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Patent 2485035 Summary

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(12) Patent: (11) CA 2485035
(54) English Title: GAS RECOVERY APPARATUS, METHOD AND CYCLE HAVING A THREE CHAMBER EVACUATION PHASE AND TWO LIQUID EXTRACTION PHASES FOR IMPROVED NATURAL GAS PRODUCTION
(54) French Title: APPAREIL EXTRACTEUR DE GAZ, METHODE ET CYCLE COMPORTANT UNE PHASE D'EVACUATION PAR TRIPLE CHAMBRE ET DEUX PHASES D'EXTRACTION DES LIQUIDES POUR AMELIORER LA PRODUCTION DE GAZ NATUREL
Status: Deemed expired
Bibliographic Data
(51) International Patent Classification (IPC):
  • E21B 43/18 (2006.01)
  • E21B 43/12 (2006.01)
(72) Inventors :
  • REITZ, DONALD D. (United States of America)
(73) Owners :
  • FORESTAR PETROLEUM CORPORATION (United States of America)
(71) Applicants :
  • REITZ, DONALD D. (United States of America)
(74) Agent: MOFFAT & CO.
(74) Associate agent:
(45) Issued: 2007-04-10
(22) Filed Date: 2004-10-18
(41) Open to Public Inspection: 2005-05-03
Examination requested: 2004-10-18
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
10/700,296 United States of America 2003-11-03

Abstracts

English Abstract

Natural gas produced from a well by executing a multiple-phase gas recovery cycle which includes a phase during which a relatively lower evacuation pressure is applied within three chambers in the well to assist in accumulating liquids at a well bottom, followed by a liquid reduction phase which clears the liquid from two of the chambers while leaving the liquid in the third chamber. The remaining liquid is thereafter lifted in subsequent liquid capture and liquid removal phases. The liquid reduction phase clears the fluid from the well more effectively with less interruption in the production of gas from the well while maintaining the full gas productivity of the well.


French Abstract

Produire du gaz naturel dans un puits à l'aide d'un cycle de récupération du gaz à plusieurs phases. Le cycle comprend une phase durant laquelle une pression d'évacuation relativement basse est appliquée dans trois chambres du puits afin de favoriser l'accumulation de liquides au fond du puits; cette phase est suivie d'une phase de réduction des liquides qui consiste à extraire les liquides dans deux chambres et à laisser ceux dans la troisième chambre. Les liquides restants sont ensuite retirés durant les phases suivantes de capture et d'extraction des liquides. Durant la phase de réduction des liquides, les liquides sont évacués plus efficacement du puits en interrompant moins souvent la production de gaz dans le puits et en maintenant la productivité totale de gaz du puits.

Claims

Note: Claims are shown in the official language in which they were submitted.



The invention claimed is:

1. A method of recovering natural gas from a well in a multiple phase
gas recovery cycle, the well having a casing chamber defined by a casing
within
the well, a production chamber within a production tubing inserted into the
casing chamber and a lift chamber defined by a lift tube inserted within the
production chamber, the well also including a one-way valve separating the
production chamber from the casing chamber; the gas recovery cycle including
a three chamber evacuation phase in which a relatively low pressure is applied
within the casing chamber, production chamber and lift chamber to cause the
relatively low pressure to augment natural earth formation pressure and flow
more liquid and gas into the casing chamber than would flow only from the
natural formation pressure, a liquid capture phase in which relatively high
pressure gas is applied to the casing chamber to move liquid within the casing
chamber through the one-way valve into the production chamber, and a liquid
removal phase in which relatively high pressure gas is applied to the
production
chamber to close the one-way valve and to isolate the production chamber from
the casing chamber and to lift liquid isolated in the production chamber up
the
lift chamber, and a liquid reduction phase executed after the three chamber
evacuation phase and before the liquid capture phase by:
applying relatively high pressure within the production chamber to
close the one-way valve and to isolate the production chamber from the casing
chamber and to lift the liquid accumulated within the production chamber
during
the three chamber evacuation phase out of the well through the lift chamber;
while
maintaining the relatively low pressure within the casing chamber.

2. A method as defined in claim 1, further comprising:
flowing natural gas from the casing chamber out of the well during
the liquid reduction phase.

3. A method as defined in claim 1, further comprising:



35


beginning the liquid reduction phase after sensing a
predetermined amount of natural gas flow from the casing chamber out of the
well
4. A method as defined in claim 1, further comprising:
beginning that liquid reduction phase after sensing a
predetermined pressure of natural gas in the casing chamber.
5. A method as defined in claim 1, further comprising:
beginning the liquid reduction phase after sensing a
predetermined reduction in natural gas flow from the casing chamber out of the
well and after sensing a predetermined pressure of natural gas in the casing
chamber.
6. A method as defined in claim 1, further comprising:
reducing the amount of liquid to be lifted during the liquid removal
phase by lifting liquid during the liquid reduction phase.
7. A method as defined in claim 6 wherein the pressurized gas used
during the gas recovery cycle to lift liquid from the lift chamber is supplied
by a
compressor having a predetermined capacity, and the method further
comprises:
establishing the quantity of liquid to be lifted during the liquid
reduction phase to not exceed the predetermined capacity of the compressor.
8. A method as defined in claim 7, further comprising:
reducing the quantity of liquid to be lifted during the liquid removal
phase by executing the liquid reduction phase; and
establishing the selected lift quantity of liquid to be lifted during the
liquid removal phase to not exceed the predetermined capacity of the
compressor.
9. A method as defined in claim 8, further comprising:



36




selecting the predetermined amount of natural gas flow from the
casing chamber and the predetermined pressure of natural gas in the casing
chamber at which to begin the liquid reduction phase to correlate to a column
of
accumulated liquid within the casing chamber at the well bottom.

10. A method as defined in claim 9, further comprising:
selectively beginning the liquid reduction phase prior to the
column of accumulated liquid presenting a hydrostatic head pressure greater
than the natural earth formation pressure.

11. A method as defined in claim 1, further comprising:
lifting quantities of liquid during the liquid reduction and liquid
removal phases to maximize the duration of the three chamber evacuation
phase.

12. A method as defined in claim 1, further comprising:
ending the liquid removal phase after sensing a predetermined
pressures in the production and lift chambers.

13. A method as defined in claim 1, further comprising:
preventing substantial liquid in the production chamber and the lift
chamber from flowing into the casing chamber during the liquid reduction
phase.

14. A method as defined in claim 1, further comprising:
preventing substantial liquid in the casing chamber from flowing
into the production chamber and the lift chamber during the liquid reduction
phase.

15. A method of recovering natural gas from a well in a multiple phase
gas recovery cycle, the well having a casing chamber defined by a casing
within
the well, a production chamber within a production tubing inserted into the
casing chamber and a lift chamber defined by a lift tube inserted within the



37


production chamber, the well also including a valve separating the production
chamber from the casing chamber; the gas recovery cycle including a casing
evacuation phase in which a relatively low pressure is applied within the
casing
chamber to cause the relatively low pressure to augment natural earth
formation pressure and flow more liquid and gas into the casing chamber than
would flow only from the natural formation pressure, a liquid capture phase in
which liquid from the casing chamber is moved through the valve into the
production chamber, and a liquid removal phase in which liquid isolated in the
production chamber by the valve is lifted up the lift chamber and out of the
well,
and a liquid reduction phase executed after the evacuation phase and before
the liquid capture phase by:
lifting liquid accumulated within the production chamber during the
evacuation phase out of the well through the lift chamber; while
maintaining the relatively low pressure within the casing chamber.
16. A method of recovering natural gas from a well extending from the
earth surface to a subterranean earth formation from which gas and liquid are
produced at a bottom of the well and transported from the bottom of the well
through a casing chamber, a production chamber and a lift chamber extending
between the well bottom and the earth surface; the method executed by using a
multiple phase production cycle, the multiple phase production cycle including
an evacuation phase in which a relatively low gas pressure is applied to the
casing chamber, the production chamber and the lift chamber to communicate
through the chambers to the well bottom and with the earth formation from
which the gas and liquid are produced, and the multiple phase production cycle
also including a liquid reduction phase which is executed separately from a
liquid removal phase during each production cycle; the liquid reduction phase
and the liquid removal phase each including:
applying a relatively high pressure to the production chamber
while applying a relatively low pressure to the casing chamber, and
opening the lift chamber to flow liquid and gas therethrough to the
earth surface; and wherein each production cycle involves:



38


removing liquid accumulated in the production chamber and lift
chamber during the evacuation phase by executing the liquid reduction phase;
and
removing liquid accumulated in the casing chamber during the gas
production cycle by executing the liquid removal phase.
17. A method as defined in claim 16 wherein the evacuation phase
includes accumulating gas and liquid from the earth formation within the
casing
chamber, the production chamber and the lift chamber at the bottom of the
well,
the method further comprising:
flowing liquid from the production chamber to the lift chamber and
from the lift chamber to the earth surface during the liquid reduction phase.
18. A method as defined in claim 17, further comprising:
preventing substantial liquid from flowing from the production
chamber into the casing chamber during the liquid reduction phase.
19. A method is defined in claim 17, further comprising:
flowing at least some of the gas from the casing chamber directly
out of the well during at least one of the liquid reduction phase or the
liquid
removal phase.
20. A method is defined in claim 17, further comprising:
establishing the relatively low pressure at a pressure which is less
than atmospheric pressure at the earth surface.
21. A gas recovery apparatus for producing natural gas from a well
and delivering the produced natural gas to a sales conduit, the well extending
from the earth surface into a subterranean earth formation where the natural
gas and liquid enter the well, the apparatus including tubing inserted into
the
well to create a casing chamber in fluid communication with the earth
formation
and a production chamber and a lift chamber which are separate from one
another within the well, the apparatus also including a one-way valve
separating



