Note: Descriptions are shown in the official language in which they were submitted.
METHODS AND SYSTEMS FOR MANAGING SOLVENT USED IN CYCLIC
SOLVENT PROCESS OPERATIONS
FIELD
[0001] This disclosure relates generally to managing solvent
logistics for Cyclic
Solvent Process (CSP) operations, and more specifically to methods and systems
for
integrating CSP operations with one or more underground reservoirs of late-
stage
and/or depleted thermal recovery processes.
INTRODUCTION
[0002] Various systems and methods are known to extract hydrocarbons
from
subterranean formations, which also may be referred to herein as reservoirs
and/or as
underground reservoirs. Typically, a particular extraction process is selected
based on
one or more properties of the hydrocarbon and/or of the subterranean
formation.
[0003] For example, hydrocarbons having a relatively lower viscosity
and
extending within relatively higher fluid permeability subterranean formations
(which may
be characterized as conventional hydrocarbons) may be pumped from the
subterranean
formation utilizing a conventional oil well.
[0004] However, conventional oil wells may be ineffective (or at
least
economically ineffective) at producing hydrocarbons having a relatively higher
viscosity
and/or extending within relatively lower fluid permeability subterranean
formations
(which may be characterized as unconventional hydrocarbons). Examples of
unconventional hydrocarbon production techniques that may be utilized to
produce
viscous hydrocarbons from a subterranean formation include thermal recovery
processes and solvent-dominated recovery processes.
[0005] Thermal recovery processes generally inject a thermal recovery
stream, at
an elevated temperature, into the subterranean formation. The thermal recovery
stream
contacts the viscous hydrocarbons within the subterranean formation, and
heats,
dissolves, and/or dilutes the viscous hydrocarbons, thereby generating
mobilized
viscous hydrocarbons. The mobilized viscous hydrocarbons generally have a
lower
viscosity than a viscosity of the naturally occurring viscous hydrocarbons at
the native
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temperature and pressure of the subterranean formation and may be pumped
and/or
flowed from the subterranean formation. A variety of different thermal
recovery
processes have been utilized, including cyclic steam stimulation processes,
solvent-
assisted cyclic steam stimulation processes, steam flooding processes, solvent-
assisted
.. steam flooding processes, steam-assisted gravity drainage processes,
solvent-assisted
steam-assisted gravity drainage processes, heated vapor extraction processes,
liquid
addition to steam to enhance recovery processes, and/or near-azeotropic
gravity
drainage processes.
[0006] Thermal recovery processes may differ in the mode of operation
and/or in
the composition of the thermal recovery stream. However, all thermal recovery
processes rely on injection of the thermal recovery stream into the
subterranean
formation at an elevated temperature, and thermal contact between the thermal
recovery stream and the subterranean formation to heat the subterranean
formation.
Thus, after performing a thermal recovery process within a subterranean
formation, a
significant amount of thermal energy may be stored within the subterranean
formation.
[0007] During a thermal recovery process, as the viscous hydrocarbons
are
produced from the subterranean formation, an amount of energy required to
produce
viscous hydrocarbons typically increases due to increased heat loss within the
subterranean formation. Similarly, a ratio of a volume of the thermal recovery
stream
provided to the subterranean formation to a volume of mobilized viscous
hydrocarbons
produced from the subterranean formation also typically increases. Both of
these factors
decrease economic viability of thermal recovery processes late in the life of
a
hydrocarbon well and/or after production and recovery of a significant
fraction of the
original oil-in-place from a given subterranean formation.
[0008] At the present time, solvent-dominated recovery processes (SDRPs)
are
not commonly used as commercial recovery processes to produce highly viscous
oil.
Solvent-dominated means that the injectant comprises greater than 50 percent
(%) 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.
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[0009] Cyclic solvent-dominated recovery processes (CSDRPs) are a
subset of
SDRPs. A CSDRP may be a non-thermal recovery method that uses a solvent to
mobilize viscous oil by cycles of injection and production. 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.
[0010] In a CSDRP, a solvent composition is injected through a well
into a
subterranean formation, causing pressure to increase. Next, the pressure is
lowered
and reduced-viscosity oil is produced to the surface of the subterranean
formation
through the same well through which the solvent was injected. Multiple cycles
of
injection and production are typically used. In some instances, a well may not
undergo
cycles of injection and production, but only cycles of injection or only
cycles of
production.
[0011] 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.
[0012] 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); U.S. 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).
