Note: Descriptions are shown in the official language in which they were submitted.
=
- 1 -
Title: SELF-FORMING TRAVELLING WAVE ANTENNA MODULE BASED ON SINGLE
CONDUCTOR TRANSMISSION LINES FOR ELECTROMAGNETIC HEATING OF
HYDROCARBON FORMATIONS AND METHOD OF USE
FIELD
[0001] The embodiments described herein relate to the field of heating
hydrocarbon
formations, and in particular to antenna modules for electromagnetically
heating
hydrocarbon formations.
BACKGROUND
[0002] Electromagnetic (EM) heating can be used for enhanced recovery of
hydrocarbons from underground reservoirs. Similar to traditional steam-based
technologies, the application of EM energy to heat hydrocarbon formations can
reduce
viscosity and mobilize bitumen and heavy oil within the hydrocarbon formation
for
production. However, the use of EM heating can require less fresh water than
traditional
steam-based technologies. As well, the heat transfer with EM heating can be
more
efficient than that of traditional steam-based technologies, leading to lower
capital and
operational expenses. The lower cost of EM heating provides the potential to
unlock oil
reservoirs that would otherwise be unviable or uneconomical for production
with steam-
based technologies such as shallow formations, thin formations, formations
with thick
shale layers, and mine-face accessible hydrocarbon formations, for example.
Hydrocarbon formations can include heavy oil formations, oil sands, tar sands,
carbonate formations, sale oil formations, and other hydrocarbon bearing
formations.
[0003] EM heating of hydrocarbon formations can be achieved by using an
EM
radiator, or antenna, or applicator, positioned inside an underground
reservoir to radiate
EM energy to the hydrocarbon formation. The antenna is typically operated
resonantly.
The antenna can receive EM power generated by an EM wave generator, or radio
frequency (RF) generator.
[0004] As the hydrocarbon formation is heated, the characteristics of the
hydrocarbon formation, and in particular, the impedance of the hydrocarbon
formation,
CA 2976107 2017-08-11
- 2 -
can change. In order to maintain efficient power transfer to the hydrocarbon
formation,
dynamic or static impedance matching networks can be used between the antenna
and
the RF generator to limit the reflection of EM power from the antenna back to
the RF
generator. As well, the RF generator can be adjusted to limit the reflection
of EM power
from the antenna back to the RF generator, Such operational adjustments and
impedance matching networks increase operational, equipment, and design costs.
SUMMARY
[0005] According to one aspect, there is provided a radio frequency
antenna module
in a radio frequency antenna for delivering electromagnetic energy generated
by a
generator into a hydrocarbon formation, the antenna module comprising: a
conductive
member; at least one conductive sheath with a first and second end surrounding
at least
one portion of the conductive member; at least one electrical coupler
electrically coupled
to the conductive member and the at least one conductive sheath for receiving
the
electrical energy; and an electrically insulating seal inserted at the first
and second end
of each of the at least one conductive sheath between the conductive member
and the
conductive sheath to maintain an enclosed cavity defined by the conductive
member,
the conductive sheath and the electrically insulating seal for electrically
separating the
conductive member and the conductive sheath.
[0006] In at least one embodiment, wherein the electromagnetic energy
radiates with
a frequency between 1 kHz and 100 MHz.
[0007] In at least one embodiment, the conductive member comprises a
first and
second connector located at a first member end and a second member end,
respectively, such that a plurality of irradiating modules are connectable to
form at least
one module chain.
[0008] In at least one embodiment, the first and second connector are
electrically
conductive such that each of the at least one module chain comprises a
contiguous
conductive member.
[0009] In at least one embodiment, the at least one module chain
comprises a
plurality of chains such that a first module chain set is configured to
radiate
independently of another module chain set.
CA 2976107 2017-08-11
. . .
- 3 -
[0010] In at least one embodiment, the first module chain set
radiates at a first target
frequency and the other module chain set radiates at a second target
frequency.
[0011] In at least one embodiment, the conductive member is a pipe
and each of the
first and second connector provides a sealed connection that prohibits flow of
fluids from
the hydrocarbon formation into the pipe.
[0012] In at least one embodiment, the at least one conductive
sheath comprises an
inner conducting surface and an outer conducting surface; and for each of the
at least
one conductive sheath, a segment of coaxial transmission line having an inner
and outer
conductor is defined by that conductive sheath and a corresponding surrounded
portion
of the conductive member such that the outer conductor comprises the inner
conducting
surface of that conductive sheath and the inner conductor comprises a
corresponding
portion of the conductive member surrounded by that conductive sheath.
[0013] In at least one embodiment, a first sheath has a diameter
that is different from
at least one other conductive sheath.
[0014] In at least one embodiment, the conductive member has at
least one
surrounded conductive member portion and at least one exposed conductive
member
portion, and the antenna module further comprises: at least one segment of an
inner
single-conductor transmission line defined by the at least one exposed
conductive
member portion; and at least one segment of an outer single-conductor
transmission
line defined by the outer conductive surface of the at least one conductive
sheath.
[0015] In at least one embodiment, the conductive member is a pipe
comprising at
least one feed transmission line that delivers the electromagnetic energy to
the antenna
module; and the at least one electrical coupler comprises at least two feed
connectors
located between two ends of the segment of coaxial transmission line such that
each
feed connector is connected to i) a feed transmission line at a first feed
connector port;
and ii) at least one of a) the inside of the hollow pipe and b) the inner
conducting
surface of at least one conductive sheath at a second port.
[0016] In at least one embodiment, the at least one feed connector
a plurality of feed
connectors are azimuthally arranged around an inner surface of the pipe.
CA 2976107 2017-08-11
- 4 -
[0017] In at least one embodiment, the at least one feed connector
comprises a
plurality of feed connectors that are arranged axially along an inner surface
of the hollow
pipe.
[0018] In at least one embodiment, the at least one feed connector is
located near
one end of the segment of coaxial transmission line.
[0019] In at least one embodiment, the segment of coaxial transmission
line has an
electrical length that is substantially one half of a wavelength of the
electromagnetic
energy oscillating at a target frequency such that a perfect electric
conductor boundary
condition is defined in a plane that is situated at a mid-point of the segment
of coaxial
transmission line and oriented transversely relative to a longitudinal axis
defined the
conductive member.
[0020] In at least one embodiment, the at least one feed connector is
located near a
midpoint of the segment of coaxial transmission line.
