Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PUMPING
LIQUID FROM WELLS
FIELD OF THE INVENTION
The invention relates to an autonomous pressure actuated liquid
pump for use in gas and oil wells. In particular, it relates to liquid lift
pumps in
which well pressure, acting against an internal bellows or diaphragm, causes
an internal flow control valve to open or close thereby releasing or shutting-
in
well gas flow. More particularly, the present invention relates to the use of
such pumps with a liner that is inserted into open hole and large diameter gas
and oil wells.
BACKGROUND
The economic viability of marginal petroleum wells, often
referred to as stripper wells, depends on the well's product flow and pressure
capacity and the rate at which undesirable liquids (i.e., brine) infiltrate
the well.
Removing liquid from gas or oil stripper wells has been accomplished with
pump jacks or casing plungers in cased wells, while siphon strings or tubing
plungers have been used in small diameter tubing. However, economic
viability has restricted most applications to passive liquid removal
techniques.
In large diameter casings (3" or larger), casing plungers, such as
the one disclosed in U.S. Patent 6,851,480 have had some success in
improving the economic viability of stripper wells. However, variations in ID,
at each new section of casing, or at joints, or at collars, cause a potential
stopping point for a plunger descending a well. These variations in the ID
also creates pressure leakage areas that could potentially stop a plunger on
its upward travel. Interconnect discontinuities also provide natural trapping
areas for well contaminants, such as salt rings, that worsen the descending
and ascending plunger problems.
Due to the problems associated with ID variations in a well,
casing plungers may become stuck in the well. Bringing a casing plunger to
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the surface when it is stuck in the well may require venting the well to dump
tanks to provide additional pressure differentials. Often lubricants and salt
dissolving chemicals are added to free stuck plungers and at times retrieval
gear is brought in to fish-out stuck plungers. All of these efforts to
retrieve a
stuck casing plunger increase the downtime of the wells and increase well
tender man-hours.
Many mechanical devices have been proposed for
accomplishing the sealing of casing and tubing plungers used in 2" inside
diameter and larger applications. Petro-chemical well environments however
are quite corrosive and contaminating for mechanical linkages and small
moving parts. Thus the industry has standardized on molded, flexible, friction
cups to provide the sealing function in full size well casings and tubing,
while
brushes rather than cups are sometimes used for small diameter tubing
applications they are not applicable to larger diameter configurations..
Several different implementations of flexible cups are being used but they are
not designed for operating in tube configurations in which the inside diameter
is reduced 5 to 20% in section-to-section couplers and well head connectors.
SUMMARY OF THE INVENTION
This invention provides a self-actuating solution to overcome the
shortcomings of the prior art devices. According to one aspect, the invention
provides 10 a system for pumping fluid from a well. The system includes an
elongated hollow tubing insertable into the casing of a well, and a casing
plunger operable within the hollow tubing. A seal may also be provided to
form a fluid tight seal between the liner and the casing of the well.
According to another aspect, the invention provides a method
for pumping fluid from a well. The method includes the step of suspending a
liner into the casing of a well. A pump is placed into the liner such that the
pump descends through the liner into the liquid. The pump is automatically
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closed in response to a pressure differential at the pump, such that the pump
forms a fluid seal to substantially impede fluid flow around the pump in the
liner. The pump is raised along with a column of fluid in the liner in
response
to a build up of fluid pressure from closing the pump. The pump is then
automatically opened in response to a decrease in pressure below the pump
relative to the pressure above the pump.
According to yet another aspect, the invention provides an
improved seal for a pump for pumping fluid from a well. The seal forms a
fluid-tight seal between the pump housing and an internal surface of the well.
The seal comprises first and second sealing elements that are axially spaced
apart from one another, and which project radially outwardly. A fluid passage
extends through the pump housing, having an inlet port below the seal and a
discharge port above the seal. A pressure sensitive valve disposed within the
fluid passage automatically closes when a pressure on the valve system is
greater than a closing pressure, and automatically opens when the pressure
on the valve system is less than an opening pressure.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a view of a well-pumping system according to the
present invention;
FIG. 2 is a cross sectional view of the pumping device of the
well-pumping system illustrated in Fig. 1;
FIG. 3 is an enlarged cross-sectional view of the well head of
the will pumping system illustrated in Fig. 1;
FIG. 4 is an enlarged cross-sectional view of a tail stop of the
well-pumping system illustrated in Fig. 1;
FIG. 5 is an enlarged fragmentary cross-sectional view of a
connector for a liner in the well-pumping system illustrated in FIG. 1;
FIG. 6 is an enlarged cross-sectional view of sealing elements of
the pumping device illustrated in Fig. 2.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Figs. I and 2, a system for pumping liquid out
of a well is illustrated. The system preferably includes a liner 30 that hangs
from the top of a well 5. A pump in the form of a casing plunger 60 forms a
fluid-tight seal with the interior wall of the liner 30.
