Note: Descriptions are shown in the official language in which they were submitted.
CA 02741916 2011-06-02
INTEGRATION OF VISCOUS OIL RECOVERY PROCESSES
FIELD
[0001] The present disclosure relates generally to viscous oil recovery
processes, for
example processes for recovering bitumen from oil sands.
BACKGROUND
[0002] Oil sands are deposits comprising bitumen, clay, sand, and connate
water, and
make up a significant portion of North America's naturally-occurring petroleum
reserves.
Depending on the type and location of the deposit, bitumen may be extracted
from mined
oil sands, or recovered using an in situ process.
[0003] The term "viscous oil recovery process" (VORP) as used herein includes
both in
situ recovery processes and the extraction of bitumen from mined oil sand.
Commercial in
situ VORPs typically exploit at least one of temperature, pressure, and
solvent to reduce
the viscosity or otherwise enhance the flow of bitumen within the formation.
Non-limiting
examples of in situ VORPs include CSS (Cyclic Steam Stimulation), SAGD (Steam
Assisted Gravity Drainage), SA-SAGD (Solvent Assisted-Steam Assisted Gravity
Drainage), VAPEX (Vapor Extraction), LASER (Liquid Addition to Steam for
Enhancing
Recovery), SAVEX (Combined Steam and Vapor Extraction Process), CSD (Constant
Steam Drainage), steam drive, solvent flood, FIRE (Fluidized In Situ Reservoir
Extraction),
and water flooding. An example of CSS is described in U.S. Patent No.
4,280,559 (Best).
An example of SAGD is described in U.S. Patent No. 4,344,485 (Butler). An
example of
SA-SAGD is described in Canadian Patent No. 1,246,993 (Vogel). An example of
VAPEX
is described in U.S. Patent No. 5,899,274 (Frauenfeld). An example of LASER is
described in U.S. Patent No. 6,708,759 (Leaute et al.). An example of SAVEX is
described in U.S. Patent No. 6,662,872 (Gutek). An example of steam drive is
described
in U.S. Patent No. 3,705,625 (Whitten). An example of solvent flood is
described in U.S.
Patent No. 4,510,997 (Fitch). An example of FIRE is described in U.S. Patent
Publication
No. 2010/0218954 (Yale et al.).
[0004] As stated above, as used herein, a "VORP" may alternatively comprise
the
extraction of bitumen from mined oil sand (also referred to herein as a
"mining" operation
or process). A non-limiting description of certain oil sand extraction
processes will now be
provided. Oil sand extraction processes are used to liberate and separate
bitumen from
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mined oil sand so that the bitumen can be further processed, for instance to
produce
synthetic crude oil. Numerous oil sand extraction processes have been
developed and
commercialized, many of which involve the use of water as a processing medium
(referred
to as aqueous-based extraction). Other processes are solvent-based processes.
One
aqueous-based extraction process is the Clark hot water extraction process
(the "Clark
Process"). This process typically requires that mined oil sand be conditioned
for extraction
by being crushed to a desired lump size and then combined with hot water (e.g.
about
95 C) and perhaps other agents to form a conditioned slurry of water and
crushed oil
sand. In the Clark Process, an amount of sodium hydroxide (caustic) is added
to the slurry
to adjust the slurry pH upwards, which enhances the liberation and separation
of bitumen
from the oil sand. Other aqueous-based extraction processes may use other
temperatures
and may include other conditioning agents, which are added to the oil sand
slurry, or may
not use a conditioning agent. Regardless of the type of aqueous-based
extraction
process employed, the process will typically result in the production of a
bitumen froth that
requires treatment with a solvent. For example, in the Clark Process, a
bitumen froth
stream comprises bitumen, fine particulate solids (also referred to as mineral
matter), and
water. Certain processes use naphtha to dilute bitumen froth before separating
the
product bitumen, for instance by centrifugation. These processes are called
naphtha froth
treatment (NFT) processes. Other processes use a paraffinic solvent, and are
called
paraffinic froth treatment (PFT) processes, to produce pipelineable bitumen
with low levels
of solids and water. In the PFT process, a paraffinic solvent (for example, a
mixture of iso-
pentane and n-pentane) is used to dilute the froth before separating the
product, diluted
bitumen, for instance by gravity. A portion of the asphaltenes in the bitumen
is also
rejected by design in the PFT process and this rejection is used to achieve
reduced solids
and water levels. In both the NFT and the PFT processes, the diluted tailings
(comprising
water, solids and some hydrocarbon) are separated from the product diluted
bitumen.