[0013] The family of processes within the Lim et al. references
describes a
particular SDRP that is also a CSDRP. These processes relate to the recovery
of heavy
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oil and bitumen from subterranean reservoirs using cyclic injection of a
solvent in the
liquid state which vaporizes upon production.
[0014] With reference to FIG. 1, which is a simplified diagram based
on Canadian
Patent No. 2,349,234 (Lim et al.), one CSDRP process 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 101
driven through
overburden 102 into reservoir 103 and is connected to a horizontal wellbore
portion 104.
The horizontal wellbore portion 104 comprises a perforated liner section 105
and an
inner bore 106. The horizontal wellbore portion comprises a downhole pump 107.
In
operation, solvent or viscosified solvent is driven down and diverted through
the
perforated liner section 105 where it percolates into reservoir 103 and
penetrates
reservoir material to yield a reservoir penetration zone 108. Oil dissolved in
the solvent
or viscosified solvent flows into the well and is pumped by downhole pump 107
through
an inner bore 106 through a motor at the wellhead 109 to a production tank 110
where
oil and solvent are separated and the solvent may be recycled to be reused in
the
process. Each instance of injection of solvent and production of oil dissolved
in solvent
is considered a "cycle".
[0015] In a SDRP, one of the key metrics to measure the efficiency of
the
process is solvent intensity (solvent volume used per unit of hydrocarbon
production),
which may also be expressed as a solvent-to-oil ratio (e.g. a ratio of solvent
injected to
oil produced), similar to a steam-to-oil ratio used in thermal recovery
processes. In a
CSDRP, solvent volumes injected grow cycle over cycle, and the efficiency of
the
process is reduced. Solvents can also vary in price and availability.
Therefore, efficient
and effective use and recovery of solvents are key to the economics and
robustness of
a SDRP.
SUMMARY
[0016] The following introduction is provided to introduce the reader
to the more
detailed discussion to follow. The introduction is not intended to limit or
define any
claimed or as yet unclaimed invention. One or more inventions may reside in
any
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combination or sub-combination of the elements or process steps disclosed in
any part
of this document including its claims and figures.
[0017] In
accordance with one broad aspect of this disclosure, there is provided a
method for managing solvent used in Cyclic Solvent Process (CSP) operations,
the
method comprising: injecting fluid comprising solvent into a first underground
reservoir,
the first underground reservoir comprising a voidage formed during a thermal
recovery
process; producing fluid from the first underground reservoir, the produced
fluid
primarily comprising solvent from the injected fluid; and injecting at least a
portion of the
produced fluid into a second underground reservoir during a CSP operation.
[0018] In some
embodiments, the first underground reservoir comprises a
reservoir depleted during the thermal recovery process.
[0019] In
some embodiments, the first underground reservoir is at an elevated
temperature due to the thermal recovery process, and the method further
comprises,
prior to producing fluid from the first underground reservoir: allowing the
injected fluid to
reside in the
first underground reservoir until at least one of: a temperature of solvent in
the produced fluid is at least 5 C greater than a temperature of solvent in
the injected
fluid; or a temperature of solvent in the produced fluid is at least 20 C.
[0020] In
some embodiments, producing fluid from the first underground reservoir
comprises producing water along with solvent from the injected fluid, such
that the
produced fluid comprises water, wherein the produced water was introduced to
the first
underground reservoir during the thermal recovery process.
[0021] In
some embodiments, injecting the at least a portion of the produced fluid
into the second underground reservoir comprises injecting water recovered from
the first
underground reservoir.
[0022] In
some embodiments, injecting the at least a portion of the produced fluid
into the second underground reservoir comprises injecting water recovered from
the first
underground reservoir as a solvent chaser for the second underground
reservoir.
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[0023] In some embodiments, the method further comprises, prior to
producing
fluid from the first underground reservoir: allowing the injected fluid to
reside in the first
underground reservoir until methane is recovered from the first underground
reservoir,
such that the produced fluid comprises methane.
[0024] In some embodiments, injecting the at least a portion of the
produced fluid
into the second underground reservoir comprises injecting methane recovered
from the
first underground reservoir.
[0025] In some embodiments, injecting the at least a portion of the
produced fluid
into the second underground reservoir comprises co-injecting methane recovered
from
the first underground reservoir along with another solvent.
[0026] In some embodiments, the method further comprises, prior to
producing
fluid from the first underground reservoir: allowing the injected fluid to
reside in the first
underground reservoir until bitumen is recovered from the first underground
reservoir,
such that the produced fluid comprises bitumen.
