Note: Descriptions are shown in the official language in which they were submitted.
CA 02777947 2015-11-06
PROCESS FOR ENHANCED PRODUCTION OF HEAVY OIL USING
MICROWAVES
FIELD OF THE INVENTION
[0003] The present invention relates generally to a process for recovering
heavy
oil from a reservoir. In particular, the invention provides for utilizing
microwaves to
heat 1120 which interacts with the heavy oil in the reservoir to lower the
viscosity of
the heavy oil.
BACKGROUND OF THE INVENTION
[0004] Heavy oil is naturally formed oil with very high viscosity but often
contains impurities such as sulfur. While conventional light oil has
viscosities
ranging from about 0.5 centipoise (cP) to about 100 cP, heavy oil has a
viscosity that
ranges from 100 cP to over 1,000,000 cP. Heavy oil reserves are estimated to
equal
about fifteen percent of the total remaining oil resources in the world. In
the United
States alone, heavy oil resources are estimated at about 30.5 billion barrels
and heavy
oil production accounts for a substantial portion of domestic oil production.
For
example, in California alone, heavy oil production accounts for over sixty
percent of
the states total oil production. With reserves of conventional light oil
becoming more
difficult to find, improved methods of heavy oil extractions have become more
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important. Unfortunately, heavy oil is typically expensive to extract and
recovery is
much slower and less complete than for lighter oil reserves. Therefore, there
is a
compelling need to develop a more efficient and effective means for extracting
heavy
oil.
[0005] Viscous oil that is too deep to be mined from the surface may be
heated with hot fluids or steam to reduce the viscosity sufficiently for
recovery by
production wells. One thermal method, known as steam assisted gravity drainage
(SAGD), provides for steam injection and oil production to be carried out
through
separate wellbores. The optimal configuration is an injector well which is
substantially parallel to and situated above a producer well, which lies
horizontally
near the bottom of the formation. Thermal communication between the two wells
is
established and, as oil is mobilized and produced, a steam chamber or chest
develops.
Oil at the surface of the enlarging chest is constantly mobilized by contact
with steam
and drains under the influence of gravity.
[0006] There are several patents on the improvements to SAGD operation.
U.S. Patent No. 6, 814,141 describes applying vibrational energy in a well
fracture to
improve SAGD operation. U.S. Patent No. 5,899,274 teaches addition of solvents
to
improve oil recovery. U.S. Patent No. 6,544,411 describes decreasing the
viscosity of
crude oil using ultrasonic source. U.S. Patent No. 7,091,460 claims in situ,
dielectric
heating using variable radio frequency waves.
[0007] In a recent patent publication (U.S. Patent Publication
20070289736/US-Al, filed May 25, 2007), it is disclosed to extract
hydrocarbons
from a target formation, such as a petroleum reservoir, heavy oil, and tar
sands by
utilizing microwave energy to fracture the containment rock and for
liquification or
vitalization of the hydrocarbons.
[0008] In another recent patent publication (US Patent Publication
20070131591/US-Al, filed December 14, 2006), it is disclosed that lighter
hydrocarbons can be produced from heavier carbon-base materials by subjecting
the
heavier materials to microwave radiations in the range of about 4 GHz to about
18
GHz. This publication also discloses extracting hydrocarbons from a reservoir
where
a probe capable of generating microwaves is inserted into the oil wells and
the
microwaves are used to crack the hydrocarbons with the cracked hydrocarbon
thus
produced being recovered at the surface.
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[0009] Despite these disclosures, it is unlikely that direct microwave
cracking or
heating of hydrocarbons would be practical or efficient. It is known that
microwave
energy is absorbed by a polar molecule with a dipole moment and bypasses the
molecules that lack dipole moment. The absorption of the microwave energy by
the
polar molecule causes excitation of the polar molecule thereby transforming
the
microwave energy into heat energy (known as the coupling effect). Accordingly,
when a molecule with a dipole moment is exposed to microwave energy it gets
selectively heated in the presence of non-polar molecules. Generally, heavy
oils
comprise non-polar hydrocarbon molecules; accordingly, hydrocarbons would not
get
excited in the presence of microwaves.
