Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND SYSTEM FOR ENABLING FLUID COMMUNICATION BETWEEN WELLS IN
A BITUMEN RESERVE
TECHNICAL FIELD
[0001] The following relates to systems and methods for enabling fluid
communication
between wells in a bitumen reserve.
DESCRIPTION OF THE RELATED ART
[0002] Bitumen is known to be considerably viscous and does not flow like
conventional
crude oil, and can be present in an oil sand reservoir. As such, bitumen is
recovered using what
are considered non-conventional methods. For example, bitumen reserves are
typically
extracted from a geographical area using either surface mining techniques,
wherein overburden
is removed to access the underlying pay (e.g., oil sand ore-containing
bitumen) and transported
to an extraction facility; or using in situ techniques, wherein subsurface
formations (containing
the pay) are heated such that the bitumen is caused to flow into one or more
wells drilled into
the pay while leaving formation rock in the reservoir in place. Both surface
mining and in situ
processes produce a bitumen product that is subsequently sent to an upgrading
and refining
facility, to be refined into one or more petroleum products, such as gasoline
and jet fuel.
[0003] Bitumen reserves that are too deep to feasibly permit bitumen
recovery by mining
techniques are typically accessed by drilling wellbores into the hydrocarbon
bearing formation
(i.e. the pay) and implementing an in situ technology. There are various in
situ technologies
available, such as steam driven based techniques. These include, for example,
Steam Assisted
Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS). In a typical
implementation of
the SAGD method, a pair of horizontally oriented wells are drilled into the
bitumen reserve, such
that the pair of horizontal wells are vertically aligned with respect to each
other and separated
by a relatively small distance, typically in the order of several meters. The
well installed closer to
the surface and above the other well is generally referred to as an injector
well, and the well
positioned below the injector well is referred to as a producer well. The
injector well and the
producer well are then connected to various equipment installed at a surface
site.
[0004] Prior to extracting bitumen from the reserve using the SAGD method,
"start-up" of
the wells is generally required. As used herein, "start-up" generally refers
to the step of
achieving or enabling fluid communication between two or more wells situated
in a bitumen
reserve. In a typical SAGD implementation, start-up is conventionally achieved
by injecting and
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circulating steam through both the injector well and the producer well. The
steam is circulated
through both wells until the region between the injector well and the producer
well (i.e. the inter-
well region) has been sufficiently heated to mobilize the bitumen and
therefore allow fluid
communication between the wells. Once start-up has been achieved, production
can begin.
During production, steam is typically introduced into the bitumen reserve
through the injector
well which, in the process of condensing, further heats up the surrounding
bitumen to lower its
viscosity. The heated bitumen and the condensate then flows towards the
producer well due to
gravity, and are then pumped to the surface through the producer well.
[0005] However, achieving start-up using the conventional method of steam
circulation can
be inefficient and/or impractical for some bitumen reserves. For example,
steam has been found
to not effectively penetrate the cold bitumen surrounding the wells in low
permeability formations
or reserves (e.g. inclined heterolithic strata units). This can result in long
start-up time and
relatively high cost in achieving start-up if steam is employed as the primary
heat source during
the start-up phase of such low permeability reserves. Furthermore, the
conventional start-up
method of steam circulation requires additional surface equipment to be
installed on-site for
steam generation, which can unfavourably delay start-up in some cases.
SUMMARY
[0006] In one aspect, there is provided a method for establishing fluid
communication
between a pair of wells positioned in a pay region of a bitumen reserve, the
method comprising:
applying rapid heat to an inter-well region between the pair of wells using at
least one heat
source and in the absence of fluid injection, the heat sufficient to cause
dilation of pores in the
inter-well region via thermal expansion of connate fluid in the pores.
[0007] In an implementation of the method, the rapid heat is provided by an
electromagnetic
heat source, the electromagnetic heat source being configured to direct radio
frequency
radiation towards the inter-well region.