[0027] In some embodiments, the method further comprises: separating
bitumen
from the produced fluid and diverting the separated bitumen to a bitumen
processing
facility.
[0028] In some embodiments, the bitumen comprises light bitumen, and
injecting
the at least a portion of the produced fluid into the second underground
reservoir
comprises co-injecting at least a portion of the light bitumen recovered from
the first
underground reservoir along with another solvent.
[0029] In some embodiments, the method further comprises, after
injecting at
least a portion of the produced fluid into the second underground reservoir:
producing
solvent from the second underground reservoir during the CSP operation.
[0030] In some embodiments, at least a portion of the injected fluid
comprises
solvent produced from the second underground reservoir during a Cyclic Solvent
Process (CSP) operation.
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[0031] In some embodiments, the method further comprises, prior to
injecting
fluid comprising solvent into the first underground reservoir: producing
solvent from the
second underground reservoir during a Cyclic Solvent Process (CSP) operation.
[0032] In some embodiments, the method further comprises: conveying
solvent
produced during the CSP operation to the first underground reservoir via a
pipeline.
[0033] In some embodiments, the pipeline is a two-way pipeline, and
the method
further comprises: conveying the at least a portion of the produced fluid to
the second
underground reservoir via the pipeline.
[0034] In some embodiments, the method further comprises: conveying
the at
least a portion of the produced fluid to the second underground reservoir via
a pipeline.
[0035] In some embodiments, the second underground reservoir is one
of a
plurality of underground reservoirs of a multi-well CSP pad.
[0036] In some embodiments, solvent in the injected fluid comprises
at least one
of ethane, propane, butane, pentane, and di-methyl ether.
[0037] It will be appreciated by a person skilled in the art that a method
or
apparatus disclosed herein may embody any one or more of the features
contained
herein and that the features may be used in any particular combination or sub-
combination.
[0038] These and other aspects and features of various embodiments
will be
described in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] For a better understanding of the described embodiments and to
show
more clearly how they may be carried into effect, reference will now be made,
by way of
example, to the accompanying drawings in which:
[0040] Figure 1 is an exemplary schematic of a cyclic solvent-dominated
recovery
process.
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[0041] Figure 2 is a simplified process flow diagram for an exemplary
standalone
Cyclic Solvent Process operation;
[0042] Figure 3 is a graph showing solvent injection rate, solvent
production rate,
and bitumen production rate of a conceptual CSP cycle;
[0043] Figure 4 is a graph showing a net solvent injection rate and net
solvent
production rate for a conceptual CSP project that invoices multi-well/pad
operation;
[0044] Figure 5 is a schematic diagram of an inter-connection between
a CSP
operation and a reservoir depleted during a thermal recovery process;
[0045] Figure 6A is a schematic longitudinal cross-section view of a
horizontal
well through a reservoir depleted during a thermal recovery process;
[0046] Figure 6B is a schematic longitudinal cross-section view of
the well and
reservoir of Figure 6A, with solvent injected into the reservoir;
[0047] Figure 6C is a schematic longitudinal cross-section view of
the well and
reservoir of Figure 66, after solvent has been produced from the reservoir;
[0048] Figure 7 is a schematic longitudinal cross-section view of a
reservoir
undergoing a CSP operation and a reservoir depleted during a thermal recovery
process; and
[0049] Figure 8 is a simplified process flow diagram for a method for
managing
solvent used in Cyclic Solvent Process (CSP) operations in accordance with one
embodiment.
[0050] The drawings included herewith are for illustrating various
examples of
articles, methods, and apparatuses of the teachings of the present
specification and are
not intended to limit the scope of what is taught in any way.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0051] Various apparatuses, methods and compositions are described below to
provide an example of an embodiment of each claimed invention. No embodiment
described below limits any claimed invention and any claimed invention may
cover
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apparatuses and methods that differ from those described below. The claimed
inventions are not limited to apparatuses, methods and compositions having all
of the
features of any one apparatus, method or composition described below or to
features
common to multiple or all of the apparatuses, methods or compositions
described
below. It is possible that an apparatus, method or composition described below
is not an
embodiment of any claimed invention. Any invention disclosed in an apparatus,
method
or composition described below that is not claimed in this document may be the
subject
matter of another protective instrument, for example, a continuing patent
application,
and the applicant(s), inventor(s) and/or owner(s) do not intend to abandon,
disclaim, or
.. dedicate to the public any such invention by its disclosure in this
document.
