Note: Descriptions are shown in the official language in which they were submitted.
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GAS DISPLACED CHAMBER LIFT SYSTEM HAVING GAS LIFT ASSIST
TECHNICAL FIELD
The present invention relates to artificial lift systems. More particularly,
the present
invention relates to chamber lift systems which are used so as to deliver oil,
water and gas from a
wellbore to a surface above the wellbore. More particularly, the present
invention relates to gas-
displaced chamber lift systems.
BACKGROUND ART
At the present time, it is common to permit oil and gas wells to flow under
their own natural
pressure as long as they will do so and then to apply a mechanical
reciprocating pump to complete
the removal of the liquids. This method, although in general use, is
cumbersome and unsatisfactory.
Because suction will only raise oil for a distance of some thirty-five feet,
it is necessary to have the
pump near the bottom of the well so that it can exert pressure instead of
suction on the liquids
coming out of the well. This involves the use of pump rods of lengths of 5,000
feet or greater. In
many instances when the pump plunger or the valves become worn, it is
necessary to remove the
pump from that depth to replace the worn parts. Furthermore, the collars on
the pump rod wear
rapidly and all the pump parts do likewise because of the small particles of
grit that remain in the
liquid and the whole device is mechanically inefficient because of the
relatively long pump rods that
must be reciprocated to perform the pumping operation.
When the natural flow of liquid from a well has ceased or becomes too slow for
economical
production, artificial production methods are employed. In many cases, it is
advantageous, at least
during the first part of the artificial production period, to employ gas lift.
Numerous types of
equipment for producing liquid by gas lift are available, but they all rely
upon the same general
principles of operation. In the usual case, dry gas consisting essentially of
methane and ethane is
forced down the annulus between the tubing and the casing and into the liquid
in the tubing. As the
liquid in the tubing becomes mixed with gas, the density of the liquid
decreases, and eventually the
weight of the column of the gasified liquid in the tubing becomes less than
the pressure exerted on
the body of liquid in the well, and the flow of liquid occurs at the surface.
While, in some cases,
the dry gas may be introduced through the tubing so as to cause production
through the annulus, this
is not preferred unless special conditions are present.
One known gas lift technique injects gas into the casing, which has been
sealed or packed
off at the bottom of the hole relative to the production tubing. A gas lift
valve is placed in the
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production tubing at the production level, and the gas lift valve permits the
gas to be injected into
or bubbled very slowly into the liquid being produced from the well. This gas
then makes the liquid
in the production tube somewhat lighter and, hence, the natural formation
pressure will be sufficient
to push the liquid up and out of the well. This means that the well can be
produced at a greater rate.
This gas lift technique is known as continuous gas lift.
A further adaptation of this gas lift technique is known as intermittent gas
lift. In this
technique, rather than letting the gas enter the production tube slowly, the
gas is injected into the
production tubing very quickly, in short bursts, thereby forming a large slug
of liquid in the
production tubing above the injected gas bubble. The gas bubble then drives
the slug of liquid in
the production tubing upwardly. The technique is repeated successively,
thereby producing
successive slugs of liquid at the wellhead.
Another type of gas lift tool involves a procedure where a string of
production tubing
extending from the surface to the zone of interest is provided with a number
of gas lift valves
positioned at spaced intervals along the length of the tubing. Gas is injected
from the annulus
between the tubing and the well pipe through the gas lift valves and into the
tubing for the purpose
of forcing liquid upwardly to the surface and ultimately into a flowline that
is connected with the
production tubing. Gas lift systems for liquid production are quite expensive
due to the cumulative
expense of the number of gas lift valves that are ordinarily necessary for
each well. Moreover, each
of the gas lift valves must be preset for operation at differing pressures
because of the vertical
spacing thereof within the tubing string and because the valves must function
in an interrelated
manner to achieve lifting of liquid within the tubing string.
In the past, various patents have issued relating to such gas lift systems.
For example, U.
S. Patent No. 5,671,813, issued on September 30, 1997 to P. C. Lima describes
a method and
apparatus for the intermittent production of oil. In this method, two
production strings extend
downwardly from a wellhead of an oil well to a point adjacent a producing
region. The lower ends
of the two production strings are connected by a coupling which allows a
mechanical interface
launched adjacent the wellhead of one of the production strings to descend
along the production
string through the coupling and upwardly through the other production string
to displace oil from
the production strings to a surge tank. High pressure gas is utilized to move
the mechanical
interface through the production strings and suitable valves are provided for
controlling the flow of
gas and oil through the production strings.
U. S. Patent No. 5,562,161, issued on October 8, 1996 to Hisaw et al.
describes a method
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of accelerating production from a well. This method includes the steps of
installing a venturi device
within the well. A gas is injected within the annulus and introduced into the
well. The venturi
device creates a zone of low pressure within the well as well as accelerating
the velocity of the
production fluid so that the inflow from the reservoir is increased.
U. S. Patent No. 5,407,010, issued on April 18, 1995 to M. D. Herschberger
teaches an
artificial lift system and method for lifting fluids from an underground
formation. This artificial lift
system includes a production tubing through which the fluid is carried from
the formation to the
surface and a pressure reducer, such as a venturi, connected to the production
tubing to artificially
raise the level of the fluid in the production tubing above the static level
associated with the head
pressure of the fluid in the fonnation.