[0010] Additionally, while the patent publication above claims to break the
hydrocarbon molecules, the energy of microwave photons is very low relative to
the
energy required to cleave a hydrocarbon molecule. Thus, when hydrocarbons are
exposed to microwave energy, it will not affect the structure of a hydrocarbon
molecule. (See, for example, "Microwave Synthesis", am Publication, 2002 by
Brittany Hayes).
BRIEF SUMMARY OF THE DISCLOSURE
[0011] A process of injecting 1120 into a subterranean region through a
first
wellbore of a steam assisted gravity draining operation. Microwaves are
introduced
into the region at a frequency sufficient to excite the H20 molecules and
increase the
temperature of at least a portion of the 1120 within the region to produce
heated H20.
At least a portion of the heavy oil in the region is contacted with the heated
1120 to
produce heated heavy oil. Heated heavy oil is produced through a second
wellbore of
the steam assisted gravity drainage operation, thereby recovering heavy oil
with the
steam assisted gravity drainage operation from the subterranean region. In
this
embodiment a portion of the H20 is injected as steam and the steam contact
with at
least a portion of the heavy oil in the region so as to heat the portion of
the heavy oil
and reduce its viscosity so that it flows generally towards the second
wellbore.
Additionally, the lateral wells of the steam assisted gravity drainage
operations are
extended with a frequency heating device along the lateral well.
[0012] In an alternate embodiment liquid 1120 is injected into a region
through a
first wellbore of a steam assisted gravity drainage operation. Microwaves are
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introduced into the subterranean region at a frequency sufficient to excite
the liquid
H20 molecules and increase the temperature of at least a portion of the liquid
H20
within the region to produce heated gaseous H20. At least a portion of the
heavy oil
in the region is heated by contact with the heated gaseous 1120 to produce a
heated
heavy oil. Heated heavy oil is produced through a second wellbore of the steam
assisted gravity drainage operation, thereby recovering heavy oil with the
steam
assisted gravity drainage operation from the subterranean region. In this
embodiment
a portion of the H20 is injected as steam and the steam contact with at least
a portion
of the heavy oil in the region so as to heat the portion of the heavy oil and
reduce its
viscosity so that it flows generally towards the second wellbore.
Additionally, the
lateral wells of the steam assisted gravity drainage operations are extended
with a
frequency heating device along the lateral well.
[0013] In yet another
embodiment a process is taught of injecting H20 into a
subterranean region through an injection wellbore of a steam assisted gravity
drainage
operation. Microwaves are introduced into the region at a frequency sufficient
to
excite the 1420 molecules and increase the temperature of at least a portion
of the 1120
within the region to produce heated H20. Heating at least a portion of the
bitumen to
below 3000cp in the region by contact with the heated 1120 to produce a heated
heavy
oil and an imposed pressure differential between the injection wellbore and a
production wellbore. Producing the heated heavy oil through the production
wellbore
of the steam assisted gravity drainage operation, thereby recovering heavy oil
with the
steam assisted gravity drainage operation from the subterranean region. In
this
embodiment a portion of the H20 is injected as steam and the steam contact
with at
least a portion of the heavy oil in the region so as to heat the portion of
the heavy oil
and reduce its viscosity so that it flows generally towards the second
wellbore.
Additionally, the lateral wells of the steam assisted gravity drainage
operations are
extended with a frequency heating device along the lateral well. Additionally,
the
injection wellbore and the production wellbore are from 3 meters to 7 meters
apart
and the injection wellbore is located higher than the production wellbore.