[0008] In another aspect, there is provided a system for establishing fluid
communication
between a pair of wells positioned in a pay region of a bitumen reserve, the
system comprising:
at least one heat source configured to apply rapid heat to an inter-well
region between the pair
of wells using at least one heat source and in the absence of fluid injection,
to cause dilation of
pores in the formation in the inter-well region by thermal expansion of
connate fluid in the pores.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Various aspects and implementations will now be described by way of
example only
with reference to the appended drawings wherein:
[0010] FIG. 1 is a cross-sectional elevation view of an in situ gravity
drainage system
deployed in a bitumen reserve;
[0011] FIG. 2A is a schematic cross-sectional enlarged view illustrating a
portion of an
inter-well region in an implementation wherein a rapid heat source is
installed in both the
injector well and the producer well;
[0012] FIG. 2B is a schematic cross-sectional enlarged view illustrating
the rapid heat
sources radiating electromagnetic radiation in the implementation of FIG. 2A;
[0013] FIGs. 3A and 3B illustrate the dilation of pores containing connate
water in the inter-
well region due to rapid heating;
[0014] FIG. 4 is a schematic cross-sectional enlarged view illustrating an
implementation
wherein the rapid heat source is installed inside the injector well;
[0015] FIG. 5 is a schematic cross-sectional enlarged view illustrating an
implementation
wherein the rapid heat source is installed inside the producer well;
[0016] FIG. 6 is a schematic diagram illustrating a configuration for
powering a pair of
electromagnetic antennas in one implementation;
[0017] FIG. 7 is a schematic diagram illustrating a configuration for
powering an
electromagnetic antenna in one implementation;
[0018] FIG. 8 is a schematic diagram illustrating a configuration for
powering an
electromagnetic antenna in another implementation;
[0019] FIG. 9 is a schematic diagram illustrating a configuration for
powering a pair of
electromagnetic antennas in another implementation;
[0020] FIG. 10 is a diagram illustrating the various stages of a
conventional SAGD
process;
[0021] FIGs. 11A-11C are diagrams illustrating the rapid heat source being
installed inside
the injector well and/or producer well in various configurations;
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[0022] FIG. 12 is a diagram illustrating the pore dilation effect caused
due to rapid heating;
[0023] FIG. 13A is a chart showing the variation of the incremental thermal
pressurization
of pure water in an exemplary formation;
[0024] FIG. 13B is a chart showing the variation of the incremental thermal
pressurization
of steam in drained condition in an exemplary formation;
[0025] FIG. 130 is a chart showing the variation of parameters for
incremental thermal
pressurization of vaporized steam in undrained condition in an exemplary
formation;
[0026] FIG. 13D is a chart showing the variation of the incremental thermal
pressurization
of vaporized steam in undrained condition in an exemplary formation;
[0027] FIG. 14A is a chart showing the pressure of water after thermal-
pressurization at
reservoir temperature of 5 C;
[0028] FIG. 14B is a chart showing the pressure of vaporized steam after
thermal-
pressurization at reservoir temperature of 5 C;
[0029] FIG. 15 is a chart showing the pressure caused by thermal
pressurization in shale
and sand formations before pressure leak-off at reservoir temperature of 5 C;
[0030] FIG. 16 is a chart showing the pressure caused by thermal
pressurization before
and after flashing in two exemplary formations at reservoir temperature of 5
C;
[0031] FIG. 17A is a phase diagram of water;
[0032] FIG. 17B is a chart of thermal-pressurization factor for water,
steam and vaporized
steam under various conditions;
[0033] FIG. 18 is a chart showing the temperature change in a formation
with respect to
distance from the rapid heat source operating at various power levels;
[0034] FIG. 19 is a chart showing the pressure change in a formation with
respect to
distance from the rapid heat source operating at various power levels; and
[0035] FIG. 20 is a chart showing the change in thermal expansion
components with
respect to porosity at various temperatures.
DETAILED DESCRIPTION
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[0036] In the following, there is provided a system and method for
establishing fluid
communication between a plurality of wells extending through a pay region of a
bitumen
reserve. The system and method operate to achieve fluid communication (i.e.
start-up) by
applying rapid heat to an inter-well region to cause dilation of the pores in
the inter-well region
via thermal expansion of connate fluid present in the pores.
[0037] As used herein, the term "inter-well region" will be understood to
refer to a region
between two or more wells positioned in a formation. In particular, it will be
appreciated that in a
typical SAGD-type well configuration, the inter-well region would generally
include at least the
portion of the pay which lay between the injector well and the producer well.
[0038] In an implementation of the system and method, the rapid heat is
applied in the
absence of fluid injection. In some implementations, the rapid heat can be
provided by an
electromagnetic heat source. The electromagnetic heat source can be configured
to direct radio
frequency radiation towards the inter-well region. The power of the
electromagnetic heat source
required to achieve dilation, can be greater than about 10 kilowatts per meter
of well length
(kW/m). For example, the power output of the electromagnetic heat source can
be between 10
kW/m and 50 kW/m according to the compressibility of the rock in the
formation. The
electromagnetic heat source can be located in at least one of the plurality of
wells.
[0039] In one implementation, the plurality of wells includes an injector
well and a producer
well, and the electromagnetic heat source is located at least inside the
injector well for rapidly
heating the inter-well region. In another implementation, the electromagnetic
heat source is
located inside both the injector well and the producer well.
[0040] Turning now to the figures, FIG. 1 illustrates an example of a SAGD
production site
30 at a surface location 10 in a particular geographical region. The SAGD
production site 30 is
positioned to allow one or more SAGD well-pairs 40 to be drilled from the
surface location 10
towards a bitumen reserve (i.e., the pay 20). In the illustrated example, the
one or more SAGD
well-pairs 40 include an injector well 42 positioned above a producer well 44.
As will be
appreciated, the injector well 42 is configured to inject steam into the pay
20 and the producer
well 44 is configured to recover a bitumen-containing fluid that has been
mobilized by the
injected steam during the typical SAGD production stage. The injector well 42
is typically
located about 4 to 6 meters above the producer well 44 to define an inter-well
region 22
therebetween, however, other relative distances between the wells are
possible. The one or
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more SAGD well-pairs 40 are drilled vertically into the overburden 15 towards
and into the
underlying pay 20, and as they are drilled become oriented substantially
horizontal, such that
the producer well 44 is above but near the formation 25 underlying the pay 20
(hereinafter the
"underlying formation 25"). The one or more SAGD well pairs 40 are operated
using a surface
equipment 60.
