Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
SYSTEM AND METHOD FOR UPGRADING BITUMEN IN SITU USING SLOW REACTING
NANO-CATALYST
TECHNICAL FIELD
[0001] The following relates to systems and methods for upgrading bitumen
in situ by
injecting a slow-reacting nano-catalyst into a hydrocarbon reservoir, for
example, using a
producer or infill well.
BACKGROUND
[0002] Bitumen is known to be considerably viscous, 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.
[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 (e.g., Steam Assisted Gravity
Drainage
(SAGD) and Cyclic Steam Stimulation (CSS)), steam-solvent co injection
techniques (e.g.,
expanding solvent-SAGD (ES-SAGD)) and waterless solvent-based techniques
(e.g.,
Electromagnetic Assisted Solvent Extraction (EASE)).
[0004] In a common 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. The injector well facilitates
steam injection into the
reservoir. The injected steam propagates vertically and laterally into the
reservoir to develop
what is referred to as a steam chamber. Latent heat released by the injected
steam mobilizes
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the bitumen, which drains due to gravity and is produced along with condensed
water in the
producer well.
[0005] Produced bitumen is a heavy crude oil which typically contains a
large fraction of
complex long-chain hydrocarbon molecules. Depending on the extraction process
used,
bitumen product may not meet pipeline specifications for transport over long
distances. Pipeline
specifications are usually met by either upgrading the bitumen, or by diluting
the bitumen with
light oil. However, the diluent used to meet pipeline specifications can be
considered expensive,
and can account for a meaningful portion of pipeline volumes, driving up
transportation costs
and limiting pipeline capacity. There is thus an ongoing need to reduce or
eliminate the use of
diluent for bitumen transportation.
[0006] A known solution to this transportation problem is to partially
upgrade bitumen after
oil recovery. This involves upgrading the quality of the bitumen just enough
to reduce or
eliminate the need for diluent for transportation. Another potential solution
is in situ upgrading of
bitumen.
[0007] In situ upgrading of bitumen and heavy oil, especially catalytic
upgrading, is currently
considered to be a desirable next-generation technology. One existing method
of in situ
upgrading involves thermal cracking at the mobile oil zone ahead of a
combustion front, and
subsequent entry of partially upgraded oil into a horizontal well that is pre-
packed with pelleted
fast reacting catalysts. A known drawback associated with this method is that
production lines
can become blocked because of coke and metals deposited on the pelleted
catalyst. It is
known that the use of less expensive, dispersed unsupported transition metal
nano-catalysts,
such as Fe-based unsupported catalysts, can minimize coke formation since nano-
sized
catalysts expose more active sites and possess shorter diffusion routes.
Still, these catalysts
can lack cracking functionality offered by supports such as zeolite, alumina
or silica, and can
require longer reaction times to achieve similar levels of upgrading.
[0008] It would be advantageous to have a process for implementing in situ
catalytic
upgrading in a bitumen recovery technique that addresses at least one of the
above-noted
issues or disadvantages.
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SUMMARY
[0009] Provided herein are systems and methods to upgrade hydrocarbons in
situ using
slow-reacting nanocatalysts. These systems and methods are particularly
applicable to thermal
bitumen recovery processes such as SAGD and CSS. The slow-reacting
nanocatalysts can
include iron, or vanadium based unsupported transitional metal catalysts due
to their low cost
and high availability. The slow-reacting nanocatalysts can be injected into
the sump around a
producer well located beneath an injector well in a reservoir undergoing SAGD
and production
can be slowed to increase the contact time between the slow-reacting catalysts
and the bitumen
in the sump to increase the extent of upgrading. The slow-reacting catalysts
can also be
injected in a reservoir undergoing CSS, particularly prior to the shut-in
phase during which the
slow-reacting catalysts are left in the reservoir for a period of time
sufficient for desired
upgrading to occur. The systems and methods provided herein can improve the
economics of
thermal bitumen recovery processes by partially or completely eliminating the
need to add
diluent to the produced bitumen prior to shipping, which can be considered
expensive.
[0010] In an aspect, there is provided a method for upgrading hydrocarbons
in a reservoir in
situ, the method comprising: delivering a slow reacting catalyst into the
reservoir to contact the
hydrocarbons; and allowing a sufficient contact time between the slow reacting
catalyst and the
bitumen to at least partially upgrade the bitumen.
[0011] In an implementation of the method, the reservoir is an oil sands
reservoir.
[0012] In another implementation of the method, the hydrocarbons comprise
bitumen.
[0013] In yet another implementation of the method, the hydrocarbons
comprise heavy oil.
[0014] In yet another implementation of the method, the slow reacting
catalyst is an
unsupported transition metal catalyst.
[0015] In yet another implementation of the method, the unsupported
transition metal
catalyst comprises pyrite-based compounds.
[0016] In yet another implementation of the method, the unsupported
transition metal
catalyst comprises iron-based compounds.
[0017] In yet another implementation of the method, the unsupported
transition metal
catalyst comprises vanadium-based compounds.