[0013a] In a further embodiment of the present invention there is provided a
process comprising: a) injecting H20 into a subterranean region through a
first
wellbore of a steam assisted gravity drainage operation; b) introducing
microwaves
into the region at a frequency sufficient to excite the H20 molecules and
increase the
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temperature of at least a portion of the H20 within the region to produce
heated H20;
c) heating at least a portion of the heavy oil in the region by contact with
the heated
1120 to produce heated heavy oil; and d) producing the heated heavy oil
through a
second wellbore of the steam assisted gravity drainage operation; thereby
recovering
heavy oil with the steam assisted gravity drainage operation from the
subterranean
region; wherein a portion of the 1120 is injected as steam and the steam
contacts with
at least a portion of the heavy oil in the region so as to heat the portion of
the heavy
oil and reduce its viscosity so that it flows generally towards the second
wellbore;
wherein at least one wellbore of the steam assisted gravity drainage
operations are
extended with a frequency heating device along the wellbore.
[0013131 In yet a further embodiment of the present invention there is
provided a
process comprising: a) injecting liquid 1120 into a region through a first
wellbore of a
steam assisted gravity drainage operation; b) introducing microwaves into a
subterranean region at a frequency sufficient to excite the liquid H20
molecules and
increase the temperature of at least a portion of the liquid 1120 within the
region to
produce heated gaseous 1120; c) heating at least a portion of the heavy oil in
the
region by contact with the heated gaseous H20 to produce heated heavy oil; and
d)
producing the heated heavy oil through a second wellbore of the steam assisted
gravity drainage operation; thereby recovering heavy oil with the steam
assisted
gravity drainage operation from the subterranean region; wherein a portion of
the
liquid 1120 is injected as steam and the steam contacts with at least a
portion of the
heavy oil in the region so as to heat the portion of the heavy oil and reduce
its
viscosity so that it flows generally towards the second wellbore; wherein at
least one
wellbore of the steam assisted gravity drainage operations are extended with a
frequency heating device along the wellbore.
[0013c] In another embodiment of the present invention there is provided a
process
comprising: a) injecting 1120 into a subterranean region through an injection
wellbore
of a steam assisted gravity drainage operation; b) introducing microwaves into
the
region at a frequency sufficient to excite the H20 molecules and increase the
temperature of at least a portion of the 1120 within the region to produce
heated H20;
c) heating at least a portion of a bitumen to below 3000cp in the region by
contact
with the heated H20 to produce a heated heavy oil and an imposed pressure
differential between the injection wellbore and a production wellbore; and d)
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producing the heated heavy oil through the production wellbore of the steam
assisted
gravity drainage operation; thereby recovering heated heavy oil with the steam
assisted gravity drainage operation from the subterranean region; wherein the
injection wellbore and the production wellbore are from 3 meters to 7 meters
apart
and the injection wellbore is located higher than the production wellbore;
wherein the
1-120 is injected as steam and the steam contacts with at least a portion of
the bitumen
in the region so as to heat the portion of the bitumen and reduce its
viscosity to
produce a heated heavy oil that flows generally towards the second wellbore;
wherein
at least one wellbore of the steam assisted gravity drainage operations are
extended
with a frequency heating device along the wellbore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A more
complete understanding of the present invention and benefits
thereof may be acquired by referring to the following description taken in
conjunction
with the accompanying drawings in which:
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[0015] Figure 1 is a schematic diagram illustrating a heavy oil heating
process,
wherein wave guides are used to introduce the microwaves to the reservoir.
[0016] Figure 2 is a schematic diagram illustrating a heavy oil heating
process
wherein the microwaves are introduced into the reservoir using a microwave
generator located within the reservoir.
[0017] Figure 3 depicts the placement of two radio frequency heating
devices
along a lateral well.
[0018] Figure 4 depicts steam assisted gravity drainage with lateral wells.
DETAILED DESCRIPTION
[0019] Turning now to the detailed description of the preferred arrangement
or
arrangements of the present invention, it should be understood that the
inventive
features and concepts may be manifested in other arrangements and that the
scope of
the invention is not limited to the embodiments described or illustrated. The
scope of
the invention is intended only to be limited by the scope of the claims that
follow.
[0020] In this description, the term water is used to refer to H20 in a
liquid state
and the term steam is used to refer to H2O in a gaseous state.
