CA2965117A1

CA2965117A1 - Methods to improve sweep efficiency in in-situ bitumen recovery processes

Info

Publication number: CA2965117A1
Application number: CA2965117A
Authority: CA
Inventors: Chakrabarty Tapantosh
Original assignee: TAPANTOSH, CHAKRABARTY; Imperial Oil Resources Ltd
Current assignee: Imperial Oil Resources Ltd
Priority date: 2017-04-25
Filing date: 2017-04-25
Publication date: 2018-10-25

Abstract

Methods to improve sweep efficiency in an in-situ bitumen recovery processes are disclosed. In some embodiments, these methods include performing a mobilizing agent chamber development stage, subsequently performing a cyclic sweep stage, and subsequently performing an optional harvesting stage. The chamber development stage renders the bitumen in the bypassed region between two adjacent mobilizing agent chambers mobile. The cyclic sweep stage allows access of the bypassed bitumen by the mobilizing agent, thereby aiding its recovery. The harvesting stage harvests additional bitumen and diluent. Advantages over prior art include accessing bypassed bitumen of prior at recovery processes, eliminating the need for infill wells, improving bitumen recovery, accelerating bitumen production, and improving mobilizing agent utilization efficiency. The methods apply to improving sweep efficiency in both continuous recovery processes, such as steam-assisted gravity drainage (SAGD), expanding solvent SAGD (ES- SAGD), solvent-assisted SAGD (SA-SAGD), vapor extraction (VAPEX) or heated VAPEX, as well as cyclical processes, such as cyclic steam stimulation (CSS) and cyclic solvent process CSP).

Description

, METHODS TO IMPROVE SWEEP EFFICIENCY IN IN-SITU BITUMEN RECOVERY
PROCESSES
Field of the Disclosure The present disclosure relates to methods to improve sweep efficiency in in-situ bitumen recovery processes.
Background of the Disclosure Mobilizing agents may be injected into a bitumen-bearing subterranean formation to mobilize bitumen. The mobilizing agents may be configured to decrease a viscosity of the bitumen, such as by heating the bitumen, diluting the bitumen, and/or dissolving the bitumen, thereby facilitating flow and/or pumping of the bitumen from the subterranean formation.
Examples of in-situ bitumen recovery processes that may include and/or utilize mobilizing agents include steam-assisted gravity drainage (SAGD), solvent-assisted SAGD (SA-SAGD), expanding solvent SAGD (ES-SAGD), vapor extraction (VAPEX), heated vapor extraction (H-VAPEX), cyclic steam stimulation (CSS), liquid addition to steam for enhancing recovery (LASER), and/or cyclic solvent processes (CSP). Of these recovery processes, SAGD, SA-SAGD, ES-SAGD are continuous processes, in that mobilizing agents are injected continuously into a horizontal injection well and mobilized bitumen is produced continuously from a horizontal production well that is about 2 to 5 meters below the injection well. Each of these processes utilizes a mobilizing agent that is steam-dominated, containing either about 100 mole percent steam, as in SAGD, or a steam-diluent mixture containing up to about 4 mole percent diluent, as in ES-SAGD and SA-SAGD. VAPEX and H-VAPEX are also continuous processes, but each of these processes utilizes a mobilizing agent that is diluent (or a solvent)-dominated, containing about 100 mole percent diluent. By contrast, recovery processes such as CSS and LASER, are cyclical, in that mobilizing agents are injected cyclically into a horizontal well and mobilized bitumen is produced cyclically from the same horizonatal well. Each of these processes utilizes a mobilizing agent that is steam-dominated, containing either about 100 mole percent steam, as in CSS, or a steam-diluent mixture containing up to about 2 mole percent diluent, as in LASER. CSP is a cyclical process, but it utilizes a mobilizing agent that is diluent (or a solvent)-dominated, containing about 100 mole percent diluent. Such bitumen recovery processes generate a bitumen-depleted chamber, which also may be referred to herein as a mobilizing agent chamber and/or as a heated chamber, within the subterranean formation.
Several wells are utilized to generate several bitumen-depleted chambers that run parallel to one another.
These in-situ bitumen recovery processes often may leave behind bitumen-rich bypassed regions, which extend between adjacent bitumen-depleted chambers. These bypassed regions may be generated because the mobilizing agent has a lower density than the surrounding rock and/or bitumen and thus preferentially rises within the subterranean formation, thereby leaving the bypassed regions in the lower portions of the subterranean formation.
The generation of bypassed regions in bitumen recovery processes reduces bitumen sweep efficiency, defined as the percent of the target region between two chambers that is swept or accessed by the mobilizing agent. The generation of bypassed regions also reduces the mobilizing agent utilization efficiency, defined as the volume of bitumen recovered per unit volume of the mobilizing agents injected, of the in-situ bitumen recovery processes. If the bypassed regions are of sufficient size, infill wells may be drilled into the bypassed region later in the life of those processes. However, drilling these infill wells is costly and time-consuming.