[0018] In yet another implementation of the method, a cyclic steam
stimulation (CSS)
process is implemented in the reservoir, comprising a well used for injection
and production.
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[0019] In yet another implementation of the method, a steam-assisted
gravity drainage
(SAGD) process is implemented in the reservoir, comprising a substantially
horizontal producer
well having an adjustable production rate and a substantially horizontal
injector well having an
adjustable steam injection rate.
[0020] In yet another implementation of the method, the slow reacting
catalyst is delivered
into the hydrocarbon reservoir by injection through the producer well into a
sump around the
producer well, the sump comprising heated bitumen and condensate water, and
the catalyst
being dispersed therethrough, to continuously produce upgraded bitumen.
[0021] In yet another implementation of the method, the production rate is
decreased to
achieve the sufficient contact time between the slow reacting catalyst and the
bitumen in the
sump to produce the upgraded bitumen.
[0022] In yet another implementation of the method, the slow reacting
catalyst is delivered
by injection through an infill well into a virgin bitumen formation above a
steam chamber in the
reservoir to induce bitumen upgrading.
[0023] In yet another implementation of the method, the slow reacting
catalyst is delivered
by injection through an infill well into a bitumen formation at the top of a
steam chamber to
accelerate bitumen upgrading.
[0024] In yet another implementation of the method, the slow reacting
catalyst is delivered
by injection through an infill well into a lean zone in the reservoir to
accelerate bitumen
upgrading.
[0025] In yet another implementation of the method, the lean zone is below
a shale layer.
[0026] In yet another implementation of the method, an upgrading reaction
between the
bitumen and the catalyst yields gases to produce a steam-assisted gravity push
(SAGP) effect
pushing bitumen in a desired direction.
[0027] In yet another implementation of the method, a steam-assisted
gravity drainage
(SAGD) process is occurring in the reservoir, the reservoir comprises at least
two pairs of
producer and injector wells, and the slow reacting catalyst is delivered by
injection through an
infill well into a bitumen formation between adjacent pairs of producer and
injector wells.
[0028] In yet another implementation of the method, in situ bitumen
upgrading is induced in
the bitumen formation between the adjacent pairs.
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[0029] In yet another implementation of the method, in situ bitumen
upgrading is
accelerated in the bitumen formation between the adjacent pairs.
[0030] In yet another implementation of the method, a steam-assisted
gravity push (SAGP)
effect pushes upgraded bitumen from the bitumen formation between the adjacent
pairs towards
the producer wells of the adjacent pairs.
[0031] In yet another implementation of the method, at least some upgraded
bitumen that is
not collected by the pair of producer wells is collected by the infill well.
[0032] In yet another implementation of the method, the method further
comprises the steps
of: injecting the catalyst into the reservoir; injecting steam into the
reservoir to heat the bitumen;
shutting in the reservoir; and producing upgraded bitumen.
[0033] In another aspect, provided is a method for winding down bitumen or
heavy oil
production in a mature reservoir having undergone a thermal bitumen or heavy
oil recovery
process, the method comprising: injecting slow reacting catalyst through at
least one of an
injector well, a producer well, and an infill well; shutting in the at least
one injector well, producer
well, or infill well; leaving the slow reacting catalyst in the reservoir to
upgrade the bitumen to a
desired extent; and producing the bitumen or heavy oil.
[0034] In an implementation of the method, the bitumen or heavy oil is left
in the reservoir
for a pre-determined length of time.
[0035] In yet another implementation of the method, the extent of upgrading
is tested at one
or more regular intervals until the desired extent is reached.
[0036] In yet another implementation of the method, the hydrocarbons
comprise bitumen.
[0037] In yet another implementation of the method, the hydrocarbons
comprise heavy oil.
[0038] In yet another aspect, provided is a method for increasing in situ
upgrading of
hydrocarbons in a reservoir having moving condensed steam, the method
comprising: injecting
a catalyst into at least one zone in the reservoir having high levels of
moving condensed steam.
[0039] In an implementation of the method, at least one zone is a lean zone
and/or a lean
zone below a shale layer.
[0040] In yet another implementation of the method, the hydrocarbons
comprise bitumen or
heavy oil.
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[0041] In yet another aspect, provided is a method for in situ upgrading of
hydrocarbons in a
sump around a producer well in a reservoir, the reservoir undergoing a steam
assisted gravity
drainage (SAGD) process, the method comprising: a) injecting slow reacting
catalyst into the
sump around a producer well to contact the hydrocarbons; b) producing the
hydrocarbons
continuously and testing the hydrocarbons at one or more regular intervals to
determine an
extent of upgrading; c) if the hydrocarbons are not upgraded to a desired
extent, slowing
production and repeating step b); and d) if the hydrocarbons are upgraded to
the desired extent,
repeating step b).
[0042] In yet another aspect, provided is a method for in situ upgrading of
hydrocarbons in a
reservoir, the reservoir undergoing a cyclic steam stimulation (CSS) process,
the method
comprising: a) injecting a slow reacting catalyst into the reservoir to
contact the hydrocarbons;
b) injecting steam into the reservoir; c) shutting in the reservoir for a pre-
determined period of
time and testing the hydrocarbons at one or more regular intervals to
determine an extent of
upgrading; d) if the hydrocarbons are not upgraded to a desired extent,
extending, shortening or
leaving unchanged the pre-determined period of time and repeating step c); and
e) if the
hydrocarbons are upgraded to the desired extent, producing the hydrocarbons.
