a central axis 35 substantially parallel to and
adjacent the interior surface of
the vortex body, thereby imparting a substantially tangential flow to fluid
entering the vortex tube or
body. The FIG. 3 embodiment includes four circumferentially spaced inlet ports
36 each positioned about
the vortex body 39.
FIG. 4 discloses another variation of a suitable desander tool 10, wherein a
filter or strainer 42
having a generally sleeve-shaped configuration is positioned about the ports
18 for filtering large solids
from the fluid before entering the interior of the tool. FIG. 4 further
illustrates a mud anchor 44 with a
lower plug 46 for collecting solids which pass downward through the vortex
body 39.
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FIG. 5 illustrates another embodiment of a desander 10. A cup shaped seal body
20 may be
preferred for some applications, with the seal preferably providing a
generally frustoconical configuration
with an apex below the seal. Fluid pressure above the seal thus tends to force
the edges of the cup seal 20
radially outward and into sealing engagement with the interior of the casing.
The seal 20 may be
positioned close to but below the inlets 18 to minimize the likelihood of
solids piling up above the seal
and sticking the desander in the well. Sand that flows down the casing annulus
will thus flow into the
desander with the liquid.
Still referring to FIG. 5, the generally sleeve-shaped vortex body 39 (not
shown) is positioned
within the body 16, and has a central axis generally aligned with the central
axis of the desander body, as
shown in FIG. 1. A cup-shaped packer 20 is run below the casing perforations.
The desander 10 as shown
in FIG. 5 is particularly suitable for positioning in a well below the casing
perforation. Other downhole
equipment, such as a pump anchor, may be suspended below the desander body 16,
as explained below. A
mud anchor may not be needed, but if used may be positioned below the desander
for receiving solid
particles. A mud anchor minimizes the danger of sticking since the sand will
not surround the mud
anchor.
A significant advantage of the desander arrangement as disclosed herein is
that an unintended
circumferential cut in the vortex tube or body allows all the components to be
retrieved to the surface with
the undamaged body 16. The risk that components of the desander might drop in
the well if sand cuts the
vortex tube is substantially reduced or eliminated. The vortex body 39 thus
protects the larger diameter,
more expensive outer body 16 from destruction and abrasive wear. If the vortex
body is cut by sand or
otherwise destroyed, the cutting action stops before the outer body 16 is
damaged. If this occurs, sand will
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no longer be stopped from passing upward through port 29 as shown in FIG. 1,
but the destroyed parts
will not plug the liquid flow to a downhole pump.
Referring now to FIG. 6, a downhole separator for use with an electrical
submersible pump is
shown consisting of a desander 10 as discussed above, with seal 20 sealing
between the casing and the
desander body 16. Coupling 70 interconnects the desander 10 to production
tubing 12, which is coupled
to body 62 of a gas separator unit 60, which carries the seal 24 which
similarly seals between the casing
and the body 62. Fluids from the producing formation conventionally enter the
interior of the casing (not
shown) through perforations, with fluid entering the casing between the upper
seal body 24 and a lower
seal body 20. The FIG. 6 embodiment is primarily intended for use with a pump
driven by an electric
submersible motor, such as an ESP.
As shown in FIG. 6, the gas separation unit 60 receives fluid through a lower
end of the tubular
body 62, and discharges fluid to the annulus exterior of tube 62 through
discharge port 64, which are
located above the seal 24 and below the inlet to the pump. Coupling 68
interconnects the body 62 to the
electric pump motor as shown in FIG. 10, so that fluid enters the pump from
the annulus interior of the
casing and above the seal 24.
Fluid is thus drawn downward to the desander 10 that is preferably positioned
about 10 feet or
more below the casing perforations, while gas inherently moves upward and is
trapped in the annulus
below the seal 24. The tubular 12 preferably has a reduced diameter to
minimize the flow rate in the
annulus and thus increase upward gas migration. The interior cavity 74 in the
seal thus receives gas, with
strainer or filter 76 preventing debris from migrating upward past the seal 24
and to the coupling 78.