[0041] To prepare the SAGD production site 30, the location where the one
or more SAGD
well-pairs 40 will be located is determined, for example, by conducting
typical computer
simulations using geological and reservoir data. The corresponding locations
of the production
site 30 are then prepared for drilling, including providing infrastructure for
water and electricity,
as is known in the art. A drilling rig is then installed at the location and
drilling commences
subject to requisite inspections.
[0042] After drilling the wells 42, 44, the surface production equipment 60
is installed for
operating the SAGD well pair 40. The wells 42, 44 are then completed according
to steps which
are generally known in the art.
[0043] Once the wells 42, 44 have been completed, one or more rapid heat
sources can be
installed within the injector well 42 and/or the producer well 44 for
initiating the start-up phase.
In one implementation illustrated in FIG. 2A, a first rapid heat source 72a is
installed inside the
injector well 42 and a second rapid heat source 72b is installed inside the
producer well 44. In
the illustrated implementation, the first rapid heat source 72a and the second
rapid heat source
72b are electromagnetic antennas. As will be explained, the electromagnetic
antennas can be
connected to a radio frequency (RF) transmitter and a controller located at
the surface location
10.
[0044] FIG. 2B schematically illustrates the first and second rapid heat
sources 72a, 72b
being used to achieve start-up, and thus establish fluid communication between
the wells 42,
44. In the implementation illustrated in FIG. 2B, the first and second rapid
heat sources 72a, 72b
are electromagnetic antennas configured to emit RF radiation 80 directed at
least towards the
inter-well region 22 of the pay 20.
[0045] As is well known in the art, many bitumen reserves contain pores
which hold connate
fluids. As used herein, the term "connate fluids" will be understood to refer
to fluids which are
trapped within the reserve and the formation. Typically, connate fluids
primarily consist of water
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=
and dissolved minerals. Accordingly, the term "connate water" will be used
interchangeably with
the term "connate fluids" herein.
[0046] FIG. 3A illustrates the pores 100 containing connate water in the
inter-well region 22
of the reserve prior to initiating start-up in the implementation illustrated
in FIGs. 2A and 2B. As
illustrated in FIG. 3A, the pores 100 have an average diameter of 0 before the
inter-well region
22 is subjected to RF radiation. However, when the inter-well region 22 is
subjected to rapid
heat in the form of RF radiation, the pores dilate as illustrated in FIG. 3B.
Specifically, in FIG.
3B, the dilated pores 100' are illustrated as having an average diameter of
0', which is greater
than 0. The size of the pores 100 prior to dilation is illustrated using
dotted lines in FIG. 3B for
reference. The dilation of the pores increases the porosity and the
permeability of the pay 20 in
the inter-well region 22, and over time, fluid communication can be
established between the
injector well 42 and the producer well 44, thus completing the start-up phase.
[0047] This pore dilation effect is further illustrated in FIG. 12, which
also takes into account
a relatively small pressure leak (i.e. pressure leak << AP) which can occur in
thermo-
hydromechanical pressurization. It will be understood that, for example, an
operator can check
to see if fluid communication has been established between the wells by
applying fluid pressure
to the injector well and seeing if a response (i.e. pressure change) is
detected in the producer
well.
[0048] It has been determined that dilation of the pores can be caused by
the thermal
expansion of the connate water. More specifically, when the connate water
trapped within the
pores 100 is rapidly heated by RF radiation, the connate water thermally
expands, thereby
exerting pressure against the formation surrounding the pores 100. As the
connate water
continues to be heated, the pressure inside the pores builds until sufficient
pressure has been
reached to cause dilation. The pressure necessary to cause dilation can depend
on a number
of factors including, but not limited to, the volume of connate water present
in the pores, and the
type of bitumen formation surrounding the pores. Reaching such a pressure via
rapid heating
can be affected by the power and frequency of the RF radiation. If connate
water is sufficiently
heated such that it is vaporized, the generation of steam can further increase
the pressure
within the pores to cause dilation. For example, this is apparent from the
chart of FIG. 17B,
which provides the thermal-pressurization factor of water, steam, and
vaporized steam under
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various conditions. Specifically, under the conditions in which vaporized
steam typically form,
the thermal-pressurization factor of the vaporized steam is higher than that
of water. As
discussed below, higher thermal-pressurization factor of the fluid trapped
inside the pores can
result in greater dilation. For greater clarity, it is noted that vaporized
steam is understood to
refer to steam which is created as a result of the connate water flashing into
vapor.
[0049] Returning to FIG. 2B, the inter-well region 22 is subjected to RF
radiation 80 until the
permeability in the inter-well region 22 has been sufficiently increased by
dilation of the pores to
enable fluid communication between the injector well 42 and the producer well
44. The
enhanced permeability in the inter-well region 22 is illustrated by a series
of arrows pointing
towards the producer well 44 in FIG. 2B.
[0050] Various RF radiation antenna configurations are illustrated in FIGs.
