U.S. patent application number 10/688719 was filed with the patent office on 2005-04-21 for recovery of heavy oils through in-situ combustion process.
Invention is credited to Jensvold, John A., Newton, Donald E..
Application Number | 20050082057 10/688719 |
Document ID | / |
Family ID | 34521233 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050082057 |
Kind Code |
A1 |
Newton, Donald E. ; et
al. |
April 21, 2005 |
Recovery of heavy oils through in-situ combustion process
Abstract
An in-situ combustion process heats an oil-bearing formation so
as to reduce the viscosity of heavy oil, and/or to extract oil from
solid or semi-solid materials in the formation. Oxygen-enriched air
for the combustion is generated non-cryogenically at the surface,
preferably with a membrane system or a pressure swing adsorption
(PSA) unit. The oxygen-enriched air may be blended with other air
to adjust its oxygen content, and is then compressed at the
surface, and conveyed into an injection well. The oxygen-enriched
air is especially intended for use in a toe-to-heel in-situ
combustion process, in which combustion proceeds along a horizontal
well. Nitrogen resulting from the production of the oxygen-enriched
air may be used to compress the oxygen-enriched air, or for other
purposes.
Inventors: |
Newton, Donald E.; (Houston,
TX) ; Jensvold, John A.; (Benicia, CA) |
Correspondence
Address: |
WILLIAM H. EILBERG
THREE BALA PLAZA
SUITE 501 WEST
BALA CYNWYD
PA
19004
US
|
Family ID: |
34521233 |
Appl. No.: |
10/688719 |
Filed: |
October 17, 2003 |
Current U.S.
Class: |
166/256 ;
166/266 |
Current CPC
Class: |
E21B 43/243
20130101 |
Class at
Publication: |
166/256 ;
166/266 |
International
Class: |
E21B 043/24; E21B
043/34 |
Claims
What is claimed is:
1. In an in-situ combustion process for oil recovery from a
formation located below a surface, the combustion process including
combusting a portion of an oil-bearing formation so as to generate
heat in the formation in order to reduce viscosity of heavy oil in
the reservoir and/or to cause oil trapped in a solid or semi-solid
material to be released, in liquid form, from the material, the
improvement comprising non-cryogenically generating an
oxygen-enriched gas stream above the surface and injecting said
oxygen-enriched gas stream into the formation so as to support
in-situ combustion in the formation.
2. The improvement of claim 1, wherein the non-cryogenic generating
step includes conveying air through a membrane system.
3. The improvement of claim 1, wherein the non-cryogenic generating
step includes conveying air through a pressure swing adsorption
system.
4. The improvement of claim 2, further comprising the step of
blending air with the oxygen-enriched gas stream so as to produce a
gas stream having a desired oxygen content.
5. The improvement of claim 3, further comprising the step of
blending air with the oxygen-enriched gas stream so as to produce a
gas stream having a desired oxygen content.
6. The improvement of claim 1, wherein the generating step produces
an oxygen-enriched stream and an oxygen-depleted stream, the
process further comprising using the oxygen-depleted stream to
operate a compressor for compressing the oxygen-enriched
stream.
7. The improvement of claim 1, wherein the in-situ combustion
process is selected to be a toe-to-heel combustion process.
8. The improvement of claim 7, wherein the in-situ combustion
process is selected to be a process which uses a catalyst to
upgrade oil before the oil has been withdrawn from the
formation.
9. The improvement of claim 1, further comprising compressing the
oxygen-enriched gas stream before injecting said stream into the
formation.
10. A method of enhancing an amount of oil recoverable from a
formation, the formation being located beneath a surface, the
method comprising: a) non-cryogenically generating an
oxygen-enriched gas stream above the surface of the formation, and
b) injecting said oxygen-enriched gas stream into the formation so
as to support combustion of a portion of the formation, wherein the
formation is heated by said combustion so as to reduce viscosity of
heavy oil in the reservoir and/or to cause oil trapped in a solid
or semi-solid material to be released, in liquid form, from the
material.
11. The method of claim 10, wherein the non-cryogenic generating
step includes conveying air through a membrane system.
12. The method of claim 10, wherein the non-cryogenic generating
step includes conveying air through a pressure swing adsorption
system.