2 Delayed bitumen production through infill wells also delays revenue flow.
Thus, there exists a need for methods to improve sweep efficiency in in-situ bitumen recovery processes.
Summary of the Disclosure Methods to improve sweep efficiency in in-situ bitumen recovery processes are disclosed herein. In some embodiments, the methods include performing a mobilizing agent chamber development stage, subsequently performing a cyclic sweep stage, and subsequently performing a harvesting stage. In these embodiments, the mobilizing agent chamber development stage includes injecting a first mobilizing agent stream into a first horizontal well system and injecting a second mobilizing agent stream into a second horizontal well system, thereby forming a first and a second mobilizing agent chamber around each well system. The mobilizing agent chamber development stage also includes producing bitumen from the subterranean formation via both the first horizontal well system and the second horizontal well system. The injecting the first mobilizing agent stream into the first horizontal well system, the injecting the second mobilizing agent stream into the second horizontal well system, and the producing bitumen from each corresponding well system may be performed at least partially concurrently.
The injecting the first mobilizing agent stream into the first horizontal well system, the injecting the second mobilizing agent stream into the second horizontal well system, and the producing the mobilized bitumen from each well system may be performed continuously, as in SAGD, SA-SAGD, ES-SAGD, VAPEX, and H-VAPEX, or cyclically, as in CSS or CSP.
In these embodiments, the cyclic sweep stage includes reducing the injection pressure (and/or injection rate) of the second mobilizing agent stream into the second horizontal well system, relative to the injection pressure (and/or injection rate) of the first mobilizing agent into

3 the first horizontal well system, to drive the mobilizing agent through the bypassed regions and the mobilized bitumen from the first mobilizing agent chamber and the bypassed regions to the second horizontal well system. The cyclic sweep stage also includes, subsequent to the step just mentioned, increasing the injection pressure (and/or injection rate) of the second mobilizing agent stream into the second well system relative to the injection pressure (and/or injection rate) of the first mobilizing agent into the first horizontal well system to drive the mobilizing agent through the bypassed regions and the mobilized bitumen from the second mobilizing agent chamber and the bypassed regions to the first horizontal well system, thereby reversing the flow direction of the mobilizing agent and the mobilized bitumen from the second mobilizing agent chamber to the fi rst horizontal well system. One cycle in the cyclic sweep stage consists of flow from the first mobilizing agent chamber through the bypassed regions to the second well system, followed by the reversed flow from the second mobilizing agent chamber through the bypassed regions to the first well system. In preferred embodiments, multiple cycles of flow direction reversal are performed to access the bitumen in the bypassed regions, resulting in improved sweep efficiency and bitumen recovery. The cyclic sweep stage also may include, at least for a certain period of time, injection of a modified mobilizing agent, the composition of which is different from that in the mobilizing agent chamber development stage. The combined effect of the modified mobilizing agent composition and multiple cycles of flow direction reversal of the mobilizing agents in the cyclic sweep stage accelerates the accessing of the bypassed bitumen, resulting in improved sweep efficiency.
In these embodiments, the harvesting stage includes changing the composition of the mobilizing agents in the cyclic sweep stage by tapering the concentration of the relatively more valuable components in the mobilizing agents and replacing them with less expensive agents so

4 as to harvest mobilizing agents and additional bitumen to improve the recovery efficiency of the processes, determined by different conventional efficiency metrics, such as the percent of injected mobilizing agent that is recovered, or the volume of bitumen recovered per unit volume of mobilizing agents injected. In these embodiments, the harvesting stage may also include at least one reversal of the flow direction of the mobilizing agents, as described in the cyclic sweep stage.
Brief Description of the Drawings Fig. 1 is a schematic cross-sectional view of a bitumen production system that may be utilized to perform the methods according to the present disclosure.
Fig. 2 is a schematic cross-sectional view of the bitumen production system of Fig. 1 taken along line 2-2 of Fig. 1.
Fig. 3 is a plot of pressure vs. time that may be utilized in bitumen production systems performing methods according to the present disclosure.
Fig. 4 is an image illustrating simulation of a conventional steam-assisted gravity drainage (SAGD) process after 1800 days of operation.
Fig. 5 is an image illustrating simulation of the conventional SAGD process of Fig. 4 after 2500 days of operation.
Fig. 6 is an image illustrating simulation of the SAGD process of Fig. 4, modified utilizing the methods according to the present disclosure, after 1800 days of operation.
Fig. 7 is an image illustrating simulation of the SAGD process of Fig. 5, modified utilizing the methods according to the present disclosure, after 2500 days of operation.

5 Fig. 8 is an image illustrating simulation of a conventional solvent-assisted steam-assisted gravity drainage (SA-SAGD) process after 1800 days of operation.
Fig. 9 is an image illustrating simulation of the conventional SA-SAGD process of Fig. 8 after 2160 days of operation.
Fig. 10 is an image illustrating simulation of the SA-SAGD process of Fig. 8, modified utilizing the methods according to the present disclosure, after 1800 days of operation Fig. 11 is an image illustrating simulation of the SA-SAGD process of Fig. 9, modified utilizing the methods according to the present disclosure, after 2160 days of operation.
Fig. 12 is a flowchart depicting methods, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process.
Fig. 13 is a flowchart depicting methods, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process.
Fig. 14 is a flowchart depicting methods, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process.
Detailed Description of the Disclosure Figs. 1-14 provide examples of bitumen production systems 10 that may be utilized to perfoim methods 300, 400, and/or 500, according to the present disclosure, and of pressures that may be utilized by methods 300, 400, and/or 500, and/or of images comparing methods 300, 400, and/or 500 to conventional bitumen production methods. With reference to Figs.
12-14, elements that are likely to be included in a particular embodiment are illustrated in solid lines, while elements that are optional are illustrated in dashed lines. However, elements that are