[0021] In at least one embodiment, the segment of coaxial transmission
line has an
electrical length that is substantially one half of a wavelength of the
electromagnetic
energy oscillating at a target frequency such that a perfect magnetic
conductor boundary
condition is defined in a plane that is situated at a mid-point of the segment
of coaxial
transmission line and oriented transversely relative to a longitudinal axis
defined the
conductive member.
[0022] In at least one embodiment, the segment of coaxial transmission
line has an
electrical length that is substantially an odd multiple of one half of a
wavelength the
electromagnetic energy oscillating at a target frequency.
[0023] In at least one embodiment, the enclosed cavity comprises at least
one
dielectric material to separate the inner and outer conductor of the segment
of coaxial
transmission line.
[0024] In at least one embodiment, the electromagnetic energy generates
electromagnetic heating to produce at least one evaporated zone in the
hydrocarbon
formation surrounding the antenna module to define a second coaxial
transmission line
comprising: a second inner conductor defined by portions of the inner single-
conductor
CA 2976107 2017-08-11
=
- 5 -
transmission line and the outer single-conductor transmission line; and a
second outer
conductor comprising an outer boundary separating the evaporated zone and the
hydrocarbon formation.
[0025] In at least one embodiment, the seal is configured with at least
one of the
following properties: i) prohibits flow of fluids from the hydrocarbon
formation into the
enclosed cavity; ii) chemically inert; and iii) electrically insulating.
[0026] In at least one embodiment, the seal is toroidal in shape with a
rectangular
cross-section and further comprises concentric inner and outer structural
rings, the inner
structural ring located proximally to the conductive member and the outer
structural ring
located proximally to the conductive sheath.
[0027] In at least one embodiment, the inner and outer structural rings
have an
electrical loss tangent of less than 0.01.
[0028] In at least one embodiment, the conductive member has a diameter
that
varies along its length such that the diameter is larger at the at least one
exposed
conductive portion relative to the at least one surrounded conductive member
portion to
produce a flared conductive member.
[0029] According to one aspect, there is provided method for
electromagnetic
heating of a hydrocarbon formation comprising: deploying at least one antenna
module
into the hydrocarbon formation; operating at least one electromagnetic wave
generator
to generate at least one electromagnetic wave having at least one target
frequency;
electrically coupling the at least one antenna module to the at least one
electromagnetic
wave generator; and delivering at least one electromagnetic wave to the
hydrocarbon
formation, the electromagnetic wave corresponding to electromagnetic energy
used to
generate heat within the hydrocarbon formation.
[0030] In at least one embodiment, the electrically coupling comprises
coupling a
first electromagnetic wave generator to a first set of antenna modules and
coupling a
second electromagnetic wave generator to a second set of antenna modules so
that the
first set of antenna modules irradiates the hydrocarbon formation
independently relative
to the second set of antenna modules.
CA 2976107 2017-08-11
. . ,
- 6 -
[0031] In at least one embodiment, the method further comprises
configuring the first
electromagnetic wave generator to generate a first electromagnetic wave at a
first
frequency; and configuring the second electromagnetic wave generator to
generate a
second electromagnetic wave a second frequency, wherein the first frequency is
different from the second frequency.
[0032] In at least one embodiment, the deploying the at least one
antenna module
comprises connecting a plurality of antenna modules to form at least one
module chain
and deploying the at least one module chain into the hydrocarbon formation,
wherein
each antenna module in the plurality of antenna modules is connectable to
another
antenna module using a first and second electrically conductive connector
located at a
respective first member end and a second member end of the conductive member
so
that each module chain comprises a contiguous conductive member.
[0033] In at least one embodiment, the method further comprises
determining a
length of the at least one conductive sheath based on at least one of i) the
at least one
target frequency; ii) an outer diameter of the conducting member the at least
one
antenna module; iii) an outer diameter of the at last one conductive sheath;
iv) material
occupying the enclosed cavity; and v) electrical characteristics of the
hydrocarbon
formation.
[0034] Further aspects and advantages of the embodiments described
herein will
appear from the following description taken together with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] For a better understanding of the embodiments described
herein and to show
more clearly how they may be carried into effect, reference will now be made,
by way of
example only, to the accompanying drawings which show at least one exemplary
embodiment, and in which:
[0036] FIG. 1 is a perspective view of an excitation module for
electromagnetic
heating of hydrocarbon formations according to at least one embodiment;
CA 2976107 2017-08-11
- 7 -
[0037] FIG. 2A is a longitudinal sectional view of the excitation module of
FIG. 1
along a longitudinal axis according to at least one embodiment;
[0038] FIG. 2B is a transverse sectional view of the excitation module of
FIG. 1 with
azimuthally distributed feed connectors according to at least one embodiment;
[0039] FIG. 2C is a longitudinal sectional view of the excitation module of
FIG. 1 with
axially distributed feed connectors according to at least one embodiment;
[0040] FIG. 2D is a longitudinal sectional view of the excitation module of
FIG. 1 with
multiple feed connectors connected to a single feed transmission line
according to at
least one embodiment;
[0041] FIG. 3 is a diagram of an excitation module with radially flared
main pipe
portions according to at least one embodiment;
[0042] FIG. 4A is a diagram of an antenna comprising an excitation module
chain
according to at least one embodiment;
[0043] FIG. 4B is a diagram of the antenna of FIG. 4A with RF generators
external to
the modules according to at least one embodiment;
[0044] FIG. 4C is a diagram of the antenna of FIG. 4A with RF generators
internal to
the modules according to at least one embodiment;
[0045] FIG. 5 is a diagram of one end of the coaxial line of the excitation
module of
FIG. 1 according to at least one embodiment;
[0046] FIG. 6 is a diagram showing an antenna deployed within an unheated
wet
zone according to at least one embodiment;
[0047] FIG. 7A is an equivalent circuit diagram of the excitation module of
FIG. 1
according to at least one embodiment;
[0048] FIG. 7B is a schematic diagram of the excitation module of FIG. 1
according
to at least one embodiment;
[0049] FIG. 70 is a diagram indicating the location of the Perfect Electric
Boundary
Condition of a half-wavelength conductive sheath according to at least one
embodiment;
CA 2976107 2017-08-11
- 8 -
[0050] FIG. 8 is a diagram indicating Poynting vectors inside the antenna
structure
of FIG. 7C indicating the Perfect Electric Boundary Condition according to at
least one
embodiment;
[0051] FIG. 9 is an equivalent circuit diagram of an excitation module of
with the
Perfect Electric Boundary Condition of FIG. 7C according to at least one
embodiment;
[0052] FIG. 10 is a plot of scattering parameter S11 versus electrical
conductivity
and relative permittivity of medium surrounding an excitation module having
the
equivalent circuit of FIG. 9 according to at least one embodiment;
[0053] FIG. 11 is a diagram of an excitation module in semi steady-state
operation
according to at least one embodiment; and
[0054] FIG. 12 is a diagram of the radiation pattern of a leaky-wave
radiator
according to at least one embodiment.
