Note: Descriptions are shown in the official language in which they were submitted.
CA 02786106 2012-08-13
METHODS AND SYSTEMS FOR IN-SITU EXTRACTION OF BITUMEN
This application claims priority to U.S. Provisional Patent Application No.
61/522,904, filed August 12, 2011, the entirety of which is hereby
incorporated by
reference.
BACKGROUND
Deposits of bituminous material can be found throughout the world, including
in the United States and Canada. Depending on the depth of the bituminous
material,
various methods can be used to extract bitumen from bituminous deposits. When
the
bituminous material is located relatively close to the surface, surface mining
can be
used to remove the bituminous material from the ground. However, deeper
deposits of
bituminous material cannot be economically obtained through surface mining.
Accordingly, methods involving the use of well bores drilled into the
bituminous
deposits have been developed.
One such method for obtaining deeper deposits of bituminous material is the
Steam Assisted Gravity Drainage (SAGD) method. The SAGD method generally
includes injecting steam into the bituminous deposit to warm the bituminous
material
and make it flowable. Once the viscosity of the bituminous material is
sufficiently
lowered, the bituminous material can flow downwardly to a horizontal
production well
that is positioned below the horizontal well used to inject steam into the
deposit.
While the SAGD method can be relatively effective in extracting bituminous
material
from bitumen deposits, other methods that do not require the use of water and
that
provide better bitumen extraction rates are desired.
The use of solvents to extract bitumen from mined oil sands or the like is
considered an effective method for separating bitumen from other components of
the
oil sands material. The solvent is generally used to dissolve the bitumen,
after which
the bitumen-loaded solvent is separated from the sand, clay, and other
components of
the oil sands. The injection of solvent into a deposit of oil sands to
dissolve the
bitumen would appear to be an effective means for extracting bitumen from a
1
CA 02786106 2012-08-13
bituminous deposit, but several problems are associated with solvent injection
into the
ground that have prevented the method from being feasible.
One primary problem with injecting solvent into the oil sands deposit is that
it
has been difficult or impossible to recover a sufficient amount of the
injected solvent
to make the process economical. For example, in some instances, only 25% of
the
solvent injected into the deposit can be recovered. The cost of having to
replenish
large amounts of solvent to continue the process generally makes the process
uneconomical.
An additional problem with injecting solvent into the oil sands deposits
relates
to the environmental concerns of injecting potentially hazardous solvent
material into
the ground without any effective way of recovering the solvent or preventing
the
solvent from migrating to a location outside of the oil sands deposit. For
example, if
the oil sands deposit is near an aquifer, then concerns arise regarding the
flow of
solvent out of the oils sands deposit and into the aquifer, where potential
well water
would be contaminated.
SUMMARY
The foregoing and other features, utilities and advantages of the invention
will
be apparent from the following more particular description of a preferred
embodiment
of the invention as illustrated in the accompanying drawings.
In some embodiments, a method of in-situ bitumen extraction is disclosed, the
method including a step of forming one or more vertical freeze walls within or
around
a deposit of bituminous material and establishing a laterally confined deposit
of
bituminous material; a step of injecting a first solvent within the laterally
confined
deposit of bituminous material; a step of withdrawing a mixture of dissolved
bitumen
and first solvent from within the laterally confined deposit of bituminous
material; a
step of injecting a second solvent within the laterally confined deposit of
bituminous
material; a step of withdrawing a mixture of first solvent and second solvent
from
within the laterally confined deposit of bituminous material; a step of
injecting
water within the laterally confined deposit of bituminous material; and a step
of
2
CA 02786106 2012-08-13
withdrawing a mixture of second solvent and water from within the laterally
confined
deposit of bituminous material.
In some embodiments, a system for in-situ bitumen extraction is disclosed, the
system including a plurality of vertical freeze wall bores formed in a deposit
of
bituminous material and aligned in a geometric pattern; a refrigerant source
in fluid
communication with the plurality of vertical freeze wall bores; a plurality of
vertical injection bores formed win the deposit of bituminous material and
located
within the geometric pattern of the plurality of freeze walls; a water source
in fluid
communication with the plurality of vertical injection bores; a first solvent
source in
fluid communication with the plurality of vertical injection bores; optionally
a
second solvent source in fluid communication with the plurality of vertical
injection
bores; and a plurality of vertical production wells formed in the deposit of
bituminous
material and located within the geometric pattern of the plurality of freeze
walls.
The foregoing and other features and advantages of the present application
will
become more apparent from the following detailed description, which proceeds
with
reference to the accompanying figures. In this regard, it is to be understood
that the
scope of the invention is to be determined by the claims as issued and not by
whether
given subject includes any or all features or aspects noted in this Summary or
addresses any issues noted in the Background.
BRIEF DESCRIPTION OF THE DRAWING
The preferred and other embodiments are disclosed in association with the
accompanying drawings in which:
Figure 1 is flow chart of embodiments of an in-situ bitumen extraction method
described herein;
Figure 2 is an aerial view of a configuration of well bores formed in a
deposit
of bituminous material in accordance with some embodiments described herein;
Figure 3 is an aerial view of a configuration of well bores formed in a
deposit
of bituminous material, including a two loop refrigerant circulation system
according
to some embodiments described herein;
CA 02786106 2012-08-13
Figure 4 is a cross-sectional view of a bituminous deposit having a vertical
injection well and a vertical production well formed therein in accordance
with some
embodiments described herein;
Figure 5 is a cross-sectional view of a bituminous deposit having a horizontal
injection well and a horizontal production well formed therein in accordance
with
some embodiments described herein; and
Figure 6 is a cross-sectional view of a composite injection according to some
embodiments described herein.