6 shown in solid lines may not be essential and, in some embodiments, may be omitted without departing from the scope of the present disclosure.
Fig. 1 is a schematic cross-sectional view of a bitumen production system 10 that may be utilized to perform the methods according to the present disclosure, while Fig. 2 is a schematic cross-sectional view of the bitumen production system of Fig. 1 taken along line 2-2 of Fig. 1.
As collectively illustrated by Figs. 1-2, bitumen production system 10 includes a horizontal well system 100. Horizontal well system 100 includes at least one well 101, which extends between a surface region 20 and a subterranean formation 40 that extends within a subsurface region 30.
Subterranean formation 40 includes bitumen 42, and bitumen production system 10 is configured to produce the bitumen from the subterranean formation via horizontal well system 100. At least a portion of well 101 extends within a mobilizing agent chamber 120, which extends within the subterranean formation.
Horizontal well system 100 may include a mobilizing agent supply system 110, which may be configured to provide a mobilizing agent stream 112, which includes a mobilizing agent, to the subterranean formation via well 101 and also to produce, through the same well 101, a mobilized bitumen stream 44, as illustrated in Fig. 2, from the subterranean foimation in a manner that may be similar to that in conventional CSS and/or CSP processes for bitumen recovery.
Additionally or alternatively, and as illustrated in dashed lines in Figs. 1-2, horizontal well system 100 further may include an upper well 102, with well 101 acting as a lower well.
Upper well 102 may extend within subterranean foimation 40 and vertically above lower well 101. Under these conditions, upper well 102 may be utilized to inject mobilizing agent stream 112, and lower well 101 may be utilized to produce the mobilized bitumen stream from the

7 subterranean founation in a manner that may be similar to that in conventional SAGD, SA-SAGD, ES-SAGD, VAPEX, and/or H-VAPEX processes for bitumen recovery.
Regardless of the exact configuration utilized to inject the mobilizing agent stream into the subterranean founation and/or to produce the mobilized bitumen stream from the subterranean formation, these recovery processes may be utilized to produce bitumen and/or generate a mobilizing agent chamber 120. As an example, injection of the mobilizing agent stream may mobilize bitumen that is proximal to horizontal well system 100, and production of this mobilized bitumen, as mobilized bitumen stream 44 in Fig. 2, may permit mobilizing agent chamber 120 to expand and/or grow in size within the subterranean formation.
As illustrated in Figs. 1-2, it is within the scope of the present disclosure that a plurality of horizontal well systems may be utilized to inject mobilizing agents into and produce bitumen from the subterranean formation. As an example, horizontal well system 100 may include and/or be a first horizontal well system 100 including a first lower well 101, a first upper well 102, and a first mobilizing agent supply system 110. First horizontal well system 100 may be configured to inject a first mobilizing agent stream 112 into a first mobilizing agent chamber 120. Under these conditions, bitumen production system 10 also may include a second horizontal well system 200, as shown Fig. 1. Second horizontal well system 200 may include a second well, or a second lower well, 201, a second upper well 202, and a second mobilizing agent supply system 210. Second horizontal well system 200 may be configured to inject a second mobilizing agent stream 212 into a second mobilizing agent chamber 220 that extends within the subterranean formation. First horizontal well system 100 and second horizontal well system 200 may be spaced apart, or horizontally spaced apart, from one another within the subterranean formation.

8 Similarly, first mobilizing agent chamber 120 and second mobilizing agent chamber 220 may be spaced apart from one another within the subterranean formation.
Sweep efficiency in an in-situ bitumen recovery process, utilizing bitumen production system 10 of Figs. 1-2, may be improved by utilizing methods 300, 400, and/or 500 according to the present disclosure, which are illustrated in Figs. 12-14, and discussed in more detail herein with reference thereto. As an example, and in one embodiment, a three-stage recovery method may be performed. The three-stage recovery method may include a mobilizing-agent chamber development stage (or may additionally referred to herein as the "chamber development stage"), a cyclic sweep stage, and a harvesting stage and may be referred to herein as an MCH method, or as an MCH recovery method.
During the mobilizing-agent chamber development stage of the MCH method, a conventional cyclical recovery process or a conventional continuous recovery process may be performed. This may include cyclical and/or continuous injection of a mobilizing agent stream into the subterranean formation and cyclical and/or continuous production of bitumen from the subterranean formation.
During the cyclic sweep stage of the MCH method, the bitumen production system may be operated to provide alternating back-and-forth drives between first horizontal well system 100 and second horizontal well system 200 for a given number of cycles. In some embodiments, first horizontal well system 100 also may be referred to herein as a first horizontal well pair 100, and second horizontal well system 200 also may be referred to herein as a second horizontal well pair 200. The cyclic sweep stage may permit the mobilizing agent stream, such as first mobilizing agent stream 112 and/or second mobilizing agent stream 212, to access regions of the subterranean fon-nation that may be bypassed by conventional cyclical or continuous recovery