[0052] Furthermore, it will be appreciated that for simplicity and
clarity of
illustration, where considered appropriate, reference numerals may be repeated
among
the figures to indicate corresponding or analogous elements. In addition,
numerous
specific details are set forth in order to provide a thorough understanding of
the example
embodiments described herein. However, it will be understood by those of
ordinary skill
in the art that the example embodiments described herein may be practiced
without
these specific details. In other instances, well-known methods, procedures,
and
components have not been described in detail so as not to obscure the example
embodiments described herein. Also, the description is not to be considered as
limiting
.. the scope of the example embodiments described herein.
[0053] Figure 2 illustrates a simplified process flow diagram for a
standalone
Cyclic Solvent Process operation. In the illustrated example, solvent from an
above-
ground solvent storage tank(s) 210 ¨ which may receive from or convey solvent
to an
external source (e.g. via trucks and/or a transmission pipeline, 205) ¨ may be
directed
.. to a pump or other high-pressure injection mechanism 215, through an
injection heater
220 for raising the temperature of the injection fluid, and then into a CSP
wellbore 230
(or into one or more CSP wellbores that form part of a CSP pad). A casing gas
compressor 235 may be provided to compress gasses in the casing, such as
methane
and/or solvent vapor (e.g. ethane, propane, dimethyl ether (DME) vapor,
depending on
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the solvent(s) used). Fluid produced from the CSP wellbore (or from one or
more CSP
wellbores that form part of a CSP pad) may be directed through a production
heater 240
for raising the temperature of the produced fluid, and then on to a solvent
separator
250. At the separator 250, bitumen and/or other hydrocarbons recovered from
the
formation may be separated out of the produced fluid stream and subsequently
directed
to a bitumen processing plant 265. From the separator 250, separated solvent
may be
directed through a compressor 255 and/or a condenser 260, and returned to
solvent
storage tank 210.
[0054] Referring to Figure 3, in a typical CSP, each cycle starts
with a relatively
high rate of solvent injection 305 over an injection period 310. Following
this initial
injection period, there is a relatively long production period 320 during
which solvent
and bitumen are produced at a lower rate compared to the injection rate.
Typically, the
solvent production rate, shown by curve 315, peaks earlier than the bitumen
production
rate, shown by curve 325, as illustrated, but it will be appreciated that this
is not always
the case. As a result, recovering all of the solvent injected for each cycle
takes place
over a much longer time period than the injection period. Also, it often takes
multiple
cycles to fully recover most or all of the solvent initially injected.
[0055] As the reservoir is depleted during the CSP, each subsequent
CSP cycle
typically takes place over a longer time period, and requires a greater volume
of solvent
during the injection phase. In later cycles, larger volumes of solvent are
injected to fill
the voidage created due to bitumen production and to re-pressurize the
formation. This
changing demand for solvent volume may present one or more challenges in
managing
solvent logistics.
[0056] For a CSP project that involves multiple wells and/or a multi-
well pad,
challenges associated with changing demand for solvent throughout a CSP
process
may be amplified. For example, there will be a net solvent shortage in the
early phase
when solvent supply is required to charge the wells and/or well pad(s). After
this initial
phase, there will typically be a period during which the net injection and net
production
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of solvent is almost balanced. Following this 'balanced' phase, in the late
phase there
will be more solvent produced than solvent injected, resulting in a net
surplus of solvent.
[0057] Operationally, solvent storage may be particularly challenging
to manage
when the injection rates and production rates of wells differ dramatically.
For instance,
solvent injection rates can be 1 to 20 times higher than solvent production
rates. In
addition, for a cyclic process, individual well injection rates can vary
dramatically in any
given cycle (i.e., cycling between no injection and a maximum injection rate)
and over
the life of the well (i.e., injection rates can vary from one cycle to
another).
[0058] For example, as illustrated in Figure 4, during an early phase
410, one or
.. more new wells (or "well pad") are put into operation and there is a net
positive demand
for solvent ¨ being the difference between the solvent injection rate, shown
by curve
405, and the solvent production rate, shown by curve 415 ¨ this difference as
indicated
by the highlighted area 425. At some point during the early phase of the field
operation,
some wells do begin producing, but they do not provide enough solvent to
supply the
injection wells. Therefore, make-up solvent must continue to be supplied by
pipeline
and/or from storage.
