Note: Descriptions are shown in the official language in which they were submitted.
1
IN SITU STARTUP PROCESS FOR MOBILIZING BITUMEN IN A RESERVOIR
TECHNICAL FIELD
[001] The technical field generally relates to startup processes for
mobilizing bitumen
contained in an underground reservoir, and more particularly to the use of
liquid solvent
in a cyclic startup process for mobilizing bitumen in a reservoir.
BACKGROUND
[002] There are various techniques for recovering bitumen from subsurface
reservoirs.
One technique is called cyclic steam stimulation (CSS), which is a widely
implemented
technique for recovering oil and bitumen. Another known technique called Steam
Assisted
Gravity Drainage (SAGD) has become a widespread process of recovering heavy
oil and
bitumen. Other in situ recovery processes use solvent injection or other
mobilizing fluids
to help mobilize bitumen in the reservoir. In situ recovery processes can use
single wells
that operate cyclically through injection and production cycles, or well pairs
that include
an injection well and a production well.
[003] Once a well pair is drilled and completed, the first phase of operations
is the so-
called startup phase. In the startup phase, fluid communication is established
between the
injection and production wells of a given well pair. Prior to startup, the
high saturation
bitumen interval separating the injection and production wells of each pair
has low fluid
mobility and the subsequent in situ recovery process relies on initially
establishing a mobile
interval in between the injection and production wells. It is important for an
effective
bitumen recovery operation to uniformly reduce the viscosity of the bitumen
between
injection and production wells prior to producing it. This procedure of
establishing fluid
communication between two wells at the initial stages can be done by
circulating a
mobilizing fluid, such as steam, through one or both wells.
Solvent based methods for well pair startup and initialization has been
attempted but
various challenges remain.
SUMMARY
[004] According to a first aspect, an in situ startup process for mobilizing
bitumen
between a gravity drainage well pair located in a bitumen containing reservoir
is provided.
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The well pair includes an injection well having a horizontal injection section
and a
production well having a horizontal production section located below the
horizontal
injection section, the horizontal injection section and horizontal production
section defining
an interwell region therebetween. The process includes, in an introduction
stage,
introducing a predetermined volume of liquid solvent via a solvent startup
well selected
from the injection and production wells, at an introduction pressure and
introduction
temperature configured to maintain the liquid solvent in liquid phase within
the solvent
startup well and the reservoir, wherein the introduction pressure is at or
above an initial
reservoir pressure of the interwell region and below a fracturing pressure
thereof. The
process further includes, in a soaking stage, ceasing introduction of the
liquid solvent and
allowing the liquid solvent to soak within the reservoir for a soaking period
in order to
mobilize bitumen in the interwell region. The process still further includes,
in a production
stage, producing fluids from the solvent startup well to recover a startup
production fluid
comprising bitumen and liquid solvent. The process further includes, in a
surface
separation stage, separating at surface the startup production fluid into a
solvent depleted
bitumen component and a recovered solvent component. Finally, the process
includes
cyclically repeating the introduction stage, the soaking stage, the production
stage and the
surface separation stage to mobilize bitumen located in the interwell region.
[005] According to a possible embodiment, the recovered solvent component is
reintroduced in the solvent startup well in a subsequent introduction stage.
[006] According to a possible embodiment, the liquid solvent is stored at
surface within
a solvent supply source, and wherein the liquid solvent is introduced within
the solvent
startup well via a tubing string.
[007] According to a possible embodiment, the solvent startup well includes a
horizontal
startup section, and wherein the tubing string is coupled to the solvent
supply source and
is configured to transfer liquid solvent within the horizontal startup
section.
[008] According to a possible embodiment, the solvent startup well includes a
vertical
section, and wherein once the horizontal startup section is filled with liquid
solvent,
displacement fluid is introduced within the vertical section to increase
pressure on the
liquid solvent.
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[009] According to a possible embodiment, the solvent startup well includes a
liner
extending along at least a portion of the horizontal startup section, and
wherein the tubing
string extends within the liner and defines an annulus region therebetween.
[0010] According to a possible embodiment, the liner is slotted to allow
liquid solvent to
exit the horizontal startup section and infiltrate the reservoir.
[0011] According to a possible embodiment, the solvent startup well includes a
packer
assembly mounted within the annulus region, the packer assembly defining an
upstream
region and a downstream region, the packer assembly being configured to
prevent fluid
communication between the upstream and downstream regions.
[0012] According to a possible embodiment, the solvent startup well includes a
transition
section connecting the vertical section and horizontal startup section, and
wherein the
downstream region includes at least a portion of the horizontal startup
section, and the
upstream region includes at least the vertical section and the transition
section.
[0013] According to a possible embodiment, the packer assembly is removably
mounted
within the annulus region to adjust a length of the downstream region.
[0014] According to a possible embodiment, the tubing string is configured to
extend
through the packer assembly to introduce liquid solvent within the downstream
region.
[0015] According to a possible embodiment, the solvent startup well includes a
pump
located within the downstream region, and wherein the production stage is
enabled by the
pump.
[0016] According to a possible embodiment, the pump is an electrical
submersible pump
(ESP).
[0017] According to a possible embodiment, during an initial introduction
stage, the
predetermined volume of liquid solvent exceeds an internal volume of the
tubing string
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extending within the downstream region added to the volume of the annulus
region located
in the downstream region.
[0018] According to a possible embodiment, during a given introduction stage,
the
predetermined volume of liquid solvent is greater than the predetermined
volume of liquid
solvent of a previous cycle by an amount determined based at least in part by
monitoring
bitumen removal from the reservoir during the previous cycle.
[0019] According to a possible embodiment, the introduction pressure is
between about
kPa and about 100 kPa above the initial reservoir pressure.
[0020] According to a possible embodiment, the soaking stage is initiated once
the
predetermined volume of liquid solvent has been introduced.
[0021] According to a possible embodiment, the soaking period substantially
corresponds
to the amount of time required for the pressure within the solvent startup
well to stabilize.
[0022] According to a possible embodiment, the production stage is initiated
once the
soaking period has elapsed.
[0023] According to a possible embodiment, during the production stage, the
startup
production fluid is produced to surface via a sub-surface pump.
[0024] According to a possible embodiment, during the surface separation
stage, the
startup production fluid is separated via a separator.
[0025] According to a possible embodiment, the separator is a flash separator.
[0026] According to a possible embodiment, the separator is a centrifugal
separator.
[0027] According to a possible embodiment, during the surface separation
stage, only a
portion of the startup production fluid is separated into the solvent depleted
bitumen
component and the recovered solvent component.