U. S. Patent No. 5,217,067, issued on June 8, 1993 to Landry et al. describes
an apparatus
for increasing flow in an oil well which includes an injection valve so as to
enable gas to be injected
and to cause the oil or other liquid within the well to be lifted to the
surface. The valve has a valve
body having an inlet at one end and an outlet at the other end which are
adapted to be fitted into
conventional production oil tubing. A gas inj ection port opens into the
outlet of the valve body and
there is at least one gas inlet opening in a side of the valve body. This gas
inlet opening is
connected to the gas injection port. This enables compressed gas to be sent
down the well between
the casing and the tubing and injected through the gas injection port and into
the flow of oil.
U. S. Patent No. 5,211,242, issued on May 18, 1993 to Coleman et al. describes
a chamber
in a well which is connected to two externally separate tubing strings to
unload liquid which is
applying backpressure against a formation so that the production of fluid from
the formation is
obstructed. Volumes of the liquid are intermittently collected in the chamber
and lifted out of the
well through one of the tubing strings in response to high pressure gas
injected solely into the
chamber through the other tubing string.
U. S. Patent No. 4,708,595, issued on November 24, 1987 to Maloney et al.
describes an
intermittent gas-lift apparatus and process of lifting liquids. This apparatus
includes a chamber on
the downhole end of a production tubing in communication with a sidestring
tube. The sidestring
tube is in communication with the high pressure gas stored within the casing
and above and below
a packer. A valve in the sidestring tube permits the entrance of a lifting gas
into the chamber to lift
the liquids flowing therein to the surface. A surface bleed-down system
minimizes the pressure in
the production tubing. This increases the pressure differential between the
formation and the
interior of the casing and lifting chamber during the operation of the
apparatus.
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German Patent No. 23 64 737, published on July 10, 1975, teaches a compressed
air lift
pump for deep wells in which the pump has a number of stages one above the
other. Liquid is raised
by air from the reservoir of one stage to the reservoir of the next. Each
stage has two air supply
pipes which contain three-way valves operated by an electronic timer to admit
and release air
alternately.
Soviet Patent No. 1204-700-A teaches an intermittent gas lift system for a
pump well which
includes a tubing, a packer, a substitution chamber and intake valve, lift
starter valves and working
valves with a seal and a seat over a space connected to the chamber. The
rising level of fluid in the
chamber raises the float so as to close off ports and thus raise pressure
above the diaphragm so as
to clear the valve and transfer gas to the chamber. This gas forces the fluid
into the tubing and uses
a pressure gradient to hold the ports closed. Gas eventually enters the tubing
after all fluid has been
expelled, thus opening the two ports by lowering the float back down. Gas is
removed entirely from
the chamber by the incoming fluid.
Soviet Patent No. 570697 teaches an oil production facility including a
displacement
chamber, two strings of compressor pipes of which one is coupled to the
surface drive. The gas
from the chamber is recuperated and expanded. When one vessel is empty, fluid
is drawn into the
displacement chamber. The second vessel pumps oil over into the empty vessel
so as to raise its
pressure to the point required to drive the hole fluid over into the lifting
string to the surface. Once
the fluid in the chamber reaches the bottom of the lift string, the motor
reverses so as to turn an
electric shaft and compress the gas in the first vessel to repeat the process
in a second hole.
U.S. Patent No. 3,617,152, issued on November 2, 1971 to Leslie L. Cummings,
discloses
a method and apparatus for the artificial lifting of well fluids. In
particular, this device utilizes an
automatic well pump which utilizes compressed power gas to displace well
production fluids from
the well bore to the earth surface. Power gas is exhausted from the pump so as
to be collected in
a chamber at a desired predetermined superatmospheric pressure to reduce the
energy required to
compress the air. This device utilizes gas assist lifting so as to move the
liquid, in stages, to the
surface. Also, the device uses the compressed gas, as opposed to the vented
gas, for the gas assist.
A publication of Otis Engineering Corporation, dated 1982, and entitled "Otis
Single and
Dual-Acting Gas Pumps" describes a gas assist system in which the pump
displaces a barrel of oil
with a barrel of gas volume at a lift depth pressure. When the gas pressures
are too low to lift wells
by positive displacement, the gas pump can be aligned with gas lift to lift
deeper with lower
pressures. The gas lift supply comes from the compressor at various stages
along the liquid string.
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U.S. Patent No. 5,806,598, issued on September 15, 1998, to M. Aniani
describes an
apparatus for removing fluids from underground wells. This device includes a
supply valve having
an open supply position to supply gas to the chamber and a closed supply
position. Tlie device
fnn-ther includes a vent valve having an open vent position to vent aas from
the chainber and a closed
vent position. An actuator commimicates with a source of pressutized fluid at
the surface for
actuating the supply and vent valves. The actuator moves the supply valve to
the open position and
the vent valve to the closed position, and altei7lately inoves the vent valve
to the open position and
the supply valve to the closed supply position.
A major problem with the aforedescribed artificial lift systems is that they
do not work
effectively in deep well and sour gas environn-ients. In particular, at depths
of greater than 10,000
feet, the temperature range encountered can be approximately 300 degrees
Fahrenheit. As such,
any mechanical punlping apparatus will not worlc effectively at such
temperatures. At such great
depths, the rod pump devices and submersible pump apparatus do not effectively
deliver oil and gas
to the surface. For example, at such great depths, the pump rod will have an
extreme length wlv.ch
camot be easily reciprocated back and forth. Furtherrriore, the cost
associated with such a lengthy
pump rod would not allow for efficient production. The high temperature and
pressures encountered
at such depth cause submersible pumps and hydraulic pumps to fail quickly.