13. The method of claim 11, further comprising the step of blending
air with the oxygen-enriched gas stream so as to produce a gas
stream having a desired oxygen content.
14. The method of claim 12, further comprising the step of blending
air with the oxygen-enriched gas stream so as to produce a gas
stream having a desired oxygen content.
15. The method of claim 10, wherein the generating step produces an
oxygen-enriched stream and an oxygen-depleted stream, the process
further comprising using the oxygen-depleted stream to operate a
compressor for compressing the oxygen-enriched stream.
16. The method of claim 10, wherein the in-situ combustion process
is selected to be a toe-to-heel combustion process.
17. The method of claim 16, wherein the in-situ combustion process
is selected to be a process which uses a catalyst to upgrade oil
before the oil has been withdrawn from the formation.
18. The method of claim 10, further comprising compressing the
oxygen-enriched gas stream before injecting said stream into the
formation.
19. A method of recovering oil from an oil-bearing formation,
comprising: a) selecting a location of the formation, and
determining parameters relating to the formation, b) choosing a
level of oxygen content for air to be injected downhole in said
formation to support in-situ combustion, the oxygen content being
chosen in accordance with said parameters, c) generating an
oxygen-enriched gas above a surface of said formation, and
adjusting an oxygen concentration of said oxygen-enriched gas
according to the level chosen in step (b), and d) injecting said
oxygen-enriched gas to a combustion site below the surface of the
formation.
20. The method of claim 19, wherein step (c) is performed by a
portable system, and wherein method further comprises the steps of
repeating steps (a) and (b) for a different formation, moving the
portable system to a vicinity of said different formation, and
repeating steps (c) and (d) in the vicinity of said different
formation.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the field of recovery of
oil from oil wells, and provides an improved method for recovery of
oil previously considered unrecoverable.
[0002] Oil formations typically include portions in which the oil
is present in liquid form, and portions in which the oil is trapped
in a solid or semi-solid form, such as a tar, bitumen, or asphalt.
Some oil exists in a heavy, viscous form, which is difficult or
impossible to pump out. The oil in the liquid form can be pumped
out relatively easily, but it is much more difficult, and
expensive, to extract the heavy oil. It is especially difficult to
extract the oil that is contained within a solid material; in their
natural state, materials such as bitumen will not flow at all. For
these reasons, in the prior art, when the liquid in a formation has
been substantially recovered, the oil well has been declared spent,
and the remaining oil has been deemed unrecoverable.
[0003] It turns out that, for many oilfields, the amount of oil
deemed unrecoverable may be as great as, or substantially greater
than, the portion that is easily recoverable. Thus, if it were
possible to recover, economically, all of the purportedly
unrecoverable oil in known oilfields, the amount of proven
petroleum reserves available to the world would increase by a very
substantial amount.
[0004] It has been proposed, in the prior art, to recover heavy
oil, and oil found within solid materials, by heating the
underground formation itself, and thereby causing heavy oil to
become less viscous, and/or causing oil trapped within a solid
material to flow out of the material. In effect, heating causes
formerly unrecoverable oil to become ordinary, liquid crude oil,
which can be pumped out by conventional means.
[0005] An obvious problem with the concept of heating an oil
reservoir is that it is difficult to heat a formation that may be
hundreds of feet, or more, below the ground. One prior art method
of providing such heat has been to generate steam at the surface of
a well, and to pump the steam into the well to heat the
formation.
[0006] A disadvantage of the use of steam is that the process
requires a large amount of energy, mainly through the burning of
natural gas to produce the steam. Also, because steam tends to
rise, it tends to flow above, or override, the oil reservoir into
which it is injected, thereby missing much of the formation
intended to be heated. As a result, the steam heating process may
recover only about 30% of the oil in the reservoir.
[0007] The problem of steam override can be reduced by providing
separate horizontal wells, wherein the steam is injected into an
upper well, and so that the resulting liquid oil flows by gravity
to a production well disposed below the first well, allowing the
liquid oil to be pumped out. The latter process is an improvement
over other steam heating methods, as it allows about 40-60%
recovery, but it still requires burning of natural gas at the
surface.