To pump fluid out of the well, the liner 30 is lowered into the
casing of the well. The liner 30 is fed into the well until the bottom end of
the
liner sinks into the fluid in the well. The pump is then inserted into the
liner
and lowered through the liner, so that it sinks into fluid in the well. Once
the
fluid pressure in the liner above the pump exceeds a threshold, the pump 60
seals-off the liner. In doing so, the device seals in the gas in the well,
causing
the fluid pressure below the pump to build up. The fluid pressure below the
pump then drives the pump upwardly along with the fluid above the pump. As
the pump 60 is driven upwardly, the fluid above the pump is discharged
through discharge lines 19, 21 connected to the well 5. When the pump
reaches the top of the well, the gas pressure below the pump drives the pump
out of the liner and into a receiver 15 that maintains the pump above the
lower
discharge line 21 while gas from the well flows from the liner and through the
lower discharge line. When the flow of gas from the well diminishes, the pump
60 is again lowered through the liner to pump more fluid out of the well.
The raising and lowering of the pump 60 is controlled
automatically in response to the fluid pressure in the well. Specifically, the
pump 60 includes a valve 70 that controls the flow of fluid through the pump.
A biasing element 80 controls the operation of the valve 70. More
specifically,
the biasing element 80 biases the valve 70 into an open position. When the
valve 70 is open, the pump 60 descends into the well, and fluid flows through
the pump. The rate of descent is limited by the friction between the pump and
the well walls and flow restrictions through the pump. When the pump
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reaches the liquid level in the liner 80, it continues to descend, but at a
reduced rate.
When the pressure differential across the pump 60 exceeds a
threshold (closing threshold) related to the biasing force of the biasing
element, the valve 70 automatically closes so that fluid can no longer flow
through the pump. As described above, the fluid pressure in the well builds
up and then drives the pump upwardly. At the top of the well 5 the pump 60 is
displaced into a receiver assembly 60 that maintains the pump. While the
pump is maintained in the receiver, the gas pressure in the well dissipates as
gas flows through the lower discharge line 21. When the fluid pressure
across the pump drops below a threshold (opening threshold), the biasing
element 80 automatically opens the valve 70 and the pump 60 descends
again into the well. In this way, the pump automatically descends and
ascends within the well to pump fluid from the well.
Referring to Fig. 3, the liner 30 will be described in greater
detail. The liner 30 need not be used in each system in which the pump 60 is
used. However, in certain applications the well is not suited for use with a
pump, such as a casing plunger. For instance, the well may be an open hole
we!l that only has a casing for the first few hundred feet of the well,
therefore,
most of the well does not have a casing that the pump can seal against.
Alternatively, the casing diameter may be too large or lack pressure integrity
for the operation of the pump. In such instances, the liner 30 may be
incorporated.
The liner 30 is an elongated hollow tubing. The liner may be a
single length of tubing, however, preferably the tubing is comprised of a
plurality of separate sections that are connected together. Accordingly,
preferably each section of liner has fittings 32 at each end to connect the
different sections using couplers 38. As discussed further below, packing
material 25 is used to maintain a fluid-tight seal between the well casing and
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the liner. If a section of tubing needs to be added to the tubing, the packer
seal 25 is relaxed so that the tubing coupler 38 can pass into the well
casing.
The tubing coupler is then repositioned around the tubing 30.
Referring to Fig. 5, the fittings are illustrated in greater detail.
The fitting provides a sufficient seal to maintain the pressure build up
within
the liner during use of the device. In addition, the fitting 32 provides a
connection having sufficient tensile strength to support the load of the
liner.
Specifically, since the liner may need to extend thousands of feet into the
well,
the weight of the liner becomes significant. In the present instance, the
approximately 4000 feet of the liner weighs approximately 5,000 pounds.
The fitting 32 comprises an external ferrule 33 and an insert 34.
The liner 30 is disposed between the ferrule 33 and the insert 34. The ferrule
33 is then crimped down onto the insert to fixedly attach the liner 30 to the
fitting 32. As shown in Fig. 5, the end of insert 34 flares outwardly forming
an
externally threaded portion 35. The threaded portions are used to connect the
sections of the tubing. More specifically, a collar 38 (shown in Fig. 4)
having
internal threads engages the threaded portions 35 of frttings from two
sections
to connect the two sections.