In those systems in which the intermittent production of "slugs" of oil is
utilized, such
systems are ineffective at such depths. In each case in which a "slug" of oil
is produced, the gas
must be relied upon so as to deliver such a slug to the surface. At great
depths, this can talce a great
deal of tinle so as to produce an economical amount of oil. Furthermore, the
pressure and energy
required so as to push such a slug to the surface may exceed the value of the
actual production.
Production at such a depth is further complicated by situations in which a
corrosive sour gas
is encountered. This is particularly tiue in those cases in which oil and gas
must be removed fi'om
Smackover wells.
U.S. Patent No. 6,021,849 which issued on February 8, 1-000 to the present
applicant, describes the original form of the gas displaced chamber lift
system. After
experimentation, study and analysis, it was found that it was important to
have a gas displaced
chainber lift system that operated in a relatively continuous mode. In the
single chamber gas
displaced chamber lift system, liquid would accumulate in the single chamber.
After sufficient
liquid had accumulated in the chaniber, then the valve would open so as to
cause the pressurized gas
to pass through the power gas string with sufficient pressure so as to
evacuate the chamber of the
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liquid mzd to pass the liquid from the outlet of the chamber into the liquid
string. After the liquid
would pass to the liquid string, the pressurized gas from the power gas
strin.g would be blocl:ed and
the remaining gas witlzin the chamber would be vented to the surface. It was
fotmd that during the
process of evacuating the chamber and during the process of venting the gas,
there was a period of
time in which production ceased. It was found 1:o be desirable to allow
production (i.e. the
accumulation of liquid in the chamber) to continue dluing the evacuation and
venting process. As
such. a double chanlber approach was devised and disclosed in this prior
application.
U.S. Patent Number 6,021,849 described a double chamber approach in which one
of the
chambers was stacked on top of the other chamber or in which one chanZber was
located interior of
and in concentric relationship with the otlier chamber. After experimentation
and analysis, it was
foLmd that such an arrangement was difficult to configure within the well
bore. Additionally, the
stacked arrangements could occasionally produce varying quantities of liquid
within the respective
chambers due to the head pressure within the well.
U.S. Patent No. 6,237,692 which issued on ivlay 29, 2001 to the present
Applica.~it describes a modified fonn of the gas displacpd c,=hamber lift
system. After ea periment and
analysis, it was found that the efficiency of the subject matter ofthis patent
application could be
improved by utilizing the vented gases for the purposes of reducing the weight
of the liquid in the
liquid string. Since the gas displaced chamber lift system would vent the
gases from the chamber,
it was felt that the vented gases could be put to better use by siniply
reinfecting such gases into the
liquid string. However, because of the pressures within the liquid string, the
gas could not be
injected, efficiently, into the liquid string when the pressures within the
liquid string are too b eat.
Furthermore, U.S. Patent No. 6,237,692 describes a valving system placed
exterior to the liquid string. As such, in order to acconuuodate both the
shifting valve anel the liquid
string, the shifting valve required a mirumal amount of space. Upon further
experimentation and
analysis, it was found that a better design could be achieved for the
placement of the shifting valve
within the well bore.
It is an object of the present invention to provide an artificial lift system
wliich works
effectively at depths of greater tha.n. 10,000 feet.
It is a furtlier object of the present invention to provide an ai-tificial
lift system which can
operate in a high temperature environment at the bottom of the well.
It is another object of the present invention to provide an artificial lift
system in which
production from the liquid string occurs continuously v,rithout the need for
transporting a"slug" of
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oil to the surface.
It is another object of the present invention to provide an artificial lift
system which works
effectively in highly corrosive sour gas environments.
It is another object of the present invention to provide an artificial lift
system which can lift
liquid volumes of approximately 500 barrels per day.
It is a further object of the present invention to provide an artificial lift
system which can
operate in a very "gassy"/high API oil gravity environment.
It is still a further object of the present invention to provide an artificial
lift system which
can handle saturated brines of greater than 200,000 parts per million.
It is still another object of the present invention to provide a double
chamber gas displaced
chamber lift system in which at least one chamber is continuously available
for the accumulation
of liquid therein.
It is a further object of the present invention to provide a double chamber
gas displaced
chamber lift system in which the chambers can be alternately evacuated and
vented without
interrupting production capacity.
It is still a further object of the present invention to provide a double
chamber gas displaced
chamber lift system which is easy to configure and easy to install within the
well bore and which
is not subject to varying head pressures within the well bore.
It is still a further object of the present invention to provide an artificial
lift system which
can improve efficiency by reinjecting the vented gas into the liquid string.
It is another object of the present invention to provide an artificial lift
system which
maximizes the space in the well bore available for the installation of the
shifting valve.
These and other objects of the present invention will become apparent from a
reading of the
attached specification and appended claims.