9 =
processes. These regions may be referred to herein as bypassed regions 46 as illustrated in Fig.
1. The mobilizing agent stream utilized during the cyclic sweep stage may be the same as, or different from, the mobilizing agent stream utilized during the mobilizing-agent chamber development stage. As an example, the mobilizing agent stream utilized during the cyclic sweep stage may be more potent than the mobilizing agent stream utilized during the mobilizing-agent chamber development stage, in terms of accessing the bypassed regions, thereby permitting faster access to and/or accelerated production from the bypassed regions.
During the harvesting stage of the MCH method, mobilizing agents may be injected to one well system and the mobilized bitumen produced from the other well system to harvest additional mobile bitumen and mobilizing agent that was left behind in the subterranean formation. During the harvesting stage, the mobilizing agent composition may be modified, for example, by progressively replacing at least one of the mobilizing agents with a non-condensable gas to further improve residual mobilizing agent recovery and/or to reduce mobilizing agent requirement in the recovery processes.
The MCH method may provide improved sweep efficiency by the mobilizing agent stream. It may permit faster production of bitumen from the subterranean foimation, reduce cumulative steam to bitumen ratio, improve bitumen and diluent recovery and/or may decrease, or eliminate, the need to drill infill wells when compared to conventional cyclical or continuous recovery processes.
The present disclosure addresses the problem of poor sweep efficiency in conventional cyclical or continuous recovery processes by visualizing the bypassed region as a "bitumen-rich hill" surrounded by two mobilizing fluid chambers, one associated with each horizontal well system. Access to the bypassed oil, it was hypothesized, might be enhanced by cyclical changes in the direction of the mobilizing agents being driven from one horizontal well system to the other.
As used herein, the terms "solvent" and "diluent" may be utilized interchangeably. In addition, and as used herein, the terms "oil," "bitumen," "heavy hydrocarbon,"
and/or "viscous hydrocarbon" may be utilized interchangeably. As used herein, the phrase "mobilizing agent"
refers to any suitable fluid that reduces the viscosity of bitumen to make the bitumen more mobile and/or amenable to production from the subterranean formation. Examples of such mobilizing agents include steam, hot water, a solvent, a diluent, and/or mixtures thereof and are discussed in more detail herein.
The above-described chamber development stage, in case of a continuous recovery process, may also be referred to as a period of steady simultaneous injection and recovery, in which the injection of the mobilizing agent stream into and the production of bitumen from each horizontal well system is continuous. The steady stage may be continued until the bitumen between two mobilizing agent chambers becomes more mobile than the virgin bitumen via heat conduction from the advancing mobilizing agent chambers. The mobilizing agent composition injected into first horizontal well system 100 and/or into second horizontal well system 200 may be 0 to 100 mole percent diluent in a diluent-steam mixture, as may be utilized in conventional SAGD, SA-SAGD, ES-SAGD, VAPEX, and/or H-VAPEX processes.
The cyclic sweep stage is a period of cyclical operation, in which the mobilizing agent stream injection pressure (or injection rate) in each horizontal well system is cycled between a high pressure (or high injection rate) and a low pressure (or low injection rate). This is illustrated in Fig. 3 as PH and PL, respectively. The cycling is out-of-phase in that, for a period t 1 , first horizontal well system 100 is at PH and second horizontal well system 200 is at PL. This pressure differential creates a forward pressure drive from the former to the latter, as shown by the solid line with an arrow in Fig. 3. For the subsequent period t2, first horizontal well system 100 is set at PL and second horizontal well system 200 is set at PH, creating a reverse pressure drive from the latter to the former, as shown by the dotted line with an arrow in Fig. 3. The alternating, back-and-forth pressure allows the mobilizing agents to access the bypassed region from both sides, thereby improving sweep efficiency in the region bypassed by conventional cyclical and continuous recovery processes.
One cycle in the cyclic sweep stage of MCH consists of one forward drive from first horizontal well system 100 to second horizontal well system 200 for a period of tl, followed by a reverse drive from second horizontal well system 200 to first horizontal well system 100 for a period of t2. The time period to complete one cycle is (t1 + t2). The number of cycles in the cyclic sweep stage may vary from 1 to 100 or from 5 to 50. Time period tl may be the same as or different from the time period t2. Period tl or t2 may cover a range of 7 to 365 days or a range of 30 to 120 days.
During the cyclic sweep stage, the injection pressure and/or the injection rate in one horizontal well system may be 10 to 90 percent of that in the other horizontal well system. The pressure difference between two well systems may be equal to the pressure difference between a maximum mobilizing agent chamber pressure and a reservoir initial pressure.
The pressure difference between two horizontal well systems additionally or alternatively may be 20 to 80 percent of the pressure difference between the maximum mobilizing agent chamber pressure and a virgin reservoir pressure.
In the cyclic sweep stage of MCH, the mobilizing agents may be the same as or different from that used in the preceding mobilizing agent chamber development stage. As discussed earlier, a more effective mobilizing agent may be utilized in the cyclic sweep stage than that in the preceding mobilizing agent chamber development stage to accelerate the mobilizing agent access to, and enhance bitumen extraction efficiency in, the bypassed regions.
This may be achieved by making the mobilizing agent in the cyclic sweep stage richer in diluent than that in the preceding mobilizing agent chamber development stage of steam-rich recovery processes, such as cyclical CSS, or continuous SAGD or SA-SAGD, or richer in steam than that in the preceding mobilizing agent chamber development stage of diluent (or solvent)-rich recovery processes, such as cyclical CSP or continuous VAPEX or H-VAPEX.
In the cyclic sweep stage of MCH, the mobilizing agent composition in first horizontal well system 100 and/or in second horizontal well system 200 may be 0 to 100 mole percent diluent in a diluent-steam mixture, such as in continuous SAGD, SA-SAGD, ES-SAGD, and/or H-VAPEX, or cyclical CSS and/or CSP. The mobilizing agents may include only steam or only diluent. The diluent in the mobilizing agents may be any of C2 to C35 alkanes, alkenes, naphthenes, aromatics, a gas plant condensate, a catalytically converted light gas, and/or a mixture thereof.
The composition of the mobilizing agent composition of at least one mobilizing agent stream may be 20 to 80 mole percent diluent in a diluent-steam mixture.
Furthermore, the diluent in the mobilizing agent stream to at least one horizontal well system may be at least 5 percent higher than that utilized during the chamber development stage for the horizontal well system. The mobilizing agents may comprise 0 to 30 mole percent non-condensable gas in a steam-non-condensable gas mixture or in a diluent-non-condensable gas mixture.
Non-condensable gas may be any of methane, nitrogen, air, CO2, or flue gas used alone or in combination with at least one other component.