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[0028] According to a possible embodiment, the recovered solvent component is
mixed
with substantially pure liquid solvent prior to reintroduction.
[0029] According to a possible embodiment, during the surface separation
stage, the
startup production fluid is subjected to gas removal, water removal, and/or
solvent make-
up.
[0030] According to a possible embodiment, the startup production fluid
includes a
bitumen concentration, and wherein the surface separation stage is initiated
if the bitumen
concentration is at or above a separation threshold.
[0031] According to a possible embodiment, the liquid solvent infiltrates the
reservoir via
gravity and/or diffusion-based mechanisms.
[0032] According to a possible embodiment, the liquid solvent comprises at
least one of
dimethyl ether, methyl ethyl ketone, toluene, )rylene, diesel, butane,
pentane, hexane,
heptane and naphtha.
[0033] According to a possible embodiment, the solvent startup well is
alternated between
the injection well and production well after each cycle.
[0034] According to a possible embodiment, the solvent startup well is
alternated between
the injection well and production well after a plurality of cycles.
[0035] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the soaking stage of a previous cycle of the
other startup
well.
[0036] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the production stage of a previous cycle of
the other startup
well.
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[0037] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the surface separation stage of a previous
cycle of the other
startup well.
[0038] According to a possible embodiment, both the injection well and the
production
well are operated as solvent startup wells simultaneously.
[0039] According to a second aspect, a startup process for mobilizing bitumen
surrounding a well positioned in a bitumen containing reservoir is provided.
The process
includes, in an introduction stage, introducing liquid solvent within the
well, the liquid
solvent having introduction parameters configured to maintain the liquid
solvent in liquid
phase within the well system and the reservoir. The process further includes,
in a soaking
stage, ceasing introduction of the liquid solvent, and allowing the liquid
solvent to soak
within the well and the reservoir fora soaking period, and, in a production
stage, producing
fluids from the solvent startup well to recover a startup production fluid
comprising bitumen
and liquid solvent. The process still further includes, in a surface
separation stage,
separating at surface the startup production fluid into a solvent depleted
bitumen
component and a recovered solvent component, which can be reused in a
subsequent
cycle. Finally, the process includes cyclically repeating the introduction
stage, soaking
stage, production stage and the surface separation stage to mobilize the
bitumen.
[0040] According to a possible embodiment, the recovered solvent component is
reintroduced in the well in a subsequent introduction stage.
[0041] According to a possible embodiment, during each introduction stage, a
predetermined volume of liquid solvent is introduced within the well.
[0042] According to a possible embodiment, the well is a solvent startup well,
and the
liquid solvent is stored at surface within a solvent supply source, and
wherein the liquid
solvent is introduced within the solvent startup well via a tubing string.
[0043] According to a possible embodiment, the solvent startup well comprises
a
horizontal startup section, and wherein the tubing string is coupled to the
solvent supply
source and is configured to transfer liquid solvent within the horizontal
startup section.
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[0044] According to a possible embodiment, the solvent startup well comprises
a vertical
section, and wherein once the horizontal startup section is filled with liquid
solvent,
displacement fluid is introduced within the vertical section to increase
pressure on the
liquid solvent.
[0045] According to a possible embodiment, the solvent startup well comprises
a liner
extending along at least a portion of the horizontal startup section, and
wherein the tubing
string extends within the liner and defines an annulus region therebetween.
[0046] According to a possible embodiment, the liner is slotted to allow
liquid solvent to
exit the horizontal startup section and infiltrate the reservoir.
[0047] According to a possible embodiment, the solvent startup well comprises
a packer
assembly mounted within the annulus region and defining an upstream region and
a
downstream region, the packer assembly being configured to prevent fluid
communication
between the upstream and downstream regions.
[0048] According to a possible embodiment, the solvent startup well comprises
a
transition section connecting the vertical section and horizontal startup
section, and
wherein the downstream region comprises at least a portion of the horizontal
startup
section, and the upstream region comprises at least the vertical section and
the transition
section.
[0049] According to a possible embodiment, the packer assembly is movably
mounted
within the annulus region to adjust a length of the downstream region.
[0050] According to a possible embodiment, the tubing string is configured to
extend
through the packer assembly to introduce liquid solvent within the downstream
region.
[0051] According to a possible embodiment, the solvent startup well comprises
a pump
located within the downstream region, and wherein the production stage is
enabled by the
pump.
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[0052] According to a possible embodiment, the pump is an electrical
submersible pump
(ESP).
[0053] According to a possible embodiment, during an initial introduction
stage, the
predetermined volume of liquid solvent exceeds an internal volume of the
tubing string
extending within the downstream region added to the volume of the annulus
region located
in the downstream region.
[0054] According to a possible embodiment, during a given introduction stage,
the
predetermined volume of liquid solvent is greater than the predetermined
volume of liquid
solvent of a previous cycle by an amount determined based at least in part by
monitoring
bitumen removal from the reservoir during the previous cycle.
[0055] According to a possible embodiment, the introduction parameters include
an
introduction temperature and an introduction pressure provided between about
10 kPa
and about 100 kPa above an initial reservoir pressure.
[0056] According to a possible embodiment, the soaking stage is initiated once
the
predetermined volume of liquid solvent has been introduced.
[0057] According to a possible embodiment, the soaking period substantially
corresponds
to the amount of time required for the pressure within the well to stabilize.
[0058] According to a possible embodiment, the production stage is initiated
once the
soaking period has elapsed.
[0059] According to a possible embodiment, during the production stage, the
startup
production fluid is produced via a surface pump.
[0060] According to a possible embodiment, during the surface separation
stage, the
startup production fluid is separated via a separator.
[0061] According to a possible embodiment, the separator is a flash separator.
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[0062] According to a possible embodiment, the separator is a centrifugal
separator.
[0063] According to a possible embodiment, during the surface separation
stage, only a
portion of the startup production fluid is separated into the solvent depleted
bitumen
component and the recovered solvent component.
[0064] According to a possible embodiment, the recovered solvent component is
mixed
with substantially pure liquid solvent prior to reintroduction.
[0065] According to a possible embodiment, during the surface separation
stage, the
startup production fluid is subjected to gas removal, water removal, and/or
solvent make-
up.
[0066] According to a possible embodiment, the startup production fluid
comprises a
bitumen concentration, and wherein the surface separation stage is initiated
if the bitumen
concentration is at or above a separation threshold.
[0067] According to a possible embodiment, the liquid solvent infiltrates the
reservoir via
gravity and/or diffusion-based mechanisms.