[0059] During the steady-state period 420, the number of active wells
in the well
pad remains roughly constant, although it may deviate some. For much of the
steady-
state period, the net solvent demand may continue to be similar to the net
solvent
supply available from the storage tanks (refreshed with recycled solvent
and/or
periodically with trucking of solvent). As the relative proportion of the
active wells that
are producers increases, less and less solvent may need to be supplied to the
CSP
pad. At some point the amount of solvent that is recycled may equal the amount
required for injection.
[0060] During the late-life period 430 of the wells or well pad, there is a
surplus of
solvent, as operations wind-down and wells become inactive. The net demand for
solvent is negative (shown by highlighted area 435). When the solvent
production
exceeds the solvent injection demand, the excess solvent may be stored on the
surface
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and/or underground. Additionally, or alternatively, surplus solvent may be
sent (e.g. by
pipeline) to a facility for resale or to a new CSP site for reuse.
[0061] Surface storage capacity may be costly, especially when
pressurization of
the solvent above atmospheric pressure is required to store the solvent as a
liquid at
ambient temperatures. Therefore, it is generally considered desirable to
minimize the
volume of the solvent storage tank(s), such as tank(s) 210.
[0062] Solvent supply logics may be one of the key commercial
challenges for
CSP operations, and may have a significant impact on CSP economics. For
example,
the solvent supply capacity and rate may determine how fast a project can be
'ramped
up' and thus may impact the bitumen production rate. Thus, improving or
preferably
optimizing the management of solvent supply and demand and the on-site solvent
storage under a solvent supply constraint may help reduce cost, increase up
time, and
improve bitumen rate and project economics.
[0063] Systems and methods described herein may be used to improve,
and
preferably to optimize, solvent logistics by integrating a CSP operation (e.g.
one or more
CSP wells and/or one or more CSP pads) with an existing CSS operation and/or
with a
future solvent flood operation. By providing a two-way inter-connection
between one or
more wells undergoing a CSP process (e.g. a CSP pad or pads) with one or more
wells
that have undergone a thermal recovery process (e.g. a well or well pad that
has
undergone Cyclic Steam Stimulation (CSS)), one or more underground reservoirs
depleted during the thermal recovery process may be used as reservoir(s) for
underground solvent storage.
[0064] For example, some CSS well pads in Alberta, Canada have
recently been
abandoned after reaching the end of their project life (e.g. the end of their
economic
life). There are also a number of early CSS pads that are presently in the
later stages of
their project life that are undergoing steam flood operation. The reservoirs
of these non-
operating or late-life operating CSS pads have been depleted. However, these
depleted
reservoirs may be retaining a significant amount of residual heat from their
exposure to
the injected thermal recovery streams during the recovery process. Using
systems and
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methods disclosed herein, these depleted reservoirs may be used as an
underground
storage `tank' for solvent needed for nearby CSP operations. Thus, the
effective 'on-site'
solvent storage capacity may characterized as the volume of above-ground
storage
tank(s) (e.g. tank(s) 210) plus the volume of underground reservoir(s)
depleted during
the thermal recovery process.
[0065] Figure 5 is a schematic diagram of an example inter-connection
between
a CSP well or a plurality of such wells (e.g. as part of a CSP well pad) and
one or more
wells that comprise a reservoir (or reservoirs) depleted during a thermal
recovery
process, e.g. a well that has undergone a CSS operation, or a plurality of
such wells
(e.g. as part of a CSS well pad). In the illustrated example, a pipeline
connection 505 is
provided between a CSP well pad 530 and a solvent storage tank 210. A pipeline
connection 515 is provided between the solvent storage tank 210 and a CSS well
pad
550. In this example, the CSP well pad 530 and the CSS well pad 550 are inter-
connected via solvent storage tank (or tanks) 210. This may be characterized
as an
indirect interconnection. An advantage of such a configuration is that solvent
may be
delivered to or from the CSP wells and/or the CSS wells and an external source
205
(e.g. via trucks and/or a transmission pipeline) via the solvent storage tank
210 and an
optional solvent offload facility 207.
[0066] Providing an increased effective on-site solvent storage
capacity may be
have one or more advantages. For example, larger volumes of solvent may be
stored
before injections begin at a CSP pad, which may allow for a faster project
'ramp up'. As
another example, greater quantities of solvent may be purchased and stored to
take
advantage of low market prices and/or stored awaiting sale to take advantage
of high
market prices. As another example, if a CSP well and/or CSP pad needs to be
shut
down unexpectedly (e.g. in the event of a well failure, a subsurface workover,
surface
equipment maintenance, extreme weather, etc.), the larger solvent storage
capacity
may help manage solvent supply logistics and contract (e.g. reducing or
eliminating a
need to turn down external supply being delivered to the site via trucks or a
pipeline),
and/or provide flexibility to ramp up injection a lot faster to mitigate
downtime impact. It
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may also help mitigate the impact of solvent supply disruption. As another
example, a
larger solvent storage capacity may be useful during periods of the operation
of a CSP
well pad in which more solvent is produced than injected.