11A-11C.
Specifically, in FIG. 11A, RF antenna is provided in each of the injector well
and the producer
well. In FIG. 11B, an RF antenna is provided in the producer well only, and in
FIG. 11C, an RF
antenna is provided in the injector well.
[0051] Shallow reservoirs (i.e. reservoirs with thin overburden) can be
relatively easily
fractured when dilation is caused by injection of fluids (e.g. cold water or
steam) into the
reservoir during the start-up phase. It can be considered undesirable to
fracture the formation
during start-up, since fracturing can create "high mobility highways" which
can direct steam
injected during the production stage away from the desired area. Furthermore,
fracturing can
result in sand production, which can prevent fluid propagation into the
reservoir. As such, in the
present method, the pores are dilated using RF radiation 80 in the absence of
fluid injection into
the pay 20 or the reservoir. For example, in a SAGD operation, the injection
of steam can be
delayed until after start-up has been achieved using the method described
herein (i.e. by way of
RF radiation). It can be particularly advantageous to achieve start-up in this
way for shallow
reservoirs, since the likelihood of fracturing the formation is reduced due to
the absence of fluid
injection during start-up.
[0052] In another implementation illustrated in FIG. 4, the rapid heat
source 72 in the form
of an electromagnetic antenna is only provided within the injector well 42. In
the illustrated
implementation of FIG. 4, it will be appreciated that RF radiation 80 emitted
by the rapid heat
source 72 will be directed at least towards the producer well 44, thereby
causing dilation of the
pores in the inter-well region 22 as explained above. In yet another
implementation illustrated in
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,
FIG. 5, the rapid heat source 72 in the form of an electromagnetic antenna is
illustrated as being
present only within the producer well 44.
[0053] As described above, the electromagnetic antenna 72 can function as a
rapid heat
applicator in some implementations. It will be understood that the
electromagnetic antenna 72
as used herein refers to a passive device that converts applied alternating
electrical current into
oscillating electromagnetic radiation, which can then be directed at least
towards the inter-well
region 22. For example, the electromagnetic antenna 72 can comprise a
directional antenna
and/or an omnidirectional antenna. The frequency of the electromagnetic
radiation emitted by
the antenna will generally be in the radio frequency range (i.e. approximately
between 3 kHz
and 300 GHz), which includes the microwave frequency range (i.e. approximately
3 to 30 GHz).
Accordingly, rapid heating of the connate water is primarily achieved through
dielectric heating.
It will be understood that, where applicable, the antenna can be configured to
operate within
specific frequency ranges which are preserved for industrial or scientific
purposes. For example,
the antenna can be configured to emit electromagnetic radiation in the
frequency ranges falling
under the industrial, scientific and medical (ISM) radio bands (e.g. 6.78 MHz
15 kHz).
[0054] As is well known in the art, dielectric heating occurs when
materials containing polar
molecules are subjected to rapidly changing or oscillating electromagnetic
fields. More
specifically, such materials are generally heated by the friction generated
from the polar
molecules continuously re-aligning themselves with the oscillating
electromagnetic field. In
comparison to other forms of heating such as resistive heating or steam
circulation, dielectric
heating can be particularly advantageous for rapidly heating the connate water
trapped in the
pores, since it does not rely on diffusion of heat or mobility of fluids
within the reservoir. Rather,
polar molecules such as water molecules trapped in the formation can be
selectively heated by
dielectric heating, since hydrocarbons and sand surrounding the water
molecules are generally
non-polar and are therefore not susceptible to dielectric heating. For this
reason, dielectric
heating generally has superior penetration and heating rate compared to
conductive heating in
hydrocarbon formations. Dielectric heating can also have properties of thermal
regulation
because steam is not susceptible to dielectric heating. In other words, once
the water is heated
sufficiently to vaporize using dielectric heating, its permittivity decreases
substantially such that
it is not further heated by continued application of electromagnetic
radiation.
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,
[0055] In order to rapidly heat the connate water trapped in the
formation using RF radiation
as described above, RF radiation will generally need to possess sufficient
power. In one
implementation, the output of the electromagnetic antenna is greater than
about 10 kW per
meter of well length. For example, the output can be approximately 10 to 50 kW
per meter of
well length. As will be appreciated, if the output power of the RF radiation
is insufficient for
rapidly heating the connate water trapped in the pores, dilation of the pores
cannot be achieved
due to slow build up and leakage of the pressure from the pores. It will also
be appreciated that
the level of power output required to cause pore dilation would depend on a
number of factors,
such as the compressibility and permeability of the formation being treated.
[0056] The simulated effects of applying RF radiation to an oil sand
formation at various
power levels are illustrated by the charts of FIGs. 18 and 19. Specifically,
FIG. 18 shows the
temperature in the region surrounding the RF antenna after RF radiation has
been applied for 6
minutes. In FIG. 18, simulated temperature results for RF power output of 1 kW
per meter of
well length (kW/m) is indicated by reference numeral 310, and similar results
for power output of
kW/m, 10 kW/m, 50 kW/m, and 100 kW/m are indicated using reference numerals
320, 330,
340, and 350, respectively.
