Note: Descriptions are shown in the official language in which they were submitted.
CA 02777790 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 H20 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
1
CA 02777790 2012-05-22
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] One
factor that can limit the economic production of the viscous oil using
SAGD is the heterogeneous nature of the reservoir. The applicability of SAGD
is
often limited by impermeable layers that act as barriers to vertical flow. The
impermeable layers effectively compartmentalize the reservoir into thin sub-
reservoirs, less than 15 meters in length at its minimum. These thin layers
cannot be
economically developed with gravity drainage processes because of the
thickness
requirement for the reservoir. In one embodiment the method utilizes hydraulic
methods to fracture the impermeable layers and establish vertical
communication
between the isolated sub-reservoirs and allow a gravity drainage process to
work.
[0007] 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.
[0008] 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.
2
CA 02777790 2012-05-22
[0009] 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.
[0010] 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.
[0011]
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", CEM Publication, 2002 by
Brittany Hayes).
BRIEF SUMMARY OF THE DISCLOSURE
[0012] A process
of drilling a borehole into a heavy oil formation comprising a
frac barrier between a first pay zone and a second pay zone wherein the frac
barrier
prevents a subterranean steam chamber region to be formed between the first
pay
zone and the second pay zone. The frac barrier is then heated with a microwave
frequency and the frac barrier is fractured to permit the subterranean steam
chamber
region to be formed within the first pay zone and the second pay zone. H20 is
then
injected into the subterranean steam chamber region through a first wellbore
of a
steam assisted gravity drainage operation. Microwaves are introduced into the
3
CA 02777790 2015-11-06
subterranean steam chamber region at a frequency sufficient to excite the H20
molecules and increase the temperature of at least a portion of the H20 within
the
region to produce heated H20. At least a portion of the heavy oil in the
region is
heated by contact with the heated H20 to produce heated heavy oil. Heated
heavy oil
is then produced through a second wellbore of the steam assisted gravity
drainage
operation. Heavy oil is then recovered with the steam assisted gravity
drainage
operation from the subterranean steam chamber region. A portion of the H20 is
injected as steam and the steam contact with at least a portion of the heavy
oil in the
subterranean steam chamber region so as to heat the portion of the heavy oil
and
reduce its viscosity so that it flows generally towards the second wellbore.
[0013] In an
alternate embodiment a process is taught of drilling a borehole into a
heavy oil formation comprising a frac barrier between a first pay zone and a
second
pay zone wherein the minimum distance of at least one pay zone is less than
about 15
meters from top to bottom and the frac barrier prevents a subterranean steam
chamber
to form between the first pay zone and the second pay zone. The heavy oil
formation
is then perforated and fracturing fluid is injected into the heavy oil
formation. The
frac barrier is then heated with a microwave frequency. The frac barrier is
then fracted
with the fracturing fluid to permit a subterranean steam chamber region to be
formed
within the first pay zone and the second pay zone. H20 is then injected into
the
subterranean steam chamber region through a first wellbore of a steam assisted
gravity drainage operation. Microwaves are introduced into the subterranean
steam
chamber region at a frequency sufficient to excite the H20 molecules and
increase the
temperature of at least a portion of the H20 within the region to produce
heated H20.
At least a portion of the heavy oil in the region is then heated by contacting
with the
heated H20 to produce heated heavy oil. Heated heavy oil is then produced
through a
second wellbore of the steam assisted gravity drainage operation, thereby
recovering
the heavy oil with the steam assisted gravity drainage operation from the
subterranean
steam chamber 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
subterranean steam
chamber region so as to heat the portion of the heavy oil and reduce its
viscosity so
that it flows generally towards the second wellbore.
