Note: Descriptions are shown in the official language in which they were submitted.
METHOD OF PRODUCING HYDROCARBON RESOURCES USING AN UPPER RF
HEATING WELL AND A LOWER PRODUCER/INJECTION WELL AND
ASSOCIATED APPARATUS
Technical Field
[0001] The present invention relates to the field of
hydrocarbon resource recovery, and, more particularly, to
hydrocarbon resource recovery methods using radio frequency
heating devices.
Background
[0002] Energy consumption worldwide is generally
increasing, and conventional hydrocarbon resources are being
consumed. In an attempt to meet demand, the exploitation of
unconventional resources may be desired. For example, highly
viscous hydrocarbon resources, such as heavy oils, may be
trapped in sands where their viscous nature does not permit
conventional oil well production. This category of hydrocarbon
resource is generally referred to as oil sands. Estimates are
that trillions of barrels of oil reserves may be found in such
oil sand formations.
[0003] In some instances, these oil sand deposits are
currently extracted via open-pit mining. Another approach for
in situ extraction for deeper deposits is known as Steam-
Assisted Gravity Drainage (SAGD). The heavy oil is immobile at
reservoir temperatures, and therefore, the oil is typically
heated to reduce its viscosity and mobilize the oil flow. In
SAGD, pairs of injector and producer wells are formed to be
laterally extending in the ground. Each pair of
injector/producer wells includes a lower producer well and an
upper injector well. The injector/production wells are
typically located in the payzone of the subterranean formation
between an underburden layer and an overburden layer.
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[0004] The upper injector well is used to typically
inject steam, and the lower producer well collects the
heated crude oil or bitumen that flows out of the formation,
along with any water from the condensation of injected steam
and some connate water in the formation. The injected steam
forms a steam chamber that expands vertically and horizontally
in the formation. The heat from the steam reduces the
viscosity of the heavy crude oil or bitumen, which allows it
to flow down into the lower producer well where it is
collected and recovered. The steam and gases rise due to their
lower density. Gases, such as methane, carbon dioxide, and
hydrogen sulfide, for example, may tend to rise in the steam
chamber and fill the void space left by the oil defining an
insulating layer above the steam. Oil and water flow is by
gravity driven drainage urged into the lower producer well.
[0005] Many countries in the world have large deposits of
oil sands, including the United States, Russia, and various
countries in the Middle East. Oil sands may represent as much
as two-thirds of the world's total petroleum resource, with at
least 1.7 trillion barrels in the Canadian Athabasca Oil
Sands, for example. At the present time, only Canada has a
large-scale commercial oil sands industry, though a small
amount of oil from oil sands is also produced in Venezuela.
Because of increasing oil sands production, Canada has become
the largest single supplier of oil and products to the United
States. Oil sands now are the source of almost half of
Canada's oil production, while Venezuelan production has been
declining in recent years. Oil is not yet produced from oil
sands on a significant level in other countries.
[0006] U.S. Published Patent Application No. 2010/0078163
to Banerjee et al. discloses a hydrocarbon recovery process
whereby three wells are provided: an uppermost well used to
inject water, a middle well used to introduce microwaves into
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the reservoir, and a lowermost well for production. A
microwave generator generates microwaves which are directed
into a zone above the middle well through a series of
waveguides. The frequency of the microwaves is at a frequency
substantially equivalent to the resonant frequency of the
water so that the water is heated.
[0007] Along these lines, U.S. Published Patent Application
No. 2010/0294489 to Dreher, Jr. et al. discloses using
microwaves to provide heating. An activator is injected below
the surface and is heated by the microwaves, and the activator
then heats the heavy oil in the production well. U.S.
Published Patent Application No. 2010/0294488 to Wheeler et
al. discloses a similar approach.
[0008] U.S. Patent No. 7,441,597 to Kasevich discloses
using a radio frequency generator to apply radio frequency
(RF) energy to a horizontal portion of an RF well positioned
above a horizontal portion of an oil/gas producing well. The
viscosity of the oil is reduced as a result of the RF energy,
which causes the oil to drain due to gravity. The oil is
recovered through the oil/gas producing well.