[0043] In an implementation of the method, the method further comprises: f)
if economically
feasible, repeating the method from step a); and g) if not economically
feasible, terminating the
CSS process.
[0044] In another implementation of the method, the pre-determined period
of time
corresponds to a sufficient contact time between the slow reacting catalyst
and the
hydrocarbons to upgrade the hydrocarbons to the desired extent.
[0045] In yet another implementation of the method, the pre-determined
period of time is at
least 5 days.
[0046] In yet another implementation of the method, the pre-determined
period of time is at
least 2 weeks.
[0047] In yet another implementation of the method, the pre-determined
period of time is at
least one month.
[0048] In an implementation of the methods, the slow reacting catalyst is
injected into the
reservoir while suspended in a solution.
CPST Doc: 297317.1
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Date Recue/Date Received 2020-10-14
[0049] In another implementation of the methods, the solution comprises one
or more
polymers.
[0050] In yet another implementation of the methods, the one or more
polymers comprise
xantham gum.
[0051] In yet another implementation of the methods, the solution comprises
one or more
surfactants.
[0052] In yet another implementation of the methods, the one or more
surfactants comprise
at least one of cetrimonium bromide (CTAB) and sodium dodecylbenzenesulfonate
(SDBS).
[0053] In yet another implementation of the methods, the one or more
surfactants are
injected into the reservoir prior to the injection of the slow reacting
catalyst.
[0054] In yet another implementation of the methods, testing the extent of
upgrading
comprises obtaining samples of the bitumen or heavy oil and measuring an API
gravity value.
[0055] In yet another implementation of the methods, testing the extent of
upgrading
comprises obtaining samples of the bitumen or heavy oil and measuring a
concentration of
saturates, aromatics, resins and asphaltenes (SARA) of the samples.
[0056] In yet another implementation of the methods, testing the extent of
upgrading
comprises measuring at least one of asphaltenes, 2-methylanthracene, and
alkanes.
[0057] In yet another implementation of the methods, the hydrocarbons
comprise bitumen
or heavy oil.
[0058] In yet another aspect, provided is a system for in situ upgrading of
hydrocarbons in a
reservoir undergoing a steam assisted gravity drainage (SAGD) process, the
system
comprising: a producer well positioned in the reservoir; an injector well
positioned in the
reservoir above the producer well; a sump around the producer well; a source
of steam; a
source of slow reacting catalyst; injection equipment for the steam; injection
equipment for the
slow reacting catalyst; equipment for determining an extent of upgrading of
the hydrocarbons as
they are produced.
[0059] In yet another aspect, provided herein is a system for in situ
upgrading of
hydrocarbons in a reservoir undergoing a cyclic steam stimulation (CSS)
process, the system
comprising: a well positioned in the reservoir; a source of steam; a source of
slow reacting
catalyst; injection equipment for the steam and slow reacting catalyst;
equipment for
determining an extent of upgrading of the hydrocarbons in the reservoir.
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[0060] In an implementation of the systems, the equipment can determine an
API gravity
value of the hydrocarbons.
[0061] In another implementation of the systems, the equipment can
determine a level of at
least one of saturates, aromatics, resins and asphaltenes.
[0062] In another implementation of the systems, the equipment can
determine a level of at
least one of asphaltenes, 2-methylanthracene, and alkanes
[0063] In yet another implementation of the systems, the source of slow
reacting catalyst is
a solution comprising a suspension of the slow reacting catalyst.
[0064] In yet another implementation of the systems, the solution comprises
one or more
polymers.
[0065] In yet another implementation of the systems, the solution comprises
one or more
surfactants.
[0066] In yet another implementation of the systems, the hydrocarbons
comprise bitumen or
heavy oil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] Embodiments will now be described with reference to the appended
drawings
wherein:
[0068] FIG. 1 is a cross-sectional view of a system for in situ upgrading
of bitumen in the
sump of a producer.
[0069] FIG. 2 is a flow chart illustrating a method for optimizing in situ
upgrading of bitumen
in the sump of a producer well in a SAGD process.
[0070] FIG. 3 is a cross-sectional view of a system for upgrading bitumen
in situ in a virgin
bitumen reservoir above a steam chamber in a SAGD process.
[0071] FIG. 4 is a cross-sectional view of a system for accelerating
upgrading of bitumen in
situ by injecting catalyst into a lean zone at the top of a steam chamber in a
SAGD process.
[0072] FIG. 5 is a cross-sectional view of a system for upgrading bitumen
in situ around an
infill well in a virgin bitumen reservoir between two steam chambers in a SAGD
process.
[0073] FIG. 6 is a cross-sectional view of a system for upgrading bitumen
in situ by
injecting catalyst at a well near the top of a steam chamber in a SAGD
process.