39


the production chamber from the casing chamber, the gas recovery apparatus
further comprising:
a compressor having a suction manifold and a discharge manifold,
the compressor creating a flow of relatively low pressure gas in the suction
manifold and a flow of relatively high-pressure gas in the discharge manifold;
control valves connecting each of the casing chamber, the
production chamber and the lift chamber to the suction manifold and the
discharge manifold to establish selective fluid communication between the
suction manifold and each of the casing chamber, the production chamber and
the lift chamber and to establish selective fluid communication between the
discharge manifold and each of the casing chamber and the production
chamber, the control valves also connecting the lift chamber and the discharge
manifold to the sales conduit to establish selective fluid communication
between the lift chamber and the discharge manifold and the sales conduit;
a controller programed to supply control signals to the control
valves to establish an opened state of each valve to permit fluid
communication
therethrough and to establish a closed state of each valve to prevent fluid
communication therethrough; the controller delivering a sequence of control
signals to the control valves to establish the opened and closed states of the
control valves which establish fluid communication conditions through the
casing chamber, the production chamber, the lift chamber and into the sales
conduit during a multi-phase gas recovery cycle; the gas recovery cycle
including a liquid capture phase during which pressurized gas supplied by the
compressor moves liquid from the casing chamber through the one-way valve
into the production chamber, a liquid removal phase in which pressurized gas
supplied by the compressor lifts liquid out of the well from the production
casing
through the lift chamber, a three chamber evacuation phase executed by
applying relatively low pressure within the casing chamber, production chamber
and lift chamber to augment natural earth formation pressure in moving liquid
and gas into the casing chamber, and a liquid reduction phase executed after
completion of the evacuation phase and before executing the liquid capture
phase, the liquid reduction phase executed by applying relatively low pressure
within the casing chamber and relatively high pressure within the production



40




chamber while the lift chamber is opened and connected to the sales conduit;
and wherein:
the controller establishes the states of the control valves during
the liquid capture phase to establish fluid communication between the
discharge manifold and the casing chamber and to establish fluid
communication between the suction manifold and the production chamber and
the lift chamber;
the controller establishes the states of the control valves during
the liquid removal phase to establish fluid communication between the
discharge manifold and the production chamber and to establish fluid
communication between the suction manifold and the casing chamber;
the controller establishes the states of the control valves during
the evacuation phase to establish fluid communication between the suction
manifold and the casing chamber, the production chamber and the lift chamber;
and
the controller establishes the states of the control valves during
the liquid reduction phase to establish fluid communication between the
suction
manifold and the casing chamber, to establish fluid communication between the
discharge manifold and the production chamber, and to establish fluid
communication between the lift chamber and the sales conduit.
22. A gas recovery apparatus as defined in claim 21, further
comprising:
pressure sensors connected to sense pressure within the casing
chamber, the production chamber and the lift chamber, the pressure sensors
delivering pressure signals to the controller related to the sensed pressure
within the casing chamber, the production chamber and the lift chamber;
flow sensors to sense the flow of natural gas from the lift chamber
to the sales conduit and from the casing chamber to the sales conduit, the
flow
sensors delivering flow signals to the controller related to the sensed flow
from
the lift chamber to the sales conduit and from the casing chamber to the sales
conduit, and wherein:



41



the controller selectively terminates each phase of the gas
recovery cycle and establishes the next phase of the gas recovery cycle based
on the pressure signals and the flow signals, and wherein the apparatus
further
comprises:
an additional control valve connecting the casing chamber to the
sales conduit to establish selective fluid communication between the casing
chamber and the sales conduit, and wherein:
the controller establishes the state of the additional control valve
to establish fluid communication between the casing chamber and the sales
conduit during the liquid reduction phase.



42

Description

Note: Descriptions are shown in the official language in which they were submitted.



CA 02485035 2004-10-18
Gas Recovery Apparatus, Method and Cycles having a Three Chamber
Evacuation Phase and Two Liquid Extraction Phases for Improved
Natural Gas Production
Field of the Invention
This invention relates primarily to producing natural gas from a well
having three chambers, and more particularly to a new and improved gas
recovery system, method and gas recovery cycle leaving one phase in which an
evacuation pressure is applied to the three chambers and a hydrocarbon-
bearing zone of the earth formation to assist natural formation pressure in
producing natural gas and liquid into the well, followed by two separate
liquid
extraction phases which remove significantly more liquid from the well to
increase the efficiency of gas production and to prevent certain types of
wells
from being slowly choked off by accumulated liquid if the technique described
in
~ s applicant's U.S. Patent No. 6,672,392, issued on January 6, 2004, is
employed
on those types of wells.
Background of the Invention
The production of oil and natural gas depends on natural pressure within
2o the earth formation at the bottom of a well bore, as well as the mechanical
efficiency of the equipment and its configuration within the well bore to move
the hydrocarbons from the earth formation to the surface. The natural
formation pressure forces the oil and gas into the well bore. In the early
stages
of a producing well when there is considerable formation pressure, the
2~ formation pressure may force the oil and gas entirely to the earth surface
without assistance. In later stages of a well's life after the formation
pressure
has diminished, the formation pressure is effective only to move liquid and
gas
from the earth formation into the well. The formation pressure pushes liquid
and gas into the well until a hydrostatic head created by a column of
30 accumulated liquid counterbalances the natural earth formation pressure.
Then, a pressure equilibrium condition exists and no more oil or gas or water
flows from the earth formation into the well. The hydrostatic head pressure
from the accumulated liquid column chokes off the further flow of liquid into
the
well bore, causing the well to "choke off' or "die," unless the accumulated
liquid
35 is pumped or lifted out of the well.


CA 02485035 2004-10-18
By continually removing the liquid, the hydrostatic head pressure from
the accumulated column of liquid remains less than the natural earth formation
pressure. Under such circumstances, the natural earth formation pressure
continues to move the liquid and gas into the well, allowing the liquid and
gas to
be recovered or produced. At some point when the natural earth formation
pressure has diminished significantly, the cost of removing the liquid
diminishes
the value of the recovered oil and gas to the point where it becomes
uneconomic to continue to work the weir. Under those circumstances, the well
is abandoned because it is no longer economically productive. A deeper well
will require more energy to pump the liquid from the well bottom, because more
energy is required to lift the liquid the greater distance to the earth
surface.
Deeper wells are therefore abandoned with higher remaining formation
pressure than shallower wells.
To keep a well in production, it is necessary to remove the accumulated
liquid to prevent the liquid from choking off the flovu of gas. Because a
considerably greater volume of gas is usually produced into a well compared to
the amount of liquid produced into the well, the greater volume of gas can be
recovered more economically by removing a relatively lesser volume of the
accumulated liquid. Consequently, there may be an economic advantage to
2o recovering natural gas at the end of a well's lifetime, because the gas is
more
economically recovered as a result of removing a relatively smaller amount of
accumulated liquid. These factors are particularly applicable to recovering
gas
from relatively deep wells.
Gas pressure lift systems have been developed to lift liquid from wells
2s under circumstances where mechanical pumps would not be effective or not
sufficiently economical. In general, gas pressure lift systems inject
pressurized
gas into the well to force the liquid up from the well bottom, rather than
rely on
mechanical pumping devices to lift the liquid. The injected gas may froth the
liquid by mixing the heavier density liquid with the Righter density gas to
reduce
so the overall density of the lifted material. Alternatively, "slugs" or
shortened
column lengths of liquid are separated by bubble-like spaces of pressurized
gas, again reducing the overall density of the lifted material. In both cases,
the
2


CA 02485035 2004-10-18
amount of energy required to lift the material is reduced, or for a given
amount
of energy it is possible to lift material from a greater depth.
One problem with injecting pressurized gas into a well casing is that the
pressurized gas tends to oppose the natural formation pressure. The injected
gas pressure counterbalances the formation pressure to inhibit or diminish the
flow of liquids and natural gas into the well. Once the injected gas pressure
is
relieved, the natural earth formation will again become effective to move the
liquid and gas into the well. However, because the casing annulus is
pressurized for a significant amount of time during each production cycle, the
~o net effect is that the injected gas pressure diminishes the production of
the well.
Stated alternatively, producing a given amount of liquid and gas from the well
requires a longer time period to accomplish. Such reductions in the production
efficiency in the later stages of the well's life may k~e so significant that
it
becomes uneconomical to work the well, even though some amount of
15 hydrocarbons remain in the formation.
One type of pressurized gas lift apparatus, method and gas recovery
cycle which is particularly advantageous for use with wells having relatively
low
down-hole natural earth formation pressure is described in the above-
identified
IJ.S. Patent. In that technique, a three chamber evacuation phase is included
2o in each gas recovery cycle to create a relatively low pressure throughout
the
well and thereby augment the natural earth formation pressure to draw more
gas and liquid from the surrounding earth formation into the bottom of the
well.
The relatively low pressure is communicated from the earth surface down into
the well through a casing chamber, a production chamber and a lift chamber.
2~ Liquid is forced from the casing chamber into the production and lift
chambers
'and is then lifted to the earth surface through the lift chamber by applying
a
relatively high pressure to the production chamber. A one-way valve at the
bottom of the production chamber allows fluid to flow from the casing chamber
into the production chamber, but the one-way valve confines the relatively
high
3o pressure in the production chamber when the liquid is lifted up the lift
chamber
to the earth surface. After the liquid is lifted in this manner, at least a
significant
portion of the gas is produced through the same path up the casing chamber,
down the production chamber and then up the lift s~hamber.
3


CA 02485035 2004-10-18
The three chamber evacuation phase in the gas recovery cycle is
particularly advantageous in improving the efficiency and maintaining the
productivity of relatively deep wells having relatively low natural earth
formation
pressures and which produce liquid at a relatively low rate. Because liquid is
s produced at a relatively low rate, it is possible to use the three chamber
evacuation phase as a primary gas production phase. The gas is produced
directly up the casing chambers and the gas is not subject to the flowing
friction
losses created by the relatively lengthy flow path Blown the smaller diameter
production chamber and then up the even smaller diameter lift chamber. The
flowing friction losses through the shortest flow path and largest diameter
casing chamber are substantially less than the more circuitous and friction-
engendering path up the casing chamber, down the production chamber and
then up the lift chamber.
The technique of the above-identified U.S. Patent is best implemented in
these low earth formation pressure-tow liquid production wells by minimizing
the
amount of time or proportion of each gas recovery cycle required to perform
the
liquid capture, liquid removal and production phases during which the liquid
is
removed from the casing chamber and lifted to the earth surface. The
relatively
low rate of liquid production by the well permits minimizing these phases
while
2o maximizing the more efficient gas producing three chamber evacuation phase.
Summary of the Invention
It has been discovered that minimizing the liquid capture, liquid removal
and production phases may not fully remove all of the removal liquid from the
2~ bottom of certain wells with low natural earth formation pressure and low
liquid
production. A slight residual amount of liquid remains in the casing chamber
after executing each gas recovery cycle, and that residual amount of liquid
will
build up with repetitions of the gas recovery cycle to the point where the
liquid
begins to choke the well and diminish gas production. While it is possible to
3o extend the liquid capture, gas removal and production phases to a greater
proportion of the gas recovery cycle to lift more liquid, extending those
phases
diminishes the gas production efficiency because of the greater flowing
friction
losses during those phases. Executing a special cycle on an aperiodic basis to
4.