[0021] Turning now to Figure 1, wellbores 14, 15 and 16 are illustrated.
Wellbore
14 extends from the surface 10 into a lower portion of subterranean region 12.
Wellbore 16 extends from the surface 10 into subterranean region 12 and
generally
will be higher than wellbore 14. Wellbore 16 will be used to inject H20 and it
is
preferred that it is located higher than wellbore 14 so that when the injected
H20 heats
the heavy oil, the heavy oil will flow generally towards wellbore 14, which is
used to
extract the heavy oil from the reservoir. In one embodiment a portion of the
H20 is
injected as steam and the steam contacts with at least a portion of the heavy
oil in the
region so as to heat the portion of the heavy oil and reduce its viscosity so
that it flows
generally towards the second wellbore. Wellbore 15 is used to introduce
microwaves
to the reservoir and it is preferred that wellbore 15 be located intermittent
to wellbores
14 and 15; although, other arrangements are possible. In this embodiment the
lateral
wells of the steam assisted gravity drainage operations are extended with a
frequency
heating device along the lateral well. The process can involve inserting a
frequency
heating device into the lateral well and operating the frequency heating
device along
the lateral well.
CA 02777947 2012-05-22
[0022] This
process can be used for any pre-existing, existing, or future planned
steam assisted gravity drainage operation where there exists a need to extend
the
lateral well or to increase production from the toe of the lateral well. In
one
embodiment the process can be used to extend the lateral well beyond 1,000
meters,
1,500 meters or even 2,000 meters. Under conventional steam assisted gravity
drainage operations extending the lateral well to these lengths would not be
economically feasible due to the increased reduction of steam quality toward
the toe
of the lateral well.
[0023] Increased
steam quality can calculate by the percentage of actual steam
versus liquid water in the well. Typically as steam is forced or produced
downhole a
certain percentage of the steam will eventually condense into liquid water.
Increased
steam is able to help the production of heavy oil by providing additional
latent heat to
the formation, thereby increasing the hydrocarbons produced by the well.
[0024] In one
embodiment steam assisted gravity drainage operation is meant to
include conventional steam assisted gravity drainage operation in addition to
expanding solvent-steam assisted gravity drainage and cyclic steam stimulation
operation.
[0025] In one
embodiment the distance along the lateral well between a first
frequency heating device and a second frequency heating device is greater than
500,
750 or even 1,000 meters. As the steam quality degrades along the horizontal
well,
the second frequency heating device increases the stream quality. The steam
quality
can be increased by the second frequency heating device to be greater than
80%, 85%,
90%, 95%, even 100% steam when compared the amount of liquid water in the
well.
By reducing the amount of liquid water and increasing the amount of steam in
the
well additional latent heat is added to the formation.
[0026] In one
embodiment a first frequency heating device is placed within 20
meters of the heel of the lateral well and the distance along the lateral well
between
the first frequency heating device and a second radio frequency heating device
is
greater than 500 meters.
[0027] In
another embodiment it is also possible to have more than two frequency
heating devices. In this embodiment to ensure the quality of the steam
frequency
heating devices can be placed every 50, 100, 200, 300, 400 500, 600, 700 or
even 800
meters apart.
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[0028] In one
embodiment a specific activator is injected into the well. By
injecting a specific activator one skilled in the art would have the requisite
knowledge
to select the exact frequency required to achieve maximum heating of the
activator.
Therefore, the current method eliminates the need to arbitrarily generate
variable
frequencies which may or may not be able to efficiently absorb the radiation.
This
method would cause the frequencies generated by the frequency heating device
to
more efficiently transfer into the water of the steam assisted gravity
drainage
operation.
[0029] In an
alternate embodiment steam generated in boiler 11 is provided into
the reservoir 12 through upper wellbore leg 16. The steam heats the heavy oil
within
zone 17 of the oil-bearing portion 13 of reservoir 12 causing it to become
less viscous
and, hence, increase its mobility. The heated heavy oil flows downward by
gravity
and is produced through wellbore leg 14. While Figure 1 illustrates a single
wellbore
for injection and a single wellbore for extraction, other configurations are
within the
scope of the invention, for example, there can be two or more separate
wellbores to
provide steam injection and two or more separate wellbores for production.