The cyclic sweep stage of MCH may be initiated at any time. As an example, the cyclic sweep stage may be initiated when a temperature at any location on a vertical plane mid-way between the two horizontal well systems reaches at least 30 C and/or when the bitumen becomes mobile. A number of cycles, n, in the cyclic sweep stage of MCH may be any number between 1 and 100 or between 5 and 50.
The time period n*(t1 + t2) to end the cyclic stage may be divided into two equal parts.
In the first part, the mobilizing agent composition may be 1 to 80 mole percent diluent in a diluent-steam mixture.
In the harvesting stage of MCH, at least one flow (drive), from one horizontal well system to the other horizontal well system, by the mobilizing agents is performed. The duration of this harvesting stage may be longer than the time period of (t1+ t2) to complete one cycle in the cyclic sweep stage. The direction of the flow may be reversed, at least once, in the harvesting stage.
The mobilizing agents utilized during the harvesting stage may be only steam.
It may also comprise 0 to 100 mole percent non-condensable gas in a steam-non-condensable gas mixture. The diluent and/or the steam in the mobilizing agent streams may be replaced continuously, step-wise, or in one step with a single and/or with a multi-component non-condensable gas, ending with 100 percent non-condensable gas, to maximize the harvesting of the diluent and mobilized bitumen from the subterranean formation, and improve overall recovery efficiency of the MCH method. Non-condensable gases may be any of methane, nitrogen, air, CO2, flue gas from steam boilers, or a mixture thereof In one embodiment, only the mobilizing agent chamber development stage and the cyclic sweep stage of MCH may be practiced. In another embodiment, the harvesting stage may be =
replaced with another mobilizing agent chamber development stage. In yet another embodiment, only the cyclic sweep stage and the harvesting stage of MCH may be practiced.
In another embodiment, only the cyclic sweep stage of MCH may be practiced.
In yet another embodiment, the methods disclosed herein may be applied to a "single"
horizontal well, in which the same well acts as an injector of mobilizing agents and a producer of mobilized bitumen, for example, as in CSS and/or CSP processes. In this embodiment, after doing several cycles of injection of mobilizing agent steam, and production of bitumen, as in conventional CSS, or after doing several cycles of injection of mobilizing agent diluent (or solvent) and production of mobilized bitumen, as in conventional CSP, at least one additional cycle of injection of mobilizing agents and production of bitumen may be performed by adding solvent to steam (in the context of CSS), or by adding steam to solvent (in the context of CSP).
This at least one additional cycle may allow the mobilizing agents to move laterally and/or to access bitumen that would have been bypassed by conventional gravity drainage processes.
The methods disclosed herein also may be applied to "multiple" cyclical horizontal wells in CSS or CSP. In this embodiment, after doing several cycles of injection of steam alone (CSS) or diluent (or solvent) alone (CSP) and production of bitumen in each well, the cyclic stage of MCH may be introduced between two adjacent horizontal well systems to promote at least one cycle of alternating, back-and-forth drives. This also may include adding diluent to steam in CSS, or adding steam to diluent (or solvent) in CSP, to allow the mobilizing agents to access bitumen that would have been bypassed in conventional cyclical recovery processes. The harvesting stage of MCH also may be practiced in this embodiment by stimulating a flow of a mobilizing agent from one well to the other. The direction of the flow may be reversed, at least once, in this stage.