CA 02485035 2004-10-18
eliminate the residual accumulated liquid that has not been removed during
each normal gas recovery cycle is also not desired. It is difficult and
inconvenient to change the operation of the well to execute only a few of
these
cycles on an aperiodic basis, and the less skilled personnel which normally
administer the production of a well may be incapable of changing the well
operation to accommodate aperiodic operational differences.
The present invention improves the gas recovery technique described in
the above-identified LJ.S. Patent, by including a liquid reduction phase in
each
gas recovery cycle. In general, the liquid reduction phase assures that all of
the
recoverable liquid from the well bottom will be lifted during each gas
recovery
cycle, thereby preventing slight residual amounts c~f liquid from accumulating
over time to the point where the productivity of the well is diminished or
terminated. The use of the liquid reduction phase also shortens the amount of
time consumed during each recovery cycle by the more inefficient liquid
capture, liquid removal and production phases. Consequently, the efficiency of
gas production from the well is improved because less time is consumed in
forcing gas through the lengthy and friction-prone path from the earth surface
down the production chamber and back up the lift chamber. In a similar sense,
the time during which gas may be produced in the more efficient three chamber
2o evacuation phase is extended, because the liquid reduction phase maintains
the relatively low pressure on the casing chamber to encourage liquid and gas
flow into the well, and because more liquid can be lifted during each gas
recovery cycle without increasing the amount of tirne when the relatively low
pressure in the casing chamber must be terminated or changed to a relatively
25 high pressure, as occurs during the liquid capture phase.
These and other improvements and benefits are realized from a method
of recovering natural gas from a well in a multiple phase gas recovery cycle.
The well has a casing chamber defined by a casing within the well, a
production
chamber within a production tubing inserted into the casing chamber and a lift
3o chamber defined by a lift tube inserted within the production chamber. The
well
also includes a one-way valve separating the production chamber from the
casing chamber. The gas recovery cycle includes a three chamber evacuation
phase in which a relatively low pressure is applied within the casing chamber,
5


CA 02485035 2004-10-18
the production chamber and the lift chamber to cause the relatively low
pressure to augment natural earth formation pressure and flow more liquid and
gas into the casing chamber than would flow only 'from the natural formation
pressure. The gas recovery cycle also includes a liquid capture phase in which
relatively high pressure gas is applied to the casing chamber to move liquid
within the casing chamber through the one-way valve into the production
chamber, and a liquid removal phase in which relatively high pressure gas is
applied to the production chamber to close the one-way valve and to isolate
the
production chamber from the casing chamber and to lift liquid isolated in the
production chamber up the lift chamber. Lastly, the gas recovery cycle
includes
a liquid reduction phase executed after the three chamber evacuation phase
and before the liquid capture phase. The liquid reduction phase is executed by
applying relatively high pressure within the production chamber to close the
one-way valve and to isolate the production chamber from the casing chamber
and to lift the liquid accumulated within the production chamber during the
three
chamber evacuation phase out of the well through the lift chamber, while
maintaining the relatively low pressure within the casing chamber.
In the context of this type of gas recovery, two other related aspects of
the present invention involve the use of a liquid reduction phase in a gas
20 recovery cycle, during which a relatively high pressure is applied to the
production chamber while a relatively low pressurE; is applied to the casing
chamber while the lift chamber is opened to flow liquid and gas therethrough
to
the earth surface; and lifting liquid accumulated within the production
chamber
during the evacuation phase out of the well through the lift chamber; while
25 maintaining the relatively low pressure within the casing chamber.
Moreover,
other aspects of the present invention relate to a controller used in
conjunction
with control valves connected to and between the casing chamber, the
production chamber, the lift chamber, and suction and discharge manifolds of a
compressor, in which the controller is programed to supply control signals to
the
3o control valves to establish opened and closed states of the control valves
to
execute this type of gas recovery cycle.
In accordance with one aspect, there is provided a method of recovering
natural gas from a well in a multiple phase gas recovery cycle, the well
having a
6


CA 02485035 2004-10-18
casing chamber defined by a casing within the well, a production chamber
within a production tubing inserted into the casing chamber and a lift chamber
defined by a lift tube inserted within the production chamber, the well also
including a one-way valve separating the production chamber from the casing
s chamber; the gas recovery cycle including a three chamber evacuation phase
in
which a relatively low pressure is applied within the casing chamber,
production
chamber and lift chamber to cause the relatively low pressure to augment
natural earth formation pressure and flow more liquid and gas into the casing
chamber than would flow only from the natural formation pressure, a liquid
capture phase in which relatively high pressure gas is applied to the casing
chamber to move liquid within the casing chamber' through the one-way valve
into the production chamber, and a liquid removal phase in which relatively
high
pressure gas is applied to the production chamber' to close the one-way valve
and to isolate the production chamber from the casing chamber and to lift
liquid
isolated in the production chamber up the lift chamber, and a liquid reduction
phase executed after the three chamber evacuation phase and before the liquid
capture phase by: applying relatively high pressure within the production
chamber to close the one-way valve and to isolate the production chamber from
the casing chamber and to lift the liquid accumulated within the production
2o chamber during the three chamber evacuation phase out of the well through
the
lift chamber; while maintaining the relatively low pressure within the casing
chamber.
In accordance with another aspect, there is provided a method of
recovering natural gas from a well in a multiple phrase gas recovery cycle,
the
2~ well having a casing chamber defined by a casing within the well, a
production
chamber within a production tubing inserted into the casing chamber and a lift
chamber defined by a lift tube inserted within the ~>roduction chamber, the
well
also including a valve separating the production chamber from the casing
chamber; the gas recovery cycle including a casing evacuation phase in which
3o a relatively low pressure is applied within the casing chamber to cause the
relatively low pressure to augment natural earth formation pressure and flow
more liquid and gas into the casing chamber than would flow only from the
natural formation pressure, a liquid capture phase in which liquid from the


CA 02485035 2004-10-18
casing chamber is moved through the valve into the production chamber, and a
liquid removal phase in which liquid isolated in the production chamber by the
valve is lifted up the lift chamber and out of the well, and a liquid
reduction
phase executed after the evacuation phase and before the liquid capture phase
s by: lifting liquid accumulated within the production chamber during the
evacuation phase out of the well through the lift chamber; while maintaining
the
relatively low pressure within the casing chamber.
In accordance with a further aspect, there is provided a method of
recovering natural gas from a well extending from the earth surface to a
subterranean earth formation from which gas and liquid are produced at a
bottom of the well and transported from the bottom of the well through a
casing
chamber, a production chamber and a lift chamber extending between the well
bottom and the earth surface; the method executed by using a multiple phase
production cycle, the multiple phase production cycle including an evacuation
15 phase in which a relatively low gas pressure is applied to the casing
chamber,
the production chamber and the lift chamber to communicate through the
chambers to the well bottom and with the earth formation from which the gas
and liquid are produced, and the multiple phase production cycle also
including
a liquid reduction phase which is executed separately from a liquid removal
2o phase during each production cycle; the liquid reduction phase and the
liquid
removal phase each including: applying a relatively high pressure to the
production chamber while applying a relatively lo~nr pressure to the casing
chamber, and opening the lift chamber to flow liquid and gas therethrough to
the earth surface; and wherein each production cycle involves: removing liquid
25 accumulated in the production chamber and lift chamber during the
evacuation
phase by executing the liquid reduction phase; and removing liquid
accumulated in the casing chamber during the ga s production cycle by
executing the liquid removal phase.
In accordance with yet another aspect, there is provided a gas recovery
so apparatus for producing natural gas from a well arid delivering the
produced
natural gas to a sales conduit, the welB extending from the earth surface into
a
subterranean earth formation where the natural gas and liquid enter the well,
the apparatus including tubing inserted into the wE;ll to create a casing
chamber
8


CA 02485035 2004-10-18
in fluid communication with the earth formation and a production chamber and a
lift chamber which are separate from one another within the well, the
apparatus
also including a one-way valve separating the production chamber from the
casing chamber, the gas recovery apparatus further comprising: a compressor
having a suction manifold and a discharge manifold, the compressor creating a
flow of relatively low pressure gas in the suction manifold and a flow of
relatively
high-pressure gas in the discharge manifold; control valves connecting each of
the casing chamber, the production chamber and the lift chamber to the suction
manifold and the discharge manifold to establish selective fluid communication
between the suction manifold and each of the casing chamber, the production
chamber and the lift chamber and to establish selective fluid communication
between the discharge manifold and each of the casing chamber and the
production chamber, the control valves also connE:cting the lift chamber and
the
discharge manifold to the sales conduit to establish selective fluid
15 communication between the lift chamber and the discharge manifold and the
sales conduit; a controller programed to supply control signals to the control
valves to establish an opened state of each valve to permit fluid
communication
therethrough and to establish a closed state of each valve to prevent fluid
communication therethrough; the controller deliveiring a sequence of control
2o signals to the control valves to establish the opened and closed states of
the
control valves which establish fluid communication conditions through the
casing chamber, the production chamber, the lift chamber and into the sales
conduit during a multi-phase gas recovery cycle; the gas recovery cycle
including a liquid capture phase during which pressurized gas supplied by the
2s compressor moves liquid from the casing chamber through the one-way valve
into the production chamber, a liquid removal phase in which pressurized gas
supplied by the compressor lifts liquid out of the well from the production
casing
through the lift chamber, a three chamber evacuailion phase executed by
applying relatively low pressure within the casing c>hamber, production
chamber
so and lift chamber to augment natural earth formation pressure in moving
liquid
and gas into the casing chamber, and a liquid redraction phase executed after
completion of the evacuation phase and before a};ecuting the liquid capture
phase, the liquid reduction phase executed by applying relatively low pressure
9