Similarly,
multiple wellbores can be used for microwave introduction to the reservoir, as
further
discussed below.
[0030]
Generally, the wellbore for steam injection, wellbore 16, will be
substantially parallel to and situated above the wellbore for production,
wellbore 14,
which is located horizontally near the bottom of the formation. Pairs of steam
injection wellbores and production wellbores will generally be close together
and
located at a suitable distance to create an effective steam chamber and yet
minimizing
the preheating time. Typically, the pairs of injection and production
wellbores will be
from about 3 meters to 7 meters apart and preferably there will be about 5
meters of
vertical separation between the injector and producer wellbores. In other
embodiments it is possible for the injection and production wellbores be
anywhere
from 1, 3, 5, 7, 12, 15, 20 even 25 meters of horizontal separation apart.
Additionally,
in other embodiments it is possible for the injection and production wellbores
be
anywhere from 1, 3, 5, 7, 12, 15, 20 even 25 meters of vertical separation
apart. In
this type of SAGD operation, the zone 17 is preheated by steam circulation
until the
reservoir temperature between the injector and producer wellbore is at a
temperature
sufficient to drop the viscosity of the heavy oil so that it has sufficient
mobility to
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flow to and be extracted through wellbore 14. Generally, the heavy oil will
need to be
heated sufficiently to reduce its viscosity to below 3000 cP; however, lower
viscosities are better for oil extraction and, thus, it is preferable that the
viscosity be
below 1500 cP and more preferably below 1000 cP. Preheating zone 17 involves
circulating steam inside a liner using a tubing string to the toe of the
wellbore. Both
the injector and producer would be so equipped. Steam circulation through
wellbores
14 and 16 will occur over a period of time, typically about 3 months. During
the
steam circulation, heat is conducted through the liner wall into the reservoir
near the
liner. At some point before the circulation period ends, the temperature
midway
between the injector and producer will reach a temperature wherein the bitumen
will
become movable typically around 3000 cP or less or from about 80 to 100 C.
Once
this occurs, the steam circulation rate for wellbore 14 will be gradually
reduced while
the steam rate for the injector wellbore 16 will be maintained or increased.
This
imposes a pressure gradient from high, for the area around wellbore 16, to
low, for the
area around wellbore 14. With the oil viscosity low enough to move and the
imposed
pressure differential between the injection and production wellbores, steam
(usually
condensed to hot water) starts to flow from the injector into the producer. As
the
steam rate is continued to be adjusted downward in wellbore 14 and upward in
wellbore 16, the system arrives at steam assisted gravity drainage operation
with no
steam injection through wellbore 14 and all the steam injection through
wellbore 16.
Once hydraulic communication is established between the pair of injector and
producer wellbores, steam injection in the upper well and liquid production
from the
lower well can proceed. Due to gravity effects, the steam vapor tends to rise
and
develop a steam chamber at the top section 19 of zone 17. The process is
operated so
that the liquid/vapor interface is maintained between the injector and
producer
wellbores to form a steam trap which prevents live steam from being produced
through the lower wellbore.
[0031] During
operation, steam will come into contact with the heavy oil in
zone 17 and, thus, heat the heavy oil and increase its mobility by lessening
its
viscosity. Heated heavy oil will tend to flow downward by gravity and collect
around
wellbore 14. Heated heavy oil is produced through wellbore 14 as it collects.
Steam
contacting the heavy oil will lose heat and tend to condense into water. The
water
will also tend to flow downward toward wellbore 14. In past SAGD operations,
this
water would also be produced through wellbore 14. Such produced water would
need
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to be treated to reduce impurities before being reheated in the boiler for
subsequent
injection. As the process continues operation, zone 17 will expand with heavy
oil
production occurring from a larger portion of oil-bearing portion 13 of
subterranean
formation 12.