SUMMARY OF THE INVENTION
The present invention is an artificial lift system for use in a well bore that
comprises at least
one chamber having an inlet and an outlet, a power gas string in valved
communication with the
chamber, a liquid string in valved communication with the outlet of the
chamber, a vent in valved
communication with the chamber and in valved communication with the liquid
string at a location
above the chamber, a compressor connected to the power gas string and adapted
to pass a
pressurized gas into the power gas string, and a valve connected to the power
gas string and to the
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chamber. The valve is adapted to selectively allow the pressurized gas to
enter the chamber so as
to cause a liquid in the cha-nber to pass through the outlet of the chamber
and into the liauid string.
hi the present invention, the vent has two components. A first venting tube
has a chccl:
valve connected to the liquid string. The check valve is adapted to pass a
portion of the vented gas
into the liquid string. Another vent tube extends fronl the chan-iber so as to
vent a remaining portion
of the vented gas into the well bore. The valved conunLuucation between the
vent and the liquid
string is at a location at least 2500 feet above the chanzber.
In the present invention, the liquid will extend continuously as an
ungassified liquid line
along the liquid string from the outlet of tlie chamber to the area of valved
coinmunication between
the vent and the liquid string. In the present invention, the compressor is
adapted to pass a
pressurized gas of greater than 5,000 p.s.i. into the power gas string. In the
present invention, the
valve is actually positioned in the liquid string. A liquid bypass extends
aroLmd the valve.
In the preferred embodiment of the present invention, there is a first
chainber having an inlet
and an outlet, and a second chamber having an inlet and an outlet. The second
chamber is arranged
in parallel relation to the first chamber. The first cliamber is, in
particular, arranged in spaced and
separate relationship to the second chaniber. The first chamber has an
approximately equal volume
to the second chamber. The first chamber has a top end aligned in a horizontal
plane with a top of
the second chamber. Also, the first chamber has a bottom end aligned in a
horizontal plane with a
bottom of the second chainber.
In the present invention, the vent is connected to the liquid string so as to
reinject vented gas
into the liquid string for the purposes of lightening the weight of the liquid
within the liquid string.
The vent tube that is connected to the liquid string nZust have sufficient
length so as to allow the
pressurized vented gas to actually enter the liquid in the liquid string.
After the pressure of the
vented gas with the pressure in the liquid line reach equilibriuni, then the
rernainder of the vented
pressurized gas will exit the chainber tlu-ough the sccond vent tube into the
well bore.
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According to one aspect of the present invention,
there is provided an artificial lift system for use in a
well bore comprising: a first chamber having an inlet and an
outlet; and a second chamber having an inlet and an outlet,
said second chamber arranged in parallel relation to said
first chamber, said first chamber arranged in spaced and
separate relationship to said second chamber, said first
chamber having an approximately equal value as said second
chamber; a power gas string in valved communication with
said first and second chambers; a liquid string in valved
communication with said outlets of said first and second
chambers; a vent in valved communication with said first and
second chambers, said vent being in valved communication
with said liquid string at a location above said first and
second chambers, said vent adapted to pass a vented gas from
said first and second chambers; a compressor connected to
said power gas string and adapted to pass a pressurized gas
into said power gas string; and a valve connected to said
power gas string and to said first and second chambers, said
valve adapted to selectively allow the pressurized gas to
enter said first and second chambers so as to cause a liquid
in said first and second chambers to pass through said
outlet of said first and second chambers and into said
liquid string.
According to another aspect of the present
invention, there is provided an artificial lift system for
use in a well bore comprising: a first chamber having an
inlet and an outlet; a second chamber having an inlet and an
outlet, said first chamber arranged in parallel spaced
relationship to said second chamber, said first chamber of
volume approximately equal to a volume of said second
chamber, said first chamber having a top end aligned in a
horizontal plane with a top of said second chamber, said
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first chamber having a bottom end aligned in a horizontal
plane with a bottom of said second chamber; a power gas
string in valved communication with said first chamber and
said second chamber; a liquid string in valved communication
with said outlet of said first chamber and with said outlet
of said second chamber; a vent in valved communication with
said first chamber and with said second chamber, said vent
being in valved communication with said liquid string at a
location above said first and second chamber, said vent
adapted to pass a vented gas from said first and second
chambers and into said liquid string; a compressor connected
to said power gas string and adapted to pass a pressurized
gas into said power gas string; and a valve connected to
said power gas string and to said first and second chambers,
said valve adapted to selectively and alternately allow the
pressurized gas to enter said first chamber and said second
chamber so as to cause a liquid in said first chamber to
pass through said outlet of said first chamber and into said
liquid string and to cause a liquid in said second chamber
to pass through said outlet of said second chamber and into
said liquid string.
According to still another aspect of the present
invention, there is provided an artificial lift system for
use in a well bore comprising: at least one chamber having
an inlet and an outlet; a power gas string in valved
communication with said chamber; a liquid string in valved
communication with said outlet of said chamber; a vent in
valved communication with said chamber, said vent adapted to
pass a vented gas from said chamber and into said well bore;
a compressor connected to said power gas string and adapted
to pass a pressurized gas into said power gas string; and a
valve connected to said power gas string and to said
chamber, said valve positioned in said liquid string, said
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liquid string having a liquid bypass extending around said
valve, said valve adapted to selectively allow the
pressurized gas to enter said chamber so as to cause a
liquid in said chamber to pass through said outlet of said
chamber and into said liquid string.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a diagrammatic cross-sectional view
showing the configuration of the artificial lift system of
the present invention.