In another embodiment, the methods disclosed herein may be applied to a single horizontal well system, in which one well acts as an injector and the other as a producer, to recover bitumen by conventional SAGD, SA-SAGD, ES-SAGD, VAPEX, and/or H-VAPEX
processes. In this embodiment, a period of continuous injection and production with a conventional mobilizing agent may be performed during the mobilizing agent chamber development stage. Subsequently, at least one additional cycle of injection and production may be performed in the cyclic sweep stage to allow the mobilizing agent to access bitumen that would have been bypassed by conventional continuous processes. The composition of the mobilizing agent may be modified in this stage and hence may be different from that in the chamber development change. For example, for SAGD, the mobilizing agent during the cyclic sweep stage may be modified to include diluent (or steam) with steam to improve sweep efficiency. For H-VAPEX, the mobilizing agent during the cyclic sweep stage may be modified to include steam with diluent (or steam) to improve sweep efficiency.
The methods disclosed herein also may be applied to "multiple" horizontal well pairs in SAGD, ES-SAGD, SA-SAGD, VAPEX, or H-VAPEX. In this embodiment, after performing the mobilizing agent chamber development stage through mobilizing agent injection and bitumen production from each well pair, the cyclic sweep stage of MCH may be introduced between two adjacent horizontal well systems to promote at least one cycle of alternating, back-and-forth drives. This also may include adding diluent to steam in SAGD, or adding steam to solvent in VAPEX or H-VAPEX, to allow the mobilizing agent to access bitumen that would have been bypassed in conventional continuous in-situ bitumen recovery processes. In the cyclic sweep stage, the production may be from the production well of each well pair. The harvesting stage of MCH also may be practiced in this embodiment by stimulating a flow of a mobilizing agent from one well system to the other. The direction of the flow may be reversed, at least once, in this stage.
In another embodiment, the method comprises a cyclic sweep stage during which mobilizing agent injection into the second horizontal well system is reduced, relative to that into the first horizontal well system, to create a drive from the first horizontal well system to the second horizontal well system. This reduction may be maintained for a time period of t 1 and may be followed by a time period of t2 during which mobilizing agent injection into the second horizontal well system is raised relative to that in the first horizontal well system. This may create a drive from the second horizontal well system to the first horizontal well system. The process may be repeated, thereby providing back-and-forth drives between the two horizontal well systems for a number of times, n, and for a total period of time, n*(t1 +
t2). The cyclic sweep stage may be used alone or in combination with the preceding mobilizing agent chamber development stage and/or with the subsequent harvesting stage. For example, the cyclic sweep stage may be preceded by the mobilizing agent chamber development stage, with continuous injection and production from each well system. For another example, the cyclic sweep stage may be preceded by the mobilizing agent chamber development stage, with continuous injection and production from each well system. The cyclic sweep stage also may be followed by the harvesting stage during which the direction of flow is from the first horizontal well system to the second horizontal well system or from the second horizontal well system to the first horizontal well system. The cyclic sweep stage additionally or alternatively also may be preceded by the mobilizing agent chamber development stage and followed by the harvesting stage.

The disclosed methods may be utilized, for example, with 20 to 200 meters well spacing between two adjacent horizontal well systems as well as for a commercial development involving more than two horizontal well systems.
Advantages of the methods disclosed herein over conventional processes include improved sweep efficiency, higher displacement efficiency, accelerated bitumen production, higher bitumen and diluent recovery, and/or elimination of infill wells. The disclosed methods apply to continuous recovery processes, such as SAGD, SA-SAGD, or ES-SAGD, VAPEX, and/or H-VAPEX, as well as to cyclical recovery processes, such as CSS or CSP.
Simulations in a reservoir with two horizontal well pairs illustrate the much better than expected benefits of the currently disclosed methods over conventional SAGD
and SA-SAGD.
Utilizing the methods disclosed herein, significant reduction in sizes of the bypassed regions for each recovery process is achieved.
Example 1: Bypassed Region in MCH vs. SAGD
A conventional SAGD was simulated within a model subterranean formation, using two horizontal well systems, each of which comprised a horizontal injection well and a horizontal production well, as shown in Fig. 1 as represented by well systems labeled 101/102 and 201/202, respectively. A 90-day warm-up period was performed with 100 percent steam in each well system. This was followed by continuous injection of 100 percent steam into injection well of each well system at 1500 KPa and continuous production of bitumen from the production well of each well system, from 90 to 3000 days. The 100 percent steam injection was followed by continuous injection of 5 mole percent steam and 95 mole percent methane into the injection well of each well system, and continuous production of bitumen from the production well of each well system, from 3000 to 4000 days. This was followed by continuous injection of 1 mole percent steam and 99 mole percent methane into the injection well of each well system, and continuous production of bitumen from the production well of each well system, up to 5000 days. Results of this simulation of the conventional SAGD processes of the prior art, depicting bitumen distribution within the subterranean formation after 1800 and 2500 days, are illustrated in Figs. 4-5, respectively.
An MCH method similar to an embodiment of the presently disclosed methods 300 in Fig. 12, which is discussed in more detail herein, was also simulated within the same model subterranean formation as used in Figs. 4-5 above, using two horizontal well systems, each of which comprised a horizontal injection well and a horizontal production well, as shown in Fig. 1.
A 90-day warm-up period was performed with 100 percent steam in each well system and was followed by a mobilizing agent chamber development stage that included continuous injection of 100 mole percent steam into the injection well of each well system at 1500 KPa, and continuous production of bitumen from the production well of each well system, from 90 to 900 days. The mobilizing agent chamber development stage was followed by a cyclic sweep stage, according to the invention, from 900 to 3000 days. During the cyclic sweep stage, injection pressure within each horizontal well system was cycled, every 30 days, between 1500 KPa and 1000 KPa such that one horizontal well system was at a higher pressure than the other, creating alternating, back-and-forth pressure drives between the two horizontal well systems. The mobilizing agent for the first 900 to 1800 days of the cyclic sweep stage in each horizontal well system was modified, according to the disclosed invention, to include 20 mole percent diluent and 80 mole percent steam, while the mobilizing agent was reverted to 100 percent steam from the second 1800 to 3000 days of the cyclic sweep stage. The cyclic sweep stage was followed by a harvesting stage from 3000 to 5000 days to harvest the residual diluent and bitumen from the subterranean formation, while injecting less steam. During days 3000 to 4000, the harvesting flow was from the first horizontal well system to the second horizontal well system and was performed utilizing a modified mobilizing agent that included 5 mole percent steam and 95 mole percent methane. During days 4000 to 5000, the flow direction was reversed from the second horizontal well system to the first horizontal well system and was perfon-ned utilizing a modified mobilizing agent that included 1 mole percent steam and 99 mole percent methane. Results of this simulation of the presently disclosed methods, depicting bitumen distribution within the subterranean fon-nation after 1800 and 2500 days, are illustrated in Figs. 6-7, respectively.
As illustrated in the comparison between Figs. 4 and 6, after 1800 days, bypassed region 46 obtained utilizing the MCH method (as illustrated in Fig. 6) has an approximately 60 percent smaller volume than that of bypassed region 46 obtained utilizing conventional SAGD (as illustrated in Fig. 4). The difference is even more pronounced after 2500 days, with bypassed region 46 obtained utilizing the MCH method (as illustrated in Fig. 7) having an approximately 90 percent smaller volume than that of bypassed region 46 obtained utilizing conventional SAGD (as illustrated in Fig. 5). The methods of invention herein resulted a 90% reduction in volume of the bypassed region which means a sweep efficiency increase of 90%
is achieved by the MCH processes herein as compared to the prior art. This is significantly better than what was expected during the conception stage of the invention through visualizing the bypassed region as being a "bitumen-rich" hill.