[0008] To overcome the problems associated with steam produced at
the surface, it has been proposed to heat the formation "in-situ",
i.e. at the location of the formation. In theory, one can start an
underground fire, combusting a small part of the formation. The
fire is supported by compressed air injected from the surface. If
the compressed air is hot enough, it can ignite the formation and
support combustion. Combustion of a portion of the formation
generates heat which heats other portions of the formation, thereby
causing the oil in the formation to become an extractable
liquid.
[0009] In practice, in-situ combustion is difficult to manage, and
has achieved only marginal results, with about 30% recovery at
most. Clearly, one seeks to burn only a small part of the
formation, leaving uncombusted liquid oil to be pumped out. It is
difficult to limit the scope of in-situ combustion in this way.
Also, it is important to be able to control the propagation of the
combustion within the formation. One might start a fire in a part
of the reservoir, but the fire might move in random directions,
based on fracture patterns in the formation. In the worst case, the
combustion might destroy the very oil that one seeks to recover.
Control of the propagation of in-situ combustion is inherently
difficult.
[0010] An improved process for in-situ combustion of an oil
formation is described in U.S. Pat. No. 5,626,191, the disclosure
of which is incorporated by reference herein. In the patented
process, a vertical injection well is positioned near a production
well having horizontal and vertical portions. The production well
has the general shape of a foot, and therefore defines a "toe"
portion and a "heel" portion. The injection well provides a path
for injection of air near the toe portion of the production well,
and the air, and the combustion front, proceeds laterally, from the
toe to the heel. This in-situ combustion process is sometimes
called TTH, for "toe-to-heel" combustion. More recently, the
process has been known in the industry by the acronym THAI, meaning
"toe to heel air injection".
[0011] An improvement to the THAI process is described in U.S. Pat.
No. 6,412,557, the disclosure of which is also incorporated by
reference herein. The latter patent discloses a catalyst deposited
in the gravel pack surrounding the production well. The catalyst,
which is similar to catalysts used in conventional refineries, not
only provides better control of the combustion process, helping to
prevent the entire formation from being burned, but it also
chemically upgrades the oil before it even comes out of the ground.
In particular, the catalyst supports reactions that separate
undesirable substances, such as sulfur, asphaltenes, and heavy
metals, from the oil. Moreover, the process inherently burns
unwanted coke while the oil is still underground. In prior art
processes, the coke would have to be removed at the surface. The
remnants of the burnt coke seal the horizontal portion of the well.
The process including the catalyst is known in the industry as
THAI/CAPRI.
[0012] The THAI/CAPRI process has further advantages over prior art
in-situ combustion methods. Entrained gases such as nitrogen rise
with the oil to the surface, and can be separated from the oil and
sold. Residual heat from the oil can be bled off to produce power.
Water produced in the process can be used for irrigation without
additional treatment. And the process does not require burning of
natural gas at the surface, making the process more environmentally
benign. The major requirement is only a source of compressed air,
and means for forcing it into a reservoir.
[0013] It is believed, based on the results of computer
simulations, that the THAI/CAPRI process could recover as much as
80% of the oil trapped within a reservoir, and previously deemed
unrecoverable. A recovery percentage this high has been
unattainable in the prior art.
[0014] An important ingredient of the THAI/CAPRI process is
compressed air which is injected into the formation. In the prior
art, such air has been derived from ambient air that has been
compressed and stored in a cylinder or other container.
Alternatively, combustion air could be supplied by vaporizing
liquid oxygen, and combining it with ambient air or nitrogen,
before injecting it into the formation. But cryogenic systems are
expensive, difficult to transport, and require regular maintenance,
which can be especially difficult in remote areas.
[0015] The present invention provides an improvement of the above
process, by providing a more desirable means of generating an
oxygen-rich gas for supporting in-situ combustion.
SUMMARY OF THE INVENTION
[0016] The present invention comprises an improved in-situ
combustion process for recovery of oil from a formation. The
in-situ combustion process generates heat which causes heavy oil in
a reservoir to become less viscous, and thus to flow readily to a
location from which it can be pumped out. In-situ combustion is
also used in order to release oil that is trapped in a solid or
semi-solid material, such as bitumen.