CA 02485035 2004-10-18
within the casing chamber and relatively high pressure within the production
chamber while the lift chamber is opened and connected to the sales conduit;
and wherein: the controller establishes the states of the control valves
during
the liquid capture phase to establish fluid communication between the
discharge manifald and the casing chamber and to establish fluid
communication between the suction manifold and the production chamber and
the lift chamber; the controller establishes the states of the control valves
during
the liquid removal phase to establish fluid communication between the
discharge manifold and the production chamber wind to establish fluid
communication between the suction manifold and the casing chamber; the
controller establishes the states of the control valves during the evacuation
phase to establish fluid communication between the suction manifold and the
casing chamber, the production chamber and the lift chamber; and the
controller establishes the states of the control valves during the liquid
reduction
15 phase to establish fluid communication between the suction manifold and the
casing chamber, to establish fluid communication between the discharge
manifold and the production chamber, and to establish fluid communication
between the lift chamber and the sales conduit.
A more complete appreciation of the present invention and its scope may
2o be obtained from the accompanying drawings, which are briefly summarized
below, from the following detail descriptions of presently preferred
embodiments
of the invention, and from the appended claims.
Brief Description of the Drawings
25 Fig. 1 is a schematic and block diagram of .a gas recovery apparatus of
the present invention installed in a schematically-illustrated natural gas
producing well, all of which also illustrates the methodology for the present
invention
Fig. 2 is cross-section view of the well shown in Fig. 1, taken
3o substantially in the plane of line 2-2 of Fig. 1.
Fig. 3 is a flowchart of a gas recovery cycle of the gas recovery
apparatus shown in Fig. 1, and a method of the present invention, comprising a


CA 02485035 2004-10-18
three chamber evacuation phase, a liquid reduction phase, a liquid capture
phase, a liquid removal phase and a production phase.
Fig. 4 is a simplified schematic and block diagram similar to Fig. 1
illustrating performance of the three chamber evacuation phase of the gas
recovery cycle shown in Fig. 3.
Fig. 5 is a simplified schematic and block diagram similar to Fig. 1
illustrating performance of the liquid reduction phase of the gas recovery
cycle
shown in Fig. 3.
Fig. 6 is a simplified schematic and block diiagram similar to Fig. 1
to illustrating performance of the liquid capture phase of the gas recovery
cycle
shown in Fig. 3.
Fig. 7 is a simplified schematic and block diagram similar to Fig. 1
illustrating performance of the liquid removal phase of the gas recovery cycle
shown in Fig. 3.
15 Fig. 8 is a simplified schematic and block diiagram similar to Fig. 1
illustrating performance of the production phase of the gas recovery cycle
shown in Fig. 3.
Detailed Description.
2o A gas recovery apparatus 20 which operates in accordance with the
present invention is shown in Fig. 1, used in a well 22 which produces liquid
24
and natural gas 26. The liquid 24, which is primarily water in a gas well but
which may contain some oil, is Lifted out of the well 22 to the surface 28 of
the
earth 30 by operation of the gas recovery apparatus 20. In general, the gas
25 recovery apparatus 20 includes a compressor 32 oNhich supplies pressurized
gas, preferably pressurized natural gas 26, to a bottom 34 of the well 22. The
pressurized gas forces the liquid 24 accumulated in the well bottom 34 to the
surface 28. Natural gas 2fi is also removed from the well at the earth surface
28, and the produced natural gas 26 is delivered to a sales conduit 36 for
later
so commercial sales and use.
The well 22 is formed by a well bore 38 which has been drilled or
othenivise formed downward into a subterranean farmation 40 of the earth 30.
The well bore 24 extends downward to a depth or level where it penetrates a
11


CA 02485035 2004-10-18
subterranean zone 42 which contains the natural c~as 26. A conventional well
casing 44 is inserted into the well bore 38 to preserve the integrity of the
well
22. The casing 44 is typically formed by a number of connected pipes or tubes
(not individually shown) which extend from a wellhead 46 at the surface 28
down to the welt bottom 34. In relatively shallow and moderate-depth wells 22,
the connected pipes which form the casing 44 extend continuously from the
wellhead 46 to the well bottom 34. In relatively deeper wells 22, a
conventional
liner (not shown) is formed by connected pipes or tubes of lesser diameter at
the lower depths of the well bore 38. The finer functions to maintain the
1o integrity of the well 22 at its lower depths. A conventional packer (not
shown) is
used to transition from the relatively larger diameter casing 44 to the
relatively
smaller diameter liner at the mid-depth location where the liner continues on
from the lower end of the casing 44. Because the liner can be considered as a
smaller diameter version of the casing 44, the term "casing" is used herein to
refer both to the circumstance where only a single diameter pipe extends from
the earth surface 28 to the well bottom 34, and to the circumstance where
larger diameter pipe extends from the earth surface 28 part way down the well
bore 38 to a point where slightly lesser diameter liiner continues from a
packer
on to the well bottom 34. The interior area circumscribed by the casing 44 is
2o referred to as a casing chamber 48 (also shown irn Fig. 2).
Perforations 50 are formed through the casing 44 at the location of the
hydrocarbon-bearing zone 42. The perforations 50 admit the liquid 24 and
natural gas 26 from the hydrocarbon-bearing zone 42 into the casing chamber
48. The perforations 50 are conventionally located a few tens of feet above
the
25 well bottom 34. The volume within the casing chamber 48 beneath the
perforations 40 is typically referred to as a catch basin or "rat hole." The
well
bottom 34 includes the catch basin.
Natural pressure from the hydrocarbon-bearing zone 42 causes the
liquid 24 and natural gas 26 to flow from the zone 42 through the perforations
30 50 and into the casing chamber 48. The liquid 24 accumulates in the casing
chamber 48 until a vertical column of the liquid exirends above the
perforations
50 within the casing 44. Generally speaking, the gas 26 enters the column of
liquid from the perforations 50, bubbles to the top of the accumulated liquid
12


CA 02485035 2004-10-18
column, and enters the casing chamber 48. As shown in Fig. 1 y the column of
liquid reaches a level represented at 52 which is established by the natural
earth formation pressure. At that height, the hydrostatic head pressure from
the
column of liquid 24 counterbalances the natural earth formation pressure, and
the flow of liquid and gas from the zone 42 into the well bottom 34 ceases
because there is no pressure differential to move the liquid and gas into the
well
bottom 34. Under these conditions, the well 22 is said to die or choke off,
because no further liquid or gas can be produced into the well because the
hydrostatic pressure of the column of accumulated liquid counterbalances the
1o natural earth formation pressure.
Until the level of accumulated liquid rises t~ the point where its
hydrostatic head pressure counterbalances the natural earth formation
pressure, natural gas flows from the zone 42 into the casing 44 and bubbles
upward from the perforations 50 through the accumulated liqbid column. If the
5 level of accumulated liquid in the well bottom 34 is not above 'the level of
the
perforations 50, the natural gas 26 will enter the casing chamber 48 from the
zone 42 without bubbling through the liquid. However when the accumulated
liquid column reaches a sufficient height to choke off the well, the
hydrostatic
pressure from that column of liquid prevents the flow of natural gas into the
20 casing chamber 48.
To prevent the well from dying and choking off, the level 52 of the
accumulated liquid column must be kept low enough that its hydrostatic head
pressure is less than the natural earth formation pressure. This is
accomplished by removing the liquid from the well bottom 34 to reduce the
2s height of the accumulated liquid column. The liquid is removed by pumping
or
lifting it out of the well 22. Reducing the height level 52 of the liquid 24
reduces
the amount of hydrostatic pressure created by the accumulated liquid, and
thereby permits the natural earth formation pressure to remain effective to
flow
more liquid and gas into the well.
3o As the well continues to produce over its lifetime, the amount of natural
earth formation pressure diminishes. It becomes more important to keep the
height level 52 of the accumulated liquid 24 low enough so that the diminished
formation pressure remains effective in moving the gas and liquid into the
well.
13


CA 02485035 2004-10-18
Moreover, as liquid 24 is removed from the well, a natural pressure transition
throughout the zone 42 occurs where the natural earth formation pressure at
the perforations 50 is somewhat less than the natural earth formation pressure
at locations spaced radially outwardly from the perforations 50. This zone of
slightly diminished natural earth formation pressure; shaped somewhat like a
cone, results because the zone 42 has certain natural permeability and flow
characteristics which inhibit instantaneous pressure equilibrium throughout
the
zone 42. Thus, as liquid is removed from the well bottom 34, there will be an
effective reduction in natural earth formation pressure simply as a result of
the
removal of the liquids. The level 52 of liquid 24 must be maintained at a low
enough level that its hydrostatic head pressure remains below this flowing
bottom hole pressure from the earth formation.
To remove the liquid 24, the gas recovery apparatus 2U includes a string
of production tubing 54 which is inserted into the casing chamber 48 and which
1 ~ extends from the surface 28 to the well bottom 34. The production tubing
54 is
of a lesser diameter than the diameter of the casing 44, thereby causing the
casing chamber 48 to assume an annular shape (Fig. 2) between the exterior of
the production tubing 54 and the interior of the casing 44. The lower end of
the
production tubing 54 extends into the catch basin or well bottom 34 at or
below
2o the perforations 50. The lower end of the production tubing 54 is closed by
a
one-way valve 56 at the bottom end of the production tubing 54. The
production tubing 54 circumscribes a production chamber 58 (Fig. 2) which is
located within the interior of the production tubing 54.
The one-way valve 56 opens to allow 6iquid to pass from the casing
25 chamber 48 into the production chamber 58, when pressure in the casing
chamber 48 at the one-way valve 56 is greater than or equal to the pressure
inside of the production tubing 54 at the one-way valve 56. However, when the
pressure inside of the production tubing 54 at the one-way valve 56 is greater
than the pressure in the casing chamber 48, the one-way valve 56 closes to
3o prevent liquids within the production chamber 58 from flowing backwards
through the valve 56 into the casing chamber 48. The one-way valve 56 is
preferably one or more conventional standing valves. Two ~r more standing
14


CA 02485035 2004-10-18
valves in tandem offer the advantage of redundancy which permits continuing
operations even if one of the standing valves should fail.
A string of lift tubing 60 is inserted within the production tubing 54. The
lift tubing 60 extends from the earth surface 28 and terminates at a lower end
s near the one-way valve 56, for example approximately a few feet above the
bottom end of the production tubing 54. An open bottom end of the lift tubing
60 establishes a fluid communication path from the production chamber 58 to
the interior of the lift tubing 60. The interior of the lift tubing 60
constitutes a lift
chamber 62 through which the liquid and gas from the well bottom 34 flow
1o upward to the earth surface 28. The lift tubing 60 causes the production
chamber 58 to assume an annular configuration, while the lift chamber 62 is
generally circular in cross-sectional size, as shown in Fig. 2.
Although shown in Fig. 2 as positioned concentrically, the production
tubing 54 and the lift tubing 60 may not necessarily be centered about the
axis
s of the casing 44. Moreover, the lift tubing 60 need not be positioned within
the
production tubing 54 along the entire depth of the well bore 38, so long as
there
is constant fluid communication between the lift chamber 62 and the production
chamber 58, and so long as there is communication between the chambers 58
and 62 and the casing chamber 48 through the one-way valve 56 in the manner
2o described herein.
The natural formation pressure from the hydrocarbon-bearing zone 42
causes liquid 24 in the casing chamber 48 to pass through the one-way valve
56 and enter the production chamber 58 and the lift chamber 62, when the
chambers 58 and 62 experience a relatively lower pressure than is present in
25 the well bottom 34 as a result of the natural earth formation pressure. The
levels of the liquid 24 within the production chamber 58 and the lift chamber
62
increase until the levels of the liquid in the chambers 58 and 52 are
approximately equal to the level of the liquid in the casing chamber 48, under
initial starting conditions where the pressure in the casing chamber 48 is
3o approximately the same as the pressure within the chambers 58 and 62. These
initial starting conditions prevail before the compressor 32 begins to create
pressure differentials between the chambers 48, 58 and 62 during the different
phases of the recovery cycle of the present invention.