FIGURE 2 is a cross-sectional view illustrating
the preferred embodiment of the present invention.
FIGURE 3 is a diagrammatic illustration showing
the operation of the shifting valve of the
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present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
Referring to FIGURE 1, there is shown diagrammatically at 10 the artificial
lift system in
accordance with the teachings of the present invention. The artificial lift
system 10 is used for the
extraction of oil, water and gas from the wellbore 12. The artificial lift
system 10 includes a
chamber 14, a power gas stringl6, a liquid string 18, a first vent stack 20
and a second vent stack
21, and a compressor 22. A suitable valving mechanism 24 is provided in
association with the
chamber 14. The valving mechanism 24 will be described in greater detail in
connection with the
illustrations of FIGURES 2 and 3.
As can be seen in FIGURE 1, the chamber 14 is located in the wellbore 12 below
the
perforations 26 that are formed in the wellbore 12. The chamber 14 could also
be positioned above
the perforations 26 in the wellbore 12. The perforations 26 can be associated
with perforations that
are formed in an existing casing or in an existing production tubing. The
power gas string 16 will
extend from the compressor 22 to the chamber 14. The valving mechanism 24 is
interactively
connected with the power gas string 16 so as to allow pressurized gas to enter
the chamber and to
cause any liquid in the chamber 14 to pass through an outlet in the chamber
and into the liquid string
18. Any liquids within the chamber 14 will enter the liquid string 18 in a
continuous flow line along
the liquid string 18. The liquid within the liquid string 18 will be
ungasified from the outlet of the
chamber 14 to the connection of the liquid string 18 with the first vent stack
20. The liquid string
18 extends from the chamber 14 to the wellhead area 28. As such, liquid, such
as oil, can be
removed from the wellbore 12. Vent stack 20 is illustrated as extending from
the chamber 14. The
vent stack 20 will extend from the chamber 14 and be connected through the use
of a check valve
29 to the liquid string 18. The vent stack 20 will be sufficiently long so as
to allow the release of
pressurized gas into the liquid string 18 at a location where the pressures
within the liquid string 18
allow for the introduction of such pressurized gas. The vent stack 21 is also
illustrated as extending
from the chamber 14. The vent stack 21 should have a suitable height so that
the outlet 30 of the
vent stack 21 is located in a position above the perforations 26. It should be
noted that when the
pressurized gas from the chamber 14 is released through the vent stack 20 and
through the check
valve 29 into the liquid string 18 that, eventually, the pressures will reach
equilibrium. As a result,
the remaining pressurized gas from the chamber 14 will be released into the
well bore 12 through
the vent stack 21.
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In FIGURE 1, the compressor 22 should be a multi-stage compressor which can
produce at
least 5,000 p.s.i. of gas pressure. This relatively large amount of gas
pressure is required so as to
push the entire line of liquid from the chamber 14 in a continuous line
through the liquid string 18.
The valving mechanisms, along with the associated tubing, should have
sufficient integrity to
withstand such pressure. The power gas string 16 and the liquid string 18 can
be formed of coiled
tubing. Such coiled tubing can be run in and pulled from the well together as
siamese strings. This
provides an enormous efficiency in the installation and removal of such power
gas and liquid
strings.
FIGURE 2 shows the preferred embodiment of the artificial lift system 40 of
the present
invention. The artificial lift system 40 is located in a well bore 42. In the
artificial lift system 40
of the present invention, a first chamber 44 is positioned within the well
bore 42 in spaced parallel
relationship to a second chamber 46. The chambers 44 and 46, preferably, have
equal volumes. So
as to avoid problems associated with differing hydrostatic pressures, the top
48 of chamber 44 and
the top 50 of chamber 46 will be in the same horizontal plane. Similarly, the
bottom 52 of chamber
44 will be in the same horizontal plane as the bottom 54 of chamber 46. It has
been found that this
side-by-side relationships of the chambers 44 and 46 to be more easily
installed within the well bore
42 without undue mechanical manipulation or structural engineering.
Furthermore, the positioning
of the chambers 44 and 46, at approximately the same location within the well
bore, avoids any
differences in the loading of chambers 44 and 46 because of the head pressure
within the well. The
arrangement of the chambers 44 and 46 in the side-by-side spaced relationship
facilitates the
automatic and continual cycling of the artificial lift system without uneven
liquid accumulation
within the chambers.
In FIGURE 2, it can be seen that the well bore 42 includes perforations 56
that are formed
along the wall of the well bore 42. As such, liquid from the subsurface earth
formation can enter
the well bore 42 and eventually accumulate within the chambers 44 and 46.
In FIGURE 2, the power gas string 58 is arranged so as to be in valved
communications with
each of the chambers 44 and 46. The liquid string 60 also extends so as to be
in valved
communication with the chambers 44 and 46. A first vent stack 62 was further
connected in valved
communication with the chambers 44 and 46. Also, a second vent stack 64 is
connected in valved
communication with the chambers 44 and 46. A shifting valve 66 is provided
within the artificial
lift system 40 so as to suitably connect each of the above-identified
components with the respective
chambers 44 and 46. The operation of the shifting valve 66 will be described
in greater detail
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hereinafter.