Example 2: Bypassed Region in MCH vs. SA-SAGD
A conventional SA-SAGD was simulated within a model subterranean formation, using two horizontal well systems, each of which comprised a horizontal injection well and a horizontal production well, as shown in Fig. 1 as represented by well systems labeled 101/102 and 201/202, respectively. A 90-day wan-n-up period was performed with 100 percent steam in each well system. This was followed by continuous injection of 97.6 mole percent steam and 2.4 mole percent diluent (diluent to steam ratio of 0.2, v/v) at 1500 KPa into the injection well of each well system, and continuous production of bitumen from the production well of each well system, from 90 to 1800 days, which was followed by 100 percent steam-only SAGD from 1800 to 3000 days. From 3000 to 4000 days, each horizontal well system received 5 mole percent steam and 95 mole percent methane; and from 4000 to 5000 days, each horizontal well system received 1 mole percent steam and 99 mole percent methane. Results of this simulation of the conventional SA-SAGD processes of the prior art, depicting bitumen distribution within the subterranean foimation after 1800 and 2160 days, are illustrated in Figs. 8-9, respectively.
An MCH method similar to an embodiment of the presently disclosed methods 300, which is discussed in more detail herein, was also simulated within the same model subterranean formation as used in Figs. 8-9 above, using two horizontal well systems, each of which comprised a horizontal injection well and a horizontal production well, as shown in Fig. 1. A 90-day warm-up period was performed with 100 percent steam in each well system and was followed by a mobilizing agent chamber development stage that included continuous injection of 97.6 mole percent steam and 2.4 mole percent diluent (diluent to steam ratio of 0.2, v/v) at 1500 KPa into the injection well of each well system and continuous production of bitumen from the production well of each well system, from 90 to 900 days. The mobilizing agent chamber development stage was followed by a cyclic sweep stage, according to the disclosed invention, from 900 to 3000 days. During the cyclic sweep stage, injection pressure within each horizontal well system was cycled, every 30 days, between 1500 KPa and 1000 KPa such that one horizontal well system was at a higher pressure than the other, creating an alternating, back-and-forth pressure drive between the two horizontal well systems. The modified mobilizing agent for the first 900 to 1800 days of the cyclic sweep stage in each horizontal well system included 80 mole percent steam and 20 mole percent diluent, while the mobilizing agent was 100 percent steam from 1800 to 3000 days of the cyclic sweep stage. The cyclic sweep stage was followed by a harvesting stage from 3000 to 5000 days. During days 3000 to 4000, the harvesting flow was from the first horizontal well system to the second horizontal well system and was performed utilizing a modified mobilizing agent that included 5 mole percent steam and 95 mole percent methane. During days 4000 to 5000, the harvesting flow was from the second horizontal well system to the first horizontal well system and was performed utilizing a mobilizing agent that included 1 mole percent steam and 99 mole percent methane. Results of this simulation of the presently disclosed methods, depicting bitumen distribution within the subterranean formation after 1800 and 2160 days, are illustrated in Figs. 10-11, respectively.
As illustrated in the comparison between Figs. 8 and 10, bypassed region 46, after 1800 days, obtained utilizing the MCH method (as illustrated in Fig. 10) has an approximately 50 percent smaller volume than that obtained utilizing conventional SA-SAGD (as illustrated in Fig.
8). The difference is even more pronounced after 2160 days, with bypassed region 46 obtained utilizing the MCH method (as illustrated in Fig. 11) having an approximately 70 percent smaller volume than that obtained utilizing conventional SA-SAGD (as illustrated in Fig. 9). As such, as compared to conventional SA-SAGD process, the methods of invention herein resulted a 50 to 70% (based on duration) reduction in volume of the bypassed region which means a sweep efficiency increase of 50 to 70% is achieved by the MCH processes herein as compared to the prior art.
Additional Method Examples Additional examples, alternative examples, additional statements, and/or alternative statements of methods, according to the present disclosure, are illustrated in Figs. 12-14 and discussed in more detail herein with reference thereto. These methods also may be referred to herein as MCH methods and may be performed with and/or utilizing bitumen production system