The tubing may be formed of a variety of materials, including
metal or plastic. Preferably, the conduit is configured so that the conduit
can
be spooled and shipped on large reels (8 to 12 feet in diameter) prior to
insertion into the well. Although a variety of plastic tubing can be utilized,
in
the present instance, the plastic tubing is a polymer plastic including fiber
bands and tension straps to support the weight of the tubing and the
operational pressures.
The liner 30 extends into the well so that the liner is within the
casing 10. The liner may extends down into the well beyond the casing or in
some applications, the liner may terminate within the casing. The liner is
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connected to the well at the well head in such a manner as to provide a fluid-
tight seal between the casing 10 and the liner 30.
Referring to Fig. 3, the connection of the liner to the well head is
illustrated in greater detail. The fitting 32 at the top end of the tubing
threadedly engages a hanger 23 having a mounting flange 24 on the well
head. The mounting flange cooperates with a flange 17 on the receiver 15 to
attach the receiver to the well head. Packing material or a packer 25 is
positioned between the liner 30 and the casing 10 to seal off the annular
space between the interior wall of the casing 10 and external wall of the
liner
10. The packer 25 provides a fluid-tight seal between the casing and the liner
30 that is able to maintain the seal under the fluid pressures created during
operation of the pump 60. In this way, when the casing plunger 60 seals off
the liner to shut in the well, the packer 25 prevents gas or other fluid from
leaking out of the well between the casing and the liner. The packer 25 may
be formed from any of a number of materials, such as elastomeric polymer.
Tubing sections are added to the liner until the lower end of the
tubing extends into the fluid in the well. Typically, the casing includes a
perforated section toward the bottom of the well. The perforations are holes
through the sidewalls in the casing that allow the marketable fluid(s) in the
ground to pass through the casing and then up the well. However,
undesirable fluid, such as brine may accumulate in the well and extend above
the perforated section, thereby reducing the delivery of desired fluid(s). The
pump 60 may be used to remove the undesired fluid so that the level of such
fluids is below the perforations thereby improving the flow of the marketable
fluid(s). Accordingly, it is desirable to extend the tubing sections into the
well
so that the bottom end of the liner 30 extends to, or below the level of the
perforations in the casing. In this way the pump can be used to pump fluid out
of the well at the level of the perforations. In other words, the liner may be
positioned so that the pump descends through the liner to a point at or below
the perforations, and then automatically closes to lift the fluid to the
surface as
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described previously. By doing so, the pump may lift sufficient undesirable
fluid to reduce the fluid level to a level below some or all of the
perforations in
the perforated section.
A tail cap 40 attached to the lower end of the tubing 30 prevents
the casing plunger from descending out of the liner in the event that the
casing plunger does not close before reaching the bottom of the liner. The
tail
cap 40 comprises an externally threaded portion that is connected to the
tubing 30 with a coupler 38, similar to the manner in which sections of the
tubing are connected. The tail cap 40 comprises a plurality of orifices 42
that
allow fluid to flow from the well 5 into the liner 30. Additionally, a bumper
stop
45 in the tail cap 40 operates as a cushion to decelerate the casing plunger
60 as the casing plunger bottoms out on the tail cap. The bumper stop
comprises a rod 47 having a flared head, and a biasing element, such as a
compression spring 48. The rod and spring are disposed within a cylindrical
housing 49 that fits over a cylindrical nipple 44 formed on the inside of the
tail
cap 40.
Referring now to Fig. 2, the details of the pump 60 will be
described in greater detail. The pump 60 includes an elongated substantially
hollow cylindrical housing 62. A lower housing 65 is fixedly attached to the
lower end of the cylindrical housing 62. An end cap 75 closes the lower end
of the lower housing. Preferably, the lower end cap 75 is releasably
connected with the lower housing 65. In the present instance the lower end
cap 75 is threadedly connected to the lower housing. A plurality of holes in
the lower end cap 75 form inlet ports 76, so that fluid can flow into the pump
60 through the inlet ports 76 when the pump descends into the well.
A top cap 90 is attached to the upper end of the housing 62.
The top 90 has a central bore providing a fluid path. The lower end of the top
cap 90 is attached to the upper end of the housing 62. Preferably the top cap
90 is releasably connected to the housing; and in the present instance, the
top
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cap 90 has external threads that mate with internal threads in the housing 62
to attach the top cap to the housing.
The upper end of the top cap 90 is generally open, and
preferably includes an internally threaded portion for mounting a stem 68.
The stem 68 preferably has an externally threaded portion cooperable with
the top cap 90 to releasably attach the stem to the top cap. In this way, the
stem threads into the top cap thereby sealing the upper end of the top cap.