[0055] The skilled person in the art will understand that the drawings,
described
below, are for illustration purposes only. The drawings are not intended to
limit the
scope of the applicants' teachings in anyway. Also, it will be appreciated
that for
simplicity and clarity of illustration, elements shown in the figures have not
necessarily
been drawn to scale. For example, the dimensions of some of the elements may
be
exaggerated relative to other elements for clarity. Further, where considered
appropriate, reference numerals may be repeated among the figures to indicate
corresponding or analogous elements.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0056] It will be appreciated that numerous specific details are set
forth in order to
provide a thorough understanding of the exemplary embodiments described
herein.
However, it will be understood by those of ordinary skill in the art that the
embodiments
described herein may be practiced without these specific details. In other
instances,
well-known methods, procedures and components have not been described in
detail so
as not to obscure the embodiments described herein. Furthermore, this
description is
not to be considered as limiting the scope of the embodiments described herein
in any
CA 2976107 2017-08-11
, . . - 9 -
way, but rather as merely describing the implementation of the various
embodiments
described herein.
[0057] It should be noted that terms of degree such as
"substantially", "about" and
"approximately" when used herein mean a reasonable amount of deviation of the
modified term such that the end result is not significantly changed. These
terms of
degree should be construed as including a deviation of the modified term if
this deviation
would not negate the meaning of the term it modifies.
[0058] In addition, as used herein, the wording "and/or" is intended
to represent an
inclusive-or. That is, "X and/or Y" is intended to mean X or Y or both, for
example. As a
further example, "X, Y, and/or Z" is intended to mean X or Y or Z or any
combination
thereof.
[0059] It should be noted that the term "coupled" used herein
indicates that two
elements can be directly coupled to one another or coupled to one another
through one
or more intermediate elements.
[0060] The electromagnetic (EM) heating of hydrocarbon formations
such as heavy
oil formations can be an attractive Enhanced Oil Recovery (EOR) technology for
reasons that include the potential for unlocking heavy oil reservoirs which
would
generally not be economically produced using more traditional steam-based
technology
(e.g. shallow formations, thin formations, formations with thick shale layers,
etc.); lower
greenhouse gas emissions and significant reduction or complete elimination of
the need
for fresh water can reduce environmental impact; and improved efficiency from
an
energy balance point of view compared to the steam-based technologies as EM
heating
creates and maintains smaller amounts of steam inside the heavy oil reservoir.
[0061] An EM radiator in EM EOR solutions generally have a form of a
single or
multiple linear or loop radiators positioned inside a heavy oil reservoir. A
radiator can be
sometimes referred to as an antenna or applicator. The EM power can be
generated on
the surface from a power source, for example, an AC or DC power source. The EM
generator is often referred to as a Radio Frequency (RF) generator. The EM
generator
generates power in the radio frequency range, typically between 100 kHz and
100 MHz.
However in some cases the EM generator can be configured to generate in other
CA 2976107 2017-08-11
, . . - 10 -
frequency ranges such as from 50 kHz to 50 MHz or 1 kHz to 100MHz. The
generated
power can then be transferred to the EM radiator using a feed transmission
line such as
a single conductor cable or a multiple conductor cable such as a coaxial
cable.
[0062] The EM radiator radiates the EM power into the formation
using a radiator
such as a resonant antenna. The resonant antenna's operating frequency depends
on
the EM properties of the formation around the antenna and the antenna's
length. This
means that antennas designed for different formations and different well
lengths may
use different operating frequencies, requiring different impedance matching
circuits and
EM generators. Therefore, current EM heating systems are generally custom
designed
for each well, increasing the cost of the system. Moreover, as the EM
properties of the
formation change during the heating process, the antenna electrical
characteristics may
also change and require some form of variable impedance matching. For example,
a
system of dynamic or static matching networks can be required in-situ between
the
transmission line delivering EM power and the antenna to improve the
efficiency of the
heating system. Alternatively, such a system for impedance may be installed on
the
surface between the EM generator and the transmission line to limit the
reflection of the
EM power from the antenna back to the generator.
[0063] Additionally, most existing EM heating applications propose
complex antenna
systems that may require at least the following: isolation of conductor
sections; an
electrically lossless casing; designs using machined surfaces, for example
grooves or
slots; the use of exotic materials such as ferrites; or special deployment
techniques.
Such considerations often increase the cost of manufacture and maintenance
making
such systems generally expensive to operate and maintain. Furthermore, such
systems
may be less mechanically robust and may increase the possibility of equipment
failure
during deployment of operation underground. While travelling wave antennas may
address some of the identified issues with respect to antenna design, they are
typically
excited from a single terminal. As a result, heating is concentrated close to
that
excitation terminal, which can increase the time required to heat the
hydrocarbon
formation or reservoir and reduces heating uniformity. In most systems, there
is no way
of increasing or decreasing power at a specific segment along the well. This
may result
in regions of excessive heating or insufficient heating, which increases
operating cost.
CA 2976107 2017-08-11
, , . - 11 -
[0064] Described herein is a radio frequency antenna which can be
used in EM EOR
processes as the radiator of EM energy into a heavy-oil formation. The antenna
may
also be used to heat bitumen and other hydrocarbon bearing formations or for
environmental remediation. In particular, the described antenna comprises an
excitation
module with an electrically separated conductive sheath surrounding a portion
of a
conductive main member to define a coaxial line for guiding EM energy along
the
excitation module for deposition into the hydrocarbon formation. Each
excitation module
may operate as a travelling wave antenna that uses a single conductor for
radiating or
delivering the EM energy into the hydrocarbon formation. The structure of each
excitation module can further function as an impedance matching circuit.
Several
excitation modules may be combined together in a modular manner to form larger
irradiating structures. As such, the same excitation modules may be deployable
into
various types of hydrocarbon formations, into wells of various lengths and
excitable at
various frequencies. The antenna described herein can also be used with a
distributed
modular in-situ RF generator as described in US patent application 14/508,423,
or with a
conventional RF generator located on the surface.