CA 02485035 2004-10-18
The casing 44, the production tubing 54 and the lift tubing 60 extend
from the well bottom 34 to the wellhead 46 located at the earth surface 28. A
cap 66 closes the top end of the casing 44 against the production tubing 54,
thus closing the upper end of the casing chamber 48 at the wellhead 46. Ports
s 68 and 70 extend through the t;asing 44 to communicate with the closed upper
end of the casing chamber 48 at the wellhead 46. A cap 72 closes the top end
of the production tubing 54 against the lift tubing 60, thereby closing the
upper
end of the production chamber 58 at the wellhead 46. A port 74 extends
through the production tubing 54 to communicate with the upper end of the
o production chamber 58 at the wellhead. A cap 76 closes the upper end of the
lift tubing 60 at the wellhead 46. Ports 78 and 80 are formed through the lift
tubing 60 to communicate with the upper end of the lift chamber 62 at the
wellhead 46. The ports 68, 70, 74, 78 and 80 connect to conduits and valves
which interconnect the casing chamber 48, the production chamber 58 and the
15 lift chamber 62 to the compressor 32 and to the sales conduit 36.
Pressure sensors 82, 84 and 86 connect to the casing chamber 48, the
production chamber 58 and the lift chamber 62 for the purpose of sensing the
pressures within those chambers, respectively. A pressure sensor 88 is also
connected to a conventional liquid-gas separator 89 which is connected to
2o receive a flow of liquid and gas from the well bottom 34. The liquid-gas
separator 89 separates the liquid from the gas, and delivers the gas to the
safe s
conduit 36. The pressure sensor 88 senses the pressure within the liquid-gas
separator 89, and that pressure is the same as the pressure within the sales
conduit 36. The pressure sensors 82, 84, 86 and 88 supply individual signals
25 indicative of the individual pressures that they sense to a system
controller 92.
The pressure signals supplied by the pressure sensors 82, 849 86 and 88 are
collectively referenced 90.
A flow sensor 83 is connected in series with the port 70 from the casing
chamber 48. The flow sensor 83 measures the amount of natural gas, if any,
30 which is volunteered by the well. The volunteered natural gas flows from
the
casing chamber 48, into the separator 89 and from there into the sales conduit
36. A flow sensor 85 is connected between the liquid-gas separator 89 and the
sales conduit 36. The flow sensor 85 measures the amount of natural gas
16


CA 02485035 2004-10-18
flowing from the well 22 and gas recovery apparatus 20 into true sales conduit
36. The flow sensors 83 and 85 supply individual signals representative of the
flow of gas through them. Each flow sensor 83 and 85 supplies an individual
flow signal representative of the volumetric gas flow through it, to the
system
controller 92. The individual flow signals from the flow sensors 83 and 85 are
collectively referenced 91.
The compressor 32 includes a suction port 94, which is connected to a
suction manifold 100, and a discharge port 98, which is connected to a
discharge manifold 96. The compressor 32 operates in the conventional
manner by creating relatively lower pressure gas at the suction port 94,
compressing the gas received at the suction port 94, and delivering the
compressed or relatively higher pressure gas through the discharge port 98.
The compressor 32 thus creates a pressure differential between the relatively
lower pressure gas at the sucfion port 94 and the. relatively higher pressure
5 compressed gas at the discharge port 98. The pressure differential created
by
the compressor 32 is used to create the phases of the gas recovery cycle of
the
gas recovery apparatus 20. The compressor 32 is sized to have a sufficient
volumetric capacity, and to create sufficient pressure differentials, to
perfiorm
the gas recovery cycle described below.
2o The suction manifold 100 and the discharge manifold 96 are preferably
connected together by conventional start-up by-pass and swing check valves
(not shown). The start-up bypass valve allows the compressor to be started
without a load on it. The swing check valve is a one-way valve that opens if
the
pressure in the suction manifold 100 exceeds the pressure in the discharge
25 manifold 96 . Higher pressure in the suction manifold compared to the
pressure
in the discharge manifold may occur momentarily during transitions between the
various phases of the gas recovery cycle.
Motor or control valves 102, 104 and 106 connect the suction manifold
100 through the ports 68, 74 and 80 to the casing chamber 48, the production
so chamber 58 and the lift chamber 62, respectively. Motor or control valves
108
and 109 connect the discharge manifold 96 through the ports 74 and 68 to the
production chamber 58 and the casing chamber 48, respectively. Motor or
control valves 110 and 112 connect the casing chamber 48 and the lift chamber
17


CA 02485035 2004-10-18
62 through the ports 70 and 78 to the sales conduit 36, respectively. Motor or
control valves 114 and 116 connect the suction manifold 100 and the discharge
manifold 96 to the sales conduit 36, respectively.
The control valves 102, 104, 106, 108, 109, 110, 112, 114 and 116 are
s opened and closed in response to valve control signals applied to each valve
by
the system controller 92. The valve control signals are collectively
referenced
118 in Fig. 1. The controller 92 preferably includes a microprocessor-based
computer or microcontroiler which executes a program to deliver the valve
control signals 118 to the control valves 102, 104, 106, 108, 109, 110, 112,
114
~o and 116 under the circumstances described below to cause the gas recovery
apparatus 20 to execute the gas recovery cycle. The controller 92 establishes
the opened and closed states of the control valves in accordance with its own
programmed functionality, by timing phases involved with the phases of the gas
recovery cycle, and/or by responding to the pressure signals 90 and the flow
15 signals 91 during the phases of the gas recovery cycle, among other things.
Although shown separately as control valves in Figs. 1 and 4-'7 for purposes
of
simplification of explanation, the flow conditions and phases described below
can be achieved by other types of valve devices, such as one-way check
valves, pressure regulators and the like used in combination with a lesser
2o number of control valves.
The phases of the gas recovery cycle are created when the system
controller 92 controls the opened and closed states of the control valves to
cause the compressor 32 to create pressure conditions within the chambers 48,
58 and 62. These pressure conditions, described in greater detail below, lift
2~ liquid through the lift tubing 60 to remove accumulated liquid 24 in the
well
bottom 34 and thereby control the level 52 of the liquid 24, to keep the well
producing natural gas 26. The gas recovery apparatus 20 offers the advantage
of removing the liquid to control the liquid level even in relatively deep
wells 22
and under conditions of diminished natural earth formation pressure.
3o The structure and equipment of the gas recovery apparatus 20 and the
characteristics of the well 22 are essentially the same as those described in
the
above-identified U.S. latent. I-lowever, the present gas recovery apparatus 20
is operated differently, resulting in a new and improved gas recovery cycle
120,
18


CA 02485035 2004-10-18
shown in Fig. 3. The gas recovery cycle 120 includes a three chamber
evacuation phase 128, a liquid reduction phase 130, a liquid capture phase
122, a liquid removal phase 124 and a production phase 126. Executing these
five phases in sequence creates the gas recovery cycle 120. By executing
these five phases 128, 130, 122, 124 and 126, accumulated liquid 24 at the
well
bottom 34 is removed more effectively and efficiently, allowing natural gas 26
to
be produced in greater volumes and with greater efficiency.
The inclusion of the liquid reduction phase 130 in the natural gas
recovery cycle 120 is the primary improvement of the present invention,
1o compared to the invention described in the above-identified U.S. Patent.
The
three chamber evacuation phase 128, the liquid capture phase 122, the liquid
removal phase 124 and the production phase 126 are essentially the same as
comparably-named phases described in the above-identified U.S. Patent.
However, because of the improvements provided by including the liquid
reduction phase 130 in the gas recovery cycle 120, the time duration of the
entire cycle 120, or the time durations of each of the phases of the cycle
120, or
the proportions of the cycle 120 consumed by each of the different phases, may
be adjusted to take maximum advantage of the improvements from the present
invention. Including the liquid reduction phase 130 with the three chamber
2o evacuation phase 128 in the gas recovery cycle 120 is particularly
important at
the end of the well's lifetime, because the well can still be worked
economically
under circumstances which might otherwise make working the well impractical.
Details of the three chamber evacuation phase 128 are understood by
reference to Fig. 4, which shows the operative state of the gas recovery
25 apparatus 20 when performing the three chamber evacuation phase 128.
During the three chamber evacuation phase 128, relatively low or suction
pressure from the compressor 32 is applied to the casing chamber 48, the
production chamber 58 and the lift chamber 62. The control valves 102, 104
and 106 are opened by the controller 92, causing the lift chamber 62, the
3o production chamber 58 and the casing chamber 48 to be connected to the
suction manifold 100 of the compressor 32, thereby subjecting all three
chambers 48, 58 and 62 to low or suction pressure. The control valve 116 is
also opened, connecting the discharge manifold 96 to the sales conduit 36
19