[0057] FIG. 19 shows the induced pressure (i.e. due to thermal
pressurization) in the region
surrounding the RF antenna after RF radiation has been applied to an oil sand
formation for 6
minutes. In FIG. 19, simulated pressure results for RF power output of 1 kW
per meter of well
length (kW/m) is indicated by reference numeral 410, and similar results for
power output of 5
kW/m, 10 kW/m, 50 kW/m, and 100 kW/m are indicated using reference numerals
420, 430,
440, and 450, respectively.
[0058] The electromagnetic antenna 72 can be powered using various
configurations.
FIG. 6 illustrates one configuration in which a pair of electromagnetic
antennas 72a, 72b is
powered by an RF transmitter 210. As will be appreciated, the RF transmitted
210 can be
located on the surface as part of the surface equipment 60. In the
implementation illustrated in
FIG. 6, the RF transmitter 210 is configured to operate both electromagnetic
antennas 72a, 72b.
For example, as illustrated in the implementation of FIGs. 2A and 2B, the
electromagnetic
antennas 72a, 72b can be installed inside the injector well 42 and the
producer well 44,
respectively. The RF transmitter 210 can be connected to a controller 220,
which is configured
to control the RF transmitter 210. For example, the controller 220 can be
configured to control
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the power and frequency of the current being outputted by the RF transmitter
210. As will be
understood, controlling the parameters such as the power and frequency of the
current being
generated by the RF transmitter 210 would effectively modulate the RF
radiation 80 generated
by the electromagnetic antennas 72a, 72b.
[0059] Other configurations of powering the electromagnetic antenna 72 are
illustrated in
FIGs. 7 and 8. In the implementation illustrated in FIG. 7, the
electromagnetic antenna 72 can
be installed inside the injector well 42, and in the implementation
illustrated in FIG. 8, the
electromagnetic antenna 72 can be installed inside the producer well 44. In
both of these
implementations, the electromagnetic antenna 72 is powered by a dedicated RF
transmitter
210. As with the implementation of FIG. 6, the RF transmitter 210 can be
connected to a
controller 220 for controlling various parameters of the current outputted by
the RF transmitter
210.
[0060] FIG. 9 illustrates yet another configuration in which each
electromagnetic antenna
72a, 72b is connected to a dedicated RF transmitter 210a, 210b. More
specifically, a first
electromagnetic antenna 72a is illustrated as being connected to a first RF
transmitter 210a and
a second electromagnetic antenna 72b is illustrated as being connected to a
second RF
transmitter 210b. As discussed above, the first electromagnetic antenna 72a
can be installed
inside the injector well 42 and the second electromagnetic antenna 72b can be
installed inside
the producer well 44. In the illustrated configuration, both the first
transmitter 210a and the
second transmitter 210b are controlled by the controller 220. However, it will
be understood that
the system can also be configured such that each transmitter 210a, 210b is
connected to a
dedicated controller.
[0061] In another implementation, rapid heating may be achieved using
inductive heating in
some formations. For example, inductive heating can be applied by generating
an
electromagnetic field in the range of 1 kHz to 200 kHz to cause an eddy
current to be generated
within the reservoir, which in turn heats the reservoir to cause pore
dilation. As will be
understood, the electromagnetic field can be generated using a solenoidal
coil, also known as
an inductor, placed within the pay and connected to appropriate power
source(s), which can be
located on the surface. For example, inductive heating can be applied in some
low permeability
formations, such as shale formations.
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[0062] Once start-up has been achieved between the injector well 42 and the
producer well
44 in accordance with the method described herein, production can begin. For
example, in a
typical SAGD operation, steam is introduced into the pay 20 through the
injector well 42 to heat
up the bitumen surrounding the injector well 42 to lower its viscosity,
thereby allowing the
heated bitumen and steam condensate to flow into the producer well 44 to be
pumped to the
surface 10.
[0063] During production, the rapid heat source 72 can be removed from the
injector and/or
producer wells. Alternatively, the rapid heat source 72 can be left inside the
injector and/or
producer wells during production. For example, the rapid heat source 72 can be
kept inside the
wells to continue heating the interwell region during production.
[0064] In one implementation, the rapid heat source 72 can be kept inside
the injector
and/or producer wells after start-up has been achieved, and steam may be
injected (e.g. bull-
heading) or circulated through the wells. In such implementation, applying RF
radiation
simultaneously with steam injection or circulation can enhance the
permeability of the formation
and therefore assist production.
[0065] In another implementation, once start-up has been achieved, an
electromagnetic
steam-assisted gravity drainage (EM-SAGD) process can be implemented on the
wells. For
example, in such implementation, electromagnetic inductive heating can be
applied
simultaneously with steam injection or circulation. As explained above,
inductive heating can be
applied by generating an electromagnetic field in the range of 1 kHz to 200
kHz using a
solenoidal coil placed within the pay, at a lower power than that used to
apply rapid heating.