DETAILED DESCRIPTION
With reference to Figure 1, some embodiments of a method of in-situ extraction
of bitumen generally include a step 100 of forming one or more vertical freeze
walls
within or around a deposit of bituminous material and establishing a laterally
confined
deposit of bituminous material, a step 110 of injecting a first solvent within
the
laterally confined deposit of bituminous material, a step 120 of withdrawing a
mixture
of dissolved bitumen and first solvent from within the laterally confined
deposit of
bituminous material, a step 130 of injecting a second solvent within the
laterally
confined deposit of bituminous material, a step 140 of withdrawing a mixture
of first
solvent and second solvent from within the laterally confined deposit of
bituminous
material, a step 150 of injecting water within the laterally confined deposit
of
bituminous material, and a step 160 of withdrawing a mixture of second solvent
and
water from within the laterally confined deposit of bituminous material. Such
embodiments can successfully confine material injected into the bituminous
deposit
within a prescribed area. Similarly, mixtures of dissolved bitumen and solvent
created
by injecting material into the bituminous deposit are maintained within the
area
defined by the freeze walls. Accordingly, contamination of, for example,
underground
water sources can be mitigated or prevented and recovery of dissolved bitumen
can be
enhanced by providing barriers around the bitumen deposit being subjected to
the
bitumen extraction processes.
In step 100, one or more vertical freeze walls are formed within or around a
deposit of bituminous material. The vertical freeze walls formed within or
around the
4
CA 02786106 2012-08-13
deposit of bituminous material form a boundary around all or a portion of the
deposit
of bituminous material and establish a laterally confined deposit of
bituminous
material. An objective of step 100 is to provide vertical boundaries that will
prevent
material injected into the deposit of bituminous material and mixture of
materials
formed within the bituminous deposit from traveling outside of the laterally
confined
area, thus alleviating environmental concerns of in-situ bitumen extraction
and making
collection of dissolved bitumen easier.
The deposit of bituminous material in which the vertical freeze walls are
formed in step 100 can be any suitable deposit of bituminous material.
Suitable
deposits of bituminous material include tar sands or oil sands formations,
such as
those located in the Athabasca region of Canada. In some embodiments, the
deposit of
bituminous material is a deposit or a portion of a deposit that is located at
a depth that
is too deep for surface mining but too shallow for traditional in-situ bitumen
extraction methods such as stream assisted gravity drainage (SAGD). In some
embodiments, the deposit of bituminous material is located at a depth of from
between
250 feet and 1,500 feet below the surface.
The one or more freeze walls formed in the deposit of bituminous material can
be any type of freeze wall capable of slowing or preventing the movement of
fluids
through the freeze wall. The freeze walls are typically made from water that
is
naturally present in the ground in a liquid form. By freezing this water, a
barrier of
ice is created in the ground. Freeze walls can be formed in deposits of
bituminous
material because bituminous material (such as oil sands deposits) typically
includes a
water content.
Any manner of forming the one or more freeze walls known to those of
ordinary skill in the art can be used in the embodiments of this method. In an
exemplary method, a series of interconnected vertical well bores are
constructed
within or around the deposit of bituminous material, and a refrigerant is
circulated
through the vertical well bores until the water in the ground proximate the
vertical
well bores freezes. The refrigerant can be continuously circulated through the
vertical
well bores to ensure the water remains frozen and the freeze walls remain
intact. Any
suitable refrigerant can be used, such as brine or ammonia. In some
embodiments. the
5
CA 02786106 2012-08-13
refrigerant is circulated within the well bores for a period of from 6 weeks
to 16 weeks
in order to establish the freeze walls.
The arrangement and spacing of the vertical well bores within or around the
deposit of bituminous material can be any suitable arrangement for providing
freeze
walls. In some embodiments, the vertical well bores are spaced close enough
together
that the water in the area between two adjacent vertical well bores can be
frozen to
create a vertical freeze wall. In some embodiments, the well bores are spaced
apart
approximately 2 to 6 meters from one another.
The dimensions of the well bores can vary based on the specific application
but
are typically selected to ensure that a suitable amount of refrigerant passes
through the
well bores to freeze the water in the surrounding ground. In some embodiments,
the
well bores have a diameter in the range of from 3 to 15 inches. The depth of
the well
bores can be dependent on a variety of factors. In some embodiments, the depth
of the
well bores is selected based on the depth of the deposit of bituminous
material and/or
the depth of any bed rock or other geological formation that might be located
beneath
the deposit of bituminous material. A bed rock or other geological formation
below
the deposit of bituminous material can serve as a lower horizontal boundary
for the
deposit of bituminous material, so it can be beneficial to extend the well
bores down
to abut a rock formation or the like. Generally speaking, the well bores will
have a
depth of from 100 to 1,500 feet.
In some embodiments, the vertical well bores are arranged in a closed
geometric pattern (when looking down at the vertical well bores from above) to
thereby create vertical freeze walls that enclose a deposit of bituminous
material. Any
suitable closed geometric shape can be used. With reference to Figure 2, the
vertical
well bores 200 are arranged in a rectangular shape, with each side of the
rectangle
including several well bores 200. The well bores 200 are spaced close enough
to
freeze the area 210 between each well bore 200 and ultimately form a series of
vertical
freeze walls arranged in a rectangular shape and enclosing a deposit of
bituminous
material 220.
The well bores used to form the freeze walls are generally constructed by
drilling vertical holes into the deposit of bituminous material and providing
piping
6
CA 02786106 2012-08-13
within the drilled holes. The piping can be any suitable type of piping, but
is typically
of a type that is impermeable to fluids and has good heat transfer for
allowing the
refrigerant to freeze the water proximate the piping. The piping may also have
structural additions to improve heat transfer, such as a plurality of fins
extending out
from the piping. As noted above, the piping provided in the drilled holes can
be
interconnected with piping in adjacent drilled holes such that the refrigerant
can
circulate throughout the plurality of well bores.