[0068] According to a possible embodiment, the liquid solvent comprises at
least one of
dimethyl ether, methyl ethyl ketone, toluene, xylene, diesel, butane, pentane,
hexane,
heptane and naphtha.
[0069] According to a possible embodiment, the solvent startup well is
alternated between
an injection well and a production well after each cycle.
[0070] According to a possible embodiment, the solvent startup well is
alternated between
an injection well and a production well after a plurality of cycles.
[0071] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the soaking stage of a previous cycle of the
other startup
well.
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[0072] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the production stage of a previous cycle of
the other startup
well.
[0073] According to a possible embodiment, the subsequent introduction stage
for one
startup well is initiated during the surface separation stage of a previous
cycle of the other
startup well.
[0074] According to a possible embodiment, an injection well and a production
well are
operated as solvent startup wells simultaneously.
BRIEF DESCRIPTION OF THE DRAWINGS
[0075] Figure 1 is a transverse cut view of a well pair and surface equipment.
[0076] Figure 2 is a transverse cut view of a well pair.
[0077] Figure 3 is a process flow diagram of an example of the startup
process.
[0078] Figure 4 is a transverse cut view of a solvent startup well, showing a
tubing string
and a liner.
[0079] Figure 5 is a transverse cut view of a section of a solvent startup
well, showing a
tubing string, a packer assembly and subsurface pump.
[0080] Figure 5a is a transverse cut view of a solvent startup well, showing a
transition
section and a horizontal section, with a subsurface pump positioned downstream
of a
packer assembly.
[0081] Figure 6 is a perspective view of a section of a well pair, showing an
annulus region
defined between a liner and a tubing string of one of the wells.
[0082] Figures 7a to 7d are transverse cut views of a well pair illustrating
example cyclic
solvent injection and production for mobilizing bitumen in the reservoir.
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[0083] Figures 8a to 8e are transverse cut views of a well pair illustrating
an example
cyclic solvent injection and production process for mobilizing bitumen in the
reservoir,
where two wells are used.
[0084] Figure 9 is a transverse cut views of a well pair and surface equipment
illustrating
an example system for cyclic startup using both wells of a well pair.
[0085] Figure 10 is a top plan view of well pads and multiple well pairs
extending from the
pads, as well as surface equipment for supplying solvent to and receiving
startup
production fluid from one or more wells of each pad for cyclic startup of
multiple well pairs
and multiple pads.
DETAILED DESCRIPTION
[0086] As will be explained below in relation to various example
implementations, a
startup process is described herein for enabling mobilization of bitumen
located in a
bitumen containing reservoir (R), for example between a well pair designated
for a
subsequent in situ bitumen recovery process. The startup process leverages the
injection
of solvent in liquid phase followed by soaking, producing back fluids
including mobilized
bitumen and liquid solvent, separating the production fluids at surface to
recover solvent,
and reinjecting solvent as part of a cyclical pattern. The interwell region
between the well
pair can thus be mobilized in order to establish fluid communication between
the two wells,
or to prepare the region by increasing mobility prior to subsequent startup
operations, such
as steam or solvent circulation.
[0087] It should be noted that the startup process can be adapted to mobilize
bitumen for
ultimately producing bitumen from the reservoir (R) via any suitable in situ
recovery
method, which may use solvent, steam, and/or other mobilizing fluids for
injection. The
startup process includes several steps carried out via a well assembly
installed within the
reservoir. The well assembly can include a single well, a well pair such as
those used in
SAGD or solvent assisted gravity drainage processes (e.g., using solvent-steam
co-
injection or solvent-only injection), or any other suitable well assembly
configuration. The
startup process uses liquid solvent introduced into the reservoir through one
or more wells
of the well assembly, referred to as a solvent startup well, in order to
mobilize bitumen
contained in the reservoir. In some implementations, the liquid solvent is
cyclically
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introduced and produced back from the well assembly, for reuse, until the
bitumen has
been sufficiently mobilized to allow ramp up of production.
[0088] The startup process includes an initial introduction stage where liquid
solvent is
introduced within the reservoir via the solvent startup well. Then, the
process includes a
soaking stage where the liquid solvent is allowed to soak within the reservoir
for a period
of time in order to diffuse into and mobilize the bitumen located around a
section of the
solvent startup well. After the soaking time period, the process includes a
production stage
where fluids are produced from the startup well to recover at least some of
the liquid
solvent introduced during the introduction stage along with mobilized bitumen.
The
process also includes a separation stage where the fluids recovered during the
production
stage are effectively separated in order to recover bitumen depleted liquid
solvent. The
introduction stage, the soaking stage, the production stage and the separation
stage can
be cyclically repeated until certain bitumen mobilization in the interwell
region has been
achieved, and optionally until fluid communication is established between the
well pair.
The liquid solvent introduced in a subsequent introduction stage can be
predominantly
composed of the recovered liquid solvent from the production and separation
stages of a
previous cycle.
[0089] A more detailed description of well assemblies and process
implementations that
can be used in the context of in situ startup operations is provided further
below. Various
examples of structural features as well as operating strategies and parameters
are
described.
Well assembly implementations for the startup well
[0090] With reference to Figures 1 and 2, the startup process 10 can be
carried out via a
well system 20 including a gravity drainage well pair 21. It should be
understood that the
processes and techniques of the present description can also be implemented
using other
well assemblies and configurations, such as single wells configured for CSS
operations or
single-well SAGD operations. The well pair 21 used in connection with the
described
startup process 10 can be a traditional SAGD well pair which can have
wellheads located
at a well pad that is part of an in situ recovery facility.
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[0091] More specifically, the well pair 21 can include an injection well 22
having a
horizontal injection section 22h and a production well 24 having a horizontal
production
section 24h. Each horizontal section 22h, 24h is located within the bitumen
containing
reservoir (R). In the illustrated implementation, the horizontal production
section 24h is
located vertically below the horizontal injection section 22h, thus defining
an interwell
region 26 therebetween. However, other arrangements of well pairs or well
groups are
also possible. It should therefore be appreciated that the startup process 10
can be
implemented to mobilize the bitumen located in the interwell region of a well
pair, and can
be further operated to establish fluid communication between the wells of the
well pair.
[0092] Still referring to Figures 1 and 2, the injection well 22 can further
include an injection
wellhead 22w, a vertical injection section 22v, and an injection transition
section 22t fluidly
connecting the vertical section 22v and the horizontal injection section 22h.
Similarly, the
production well 24 can include a production wellhead 24w, a vertical
production section
24v, and a production transition section 24t fluidly connecting the vertical
section 24v and
the horizontal section 24h. It should be understood that the wellheads 22w,
24w can be
positioned on the well pad which is located at the surface. Alternate
configurations of the
well pair or group can also be used in the context of the techniques described
herein.