[0066] In addition to or as an alternative to using the typical SAGD method
for producing the
bitumen, solvent can be injected into the pay 10 once start-up has been
achieved. For example,
the Enhanced Solvent Extraction Incorporating Electromagnetic Heating (ESEIEH)
advanced oil
recovery technique as described in U.S. Patent No. 8,616,273, can be used to
produce bitumen
from the pay 10. As will be appreciated, solvent can be used to mobile the
bitumen at lower
temperatures than, for example, steam-based heating techniques.
[0067] In an implementation where the ESEIEH process is used during
production, RF
heating can be used to heat the pay 10 prior to solvent injection. When the
pay 10 reaches the
desired temperature within a desired region, an appropriate solvent can be
injected into the pay
10. The solvent partially mixes with the bitumen and further reduces its
viscosity and partially
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displaces the hot-diluted bitumen towards the producer well 44. The choice of
solvent can be
similar to existing solvent injection processes. As described above, rapid
heating can be used
during start-up to establish fluid communication between the injector well 42
and the producer
well 44. The flow pathway thus created is then used as the primary conduit to
inject a solvent
from an appropriate well (e.g. the injector well 42).
[0068] The effects of pore dilation caused by electromagnetic radiation
will now be
described with reference to various equations below.
[0069] When the connate water trapped inside the pores is rapidly heated,
such as by RF
radiation, the leakage of pressure from the pores is negligible, especially in
formations with low
permeability. In other words, the hydraulic permeability is effective zero in
such formations, and
therefore a closed boundary system (i.e. undrained system) can be used to
simulate the
pressure change in such formations. Specifically, the change in fluid pressure
per unit change in
the temperature in a bulk porous medium maintaining a constant volume in such
systems can
be given by:
aP 4) f + + 0)Ys Ysf
= (Equation 1)
aT (1)13f ¨ (1 ¨ (1)13saBio, Psf
in which 4) is the porosity of the caprock, yf is the volumetric coefficient
of thermal expansion of
the pore fluid (1/ C), ysf is the volumetric coefficient of thermal expansion
of the porous medium
(1/ C), Pf is the compressibility of the fluid in pore space (1/Pa), 13s is
the compressibility of solid
grains (1/Pa), f3sf is the compressibility of porous medium (1/Pa), and abiot
is the Biot-Willis
coefficient. It is noted that apiaT can also be referred to as the thermal-
pressurization factor
(A), and therefore the above equation can also be written as:
Of 4- (2 HOY, ¨ Ysf
A = (Equation 2)
(I) Pf + (1¨ (I) )PsaBiof + Psf
It is also noted that for water saturated formations, the thermal-
pressurization factor can be
determined based on the chart of FIG. 13A.
[0070] As illustrated in FIG. 20 which compares the thermal expansion of
the fluid portion
(i.e. 4) yf ) and the thermal expansion of the solid-matrix portion (i.e. (2-
1)) Vs - '1s0, the factor
associated with the thermal expansion of the solid-matrix portion is
negligible in comparison to
13
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CA 02883967 2015-03-05
=
the factor associated with the thermal expansion of the fluid portion for
formations with
porosities greater than 8% and temperatures above 25 C. This can be expressed
as:
4)Yf >>(2¨ ()y,¨ Ysf >0.082 .... (Equation 3)
[0071] Table 1 provided below lists the values of the properties used to
generate a
comparison between the thermal expansion of the fluid portion and the thermal
expansion of the
solid-matrix portion in Equation 3.
Table 1: Table of parameters for Clearwater caprock (or shale) formation
Parameter Value
Caprock Thermal Expansion Properties:
Shale porous medium thermal expansion, (ysf),1PC 0.1 x 10-4 A
Shale solid thermal expansion, (y,),1/ C (0.2-0.3) x 104 AB
Pore Fluid Thermal Expansion Properties:
Water thermal expansion (y),1/ C
at 25 C 3.49 x 104
at 100 C 7.73 x 104
at 200 C 12.28 x 10-4
at 300 C 15.29 x 10-4
A Given in Mase, C. W., Smith, L., 1987. Effects of Frictional Heating on the
Thermal, Hydrologic, and Mechanical
Response of a Fault, Journal of Geophysical Research, 92(B7), pp. 6249-6272.
B Given in Wong, R.C.K., Samieh, A.M., 2000. Geomechanical Response of the
Shale in the Colorado Group Near a
Cased Wellbore Due to Heating, Journal of Canadian Petroleum Technology, Vol.
39, No. 8, pp. 30-33.
[0072] It has been found that for media with appreciable porosity, such as
Clearwater shale
formation, the Biot's coefficient (abiot) is approximately equal to 1.
Although it is possible to
measure the Biot's coefficient in a lab using a core sample obtained from a
formation, this test is
rarely performed and therefore experimental value for the Biot's coefficient
of formations such
as Clearwater shale and Colorado shale are generally not readily available.