It can be seen that the first vent stack 62 is connected with a check valve 68
to the liquid
string 60. As such, gas will flow from the first vent stack 62, through the
check valve 68 and into
the liquid string 60. As will be described hereinafter, an emperial analysis
of the pressures within
the well bore 42 would indicate that the vent stack 62 should have a length of
at least 2,500 feet.
If the first vent stack 62 is not sufficiently long, then the pressure of the
liquid within the liquid
string 60 will prevent the introduction of pressurized vent gases into the
liquid string 60. As such,
the vented gases should be introduced into the liquid string 60 at a location
where the pressure of
the liquid within the liquid string 60 allows for the introduction of such
gases at an economically
and energy efficient manner. - The second vent stack 64 has an outlet which is
located above
the perforations 56 in the casing of the well bore 42. As such, the second
vent stack 64 is suitable
for venting gas into the annulus 70 of the well bore 42. Alternatively, the
vent stack 64 could be
connected to the compressor 22 (as shown in FIGURE 1) at the surface of the
well to improve the
efficiency of the compressor. Alternatively, and still further, the vent stack
64 could extend to the
surface so that the gases received therefrom could be stored and reused.
With respect to the accumulation of liquids within the chambers 44 and 46, it
is to be noted
that there is a system of check valves 74, 84, 92 and 100 implemented in the
bottom packing 72 of
the system 40. Initially, an inlet check valve 74 is positioned adjacent to
the passageway 76. Inlet
check valve 74 allows any liquids from the annulus 70 of the well bore 42 to
pass thereinto and
through passageway 78 and 80 and into the chamber 44. Check valve 74 will
prevent any liquids
from passing out of passageway 76. During the injection of pressurized gas
into the chainber 44,
any liquids on the interior of the chamber 44 will pass through passageway 80,
through passageway
82, through check valve 84, through passageway 86, and into the liquid string
60. Check valve 84
will prevent any liquids within the liquid string 60 from passing back into
and through the various
passageways into the first chamber 44.
For the loading of the second chamber 46, initially, liquids from the well
bore 42 will pass
through the opening 88 and into passageway 90. These liquids will flow through
passageway 90,
through check valve 92 and into passageway 94. These liquids will then flow
through passageway
96 and into the second chamber 46. The check valve 92 will prevent the liquids
in the chamber 46
from exiting through the various passageways and out of opening 88. Upon the
introduction of
pressurized gas into the interior of the second chamber 46, the liquid within
the second chamber 46
will pass outwardly therefrom through passageway 96, through passageway 98 and
through check
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valve 100 into the liquid string 60. Check valve 100 will prevent the liquids
within the liquid string
60 from passing therethrough and back into the chamber 46.
A shifting valve 66 is provided so as to have a suitable action for the
purpose of allowing
the power gas string 58 to selectively connect with the chambers 44 and 46 and
for allowing the
chambers 44 and 46 to be connected to the vent stack 62 and 64. Shifting valve
66 can be of a
standard form of valve design which is adapted for the downhole pressures. The
shifting valve 66
is wireline retrievable. Unique to the present invention, the shifting valve
66 is actually positioned
within the liquid string 60. A liquid bypass line 102 extends around the
shifting valve 66 so as to
allow liquid in the liquid string 60 to flow in a continuous line therearound.
Unlike the parent
applications to the present invention where the shifting valve was placed in a
side pocket mandrel,
in the present invention, the shifting valve 66 is placed directly into the
liquid string 60. The liquid
bypass line 102 extends around the shifting valve 66. This allows the shifting
valve 66 to be of a
larger shape. For example, using estimated sizes, if the shifting valve 66 is
placed within the liquid
string 60, then the shifting valve 66 can have a diameter of 21/4 inches.
However, if it is used in a
side pocket mandrel, the shifting valve 66 can only have a size of 1 1/4
inches. As a result, the
present invention provides greater amount of room for the proper installation
and configuration of
the shifting valve 66. The liquid bypass line 102 can have any suitable
diameters since the liquids
will simply flow through the bypass line 102 in a faster manner if the bypass
line 102 is of smaller
diameter than the remainder of the liquid string 60.
As shown in FIGURE 2, the shifting valve 66 can have two positions. When the
shifting
valve 66 is in the first position, it connects the power gas string 58 with
the passageway 104 to the
first chamber 44. In this same position, the connection of the first chamber
44 to the vent stacks 62
and 64 is blocked. As such, the chamber 44 will not communicate with the vent
stack 62 and 64.
When the shifting valve 66 is in this first position, it will connect the vent
stack 62 and 64 with
passageway 106 so as to allow the second chamber 46 to vent any pressurized
gas into the vent stack
62 and 64. Within the present invention, it should be noted that the vent
stack 62 and the vent stack
64 can be suitably timed so that the release through the vent stack 64 will
only occur after the
pressure equilibrium has been achieved between the pressure of the gas and the
vent stack 62 and
the pressure of the liquid in the liquid string 60. Alternatively, a single
vent stack 62 can be used
in which the remaining vented gases can exit through opening 108 after the
pressure equilibrium
has been reached between the pressure of the gas in the vent stack 62 and the
liquid string 60. In
this first position, the power gas string 58 is blocked from entering
passageway 106. As a result,
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the second chamber 46 will not connect with the power gas string 58. When the
shifting valve 66
is in this first position, power gas will displace any liquids in the chamber
44 into the liquid string
60. In particular, the liquids within the chamber 44 will flow outwardly
therefrom through
passageway 80, through passageway 82, through check valve 84, through
passageway 86, and
outwardly therefrom into the liquid string 60. Chamber 46 will simultaneously
depressurize and
allow any gases to flow therefrom into the vent stack 62 and 64.