In some embodiments, the well bores constructed for establishing freeze walls
in the deposit of bituminous material can include a two loop system of
interconnected
well bores. The two loop system allows for refrigerant to be supplied into the
interconnected well bores in a first loop and for refrigerant to be removed
from the
interconnected well bores in a second loop. With reference to Figure 3, the
two loop
system 300 provides a first loop 310 where refrigerant is introduced into the
system to
flow through the well bores 350 and create and/or maintain freeze walls. The
first
loop 310 extends around the closed geometric arrangement of well bores 350 and
is in
fluid communication 315 with each of the well bores 350 such that refrigerant
introduced into the first loop 310 can travel to each of the well bores 350
and provide
refrigerant into the well bores 350. The two loop system also includes a
second loop
320. Like first loop 310, second loop 320 extends around the closed geometric
arrangement of well bores 350 and is in fluid communication 325 with each of
the well
bores 350. Second loop 320 receives refrigerant that has flowed through the
well
bores 350 and provides a path 360 for the refrigerant to leave the system 300.
In some
embodiments, the first loop 310 will be in fluid communication at a bottom end
of
each well bore 350 and the second loop 320 will be in fluid communication with
the
top end of each well bore 350 such that new refrigerant is introduced into
each well
bore 350 at the bottom via the first loop 310 and then exits the well bore 350
at the top
via the second loop 320. The opposite arrangement can also be used. The two
loop
system 300 provides a manner for fresh refrigerant to be introduced into the
system
and for used refrigerant to be taken out of the system, where it can be
reconditioned
and reinjected back into the well bores 350.
7
CA 02786106 2012-08-13
Well bores as described above are not the only mechanism that can be used to
create the freeze walls in step 110. In some embodiments, freeze walls can be
formed
using thermosyphons. Thermosyphons generally include a fully enclosed system
having a low temperature fluid (such as liquid CO2, or ammonia) circulating
inside.
Natural convection allows the liquid to pick up heat from the bed rock at the
bottom of
the closed system below and convert to a vapor. The vapor rises to the top of
the
system, where cooling occurs (such as wind cooling via radiators) to convert
the vapor
back to liquid. The cooled liquid drains back to the bottom of the system, and
the
process repeats.
As noted above, bed rock or other geological formations can be used to serve
as
a lower horizontal barrier of the confined deposit of bituminous material.
However,
natural barriers may not always be available. Accordingly, in some
embodiments,
steps can also be taken to form a horizontal freeze wall that will serve as a
barrier that
vertically confines the deposit of bituminous material. Generally speaking,
such a
horizontal freeze wall will extend up to or beyond the vertical freeze walls
laterally
confining the deposit of bituminous material. It can also be preferable to
have the
horizontal freeze wall abut the bottom end of the vertical freeze walls. In
this manner,
the material injected into the confined deposit of bituminous material will be
prevented from leaving the confined area in both a lateral direction and in a
downward
direction.
Any suitable manner of forming horizontal freeze walls can be used. In some
embodiments, the manner of forming the horizontal freeze wall is similar or
identical
to the manner in which the vertical freeze walls are used. For example,
directional
drilling techniques can be used to form a plurality of horizontal well bores
through
which refrigerant can flow in order to freeze the water in the ground between
adjacent
horizontal well bores.
In step 100, the vertical freeze walls formed serve to laterally confine a
deposit
of bituminous material. When bed rock (or other geological formation) or a
horizontal
freeze wall are used in conjunction with the vertical freeze walls, a "bath
tub"
configuration is provided that is capable of retaining liquid material within
the
confined "bath tub" area. Accordingly, when solvents are injected into the
confined
8
CA 02786106 2012-08-13
area of bituminous material, the "bath tub" configuration mitigates or
eliminates
concerns related to injected solvent drifting out of the area undergoing
bitumen
extraction and into, for example, underground water sources. Similarly, the
"bath tub"
configuration helps to keep dissolved bitumen within a confined area, which
helps
make withdrawing dissolved bitumen from the deposit of bituminous material
more
effective and efficient.
In step 110, a first solvent is injected into the laterally confined deposit
of
bituminous material. The injected first solvent is injected to dissolve
bitumen and
create a dissolved bitumen (or "disbit") phase within the deposit. Once
dissolved, the
mixture of bitumen and solvent can be withdrawn from the deposit to thereby
extract
bitumen.
The first solvent used in step 110 may include a hydrocarbon solvent. Any
hydrocarbon solvent or mixture of hydrocarbon solvents that is capable of
dissolving
bitumen can be used. In some embodiments, the hydrocarbon solvent is a
hydrocarbon
solvent that does not result in asphaltene precipitation. The hydrocarbon
solvent or
mixture of hydrocarbon solvents can be economical and relatively easy to
handle and
store. The hydrocarbon solvent or mixture of hydrocarbon solvents may also be
generally compatible with refinery operations.
In some embodiments, the first solvent is a light aromatic solvent. The light
aromatic solvent is an aromatic compound having a boiling point temperature
less than
about 400 C at atmospheric pressure. In some embodiments, the light aromatic
solvent used in the first mixing step is an aromatic having a boiling point
temperature
in the range of from about 75 C to about 350 C at atmospheric pressure, and
more
specifically, in the range of from about 100 C to about 250 C at atmospheric
pressure.
It should be appreciated that the light aromatic solvent need not be 100%
aromatic compounds. Instead, the light aromatic solvent may include a mixture
of
aromatic and non-aromatic compounds. For example, the first solvent can
include
greater than zero to about 100 wt% aromatic compounds, such as approximately
10
wt% to 100 wt% aromatic compounds, or approximately 20 wt% to 100 wt% aromatic
compounds.
9
CA 02786106 2012-08-13
Any of a number of suitable aromatic compounds may be used as the first
solvent. Examples of aromatic compounds that can be used as the first solvent
include
benzene, toluene, xylene, aromatic alcohols and combinations and derivatives
thereof.
The first solvent can also include compositions, such as kerosene, diesel
(including
biodiesel), light gas oil, light distillate, commercial aromatic solvents such
as
Solvesso 100, Solvesso 150, and Solvesso 200 (also known in the U.S.A. as
Aromatic
100, 150, and 200, including mainly C10-C11 aromatics, and produced by
ExxonMobil),
and/or naphtha. In some embodiments, the first solvent may have a boiling
point
temperature of approximately 75 C to 375 C. Naphtha, for example, is
particularly
effective at dissolving bitumen and is generally compatible with refinery
operations.