[0009] U.S. Patent No. 7,891,421, also to Kasevich,
discloses a choke assembly coupled to an outer conductor of a
coaxial cable in a horizontal portion of a well. The inner
conductor of the coaxial cable is coupled to a contact ring.
An insulator is between the choke assembly and the contact
ring. The coaxial cable is coupled to an RF source to apply RF
energy to the horizontal portion of the well.
[0010] U.S. Patent Application Publication No. 2011/0309988
to Parsche discloses a continuous dipole antenna. More
particularly, Parsche disclose a shielded coaxial feed coupled
to an AC source and a producer well pipe via feed lines. A
non-conductive magnetic bead is positioned around the well
pipe between the connection from the feed lines.
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[0011] U.S. Patent Application Publication No. 2012/0085533
to Madison et al. discloses combining cyclic steam stimulation
with RF heating to recover hydrocarbons from a well. Steam is
injected into a well followed by a soaking period wherein heat
from the steam transfers to the hydrocarbon resources. After
the soaking period, the hydrocarbon resources are collected,
and when production levels drop off, the condensed steam is
revaporized with RF radiation to thus upgrade the hydrocarbon
resources.
[0012] Unfortunately, long production times, for example,
due to a failed start-up, to extract oil using SAGD may lead
to significant heat loss to the adjacent soil, excessive
consumption of steam, and a high cost for recovery.
Significant water resources are also typically used to recover
oil using SAGD, which may impact the environment. Limited
water resources may also limit oil recovery. SAGD is also not
an available process in permafrost regions, for example, or in
areas that may lack sufficient cap rock, are considered "thin"
payzones, or payzones that have interstitial layers of shale.
[0013] Additionally, production times and efficiency may be
limited by post extraction processing of the recovered oil.
More particularly, oil recovered may have a chemical
composition or have physical traits that may require
additional or further post extraction processing as compared
to other types of oil recovered.
Summary
[0014] A method of producing hydrocarbon resources from a
subterranean formation may include heating the subterranean
formation with at least one radio frequency (RF) antenna
located in an upper well within the subterranean formation.
The method may further include producing hydrocarbons from a
lower well within the heated subterranean formation and
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vertically beneath the upper well to create a void within the
subterranean formation, and injecting a solvent into the void
within the heated subterranean formation from the lower well.
[0015] More particularly, heating may include pre-heating
the subterranean formation with the at least one RF antenna
prior to producing the hydrocarbon resources. By way of
example, pre-heating may include pre-heating the subterranean
formation to a temperature in a range of 80-100 C prior to
initiating producing.
[0016] In accordance with one example implementation,
producing and injecting may be cycled over time. Furthermore,
in accordance with another example implementation, injecting
may comprise injecting the solvent into the void from the
lower well while simultaneously producing hydrocarbons from
the lower well. Furthermore, heating may comprise continuously
heating the subterranean formation with the at least one RF
antenna from the upper well during producing and injecting.
[0017] By way of example, the upper and lower wells may be
parallel to one another. Furthermore, a pressure of the
solvent injected into the void may be decreased over time. In
addition, the lower well may include a solvent supply pipe and
a producer pipe adjacent thereto.
[0018] A related apparatus for producing hydrocarbon
resources from a subterranean formation may include a radio
frequency (RF) source and at least one radio frequency (RF)
antenna located in an upper well within the subterranean
formation and configured to heat the subterranean formation
based upon RF power from the RF source. The apparatus may
further include a producer pipe and a solvent supply pipe
positioned within a lower well vertically beneath the upper
well, a recovery pump coupled to the producer pipe and
configured to recover hydrocarbon resources from the
subterranean formation from the lower well, and a solvent
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source coupled to the solvent supply pipe and configured to
inject a solvent into the subterranean formation from the
lower well.