[0017] An in-situ combustion process requires that air be supplied
to the location of the combustion. According to the present
invention, the combustion air is oxygen-enriched air that is
generated non-cryogenically above the surface and injected into a
well. The oxygen-enriched air may be produced by a membrane system
or a pressure swing adsorption (PSA) system. Preferably, the
oxygen-enriched air is compressed before being injected into the
well.
[0018] The non-cryogenically produced oxygen-enriched air may be
blended with ambient air, or other air, so as to produce a gas
having a desired oxygen content. In this way, the oxygen content of
the gas can be easily adjusted to suit the requirements of the
particular application.
[0019] The membrane or PSA system produces an oxygen-enriched
stream and an oxygen-depleted stream. In another embodiment, the
oxygen-depleted stream, which is normally mostly nitrogen, can be
used to operate a compressor for compressing the oxygen-enriched
stream before it is injected into the well. The nitrogen could be
used instead for other purposes.
[0020] The present invention is especially useful with a
toe-to-heel combustion process, which is a process in which air is
conveyed into an injection well, to support combustion in a
horizontal well having an identifiable "toe" and "heel" structure.
The present invention provides oxygen-enriched air in the latter
process, instead of ordinary air. The invention is also useful in
an improved version of the toe-to-heel combustion process, in which
the process employs a catalyst which chemically upgrades the oil
before the oil is pumped out of the ground.
[0021] The present invention therefore has the primary object of
providing an improved process for extracting heavy oil, and/or oil
trapped in a solid or semi-solid material, from an underground
formation.
[0022] The invention has the further object of providing an
economical and convenient source of oxygen-enriched air, for use in
an in-situ combustion process for oil recovery.
[0023] The invention has the further object of reducing or
eliminating environmental hazards associated with an in-situ
combustion process for oil recovery.
[0024] The invention has the further object of providing an
improved process for oil recovery, wherein the process can be
operated with equipment that is readily portable.
[0025] The invention has the further object of providing
oxygen-enriched air for use in an in-situ combustion process for
oil recovery, wherein the oxygen content of the oxygen-enriched air
can be easily adjusted to suit the requirements of the combustion
process.
[0026] The reader skilled in the art will recognize other objects
and advantages of the present invention, from a reading of the
following brief description of the drawing, the detailed
description of the invention, and the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
[0027] The Figure provides a schematic diagram of an apparatus used
for practicing the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present invention includes a method and apparatus for
providing oxygen-enriched air for use in recovering heavy oil, or
oil that is trapped in a solid or semi-solid material, from an
underground oil reservoir. The oxygen-enriched air is used in an
in-situ combustion process, wherein the air is injected into a well
to support combustion of a portion of the reservoir, so as to
generate heat in the formation. The resulting heat causes the
uncombusted oil in the vicinity of the combustion to become less
viscous, so that the oil can flow to a location from which it can
be removed by conventional means.
[0029] In particular, the present invention can be considered an
improvement to the THAI, or THAI/CAPRI process, for oil recovery,
described above. More generally, the invention can be used with any
in-situ combustion process, wherein a portion of an oil formation
is combusted to heat an adjacent portion of the same formation. The
invention is therefore not necessarily limited to use with THAI or
THAI/CAPRI processes.
[0030] In its basic form, the invention comprises generating
oxygen-enriched air, using a non-cryogenic process, above the
surface of a well, and injecting the oxygen-enriched air downhole
to support combustion underground. The non-cryogenic process
preferably uses a gas separation membrane system or a pressure
swing adsorption (PSA) system. The oxygen content of the
oxygen-enriched air may be adjusted by mixing the oxygen-enriched
air with ambient air, or other air, to obtain a stream having a
desired percentage of oxygen. Controlling the percentage of oxygen
provides additional control over the downhole combustion, and
enables the operator to tailor the composition of the air to the
parameters of the oilfield, including the type of oil to be
recovered, the temperature of the reservoir, etc.
[0031] In another embodiment, the invention includes capturing the
oxygen-depleted gas stream produced by the membrane or PSA system,
and using this stream to drive a turbocompressor that further
compresses the product oxygen-enriched gas.
[0032] The use of oxygen-enriched air, instead of ordinary air, in
supporting in-situ combustion, has several advantages.