[0067] Also, using one or more reservoirs depleted during a thermal
recovery
process to store solvent may have one or more advantages over alternative ways
to
provide increase solvent storage capacity, e.g. by providing larger and/or
additional
above-ground solvent storage tanks.
[0068] For example, the depleted underground reservoir may retain a
significant
amount of residual heat (i.e. thermal energy) imparted to it during the
thermal recovery
process. Accordingly, solvent injected into the depleted underground reservoir
may
absorb some of this heat during its residency in the underground reservoir,
such that
when the solvent is later produced from the reservoir (e.g. for subsequent
injection or
re-injection into a CSP well) it may be at an elevated temperature relative to
the
temperature at which it was injected into the depleted reservoir. This may
advantageously reduce the requirement for heating solvent that was stored in
the
depleted reservoir prior to its injection or re-injection into a CSP well.
[0069] This concept is illustrated schematically in Figures 6A to 6C.
In Figure 6A,
a reservoir 605 depleted during a thermal recovery process has a voidage 610
that is an
elevated temperature due to residual heat (i.e. thermal energy) from the
thermal
recovery process. In Figure 6B, solvent 635 has been injected into the voidage
610 via
wellbore 615. Where the injected solvent is at a lower temperature than that
of the
reservoir 605, over time heat will be transferred from the reservoir 605 to
the solvent,
raising the temperature and/or pressure of the solvent. For example, if the
temperature
of the depleted thermal reservoir is high, light solvent may vaporize after
absorbing the
heat. Over time, the pressure will rise, which may promote some light solvent
(or light
components of injected fluid) condense, and thus increase the effective
storage
capacity of the reservoir. As discussed further below, condensed solvent may
assist in
recovering residual oil from the thermal reservoir. In Figure 6C, heated
solvent 640 (i.e.
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having a higher temperature than when it was injected) has been produced from
the
heated solvent filled voidage 610 of the reservoir 605, leaving a cooler
reservoir.
[0070] In addition to potentially harvesting residual heat, storing
solvent in
reservoirs depleted during a thermal recovery process may improve the overall
recovery
from such reservoirs. For example, at or near the end of a thermal recovery
process,
the well may be undergoing (or have recently undergone) a steam flood process,
which
may be characterized as having a relatively high energy intensity, and a
relatively high
steam-to-oil ratio (SOR). By injecting solvent, the well may switch from a
steam flood
process to a solvent flood process. When the injected solvent is later
produced from the
reservoir (e.g. for subsequent injection or re-injection into a CSP well), the
produced
fluids may include solvent flood-mobilized viscous hydrocarbons (e.g.
bitumen). In some
embodiments, some of the bitumen produced along with the recovered solvent may
not
otherwise have been economically producible during a steam flood process.
[0071] Additionally, when producing solvent that was stored in
reservoirs
depleted during a thermal recovery process, the produced fluids may include
some
methane (Cl) and/or hot water along with the recovered solvent. Also, as
solvent
concentration is expected to be relatively high in the reservoir, the solvent
may extract
some light components of the bitumen, and so some upgraded oil may be produced
as
well.
[0072] These concepts are illustrated schematically in Figure 7. In the
illustrated
example, reservoir 605 was depleted during a thermal recovery process
resulting in a
voidage 610, and reservoir 705 is undergoing a CSP operation. Pipelines 505,
515 are
provided for conveying solvent and/or other fluids between the well operations
and
surface storage tank(s) 210. It will be appreciated that in alternative
embodiments,
solvent may be conveyed directly between the wells. Surplus solvent from the
CSP
operation (e.g. solvent recovered during a CSP production cycle and/or solvent
stored
in anticipation of an upcoming net solvent deficit for a CSP well or pad) is
injected into
voidage 610 of reservoir 605 for storage. When fluid is produced from this
reservoir
(e.g. for subsequent injection or re-injection into a CSP well), the fluid
stream may
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include solvent 10 (e.g. propane) along with other light hydrocarbons 20 (e.g.
methane),
light bitumen 30, and/or water 40. As discussed, the produced solvent and
water may
advantageously be at elevated temperatures due to the residual heat in
reservoir 605.