[0013a] In another embodiment there is provided a process comprising: drilling
a
borehole into a heavy oil formation comprising a frac barrier between an upper
pay
4
CA 02777790 2015-11-06
zone and a lower pay zone wherein the minimum distance of at least one pay
zone is
less than about 15 meters from top to bottom and the frac barrier prevents a
thermal
connection between the upper pay zone and the lower pay zone; perforating the
heavy
oil formation; injecting a fracturing fluid into the heavy oil formation,
wherein the
liacturing fluid contains a proppant; heating the frac barrier with a radio
frequency;
vertically fracturing the frac barrier with the fracturing fluid to permit a
thermal
connection within the upper pay zone and the lower pay zone, wherein the
pressure
used to fracture the frac barrier is less than what is necessary to fracture
the frac
barrier prior to heating with the railio frequency; injecting H20 into a
subterranean
steam chamber region through a first wellbore of a steam assisted gravity
drainage
operation; introducing microwaves into the subterranean steam chamber region
at a
frequency sufficient to excite the 1120 molecules and increase the temperature
of at
least a portion of the H20 within the region to produce heated 1120; heating
at least a
portion of the heavy oil in the region by contact with the heated H20 to
produce
heated heavy oil; and 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 steam chamber
region;
wherein a portion of the H20 is injected as steam and the steam contacts with
at least
a portion of the heavy oil in the subterranean steam chamber region so as to
heat the
portion of the heavy oil and reduce its viscosity so that it flows generally
towards the
second wellbore and wherein the subterranean steam chamber region extends from
the
lower pay zone into the upper pay zone.
4a
CA 02777790 2012-05-22
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A more complete understanding of the present invention and benefits
thereof may be acquired by referring to the follow description taken in
conjunction
with the accompanying drawings in which:
[0015] Figure 1 depicts a heavy oil formation with a frac barrier.
[0016] Figure 2 is a schematic diagram illustrating a heavy oil heating
process,
wherein wave guides are used to introduce the microwaves to the reservoir.
[0017] Figure 3 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.
DETAILED DESCRIPTION
[0018] 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.
[0019] 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.
[0020] The present embodiment describes a method of producing heavy oil
from a
heavy oil formation with steam assisted gravity drainage. The method begins by
drilling a borehole into a heavy oil formation comprising a frac barrier
between a first
pay zone and a second pay zone, wherein the frac barrier prevents a steam
chamber to
be formed between the first pay zone and the second pay zone. The frac barrier
is
then heated with a radio frequency. The frac barrier is then fractured to
permit a
subterranean steam chamber to be formed within the first pay zone and the
second pay
zone. Water (H20) is then injected into the subterranean steam chamber region
through a first wellbore of a steam assisted gravity drainage operation.
Microwaves
are introduced into the subterranean steam chamber region at a frequency
sufficient to
excite the water molecules and increase the temperature of at least a portion
of the
water within a region to produce heated water. At least a portion of the heavy
oil is
heated in the region by contact with the heated water to produce heated heavy
oil.
This is subsequently followed by producing the heated heavy oil through a
second
wellbore of the steam assisted gravity drainage operation. Heavy oil is then
recovered
CA 02777790 2012-05-22
with the steam assisted gravity drainage operation from the subterranean steam
chamber region. In this embodiment, a portion of the water is injected as
steam and
the steam contact with at least a portion of the heavy oil in the subterranean
steam
chamber region so as to heat the portion of the heavy oil and reduce its
viscosity so
that it flows generally towards the second wellbore.
100211 In one embodiment the borehole can be either the first wellbore or
the
second wellbore.
100221 As shown in Figure 1, the first pay zone 2 and the second pay zone 4
are
separated by a frac barrier 6. The frac barrier 6 prevents a subterranean
steam
chamber to be formed between the first pay zone and the second pay zone,
thereby
reducing the effectiveness of producing oil via steam assisted gravity
drainage. In one
embodiment the steam to oil ratio is higher than 3.5 when steam assisted
gravity
drainage is performed in either the first pay zone or the second pay zone
prior to
fracturing the frac barrier.
[0023] The present embodiment can be used in any situation where a frac
barrier
prevents the formation of a subterranean steam chamber between two or more pay
zones to a bitumen thickness greater than 20 meters. In one embodiment the
subterranean steam chamber region extends from the first pay zone into the
second
pay zone. In an alternate embodiment the minimum distance of at least one pay
zone,
indicated by x in Figure 1 is less than about 20 meters. The cost of operating
a steam
assisted gravity drainage operation in a pay zone less than about 20 meters
would
typically cause the operation not to be cost effective. In yet another
alternate
embodiment the pay zone is less than about 19, 18, 17, 16, 15, 14, 13, 12, 11,
10, 9, 8,
7, 6, 5, 4, 3, 2 or 1 meter in distance.