In some embodiments, a portion or all of the first solvent is derived from
bitumen recovered by the in-situ bitumen extraction process described herein.
The
bitumen extracted by the process described herein can be subjected to
distillation
processing to separate a light end portion of the bitumen that is suitable for
use as a
first solvent in the process described herein. In some embodiments, the light
end
portion of the recovered bitumen is a fraction of the bitumen having a boiling
point
temperature in the range of up to 225 C.
Any distillation methods capable of separating fractions of bitumen material
known to those of ordinary skill in the art can be used, including the use of
atmospheric or vacuum distillation towers. In some embodiments, a make-up
first
solvent, such as any of the above discussed first solvents, can be mixed with
the light
end portion of the bitumen in order to provide a suitable amount of first
solvent for the
process. Obtaining a portion or all of the first solvent from the bitumen
recovered by
the in-situ bitumen extraction process described herein can be useful in that
the
process can become essentially self-sustainable. Additionally, use of first
solvent
derived from the recovered bitumen can reduce or eliminate environmental
concerns
associated with using non-indigenous or commercial solvents.
In some embodiments, the first solvent suitable for use in step 110 includes a
bitumen content, and can therefore be considered as disbit or dilbit. The
first solvent
having a bitumen content may be solvent obtained from a step of solvent
extraction
process performed on bituminous material, such as tar sands or oil sands.
CA 02786106 2012-08-13
The amount of first solvent injected into the laterally confined deposit of
bituminous material can be any suitable amount of first solvent needed for
dissolving
bitumen. In some embodiments, the amount of solvent injected into the deposit
of
bituminous material will depend on the quality of the deposit of bituminous
material
(i.e., the bitumen content of the bituminous material). Larger bitumen
contents can
require larger amounts of first solvent to ensure as much bitumen as possible
is
dissolved into a disbit phase. The amount of first solvent injected into the
deposit of
bituminous material can also vary on the size of the area being subjected to
bitumen
extraction. In some embodiments, the amount of first solvent injected into the
deposit
ranges from 0.5:1 to 5:1.
In some embodiments, the desired amount of first solvent is injected into the
deposit of bituminous material and is then allowed to stay in the deposit of
bituminous
material for a period of time before production wells are used to remove any
disbit
formed. Holding the first solvent into the deposit of bituminous material
allows for
the first solvent to migrate to a larger area and have sufficient time to
dissolve the
bitumen. In some embodiments, the first solvent is held in the deposit of
bituminous
material for a period of from I day to 1 month.
Any suitable technique for injecting solvent into the laterally confined
deposit
of bituminous material can be used in step 110. In some embodiments, one or
more
injection wells are formed in the laterally confined area, which allows for
solvent to
flow down and into the bituminous material bound by the freeze walls. Once the
solvent is injected into the confined deposit of bituminous material, the
solvent works
to dissolve the bitumen and create a disbit phase within the deposit of
bituminous
material. The injection wells can be paired with production wells capable of
drawing
the disbit phase out of the deposit of bituminous material and up to the
surface.
The injection wells can be any type of injection wells suitable for injecting
solvent into a deposit of bituminous material, and can be constructed by any
suitable
technique used by those or ordinary skill in the art to construct injection
wells.
Similarly, production wells used to draw fluid material out of the deposit of
bituminous material (such as disbit) can be any suitable type of production
well and
can be constructed by any suitable technique for constructing production
wells. In
11
CA 02786106 2012-08-13
some embodiments, the injection wells and productions wells are similar enough
that
injection wells can be transformed into production wells with minimal
modifications.
The dimensions of the production wells and injection wells can be any suitable
dimensions needed to carry out the in-situ bitumen extraction. The length of
the
injection wells and the production wells will generally be equal to or
slightly shorter
than the depth of the deposit of bituminous material. The diameter of the
injection
wells and production wells can vary, and in some embodiments, range from 6 to
12
inches.
With reference to Figure 4, the injection wells formed in the laterally
confined
area can be vertical injection wells 410 that have a plurality of injection
ports 415
located along the height of the injection well 410 for injecting solvent into
the deposit
of bituminous material 400 at various depths. The injection ports 415 are
capable of
injecting solvent into the deposit of bituminous material 400, and in some
cases will
generally inject solvent into the bituminous deposit 400 at a direction
perpendicular to
the vertical injection well 410. The vertical injection wells 410 can be
paired with
vertical production wells 430 that are spaced apart a distance from the
injection wells
410. In this manner, the vertical production wells can collect the mixture of
solvent
and dissolved bitumen produced upon injecting solvent into the deposit of
bituminous
material 400.
With reference to Figure 5, the injection wells formed in the laterally
confined
area can also be a series of horizontal injection wells 510. The horizontal
injection
wells 510 generally have an L-shaped configuration that includes a vertical
portion
510a and a horizontal portion 510b. Solvent travels down into the deposit of
bituminous material 500 via the vertical portion 510a and is injected into the
deposit
of bituminous material 500 via the horizontal portion 510b. In some
embodiments, a
plurality of injection ports 515 are located along the length of the
horizontal portion
510b of the horizontal injection well 510 such that solvent is injected into
the deposit
of bituminous material 500 at various locations along the length of the
horizontal
portion 510b of the horizontal injection well 510. In some embodiments, the
injection
ports 515 are oriented to inject solvent upwardly into the bituminous deposit
500.
Horizontal production wells 530 can also be included to withdraw the disbit
formed
12
CA 02786106 2012-08-13
upon the injection of solvent into the deposit of bituminous material 500 via
the
horizontal injection well 510. In some embodiments, the horizontal production
wells
530 have a vertical portion 530a and horizontal portion 530b. The horizontal
portion
530b can be located parallel to and below the horizontal portion 510b of the
horizontal
injection well 510. The disbit formed above the horizontal portion 510b flows
downwardly where it collected in the horizontal portion 530b of the horizontal
production well 530. The collected disbit is then transported up the vertical
portion
530a of the horizontal production well 530 to the surface.