CA 02485035 2004-10-18
through the separator 89. The control valves 108, 109, 110, 112 and 114 are
closed by the controller 92. Depending upon the circumstances of the well, the
control valve 110 may be opened to allow volunteer gas to flow directly into
the
separator 89 and the sales conduit 36, although normally the control valve 110
s will not be opened.
With the control valves in this described state, the natural gas is
evacuated from the chambers 48, 58 and 62, is compressed by the compressor
32 and is delivered to the sales conduit 36. Compressing the natural gas
before delivering it through the opened control valve 116 to the sales conduit
assures that there is sufficient pressure to flow the natural gas directly
into the
sales conduit, even under circumstances where the pressure within the sales
conduit is relatively high.
The reduced pressure within the casing chamber 48 creates a greater
pressure differential than would otherwise be created by the formation
pressure
~ s itself. This greater pressure differential augments the natural earth
formation
pressure and causes the liquid in gas within the zone 42 to flow more readily
through the perforations 50 and into the well bottom 34, thereby decreasing
the
amount of time required to produce specific volumes of gas and liquid.
Although the liquid reduction phase 130 (Fig. 5), the liquid removal phase 124
20 (Fig. 7) and the production phase 126 (Fig. 8) also apply relatively low
pressure
through the casing chamber 48 to the hydrocarbon zone 42 and thereby
increase the flow of liquid and gas into the well bottom 34, the three chamber
evacuation phase 128 is primarily responsible for producing the substantial
majority of the gas and liquid during the gas recovery cycle 120.
2s The natural gas is produced primarily out of the casing chamber 48, as a
result of the low or suction pressure of the compressor 32 lifting the gas to
the
earth surface as gas enters the casing chamber 48 from the I-oydrocarbon
producing zone 42, and as a result of any effective natural earth formation
pressure forcing the natural gas into the casing chamber 48. The gas
3o production is directly up the casing chamber 48, through the compressor 32
and
into the sales conduit 36. The production path directly up the casing chamber
48 is the shortest path for recovering the gas up the well, thereby reducing
the
flowing friction losses and increasing the efficiency and producing the
natural


CA 02485035 2004-10-18
gas. In addition, the cross-sectional size of the casing chamber 48 is
relatively
large, and this relatively large cross-sectional size also diminishes flowing
friction losses. Therefore, producing natural gas up the casing chamber 48
offers the shortest and largest cross-sectional size flow path and results in
more
efficient gas production because of lower flowing friction losses. The
beneficial
effect of the natural formation pressure in producing the natural gas directly
up
the casing chamber 48 is not diminished, which also contributes to gas
production efficiency.
The substantially equal and relatively low pressures within the casing,
1o production and lift chambers 48, 58 and 62 created during the three chamber
evacuation phase 128 open the one-way valve 56, because the pressure in the
production chamber 58 is no greater than the pressure in the casing chamber
48. The open valve 56 allows liquid from the bottom of the casing chamber 48
to move into the bottom of the production chamber 58 and the lift chamber 62.
~5 Moving some of the accumulated liquid into the production chamber 58 and
the
lift chamber 62 during the three chamber evacuation phase 128 has the net
effect of eliminating some of the accumulated liquid within the casing chamber
48. Reducing the accumulated volume of liquid in the casing chamber 48
diminishes the height of the liquid column, reduces hydrostatic pressure
within
2o the casing chamber 48, and extends the time period during which the liquid
and
gas flows into the well before the liquid accumulates sufficiently to diminish
the
flow rate into the well. This has the effect of extending the proportion of
the gas
recovery cycle 120 during which gas and liquid flows into the well.
The three chamber evacuation phase 128 should not continue for such a
25 long time to accumulate so much liquid to make the compressor 32 incapable
oi~
delivering enough pressure to lift the accumulated liquid or to the point
where
the well is totally loaded up with liquid and choked off. Furthermore, the
liquid
should not accumulate in the casing chamber 48 to such an extent that the
production phase 126 {Fig. 8) must extend for a relatively long time period in
30 order to lift the greater amount of accumulated fluid to the surface.
The pressure of the sales conduit 36 is not a limiting factor on the ability
to deliver the produced natural gas into the sales conduit. Some gas pipelines
or sales conduits have relatively high pressures, making it difficult to
deliver the
21


CA 02485035 2004-10-18
gas directly from the well to the sales conduit, particularly under
circumstances
where the earth formation pressure in the well is already diminished at the
end
of a well's lifetime. By connecting all three chambers 48, 58 and 62 through
the
open valves 102, 104 and 106, respectively, to the suction manifold 100 of the
compressor 32, the compressed gas supplied at the discharge manifold 96
through the open control valve 116 is sufficient to overcome the pressure
within
the sales conduit 36. Thus, the use of the three chamber evacuation phase
128 also assures that the pressure of the sales conduit 36 will not be a
limiting
factor on the ability to deliver the recovered natural gas.
1o If the natural earth formation pressure is sufficient to volunteer natural
gas within the casing chamber 48 at a pressure sufficient to directly enter
the
sales conduit 36, the valve 110 may be opened to deliver that volunteered gas
directly to the sales conduit in addition to delivering the compressed gas
from
the compressor 32 through the opened control valve 116.
The duration of the three chamber evacuation phase 128 is established
by monitoring the flow volume through the flow sensor 85 and the pressure in
the casing chamber 48, the production chamber 58 and the lift chamber 62. A
diminished flow through the flow sensor 85 and an decreased pressure in the
chambers 48, 58 and 62, compared to the flow and pressure levels which
zo existed at the commencement of the three chamber evacuation phase 128,
indicate an increasing level of liquid at the well bottom 34. Monitoring these
conditions establishes the duration of the three chamber evacuation phase, and
thereby limits the amount of liquid accumulated at the well bottom during the
three chamber evacuation phase. In addition or as an alternative, the time
duration of the three chamber evacuation phase 128 may be timed by the
controller 92. Upon terminating the three chamber evacuation phase 128, the
controller 92 changes the states of various control valves to commence
executing the liquid reduction phase 130 shown in Figs. 3 and 5.
Details of the liquid reduction phase 130 are understood by reference to
so Fig. 5, which shows the operative state of the gas recovery apparatus 20
when
performing the liquid reduction phase 130. During the liquid reduction phase
130, the liquid which accumulated within the production chamber 58 and the
lift
chamber 62 during the preceding three chamber evacuation phase is removed
22


CA 02485035 2004-10-18
to the earth surface. To execute the liquid reduction phase 130, relatively
low
or suction pressure from the compressor 32 is applied to the casing chamber
48, and relatively high pressure from the compressor 32 is applied to the
production chamber 58. The control valves 102, 108 and 112 are opened by
the controller 92, causing the casing chamber 48 to be connected to suction
manifold 100 of the compressor 32, the production chamber 58 to be connected
to the discharge manifold 96 of the compressor 32, and the lift chamber 32 to
be connected to the sales conduit 36 through the separator 89, respectively.
Depending upon the pressure from the volunteered gas in the casing chamber
48, the control valve 110 may also be opened by the controller 92 to allow gas
from the casing chamber 48 to flow directly into the separator 89 in the sales
conduit 36.
With the control valves in this described state during the liquid reduction
phase 130, the compressor creates a relatively low pressure in the casing
1 s chamber 48 and a relatively high pressure in the production chamber 58.
The
relatively high pressure in the production chamber 58 and the relatively low
pressure in the casing chamber 48 cause the one-way valve 56 to close, which
traps the liquid accumulated within the production chamber 58 during the
preceding three chamber evacuation phase and prevents liquid or gas from
2o moving out of the production chamber 58 and into the casing chamber 48.
These applied pressures hold the one-way valve 56 closed during the liquid
reduction phase 130.
The relatively low pressure in the lift chamber 62 and relatively high
pressure in the production chamber 58 push the liquid accumulated in the
2s bottom of the production chamber 58 into the lift chamber 62 and move that
liquid up the lift chamber 62, through the opened valve 112 and into the
separator 89. The gas separates from the liquid in the separator 89, and the
gas flows to the sales conduit 36. Thus, the gas which is used to lift the
liquid
up the lift chamber 62 is recovered, although this gas recovery occurs at some
so efficiency loss due to the lengthy and relatively small cross-sectional
size of the
path that the gas must traverse down the production chamber 58 and up the lift
chamber 62. Nevertheless, some gas production does occur during the liquid
reduction phase 130.
23


CA 02485035 2004-10-18
While the liquid reduction phase 130 is discussed as being executed
from applying a relatively high pressure in the production chamber 58 and a
relatively low pressure in the lift chamber 62 to lift the liquid through the
lift
chamber 62, reversing the application of pressure in the chambers 58 and 62
can accomplish similar results. Of course, to apply the pressure in this
reverse
manner will also require changing the opened and close to states of other
valves associated with the chambers 58 and 62.
The gas flow continues in the described manner during the liquid
reduction phase 130, until signals 90 from the pressure sensor 84 and 86 are
1o interpreted by the controller 92 to indicate that substantially all of the
liquid has
been transferred up the Lift chamber 62. Alternatively, the length of the
liquid
reduction phase 130 may be timed by timer of the controller 92. lJpon
terminating the liquid reduction phase 130, the controller 92 changes the
states
of various control valves to commence executing the liquid capture phase 122
~ 5 shown in Figs. 3 and 6.
Details of the liquid capture phase 122 are understood by reference to
Fig. 6, which shows the operative state of the gas recovery apparatus 20 when
performing the liquid capture phase 122. During the liquid capture phase 122,
relatively low or suction pressure is applied to the production chamber 58 and
2o the lift chamber 62, and relatively high pressure is applied to the casing
chamber 48. The control valves 104, 106 and 109 are opened by the controller
92, causing the lift chamber 62 and the production chamber 58 to be connected
to the suction manifold 100 of the compressor 32 and causing the casing
chamber 48 to be connected to the discharge manifold 96. The control valves
25 102, 108, 112, 114 and 116 are closed by the controller 92.
The compressor creates a relatively low or suction pressure within the
production chamber 58 and the lift chamber 62, and creates a relatively high
pressure in the casing chamber 48. The relatively low pressure within the
production and lift chambers 58 and 62 is below the hydrostatic head pressure
30 of the accumulated column of liquid 24 at the well bottom 34. The
relatively
high pressure in the casing chamber 48 may slightly increase the pressure at
the well bottom 34 beyond that pressure created by the head of the
accumulated liquid.
24