[0032] Turning again to Figure 1, the current invention provides for
microwave generator 18 to generate microwaves which are directed underground
and
into zone 17 of the reservoir through a series of wave guides 20. The diameter
of the
wave guides will preferably be more than 3 inches in order to ensure good
transmission of the microwaves. Within the reservoir, the microwaves will be
at a
frequency substantially equivalent to the resonant frequency of the water
within the
reservoir so that the microwaves excite the water molecules causing them to
heat up.
Optimally, the microwaves will be introduced at or near the liquid vapor
interface so
that condensed steam is reheated from its water state back into steam further
supplying the steam chamber. In some embodiments the microwave frequency will
be not greater than 3000 megahertz and/or at a resonant frequency of water.
Based on
the resonant frequency of water, the optimum frequency will be 2450 megahertz;
however, power requirements and other factors may dictate that another
frequency is
more economical. Additionally, salt and other impurities may enhance the
coupling
effect (production of heat by resonance of a polar or conductive molecule with
microwave energy); thus, the presence of salt is desirable.
[0033] Turning now to Fig. 2, a further embodiment of the invention is
illustrated wherein, instead of using wave guides, power is supplied through
electrical
wire 22 to microwave generating probe 24. The electrical power can be supplied
to
wire 22 by any standard means such as generator 26.
[0034] In still another embodiment of the invention, also illustrated in
Fig. 2,
no steam boiler is used. Instead water is introduced directly into wellbore 16
through
pipe 28 and valve 30. Wellbore 16 then introduces water into the reservoir
instead of
steam and the entire steam production would be accomplished through use of the
microwave generators. This embodiment of the invention has the added advantage
of
avoiding costly water treatment that is necessary when using a boiler to
generate
steam because, as discussed above, salt and other impurities can aid in heat
generation. In a preferred embodiment, the water introduced into the reservoir
would
have a salt content greater than the natural salt content of the reservoir,
which is
typically about 5,000 to 7,000 ppm. Accordingly, it is preferred that the
introduced
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water has a salt content greater than 10,000 ppm. For enhanced heat generation
30,000 to 50,000 ppm is more preferred.
[0035] Figure 3 depicts the placement of two radio frequency heating
devices 12,
14 along a lateral well 16. In this embodiment line 18 demonstrates the
current
feasible well length. By added in the second radio frequency heating device 14
the
length of the lateral well 16 is extended.
[0036] Figure 4 depicts two scenarios. In the figure 4a the length of
lateral wells
are not extended. As a result it can be shown that additional well pads are
needed to
effectively produce oil. Figure 4b shows an embodiment of this process where
the
lateral wells are extended thereby eliminating the need for additional
horizontal wells
and additional well pads.
[0037] Microwave generators useful in the invention would be ones suitable
for
generating microwaves in the desired frequency ranges recited above. Microwave
generators and wave guide systems adaptable to the invention are sold by Cober
Muegge LLC, Richardson Electronics and CPI International Inc.
[0038] Steam to oil ratio is an important factor in SAGD operations and
typically the amount of water required will be 2 to 3 times the oil
production. Higher
steam to oil production ratios require higher water and natural gas costs. The
present
invention reduces water and natural gas requirements and reduces some of the
water
handling involving recycling, cooling, and cleaning up the water.
[0039] In closing, it should be noted that the discussion of any reference
is not an
admission that it is prior art to the present invention, especially any
reference that may
have a publication date after the priority date of this application. At the
same time,
each and every claim below is hereby incorporated into this detailed
description or
specification as additional embodiments of the present invention.
[0040] Although the systems and processes described herein have been
described
in detail, it should be understood that various changes, substitutions, and
alterations
can be made without departing from the scope of the invention as defined by
the
following claims. Those skilled in the art may be able to study the preferred
embodiments and identify other ways to practice the invention that are not
exactly as
described herein. The scope of the claims should not be limited by the
preferred
embodiments set forth in the description, but should be given the broadest
interpretation consistent with the description as a whole.