The injection wells and production wells are formed within the area of
bituminous material confined by the freeze walls established in step 100. The
arrangement of the plurality of injection wells and production wells is
generally not
limited and can include any arrangement that will provide for multiple solvent
injection locations and multiple disbit production locations. Generally
speaking, the
injection wells and production wells are located close enough to one another
that the
production wells can receive the disbit created by injecting solvent into the
deposit of
bituminous material via the injection wells. In some embodiments, a production
well
is located from 50 to 100 feet from an injection well.
In some embodiments, more injection wells than production wells will be
provided within the deposit of bituminous material confined by the freeze
walls, such
as from 2 to 6 injection wells per production well. The arrangement of
injection wells
and production wells can include various geometric shapes and patterns. One
exemplary arrangement involves a hexagonal matrix of production wells
surrounding
an injection well located in the middle of the hexagon.
In some embodiments where vertical injection wells and production wells are
used, the arrangement of injection wells and production wells can be a
straight line
arrangement of injection wells and a straight line arrangement of production
wells
parallel to the injection wells and spaced apart a suitable distance. The
straight lines
of injection wells and production wells can be located relatively close to one
of the
freeze walls making up the boundary of the confined deposit of bituminous
material,
and can also be oriented in parallel to that freeze wall. Thus, for example,
in a
rectangular shaped confined deposit of bituminous material, a straight line of
injection
13
CA 02786106 2012-08-13
wells can be located next to and in parallel with a freeze wall, while a
straight line of
production wells can be located next to and in parallel with the straight line
of
injection wells, and further away from the freeze wall then the injection
wells. The
injection ports on the injection wells can be pointed in a direction towards
the
production wells (i.e., away from the freeze wall) to extract bitumen from the
area
closest to the freeze wall. Once this area has been sufficiently treated, the
injection
wells can be decommissioned, the production wells can be converted to
injection wells
(including positioning injection ports in a direction away from the freeze
wall), and a
new straight line of production wells can be formed further into the confined
area and
in parallel with the straight line of injection wells. The space between the
new
injection wells and the new production wells can be treated for a sufficient
period of
time, after which the above described process of converting production wells
into
injection wells and forming new production wells is repeated. This cycle can
be
repeated until the entire length of the rectangular confined area is subjected
to bitumen
extraction. Such a system can be referred to as a "line drive" process of
extracting
bitumen.
In some embodiments, the injection of first solvent is followed by an
agitation
step in order to promote mixing between the solvent and the bituminous
material. Any
suitable manner of causing agitation within the bituminous deposit can be
used. In
some embodiments, the agitation step includes a gas injection or gas pulsation
step. In
both gas injection and gas pulsation, the introduction of the gas into the
deposit leads
to improved mixing between the solvent and the bituminous material, which in
turn
leads to more bitumen dissolving in the solvent.
The gas injection or gas pulsation step can be carried out using the injection
wells described in greater detail above. For example, in gas injection, the
gas is
injected into the deposit via the same injection wells used to inject the
solvent into the
bituminous deposit. Any gas suitable for use in agitating the solvent in the
bituminous
deposit can be used. In some embodiments, the gas is unreactive to the
materials in
the bituminous deposit such that the injection of the gas leads to primarily
the
mechanical agitation of the solvent and not to the reaction between the gas
and the
14
CA 02786106 2012-08-13
solvent or materials in the bituminous deposit. Exemplary gasses that can be
used
include but are not limited to natural gas, nitrogen, air, and carbon dioxide.
In some embodiments, the gas is preferably injected into the bituminous
deposit
at relatively high volumes to ensure agitation. In some embodiments, the gas
is
injected into the bituminous deposit at a rate of 0.20 to 1.45 BCFD (depending
on the
geologic conditions and oil production rate) or, in some embodiments, from 130
BOPD to 600 BOPD per MMCFD of gas injected. When gas pulsation is used, the
frequency of the gas pulsation can be between 2 and 10 Hz. The injection of
first
solvent into the bituminous deposit can be carried out in several cycles, and
in some
embodiments, the agitation step is carried out after every cycle of injecting
first
solvent into the bituminous deposit.
In step 120, a mixture of first solvent and dissolved bitumen produced from
injecting solvent into the deposit of bituminous material in step 1 10 is
withdrawn from
within the laterally confined deposit of bituminous material. Any suitable
manner of
withdrawing the disbit from within the deposit of bituminous material can be
used to
carry out step 120. As discussed in greater detail above, in some embodiments
the
disbit is withdrawn from within the deposit of bituminous material using
production
wells that are located proximate the injection wells. Production wells can be
operated
for extended periods of time, such as up to 9 months, to ensure that the vast
majority
of the disbit produced in step 110 is withdrawn from the deposit. In some
embodiments, the production wells are operated until 90% of the disbit
produced in
step 110 is removed. Step 120 is usually performed after step 110 is
completed, but is
some embodiments, step 120 can be commenced prior to step 1 10 being
completed.
The fluid material withdrawn from within the deposit of bituminous material in
step 120 generally includes first solvent and dissolved bitumen. Other
materials that
can be present in the fluid material include water, and organic and inorganic
solids.
Generally speaking, the fluid material withdrawn in step 120 includes from 40
to 75%
first solvent, from 25 to 60% bitumen, from 0 to 5% water. and less than 2%
other
materials. The rate of withdrawing the fluid material is generally not
limited, and in
some embodiments, the fluid is withdrawn from within the deposit of bituminous
material via the production wells at a rate of from about 5,000 to 25.000
bbls/day.
CA 02786106 2012-08-13
Once the mixture of dissolved bitumen and first solvent is brought to the
surface in step 120, various separation steps can take place to separate the
bitumen,
first solvent, and water. Any suitable separation unit or series of separation
units can
be used to separate the bitumen, first solvent, and water, such as
distillation towers.
Once separated, the bitumen can be further processed, such as by being
subjected to
upgrading to produce useful lighter hydrocarbons. The recovered first solvent
can be
reused in the bitumen extraction process, such as by reusing the first solvent
in step
110.