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Coupling 78 in turn is connected to small diameter tube 72, which extends
upward so that its upper end is
conventionally 20 feet or more above the inlet to the electric submersible
pump.
The upper end of the tube 72 is positioned sufficiently high from the lower
end of the tube so that
the fluid in the cavity 74 and thus the tube inlet creates a sufficient head
differential to pass gas upward
through the tube 72 and discharge gas above the inlet to the pump, so that gas
desirably does not enter the
pump. In the event that a shroud is used, as shown in FIG. 11, the tubular
body 16 and attachment
components are not needed. As shown in FIG. 11, the desander 10 includes a
packer body sealed to the
production tubing 12 and sized for sealing with the interior of downhole
casing. In this case, an ESP
shroud 120 encloses the ESP, with the top of the shroud being connected to a
pup joint 122 for fluid
communication with a production tubing string. Electric cable 124 extends
downward from the surface
into the shroud, and powers the ESP motor.
A principle feature of the gas separator disclosed herein involves the benefit
of removing gas
from the annulus so that it does not enter the pump inlet. When the pump motor
is positioned below the
pump, as is conventionally the case for an ESP, the pump inlet is going to be
in fluid communication with
this annulus. Gas separated by the gas separator rises upward to a position
above the pump inlet while
liquids enter the interior of the separator from below, regardless of whether
a desander is provided. If a
desander 10 is not used with a conventional gas separator, a perforated inlet
nipple 82 as shown in FIG.
12 may be positioned several feet below the casing perforations to form a
natural gas separator. FIG. 12
also depicts cup-type packer 130 positioned below the exit ports 132, with
vent line 134 having a lower
end in fluid communication with the cavity between the packer 130 and the
tubular 16, as in the FIG. 6
embodiment, with the upper end of the tube being positioned above the inlet to
the pump. A high-capacity
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gas separator alternatively may be used instead of nipple 82, and could be
positioned higher in the well
with much larger pumping rates.
The desander with outer body seal as shown in FIGS. 5 and 6 may be run below
the casing
perforations in a gassy well to produce liquid free of both sand and gas to
the ESP. An upper seal or
packer may be run below the ESP and above the perforations. The gas that
collects in the casing annulus
below the upper seal may flow up past the ESP inlet ports in the gas tube, as
shown in FIG. 6. The gas
tube may be omitted if the ESP has a built in gas separator, or if the gas
flow is small enough for the ESP
to handle the gas without a significant loss in pumping efficiency. The flow
area for the gas past the upper
seal should be relatively small to prevent excess liquid flow that carries
solids, but large enough for the
gas to escape.
The desander as shown in FIG. 7 may be run with a gas separator to remove gas
and solids from
liquid flowing to the pump. The liquid passes through the gas separator first,
then flows down through the
desander and then back up through a flow tube 82 to the pump.
In the FIG. 7 embodiment, liquid flows from the annulus 86 into the space
between separator
housing 84 and the flow tube 82, then flows down into the desander 10. Liquid
passing from the desander
10 will continue upward through the flow tube 82 and to the pump, while gas in
the annulus 86 moves
upward and passes out through the inlet port 64 to the annulus surrounding the
tool while liquids pass
downward to the desander. The FIG. 7 embodiment thus illustrates an
inexpensive form of a gas
separator.
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Referring now to FIG. 10, a desander 10 is shown with an upper cup-type packer
24 and a lower
cup-type packer 20 each for sealing with the interior of a casing (not shown).
Discharge port 64 and the
tube 62 are shown in a manner similar to the FIG. 6 embodiment. Electric motor
110 is provided below
the intake 112 to the pump 144, and a pup joint 116 and coupling 68 are
provided for interconnection
with a production tubing string. Fluid line 72 extends from the interior of
the cup-type packer 24 to a
position above the pump intake 11 2, and an electric cable 116 extends from
the surface down to the pump
144 for powering electric motor 110. The gas separator as shown in FIG. 10 has
particular utility when
used with a beam pump driving a reciprocating rod, which provides intermediate
rather than continuous
flow from the well.