Structure of the Excitation Module
[0065] Referring to FIGS. 1 and 2A, shown therein is a perspective
view and a
sectional view along the longitudinal axis, respectively, of an excitation
module 100 of
the antenna for EM heating of a hydrocarbon formation according to at least
one
embodiment. As shown in FIG. 1 the module comprises a conductive member 102, a
first connector 104, a second connector 106, a conductive sheath 108 of a
particular
physical length, seals 110, and feed connectors 122.
[0066] The conductive member 102 may be used to provide structural
integrity to the
module 100 and thus to the antenna and for providing the energy transfer into
the
hydrocarbon formation or reservoir by guiding an electromagnetic wave such as
a
travelling wave along its exterior.
[0067] In the present embodiment, as shown in FIGS. 1 and 2A, the
main conductive
member can be constructed using a rigid conductive pipe (hereinafter the "main
pipe
CA 2976107 2017-08-11
- 12 -
102") that is hollow with a wall having an outer surface 112 and inner surface
114 that
defines an interior 116.
[0068] The main pipe 102 can be fabricated using any appropriate
conductive
material including, but not limited to, aluminum, stainless steel, and carbon
steel. It can
also be built using composite materials, and may have a surface that's
corrugated or
cladded with other metals to achieve certain advantages. For example, in some
embodiments, the main pipe 102 may be a carbon steel pipe cladded with
aluminum.
Such a pipe has higher mechanical strength than an aluminum pipe of the same
dimensions, but can exhibit electrical conductivity of an aluminum pipe.
[0069] The cross-section of the main pipe 102 along a transverse axis
can be, but is
not limited to, circular as shown in FIG. 2B, rectangular, hexagonal, etc. The
outer
dimension of the main pipe 102 can range between 2 and 15 inches (between 5.08
cm
and 38.1 cm). In some embodiments, however, the main pipe 102 need not have a
constant diameter down its length. For example, the main pipe 102' as shown in
FIG. 3
may flare radially once outside of the conductive sheath 108.
. [0070] In some embodiments, the interior 116 of main pipe 102 may
carry one or
more AC or DC cables, control electronics, and other components of a
distributed RF
generator (not shown) provided with the main pipe. In some embodiments, feed
transmission lines 120 can be used to carry RF power generated by RF power
generation points located away from the main pipe 102 to electrical couplers
located
inside the main pipe 102. For example, the electrical couplers comprise of one
or more
module feed connectors 122 connected to the conductive sheath 108 as shown in
FIG.
2B. The feed transmission lines 120 can be any suitable transmission line for
carrying
electrical power at the operating frequency and can include, but not limited
to, single
conductor cables or multi-conductor cables such as coaxial cables.
[0071] RF power generation points may be located at the surface,
underground, or a
combination of both. For example, if a surface RF generator is used, the RF
power
generation point is the surface RF generator itself and the feed transmission
line 120,
such as a coaxial cable, can carry the RF power from the surface to the module
feed
connectors 122. On the other hand, if an in-situ distributed RF generator is
used, the RF
CA 2976107 2017-08-11
,
, . - 13 -
power generation points may be located inside the main pipe 102, proximate to
the
module feed connectors 122. Therefore, a short section of the feed
transmission line
120 such as coaxial cable may be needed to connect the power generation point
and
the module feed connector 122.
[0072] Referring still to FIGS. 1 and 2A, the first and second pipe
connectors 104
and 106 can be located at first and second member end portions 104a and 106a
of the
main pipe 102, respectively. The type of connector can vary and may be, for
example, a
threaded connector (as shown in FIGS. 1 and 2A), clamp connector, or a
combination of
the two types of connectors. While a single excitation module can be used to
operate as
an antenna for radiating EM energy, the first and second pipe connectors 104
and 106
can be used to connect additional excitation modules together end-to-end as
shown in
FIG. 4 to extend the length of the antenna.
[0073] The extended antenna comprising a number of excitation
modules 100
connected end-to-end can be regarded as a module chain 400 as shown in FIG. 4.
In
such a case, the connectors are preferably conductive so that the module chain
400
comprises a contiguous conductive member. For example, the module chain 400
may
be viewed as having one long "main pipe" (e.g. made up of several main pipes
or pipes
string 102 electrically connected end-to-end) with a number of conductive
sheaths 108
distributed along its length. In some cases, excitation modules of different
sizes (e.g.
lengths of the main pipe 102 and/or conductive sheath 108, or diameter of the
conductive sheath 108) may similarly be connected together to form the module
chain
400. In other cases, all of the excitation modules are identical and are
connected to form
the module chain 400. RF generators used to excite the feed transmission lines
of each
module may be external to the modules or internal to each of the modules, and
is similar
to the configurations discussed in US patent application 14/508,423. For
example, RF
generators 410 are external to the modules in FIG. 4B. In contrast, RF
generators 420
are internal to the modules in FIG. 4C.
[0074] The module chain 400 can be connected to the RF generator to
receive
power to radiate EM energy into the hydrocarbon formation. In some
embodiments,
several of such module chains 400 may be deployed into the hydrocarbon
formation.
CA 2976107 2017-08-11
- 14 -
Where several module chains 400 are used, a group of module chains 400 may be
formed. In some cases each module chain 400 may share the same RF generator or
obtain EM energy from its own dedicated RF generator. In the latter case, a
module
chain in the group of module chains 400 can be operable to radiate
independently of
another module chain within the group. In yet other embodiments, each RF
generator
may operate at a different target frequency. Such configurations can be used
to obtain
the desired heating of the hydrocarbon formation.
[0075] It may be noted that while such configurations are described with
respect to
module chains, the same configurations may be applicable to individual
excitation
modules 100 (or combination of module chains and individual modules) being
deployed
into the hydrocarbon formation. For example, a number of excitation modules
100 can
be individually deployed into a hydrocarbon formation to provide EM heating. A
generator can be connected to one or a group of excitation modules 100
allowing the
one module or group of modules 100 to irradiate EM waves into the hydrocarbon
formation. In other cases several RF generators may be used to deliver EM
energy to
several corresponding excitation modules 100 or several groups of excitation
modules
100. Each excitation module 100 or group of modules 100 can irradiate
independently of
each other. The frequency of irradiation may also vary depending on the
configuration of
the respective RF generator so that each excitation module 100 or group of
modules
100 irradiate at a different frequency.
[0076] In some embodiments, it may be preferable for the first and second
pipe
connectors 104 and 106 to be sealed to impede or prohibit mixing of fluids
such as the
liquid or gaseous compounds located in the hydrocarbon formation and inside of
the
main pipe 102. This separation may be particularly relevant when different
liquids or
gasses, or the same liquid or gas, but of different purities, are located
inside and outside
of the main pipe 102.