Recovery of solvent from the diluted bitumen component is currently required
before the
bitumen may be delivered to a refining facility for further processing. An
example of a PFT
process is described in Canadian Patent No. 2,587,166 (Sury). Non-limiting
examples of
bitumen extraction from mined oil sand are described in U.S. Patent No.
7,585,407
(Duyvesteyn et al.), U.S. Patent Publication No. 2010/0147516 (Betzer-
Zilevitch), and
U.S. Patent Publication No. 2010/0276341 (Speirs et al.).
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[0005] One type of in situ VORP is a solvent-dominated recovery process
(SDRP). At the
present time, solvent-dominated recovery processes (SDRPs) are not commonly
used as
commercial recovery processes to produce highly viscous oil. Highly viscous
oils are
produced primarily using thermal methods in which heat, typically in the form
of steam, is
added to the reservoir. Cyclic solvent-dominated recovery processes (CSDRPs)
are a
subset of SDRPs. A CSDRP is typically, but not necessarily, a generally non-
thermal
recovery method that uses a solvent to mobilize viscous oil by cycles of
injection and
production. Solvent-dominated means that the injectant comprises greater than
50% by
mass of solvent or that greater than 50% of the produced oil's viscosity
reduction is
obtained by chemical solvation rather than by thermal means. One possible
laboratory
method for roughly comparing the relative contribution of heat and dilution to
the viscosity
reduction obtained in a proposed oil recovery process is to compare the
viscosity obtained
by diluting an oil sample with a solvent to the viscosity reduction obtained
by heating the
sample.
[0006] In a CSDRP, a viscosity-reducing solvent is injected through a well
into a
subterranean viscous-oil reservoir, causing the pressure to increase. Next,
the pressure
is lowered and reduced-viscosity oil is produced to the surface through the
same well
through which the solvent was injected. Multiple cycles of injection and
production are
used.
[0007] CSDRPs may be particularly attractive for thinner or lower-oil-
saturation reservoirs.
In such reservoirs, thermal methods utilizing heat to reduce viscous oil
viscosity may be
inefficient due to excessive heat loss to the overburden and/or underburden
and/or
reservoir with low oil content.
[0008] References describing specific CSDRPs include: Canadian Patent No.
2,349,234
(Lim et al.); G. B. Lim et al., "Three-dimensional Scaled Physical Modeling of
Solvent
Vapour Extraction of Cold Lake Bitumen", The Journal of Canadian Petroleum
Technology, 35(4), pp. 32-40, April 1996; G. B. Lim et al., "Cyclic
Stimulation of Cold Lake
Oil Sand with Supercritical Ethane", SPE Paper 30298, 1995; US Patent No.
3,954,141
(Allen et al.); and M. Feali et al., "Feasibility Study of the Cyclic VAPEX
Process for Low
Permeable Carbonate Systems", International Petroleum Technology Conference
Paper
12833, 2008.
[0009] The family of processes within the Lim et al. references describe
embodiments of a
particular SDRP that is also a cyclic solvent-dominated recovery process
(CSDRP).
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These processes relate to the recovery of heavy oil and bitumen from
subterranean
reservoirs using cyclic injection of a solvent in the liquid state which
vaporizes upon
production. The family of processes within the Lim et al. references may be
referred to as
CSPTM processes.
[0010] With reference to Figure 1, which is a simplified diagram based on
Canadian
Patent No. 2,349,234 (Lim et al.), one CSPTM process embodiment is described
as a
single well method for cyclic solvent stimulation, the single well preferably
having a
horizontal wellbore portion and a perforated liner section. A vertical
wellbore (1) driven
through overburden (2) into reservoir (3) is connected to a horizontal
wellbore portion (4).
The horizontal wellbore portion (4) comprises a perforated liner section (5)
and an inner
bore (6). The horizontal wellbore portion comprises a downhole pump (7). In
operation,
solvent or viscosified solvent is driven down and diverted through the
perforated liner
section (5) where it percolates into reservoir (3) and penetrates reservoir
material to yield
a reservoir penetration zone (8). Oil dissolved in the solvent or viscosified
solvent flows
into the well and is pumped by downhole pump through an inner bore (6) through
a motor
at the wellhead (9) to a production tank (10) where oil and solvent are
separated and the
solvent is recycled.