CA 02485035 2004-10-18
The control valve 110 can be partially opened and used as a pressure
regulation valve to regulate the amount of relatively high pressure within the
casing chamber 48. Gas in excess of what is needed to maintain a desired
high pressure within the casing chamber 48 is conducted through the partially
s opened control valve 110 and delivered to the sales conduit 36. Regulating
the
partially opened condition of the control valve 110 permits the pressure
within
the casing chamber 48 to remain relatively high white still permitting some
gas
to be produced under those circumstances where the well is capable of doing
so.
~o The reduced pressure within the production and lift chambers 58 and 62
creates a pressure differential relative to the higher pressure in the casing
chamber 48, and that pressure differential opens the one-way valve 56 to admit
the liquid from the casing chamber 48 into the production and lift chambers 58
and 62. The liquid from the casing chamber 48 has been previously
~5 accumulated during the preceding three chamber evacuation and liquid
reduction phases, but this liquid was not lifted during the liquid reduction
phase
130 because the one-way valve 56 was closed to prevent this accumulated
liquid from entering the production chamber 58 during the liquid reduction
phase 130.
2o The one-way valve 56 remains open until substantially all of the liquid
above the one-way valve 56 has been transferred into the bottom of the
production chamber 58 and lift chamber 62. The production chamber 58 and
the lift chamber 62 are available to accept this liquid from the casing
chamber
48, as a result of having been cleared of liquid during the previously
executed
2s the liquid reduction phase 130 (Fig. 5). Thus, including the liquid
reduction
phase 130 in the gas recovery: cycle 120 makes it possible to accept and lift
liquid twice during each gas production cycle 20, and also makes it possible
to
more effectively eliminate liquid from the well bottom to extend the time
period
for the recovery of natural gas. The remaining liquid in the casing chamber 48
3o is loaded into the production chamber 58. This liquid will thereafter be
lifted to
the earth surface during the subsequently executed liquid removal phase 124
(Fig. 7) and the production phase 126 (Fig. 8). The casing chamber 48 is
essentially dried out of liquid above the one-way valve 56. Eliminating


CA 02485035 2004-10-18
essentially all of the liquid in the casing chamber 48 above the one-way valve
56 assures that the maximum amount of liquid can be accumulated in the well
bottom during the three chamber evacuation phase 128, thereby extending the
opportunity to recover natural gas during each gas recovery cycle 120.
During the liquid capture phase 122, the relatively high pressure which is
applied into the casing chamber 48 from the compressor 32 has the effect of
countering or diminishing the natural earth formation pressure. Reducing or
blocking the effect of the natural earth formation pressure diminishes the
amount of natural gas and liquid which flows from the hydrocarbons-bearing
1o zone 52 through the perforations 50 and into the bottom of the well. Gas
production is diminished or temporarily suspended under these conditions.
Some amount of the liquid which has risen to a level above the perforations 50
may even be forced back into the hydrocarbons-bearing zone 42. It is therefore
important that as much liquid as possible be recovered during each gas
recovery cycle, without leaving any more residual liquid behind than is
necessary. The liquid reduction phase 130 assists in this regard by increasing
the amount of liquid which may be lifted during each natural gas production
cycle 120 and by diminishing tl~e time duration of the liquid capture phase
122.
Eliminating the time duration of the liquid capture phase also limits the
amount
of time when the casing chamber 48 is pressurized, thereby reducing the
amount of liquid that may be pushed back into the zone 42.
In some wells with relatively high natural earth formation pressures and
gas flow rates, it may not be necessary to apply the relatively high pressure
from the compressor 32 to the casing chamber 48 during the liquid capture
z5 phase 122. Instead, the well may volunteer or naturally produce gas at a
sufficient natural pressure within the casing chamber 48 so that an adequate
pressure differential is created at the one-way valve 56 to move the
accumulated liquid from the casing chamber 48 through the valve 56 and into
the production chamber 58. When this is the case, the control valve 110 is
opened slightly so as to maintain a preset pressure in the casing chamber 48.
The compressed natural gas delivered through the open control valve 109 flows
into the casing chamber 48 and then through the opened valve 110 and through
the separator 89 into the sales conduit 36. Thus, under these circumstances,
26


CA 02485035 2004-10-18
the gas removed from the production chamber 58 and the lift chamber 62 is
conducted through the compressor 32, and the opened valves 109 and 110 into
the sales conduit 36. Another configuration would be to leave valves 109 and
110 closed and open valve 115 to deliver gas to the sales conduit 36. This
will
allow pressure in the casing chamber 48 to build at a rate determined only by
the gas contributed from the formation.
Once the pressure sensors 84 and 86 have supplied signals indicating
that the pressure within the production chamber 58 has increased to a
predetermined level signifying that the liquid has entered the production
o chamber 58, or once a predetermined time period for performing the liquid
capture phase 122 has elapsed, the controller 92 changes the states of the
control valves to commence executing the liquid removal phase 124 shown in
Figs. 3 and 7.
Details of the liquid removal phase 124 are understood by reference to
Fig. 7, which shows the operative state of the gas recovery apparatus 20 when
performing a beginning part of the liquid removal phase 124. During the liquid
removal phase 124, the control valves 102 and 108 are opened, and the valves
104, 106, 109, 110, 112, 114 and 116 are closed, by the controller 92
delivering
the control signals 118 to these valves. With the valves in these states, the
2o casing chamber 48 is connected to the relatively low or suction pressure
from
the suction manifold 100 of the compressor 32; and the production chamber 58
is connected to the relatively high pressure from the discharge manifold 9fi
of
the compressor 32. The relatively low pressure within the lift chamber 62
which
was established in the previous liquid capture phase 122 (Fig. 6) is trapped
within the lift chamber 62 by the closure of valve 106.
The relatively low pressure created in the casing chamber 48 by the
suction of the compressor 32 immediately starts to assist the natural earth
formation pressure in moving the liquids and natural gas from the zone 42 into
the well. The gas removed from the casing chamber 48 is compressed by the
3o compressor 32 and is delivered into the production chamber 58. The gas
removed from the casing chamber 48 is used to lift the liquid. Any excess gas
volunteered by the well beyond that required for compression and injection
into
2~


CA 02485035 2004-10-18
the production chamber 58 may be delivered to the sales conduit 36 by opening
the control valves 110 and/or 116.
The relatively high pressure from the discharge of the compressor 32
creates a relatively higher pressure in the production chamber 58, which
closes
the one-way valve 56, thereby confining the high pressure and the accumulated
liquid within the production chamber 58. The relatively low pressure in the
lift
chamber 62 from the liquid capture phase 122 (Fig. 6), which has been trapped
by closing the valve 106, is separated from the relatively higher pressure in
the
production chamber 58 by the liquid at the bottom of the production tubing 54
o above the one-way valve 56. The relatively higher pressure in the production
chamber 58 and the trapped relatively lower pressure in the lift chamber 62
move the liquid from the bottom of the production chamber 58 into the lift
chamber 62, thus filling the lift chamber fit with the liquid captured during
the
preceding liquid capture phase 122 (Fig. 6).
~5 The displacement of the liquid up and into the lift chamber 62 causes
gas to flow around the lower terminal end of the lift tubing 60 and to begin
bubbling up through the fluid column of liquid located in the bottom end of
the
lift chamber 62. The gas flow through the liquid at the bottom end of the lift
chamber 62 causes the pressure in the lift chamber 62 to increase (the trapped
2o relatively lower pressure decreases), and this increase in pressure is
sensed by
the pressure sensor 86. The increase in pressure in the lift chamber 62
indicates that the liquid from the bottom of the production chamber has
entered
the lift chamber 62. The controller 92 recognizes a predetermined increase of
pressure within the lift chamber 62 as signifying that the liquid from the
bottom
25 of the production chamber has been loaded into the lift chamber. At this
point
the end part of the liquid removal phase 124 begins. The state of the control
valves in the end part of the liquid removal phase 124 are the same as those
during the production phase 126, shown in Fig. 8. The controller 92 opens the
valve 112, and the relatively high pressure within the production chamber 58
so pushes the column of liquid up the lift chamber 62.
The liquid lifted up the lift chamber 62 and the pressurized natural gas
which pushes the liquid up the lift chamber 62 are delivered through the
opened
control valve 112 into the gas-liquid separator 89. Within the separator 89,
the
28


CA 02485035 2004-10-18
liquid falls to the bottom while the gas flows through the flow sensor 85 to
the
sales conduit 36. The separator 89 thereby assures that the liquid from the
well
will not be delivered to the sales conduit 36, and permits the natural gas
used to
push the liquid up the lift chamber 62 to be delivered to the sales conduit
36.
s The liquid within the separator 89 is periodically removed.
The duration of the liquid removal phase 124 continues until the liquid in
the lift tubing 62 has been delivered into the separator 89. This condition is
sensed when the pressure sensor 86 supplies a signal 90 indicating that liquid
has cleared from the lift tubing 60 and the flow sensor 85 signals a
significant
o increase in the passage of gas into the sales conduit 36. Alternatively, the
liquid removal phase 124 may be continued for a predetermined amount of
time.
Details of the production phase 126 are understood by reference to Fig.
8, which shows the operative state of the gas recovery apparatus 20 when
performing the production phase 26. The production phase begins after the
liquid has been lifted to the earth surface and has been delivered into the
separator 89. The valve 112 has been opened by the controller 92 during the
preceding liquid removal phase 124, and the control valve 106 remains closed,
just as in the previous liquid removal phase. !n essence, all of the valves
2o remain in the same state in the production phase 126 as existed at the end
part
of the liquid removal phase 124. In this regard, the production phase 126 may
be considered as an extension of the liquid removal phase 124, or
alternatively,
the production phase 126 may be considered as beginning at the end part of
the previously-described liquid removal phase 124 when the controller 92 has
2s recognized from the pressure signals 90 from the sensors 84 and 86 that the
substantial majority of the liquid has been transferred up the (ift chamber 62
and
out of the well. The point at which the previous liquid removal phase 124
terminates and the present production phase 126 commences is therefore not
specific. In the context of the present invention, the production phase 126
need
so only continue for so long as necessary to lift any residual liquid up the
lift
chamber 62 and out of the well. Indeed, the production phase 126 as presently
discussed in conjunction with Fig. 8 may be eliminated altogether, provided
that
29