Brief Description of the Drawings
[0019] FIG. 1 is a schematic block diagram of an apparatus
for hydrocarbon resource recovery including an upper RF
heating well and a lower producer/solvent injection well in
accordance with an example embodiment.
[0020] FIGS. 2 is a flow diagram illustrating example
method aspects associated with the apparatus of FIG. 1.
[0021] FIGS. 3A and 3B are parts of a flow diagram
illustrating an example cyclical production/injection
hydrocarbon resource recovery approach for the apparatus of
FIG. I in accordance with an example embodiment.
[0022] FIG. 4 is a graph of oil produced vs. time comparing
the hydrocarbon resource recovery approach of FIGS. 3A and 3B
with a prior hydrocarbon resource recovery approach.
[0023] FIG. 5 is a flow diagram illustrating an example
continuous production/injection hydrocarbon resource recovery
approach for the apparatus of FIG. 1 in accordance with an
example embodiment.
Detailed Description
[0024] The present invention will now be described more
fully hereinafter with reference to the accompanying drawings,
in which preferred embodiments of the invention are shown.
This invention may, however, be embodied in many different
forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and
complete, and will fully convey the scope of the invention to
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those skilled in the art. Like numbers refer to like elements
throughout.
[0025] By way of background, some RF hydrocarbon recovery
systems include an upper solvent injector well, and a producer
well below the injector well. Solvents (e.g., propane, light
alkanes or other relatively light hydrocarbons) are injected
into a deposit to dilute the heavy oil or bitumen. The solvent
advantageously reduces the native viscosity of or thins the
hydrocarbon resources. Furthermore, an RF antenna is
positioned within the injector well to apply RF heating to the
formation, which also reduces the viscosity of the heavy oil
and allows it to flow more easily into the producer well below
for recovery. One such example well configuration is set forth
in U.S. Pat. No. 9,739,126 to Trautman et al., which is
assigned to the present Assignee. While this configuration is
highly effective, the flow cross sectional area required to
deliver the solvent through the antenna may, in some
instances, increase the well casing to non-conventional, and
therefore more expensive, sizes.
[0026] Generally speaking, the present approach
advantageously allows installation of an RF antenna within
smaller conventional casing sizes, as it provides RF heating
from an upper antenna well, but moves the solvent injection
function to the lower well. That is, the upper (antenna) well
provides RF energy to the formation, and there is no solvent
injection from the upper well. Rather, solvent injection and
hydrocarbon production are both provided through the lower
well.
[0027] Referring initially to FIG. 1 and the flowchart 60
of FIG. 2, an apparatus 30 and associated method of recovering
hydrocarbon resources in a subterranean formation 31 is now
described. The subterranean formation 31 illustratively
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includes an upper well 32 and a lower well 33 therein, with
the lower well being vertically below the upper well. The
upper and lower wells 32, 33 illustratively initially extend
diagonally from the surface of the subterranean formation to a
desired depth, and then laterally within the subterranean
formation along a payzone 34 where hydrocarbon (e.g., bitumen
or heavy oil) recovery is to occur. The payzone 34 will be
located at various depths depending on the location of the
subterranean formation 31, and the length of the payzone may
also vary between different implementations. By way of
example, a relatively thin payzone may be in a range of ten
meters or less, while a larger payzone may be between thirty
and forty meters, though again other ranges of payzones may be
accommodated by the apparatus 30 and recovery techniques
discussed herein.
[0026] In the illustrated example, the apparatus includes a
radio frequency (RF) source 35 at the wellhead, and one or
more RF antennas located in the upper well 32 and configured
to heat the subterranean formation 31 based upon RF power from
the RF source, at Block 62. More particularly, the RF power is
supplied from the RF source 35 to an RF transmission line 39
having an RF feed section 36, which is within and coupled to
an electrically conductive well pipe 43. The RF transmission
line 39 may be a coaxial transmission line, for example. The
electrically conductive well pipe 43 may be a wellbore liner,
for example, and defines an RF antenna (e.g., a dipole
antenna) with the RF feed portion 36. Of course, other antenna
configurations may be used in different embodiments.