Steps 110 and 120 described above can be repeated several times prior to
moving on to the injection of a second solvent. Performing multiple cycles of
injecting first solvent and withdrawing a mixture of first solvent and bitumen
can help
to improve the overall amount of bitumen recovered using the methods described
herein.
In some embodiments, step 120 will not be capable of withdrawing all of the
first solvent injected into the deposit of bituminous material in step 110.
For example,
from 10 to 50% of the first solvent injected into the deposit of bituminous
material
may remain in the deposit after the completion of step 120. For environmental
and
economical reasons, additional steps should be taken to attempt to remove the
first
solvent from the deposit of bituminous material.
In steps 130 and 140, a second solvent is injected into the bituminous
material
to form a mixture of first solvent and second solvent, and then the mixture of
first
solvent and second solvent is withdrawn from the laterally confined deposit of
bituminous material. The second solvent is injected into the bituminous
material in an
effort to mix with and/or displace the first solvent. Injection of the second
solvent can
result in the second solvent pushing the residual first solvent towards the
production
wells, where the production wells can then be used to withdraw the mixture of
first
solvent and second solvent. Additionally, the second solvent may dissolve
further
bitumen not dissolved by the first solvent, and therefore the injection of the
second
solvent can also increase the bitumen extraction rate.
Any suitable solvent capable of mixing with and/or displacing the first
solvent
can be used as the second solvent. In some embodiments, the second solvent
includes
16
CA 02786106 2012-08-13
one or more aliphatic compounds that are capable of solvating bitumen and/or
the first
solvent. Suitable aliphatic compounds can include compounds such as alkanes or
alkenes. Any of these aliphatic compounds can be functionalized or non-
functionalized. In some embodiments, the second solvent includes one or more
aliphatic hydrocarbons having 3 to 5 carbon atoms. In some embodiments, the
second
solvent includes aliphatic hydrocarbons having no more than 5 carbon atoms.
The
second solvent can also include lower carbon paraffins, such as cyclo- and iso-
paraffins having 3 to 5 carbon atoms. Exemplary second solvents include, but
are nor
limited to, methane, ethane, propane, butane, and/or pentane, alkene
equivalents of
these compounds and/or combinations and derivatives thereof.
In some embodiments, the second solvent is a polar solvent. Any polar solvent
capable of displacing the first solvent can be used in step 130. In some
embodiments,
the polar solvent may be an oxygenated hydrocarbon. Oxygenated hydrocarbons
may
include any hydrocarbons having an oxygenated functional group. Oxygenated
hydrocarbons may include alcohols, ketones and ethers. Oxygenated hydrocarbons
as
used in the present application do not include alcohol ethers or glycol
ethers.
Suitable alcohols for use as the polar solvent may include methanol, ethanol,
propanol, and butanol. The alcohol may be a primary (e.g., ethanol), secondary
(e.g.,
isopropyl alcohol) or tertiary alcohol (e.g., tert-butyl alcohol).
As noted above, the polar solvent may also be a ketone. Generally, ketones are
a type of compound that contains a carbonyl group (C=O) bonded to two other
carbon
atoms in the form: R1(CO)R2. Neither of the substituents RI and R2 may be
equal to
hydrogen (H) (which would make the compound an aldehyde). A carbonyl carbon
bonded to two carbon atoms distinguishes ketones from carboxylic acids,
aldehydes,
esters, amides, and other oxygen-containing compounds. The double-bond of the
carbonyl group distinguishes ketones from alcohols and ethers. The simplest
ketone is
acetone, CH3-CO-CH3 (systematically named propanone).
In some embodiments, the polar solvent is a polar solvent that is miscible
with
the first solvent. By selecting a polar solvent that is soluble in the first
solvent (or in
which the first solvent is soluble), the polar solvent may form a homogenous
mixture
with the first solvent. As some bitumen may be present in the first solvent,
the
17
CA 02786106 2012-08-13
homogenous mixture may also include a bitumen content. This homogenous mixture
of polar solvent and first solvent (and possibly bitumen) can then be
withdrawn from
the deposit of bituminous material via the production wells to help remove
first
solvent from the deposit.
The polar solvent or mixture of polar solvents can be economical and
relatively
easy to handle and store. The polar solvent or mixture of polar solvents may
also be
generally compatible with refinery operations. The polar solvent need not be
100%
polar solvent, although in some embodiments, the polar solvent is made up
entirely of
polar solvent. The polar solvent may include a mixture of polar compounds and
non-
polar compounds. However, in some embodiments, the polar solvent used in step
130
includes more than about 50 wt% polar solvent, and preferably more than about
70
wt% polar solvent.
In some embodiments, the second solvent is a mixture of water and peroxide.
Suitable peroxides for use as the second solvent include those which produce
oxygen
micro-bubbles upon being mixed with hydrocarbon liquids or solids. Exemplary
peroxides suitable for use as the second solvent include hydrogen peroxide,
peroxide
salts, and any compounds capable of producing hydrogen peroxide on
decomposition
in water (e.g., sodium percarbonate).
The presence of the peroxide in the water can help to remove bitumen and
bitumen-laden solvent. The peroxide accomplishes this at least in part by
altering
surface conditions, such as reducing interfacial tension between oil, water,
and
inorganic material of the bituminous deposit (including rocks). Reduced
interfacial
tension can, for example, help release bitumen from within pores in the
bituminous
deposit. Exothermic heat release associated with the use of the peroxides can
also
assist in removal of bitumen and solvent due to the heat release decreasing
the
viscosity of the bitumen and solvent. The decreased viscosity of these
materials
improves flowability and drainage and ultimately makes the material easier to
recover.
The oxygen micro-bubbles formed from the mixing of peroxide and
hydrocarbon material can also be useful in stripping hydrocarbon material such
as
bitumen from inorganic material (such as sand) in the bituminous deposit. It
is
believed that the oil stripped from the sand will form a film on the oxygen
micro-
18
CA 02786106 2012-08-13
bubbles. The stripped bitumen material can then be recovered in the same
manner as
other free bitumen in the bituminous deposit, i.e., by injecting additional
wash
materials (solvents or water) into the bituminous deposit to mix with the
oxygen
micro-bubbles and carry the stripped bitumen out of the deposit via production
wells.