[0077] In other embodiments, it may be preferable for the first and second
pipe
connectors 104 and 106 not be sealed. These types of connectors would
generally be
less expensive and easier to fabricate. Such connectors can be used in
situations where
the same liquid and/or gas are present inside and outside of the main pipe 102
so that
CA 2976107 2017-08-11
- 15 -
their mixing would not interfere with operation of any components interior to
the main
pipe 116 via mechanical, chemical or electrical means.
[0078] The conductive sheath 108 with an inner conducting surface 130 and
outer
conducting surface 132 may be provided to surround or enclose a portion of the
length
of the main pipe 102 to operate as a waveguide structure to provide EM
excitation and
impedance matching to a variety of electrical environments, as will be
described in
further detail subsequently. Each section of main pipe 102 of the excitation
module 100
has at least one conductive sheath 108. In some embodiments, the excitation
module
100 can have two, three or more conductive sheaths distributed along its
length. In other
embodiments in which multiple conductive sheaths are present, the diameters of
the
sheaths may vary in size so that the diameter of one conductive sheath is
different from
the diameter of another conductive sheath.
[0079] According to one embodiment, the conductive sheath 108 as shown in
FIG.
2A can be made to have a particular physical length with two ends. The sheath
108 can
be fabricated using a metal pipe made of a conductive material including, but
not limited,
to aluminum, stainless steel, and carbon steel. In some cases the conductive
sheath
108 can be made of a composite material such as fiberglass that is covered
with a
conductive material like metal or embedded with metal layers. Similar to the
main pipe
102, the cross section of the conductive sheath may be, but is not limited to
circular,
rectangular, and hexagonal.
[0080] The inner diameter of the conductive sheath 108 is larger than the
outer
diameter of the main pipe 102. The conductive sheath 108 may be concentric to
the
main pipe 102. However in some embodiments, the conductive sheath 108 does not
surround or enclose the main pipe 102 concentrically. It may be noted that a
cavity 124
can be created between the conductive sheath 108 and the surrounded portion of
main
pipe 102. The existence of the cavity allows for electrically separating the
conductive
sheath 108 and the main pipe 102. Both ends of the conductive sheath 108
further
define apertures, i.e. they are not electrically connected to the main pipe
102 using a
metal or any other electrically conducting material. As shown in FIG. 2A, the
conductive
sheath can be connected to an RF source through the feed connector 122 using,
for
CA 2976107 2017-08-11
- 16 -
example, a metal post connected with the inner conductor of the coaxial feed
transmission line 122.
[0081] Portions of the main pipe 102 surrounded by the conductive sheath
108,
together with the material(s) provided in the cavity 124 therebetween, may
define a
length or segment of coaxial transmission line with an aperture at either end.
In some
embodiments, a dielectric material can be provided to fill the cavity 124. In
other cases,
several types of dielectric materials may be used. The dielectric material can
be
introduced to provide structural support for the excitation module 100 and/or
to control
the electrical properties such as the electrical length. Such dielectric
material can include
fluids (e.g. pressurized fluids), or one or more solid dielectric materials,
or surface
structures such as corrugations, or combinations thereof. Dielectric materials
can be, but
are not limited to ceramics such as alumina, zirconia, titanium dioxide, etc.;
glass;
quartz; or synthetic polymers such as PEEK, Teflon, polyethylene (PE), etc.;
structural
ceramics or other composite materials.
[0082] As shown in FIG. 2A, the surrounded portion 102a of the main pipe
102 may
correspond to an inner conductor of the coaxial transmission line and the
inner
conducting surface 130 of the conductive sheath 108 may correspond to an outer
conductor of the coaxial transmission line as shown in FIG. 7B. The EM field
geometry
created by this coaxial transmission line may be capable of exciting single
conductor
transmission lines and/or leaky transmission lines defined on the excitation
module 100
as will be described in more detail below.
[0083] Impedance matching between the excitation module 100 and the
surrounding
hydrocarbon formation generally depends upon the electrical length of the
coaxial
transmission line defined by the conductive sheath 108 and the diameter of the
main
pipe 102. The physical length of the conductive sheath 108 can thus affect the
electrical
length. Selection of the physical length may depend upon the operating
frequency, outer
diameter of the main pipe 102, outer diameter of the conductive sheath 108,
electrical
parameters of the surrounding medium (e.g. the hydrocarbon formation) and the
material provided in the cavity 124 between the main pipe and the conductive
sheath.
CA 2976107 2017-08-11
- 17 -
Details with respect to selecting the length of the conductive sheath shall be
described
in detail subsequently.
[0084] Electrical couplers can be used as a bridge for transferring EM
energy from
the feed transmission line 120 inside the main pipe 102 to the conductive
sheath 108 as
shown in FIG. 2A. An electrical coupler can comprise of one or a number of
feed
connectors 122. Each feed connector 122 can be connected to a single feed
transmission line at a first feed connector port, and connected to at least
one of the inner
conductive surface 130 of the conductive sheath 108 and the inner surface 114
of the
conductive pipe 102 at a second connector port. An example of a single feed
connector
122 is provided in FIG. 2A. The feed connector 122 can be configured to
electrically
connect one conductor of a coaxial feed transmission line 120 to the
conductive sheath
and the other conductor to the main pipe 102.
[0085] Generally, each module has at least one feed connector located
along the
length coaxial transmission line (i.e. between two ends of the conductive
sheath 108). In
some embodiments, the feed connector can be provided at one end of the length
of
coaxial transmission line. In other embodiments, the excitation module 100 can
have
one, two, three or more feed connectors 122 depending on the number of feed
transmission lines or feed transmission line conductors. The feed connectors
122 can be
distributed azimuthally or radially around the main pipe 102 as shown in FIG.
2B which
shows a transverse cross-sectional view of the excitation module 100 with
multiple feed
connectors 122. Alternatively, the feed connectors 122 may be distributed
axially or
linearly along the length of the main pipe 102 inside the portion of the
surrounded by the
conductive sheath 108 as shown in FIG. 2C, or as a combination of the two
arrangements.
[0086] In some embodiments, multiple feed connectors may be connected to
a
single feed transmission line, as shown FIG. 2D. First feed connector 122A and
second
feed connector 122B can be configured to electrically connect first and second
conductors of the coaxial transmission line 120 to the conductive sheath 108.
7601403
Date Recue/Date Received 2022-06-21
- 18 -
[0087] The end portions of the coaxial transmission line defined by the
main pipe
102 and conductive sheath 108, which interfaces with the hydrocarbon formation
or
reservoir, is preferably sealed structurally to separate the formation form
the cavity 124.