[0011] It would be desirable to improve at least one aspect of a current VORP.
SUMMARY
[0012] It is expected that certain SDRP projects may be near an existing
and/or a future
VORP. The present disclosure relates generally to the integration of at least
two different
viscous oil recovery processes (VORPs), at least one of which is a solvent-
dominated
recovery process (SDRP). Integration of the SDRP and the VORP may be achieved
through at least one of: solvent, heat, a production stream, and a viscous oil
reservoir.
[0013] In a first aspect, there is provided a method of operating at least two
different
viscous oil recovery processes, the method comprising: operating a solvent
dominated
recovery process (SDRP); operating a viscous oil recovery process (VORP); and
integrating the SDRP and the VORP through at least one of: solvent, heat, a
production
stream, and a viscous oil reservoir.
[0014] Other aspects and features of the present disclosure will become
apparent to
those ordinarily skilled in the art upon review of the following description
of specific
embodiments of the invention in conjunction with the accompanying figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Embodiments of the present invention will now be described, by way of
example
only, with reference to the attached Figures, wherein:
[0016] Fig. 1 is a schematic of a CSPTM process in accordance Canadian Patent
No.
2,349,234 (Lim et al.).
[0017] Figure 2 is a flow chart outlining the integration of a SDRP with a
VORP,
according to a disclosed embodiment.
DETAILED DESCRIPTION
[0018] The term "viscous oil" as used herein means a hydrocarbon, or mixture
of
hydrocarbons, that occurs naturally and that has a viscosity of at least 10 cP
(centipoise)
at initial reservoir conditions. Viscous oil includes oils generally defined
as "heavy oil" or
"bitumen". Bitumen is classified as an extra heavy oil, with an API gravity of
about 100 or
less, referring to its gravity as measured in degrees on the American
Petroleum Institute
(API) Scale. Heavy oil has an API gravity in the range of about 22.3 to about
10 . The
terms viscous oil, heavy oil, and bitumen are used interchangeably herein
since they may
be extracted using similar processes.
[0019] In situ is a Latin phrase for "in the place" and, in the context of
hydrocarbon
recovery, refers generally to a subsurface hydrocarbon-bearing reservoir. For
example, in
situ temperature means the temperature within the reservoir. In another usage,
an in situ
oil recovery technique is one that recovers oil from a reservoir within the
earth.
[0020] The term "formation" as used herein refers to a subterranean porous
media.
The terms "reservoir" and "formation" may be used interchangeably.
[0021] As discussed in the background section, a CSDRP is one type of in situ
VORP.
Another description of a CSDRP is provided in Canadian Patent Application No.
2,688,392, filed December 9, 2009 (Lebel et al.).
[0022] As discussed in the background section, solvent-based extraction of
mined oil
sand is one type of VORP. An example of solvent-based extraction is provided
in
Canadian Patent Application No. 2,724,806 filed December 10, 2010 (Adeyinka et
al.).
[0023] When referring to "SDRP", "CSDRP", "in situ VORP", "oil extraction of
mined oil
sand", or the like, this includes the associated facilities. To cite but one
example, in a
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CSDRP, the facilities for recovering solvent from the produced viscous oil and
solvent are
meant to be included in the scope of CSDRP.
[0024] As discussed in the summary section above, it is expected that certain
SDRP
projects may be near an existing and/or a future VORP. The present disclosure
relates
generally to the integration of at least two different viscous oil recovery
processes
(VORPs), at least one of which is a solvent-dominated recovery process (SDRP).
Integration of the SDRP and the VORP may be achieved through at least one of:
solvent,
heat, a production stream, and a viscous oil reservoir. The expression "two
different
viscous oil recovery processes", means that the processes are different but
may fall within
the same category; for instance VAPEX and CSDRP are different processes, but
fall
within the SDRP category. While the integration may be more beneficial, in
certain
instances, when the two different processes are close to one another,
proximity is not
essential.