Simultaneously, chamber 46 will
begin to be filled with liquid from the annulus 70 of well bore 42. Chamber 46
receives this liquid
through inlet opening 88, through passageway 90, through check valve 92,
through passageway 94
and through passageway 96.
When the shifting valve 66 switches to a second position, the connections are
reversed. In
other words, chamber 44 will communicate with the vent stacks 62 and 64
through passageway 104.
Chamber 46 will communicate with the power gas string 58 through passageway
106. In this
manner, the present invention is able to achieve simultaneous displacement of
one chamber while
the other chamber is being depressurized and refilled. It is believed that
this double chamber
configuration can lift twice as much liquid as a single chamber arrangement.
Production capacity
is not interfered with since at least one of the chambers 44 and 46 will be
continuously receiving
liquid from the annulus 70 through passageway 76 or opening 88. This
arrangement allows for
continuously cycling of the various components rather than an on/off
arrangement of a single
chamber arrangement.
Within the concept of the present invention, it is to be noted that the
shifting valve 66 can
move to other positions, if so desired. Under certain circumstances, it may be
desirable that the
pressurized gas accumulate within the pressurized gas string 58 before being
introduced into either
of the chambers 44 and 46. As such, the shifting valve 66 can move to a third
position in which
power gas flow is blocked from either of the chambers 44 and 46. In such an
arrangement, the
chambers 44 and 46 can simultaneously vent through vent stacks 62 and 64
and/or be filling with
liquid from the annulus 70. Another position of the shifting valve 66 would
have chambers 44 and
46 communicating with each other and not in communication with vent stacks 62
and 64 nor the
power gas string 5 8. This position of the shifting valve 66 would allow the
flow from one chamber
to the other. This position of the shifting valve 66 might occur at the point
in the lift cycle in which
one chamber had completed the displacement of liquids into the liquid string
60 (filled with power
gas) and the other chamber had been vented and filled with liquids from the
annulus 70. The flow
of gas from the just displaced chamber would "precharge" the liquid filled
chamber with high
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pressure gas and thus raise the pressure in said liquid filled chamber. This
precharge would reduce
the volume of power gas that would be required to raise the pressure in the
liquid filled chamber to
the pressure required to displace liquids from the chamber to the liquid
string 60. The precharge
stage will reduce the energy requirements of the system and thus make it more
efficient. Still
further and alternatively, the shifting valve 66 can be configured so that the
shifting valve 66 will
move to a position such that the high pressure gases from one of the chambers
44 and 46 will
initially vent through the vent stack 62 through the check valve 68 and into
the liquid string 60.
After a predetermined period of time or a predetermined reduction in pressure,
the shifting valve
66 can move to another position so that the remaining vented gases from either
of the chambers 44
and 46 will be released through the vent stack 64 into the annulus 70.
FIGURE 3 illustrates, diagrammatically, how the various fluids flow within the
system and
through the shifting valve 66. Initially, with respect to the power gas string
58, the power gas is
illustrated with broken lines. Depending upon the position of the shifting
valve 66, the power gas
110 will pass downwardly through the shifting valve 66 and into the passageway
106 or upwardly
into the passageway 104. In the first position of the shifting valve 66, the
power gas 110 will flow
upwardly into the passageway 104. In the second position, the power gas 110
will flow downwardly
into the passageway 106. The vented gases are illustrated by dashed lines. The
vented gases 112
from chamber 44 will pass through passageway 104 and downwardly through
shifting valve 66 so
as to exit either the first vent stack 62 or the second vent stack 64.
Similarly, the vented gases 114
from the chamber 46 will enter through passageway 106 and will exit through
the vented gas stacks
62 and 64. The liquid, which has been evacuated from the chambers 44 and 46
will exit through
bypass line 102 of liquid string 60 in the manner illustrated by solid line
116.
An important aspect of the present invention is the economic efficiency
achieved by the
present invention in the delivery of spent power gas into the liquid string.
It is important to note that
such economic and energy efficiencies are not achieved throughout the entire
length of the liquid
string. An analysis of the economic efficiencies of the introduction of gas
into the liquid string are
shown hereinbelow in Tables I and II.