Solvent introduction stage
[0093] Referring to Figures 3 and 4, in addition to Figures 1 and 2, the
startup process
can be initiated with an introduction stage 10a where liquid solvent is
introduced within the
reservoir via a solvent startup well 30. It should be readily understood that,
in the context
of the present disclosure, the expression "solvent startup well" can refer to
the injection
well 22 or the production well 24 or both, as will become apparent from the
following
detailed description. It should be understood that the solvent startup well 30
can include
all of the structural features of the injection well 22 and/or the production
well 24, as
described above. More specifically, the solvent startup well 30 can include a
startup
wellhead 30w, a horizontal startup section 30h, a vertical startup section
30v, and a startup
transition section 30t fluidly connecting the vertical startup section 30v and
the horizontal
startup section 30h.
[0094] In some implementations, the liquid solvent can be introduced within
the reservoir
(R) without the use of heat, such as the temperatures at which steam is
traditionally
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introduced during regular SAGD startup and normal operations. Alternatively,
the liquid
solvent can be pre-heated prior to introduction down the startup well.
Additionally, the
liquid solvent can be introduced within the reservoir without the use of high
pressures, or
pressure gradients compared to reservoir pressures, such as pressures for
fracturing
operations. In some implementations, the liquid solvent can be introduced
within the
reservoir via the solvent startup well at predetermined introduction
parameters, such as
an introduction pressure and an introduction temperature. The introduction
parameters
can be configured to maintain the liquid solvent in liquid phase throughout
the main stages
of the startup process and within the startup well and the reservoir. It
should be understood
that the introduction pressure can be at or above an initial reservoir
pressure of the
interwell region, but preferably exceeds the reservoir pressure in order to
facilitate the
introduction of liquid solvent within the reservoir (R). For example, the
introduction
pressure can be at most 40 kPa, 50 kPa, 70 kPa, 100 kPa, or 150 kPa above the
reservoir
pressure surrounding the startup well 30. The introduction pressure can be
determined
based on various reservoir properties, such as water mobility for example. In
other words,
a reservoir having high water mobility can require a lower introduction
pressure (e.g.,
about 40 kPa) than a reservoir having low water mobility which can require a
greater
introduction pressure (e.g., about 100kPa to 150kPa). It should also be
understood that
the introduction pressure can be below a fracturing pressure of the interwell
region. The
introduction parameters can be determined and/or calculated using various
techniques,
such as pressure transient analysis (PTA) among other known techniques. The
introduction pressure can thus be provided to ensure the solvent is in liquid
phase within
all sections of the startup well, and also to provide a slight pressure
gradient (e.g., within
the range of 10 kPa to 100 kPa) compared to the interwell region to encourage
penetration
of the solvent from the well into the reservoir while avoiding reservoir
fracturing.
[0095] With reference to Figures 4 and 5, the liquid solvent can be introduced
within the
solvent startup well 30 via a tubing string 32. The tubing string 32 can be
inserted via the
startup wellhead 30w to extend down and within the horizontal section 30h in
order to
provide liquid solvent within the solvent startup well 30. It should be
understood that in
order to introduce liquid solvent within the reservoir (R) located in the
interwell region, it
can be desirable to at least partially or fully fill the horizontal startup
section 30h to allow
the liquid solvent from the well to penetrate into the reservoir. The liquid
solvent can flow
from the horizontal startup section for reservoir penetration via gravity
and/or diffusion
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mechanisms of the liquid solvent within the reservoir (R). The liquid solvent
can also be
forced within the reservoir by substantially filling the horizontal startup
section 30h, and
exerting a penetration pressure on the liquid solvent which effectively fills
the tubing string
32 and annulus surrounding the tubing string within the wellbore. The
penetration pressure
can be maintained during the introduction stage as well as the subsequent
soaking stage.
[0096] In an alternative implementation, once the liquid solvent has
substantially filled the
horizontal startup section 30h, a displacement fluid can be introduced in an
upstream
portion of the well, e.g., the vertical startup section 30v, in order to exert
pressure on the
solvent in the downstream portion of the well, e.g., the horizontal startup
section 30h. It
should be understood that the displacement fluid can be different than the
liquid solvent,
and could be liquid or gas phase, for example water and/or nitrogen gas can be
used as
displacement fluids. It should be understood that introducing a displacement
fluid in an
upstream portion of the well can reduce the volume of liquid solvent required
during the
startup process.
[0097] In some implementations, the tubing string 32 can extend within the
solvent startup
well 30 in order to introduce liquid solvent directly within the horizontal
startup section 30h
and can be operated in combination with various other well features, as will
be described
in greater details hereinbelow.
Completions of solvent startup well
[0098] Referring to Figure 6, in addition to Figures 4 and 5, the solvent
startup well 30 can
include a liner 34 extending within a wellbore thereof. The liner 34 can be
configured to
extend from an upstream part of the horizontal section of the well, along a
length of the
horizontal startup section 30h and can terminate near its end. It should thus
be understood
that the horizontal portion of the tubing string 32 can extend within the
liner 34 of the
solvent startup well in order to introduce liquid solvent therein. In some
implementations,
the liner 34 can be slotted or include other types of apertures along a length
thereof in
order to allow the liquid solvent contained within the liner to infiltrate the
reservoir and also
to eventually allow production of reservoir fluids.
[0099] Still referring to Figures 4 to 6, in some implementations, the tubing
string 32 and
liner 34 define an annulus region 36 therebetween. Furthermore, the solvent
startup well
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30 can include a packer assembly 40 (see Figures 5 and 5a) mounted within the
annulus
region 36. The packer assembly 40 can define a downstream region 42 and an
upstream
region 44 within the solvent startup well 30, and can be configured to
substantially prevent
fluid communication between the upstream and downstream regions. More
specifically,
the packer assembly 40 can substantially block the cross-sectional area of the
annulus
region 36, therefore sealing the downstream region 42 from the upstream region
44. In
some implementations, the packer assembly 40 can be positioned at a first end
of the
horizontal startup section 30h to prevent fluid communication between the
vertical startup
section 30v and the horizontal startup section 30h. It should be understood
that preventing
fluid communication between the vertical and horizontal startup sections can
reduce the
volume of liquid solvent required during the introduction stage. It should be
further
understood that the tubing string 32 can be configured to extend through the
packer
assembly 40 in order to introduce liquid solvent in the downstream region of
the well 42.