[0025] Certain underground viscous oil deposits, for instance certain Alberta
oil sands,
involve naturally occurring thick high oil saturation zones adjacent to lower
oil saturation
formations. The high oil saturation zones have historically been exploited
first using
thermal-solvent based in situ recovery methods. Thick high quality and deep
deposits, too
deep to be mined, are quite often surrounded by thinner and lower quality oil
bearing
zones. While viscous oil from the thick zones can be economically recovered by
using
thermal-solvent in situ recovery methods, the same processes would provide
uneconomic
yields in the thin lower quality zones due to excessive heat loss. Generally
non-thermal
SDRPs, can be employed effectively in many of those poorer quality reservoirs.
In the
future, SDRP projects may be developed next to existing thermal in situ
operations when
the poorer quality deposits are accessed. By integrating two different VORPs
(for
instance which are close to each other), it may be possible to improve energy
use, to
reduce infrastructure, to combine product streams (for instance two nearby
operations),
and/or to apply a hybrid recovery scheme (for instance to increase oil and
solvent
recoveries).
[0026] A similar trend also exists between mineable and shallow oil sand
deposits (for
instance 100 to 200m burial depth), such as in the Athabasca oil sands in
Alberta.
Thermal in situ methods such as SAGD and CSS may not be suitable in the
shallow
deposits due to fluid leakage to surface, and the absence of dissolved
methane,
respectively. Historically, the mineable deposits were developed first using
surface
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mining combined with aqueous and other separation methods. In the future, if
the shallow
deposits, too deep for mining, are developed using non-thermal in situ solvent-
based
recovery methods, surface mining processing facilities may be located next to
solvent-
based in situ projects. By integrating two different operations (for instance
two nearby
operations), it may be possible to improve energy use, recycle by-production,
and/or
reduce infrastructure.
[0027] In one embodiment, heat (for instance low-grade, for instance at less
than100 C)
produced by a recovery process could be used in another VORP.
[0028] Some operations also produce or consume hydrocarbon solvents, which are
purchased at a significant cost. Due to impurity or irregular timing, excess
hydrocarbon
solvent produced by the recovery operations could be used elsewhere, for
instance as
boiler fuel. Although this approach does not generate high utilization value
for the solvent,
it may be preferable to building solvent recovery units and associated storage
facilities.
[0029] Resources targeted by SDRPs include bitumen deposits where thermal
recovery
operations are not feasible or preferred due to low bitumen saturation or thin
resource
thickness. It is expected that these relatively marginal resources may often
be adjacent to
thermal operations exploiting thicker, higher bitumen saturation resources, or
adjacent to
mining operations exploiting shallow resources. The relatively marginal
resources may
also be located deeper or shallower than the resource being exploited by the
thermal
process. In one embodiment, a SDRP is integrated with another VORP at the same
or a
nearby location, while accessing different subsurface resources. One SDRP may
also be
practiced nearby another SDRP; and to cite but one example, a CSDRP may be
integrated with VAPEX.
[0030] Figure 2 is a flow chart outlining the integration of a SDRP with a
VORP, according
to a disclosed embodiment. As shown in Figure 2, an SDRP is operated (202), a
VORP is
operated (204), and the two are integrated (206) through at least one of:
solvent, heat, a
production stream, and a viscous oil reservoir.
[0031] Various embodiments of this integration will now be described. These
embodiments are arranged in three categories. In the first category, a SDRP is
integrated
with a mining operation. In the second category, a SDRP is integrated with an
in situ
VORP. In the third category, a SDRP and in situ VORP are operated on a common
reservoir.
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[0032] 1: First category: SDRP integrated with a mining operation
[0033] 1-A: Solvent Sharing
[0034] In this embodiment, solvent is shared between a mining process and a
SDRP.
The mining process uses a solvent (for instance a light hydrocarbon such as
propane to
hexane to partially or fully de-asphalt bitumen, or naphtha for upgrading). A
SDRP injects
solvent and recovers solvent and viscous oil. These two processes can share a
common
solvent source and/or method of transportation, for instance a pipeline
network. The
processes can also share solvent storage. In this way, facilities are reduced.
The solvent
recovery unit of a mining process may produce a product stream that does not
meet
quality specification for the next stage of processing and is recycled through
the facility
during period of plant upsets. As an example, due to a lower than design
temperature in
the solvent recovery unit, higher molecular weight hydrocarbon liquids are now
mixed with
solvent and will foul the de-asphalting process, if recycled. While this
product is
detrimental to the mineable oil sands processing operation, it may actually be
beneficial to
an SDRP as the higher molecular weight hydrocarbon liquids may improve
miscibility and
solvent solubility with viscous oil. Therefore, this product can be injected
into the
underground formation targeted for the SDRP to improve recovery or extraction
efficiency.