Oxygen-enriched air reduces the amount of gas needed for
combustion, because of its higher oxygen content. Because different
reservoir sites have different parameters (i.e. type of oil,
temperature, etc.), the same system can be used at different sites,
possibly with different settings of the oxygen content of the
injected air. Thus, the present invention effectively increases the
number of viable reservoir sites from which oil can be recovered
with the same system. It is easy to adjust the oxygen content,
simply by mixing the product oxygen-enriched gas with ambient
air.
[0033] The use of oxygen-enriched air produced by a membrane or a
PSA system has advantages over the use of a cryogenic system, in
that membranes or PSA systems cost less than cryogenic systems, are
more readily portable, and are easier to use. Membrane or PSA
systems do not require costly equipment for storage and transport
of cryogenic liquids.
[0034] The Figure provides a schematic diagram of the components of
a system used to practice the present invention. Air compressor 1
takes ambient air and compresses it. The compressed air passes
through receiver 2 and moisture separator 3. The air may then pass
through an optional air dryer 4. The air passes through coalescing
filters 5 and 6, and heater 7. Air leaving the heater may pass
through an optional carbon bed 8, and then through particulate
filter 9.
[0035] Air leaving the particulate filter enters air separator 10,
which may be either a membrane or a pressure swing adsorption (PSA)
unit. The air separator converts the incoming air into two streams,
one which is oxygen-enriched and the other which is
oxygen-depleted. In the extreme case, the separator may produce one
stream that is virtually all, or nearly all, oxygen, and another
stream which is almost all nitrogen. In the more general case, the
separation of oxygen is less than complete.
[0036] The oxygen content of the output of the separator 10 may be
controlled by blending air, which may be ambient air or other air,
with the oxygen-enriched stream as it exits the separator. The
Figure shows blending air being injected through conduit 13.
Conduit 13 is preferably positioned upstream of all compressors in
the system, so that the air streams may be blended at ambient
pressure.
[0037] The resulting product stream comprising oxygen or
oxygen-enriched air is compressed in compressor 12. The output of
compressor 12 is a compressed oxygen-enriched gas stream, which is
then directed to an injection well, for supporting an in-situ
combustion process, as discussed above.
[0038] In an alternative embodiment, also illustrated in the
Figure, the nitrogen (or, more generally, the oxygen-depleted gas
stream produced by the membrane or PSA system) is used to drive a
turbocompressor 11, which helps to boost the pressure of the
oxygen-enriched product gas. The latter arrangement is especially
useful in situations where the nitrogen (or oxygen-depleted air) is
not needed, or not needed at pressure, since the normal operation
of a membrane would yield nitrogen at near feed pressure of the
membrane system.
[0039] Alternatively, the nitrogen (or oxygen-depleted gas)
produced by the separator 10 can be used for inerting the oil
product, or for any other use in which nitrogen or an
oxygen-depleted gas is needed in the vicinity of an oil well. Such
nitrogen could be used for enhancing oil recovery, for drilling, or
for other uses.
[0040] The nitrogen or oxygen-depleted air produced by the
separator could be discarded instead of being used as stated above.
The present invention is intended to include this possibility
also.
[0041] The method described above has significant advantages over
the prior art. The components shown in the Figure can be provided
in a housing which can be relatively easily moved from one oil
recovery site to another. The use of oxygen-enriched air to support
in-situ combustion can reduce the amount of gas needed to support
such combustion, and can effectively increase the number of viable
reservoir sites from which oil can be recovered.
[0042] Membrane systems can provide up to about 60% oxygen, while
PSA systems can provide up to about 99% oxygen, using
currently-available technology. Membrane systems may be preferred
over PSA systems, in that by limiting the oxygen content to 60%, it
may be possible to avoid safety precautions that would be required
for gases having a higher oxygen content.
[0043] The invention can be modified in various ways. Any or all of
the elements in the Figure labeled "optional" can be omitted or
included. The oxygen-enriched air can be used to support various
kinds of in-situ combustion processes, not just the THAI or
THAI/CAPRI processes. These modifications, and others which will be
apparent to those skilled in the art, should be considered within
the spirit and scope of the following claims.
* * * * *