[00100] As the liquid solvent is introduced into the horizontal startup
section 30h,
the packer assembly 40 prevents the liquid solvent from entering and filling
the upstream
region (i.e., the vertical startup section 30v and the transition section
30t). Additionally, the
packer assembly 40 can reduce the desirability to introduce displacement
fluid, or any
other fluid, within the vertical startup section 30v in order to increase
pressure on the
solvent within the horizontal startup section 30h. It should be understood
that the packer
assembly can be positioned at any suitable location along the transition or
horizontal
startup section, and that positioning the packer assembly 40 further along the
horizontal
startup section 30h can reduce the required volume of liquid solvent needed to
substantially fill the downstream region 42 and infiltrate the reservoir (R).
The packer
assembly 40 can also be displaced during the startup process, e.g., changing
locations
between cycles.
[00101] In one implementation, the packer assembly 40 is located
relatively
upstream and close to the transition section of the startup well 30t, thereby
defining an
annulus volume. The tubing string 32 can extend the length of the liner 34 and
can have
an outlet 32a at its end for expelling the liquid solvent into the liner
annulus 36. The volume
of the annulus region defined between the packer assembly 40 and the end of
the well, as
well as the volume defined by the tubing string 32, can be used to determine
the overall
solvent volume that is introduced. For cycles later in the startup process,
the solvent
CA 3011675 2018-07-18
17
volume can also be determined based on a determined depletion volume of the
reservoir
itself due to preceding cycles of the startup process. It should be noted that
depending on
the completion of the well, different solvent volume determinations can be
made in order
to determine the solvent volume to be introduced into the startup well for a
given cycle.
[00102] In addition, it should be noted that the solvent that is
introduced can be
relatively fresh solvent obtained from a solvent source, recovered solvent
obtained from
the separation stage, or in some cases production fluid that is predominantly
solvent and
not subjected to separation to remove bitumen. This latter case would mainly
occur at
early stages or cycles of the startup process, e.g., after the first and
second cycles, since
smaller amounts of bitumen may have been mobilized and produced back along
with the
solvent. In this case, the predominantly solvent production fluid could be
produced back
to the surface in its entirety and then reintroduced. Alternatively, only a
portion of the
predominantly solvent production fluid could be produced back to ensure that
some of the
diluted bitumen has been displaced out of the reservoir, and then the produced
fluid could
be reintroduced back into the startup well.
[00103] It should also be noted that part of the introduction stage can
include a
preliminary operations where fluids, such as drilling mud and the like, can be
removed
from the wellbore volume. In some implementations, the liquid solvent can
displace/push
out residual fluids (e.g., drilling mud) or slurries from within the wellbore
to the surface,
substantially cleaning the wellbore prior to regular operations. It should be
understood that
removing the residual fluids from the wellbore prior to regular startup
operations can
advantageously prevent these fluids from being produced during subsequent
production
stages.
Soaking stage
[00104] Following the initial introduction stage 10a (Figure 3), the
startup process
includes a soaking stage 10b. During the soaking stage, some of the liquid
solvent
located within the horizontal startup section 30h can infiltrate into the
reservoir (R) in the
interwell region to contact and locally reduce the viscosity of the bitumen in
the reservoir.
Solvent penetration into the reservoir can mobilize a portion of the bitumen
sufficiently to
be producible, while some of the solvent will penetrate in lower
concentrations to reduce
CA 3011675 2018-07-18
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viscosity but not enable production after that particular soaking cycle. In
that sense, a
portion of the solvent remains in the reservoir after soaking.
[00105] In some implementations, the soaking stage can be initiated once
the
horizontal startup section 30h, or downstream region 42, has been
substantially filled with
liquid solvent. Alternatively, the soaking stage of any given cycle can be
initiated once a
predetermined volume of liquid solvent has been introduced during the
introduction stage
of that cycle.
[00106] It should be understood that during the soaking stage, the liquid
solvent is
allowed to effectively soak into and within the reservoir for a certain amount
of time defined
as a soaking period. The soaking period can be predetermined, determined based
on
active monitoring, or determined based on other factors of the overall
process. In some
implementations, the soaking period can be a determined amount of time, such
as
approximately a day (i.e., 24 hours), a week, or any other suitable amount of
time which
would allow the liquid solvent to penetrate and at least partially mobilize
bitumen contained
within the reservoir. The soaking period can alternatively be the amount of
time required
for the pressure within the horizontal startup section 30h, or downstream
region 42, to
stabilize once the introduction stage has concluded. It should be understood
that the
pressure within the horizontal startup section 30h can be greater than the
pressure within
the reservoir, and will therefore decrease over time as the liquid solvent
infiltrates the
reservoir.
[00107] In some scenarios, the liquid solvent can penetrate the reservoir
and
encounter a thief or high mobility zone, resulting in loss of at least some
liquid solvent.
This can be detected by monitoring pressure during the soaking phase. Once the
high
mobility zone has been detected, the process can be adapted accordingly, e.g.,
one or
more additional packer assemblies can be mounted within the solvent startup
well or the
existing packer can be moved to isolate the thief zone. In addition, pressures
exerted on
the solvent can be modified to reduce solvent loss via the high mobility zone
or the cyclic
process terminated to mitigate further solvent loss.
Production stage
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[00108] Once the soaking period has elapsed, the startup process 10 can
proceed
to the production stage 10c (Figure 3). The production stage can include
producing fluids
from the solvent startup well 30 to recover a startup production fluid which
can include
liquid solvent and mobilized bitumen. It should be understood that the startup
production
fluid can have a bitumen concentration that can increase after each cycle due
to the
mobilization of the bitumen within the reservoir and the increased access to
reservoir
bitumen as the solvent treatment zone expands around the startup well. As
bitumen is
mobilized after each cycle of the startup process, the production stage can
produce startup
production fluid including greater amounts of bitumen mixed in with the liquid
solvent. In
some implementations, the production stage can be enabled by a pump, such as
an
electrical submersible pump (ESP) deployed in the well and configured to lift
the startup
production fluid from within the solvent startup well 30, and direct the fluid
toward the
surface. Other production methods such as gas lift and the like are also
possible,
depending on the reservoir properties.
[00109] Referring to Figures 5 and 5a, the ESP 46 can be mounted within
the
wellbore of the solvent startup well 30 in order to perform the production
stage. It should
be understood that the ESP 46 can be mounted upstream of the packer assembly
40 in
the transition section of the startup well, and would thus not be within the
downstream
section 42 filled with liquid solvent. In some implementations, the ESP 46 can
be mounted
within the transition section 30t proximate to or generally part of the
horizontal startup
section 30h. Other pump arrangements and locations are also possible.
