CA3026109C - Methods and systems for managing solvent used in cyclic solvent process operations - Google Patents

Abstract

Methods and systems for managing solvent used in Cyclic Solvent Process (CSP) operations are disclosed. Methods include 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.

Description

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 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.

[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 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 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.

[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.

[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.

[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 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 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 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 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 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 (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 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.

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 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-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 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 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.

[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.

Claims (22)

CLAIMS:

1. 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.

2. The method of claim 1, wherein the first underground reservoir comprises a reservoir depleted during the thermal recovery process.

3. The method of claim 1 or claim 2, wherein 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.

4. The method of claim 3, wherein 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.

5. The method of claim 4, wherein injecting the at least a portion of the produced fluid into the second underground reservoir comprises injecting water recovered from the first underground reservoir.

6. The method of claim 5, wherein 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.

7. The method of any one of claims 1 to 6, further comprising, 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.

8. The method of claim 7, wherein injecting the at least a portion of the produced fluid into the second underground reservoir comprises injecting methane recovered from the first underground reservoir.

9. The method of claim 8, wherein 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.

10. The method of any one of claims 1 to 9, further comprising, prior to producing fluid from the first underground reservoir:
flooding the injected fluid into the first underground reservoir via the voideage formed during the thermal recovery process in order to generate solvent flood-mobilized viscous hydrocarbons within the first underground reservoir, and producing solvent flood-mobilized viscous hydrocarbons from one or more wellbores proximate the voidage.

11. The method of any one of claims 1 to 10, further comprising, 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.

12. The method of claim 11, further comprising:
separating bitumen from the produced fluid and diverting the separated bitumen to a bitumen processing facility.

13. The method of claim 11, wherein 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.

14. The method any one of claims 1 to 13, further comprising, 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.

15. The method of any one of claims 1 to 14, wherein at least a portion of the injected fluid comprises solvent produced from the second underground reservoir during a Cyclic Solvent Process (CSP) operation.

16. The method any one of claims 1 to 15, wherein at least a portion of the injected fluid comprises solvent received from an external source.

17. The method of claim 15, further comprising, 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.

18. The method of claim 17, further comprising:
conveying solvent produced during the CSP operation to the first underground reservoir via a pipeline.

19. The method of claim 18, wherein 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.

20. The method any one of claims 1 to 19, further comprising:
conveying the at least a portion of the produced fluid to the second underground reservoir via a pipeline.

21. The method any one of claims 1 to 20, wherein the second underground reservoir is one of a plurality of underground reservoirs of a multi-well CSP
pad.

22. The method any one of claims 1 to 21, wherein solvent in the injected fluid comprises at least one of ethane, propane, butane, pentane, and di-methyl ether.