As shown in Fig. 2, a plurality of holes through the sides of the
top cap 90 provide outlet ports 92. In this way, fluid flowing through the
pump
60 flows through the top cap 90 and out the outlet ports 92.
A plurality of sealing elements or cups 85, 86 disposed around
the housing provide a fluid-tight seal between the housing and the inner wall
of the well 5. The cups 85, 86 are disposed between the inlet ports 76 at the
bottom of the pump 60 and the outlet ports 92 at the top of the pump. The
cups 85, 86 are elastomeric elements having a central bore. The cups 85, 86
are spaced apart axially from one another by a spacer 88. The spacer 88 is
an elongated cylindrical collar having an internal diameter slightly larger
than
the external diameter of the housing.
The cups 85, 86 and spacer 88 are captured on the housing
between a locking ring 95 and a lip that is the formed by the top edge of the
lower housing 65. Specifically, an internal annular shoulder of the lower cup
86 abuts both the top edge of the lower housing, and the locking ring 95
threaded onto the top cap 90 engages the top edge of the upper cup 85.
The locking ring 95 is a threaded collar or nut that cooperates
with external threads on the top cap 90. In this way, the locking ring 95 is
operable to tighten down or compress the cups 85, 86. Since the cups 85, 86
are formed of elastomeric material, preferably a metal washer is disposed
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between the locking ring 95 and the upper cup 85. The metal interface
between the locking ring and the washer facilitates turning the ring to
tighten
down on the cups 85, 86.
During use, the cups may wear and need to be replaced.
Accordingly, preferably the pump 60 is configured so that the cups 85, 86 can
be readily removed and replaced without disassembling the pump. Therefore,
in the present instance the top cap 90 is preferably configured so that it
need
not be removed to replace the cups. Specifically, preferably the exterior
diameter of the top cap 90 is small enough to allow the cups to slide over the
top cap. In particular, preferably the external diameter of the top cap 90 is
approximately the same as, or less than, the external diameter of the housing.
Referring now to Fig. 6, the lower cup 86 is illustrated in more
detail. The lower cup 86 comprises a generally cylindrical body 102 and a
pair of spaced apart seals 104, 106 in the form of circumferential flanges
that
project outwardly from the body. The body 102 and the seals 104, 106 may
be formed of separate materials. However, in the present instance the body
and the seals 104, 106 are a unitary piece of molded elastomeric material.
The seal 104, 106 are formed of material that is resiliently deformable
radially.
In the present instance, each flange has an axial thickness "t" and a radial
width "w". The width "w" is greater than the thickness "t" and the width may
be twice the thickness "t".
The seals 104, 106 form a fluid-tight seal, sealingly engaging the
casing of the well, or if a liner 30 is used. Additionally, the seals 104, 106
are
configured to form a sliding seal with the interior wall of the casing or the
liner,
if used. Since the flanges 104, 106 are spaced apart, the flanges sequentially
seal the well when the cups encounter a restriction in the path that the pump
is traveling (i.e. the casing or the liner). For instance, as described above,
the
liner 30 may be formed of a number of sections connected together by fittings
32. As shown in Fig. 5, the insert 34 of the fittings 32 creates a restriction
in
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the internal diameter of the liner. Preferably the fltting is relatively thin
and
only restricts the diameter minimally. Nonetheless, the fitting creates a
restriction. As the casing plunger 60 travels upwardly after shutting in the
well, the upper seal 104 engages the fitting 32 first, and deflects radially
inwardly. The upper seal 104 is configured to maintain a seal with the liner
even as the seal deflects radially inwardly. However, even if the restriction
deflects the upper seal in such a way that releases a portion of the sealing
engagement between the upper seal and the liner, the lower seal 106
maintains the seal with the liner to prevent leakage past the cup.
Subsequently, as the lower seal 106 encounters the restriction, the upper seal
104 maintains the seal with the liner in the event that the lower seal loses
sealing engagement with the liner.
As described above, the cups 85, 86 are configured to maintain
a seal while passing through a constriction in either the casing or the liner,
if
one is used. Similarly, if a liner 30 is used, the wall of the liner may
become
out of round. For instance, when the liner is spooled onto a reel, the liner
may
flatten to become more of an oval or eccentric cross-section rather than a
circular cross-section. The cups are formed so that the seals 104, 106 deform
radially and/or axially to conform to the oval or eccentric cross-section of
the
liner. In this way, the cups are able to maintain a sliding fluid-tight seal
with
the out of round interior of the liner.