[00110] The ESP 46 can be positioned in the upstream region 44 (Figure 5)
or in
the downstream region 42 (Figure 5a). Referring more specifically to Figure 5,
the packer
assembly 40 can be configured to be operated in order to selectively allow
fluid
communication between the upstream and downstream regions. It should be
understood
that the packer assembly 40 can be operated once the soaking period has
elapsed for any
given soaking stage, to allow startup production fluid to be produced via the
ESP 46 and
other corresponding equipment, such as a production line 33. With reference to
Figure 5a,
the packer assembly 40 can be a passive packer assembly (i.e., the packer
assembly
does not need to be operated dynamically) provided upstream of the ESP 46
within the
wellbore. It should be understood that the ESP 46 is therefore within the
liquid solvent
CA 3011675 2018-07-18
20
once the downstream region 42 is filled and can be operated therefrom to
initiate the
production stage.
[00111] In some implementations, as illustrated in Figure 1, the startup
production
fluid can be produced via a surface pump 47, and transferred to a production
fluid holding
tank 48 for storage, prior to a subsequent separation stage, as will be
described below.
Alternatively, the surface pump 47 can be configured to produce the startup
production
fluid, and transfer said fluid directly to a separator 49. The surface pump 47
can be coupled
to the tubing string 32 in the event production is to occur via the same
conduit as solvent
injection. A combination of pumping arrangements and systems can also be
provided, and
different pumps can be used for different cycles of the startup process (e.g.,
surface pump
for initial cycles; ESP for later cycles).
Surface separation stage
[00112] Referring back to Figure 3, in addition to Figure 1, the startup
process 10
can include various implementations of a surface separation stage 10d. As
mentioned
above, the bitumen located within the reservoir (R) is progressively mobilized
after the
cycles of the startup process 10, and can therefore be produced back during
the
production stages. As the bitumen concentration within the startup production
fluid
increases, the bitumen containing liquid solvent would become increasingly
inefficient at
mobilizing the bitumen in subsequent cycles of the startup process. Therefore,
it can be
desirable to include the separation stage 10d for separating the startup
production fluid
into a solvent depleted bitumen component, and a recovered solvent component,
which
can be reintroduced in subsequent cycles.
[00113] In some implementations, the separator 49 can be configured to
effectively
separate the startup production fluid to recover a bitumen depleted liquid
solvent, which
can be a substantially bitumen free liquid solvent or can include a notable
yet acceptable
bitumen content. The separator 49 can be coupled to the production fluid
holding tank 48
so as to receive the production fluid therefrom in the event separation is
required. Non-
limiting examples of the separator 49 can include a flash separator, a
centrifugal separator,
or any other suitable separator and/or separating method. It is nevertheless
noted that
relatively simple separation equipment can be used to separate a suitable
quantity of the
CA 3011675 2018-07-18
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bitumen from the startup production fluid, since high purity recovered solvent
is not
necessary for continued solvent cycling in the startup process.
[00114] In some implementations, the initial cycles of the startup
process 10 can
avoid the surface separation stage altogether, as the concentration of bitumen
in the
startup production fluid may be substantially low and acceptable for direct
reintroduction.
The produced startup fluid can be reused in subsequent cycles of the startup
process
without having to be transferred to the separator, reducing downtime between
cycles and
operating costs.
[00115] The startup production fluid can be analyzed in order to
determine various
properties, such as the bitumen concentration thereof. In some
implementations, the
startup production fluid can be analyzed during the production stage, either
simultaneously
while the fluid is being produced via the pump, or from the production fluid
holding tank 48
after having been produced. It should thus be understood that the separation
stage can
be initiated once the bitumen concentration is at or above a separation
threshold. In some
implementations, the separation threshold can be approximately 5 wt%, 10 wt%
or 15 wt%
bitumen, for example. Therefore, when the bitumen concentration of the startup
production
fluid is below 10 wt%, the startup production fluid can be reintroduced via
the solvent
startup well as part of the subsequent cycle. However, when the bitumen
concentration is
above 10 wt%, the cycle can include the separation stage to separate the
startup
production fluid to recover a bitumen component and reusable bitumen depleted
liquid
solvent.
[00116] In addition, the separation stage can be operated to treat all or
a portion of
the startup production fluid in order to produce a recovered solvent having
certain
properties, e.g., bitumen content. For example, if the solvent for
introduction has a target
maximum bitumen threshold (e.g., 10 wt%) and the startup production fluid has
a bitumen
content exceeding the threshold (e.g., 12 wt%), then a portion of the
production fluid can
be subjected to separation and then the recovered solvent can be combined back
with the
remaining production fluid to provide an overall bitumen content below the
threshold. In
addition, since the production fluid that is produced during a given cycle may
have a
variable concentration (e.g., low bitumen content initially and high bitumen
content near
the end of production), the low bitumen production fluid can be put aside, and
the high
CA 3011675 2018-07-18
22
bitumen production fluid can be subjected to separation prior to combining the
solvent
streams for reintroduction. Thus, various management techniques can be
employed in
terms of selecting certain portions of the production fluid for separation or
not.
[00117] It is also noted that the startup production fluid can be
subjected to other
surface treatments, such as gas removal, water removal, and solvent make-up.
These
additional treatments can be used for certain cycles in certain cases. For
example, in later
startup cycles, it is possible that the startup production fluid include water
from the
reservoir, in which case the fluid can be supplied to a water separator (e.g.,
free water
knockout drum) to remove most of the water. Solvent loss to the reservoir and
the
increasing volume of reservoir to be filled with solvent in later cycles can
require adding
solvent make-up to the recovered solvent prior to reintroduction.
[00118] Referring to Figures 9 and 10, the surface separation equipment
can be
configured to facilitate cyclic solvent startup in multiple wells and also for
multiple well
pads. For example, Figure 9 illustrates that a same separation unit 50 can be
used for
separation of startup production fluid retrieved from both the injection well
22 and the
production well 24 that form a well pair, and same surface pumps 47 can be
used for
producing and injecting. Alternatively, each startup well could have its own
dedicated
production pump and injection pump (which could be the same or different
pumps), and
could also have its own dedicated separator 49 and associated piping and
tankage, such
as a recovered solvent holding tank 51. The recovered solvent holding tank 51
can be
fluidly connected to the separator 49 for receiving bitumen depleted
production fluid
therefrom prior to reintroduction. In addition, the recovered solvent holding
tank 51 can be
further connected to a solvent supply source 54 when additional solvent is
required for a
given introduction stage for example. The production lines of the startup
wells can also
have monitoring devices for monitoring various parameters, such as
composition,
pressure, temperature, and the like. Figure 10 illustrates two well pads 52,
each having
multiple well pairs 21, which are serviced by a single integrated system for
solvent
injection, production and separation. By associating a surface system with
multiple wells,
which can be part of several well pads 52, the surface equipment can be
leveraged for
multiple cyclic startup processes that may be occurring at the same time.