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[0074] FIG. 7 is a cross-sectional view of a system for upgrading bitumen
in situ by
injecting catalyst into a reservoir in a CSS process.
[0075] FIG. 8 is a flow chart illustrating a method for upgrading bitumen
in situ in a cyclic
steam stimulation system.
DETAILED DESCRIPTION
[0076] The use of catalysts for in situ bitumen upgrading has been
considered in existing
research. Such existing research shows that nano-particles can cause upgrading
of bitumen by
breaking the sulfur bonds holding the asphaltenes together, thereby reducing
the asphaltene
content and viscosity of the bitumen. However, a significant focus of previous
work has been on
examining catalysts that react very quickly, such as those used in upgraders
and refineries.
Catalysts typically used for upgrading or cracking bitumen in refineries or
upgraders on surface,
such as molybdenum and nickel, work at high temperatures and have to be very
fast reacting
because of the large volumes of bitumen being upgraded each day. Such
catalysts are typically
supported by zeolite, alumina, or silica, which can provide enhanced cracking
functionality.
These fast reacting catalysts can be considered expensive and are therefore
not economical to
inject into a subsurface formation to upgrade bitumen in situ. Other
catalysts, such as
unsupported transition metal nanocatalysts, cannot react with bitumen quickly
enough to be
used in a refinery. However, these catalysts can be of lower cost and can thus
be more
economical to inject into a reservoir, particularly where all or some of the
catalysts are
unrecoverable from the reservoir. These slower reacting catalysts can
sufficiently upgrade
bitumen in situ in a thermal recovery process such as SAGD, as a longer
contact time between
the bitumen and the catalyst can be achieved in the subsurface relative to in
a refinery. The
contact time in the subsurface can be on the order of days to weeks, and
potentially years.
[0077] Known unsupported transition metal catalysts can include, but are
not limited to,
molybdenum-, nickel-, iron-, tungsten-, and vanadium-based catalysts. Examples
of
unsupported molybdenum-based catalysts can include, but are not limited to,
molybdenum (IV)
sulfide (MoS2) and molybdenum (VI) oxide (Mo03). An example of unsupported
nickel-based
catalysts includes nickel (II) oxide (NiO). Examples of unsupported iron-based
catalysts can
include, but are not limited to, pyrite (FeS2), troilite (FeS) and pyrrhotite
(Fei,S). It can be
appreciated that Fe-based unsupported catalysts, and in particular, pyrite,
are considered to be
attractive with respect to cost and availability.
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[0078] The terms "catalyst", "catalysts", " nano-catalyst", and "nano-
particle catalyst" are
used interchangeably from hereon in and all refer to slow-reacting catalysts
having a particle
size on the nanoscale. The term "slow-reacting catalyst" will be understood to
mean a catalyst
that upgrades bitumen too slowly to be economically or commercially feasible
for use in bitumen
refineries or that upgrades bitumen slower than those conventionally used in
bitumen refineries.
Suitable slow-reacting catalysts include pyrite. In some implementations, some
other iron- and
vanadium-based compounds may be suitable slow-reacting catalysts.
[0079] The phrases "residence time of the catalyst" or "residence time of
the slow-reacting
catalyst" or "contact time" as used herein refer to the amount of time that
the bitumen is in
contact with the injected catalyst.
[0080] The terms "level of upgrading", "degree of upgrading" and "extent of
upgrading" used
herein all refer to the extent to which bitumen or heavy oil has been
upgraded. One method of
estimating the extent of upgrading of bitumen of a bitumen sample taken from a
reservoir is to
measure the concentration of 2-methylanthracene, alkanes and asphaltenes. High
concentrations of 2-methylanthracene and alkanes, and a low concentration of
asphaltenes can
be indicative of upgrading.
[0081] The term "sufficient contact time" used herein refers to a contact
time between the
bitumen and the catalyst that is sufficient to at least partially upgrade the
bitumen. At least
partially upgraded bitumen may be suitable for pipeline transportation without
adding any
diluent, or it may require a lesser amount of dilution prior to transportation
as compared to
bitumen that has not been at least partially upgraded.
[0082] As noted above, an advantage of using a slow reacting nano-catalyst,
is that the
catalyst is generally much cheaper than a fast reacting catalyst, which is too
expensive to inject
into the ground. The slow reacting and cheaper catalyst can be injected into
the sump of a
producer well, particularly one that is mature and/or approaching the end of
its production life
and/or in infill wells to take advantage of the longer contact time.
Particularly, the catalyst can
be injected into the sump of a well that has slowed or ceased production. The
catalyst can be
left in the reservoir for an extended period of time during which the bitumen
would slowly be
upgraded by the catalyst in the presence of the residual heat. After this
extended period of
time, which can be as long as multiple years, the residual upgraded bitumen
can be collected
using the producer well.