[0029] The electrically conductive well pipe 43 may have a
tubular shape, for example, to allow for equipment, sensors,
etc. to be passed therethrough. More particularly, a
temperature sensor and/or a pressure sensor may be positioned
on or within the RF transmission line 39 and/or RF feed
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section 36. A temperature and/or a pressure sensor may
alternatively or additionally be positioned on or within the
electrically conductive well pipe 43 to read temperatures and
pressures of the subterranean formation 31, as will be
discussed further below.
[0030] The apparatus 30 further illustratively includes a
producer pipe 37 and a solvent supply pipe 38 positioned
within the lower well 33. A recovery pump 40 is coupled to the
producer pipe 37 and configured to recover hydrocarbon
resources from the subterranean formation 31 from the lower
well 33, at Block 63. In the illustrated example the recovery
pump 40 is a submersible pump positioned within the
electrically conductive well pipe of the second well 33,
although in some embodiments the recovery pump may be
positioned above the subterranean formation 31 at the
wellhead. The recovery pump 40 may be an artificial gas lift
(AGL), or other type of pump, for example, using hydraulic or
pneumatic lifting techniques.
[0031] The initial production begins to create a void 42
within the payzone 34 as oil is drawn from the subterranean
formation 31, as will be discussed further below. Furthermore,
a solvent source 41 is coupled to the solvent supply pipe 38
and configured to inject a solvent into the subterranean
formation 31 from the lower well 33, at Block 64, which
illustratively concludes the method of FIG. 2 (Block 65). The
solvent supply pipe 38 illustratively includes openings 44
spaced along a length thereof within the payzone 34. However,
the number of injection points shown is just an example, and
different numbers and spacings of the openings 44 may be used
in different configurations, depending on the length of the
payzone 34, type of solvent being used, etc. In the
illustrated configuration, the openings 44 may be spaced apart
from an inlet 45 of the producer pipe 37 to help avoid
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extraction of solvent before it has a chance to enter the
formation 31.
[0032] Referring additionally to the flow diagram 70 of
FIGS. 3A-33, an example implementation of the above-described
hydrocarbon production method is now described which utilizes
a cyclical production/injection approach, alternating between
hydrocarbon production and solvent injection from the lower
well 33. Beginning at Block 71, RF heating is initiated from
the RF source 35 to begin pre-heating the formation 31 to a
desired starting temperature, at Blocks 72-73. In one example
embodiment, the target production starting temperature may be
in a range of 50 to 200 C, and more particularly 80 to 100 C,
measured from a temperature sensor(s) within the lower well 33
(and/or upper well 32 in some embodiments). However, other
target temperatures may be used in different embodiments as
well. The pre-heating phase may take two to three months in a
typical implementation, although slower or faster pre-heating
may occur with different geological formations and
implementations.
[0033] Once the desired temperature is reached, oil may
then be produced from the lower well 44 to create the void 42
within the formation 31, through which the solvent will enter
the formation, at Block 74. Production may continue until the
desired operational target is reached, at Block 75. By way of
example, the target may be production for a certain period of
time, for a certain initial quantity of oil, while above a
target oil rate, etc., to create the desired initial void size
within the formation 31. Once production ceases (e.g., the
recovery pump 40 is turned off), then solvent injection from
the lower well 33 commences (e.g., by turning on the solvent
source 41), at Block 76, until an injection operational target
is reached, at Block 77. Here again, this may be based upon an
amount of time solvent is injected, a quantity of solvent
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injected, etc. Once the target is reached, then solvent
injection may be stopped (e.g., by shutting off the solvent
source 41) and oil production resumed (e.g., by turning back
on the recovery pump 40), at Blocks 78-79. Here again,
production continues until the desired operational target is
reached for the current cycle, at Block 80.