Liquid solvent implementations
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[00119] In some implementations, the liquid solvent introduced during the
introduction stage can have a predetermined volume based on various factors.
The
predetermined volume can be determined and/or calculated by analyzing the
volume of
the various sections of the solvent startup well and relevant volumes of the
bitumen
reservoir. Non-limiting examples of the predetermined volume can be the volume
required
to substantially fill the horizontal startup section, or the volume required
to substantially fill
the downstream region when the packer assembly is mounted within the solvent
startup
well. The predetermined volume can take into consideration the wellbore
dimensions, the
volume of the solid components in the wellbore, as well as solvent properties
in terms of
volume dependence on temperature, pressure, and composition. The predetermined
volume can also include the bitumen depleted volume in the reservoir,
particularly for later
cycles, and can be determined based on measurements and monitoring of bitumen
content of the startup production fluid. The depleted volume in the
surrounding reservoir
can be determined and tracked for each cycle to aim in the determination of
the solvent
volume of a subsequent cycle.
[00120] It should be understood that the introduction of a predetermined
volume of
liquid solvent can increase effectiveness and efficiency of the startup
process and reduce
unnecessary loss of liquid solvent. In addition, the soaking stage of any
given cycle can
begin once the predetermined volume of liquid solvent has been introduced
during the
introduction stage of that cycle. Solvent inventory can also be efficiently
managed by using
determined volumes of solvent.
[00121] Referring to Figures 1, 9 and 10 the liquid solvent can be stored
at surface
within a solvent supply source 54, such as a container, a tank or a tanker for
example,
prior to the introduction stage of a given cycle. It should be understood that
the tubing
string 32 or other piping can be fluidly connected to the solvent supply
source 54 to provide
liquid solvent from the supply source 54 to within the solvent startup well.
It is appreciated
that following a separation stage, the recovered liquid solvent can be
transferred to the
solvent supply source 54 prior to initiating a subsequent cycle. The recovered
bitumen
component can be stored within a bitumen holding tank 56 (Figures 1 and 10) or
directly
supplied by pipeline for additional processing (Figure 9).
CA 3011675 2018-07-18
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[00122] In some implementations, the liquid solvent can have a low
density to
facilitate infiltration within the reservoir and reduce the viscosity of the
bitumen contained
therein. The low solvent density can cause the liquid solvent to tend to move
upwardly
relative to the bitumen, which has a greater density and would mobilize and
flow
downwardly by gravity. Due to the tendency of low density solvent to displace
upwardly
within the reservoir, introduction of the solvent via the underlying
production well of the
well pair may be advantageous to mobilizing the interwell region. In addition,
solvent
selection can be coordinated with the well that is used as the startup well.
For example, a
lower density solvent can be preferred for introduction via the production
well to leverage
density and gravity effects, while a higher density solvent may be preferred
for introduction
via the injection well. In one possible implementation, multiple different
solvents can be
used, and different solvents can be used in different wells of a given pair.
The upward flow
of the low density liquid solvent can also influence the separation stage of
the startup
process in a manner that will be further described below.
[00123] The solvent is maintained in liquid phase during introduction,
soaking, and
production. During separation, the solvent can be flashed as part of the
separation
method, in which case the solvent would be cooled so as to be liquid prior to
reintroduction
in a following cycle. Regarding the liquid phase of the solvent, it should be
noted that there
can be relatively small amounts of solvent vapour present depending on the
operating
conditions and the vapour pressure of the solvent used in the process.
However, the
operating conditions are selected so as to be well below the solvent's boiling
point, for
example, the solvent can be subcooled by about 10-20 C below flashing
conditions so as
to ensure having the solvent in liquid phase, preferably during each stage of
the process.
Furthermore, the solvent can be selected by analyzing the parameters of the
reservoir. In
some embodiments, the reservoir pressure can be between about 500 kPa and
about 800
kPa, and the reservoir can have a temperature substantially around 7-8 C.
Therefore, the
solvent can be selected so as to be in liquid phase in the aforementioned
conditions.
[00124] Various different types of solvents can be used. Non-limiting
examples of
the liquid solvent can comprise dimethyl ether (DME), methyl ethyl ketone
(MEK), toluene,
xylene, diesel, hexane, heptane and/or naphtha. Other ethers and ketones with
relatively
low density, high bitumen solubility, and good separability from bitumen can
also be used.
CA 3011675 2018-07-18
25
Cyclic patterns and operations & end of startup process
[00125] The startup process can include various implementations of cyclic
patterns
for mobilizing bitumen within the interwell region, some of which were touched
on above.
The solvent startup well can be selected from the injection and/or production
wells that
form the well pair. During some implementations of the startup process, both
wells in the
pair can be used as solvent startup wells, and they can be alternated or
synchronized in
terms of the stages and cycles of operation. In other words, a first cycle can
be initiated
via the injection well, and a second cycle can be initiated via the production
well, either
during or after the first cycle is completed, as will be explained below. In
other
implementations, the solvent startup well can be a single well, either the
injection or
production well, for the entire startup process.
[00126] Referring to Figures 7 through 7d, the solvent startup well 30
can be the
injection well 22 for each cycle of the startup process. It should be
understood that the
injection well 22 can include the packer assembly 40, the ESP 46 (Figure 5) or
other
production pump, the tubing string, and/or any other component related to the
bitumen
mobilization operation of the startup process. It should also be understood
that the
interwell region 26 is located below the horizontal injection section 22h, and
that the liquid
solvent thus penetrates that region of the reservoir from above (i.e. from the
horizontal
injection section).
[00127] During the startup process, a first introduction stage can be
initiated within
the injection well 22, followed by the soaking stage (Figure 7a). Once the
soaking period
has elapsed, the production stage is initiated, and the liquid solvent is
recovered from the
injection well 22, and a portion of the bitumen is mobilized (Figure7b). If
necessary, the
liquid solvent is separated at surface and reintroduced in a subsequent
introduction stage
(Figure 7c), followed yet again by soaking and production stages, effectively
mobilizing a
greater portion of bitumen until a flow of bitumen reaches the production well
24 (Figure
7d). It should be understood that the cycle is thus repeated until a desired
mobilization or
bitumen depletion or that fluid communication has been established between the
injection
and production wells 22, 24.