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[0083] The catalyst can be injected into the reservoir as a suspension of
catalyst
nanoparticles in water. It is known that when nanoparticles are injected into
a porous medium,
they have a tendency to agglomerate due to the attractive forces between
particles. Such
agglomeration can result in the formation of larger particles from the
nanoparticles, which can
result in deposition and destabilization of the suspension of nanoparticles in
the aqueous
medium. This, in turn, can clog pores in the formation into which the
suspension is injected,
thereby inhibiting the dispersion of the catalyst particles. It has been shown
that suspensions of
nickel nanoparticles in water can be at least partially stabilized by xantham
gum. Thus, in order
to mitigate the clogging of pores in the reservoir, the injected catalyst
nanoparticle suspension
can comprise polymers, such as xantham gum, that are known to stabilize
nanoparticle
suspensions.
[0084] It is known that the concentration of surfactant in a nanoparticle
suspension can play
an important role in the transfer of particles to the oil-water interface. A
surfactant such as
cetrimonium bromide (CTAB) and/or sodium dodecylbenzenesulfonate (SDBS) can be
injected
into the reservoir prior to the introduction of the particles. The injected
surfactant solution can
create an oil-water emulsion, thereby increasing the oil-water interface area
and also positively
charging these interfaces. Then, catalyst nanoparticles, suspended in a
solution of xantham
gum in water, can be injected. The electrostatic interactions between polymer
and surfactant
molecules can move the nanoparticles to oil-water interfaces. Movement of the
catalyst
nanoparticles to the oil-water interface can be necessary to allow interaction
between the
catalyst and the oil (i.e., to allow the reaction between the catalyst and the
bitumen). It can be
appreciated that other known surfactants can be used, preferably at a
concentration conducive
to the migration of catalyst nanoparticles to the oil-water interface, to
create an oil-water
emulsion in the reservoir prior to the introduction of the catalyst
nanoparticles. It can also be
appreciated that other known polymers can be used in preparing nanoparticle
suspensions for
injection into the reservoir.
[0085] Slow reacting catalysts can also be implemented as part of a wind-
down strategy in a
SAGD process. During wind-down, steam injection is gradually reduced and the
amount of
recoverable oil in the drainage volume gradually decreases. Catalyst can be
injected during the
wind-down phase to upgrade the remaining bitumen in situ. Although the
pressure and
temperature of the steam chamber decrease during the wind-down phase, the
residual heat can
be sufficient to help facilitate the reaction between the catalyst and the
bitumen. When the
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wind-down phase is completed, the remaining bitumen in contact with the
catalyst can be left to
upgrade over an extended period of time, as discussed above.
[0086] Slow reacting nano-catalysts can also be injected into the sump of a
producer well
during normal SAGD operation. Since the catalyst reacts slowly, it can be
important to ensure
that the bitumen is in contact with the catalyst long enough for a desired
degree of upgrading to
occur. To increase the contact time to achieve a sufficient contact time
between the catalyst
and the bitumen, production can be slowed. If production is slowed, the size
of the sump can
increase, and thus injection of steam can be adjusted as necessary to maintain
the interface
between the producer and injector wells. The bitumen in the sump can be in
contact with the
nano-catalyst for up to several weeks, depending on sump size and production
rates.
[0087] Recent geochemical data from a post steam core well (observed well)
suggests that
in situ upgrading can be occurring in the absence of injected catalyst during
a SAGD process. It
is found that in situ upgrading can be occurring in the absence of injected
catalyst due to the
presence of moving steam in at least some SAGD fields having mobile water. The
observed
well is located in an area where the steam chamber is less developed compared
to surrounding
areas. Alkanes and elevated levels of 2-methylanthracene were found in the
bitumen in that
well. The presence of alkanes and elevated levels of 2-methylanthracene is
indicative of in situ
bitumen upgrading. Alkanes and elevated levels of 2-methylanthracene are not
normally
present in virgin bitumen reservoirs in that geographical area. It was also
found that the
concentrations of such compounds increase with increasing reservoir
temperature. All samples
taken from the observed well showed a reduced asphaltene content relative to
virgin reservoirs,
which is also indicative of upgrading. The most upgraded of these samples is
believed to be
from a reservoir zone that has been in contact with hot moving steam
condensate longer than
the other zones from which samples were obtained. In view of these
observations, it may be
that the more readily available a sample is to the movement of condensed
steam, the more
upgraded the sample can be. As such, mass transfer allowed by water mobility
could be a key
controlling parameter for in situ upgrading. Moreover, the presence of natural
materials that can
catalyze bitumen upgrading, such as nodules of pyrite, could contribute to
such in situ
upgrading.
[0088] Lean zones often exist in reservoirs undergoing SAGD. The presence
of lean zones
can result in high steam-to oil ratios (SORs) since they behave as "thief
zones" which absorb
heat and steam due to high levels of mobile water. In view of their high
levels of mobile water,
the lean zones could act as conduits for the injected catalyst. In other
words, catalyst can be
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injected into lean zones to help disperse catalyst deep into the reservoir to
contact a maximal
amount of bitumen. Additionally, lean zones can be conduits for steam. Bitumen
that is
exposed to both moving steam and catalyst can have an accelerated rate of
upgrading relative
to bitumen that is exposed to moving steam or catalyst alone.