[0073] The produced fluids from reservoir 605 may be used to improve
the CSP
operation of reservoir 705 in a number of ways. For example, some or all of
the light
hydrocarbons 20 may be co-injected into a voidage 710 in the reservoir 705
(e.g. via
wellbore 715) along with the produced solvent 10, which may improve the
recovery
performance for the CSP reservoir. For example, see Canadian Patent No.
2,900,179
(Wang et al.).
[0074] As another example, the light bitumen 30 may be separated for sale.
Alternatively, or additionally, some or all of the light bitumen 30 may be co-
injected into
the voidage 710 in the reservoir 705 along with the produced solvent 10, which
may
save separation costs and/or enhance the mixing between solvent (e.g. propane)
and
bitumen in the CSP reservoir.
[0075] As another example, the produced hot water 40 may be used for late-
stage injection of a CSP cycle, where the hot water can deliver extra solvent
into the
near-well region and/or serve as a chaser to the solvent to reduce the solvent
intensity
of the CSP process. For example, see Canadian Patent No. 2,972,203 (Wang et
al.).
Alternatively, or additionally, some or all of the hot water 40 may be used to
help move
bitumen from the CSP operation to a central processing facility. For example,
where the
CSP is a non-thermal process, the produced bitumen typically has a relatively
high
viscosity after separation of solvent. Since water has a relatively high heat
capacity, a
significant amount of heat may be transferred from the hot water to the
bitumen, raising
its temperature, which can reduce the viscosity of bitumen in the pipeline (as
the
bitumen is expected to have a lower viscosity at higher temperatures).
[0076] Additionally, or alternatively, fluids produced during a CSP
operation may
be injected to reservoir 605 along with excess solvent from the CSP operation.
For
example, light hydrocarbons 40 (e.g. methane) produced from reservoir 705 may
be re-
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injected into the reservoir 605 depleted during a thermal recovery process
along with
solvent 10, e.g. to serve as a blanket for the solvent stored in reservoir
605.
[0077] Using systems and methods described herein, a CSP operation
and a
thermal recovery operation (e.g. a CSS operation) may be integrated to form a
synergized operation, which may improve the value of produced streams from one
or
both operations. For example, the integration may facilitate or improve one or
more of:
management of solvent logistics challenges in CSP operations; reducing surface
solvent storage requirements; providing CSP operations with additional
flexibility in
solvent supply capacity (e.g. improved allocation of solvent for faster ramp
up of
bitumen rate); harvesting residual heat from the reservoirs depleted during a
thermal
recovery process; providing additional flexibility for late-stage thermal
recovery
operations (e.g. solvent flood following a CSS operation); improving safety of
operation
(e.g. facilitating off-pad surface solvent storage and offloading); utilizing
waste streams
(e.g. Cl and hot water) from thermal recovery operations (e.g. CSS) to enhance
CSP
performance, reducing operational costs; and an ability to take advantage of
solvent
price volatility (e.g. having the flexibility to buy ¨ and store ¨ more
solvent during periods
of relatively low market prices.
[0078] The flowing is a description of a method for managing solvent
used in
Cyclic Solvent Process (CSP) operations, which may be used by itself or in
combination
with one or more of the other features disclosed herein including the use of
any of the
apparatus and/or any of the methods disclosed herein.
[0079] Referring to Figure 8, there is illustrated a method 800 for
managing
solvent used in Cyclic Solvent Process (CSP) operations. Method 800 may be
performed using apparatus described with reference to Figures 1, 2, 5, 6,
and/or 7, or
any other suitable apparatus. Figure 8 exemplifies a method in which a first
underground reservoir is used to temporarily store solvent and solvent
produced from
this reservoir is injected into a second underground reservoir during a CSP
operation.
As discussed herein, solvent may be injected into two or more underground
reservoirs
for temporary storage, and solvent produced from these reservoirs may be
injected into
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two or more underground reservoirs as part of a CSP operation (e.g. two or
more CSP
wells within a CSP well pad).
[0080] Optionally, at 805, solvent may be obtained from an external
source (e.g.
via trucks and/or a transmission pipeline).
[0081] Optionally, at 810, solvent may be produced during a CSP operation.