CA 3011675 2018-07-18
26
[00128] Referring to Figures 8a to 8e, the solvent startup well 30 can be
alternated
between the injection well 22 and the production well 24 during the startup
process. For
example, a first cycle can be completed via the injection well 22 (Figure 8a),
and a second
cycle can be completed via the production well 24 (Figure 8b), and so on until
fluid
communication is established between the wells (Figure 8e). Thus, once the
solvent is
recovered from one well and ready for reintroduction, it is introduced via the
other well.
This alternating cyclic pattern can then be reproduced a number of iterations.
It is noted
that more than one cycle in a row can be completed via one of the wells before
alternating
to the other well of the well pair. Additionally, the startup process
equipment (e.g., packer
assembly, pumps, tubing string, piping, etc.) can be provided in both wells of
the pair to
facilitate such operations.
[00129] In some implementations, both wells in a pair can be operated as
solvent
startup wells and the cycles of the two wells can be offset and thus the same
stages are
not necessarily operated at the same time for the two wells. For example, the
introduction
stage of any given cycle for one well can be initiated during the soaking
stage of a previous
first cycle of the other well. The cycles can be coordinated such that the
separator only
has to handle production fluid from one of the well at a time, which can
facilitate efficient
equipment utilization. As another example, the introduction stage of a cycle
for one well
can be initiated during the production or separation stage of a previous cycle
for the other
well. In some alternative implementations, cycles, and/or the same stages, of
the startup
process can be conducted via both wells simultaneously.
[00130] As described above, the liquid solvent can have low density,
especially
when compared to the bitumen contained within the reservoir, and can
infiltrate the
reservoir via gravity and/or diffusion based mechanisms. In some
implementations, the
liquid solvent can be generally clear (i.e., without dark coloration) when
introduced within
the solvent startup well to initiate a cycle of the startup process. As the
liquid solvent
penetrates the reservoir, the bitumen is diluted/solubilised into the liquid
solvent, which
reduces the viscosity of the bitumen.
[00131] It should be noted that, during the initial cycles of the startup
process (e.g.,
the first and second cycles), solvent penetration within the reservoir can be
limited due to
the high density and low initial mobility of the bitumen. This can result in
the startup
CA 3011675 2018-07-18
27
production fluid having low bitumen concentrations during these cycles, as
described
above. However, in later cycles, solvent penetration within the reservoir can
be facilitated
because of the mobilization and/or partial removal of the bitumen. It should
also be noted
that some of the liquid solvent can remain within the reservoir after a given
cycle (i.e., the
solvent was not produced back during the production stage of that cycle), and
can thus
maintain treatment of the bitumen while soaking in the reservoir. Therefore,
during a
subsequent cycle, solvent penetration can be facilitated as a result of the
"pre-treatment"
of bitumen due to leftover liquid solvent from a previous cycle. Therefore,
later cycles can
require greater volumes of liquid solvent during the introduction stage since
the bitumen
is mobilized and/or removed, thus leaving pockets needing to be filled (e.g.,
pore space
between solid minerals) within the reservoir to reach the remaining bitumen.
In some
implementations, the startup process can be deemed completed once the volume
of liquid
solvent required during a given introduction stage is at or above an
introduction threshold.
For example, when the volume of liquid solvent required for introduction has
doubled since
the first introduction cycle, the introduction threshold has been reached, and
the startup
process is completed. It should be understood that other methods of
determining the
introduction threshold can be implemented.
[00132] As the
bitumen mobilizes, the startup production fluid can include a certain
bitumen concentration, and is thus produced as a colored fluid, such as dark
brown or
black for example. Moreover, the bitumen can flow downwardly toward the
horizontal
production section under the effect of gravity. Referring back to Figure 3,
the startup
production fluid can include a bitumen concentration having a startup
completion
threshold. The completion threshold can mark the end of the startup process
10e or the
end of the solvent assisted process, as the bitumen within the reservoir has
been
sufficiently mobilized to be produced back consistently and in non-negligible
concentrations. Therefore, once the startup production fluid is at or above
the production
threshold, the startup process can be replaced by regular bitumen recovery
operations.
Alternatively, the startup process can be deemed completed once a
predetermined
volume of the reservoir has been extracted (i.e., depleted of bitumen). For
example, the
predetermined volume can be the volume substantially corresponding to the
interwell
region, or the volume defined by a distance around the injection and
production wells such
as 0.5m, 0.75m, lm, 1.5m, 2m or 2.5m, among other possibilities. The distance
from the
startup well can define a radius of a generally cylindrical volume around the
well. The
CA 3011675 2018-07-18
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volume can also be determined by subtracting the volume within the well itself
so that the
volume is a cylinder with a hollow small cylinder along its center axis. Other
more complex
volume determinations are also possible, where certain reservoir and fluid
dynamics
factors are taken into consideration to determine the volume. In some
implementations,
the predetermined volume can be determined/monitored via analysis of the
wellbore and
surrounding reservoir. The depletion volume may be determined before
initiating the
startup process or may be determined at some point during startup operations.
[00133] In some scenarios, the startup process can be implemented to
reduce
viscosity of the bitumen, while fluid communication between the wells of a
given pair can
be established using a subsequent method. In other words, the liquid-based
startup
process can be a conditioning or pre-treating phase which can be followed
and/or
completed using other startup methods or techniques, such as steam circulation
for
example. Transitioning from the startup process to conventional/normal startup
operations
can require the introduction of a mobilizing fluid (e.g., steam, solvent,
steam-solvent co-
injection) via the injection well, and the initialization of traditional
production operations via
the production well.
[00134] It should be noted that the solvent based techniques described
herein can
be used as the sole or primary startup process prior to ramping up to normal
production,
or can be combined simultaneously or serially with other startup methods. For
example,
the cyclic solvent startup process can be performed after an earlier pre-
treatment of the
reservoir that may use the injection of chemical compounds that can facilitate
bitumen
mobilization. The cyclic solvent startup process can be performed in
conjunction with a
radiofrequency (RF) based startup technique where RF energy is used to heat
and
mobilize bitumen in the reservoir; an RF generating device could be deployed
in the
solvent startup well or in an adjacent or proximate well and can be used
simultaneously
or serially with the cyclic solvent startup process. The cyclic solvent
startup process could
also be followed by a further startup method that employs other mobilizing
fluids and/or
heating techniques (e.g., steam circulation, bullheading, use of different
solvents using
different injection, circulation and/or soaking strategies, and so on).
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