The "off-specification" solvent stream can also be blended with source solvent
to be
injected into the SDRP targeted underground reservoir(s).
[0035] 1-B: Blending SDRP and Mining Production to Capture Product Value
[0036] The production stream from a SDRP using a light hydrocarbon solvent
(for
instance propane to pentane), may produce a light liquid phase at the early
stage of
production. This light stream is nearly de-asphalted with pentane-insoluble
components
removed and has a higher value than bitumen. This quality improvement value is
lost if
the product is mixed and sold with heavier components such as whole bitumen.
Given
that a mining process may produce partially or fully de-asphalted bitumen, in
this
embodiment, the light stream from the SDRP is combined and sold with the
mining up-
graded stream to take better advantage of its increased product value.
[0037] The mid- to late-stage production from a SDRP may produce a heavy phase
that
comprises a higher proportion of pentane-insoluble components than whole
bitumen. This
heavy stream provides a higher asphalt yield than bitumen and asphalt value
peaks during
high demand periods. This heavy stream can be combined with the bottom
fraction from
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the de-asphalting facility in the operation to be processed or transported to
a nearby
facility to maximize asphalt production during peak demand season. In the low
demand
periods, the heavy phase can be blended with other streams to be sold as
bitumen,
sometimes further diluted with a diluent such as a gas condensate.
[0038] 1-C: Heat Sharing
[0039] The tailings stream from a froth separation unit in a mining operation
may be about
901 C. In this embodiment, the waste heat from the tailings stream may be used
in one of
more of the following ways:
[0040] (a) to pre-heat a solvent injection stream (for instance up to 90 C)
for SDRP
injection
[0041] (b) to circulate down a SDRP well via a carrier fluid (for instance
glycol, for
instance in a slim tube) to heat (for instance to 55 C) and reduce the
viscosity of the
production stream from a SDRP to increase production rate.
[0042] (c) to heat a surface production system in a SDRP facility (for
instance up to 55 C)
for providing flow assurance; and
[0043] (d) to heat a SDRP production stream to vapourize and recover solvent
(for
instance at 50 to 90 C) above ground, for instance in a separator.
[0044] The waste heat may be captured using heat exchangers.
[0045] 1-D: Other Product Sharing Synergy
[0046] The miscibility of light hydrocarbon solvents with viscous oils can be
altered by
blending the solvent with higher molecular weight hydrocarbon liquids. De-
asphalted or
upgraded bitumen from a mining operation (including from a stand-alone
upgrader) can be
added to source solvent to be injected into SDRP wells to improve miscibility
and increase
bitumen recovery.
[0047] Mining processing byproduct gases such as CO2, CH4 and SO2 can be added
to
SDRP solvent and injected to target wells to enhance bitumen and solvent
recovery.
[0048] Mining processing byproduct gas can be used as a gas lift gas for SDRP
wells.
[0049] Blending SDRP and mining bitumen streams can reduce demand for diluent
for
pipelining when de-asphalted bitumen is blended with heavy components of
bitumen as a
result of in situ separation of bitumen in SDRP.
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[0050] 2: Second category: SDRP integrated with an in situ VORP
[0051] 2-A: Solvent and Product Sharing
[0052] In this embodiment, a common solvent source and transportation system
(for
instance a pipeline network) is used to meet in situ VORP and SDRP needs. For
cyclic
SDRP (CSDRP) methods, integrating with an in situ VORP operation provides more
wells
for injecting solvent and more wells as storage for recycling solvent, thus
providing more
flexibility for scheduling wells for injection and production, especially
during the startup
phases of both processes. Blending early SDRP production, i.e. the light
phase, with an
in situ VORP bitumen stream reduces the demand for diluent for pipelining.
[0053] 2-B: Heat Sharing
[0054] In this embodiment, waste heat from VORP facilities (for instance CSS
facilities)
such as boiler exhaust (for instance at 200 C to 300 C), a hot flow-back
production stream
(for instance at 220 C), or waste heat from glycol systems (for instance 80 C)
is used
through heat exchangers to:
[0055] (a) pre-heat a solvent injection stream (for instance up to 90 C) for
SDRP injection;
[0056] (b) circulate down a SDRP well via a carrier fluid (for instance
glycol, for instance
in a slim tube) to heat (for instance to 55 C) and reduce the viscosity of the
production
stream from a SDRP to increase production rate;
[0057] (c) heat a surface production system in a SDRP facility (for instance
up to 55 C)
for providing flow assurance; and
[0058] (d) to heat a SDRP production stream to vapourize and recover solvent
(for
instance at 50 to 90 C) above ground, for instance in a separator. A heat
exchange (for
instance using counter-current flow) may be used. This offers beneficial
cooling to the in
situ VORP facilities.