[0024] The perforation of the well can be done by any conventional method
known to one skilled in the art. Typically perforation refers to a hole
punched in the
casing or liner of an oil well to connect it to the reservoir. In cased hole
completions,
the well will be drilled down past the section of the formation desired for
production
and will have casing or a liner run in separating the formation from the well
bore. The
final stage of the completion will involve running in perforating guns, a
string of
shaped charges, down to the desired depth and firing them to perforate the
casing or
liner. A typical perforating gun can carry many dozens of charges.
[0025] After the perforation of the well a fracturing fluid can then be
injected into
the fracture to form a hydraulic fracture. A hydraulic fracture is typically
formed by
6
CA 02777790 2012-05-22
pumping the fracturing fluid into the wellbore at a rate sufficient to
increase the
pressure downhole to a value in excess of the fracture gradient of the
formation rock.
The pressure causes the formation to crack, allowing the fracturing fluid to
enter and
extend the crack further into the formation.
[0026] To keep this fracture open after the injection stops, a solid
proppant can be
added to the fracture fluid. The proppant, which is commonly a sieved round
sand, is
carried into the fracture. This sand is chosen to be higher in permeability
than the
surrounding formation, and the propped hydraulic fracture then becomes a high
permeability conduit through which the formation fluids can flow to the well.
[0027] Different fracturing fluids can be used as long as they have
characteristics
such as:
= fluid enough to be easily pumped by the usual well completion pumps
= capable of holding a propping material while being pumped down the
well but also must be capable of depositing the propping material in
the cracks of the formation
= able to flow into the cracks in the formation with minimal fluid loss
into the pores
= should not plug pores of the formation permanently or the capacity of
the formation to produce oil will be damaged
= compatible with the hydrocarbon production from the well being
fractured under the pressure and temperature conditions found in the
well bore
[0028] Examples of fracturing fluids that can be used include: water to
gels,
foams, nitrogen, carbon dioxide or air. In addition to the fracturing fluids
different
additives can be added to enhance the fracturing fluids such as: acid,
glutaraldehyde,
sodium chloride, n,n-dimethyl formaide, borate salts, polyacrylamide,
petroleum
distillates, guar gum, citric acid, potassium chloride, ammonium bisulfite,
sodium or
potassium carbonate, various proppants, ethylene glycol, and/or isopropanol.
[0029] Microwave frequency generators are operated to generate microwave
frequencies capable of causing maximum excitation of the substances in the
frac
barrier. In some embodiments the microwave frequency will be not greater than
3000
megahertz and at a resonant frequency of water. Examples of substances present
in
the frac barrier include: water or salt water used in SAGD operations,
asphaltene,
7
CA 02777790 2012-05-22
heteroatoms and metals. For some embodiments, the microwave frequency
generator
defines a variable frequency source of a preselected bandwidth sweeping around
a
central frequency. As opposed to a fixed frequency source, the sweeping by the
microwave frequency generator can provide time-averaged uniform heating of the
hydrocarbons with proper adjustment of frequency sweep rate and sweep range to
encompass absorption frequencies of constituents, such as water and the
microwave
energy absorbing substance, within the mixture. In some embodiments the
microwave frequency will be not greater than 3000 megahertz and/or at a
resonant
frequency of water. For example, the microwave frequency generator may
introduce
microwaves with power peaks at a first discrete energy band around 2.45 GHz
associated with water and a second discrete energy band spaced from the first
discrete
energy band and associated with the components with existing dipole moments in
the
frac barrier.
[0030] By heating the frac barrier with a radio frequency the pressure
required to
fracture the frac barrier is less than what is necessary the fracture the frac
barrier prior
to heating with the radio frequency. The pressure can be reduced with this
method
anywhere from 3 psi to .05 psi. In alternate embodiments the pressure can be
reduced
by 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 or even 2 psi.
[0031] In one embodiment the fracturing of the frac barrier permits a steam
chamber to be formed within the first pay zone and the second pay zone. By
enlarging the space for the subterranean steam chamber the steam to oil ratio
is lower
than 3.5 when the steam assisted gravity drainage is performed in the
subterranean
steam chamber.
[0032] In one embodiment processes such as cyclic steam stimulation, vapor
extraction, J-well steam assisted gravity drainage, in situ combustion, high
pressure
air injection, expanding solvent steam assisted gravity drainage or cross-
steam
assisted gravity drainage can be used to produce oil from the heavy oil
formation.