[0089] The above principles can also apply to a CSS process. During the
soak, or shut in
phase of a CSS process, heat from the steam injected through a
producer/injector well during
the injection phase can be distributed through the reservoir. As discussed in
greater detail
below, the well can be shut in for a period of time sufficient for uniform
heat distribution to occur.
It is known that the bitumen in the steam chamber is at least partially heated
by convective heat
transfer. Accordingly, the catalyst can be injected into areas of the
reservoir where the bitumen
is exposed to the highest levels of convective heat transfer (i.e., moving
condensed steam). As
discussed above, bitumen that is exposed to both moving condensed steam and
catalyst can
have an accelerated rate of upgrading relative to bitumen exposed to moving
condensed steam
or catalyst alone. If the reservoir undergoing CSS contains geological
features such as lean
zones, which are often located below shale layers, the catalyst can be
injected into such zones
to help disperse catalyst deep into the reservoir to contact a maximal amount
of bitumen. In
view of their high levels of mobile water, the lean zones could act as
conduits for the injected
catalyst and for steam. Bitumen exposed to steam and catalyst moving through
the lean zones
can have a higher rate of upgrading.
[0090] When lean zones are present in a reservoir undergoing SAGD, the
operating steam
pressure is typically reduced to reduce the water loss to the lean zone, which
can accentuate
the impact of any barriers in the formation, thereby giving rise to high SORs
and low production
rates. Additionally, if the cap rock above the pay in a SAGD process is
compromised, the
operating steam pressure can also be reduced, giving rise to the same issues.
The lower
production rates are a result of the slower drainage of the more viscous
bitumen at the lower
temperature of the steam chamber. Slow reacting catalyst can be utilized to
further decrease
the viscosity of the bitumen via in situ upgrading to increase the rate of
bitumen drainage in a
steam chamber having a lower temperature as a result of the necessary
reduction of steam
operating pressure due to the presence of lean zones, and compromised cap
rock.
[0091] It is also known that the upgrading reactions between bitumen and
catalysts can
produce CO2 and other gases. Instead of solely relying on co-injecting gases
through injector
wells during a SAGD process, the gases produced as a result of the upgrading
reactions can
contribute a steam-assisted gravity push (SAGP) effect. Leveraging this
effect, a nano-catalyst
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can be injected through an infill or other additional well that is positioned
above the injector-
producer well pair to both upgrade the bitumen in situ and, through the
production of CO2 and
other gases (such as methane and possibly H2S), push the bitumen being
upgraded down
towards the producer well(s). Additionally, CO2 production can reduce bitumen
viscosity,
facilitating gravity drainage.
[0092] While the example systems and methods provided herein are directed
to SAGD and
CSS processes, it can be appreciated that these principles can be applied to
any other in situ oil
recovery techniques, and in particular, thermal recovery techniques, where the
slow reacting
catalyst can be kept in contact with bitumen for periods of time that allow
sufficient upgrading of
the bitumen. It has been shown that SAGD processes are generally carried out
at pressures
and temperatures that are compatible with in situ upgrading reactions,
particularly in situ
upgrading reactions using unsupported dispersed nanocatalysts such as
trimetallic
nanocatalysts.
[0093] Turning now to the figures, FIG. 1 illustrates a bitumen reserve
such as that found in
the Canadian oil sands, hereinafter referred to as the "pay 180"; which is
accessed for in situ
bitumen recovery. The pay 180 typically includes a number of geological
materials such as a
rock matrix, sand, and fluid such as the bitumen that is being targeted. A
formation at least
partially underlies the pay 180 and is hereinafter referred to as the
"underlying formation 190".
In the example shown in FIG. 1, the pay 180 itself underlies a layer of
overburden 170 between
the pay 180 and the surface 160. In the implementation shown in FIG. 1, a
producer well 120
and an injector well 110 are situated within the pay 180. A sump 100 exists
around the
producer well 120, and the sump 100 is a liquid pool comprising heated bitumen
and
condensate water. Slow reacting nano-catalyst particles 130 are injected
through the producer
120 into the sump 100 where they disperse throughout the sump 100. The slow
reacting nano-
catalyst particles 130 come into contact with bitumen and break the sulfur
bonds holding the
asphaltenes together, reducing the ashpaltene content and viscosity of the
bitumen. It can be
appreciated that the slow reacting nano-catalyst can be injected concurrently
with, or after,
surfactants and/or polymers into the sump 100 to prevent aggregation of nano-
catalyst particles.
It is known that certain surfactants and/or polymers can also allow the nano-
catalyst particles to
become attached to sand grains. The bitumen can be in contact with the nano-
catalyst for up to
several weeks, depending on sump size and production rates.