[0059] 2-C: Greenhouse Gas (GHG) Capture
[0060] An in situ VORP may produce greenhouse gases. In this embodiment,
greenhouse gases are removed and injected with solvent into SDRP wells. In
this way,
greenhouse gases may be sequestered and SDRP viscous oil and solvent
recoveries may
be improved. Integrating VORP and SDRP operations may lower the greenhouse gas
intensity of the combined operations since SDRP may have a lower greenhouse
gas
intensity (for instance 10% of the greenhouse gas intensity as compared to a
thermal in
situ VORP).
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[0061] 2-D: Gas Sharing
[0062] By integrating in situ VORP and SDRP operations, a single casing gas
compression system can be used for both processes when their respective
facilities are in
close proximity (for instance up to 5 km) to each other. Non-recyclable
combustible gases
from an SDRP operation can be used to fuel VORP boilers. Non-condensable gases
from
an in situ VORP operation can be used to pressurize annulus gas or as lift gas
in SDRP
wells.
[0063] 3: Third category: SDRP and in situ VORP are operated on a common
reservoir
[0064] Various SDRPs (for instance VAPEX) can be implemented as a follow-up
process
to another in situ VORP which may leave a sufficient residual hydrocarbon base
to justify
the follow-up SDRP. The remnant heat in the VORP reservoirs (for instance up
to 120 C)
may provide energy needed to generate vapour solvent for some of the SDRP
follow-up
operations.
[0065] Various VORP displacement methods, such as SAGD, SA-SAGD, or steam-
flood,
require that fluid communication be established between injection and producer
wells
before such operation can be sustained. Some SDRPs, such as CSDRPs, can be
implemented first in viscous oil reservoirs until fluid communication is
established between
wells and then these wells may be converted to in situ VORP displacement
operations.
Some in situ VORPs, especially the ones that are gravity-stabilized, may have
high oil
recovery efficiency (for instance greater than 60% of original oil in place).
[0066] Various in situ VORPs (for instance steam flood) can be implemented as
a follow-
up process to a SDRP which may leave a sufficient residual hydrocarbon base
remaining
to justify the implementation of the follow-up operation. The remnant solvent
in the SDRP
reservoirs (for instance up to 10 volume percent of injected value) may
provide the
required mobility in the reservoir fluid to effectively carry out the in situ
VORP operation
without excessive bypassing of the viscous oil related to drive fluid
fingering.
[0067] The at least two processes may be operated simultaneously,
consecutively, with
overlap, or as a hybrid process, and on the same or separate reservoirs.
[0068] CSDRP
[0069] In one embodiment, the CSDRP comprises: (a) injecting a volume of fluid
comprising greater than 50 mass % of a solvent, wherein the solvent is a
viscosity-
reducing solvent, into an injection well completed in the reservoir; (b)
halting injection into
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the injection well and subsequently producing at least a fraction of the
injected fluid and
the in situ viscous oil from the reservoir through a production well; (c)
halting production
through the production well; and (d) subsequently repeating the cycle of steps
(a) to (c);
wherein, in at least one subsequent cycle, an in situ volume of fluid injected
in step (a) is
equal to a net in situ volume of fluids produced from the production well in
an immediately
preceding cycle plus an additional in situ volume of the fluid. Immediately
after halting
injection into the injection well, at least 25 mass % of the injected solvent
may be in a
liquid state in the reservoir.
[0070] In the preceding description, for purposes of explanation, numerous
details are set
forth in order to provide a thorough understanding of the embodiments of the
invention.
However, it will be apparent to one skilled in the art that these specific
details are not
required in order to practice the invention.
[0071] The above-described embodiments of the invention are intended to be
examples
only. Alterations, modifications and variations can be effected to the
particular
embodiments by those of skill in the art without departing from the scope of
the invention,
which is defined solely by the claims appended hereto.
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