[0082] At 815, solvent is injected into a first underground reservoir
comprising a
voidage formed during a thermal recovery process (e.g. a reservoir that has
undergone
a CSS operation). The solvent injected into the first underground reservoir
may
comprise solvent obtained from an external source at 805, and/or solvent
produced
during a CSP operation at 810. The solvent may be injected on its own or as
part of a
fluid stream with other components. For example, one or more light
hydrocarbons may
also be injected into the reservoir to serve as a blanket for the stored
solvent. It will be
appreciated that the solvent may be introduced into the reservoir at any
suitable
pressure and/or temperature.
[0083] Optionally, at 820, the injected solvent may be allowed to reside in
the
reservoir to recover residual heat from the reservoir. For example, the
solvent may be
allowed to reside in the underground reservoir until its temperature when
produced from
the reservoir is at least 5 C greater than when it was injected into the
reservoir.
Additionally, or alternatively, the solvent may be allowed to reside in the
underground
reservoir until its temperature when produced fluid is at least 20 C.
[0084] Optionally, at 825, the injected solvent may be allowed to
reside in the
reservoir to recover methane and/or other light hydrocarbons from the
reservoir. For
example, the solvent may be allowed to reside in the underground reservoir
until one or
more light hydrocarbons are dissolved and/or otherwise mobilized from the
reservoir by
the solvent such that they are present in the produced fluid.
[0085] Optionally, at 830, the injected solvent may be allowed to
reside in the
reservoir to recover bitumen from the reservoir. For example, the solvent may
be
allowed to reside in the underground reservoir until bitumen is dissolved
and/or
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otherwise mobilized from the reservoir by the solvent such that bitumen is
present in the
produced fluid.
[0086] Optionally, at 835, the injected solvent may be forced from
the reservoir
during a solvent flood process. For example, the solvent may be injected into
the
voidage formed during the thermal recovery process as part of a solvent flood
vapor
stream in order to generate solvent flood-mobilized viscous hydrocarbons
within the
subterranean formation, which may be produced from one or more wellbores
proximate
the flooded voidage. Examples of solvent flooding methods are described in CA
Patent
Publication No. 2,974,712 Al (Motahhari et al.).
[0087] At 840, fluid is produced from the first reservoir. The fluid
primarily
comprises solvent injected at 810. For example, the produced fluid may be at
least
55%, 75%, 90%, or greater than 95% solvent. The produced fluid may also
include one
or more light hydrocarbons, bitumen, and/or water recovered from the reservoir
as a
result of injecting and subsequently producing solvent.
[0088] Optionally, at 845, bitumen may be separated from the produced fluid
and
diverted to a bitumen processing facility. For example, there may be a central
processing facility as part of a CSP well pad. Additionally, or alternatively,
separated
bitumen may be conveyed to an external source (e.g. via trucks and/or a
transmission
pipeline) for sale and/or offsite processing.
[0089] At 850, at least a portion of the fluid produced at 840 (e.g.
solvent injected
at 815) is injected into a second underground reservoir during a CSP
operation. The
solvent injected at 850 may be injected on its own or as part of a fluid
stream with other
components. For example, it may be co-injected with additional solvent from an
above-
ground storage facility. As another example, hot water recovered from the
first reservoir
at 840 may be injected as a solvent chaser along with the solvent during the
CSP
operation.
[0090] Optionally, at 855, solvent may be produced from the second
underground
reservoir during the CSP operation.
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[0091] Optionally, at 860, some or all of the solvent produced from
the second
underground reservoir during the CSP operation may be conveyed to the first
reservoir
(i.e. the reservoir formed during the thermal recovery process), e.g. for
injection and
storage. In Figure 8, this is represented by the line connecting 860 and 815.
For
example, solvent produced during the CSP operation may be conveyed to the
first
underground reservoir via a pipeline.
[0092] As used herein, the wording "and/or" is intended to represent
an inclusive
- or. That is, "X and/or Y" is intended to mean X or Y or both, for example.
As a further
example, "X, Y, and/or Z" is intended to mean X or Y or Z or any combination
thereof.
[0093] While the above description describes features of example
embodiments,
it will be appreciated that some features and/or functions of the described
embodiments
are susceptible to modification without departing from the spirit and
principles of
operation of the described embodiments. For example, the various
characteristics which
are described by means of the represented embodiments or examples may be
selectively combined with each other. Accordingly, what has been described
above is
intended to be illustrative of the claimed concept and non-limiting. It will
be understood
by persons skilled in the art that other variants and modifications may be
made without
departing from the scope of the invention as defined in the claims appended
hereto. The
scope of the claims should not be limited by the preferred embodiments and
examples,
but should be given the broadest interpretation consistent with the
description as a
whole.
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