[0033] One example of a steam assisted gravity drainage system is as
follows. In
the steam assisted gravity drainage process, two parallel horizontal oil wells
are
drilled in the formation, one about 4 to 6 meters above the other. The upper
well
injects steam, possibly mixed with solvents, and the lower one collects the
heated
crude oil or bitumen that flows out of the formation, along with any water
from the
condensation of injected steam. The basis of the process is that the injected
steam
forms a "subterranean steam chamber" that grows vertically and/or horizontally
in the
8
CA 02777790 2012-05-22
heavy oil 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 wellbore. The steam
and
gases rise because of their low density compared to the heavy crude oil below,
ensuring that steam is not produced at the lower production well. The gases
released,
which include methane, carbon dioxide, and usually some hydrogen sulfide, tend
to
rise in the subterranean steam chamber, filling the void space left by the oil
and, to a
certain extent, forming an insulating heat blanket above the steam. Oil and
water flow
is by a countercurrent, gravity driven drainage into the lower well bore. The
condensed water and crude oil or bitumen is recovered to the surface by pumps
such
as progressive cavity pumps that work well for moving high-viscosity fluids
with
suspended solids.
100341 The
depiction of Figure 2 describes the situation where a subterranean
steam chamber has already formed. Wellbore 114 extends from the surface 110
into a
lower portion of subterranean steam chamber region 112. Wellbore 116 extends
from
the surface 110 into subterranean steam chamber region 112 and generally will
be
higher than wellbore 114. Wellbore 116 will be used to inject H20 and it is
preferred
that it is located higher than wellbore 114 so that when the injected H20
heats the
heavy oil, the heavy oil will flow generally towards wellbore 114, 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 115 is used to introduce
microwaves to the reservoir and it is preferred that wellbore 115 be located
intermittent to wellbores 114 and 115; although, other arrangements are
possible.
100351 In
operation, steam generated in boiler 111 is provided into the
subterranean steam chamber region 112 through upper wellbore leg 116. The
steam
heats the heavy oil within zone 117 of the oil-bearing portion 113 of
subterranean
steam chamber region 112 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 114. 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
9
CA 02777790 2012-05-22
wellbores can be used for microwave introduction to the reservoir, as further
discussed below.
[0036]
Generally, the wellbore for steam injection, wellbore 116, will be
substantially parallel to and situated above the wellbore for production,
wellbore 114,
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 117 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
flow to and be extracted through wellbore 114. 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 117 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
114 and 116 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 114 will be gradually
reduced
while the steam rate for the injector wellbore 116 will be maintained or
increased.
This imposes a pressure gradient from high, for the area around wellbore 116,
to low,
for the area around wellbore 114. 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
CA 02777790 2012-05-22
the steam rate is continued to be adjusted downward in wellbore 114 and upward
in
wellbore 116, the system arrives at steam assisted gravity drainage operation
with no
steam injection through wellbore 114 and all the steam injection through
wellbore
116. 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 119 of zone 117. 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.
[0037] During operation, steam will come into contact with the heavy oil
in
zone 117 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 114. Heated heavy oil is produced through wellbore 114 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 114. In past SAGD
operations, this water would also be produced through wellbore 114. Such
produced
water would need to be treated to reduce impurities before being reheated in
the boiler
for subsequent injection. As the process continues operation, zone 117 will
expand
with heavy oil production occurring from a larger portion of oil-bearing
portion 113
of subterranean steam chamber formation 112.
[0038] Turning again to Figure 2, the current invention provides for
microwave generator 118 to generate microwaves which are directed underground
and into zone 117 of the reservoir through a series of wave guides 120. 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
11
CA 02777790 2015-11-06
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.
[0039] Turning now to Fig. 3, a further embodiment of the invention is
illustrated
wherein, instead of using wave guides, power is supplied through electrical
wire 122
to microwave generating probe 124. The electrical power can be supplied to
wire 122
by any standard means such as generator 126.
[0040] In still another embodiment of the invention, also illustrated in
Fig. 3, no
steam boiler is used. Instead water is introduced directly into wellbore 116
through
pipe 128 and valve 130. Wellbore 116 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
water has a salt content greater than 10,000 ppm. For enhanced heat generation
30,000 to 50,000 ppm is more preferred.
[0041] 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.
[0042] 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.
12
CA 02777790 2015-11-06
[00431 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.
13