During use, if water, clay, drilling mud or other types of electrically
conductive materials
from the hydrocarbon formation or well reach the feed connector inside the
cavity 124, a
number of outcomes may arise, including i) formation of a short-circuit or
near short-
circuit of the feed point; ii) cause physical damage to the feed connector 122
by
chemical or mechanical means; iii) modification of electrical properties or
physical
damage to electrical components on the interior 116 of the main pipe 102 (such
as feed
transmission lines, in-situ RF generators, etc.) by chemical or mechanical
means.
[0088] These identified scenarios, alone or in combination, may cause a
whole or
significant part of the EM energy intended to be delivered to the hydrocarbon
formation
to be reflected by the feed connector back toward the RF generator or
excessively heat
the excitation module 100 or antenna. To avoid such undesirable outcomes,
seals 110,
as shown in FIG. 5, may preferably be disposed at the ends of the conductive
sheath
and used to maintain the cavity by physically sealing the cavity space to
separate the
feed connector from the hydrocarbon formation so that no materials from
outside can
reach the electrically sensitive area. In other words, an enclosed cavity can
be defined
by the surrounded portion of the main pipe 102, the conductive sheath 108 and
the
seals 110. As noted previously, this cavity is a part of the coaxial
transmission line and
may be filled with a dielectric material to control the electrical properties
of the coaxial
transmission line.
[0089] The seal is preferably made of materials which are electrically
insulating,
lossless or have low loss (loss tangent less than 0.01) at the frequency of
operation;
capable of withstanding high temperatures, such as 100 C, 200 C, 250 C, 300
C, or
500 C; prohibits flow of fluids from the hydrocarbon formation and do not
react
chemically with the materials existing inside the well or formation, such as
hydrocarbons,
water, natural gas, drilling mud, etc. Suitable materials include, but not
limited to,
ceramics such as alumina, zirconia, titanium dioxide; synthetic polymers
including, but
not limited to, PEEK, UltemTM, TeflonTiv', Polyethilene and various elastomers
(e.g.
CA 2976107 2017-08-11
- 19 -
silicone). In some cases, a combination of one or more of such materials may
be
suitable materials for seals.
[0090] A cross sectional view of one end of the excitation module 100
showing an
example of a feed connector seal 110 is presented in FIG. 5. In the embodiment
presented, the seal 110 may have a torus of rectangular cross-section
(toroidal shape)
with an inner diameter equal to or slightly larger than the outer diameter of
the main pipe
102, and an outer diameter equal to or slightly smaller than the inner
diameter of the
conductive sheath 108.
[0091] In some embodiments, inner and outer concentric structural rings
such as 0-
rings 140 (two at each end), or, alternatively, tolerance rings, or
combination thereof,
can be used to allow for tolerance/variation in the fabrication of the seal
110 and
conductive sheath 108 as well as to maintain the seal 110 in position when the
dimensions of the various components such as the main pipe 102 and conductive
sheath 108 change due to thermal expansion of the materials. The inner ring
may be
provided proximally to the conductive pipe 102 and the outer ring can be
positioned
proximal to the conductive sheath 108. Where 0-rings 140 are used, the 0-rings
140
are preferably made of materials with low electrical loss (e.g. loss tangent <
0.01) and
can withstand high temperatures such as 100 C, 200 C, 250 C, 300 C, or 500
C.
Some examples of 0-ring materials include, but not limited to, Viton TM,
Teflon TM, nitrile,
neoprene and KalrezTM. The actual shape of the seal generally does not have
significant
influence on the operation of the excitation module 100 if the seal thickness
is smaller
than 0.05 wavelengths.
EM Irradiation and Impedance Matching in the Initial State Operation
[0092] One or more excitation modules 100 can be coupled to a generator
and
deployed into the hydrocarbon formation. Once an antenna comprising one or
more
excitation modules 100 has been deployed into the hydrocarbon formation, the
generator can be operated to deliver EM power to the antenna. It can be
assumed that
the "Initial State" of each of the excitation module 100 is surrounded by an
unheated,
electrically conductive reservoir in what can be denoted as the "unheated wet
zone" 602,
CA 2976107 2017-08-11
- 20 -
as shown in FIG. 6. The aperture at the end of the coaxial transmission line
can be used
for exciting a travelling wave mode of EM propagation on a single conductor.
Specifically, in the excitation module 100 described above, both the main pipe
102 and
the outer surface of the conductive sheath 108 may be used as these single
conductor
transmission lines. It may be noted that these single conductor transmission
lines are
generally lossy, since they are enveloped by an electrically conductive medium
(e.g. a
hydrocarbon bearing formation with a saturation of water), where guided
electromagnetic energy can be converted to heat in the reservoir. A detailed
discussion
of single conductor transmission lines in general may be found in [A.
Sommerfeld,
Lectures on Theoretical Physics, vol. 3, Academic Press, 1959.] and [J. A.
Stratton,
Electromagnetic Theory. John Wiley & Sons, 20071.
[0093] Impedance matching to a variety of hydrocarbon formations or
reservoirs with
different electrical parameters may be achieved using these lossy single
conductor
transmission lines in conjunction with a selection of coaxial transmission
line section
length (i.e. length of the conductive sheath 108), coaxial transmission line
characteristic
impedance and placement of the feed connector 122 along the coaxial
transmission line.
Determination of the electrical length of the coaxial transmission line and
placement of
the connector will be discussed below,
[0094] To explain how impedance can be matched, allow, as an example, the
physical length of the coaxial transmission line defined by the conductive
sheath 108
and main pipe 102 bell + 2, where the feed connector 122 is a distance S.1
from a far
end of the section of coaxial transmission line and distance 9.2 from a near
end of the
section of coaxial transmission line. If the operating wavelength is large
compared to the
outer radii of the main pipe 102 and conductive sheath 108 (the wavelength is
> 20
times whichever radius is largest), then the equivalent circuit of the
corresponding
antenna structure may be simplified to the circuit shown in FIG. 7A.
[0095] Specifically, the circuit of FIG. 7A is depicted from the point of
view of the
feed connector, where a generator with system impedance Rg, represents the
applied
signal (i.e. the EM wave). The generator can "see" the far and near ends of
the coaxial
CA 2976107 2017-08-11
- 21 -
transmission line section through two different lengths of the coaxial
section, which has
characteristic impedance Zcoax.