The continuous injection of a second solvent including water and peroxide will
continue to produce the oxygen micro-bubbles having bitumen films within the
deposit
of bituminous material and provide additional free bitumen for recovery from
subsequent in situ wash cycles.
The ratio of peroxide to water injected into the deposit as a second solvent
can
be any suitable ratio that provides for the creation of oxygen micro-bubbles
upon
mixing with hydrocarbon material. In some embodiments, a 10 to 60%
concentration
of peroxide in water is provided.
The manner of injecting second solvent is similar or identical to the manner
in
which the first solvent is injected into the deposit of bituminous material.
The same
injection wells used for injecting first solvent can be used to inject second
solvent.
The amount of second solvent injected into the laterally confined deposit of
bituminous material can be any suitable amount of second solvent needed for
removing the first solvent. In some embodiments, the amount of second solvent
injected into the deposit of bituminous material will depend on the amount of
first
solvent in the deposit. The amount of second solvent injected into the deposit
of
bituminous material can also vary on the size of the area being subjected to
bitumen
extraction. In some embodiments, the amount of second solvent injected into
the
deposit ranges from 5,000 to 25,000 bbls.
In some embodiments, the desired amount of second solvent is injected into the
deposit of bituminous material and is then allowed to stay in the deposit of
bituminous
material for a period of time before production wells are used to remove the
mixture
of first solvent and second solvent. In some embodiments, the second solvent
is held
in the deposit of bituminous material for a period of from I day to I month.
The manner of withdrawing a mixture of first and second solvent from within
the deposit if bituminous material is similar or identical to the manner in
which the
mixture of first solvent and dissolved bitumen is withdrawn from the deposit
of
19
CA 02786106 2012-08-13
bituminous material. The same production wells used to withdraw disbit from
the
deposit can be used to withdraw a mixture of first and second solvent from the
deposit.
The fluid material withdrawn from within the deposit of bituminous material in
step 140 generally includes first solvent and second solvent. Other materials
that can
be present in the fluid material include water, bitumen, and organic and
inorganic
solids. Generally speaking, the fluid material withdrawn in step 140 includes
from 40
to 75% first solvent, from 0 to 80% second solvent, from 0 to 5% water, from
25 to
60% bitumen, and less than 2% other materials. The constituency of the fluid
withdrawn in step 140 can also change over time as the second solvent reaches
the
well head. The rate of withdrawing the fluid material is generally not
limited, and in
some embodiments, the fluid is withdrawn from within the deposit of bituminous
material via the production wells at a rate of from about 5,000 to 25,000
bbls/day.
Once the mixture of first solvent and second solvent is brought to the surface
in
step 140, various separation steps can take place to separate the first
solvent from the
second solvent. Any suitable separation unit or series of separation units can
be used
to separate the first solvent from the second solvent. Once separated, the
first solvent
and the second solvent can both be reused in the extraction process, with the
first
solvent reused in step 1 10 and the second solvent reused in step 130.
As with steps 110 and 120, steps 130 and 140 can be carried out multiple times
in order to improve bitumen extraction and solvent recovery rates. Also, step
130 can
be followed by an agitation step similar or identical to the agitation step
performed
after step 110 as described in greater detail above. Thus, in some
embodiments, each
time second solvent is injected into the bituminous deposit, a gas injection
or gas
pulsation step can be carried out in order to promote mixing between the
injected
second solvent and the residual first solvent and bitumen located in the
bituminous
deposit.
In some embodiments, step 140 will not be capable of withdrawing all of the
second solvent injected into the deposit of bituminous material in step 130.
For
example, from 10 to 50% of the second solvent injected into the deposit of
bituminous
material may remain in the deposit after the completion of step 140. For
CA 02786106 2012-08-13
environmental and economical reasons, additional steps should be taken to
attempt to
remove the second solvent from the deposit of bituminous material.
In steps 150 and 160, water is injected into the bituminous material to
displace
the residual second solvent towards the production wells, where the second
solvent
and water may then be withdrawn from the laterally confined deposit of
bituminous
material. In embodiments where the second solvent is a polar solvent, the
injection of
water is especially useful at displacing the second solvent towards the
production
wells due to the difference in polarity between the polar solvent and water.
The water
injected into the deposit can be in the form of steam or as liquid water.
The manner of injecting water is similar or identical to the manner in which
the
first solvent and second solvent is injected into the deposit of bituminous
material.
The same injection wells used for injecting first solvent and second solvent
can be
used to inject water. The amount of water injected into the laterally confined
deposit
of bituminous material can be any suitable amount of water needed for removing
the
second solvent. In some embodiments, the amount of water injected into the
deposit
of bituminous material will depend on the amount of second solvent in the
deposit.
The amount of water injected into the deposit of bituminous material can also
vary
based on the size of the area being subjected to bitumen extraction. In some
embodiments, the amount of water injected into the deposit ranges from 3:1 to
10:1 on
a water:bitumen ratio.
In some embodiments, the desired amount of water is injected into the deposit
of bituminous material and is then allowed to stay in the deposit of
bituminous
material for a period of time before production wells are used to remove the
mixture
of water and second solvent. In some embodiments, the water is held in the
deposit of
bituminous material for a period of from I day to I month.
In some embodiments, the water can include peroxide in order to improve the
solvent and bitumen recovery. Any suitable peroxide can be added to the water
used
in step 150, including but not limited to, hydrogen peroxide. In some
embodiments,
the amount of peroxide included in the water used in step 150 is 10 to 60%.
The addition of peroxide to the water is considered beneficial for two
reasons.