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TABLEI
INJErT D PTH(FT1 LIQUID STRING BOTTOMHOLE PRESSIPRESS 3 GLA INJECTION
DEPTH(PSII
9 14 24 u 411 511 fiSl 74 64 9.4 ]d14
(0) (310) (620) (928) (1238) (1548) (1858) (2168) (2476) (2786) (3096)
25M 6108 5810 5702 5676 5667 5669 5680 5696 5722 5744 5753
1188 891 794 761 753 755 765 789 812 832 839
5000 6108 5641 5363 - 5244 5191 5171 5170 5191 5214 5235 5256
2175 1711 1434 1315 1263 1243 1243 1263 1285 1307 1327
7500 6108 5597 5159 4922 4798 4735 4709 4714 4728 4745 4769
3161 2651 2215 1979 1856 1793 1767 1772 1786 1803 1827
1(),000 6108 5558 5054 4697 4490 4371 4306 4287 4284 4289 4305
4145 3596 3093 2738 2531 2412 2348 2329 2326 2331 2347
12,500 6108 5520 4979 4544 4252 4070 3961 3910 3884 3872 3876
5127 4540 3999 <35653247 3092 2983 2932 2907 2895 2898
TABLE II
CASE GL ASSIST VOLUME POWER GAS DATA
RATE CYCLE GAS SURFAC DISP
(MCFD) (SCF) RATE PRESS RATIO
(MCFD) (PSI) (SCFIBBL)
20% @ 10,000FT 620 310 2707 4618 1354
30% @ 12,500FT 928 464 2477 4134 1239
30% @ 10,000FT 928 464 2549 4278 1273
CHAMBER CONDITIONS GAS LIFT ASSIST FLOW DATA POWER REQUIREMENTS
PREIPOST GAS L1FT ASSIST INITIAUFINAL CONDITIONS W/OM11TH GAS LIFT ASSIST
PRESS DENSITY GAS VOL CHAMBER LIQ STG DIFFER FLOW FLOW 8HP DELTA Y. EFFIC
(DIFF) PRESS PRESS PRESS RATE T1ME (SHP) (8HP) ("/o)
(PSI) (PPG) (SCF) (PSI) (PSI) (PSI) (MCFD) (SEC)
5054J3671 1.4411.11 1354/1039 505413671 3093/3093 1961/578 673212714 4/10
540/434 96 40149
(315)
4544/3565 1.3211.08 1236/1011 NO FLOW-ONLY 225SCF AVAIL-NEED 464SCF Q 12.500'
TO ACHIEVE THE FBHP IN L1Q STQ
(225)
4697/2738 1.38/.86 1273/805 4697/2738 2738/2738 1959/0 6488/0 6/- 540/403 =
137 40/54
468 WILL NOT WORK-FINAL CHAM PRESS SAME AS PRESS @ INJECT POINT-NO FLOW Q
FINAL COND
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The above tables are gas lift assist calculations based upon the double
chamber arrangement
(illustrated in FIGURE 2) as delivering 2,000 BFPD in which the chambers are
located at 15,000
feet of depth. The analysis of Table I is based, in the vertical columns, on
the percent of power gas
which is utilized and reinjected into the liquid string. The volume of power
gas (MCFD) is
identified within the parenthesis below the percentage shown in 10%
increments.
A brief analysis of the respective pressure analysis which indicate the
economic efficiencies
are shown in the range in which the spent power gas is reinjected into the
liquid string in an amount
of 30% at 12,500 feet of depth or in an amount of between 20 and 30% at 10,000
feet of depth. A
more detailed analysis of the associated economics are shown in Table II. The
ultimately most
efficient situation is achieved in which 20% of the spent power gas is
injected at 10,000 feet. Horse
power requirements of the compressor are reduced from 540 to 444. As such, in
such an
arrangement, an energy efficiency is achieved. Given the long operating
conditions of such a well,
such an energy efficiency will translate into significant cost savings. The
analysis showed that the
economic and energy efficiency was at very marginal levels in which 30% of the
spent power gas
is injected at either 10,000 feet or 12,500 feet. As such, within the concept
of the present invention,
it is believed that, in order to achieve certain economic efficiencies where
the chamber is positioned
at 15,000 feet of depth (for example), the first vent gas stack 62 (as shown
in FIGURE 2) must
extend at least 2,500 feet from the chamber.
The artificial lift system of the present invention is particularly useful for
restoring
production in depleted high condensate yield sour gas wells. In particular,
this system can be
applied to Smackover wells. The present invention achieves flowing bottom hole
pressures of
approximately 600 p.s.i. at 13,000 feet with flowing wellhead pressures of 300
p.s.i. The
configuration of the present invention employs an apparatus that can withstand
bottonihole
temperatures of greater than 300 degrees F. The present system can handle
produced gas volumes
of 3,000 MCFD. The present invention can achieve the production of liquid
volumes exceeding 500
barrels per day. The present invention is suitable for operating in a very
"gassy" high API oil
gravity environment. Since the wells in which the present invention are
intended to be used for
producing in sour gas environments, the present invention minimizes the
downhole parts. As a
result, the present invention avoids the destructive effects of the corrosive
environment into which
it is placed. The downhole moving parts are wireline retrievable. The present
invention can work
with saturated brines having greater than 200,000 parts per million chlorides.
The present invention
is compatible with conventionally-sized production casing. Despite the fact
the present invention
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can be used at very deep depths, the present invention is cost competitive
with other forms of lift.
It is possible that the present invention can be utilized in depths of up to
25,000 feet and can lift
higher volumes of up to 2,000 barrels per day. Unlike intermittent systems,
the present invention
pushes an entire line of liquid through the liquid string. As such, the
transit time of individual
"slugs" of liquid is avoided. The liquid string continuously allows the
outflow of liquid therefrom.
The ability to control and utilize high gas pressures allows for the necessary
"brute" force so as to
deliver the continuous string of liquid from the liquid string.
The foregoing disclosure and description of the invention is illustrative and
explanatory
thereof. Various changes in the details of the illustrated construction or in
the steps of the described
method can be made within the scope of the appended claims without departing
from the true spirit
of the invention. The present invention should only be limited by the
following claims and their
legal equivalents.