[0096] At each end of the coaxial section, an effective shunt capacitance
can be
considered, which can result from the fringing fields at this transmission
line discontinuity
702 as shown in FIG. 7B. Calculation of this capacitance can be found in [N.
Marcuvitz,
Waveguide Handbook. McGraw-Hill, 1951.]. Beyond the capacitance, there exist
two
single conductor transmission lines sharing the same ground reference.
Referring to
again FIG. 7B, the inner conductor of the coaxial section 102a connects with a
single
conductor transmission line formed by portions of the main pipe 102 that are
not
enclosed by the conducting sheath 108. This single conductor transmission line
can be
referred to as the inner single conductor transmission line 704, which has
characteristic
impedance Z, as shown in FIG. 7A. For simplicity, the main pipe 102 can be
considered
to be infinitely long such that this inner single conductor transmission line
704 is
matched. In the final design stage, where the single conductor transmission
line need be
modelled as finite, e.g. when a reflection from the end of the main pipe need
be
considered, the impedance terminating the single conductor line should be an
equivalent
representation of this reflection, and would typically be determined from
computer
simulations. In cases where several conductive sheaths are present along the
main
pipe, several of such inner single conductor transmission lines 704 may be
present and
the circuit model in the circuit of FIG. 7A may be modified.
[0097] The outer conductor of the coaxial section, in other words, the
inner surface
130 of the conductive sheath 108, connects with the outer surface 132 of the
conductive
sheath, the latter forming another single conductor transmission line. This
other single
conductor transmission line can be referred to as the outer single conductor
transmission line 132, which has characteristic impedance Zo as shown in FIG.
7A. The
inner and outer single conductor transmission lines of the present embodiment
can be
said to be separated by the electrical discontinuity 702. It can be noted that
the
capacitance and the characteristic impedances of the inner and outer single
conductor
transmission lines can depend upon the electrical size of the structure of the
excitation
module (e.g. the sheath 108) and the electrical properties of the surrounding
medium.
CA 2976107 2017-08-11
- 22 -
[0098] With reference to the circuit of FIG. 7A, the two lengths of coaxial
transmission line seen by the feed connector (R1 and 2) are coupled with the
total length
of the outer single conductor transmission line al + 2). The capacitances (co
and Cj2)
and the characteristic impedances (Zõ Zo and Zcoax) are all coupled, and
depend upon
the frequency of operation, radii of the conductive sheath, the radius of the
main pipe
and the reservoir electrical characteristics. To aid in the explanation of
operation, a
usage case is presented in which the conductive sheath has a length that is
half
wavelength (relative to the guided wavelength inside the coaxial section) or
substantially
half wavelength (e.g. ranging between 40% to 60% of the guided wavelength
inside the
coaxial section) of the irradiation frequency and in which the feed connector
122 is
placed close to one or both ends of the coaxial section can be considered.
When the
coaxial transmission line is chosen to have an electrical length of half or
substantially
half wavelength with the feed connector position close to one end of the
coaxial section,
the EM fields at either end of the coaxial transmission line would be about
180 degrees
out of phase (in the case of two feed connectors at either end of the coaxial
section, the
signals applied to each end will need to be 180 degrees out of phase). In
turn, the
nature of the fields can impose a virtual perfect electric conductor (PEC)
boundary
condition 710 in the transverse mid-plane surrounding the antenna structure
(i.e. at the
mid-point of the length of coaxial transmission line), as shown in FIG. 7C.
[0099] In some cases, one or more feed connectors 122 may be positioned
near the
midpoint position to provide EM power to the excitation module. FIG. 8 shows
the
directions of the Poynting vector outside this antenna structure, indicating
the presence
of a PEC boundary 710. In the case of a module chain, this model is applicable
in the
initial state only, assuming adjacent models do not influence each other, in
cases where
the fields are largely absorbed by the reservoir before reaching neighboring
modules. In
other cases e.g. periodic system analysis, or other system simulations are
performed
numerically.
[00100] This virtual PEC boundary 710 can be modeled by splitting the outer
single
conductor transmission line shown in FIG. 7A into two lossy short-circuited
stubs with
impedance Zo, as shown in FIG. 9. In this configuration the operation of the
structure
CA 2976107 2017-08-11
- 23 -
may be observed more intuitively: the shorted stubs add an additional degree
of
freedom that can assist with impedance matching the electromagnetic wave at
the feed
connector of the antenna structure moving to the inner single conductor
transmission
line with characteristic impedance Z,. This determines how to select the
required module
dimensions (determining qi and Cj2, Zi, Z0 and Zcoax) for a specific operating
frequency
and expected reservoir conditions. Again, this PEC boundary, feed connector
position
and the selection of a half wavelength conductive sheath is for illustration
purposes and
the electrical length in use can be greater or less than a half wavelength. In
the event
the designer cannot find module dimensions that are satisfactory, the feed
connector
position and conductive sheath length needs to be adjusted and the process
repeated.
Generally, an arbitrary virtual impedance boundary would be present at or near
the mid-
plane surrounding the antenna structure with a conductive sheath of any length
or feed
connector position.
[00101] In some embodiments, when the coaxial transmission line is chosen to
have
an electrical length of half or substantially half wavelength of the
irradiation frequency
with one feed connector near the midpoint of the coaxial transmission line or
two feed
connectors near both ends of the coaxial transmission line, a perfect magnetic
conductor (PMC) boundary condition using magnetic field symmetry can be formed
if the
magnetic fields from either end arrive at the midpoint of the conductive
sheath out of
phase (in the case of two feed connectors at either end of the coaxial
section, the
signals applied to each end will need to be in phase). The PMC boundary
condition may
also be located in a transverse mid-plane of the coaxial transmission line
that is
transverse to the main axis of the antenna structure.
[00102] In yet other embodiments, the length of the coaxial transmission line
can be
chosen such that it is an odd multiple of one half of the wavelength of the
oscillation
frequency of the EM energy.
[00103] The physical length of the coaxial transmission line can be affected
by at
least one of: the target frequency; outer diameter of the main pipe 102; outer
diameter of
the conductive sheath 108; the material occupying the cavity 124; and the
electrical
characteristics of the hydrocarbon formation. Having regard to the identified
factors in
CA 2976107 2017-08-11
. . - 24 -
consideration, a selection of structural dimensions of the excitation module
can be made
so that the resultant antenna can be electrically matched to a broad range of
external
media, or to media which undergo changes in its physical or electrical
properties over
the course of heating.