Firstly, the peroxide improves the removal of residual solvent form within the
21
CA 02786106 2012-08-13
bituminous deposit. As discussed above, this is due at least in part to the
peroxide
reducing interfacial tension between hydrocarbon material, water, and
inorganic
material. Secondly, the peroxide is believed to reduce the viscosity of
bitumen, which
improves the drainage of the bitumen from the deposit via the production
wells.
Peroxides are believed to reduce the viscosity of bitumen by oxidizing the
sulfur
contained in the bitumen.
The use of peroxides to improve solvent and bitumen removal from the
bituminous deposit is also beneficial because the peroxide does not leave
behind
harmful residual chemicals in the deposit. For example, when hydrogen peroxide
is
used in the water wash, the hydrogen peroxide will break down to oxygen and
water.
The manner of withdrawing a mixture of water and second solvent from within
the deposit if bituminous material is similar or identical to the manner in
which the
mixture of first solvent and dissolved bitumen and the mixture of first
solvent and
second solvent is withdrawn from the deposit of bituminous material. The same
production wells used to withdraw disbit and mixtures of first and second
solvent from
the deposit can be used to withdraw a mixture of water and second solvent from
the
deposit.
The fluid material withdrawn from within the deposit of bituminous material in
step 160 generally includes water and second solvent. Other materials that can
be
present in the fluid material include water, bitumen, and organic and
inorganic solids.
Generally speaking, the fluid material withdrawn in step 160 includes from 40
to 90%
water, from 60 to 95% second solvent, from 2 to 10% first solvent, from 2 to
10%
bitumen, and less than 2% other materials. The constituency of the fluid
withdrawn in
step 160 can change over time as the injected water reaches the well head. The
rate of
withdrawing the fluid material is generally not limited, and in some
embodiments, the
fluid is withdrawn from within the deposit of bituminous material via the
production
wells at a rate of from about 500 to 2,000 bbls/day per well head (by gravity
drainage).
Once the mixture of water and second solvent is brought to the surface in step
160, various separation steps can take place to separate the water solvent
from the
second solvent. Any suitable separation unit or series of separation units can
be used
22
CA 02786106 2012-08-13
to separate the water from the second solvent. In embodiments where the second
solvent is polar solvent, separation may occur naturally or with minimal
effort due to
the difference in polarity. Once separated, the second solvent can be reused
in the
extraction process.
Any water left in the deposit of bituminous material can remain in the
deposit,
as the water is not an environmental concern. In some embodiments, 5 to 50% of
the
water injected into the deposit in step 150 will remain in the deposit.
The above described method can be performed one or more times on a confined
deposit of bituminous material. Similarly, any one step or pairs of steps
(e.g., step
110 and 120) can be repeated multiple times before moving on to the next step
of the
method. Repeating certain steps of pairs of steps may help to increase the
bitumen
extraction efficiency.
Once a confined deposit of bituminous material has been subjected to the
above-described in-situ bitumen extraction process, the same process can be
carried
out on adjacent deposits of bituminous material. In some embodiments, one or
more
freeze walls established for carrying out the in-situ bitumen extraction
process on a
first deposit of bituminous material can be re-used when confining an
adjoining
deposit of bituminous material. For example, when a confined deposit of
bituminous
material has a square shape, three of the freeze walls can be decommissioned
while a
fourth wall can be used as the first wall of a new confined deposit of
bituminous
material located next to the first deposit.
Additional pretreatment steps can also be carried out prior to or during the
method described above. For example, any of a variety of fracturing steps or
method
to increase porosity can be carried out prior to any of the solvent injection
steps in an
attempt to create more passageways for solvent and other materials to pass
through.
Additionally, hot water or sloppy steam can be injected into the deposit of
bituminous material prior to or during the injection of the first solvent in
an effort to
soften the oil sands and the bitumen component or create channels for the
subsequently injected solvent to pass through. In some embodiments, the
injection
wells can be adapted to allow for the simultaneous injection of water and
solvent
through the same injection wells. The injection wells can be "composite"
injection
23
CA 02786106 2012-08-13
wells that include multiple passage ways within the same general piping. With
reference to Figure 6, a composite injection well 600 can include a co-annular
inner
passage 610 and a co-annular outer passage 620, with the inner passage 610
having
injection ports 615 that extend through the outer passage to the exterior of
the
injection well 600. In this manner, steam or water can travel down the inner
passage
610 of the injection well 600 and be injected into the deposit at the same
time that
solvent passes down the outer passage 620 of the injection well 600 and is
injected
into the deposit through standard injection ports 625 in fluid communication
with the
outer passage 620.
The majority of the system used to carry out the in-situ bitumen extraction
methods described herein is discussed above, including the vertical freeze
walls, the
optional horizontal freeze wall, the plurality of injection bores, and the
plurality of
production wells. Also discussed above are the separation units that can be
provided,
including the separator for separating disbit into bitumen and solvent, the
separator for
separating a mixture of first solvent and second solvent, a separator for
separating a
mixture of second solvent and water, and distillation units for producing
solvent from
recovered bitumen.
Additional components that can be part of the system include a refrigerant
source, a first solvent source, a water source, and a second solvent source.
Each
source can include any type of supply vessel that is capable of supplying the
desired
fluid needed for the method. The supply vessels may also include recycle
inputs for
receiving fluid material that is recovered from the process and sent back into
the
system. The refrigerant source is in fluid communication with the
interconnected well
bores used to establish the freeze walls and, when a two loop system as
described
above is used, can include a recycle input for receiving refrigerant that has
passed
through the two loop system back into the refrigerant source for storage and
further
use. The first solvent and water sources can be in fluid communication with
the outer
and inner passage of a composite injection well, respectively. Additionally,
the
second solvent source can be in fluid communication with the injection well.
While the invention has been particularly shown and described with reference
to a preferred embodiment thereof, it will be understood by those skilled in
the art that
24
CA 02786106 2012-08-13
various other changes in the form and details may be made without departing
from the
spirit and scope of the invention.
A presently preferred embodiment of the present invention and many of its
improvements have been described with a degree of particularity. It should be
understood that this description has been made by way of example, and that the
invention is defined by the scope of the following claims.