CA 02485035 2004-10-18
the functionality associated with Fig. 8 is part of the liquid removal phase
124
discussed in conjunction with Fig. 7.
Once the production chamber 58 and lift chamber 62 are essentially free
of liquid, a gas flow path, unimpeded by liquid, extends from the casing
s chamber 48, through the compressor 32, into the production chamber 58 and
up the lift chamber 62 into the sales conduit 36. This flow path allows
natural
gas from the casing chamber 48 to be produced and delivered to the sales
conduit 36, although the flow path for doing so requires passage up the well
in
the casing chamber 48, down the production chamber 58 and up the lift
~o chamber 62 to the sales conduit. Circulating gas through the production
chamber 58 and up the lift chamber 62 is also effective to lift any residual
liquids in the interior of the production chamber 58 and lift chamber 62
thereby
more effectively clearing the liquids that were captured during the liquid
capture
phase 122 (Fig. 6). Any gas volunteered by the well during the production
15 phase is transferred from the casing chamber 48 directly to the sales
conduit 36
through the opened control valve 110. Again, whether the control valve 110 is
opened during the production phase depends on the flow conditions and
circumstances of the well.
The production phase 126 ends after the sensed pressure in the
2o production chamber 58 drops to a predetermined pressure level which
indicates
that the flow path through the production chamber 58 and the lift chamber 62
is
essentially free of liquid. Alternatively, the controller 92 may terminate the
production phase 126 after a predetermined time for the production phase 126
has elapsed.
25 At the conclusion of the production phase 126 (Fig. 8), which may also
be at the conclusion of the end part of the liquid removal phase 124 (Fig. 7)
as
described above, the controller 92 transitions the state of the control valves
back to the new three chamber evacuation phase 128 (Figs. 3 and 5) to
commence the next subsequent gas recovery cycle 120.
30 The inclusion of the liquid reduction phase 130 in the gas recovery cycle
120 achieves a number of improvements and advantages. The liquid reduction
phase 130 improves the efficiency of the gas recovery cycle 120 by removing
more liquid during each gas recovery cycle 120. The increase in efficiency is


CA 02485035 2004-10-18
achieved by removing the liquid from the production chamber 58 and the lift
chamber 62 during the liquid reduction phase 130, thereby making this empty
volume available to receive more liquid from the casing chamber 48 during
subsequent phases of the cycle 120.
s Although the present invention may be advantageously applied in
different types of wells, using the three chamber evacuation phase 128 in the
cycle 120 is particularly advantageous in improving the efficiency and
maintaining the productivity of relatively deep wells having relatively low
natural
earth formation pressures and which produce liquid at a relatively low rate.
The
o relatively low pressure from the compressor 32 is applied to the casing
chamber'
48 and augments the relatively low natural formation pressure to cause gas and
liquid to flow into the well to a greater extent than would otherwise occur.
The
relatively low production rate of liquid allows the three chamber evacuation
phase 128 to continue for a sizable portion of the gas recovery cycle 120,
~ before the amount of accumulated liquid builds up to the point where it
diminishes gas recovery. While doing so, the gas is produced efficiently
directly
up the casing chamber in a direct flow path that offers relatively large cross-

sectional size and the shortest distance from the well bottom to the earth
surface, thereby achieving gas production with the lowest possible flowing
2a friction losses. It is therefore desirable to maximize the duration of the
three
chamber evacuation phase, and to use the three chamber evacuation phase as
the primary phase for gas production and not the production phase. By doing
so, the gas is more efficiently produced without forcing gas through a
relatively
lengthy and small cross-sectionaPly sized flow path from the earth surface
down
25 the production chamber 58 to the well bottom and then back up the lift
chamber
62 to both remove the liquid and produce the gas. Such a lengthy and
circuitous flow path may extend several miles and has considerable flowing
friction losses which diminish the productivity efficiency. Therefore,
compared
to the invention described in the above-identified U.S. Patent, the present
3o invention utilizes the liquid reduction phase 130 to maximize the time
duration
and gas productivity of the three chamber evacuation phase 128 while
diminishing the amount of time and inefficiency associated with lifting the
31


CA 02485035 2004-10-18
accumulated liquid from the well bottom and producing gas through the same
path.
Using the liquid reduction phase 130 reduces the proportion of each gas
recovery cycle 120 which is committed to producing gas through the high
friction-loss flow path. By removing the liquid twice during each cycle, gas
can
be produced directly up the lesser frictional path casing chamber during a
larger
proportion of the gas recovery cycle, thereby reducing flowing friction losses
and increasing production efficiency. Moreover, it is possible 'to lift the
lesser
amounts of liquid from greater depths. By lifting the liquid twice during each
1o gas recovery cycle, the liquid does not accumulate to the point where the
compressor has difficulty in lifting the liquid or a very lengthy portion of
the gas
recovery cycle is consumed by lifting the liquid.
Moreover, by lifting the liquid twice during each cycle 120, substantially
all of the liquid from the casing chamber 48 will be removed during each gas
~5 recovery cycle 120, leaving no residual liquid in the casing chamber 48.
Removing substantially all of the removable liquid assures that no slight
residual
amount of liquid will slowly accumulate over a number of subsequent natural
gas recovery cycles 120 to the point that the accumulated residual liquid
diminishes or chokes off gas production.
20 Additionally, the liquid removal phase 124' and the production phase 126
are required to lift only that liquid accumulated in the casing chamber 48
during
the three chamber evacuation phase 128 and the liquid reduction phase 130,
rather than all of the liquid accumulated in the well bottom. Less effort and
less
capacity is required from the compressor 32. The amount of liquid accepted for
25 removal from the casing chamber 48 is not so much as to overwhelm the
capacity for lifting the liquid during each cycle, even in relatively deep
wells.
Alternatively, more liquid in the well bottom can be allowed to accumulate
since
the compressor 32 will not have to create sufficient gas pressure to lift the
amount of liquid at one time during each gas recovery cycle, as is the case in
30 the invention described in the above-identified U.S. patent.
Also, because less liquid is being lifted during the subsequent liquid
removal and production phases 124 and 126, these phases may be more
quickly executed thereby allowing the gas recovery cycle 120 to return more
32


CA 02485035 2004-10-18
rapidly to the three chamber evacuation phase 128 where the bulk of the
natural gas is produced. Alternatively, the time duration of the three chamber
evacuation phase 128 can be extended during each recovery cycle 120 to
produce more gas. Since the three chamber evacuation phase 128 is the
portion of the gas recovery cycle 120 during which the most gas is recovered
from the well, it is beneficial to extend the three chamber evacuation phase
128
for as long as possible.
Furthermore, the liquid which is transferred into the production chamber
58 and lift chamber 62 during the three chamber evacuation phase 128 reduces
1o the time duration of the liquid capture phase 122, because the liquid
reduction
phase 130 results in vacating the bottom of the production chamber 58 and the
lift chamber 62 so that the liquid remaining at the bottom of the casing
chamber
48 is more readily transferred during the liquid capture phase 122. Reducing
the time duration of the liquid capture phase 122 reduces the amount of time
that pressurized gas is applied through the casing chamber 48. During the time
that the casing chamber 48 is pressurized, the natural formation pressure is
ineffective or less effective to produce natural gas. Minimizing the time
duration
of the liquid capture phase 122 therefore allows the natural earth formation
pressure to remain more effective and less impeded to flow gas and liquid into
2o the well for larger proportion of each gas recovery cycle 120.
The gas recovery apparatus 20 of the present invention has the potential
to continue producing natural gas from wells significantly beyond the
commonly-considered end of a well's lifetime. Consequently, it may be possible
to produce the last few percent of the oil and gas reserves contained in the
hydrocarbon-bearing zone. The well will be commercially viable at a far lower
formation pressure before abandonment. A typical plunger lift system needs
about 300 PSI of natural formation pressure to produce from a 5,000 foot well.
The gas recovery apparatus 20 of the present invention can operate the well
down to 5 PSI of pressure in the casing chamber and less than 50 PSI of
3o natural formation pressure. Most importantly, the liquid reduction phase
used in
conjunction with the three chamber evacuation phase benefits the other phases
of the gas recovery cycle to achieve improved and more efficient gas
production, thereby making it efficient and economic to work wells that may
33


CA 02485035 2004-10-18
have already reached a point where it would otherwise be uneconomical to
work those wells using other techniques. Many other advantages and
improvements will be apparent upon gaining a complete understanding of the
improvements and significance of the present invention.
A presently preferred embodiment of the present invention and many of
its improvements have been described with a degree of particularity. This
description is a preferred example of implementing the invention, and is not
necessarily intended to limit the scope of the invention. The scope of the
invention is defined by the following claims.
34

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 2007-04-10
(22) Filed 2004-10-18
Examination Requested 2004-10-18
(41) Open to Public Inspection 2005-05-03
(45) Issued 2007-04-10
Lapsed 2018-10-18

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $800.00 2004-10-18
Application Fee $400.00 2004-10-18
Maintenance Fee - Application - New Act 2 2006-10-18 $100.00 2006-09-06
Final Fee $300.00 2007-01-26
Maintenance Fee - Patent - New Act 3 2007-10-18 $100.00 2007-08-31
Maintenance Fee - Patent - New Act 4 2008-10-20 $100.00 2008-09-19
Registration of a document - section 124 $100.00 2008-11-28
Maintenance Fee - Patent - New Act 5 2009-10-19 $200.00 2009-08-12
Maintenance Fee - Patent - New Act 6 2010-10-18 $200.00 2010-08-13
Maintenance Fee - Patent - New Act 7 2011-10-18 $200.00 2011-08-19
Maintenance Fee - Patent - New Act 8 2012-10-18 $200.00 2012-09-19
Registration of a document - section 124 $100.00 2012-10-16
Registration of a document - section 124 $100.00 2012-10-16
Maintenance Fee - Patent - New Act 9 2013-10-18 $200.00 2013-07-30
Maintenance Fee - Patent - New Act 10 2014-10-20 $250.00 2014-10-06
Maintenance Fee - Patent - New Act 11 2015-10-19 $250.00 2015-05-19
Maintenance Fee - Patent - New Act 12 2016-10-18 $450.00 2016-10-24
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
FORESTAR PETROLEUM CORPORATION
Past Owners on Record
CREDO PETROLEUM CORPORATION
REITZ, DONALD D.
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Abstract 2004-10-18 1 22
Cover Page 2005-04-15 1 52
Representative Drawing 2005-04-05 1 21
Drawings 2004-10-18 7 372
Claims 2004-10-18 8 418
Description 2004-10-18 34 2,367
Cover Page 2007-03-23 2 58
Assignment 2004-10-18 3 148
Fees 2011-08-19 1 50
Fees 2006-09-06 1 39
Correspondence 2007-01-26 1 49
Fees 2007-08-31 1 61
Fees 2008-09-19 1 63
Assignment 2008-11-28 7 359
Fees 2009-08-12 1 51
Fees 2010-08-13 7 279
Fees 2013-07-30 1 49
Assignment 2012-10-16 15 421
Fees 2012-09-19 1 48
Fees 2014-10-06 1 58
Fees 2015-05-19 1 66