Referring now to FIGS. 8 and 9, another embodiment of desander 10 is shown,
comprising an
outer tubular body 16 with input ports 18, an upper coupling 14, and a lower
coupling 22. As shown in
FIG. 8, fluid enters the outer tubular body through the openings 18, then
travels upward in the space 92
between the plurality of vortex bodies 94 and between the interior of the
tubular body 16 and the vortex
bodies. Fluid enters each vortex body through the tangential ports 96
positioned about each vortex body,
then travels downward through the frustoconical portion of each vortex body so
that solids exit through
lower port 97 at the lower end of each vortex body, while cleaned fluid passes
upward through the
opening 98 at the upper end of each vortex body, to be passed on to the pump.
Each of the vortex bodies
is thus arranged in parallel, and may be distributed throughout the interior
of the tubular body 16, with the
vortex bodies being arranged circumferentially about the interior of the
tubular body 16, and optionally an
additional vortex body centered within the tubular body.
By providing the desander with multiple vortex bodies, the vortex bodies may
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in axial length, thereby reducing the overall length of the desander. Since a
plurality of vortex bodies are
provided for this embodiment, each vortex body may have a high efficiency, and
together accommodate a
large range of flow rates. The number of vortex bodies for this design may
depend upon the application.
Some applications may use less than seven vortex bodies as shown in FIG. 9,
while other applications
may use more than seven vortex bodies. As with the earlier embodiments, the
vortex bodies 94 protect the
outer tubular body 16 from destruction due to abrasive wear, since the cutting
action stops before the
outer tubular body is damaged. The vortex bodies may be machined, or may be
cast in a wide range of
sizes and materials.
With respect to the tangential input ports, the number of ports provided for
each vortex body will
depend on the anticipated flow rates. Two or more narrow, slotted ports may
provide higher separator
efficiencies than a single port. A single small circular port may be best,
however, for low flow rates to
avoid plugging. Pressure losses, flow velocities, and abrasive wear should be
less when several small
vortex bodies are used with a single larger diameter vortex body. A strainer
as shown in FIG. 4 may also
be used in the embodiment as shown in FIG. 8.
Either a left-hand release joint or a break-away sub may be provided if there
is concern about the
desander sticking, particularly if body seals are utilized below the casing
perforations. The release joint or
the break-away sub may thus allow separation so that, at a minimum, the pump
may be returned to the
surface with the tubular body 16 even if the outer desander body becomes stuck
in the well.
When a seal is provided between the desander body and the casing, the seal is
preferably located
below the casing perforations. Various types of elastomeric seals may be used
for sealing between an
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exterior surface of the body 16 and interior surface of casing in which the
desander is positioned, as
discussed below. This seal allows solids to enter the desander and fall into
the casing cavity below the
seal. The seal may be provided close below the desander inlets and run close
below the casing
perforation, so the sand will not accumulate around the assembly and stick the
desander in the well.
The desander with the body seal as disclosed herein may be used with rod
pumps, progressive
cavity pumps, ESP shrouds, or ESP's with a casing seal above the casing
perforations. Pump anchors for
rod pumps or rotation preventers for progressive cavity pumps may be attached
below the seal without
sticking in the well. The tool may also serve as a natural gas anchor if it is
positioned in the casing below
the casing perforations. Small diameter pup joint above the assembly will
improve a separation for large
liquid flow rates.
Although specific embodiments of the invention have been described herein in
some detail, this
has been done solely for the purposes of explaining the various aspects of the
invention, and is not
intended to limit the scope of the invention as defined in the claims which
follow. Those skilled in the art
will understand that the embodiment shown and described is exemplary, and
various other substitutions,
alterations and modifications, including but not limited to those design
alternatives specifically discussed
herein, may be made in the practice of the invention without departing from
its scope.
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