[00104] Returning back to the half wavelength conductive sheath antenna
structure
as an example once more, this configuration may be regarded as the structure
having
physical dimensions and characteristic impedances being optimized for a
certain
operating frequency. The reflection coefficient seen by a generator, in the
form of the
scattering parameter S11, is plotted versus the external medium's electrical
conductivity
and relative permittivity in FIG. 10. The values of electrical conductivity
and relative
permittivity are based upon the experimental results in [F. S. Chute, F. E.
Vermeulen, M.
R. Cervenan, and F. J. McVea, "Electrical Properties of Athabasca Oil Sands,"
Can. J.
Earth Sci., vol. 16, pp. 2009-2021, 19791. An S11 parameter less than or equal
to -10
dB indicates that the structure matches the impedance of the external medium
for most
test cases. Note that the impedance match is only lost for cases along the
periphery of
the test space. This impedance robustness can be attributed to how the
characteristic
impedance of both single conductor transmission lines and discontinuity
capacitance
changes with permittivity and conductivity of the external medium.
Semi Steady-State Operation
[00105] Electromagnetic heating can be regarded to have reached a semi steady-
state of operation when the hydrocarbon formation or reservoir volume
immediately
adjacent to the radiating source (e.g. excitation module 100, irradiating
modules, or
module chain(s)) has been heated along the length of the main pipe 102 and
along the
length of the conductive sheath 108 to a point where water within the pore
spaces of the
hydrocarbon formation or reservoir has evaporated. These evaporated zones that
surround the excitation module can be called "dry-out" zones. Both the
dielectric
constant and electrical conductivity of the dry-out zones are generally lower
than the
unheated volumes of the hydrocarbon formation or reservoir.
CA 2976107 2017-08-11
- 25 -
[00106] Measurements of oil sand permittivity and conductivity as a function
of water
saturation can be found in [F. S. Chute, F. E. Vermeulen, M. R. Cervenan, and
F. J.
McVea, "Electrical Properties of Athabasca Oil Sands," Can, J. Earth Sci.,
vol. 16, pp.
2009-2021, 19791. The exact difference in electrical properties between
unheated and
heated zones varies reservoir to reservoir, but, as a rough example at 1 MHz
based on
the cited study, the permittivity and conductivity may change from about 30
and 0.02
Sim to about 10 and 0.0001 S/m. It may be noted that semi steady-state
conditions is
not signaled or indicated by a specific dry-out zone size, but rather, it can
be achieved
when the dry-out zone is present everywhere around the antenna. Furthermore,
this
state of operation is regarded as a "semi steady-state" since the volume of
the dry-out
zone is increasing as the heating process advances.
[00107] Formation of the dry-out zone can create lossy coaxial transmission
lines
defined along the main pipe and along the outer surface of the conductive
sheath of an
excitation module as shown in FIG. 11. For each excitation module 100 (or
alternatively,
chain(s) of modules) the effective outer conductors of these transmission
lines can be
the boundary 1110 between the low and high electrical conductivity regions
corresponding to the heated dry-out zone 1120 and unheated wet zone 1130 of
the
hydrocarbon formation or reservoir, respectively. The inner conductor of the
lossy
coaxial transmission lines may be defined by the portions of the main pipe 102
that are
not surrounded by the conductive sheath 108 (i.e. the inner single conductor
transmission line) and the outer surface of the conductive sheath 108 (i.e.
the outer
single conductor transmission line). Since the outer conductors of these "dry-
out coaxial
transmission" lines are defined by the boundaries of a medium with a higher
dielectric
constant (i.e the unheated wet zone 1130), the structure can behave as a
uniform leaky-
wave radiator. An example of a radiation pattern of leaky wave radiation from
one end of
the sheath coaxial line is shown in FIG. 12. This leaky-wave radiation can
continue
heating the hydrocarbon formation or reservoir outside the dry-out zone 1120,
and the
dry-out zone can slowly expand with time as more heat is deposited.
[00108] Once the semi steady-state of operation is reached, impedance matching
can
become easier since the apertures 1140 of the conductive sheath are surrounded
by the
dry-out zone 1120. The operation of the excitation module in the semi steady-
state can
CA 2976107 2017-08-11
- 26 -
be described again by considering an example case where the coaxial
transmission line
formed by the conductive sheath and the main pipe is one half of the operating
wavelength. The initial state circuit model as shown in FIG. 9 may be applied
to an
isolated module in the semi steady-state since the perfect electric conductor
boundary
condition at the conductive sheath's transverse mid-plane (FIGS. 7C and 8) and
additional capacitance from fringing fields at the transmission line
discontinuity are still
present. Note that if this model is reapplied, the single conductor
transmission lines are
replaced by the dry-out coaxial transmission lines. Because the fringing
fields exist
predominately inside the dry-out zone 1120 with a generally consistent
dielectric
constant, the capacitance in the circuit model may have a small dependence on
the
dielectric constant of the unheated reservoir. In turn, the input impedance of
the
resultant circuit may stabilize, and impedance matching can become less of a
concern
once a dry-out zone has formed.
[00109] In some embodiments where several modules are connected together
underground in a modular deployment, the dry-out zones surrounding each
coaxial
transmission line may connect, forming a longer uniform leaky-wave antenna
with
distributed sources. The power and phase of the EM energy of each module
source may
be controlled to obtain an overall heating pattern along the hydrocarbon
formation or
well, as suggested in US patent application Ser. No. 14/508,423. For example,
multiple
excitation modules 100 or module chains 400 may be irradiating EM waves having
the
same phase. Alternatively, one or more modules may be configured to irradiate
EM
waves that are out of phase (e.g. 180 degrees out of phase or some other phase
relationship). The emitted EM waves may generate a desired irradiation pattern
as a
result of constructive and destructive interference thereof. For example, if
one area of
the hydrocarbon formation is being underheated or overheated, the power and/or
phases of the nearest modules can be configured to correct the heating of the
problem
region. In general, adjusting phases and power levels of modules provides new
means
of establishing and controlling radiation patterns of the distributed antenna
(as taught in
US patent application Ser. No. 14/508,423).
[00110] Numerous specific details are set forth herein in order to provide a
thorough
understanding of the exemplary embodiments described herein. However, it will
be
7601403
Date Recue/Date Received 2022-06-21
- 27 -
understood by those of ordinary skill in the art that these embodiments may be
practiced
without these specific details. In other instances, well-known methods,
procedures and
components have not been described in detail so as not to obscure the
description of
the embodiments. Furthermore, this description is not to be considered as
limiting the
scope of these embodiments in any way, but rather as merely describing the
implementation of these various embodiments.
CA 2976107 2017-08-11