Configured as described above, the cups 85, 86 are able to
maintain a sealing engagement with the casing or the liner if one is used,
while being able to deflect sufficiently to allow the casing plunger to pass
through a restriction in the liner or casing. More specifically, the cups are
configured such that the seals deflect radially inwardly sufficiently to pass
through a restriction of 5-20% of the diameter of the casing or liner.
Referring to Fig. 2, the valve 70 controls the flow of fluid through
the housing 62. In Fig. 2, the valve 70 and biasing element 80 are shown in
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elevation. The valve 70 comprises a valve element 72 that cooperates with a
valve seat 73 to form a fluid-tight seal. Preferably, the valve element 72 is
formed of an elastomeric material. The valve seat 73 is preferably a tapered
annular surface formed in the interior wall of the lower housing.
When the valve is closed, fluid does not flow through the pump.
In addition, since the cups 85, 86 provide a fluid-tight seal between the
housing 62 and the wall of the well 5, fluid does not flow around the pump.
Accordingly, when the valve 70 is closed, the pump 60 operates as a seal,
sealing the well closed. This allows a pressure differential to build up
across
the tool. Speciflcally, when the valve is closed, the pressure below the cups
increases relative to the pressure above the cups.
The biasing element 80 is a pressurized bellows that bias the
valve 70 toward an open position in which fluid can flow through the pump
through the inlet and outlet ports 76, 92. The bellows 35 are operable to
expand and contract vertically. The lower end of the canister is generally
open, having an annular flange extending radially inwardly to form a lip.
The bias of the bellows 80 is controlled in part by the fluid
pressure within the bellows. A cavity is formed within the bellows and a fill
valve attached to the housing of the bellows controls the flow of fluid into
the
bellows. In this way, the bellows can be charged by filling the bellows with
pressurized air through the fill valve. As the bellows are filled with
pressurized
air, the bellows expand outwardly, displacing the valve element 72
downwardly.
The bellows 80 compresses in response to hydrostatic pressure
on the bellows when the pump is in the liquid in the well. As the bellows
compresses, the valve 70 closes. The stroke of the valve element 72
between the opened position and the closed position corresponds to the
compression of the bellows from the charged length to the compressed length
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when the valve 70 is closed.
Referring to Fig. 1, an upper discharge line 19 and lower
discharge line 21 are connected to the well 5 for receiving the fluid from the
well. The upper discharge line 19 extends between the well 5 and the lower
discharge line 21. Preferably, the lower discharge line 21 is approximately
twice as large in diameter as the upper discharge line 19. The opening from
the well 5 to the upper discharge line 19 is vertically spaced along the well
from the opening to the lower discharge line 21 a distance that is greater
than
the distance from the point that the lower cup 86 seals with the well to the
point that the upper cup 85 seals with the well. In this way, when the device
60 is at the top of the well the upper and lower cups 85, 86 form seals with
the
walls of the receiver between the upper and lower discharge lines 19, 21. In
this way, fluid from the well flows through the liner 30 and to the lower
discharge line 21 while the pump 60 is disposed in the receiver.
A check valve 75 is disposed along the upper return line. The
check valve 75 is configured to allow higher pressure fluid in the upper
discharge line 70 to flow into the lower discharge line 80 and to impede fluid
flow from the lower discharge line up into the upper discharge line. In this
way, the fluid in the upper discharge line remains at a lower pressure than
the
fluid in the lower discharge line. An upper shut-off valve 72 is provided on
the
upper discharge line 70 to shut-off the upper discharge line, and a lower
discharge valve 82 is provided to shut-off the lower discharge line. The shut-
off valves 72, 82 may be any one of a number of types of valves, such as a
ball valve.
When the friction cups 85, 86 pass above the lower discharge
line 80, the shut-in well gas pressure discharges into the lower discharge
line.
The flow control valve 70 in the pump remains in the closed position as the
shut-in pressure dissipates. The check valve 75 provides separation between
the pressure above the pump (i.e. above the friction cups 85, 86) and the
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dissipating shut-in pressure in the lower discharge line 80, thereby
maintaining a positive pressure differential across the pump 60. The gas
pressure in the well is sufficient to support the pump to maintain it in the
receiver until the valve 70 opens. As the fluid pressure in the well decreases
below the preset pressure differential across the pump (from the high shut-in
pressure), the flow control valve 70 opens. When the valve is opened, the
pressure differential across the pump approaches zero and the pump
descends into the well for additional liquid pumping.
It will be recognized by those skilled in the art that changes or
modifications can be made to the above-described embodiments without
department from the broad inventive concept of the invention. It should
therefore be understood that this invention is not limited to the particular
embodiments described herein but is intended to include all changes and
modifications that are within the scope and spirit of the invention as set
forth
in the following claims.