[0094] The flow chart shown in FIG. 2, illustrates a process whereby
bitumen is upgraded in
situ by injecting nano-catalyst into the sump 100 around a producer well 120
during normal
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operation in a SAGD process. Nano catalyst particles can be injected into the
sump 100 at step
200. Bitumen in the sump can then be catalytically upgraded in situ at step
210 as it is produced
at a low rate in step 220. The extent of upgrading of the bitumen being
continuously produced can
be determined at regular intervals at step 230. If the bitumen is upgraded to
the extent that it, for
example, meets pipeline specifications for shipping, the parameters of the
SAGD process can be
maintained and the extent of upgrading can be measured again a short time
thereafter. If the
bitumen is not upgraded to a sufficient extent, and it is feasible to slow
production (240),
production can be slowed at step 250. It may be noted that it would not be
feasible to slow
production if, for example, the production rate was so slow that the process
was not economical
(240). In this case, the process can revert back to step 200 and inject more
catalyst. This can
help to increase the extent of upgrading if, for example, the catalyst has not
spread throughout the
entirety of the sump 100, and thus not a meaningful portion or none of the
bitumen has been in
contact with the catalyst. At step 200, the nano-catalyst can be coated with
surfactant so that it
can attach to quartz grains, and to prevent the catalyst from aggregating
and/or blocking pores in
the reservoir. Furthermore, steam injection can either be stopped or continue
while the catalyst is
injected at step 200.
[0095] It can be appreciated that in the process of FIG. 2, at step 200,
the catalyst can be
injected into the sump through a producer well 120 and/or an injector well
110.
[0096] The extent of bitumen upgrading can be estimated by obtaining
samples of the bitumen
or heavy oil and measuring an API gravity value and/or a concentration of
saturates, aromatics,
resins and asphaltenes (SARA) of the samples. It will be appreciated that any
appropriate known
or future known methods of determining the extent of bitumen upgrading can be
implemented
alternatively to, or concurrently with, the above-noted methods.
[0097] In the implementation shown in FIG. 3, slow reacting nano-catalyst
particles 340 are
injected through an infill well 300 into a virgin zone 350 above steam chamber
330. Steam
chamber 330 can be created by injecting steam through the injector well 110,
and heated bitumen
and condensate water flows down the edges of the chamber and is collected at
producer well 120.
In this implementation, bitumen upgrading is introduced into virgin zone 350.
The bitumen that is
upgraded in virgin zone 350 can be collected by the infill well 300 and can
also flow down and
enter steam chamber 330 where it is eventually collected by producer well 120.
[0098] As noted above, some experimental data has shown that the largest
amount of
upgrading occurs at the top of the steam chamber, corresponding to the part of
the reservoir
CPST Doc: 297318.1
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that has been in contact with hot moving steam condensate the longest. It is
therefore assumed
from the distribution of upgrading that the more readily available a part of
the reservoir is to the
movement of condensed steam, the more upgraded it will be. The delivery of the
slow reacting
nano-catalyst into the reservoir can be targeted accordingly; to either
accelerate upgrading
occurring in areas of the reservoir having been in contact with hot moving
steam condensate, or
to introduce upgrading to other areas of the reservoir. Catalyst can thus be
injected into "lean
zones", which have high levels of mobile water and can act as conduits for
steam and catalyst.
Thus, lean zones can be utilized to facilitate the dispersion of catalyst
through the reservoir to
contact bitumen being exposed to mobile water. Moreover, injection of catalyst
into lean zones
can accelerate upgrading of bitumen that can already be occurring due to
exposure to moving
condensed steam.
[0099] In the implementation shown in FIG. 4, catalyst 440 is injected
through infill well 400
into lean zone 460. Lean zone 460 is located below shale layer 450. Lean zone
460 is located
at the top of steam chamber 430 in this example illustration. Bitumen in and
near lean zone 460
is exposed to high levels of moving condensed steam and can be upgraded from
the steam
exposure alone. As such, by introducing catalyst 440 in and near lean zone
460, and at the top
of steam chamber 430, upgrading can be accelerated. The upgraded bitumen in
zone 460 can
be collected by the infill well 400 and/or the producer well 120.
[00100] In the implementation shown in FIG. 5, an infill well 540 is
located in virgin bitumen
zone 550 between two producer wells 500 and two injector wells 510. Slow
reacting nano-
catalyst particles 520 can be injected into the virgin bitumen zone 550
located somewhere
between the two steam chambers 530. In this implementation, bitumen upgrading
is introduced
into virgin zone 550. The arrows in FIG. 5 are provided only to illustrate a
possible flow path of
bitumen in the steam chambers 530 and virgin bitumen zone 550. A portion of
the upgraded
bitumen that cannot be collected by producer wells 500 can be collected by
infill well 540. The
upgrading reactions between the catalyst 520 and the bitumen in virgin zone
550 produce gases
which can push upgraded bitumen from virgin zone 550 towards steam chambers
530 through a
SAGP effect, where the upgraded bitumen is heated and collected by producer
wells 500.
Additionally, the decrease in viscosity resulting from upgrading of the
bitumen in virgin zone 550
can facilitate its collection by infill well 540.
[00101] It can be appreciated that bitumen upgrading already occurring in a
heated bitumen
zone between producer and injector pairs can be accelerated by injecting nano-
catalyst through
an infill well.