[0034] Numerous injection/production cycles may then be run
(i.e., Blocks 76-79) until an overall recovery target is
reached for the formation 31, at Block 81. Different
operational considerations may be applicable depending upon
the geographical region of operation, the geological
formation, etc., as will be appreciated by those skilled in
the art. By way of example, 20-100 cycles may be appropriate
depending upon the particular geological area where production
occurs, although different numbers of cycles may be used in
different embodiments. Solvent injection and/or RF heating may
be suspended, at Block 82, and a final production phase
performed (Block 83) until the oil rate falls below a minimum
recovery rate, at Block 84. At this point oil production is
discontinued, and the solvent may be recovered from the
formation 31, if desired, at Block 85. This concludes the
method illustrated in FIGS. 3A-3B, at Block 86.
[0035] In some embodiments, it may be advantageous to
continuously apply RF heating throughout the cyclical process.
The RF heating extends the production period and thereby
increases the aggregate oil rate by ref luxing a portion of the
solvent in the bitumen draining to the lower well 33. As the
mixture approaches the producer it is heated from the RF
heating, which causes some of the solvent to flash off. The
liberated solvent vapor is available to support the vapor
chamber pressure, and it migrates to the vapor chamber
boundary where it is once again diffused into raw bitumen,
diluting it and reducing the viscosity so that it drains to
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the lower well 33 by gravity. This ref lux reduces the amount
of makeup solvent required, which permits longer production
and shorter injection cycles, respectively. This is unlike
traditional processes like cyclic steam (e.g., SAGD) where the
injected fluid also supplies the heat and pressure support to
the reservoir. Once the steam injection phase is complete the
chamber pressure immediately begins to decrease as the steam
cools and condenses to liquid, resulting in relatively shorter
production cycles. In some embodiments, further pressure
control may also be achieved by introducing additional gas
(e.g., an inert gas such as nitrogen) into the void 42 along
with the solvent in some embodiments.
[0036] Referring additionally to the graph 50 of FIG. 4, a
comparison of cumulative oil production over time for a
simulated example using the apparatus 30 and the cyclic
recovery approach described above is represented by the dashed
plot line 51. By way of comparison, a plot line 52 represents
simulated oil production using the above-noted approach set
forth in U.S. Pat. No. 9,739,126, i.e., where solvent
injection occurs from the same upper well where the antenna is
located. While the simulated results from the 1126 patent
approach provide slightly higher output over the same time
period, the output from the present approach is comparable,
yet the present approach advantageously allows for smaller
(i.e., standard) size well casings and a potential for reduced
solvent injection, and, accordingly, lower operating costs.
[0037] Turning now to the flow diagram 90 of FIG. 5,
another example operating method for the apparatus 30 is
described. Beginning at Block 91, the method illustratively
includes pre-heating the formation 31 from the upper well 32
to a target temperature, and then oil production begins to
create the void 42 within the formation, as described above
(Blocks 92-94). However, rather than ceasing production at
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this point as described above, production (and optionally RF
heating) continues and solvent injection commences from the
lower well, at Block 95. This process may then continue until
the overall recovery target for the well is reached, at Block
96. At this point, solvent injection and/or RF heating are
suspended (Block 97) while an optional final production occurs
until the oil recovery rate falls below a minimum level, at
which point production is discontinued and the solvent
optionally recovered, at Blocks 98-100, as discussed above.
The method of FIG. 5 illustratively concludes at Block 101. It
should be noted that in some embodiments, a combination of
sequential operation and continuous operation may be
performed, if desired.
[0038] Further details of recovering or producing
hydrocarbon resources may be found in U.S. Pat Nos. 9,044,731;
9,057,237; 9,200,506; 9,103,205; and U.S. Pub. Nos.
2014/0014324 and 2014/0014326, which are all assigned the
Assignee of the present application. Many modifications and
other embodiments of the invention will come to the mind of
one skilled in the art having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. The scope of the claims should not be limited by the
preferred embodiments set forth in the examples, but should be
given the broadest interpretation consistent with the
description as a whole.
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