[0073] By assuming that the Biot's coefficient (abo) is 1 and neglecting
both the thermal
expansion of the solid-matrix portion (i.e. (2- 4)) Vs - ysf) and the solid
grains compressibility (13),
Equation 2 can be simplified as:
4YY f
A ¨ (Equation 4)
(1)13f Psf
14
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CA 02883967 2015-03-05
[0074] Further, for cases in which the porous medium compressibility (NO is
much greater
than the fluid compressibility (13f), such as in the case for water-saturated
shale formations,
Equation 4 can be further simplified as:
A ,z, 4)7 f (Equation 5)
130
since ii sf ,i)pf and it is assumed that:
13sf>> fly; Orf >>(2-4)7s---isf
However, it is noted that in cases where steam is introduced to the medium
either from
vaporization or from diffusion from the steam chamber into the caprock, the
fluid compressibility
would be taken into account in Equation 4.
[0075] In contrast to the above, for cases in which the porous medium
compressibility (13sf)
is much less than the fluid compressibility (I3f), the thermal pressurization
factor (A) equation of
Equation 4 can be simplified as:
A ,,z-,' -.) - - = = (Equation 6)
R f
since of 13,f and it is assumed that:
13sf<<
It is noted that the above assumption is not valid for water-saturated shale
formations, but that
assumption can be valid for steam-saturated caprocks at low temperatures such
as in the case
of shallow caprocks. Using Equation 6 and substituting fluid thermal expansion
and
compressibility with known properties of water, the thermal pressurization
factor for stiff
caprocks saturated with water can be given by the following:
A = ¨aP\ = ________________________ l'w = - - = (Equation 7)
(
aTip 13,,
in which 7w is the thermal expansion of water and 13 w is the compressibility
of the water.
Variation of the incremental thermal pressurization (or thermal pressurization
coefficient) of
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CA 02883967 2015-03-05
water is calculated based on Equation 7 and presented in FIG. 13A for a stiff
caprock (i.e.,
13.0 =0-
[0076] Similarly, using Equation 6 and substituting the fluid thermal
expansion and
compressibility with known properties of steam, the thermal pressurization
factor for stiff
caprocks saturated with steam can be given by the following:
A = (¨al) = 1st = = = (Equation 8)
Pst
in which Yst is the thermal expansion of steam and Rt is the compressibility
of the steam.
[0077] Variation of the incremental thermal pressurization (or thermal
pressurization
coefficient) of steam for drained conditions is calculated based on Equation 8
and presented in
FIG. 13B for a stiff caprock (i.e., põ .0). Variation of other important
parameters for incremental
thermal pressurization of vaporized steam in undrained condition is shown in
the chart of FIG.
13C, and variation in the incremental thermal pressurization of vaporized
steam in undrained
condition vs. injection temperature and pressure is shown in the chart of FIG.
13D.
[0078] Neglecting the condensate convection and temperature independent
thermal
conductivity, the partial differential equation governing the thermal
transport in RF heating can
be expressed as:
a21" 1T 1 __ x 2 2 ( r a)] = 1 1'1 ....
F exp[ zA
(Equation 9)
ar2 r or K x 2nr L oRF ntenna Antenn
"RF KThermal )
in which K is the oil sand thermal conductivity (W/m- C), L is the length of
antenna, 6RF is the
penetration depth of RF radiation (m), -15174F is the total RF power radiated
across the radius
(J/sec=m3), ZAntenna is the vertical distance from antenna center (m),
rAntenna is the mean radius of
the RF antenna (m), [(Thermal is the thermal diffusivity (m2/sec).
[0079] For medium with low conductivity (i.e. non-metallic) and/or relative
permeability of
approximately one, such as typical oil sands at high frequencies, the
penetration depth (5RF) of
RF radiation can be determined based on the following equation:
8õ 0.0053 piTE7 = 0.0053 r .............. l CT/WCoer
(Equation 10)
a
16
22690332.1
CA 02883967 2015-03-05
in which Er is the relative permittivity, which is also known as the
dielectric constant of the
medium, and a is the electric conductivity.
[0080] As previously described, the connate water can be rapidly heated
using RF radiation
in absence of any fluid injection. In such an implementation, the dissipation
of heat generated by
RF heating is negligible and therefore the conductive term can be neglected to
simplify Equation
9 as follows:
1
___________ X __ 2 exp [ RF at 2 (Z Antenna ) ¨aT
(Equation 11)
6 Antenna r Antenna -
27crL pr cpr oRF
in which Pr is the bulk density of the oil sand (kg/m3), and cpr is the
specific heat capacity of the
medium (J/kg= C).
[0081] Solution for Equation 11 is given by:
1
- Tres = __________________ !IF exp [- R2 (zAntenna -rAntenna)] t
(Equation 12)
n Pr Cpr6RFzAntenn L "RF
in which Tres is the initial reservoir temperature and Tz is the temperature
of the reservoir at a
distance of z meters from the antenna.
[0082] Based on the above, the pressure induced in the formation by RF
heating can be
expressed as:
APRF =
-F(2-4)'y s -7sf 1 ____________ (ZAntenna rAntenna ) ........ t
(Equation 13)
(1)13f (1¨ 4)13sa5l0t Psf n Pr CprkFzAntenn L RF exp[- "RFii
[0083] For "stiff" formations in which the porous medium compressibility
(I3g) is much less
than the fluid compressibility (I3f), it can be seen that 413r >> f3sr, and
therefore the change in
pressure can be expressed as:
1 2 2
APRF ={ YwRFexp(zAntenna rntenna) t =CRF exp
Ar ntenna t = = = (Equation 14)
13 ¨A
I3w it Pr Cpr6RFZAntenn "RF \ "RF
in which:
1
CRF eXP ¨ ¨2ZAntenna = = = = (Equation 15)
13w TCPr Cpr8RFzAntenn SRF
17
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[0084] The pressure of water and vaporized steam after thermal-
pressurization at reservoir
temperature of 5 C is shown in FIGs. 14A and 14B. Similar data for thermal
pressurization in oil
sand and clay and other known formations are shown in FIGs. 15 and 16.