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[00102] In the implementation shown in FIG. 6, the nano-catalyst particles
630 are injected into
the reserve through the infill well 640 in the steam chamber 650. The
upgrading reaction between
the slow reacting nano-catalyst particles and the bitumen causes the
production of gases including
carbon dioxide and methane. The generation of these gases can cause a SAGP
effect. The SAGP
effect can push the heated bitumen downwards in the general direction of the
arrows illustrating a
postulated flow path of heated bitumen, down past injector well 610 towards
producer well 620.
[00103] Known techniques of using SAGP rely on co-injecting gas with steam
through injector
wells. It can be appreciated that the methods described herein provide a
method of producing the
SAGP effect without needing to co-inject gas through the injector wells, which
can result in cost
savings. The methods described herein can also be used to decrease the amount
of gas co-
injected into the reservoir, if combined with existing methods of leveraging
SAGP.
[00104] FIG. 7 illustrates a bitumen reservoir such as that found in the
Canadian oil sands,
hereinafter referred to as the "pay 742"; which is accessed for in situ
bitumen recovery. The pay
742 typically includes a number of geological materials such as a rock matrix,
sand, and fluid such
as the bitumen that is being targeted. A formation at least partially
underlies the pay 742, and is
hereinafter referred to as the "underlying formation 744". In the example
shown in FIG. 7, the pay
742 itself underlies a layer of overburden 746 between the pay 742 and the
surface 748. In the
implementation shown in FIG. 7, a CSS process is provided wherein in situ
upgrading of bitumen
using a slow reacting catalyst is implemented. The CSS process is split into
four phases. In
phase 700, catalyst 702 is injected through vertical producer/injector well
750 into pay 742.
Catalyst 702 can be coated with surfactant so that it can attach to quartz
grains, and to prevent the
catalyst from aggregating and/or blocking pores in the reservoir. The arrows
in phase 700
illustrate the flow of the catalyst 702 into pay 742. In phase 710, or the
"huff' phase, steam 712 is
injected through well 750 to produce heated zone 740. The arrows in heated
zone phase 710
illustrate the flow of steam 712 down well 750 into heated zone 740. In phase
720, which is
commonly referred to as the "soak" or "shut in phase", the bitumen is heated
by the convection of
water in heated zone 740. The bitumen upgrading can be accelerated during the
shut-in phase
due to heating resulting from the convection of water. The duration of phase
720 can be extended
as long as is necessary to allow sufficient in situ upgrading of the bitumen.
In phase 730, which is
commonly referred to as the "puff" or "production phase", the bitumen in
heated zone 740 can be
produced over a period of weeks or months. The arrows in phase 730 illustrate
the flow of heated,
at least partially upgraded bitumen 732 as it is produced through well 750.
CPST Doc: 297319.1
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[00105] The flow chart shown in FIG. 8 illustrates a process for controlling
in situ upgrading
according to the modified general CSS process described in FIG.7. At step 800,
slow reacting
catalyst is injected into the reservoir. As discussed above, the catalyst can
be injected as a
suspension in a solution comprising dissolved polymer and/or surfactant which
can stabilize the
catalyst nanoparticle suspension and/or allow the catalyst nanoparticles to
attach to rock or
sand grains. A surfactant solution can also be injected prior to the injection
of nanocatalyst for
the reasons discussed above. Steam is then injected into the reservoir at step
810, which is
immediately followed by step 820 which is the shut-in phase. At step 830, the
extent of bitumen
upgrading can be estimated at regular time intervals by analyzing core samples
at various
locations in the heated zone to determine the amount of alkanes, 2-
methylanthracene, and
asphaltenes present relative to the composition of the virgin reservoir. If
the bitumen is not
sufficiently upgraded, the shut-in phase can continue until a desired level of
upgrading is
reached. If at step 830, the bitumen has upgraded to a desirable extent, the
production phase
begins at step 840. When production is done, at step 850, it is decided
whether to start another
cycle of the process. If it is not desirable to start another cycle, the
process moves to step 870
and the cycle is terminated. Otherwise, if it is believed that more catalyst
is needed (step 860),
the process starts again at step 800. If no more catalyst is needed (step
860), the process
starts again at step 810.
[00106] The methods described herein can result in, or at least contribute to,
a higher valued
product that is easier to produce and ship with less total energy input.
Accordingly, this can
increase revenue and lower the environmental footprint resulting from in situ
bitumen recovery
operations.
[00107] For simplicity and clarity of illustration, where considered
appropriate, reference
numerals may be repeated among the figures to indicate corresponding or
analogous elements.
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 may be practiced without these specific
details. In other
instances, well-known methods, procedures and components have not been
described in detail
so as not to obscure the examples described herein. Also, the description is
not to be
considered as limiting the scope of the examples described herein.
[00108] The examples and corresponding diagrams used herein are for
illustrative purposes
only. Different configurations and terminology can be used without departing
from the principles
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expressed herein. For instance, components and modules can be added, deleted,
modified, or
arranged with differing connections without departing from these principles.
[00109] The steps or operations in the flow charts and diagrams described
herein are just for
example. There may be many variations to these steps or operations without
departing from the
principles discussed above. For instance, the steps may be performed in a
differing order, or
steps may be added, deleted, or modified.
[00110] 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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