[0085] Assuming radial flow into a well opened over entire thickness,
single phase, slightly
compressible fluid, constant viscosity, ignoring the gravity, constant
permeability and porosity,
the governing equation for pressure distribution including pressure rise due
to RF-heating is as
follows:
a2p ap 1 (ap)
2+ APRF = = = = = (Equation 16)
¨ar1j¨tar
KHydraulic at
in which KHydraulic is the hydraulic diffusivity (m2/sec).
[0086] Substituting Equation 14 into Equation 16, the following is
obtained:
a2p 1P 2 1
¨+--+CRF exp ______________ rAntenna t = = ' ' = ' (Equation 17)
ar2 r ar \,61iF ) KHydraulic
[0087] For Equation 17, boundary conditions can be given as follows:
P( rw)=13,,,
P(co) =
and the initial condition can be as follows:
P(t=0)=P,
[0088] Additional details relating to the mathematical equations discussed
above are
provided in the following references, which are incorporated herein by
reference in their entirety:
- Ghannadi, S., Irani, M., Chalaturnyk, R., 2014a. Evaluation of Induced
Thermal
Pressurization in Clearwater Shale Caprock in Electromagnetic Steam-Assisted
Gravity-
Drainage Projects, SPEJ, 19(03): 443-462.;
- Ghannadi, S., Irani, M., Chalaturnyk, R., 2014b. Induction and Radio
Frequency Heating
Strategies for Steam-Assisted Gravity Drainage Start-Up Phase, SPE Heavy Oil
Conference-Canada, 10-12 June, Alberta, Canada.
18
22690332.1
CA 02883967 2015-03-05
- Ghannadi, S., Irani, M., Chalaturnyk, R., 2014c. Understanding the
Thermo-
Hydromechanical Pressurization in Two-Phase (Steam/Water) Flow and its
Application
in Low-Permeability Caprock Formations in Steam-Assisted-Gravity-Drainage
Projects,
SPEJ.
[0089] Various charts related to properties of water, steam, and vaporized
steam are
shown in FIG. 17.
[0090] It will be appreciated that although various aspects and embodiments
of the present
method and system have been described in relation to SAGD-type well
configurations, the
method and system can be similarly implemented in other types of well
configurations, and in
particular, other gravity drainage well configurations. It will also be
appreciated that while
various aspects and embodiments of the present method and system have been
described with
reference to a pair of wells (i.e. the injector well 42 and the producer well
44), the present
method and system can be similarly implemented in other well configurations in
which there are
lesser or greater number of wells drilled into the reservoir.
[0091] It will be appreciated that any module or component exemplified
herein that
executes instructions can include or otherwise have access to computer
readable media such
as storage media, computer storage media, or data storage devices (removable
and/or non-
removable) such as, for example, magnetic disks, optical disks, or tape.
Computer storage
media can include volatile and non-volatile, removable and non-removable media
implemented
in any method or technology for storage of information, such as computer
readable instructions,
data structures, program modules, or other data. Examples of computer storage
media include
RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital
versatile
disks (DVD) or other optical storage, magnetic cassettes, magnetic tape,
magnetic disk storage
or other magnetic storage devices, or any other medium which can be used to
store the desired
information and which can be accessed by an application, module, or both. Any
such computer
storage media can be part of the controller 220, RF transmitters 210, or any
component of or
related thereto, or accessible or connectable thereto. Any application or
module herein
described can be implemented using computer readable/executable instructions
that can be
stored or otherwise held by such computer readable media.
[0092] For simplicity and clarity of illustration, where considered
appropriate, reference
numerals can be repeated among the figures to indicate corresponding or
analogous elements.
19
22690332.1
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In addition, numerous specific details are set forth in order to provide a
thorough understanding
of the examples described herein. However, it will be understood by those of
ordinary skill in the
art that the examples described herein can 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 examples described herein. Also, the description is
not to be
considered as limiting the scope of the examples described herein.
[0093] The examples and corresponding diagrams used herein are for
illustrative purposes
only. Different configurations and terminology can be used without departing
from the principles
expressed herein. For instance, components and modules can be added, deleted,
modified, or
arranged with differing connections without departing from these principles.
[0094] The steps or operations in the flow charts and diagrams described
herein are just for
example. There can be many variations to these steps or operations without
departing from the
principles discussed above. For instance, the steps can be performed in a
differing order, or
steps can be added, deleted, or modified.
[0095] Although the above principles have been described with reference to
certain specific
examples, various modifications thereof will be apparent to those skilled in
the art as outlined in
the appended claims.
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