10 of Figs. 1-2.
Fig. 12 is a flowchart depicting methods 300, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process. Methods 300 utilize a first horizontal well system, such as first horizontal well system 100 of Figs. 1-2, and a second horizontal well system, such as second horizontal well system 200 of Fig. 1, that is spaced-apart from the first horizontal well system within a subterranean for-nation, such as subterranean formation 40 of Figs. 1-2. Methods 300 include a mobilizing agent chamber development stage at 310, which includes injecting a first mobilizing agent stream at 312 into the first horizontal well system, injecting a second mobilizing agent stream at 314 into the second horizontal well system, and producing bitumen at 316 from each horizontal well system. Methods 300 also include a cyclic sweep stage at 320, which includes back-and-forth alternating drive between each well system by reducing a relative injection of the second mobilizing agent stream at 322 and increasing the relative injection of the first mobilizing agent stream into the first horizontal well system at 324, and vice versa. The mobilizing agent composition in the cyclic sweep stage may also be modified by increasing or decreasing the proportion of the diluent in the diluent-steam mixture. Methods 300 further include a harvesting stage at 330, which includes reducing a relative injection of the second mobilizing agent into the second well system at 332 and also may include increasing the relative injection of the first mobilizing agent into the first well system at 334 and/or progressively increasing a fraction of non-condensable gas at 336.
Methods 300 further include a harvesting stage at 330, which includes reducing a relative injection of the first mobilizing agent into the first well system at 332 and also may include increasing the relative injection of the second mobilizing agent into the second well system at 334 and/or progressively increasing a fraction of non-condensable gas at 336.
Mobilizing agent chamber development stage 310 may be performed prior to cyclic sweep stage 320 and/or prior to harvesting stage 330. However, this is not required for all embodiments, and is within the scope of the present disclosure that mobilizing agent chamber development stage 310, cyclic sweep stage 320, and/or harvesting stage 330 may be performed in any suitable order and/or that one or more of the stages may be repeated subsequent to one or more other of the stages. Mobilizing agent chamber development stage 310 generally will be performed continuously, or at least substantially continuously. This may include performing the injecting at 312, the injecting at 314, and the producing at 316 continuously, or at least substantially continuously. However, this is not required to all embodiments, and it is within the scope of the present disclosure that one or more of the injecting at 312, the injecting at 314, and the producing at 316 may be performed intermittently and/or cyclically during steady stage 310.
In general, mobilizing agent chamber development stage 310 may be similar, or at least substantially similar, to conventional in-situ bitumen recovery processes.
Examples of such conventional gravity drainage-dominated bitumen recovery processes are discussed in more detail herein and include SAGD, SA-SAGD, ES-SAGD, VAPEX, H-VAPEX, CSP, and/or CSS.
With this in mind, and during mobilizing agent chamber development stage 310, the first mobilizing agent stream and/or the second mobilizing agent stream may include, consist of, and/or consist essentially of one or more of steam, hot water, a solvent, a diluent, and/or mixtures thereof at any suitable concentration, or relative concentration. Examples of suitable concentrations include at least 0 mole percent, at least 5 mole percent, at least 10 mole percent, at least 20 mole percent, at least 30 mole percent, at least 40 mole percent, at least 50 mole percent, at least 60 mole percent, at least 70 mole percent, at least 80 mole percent, at least 90 mole percent, at least 95 mole percent, 100 mole percent, at most 100 mole percent, at most 95 mole percent, at most 90 mole percent, at most 80 mole percent, at most 70 mole percent, at most 60 mole percent, at most 50 mole percent, at most 40 mole percent, at most 30 mole percent, at most mole percent, at most 10 mole percent, at most 5 mole percent, and/or 0 mole percent steam, hot water, solvent, and/or diluent.
Examples of suitable diluents and/or solvents include alkanes, alkenes, naphthenes, 15 aromatics, gas plant condensates, catalytically converted light gas, and/or mixtures thereof Such diluents may include any suitable number of carbon atoms, such as at least 2, at least 3, at least 4, at least 6, at least 8, at least 10, at least 15, at least 20, at least 25, at least 30, at most 35, at most 30, at most 25, at most 20, at most 15, and/or at most 10 carbon atoms.
Injecting the first mobilizing agent stream at 312 may include injecting the first 20 mobilizing agent stream into a first mobilizing agent chamber with, via, and/or utilizing the first horizontal well system. The first mobilizing agent chamber may extend within the subterranean formation, and an example of the first mobilizing agent chamber is illustrated in Figs. 1-2 at 120.
An example of the first mobilizing agent stream is illustrated in Figs. 1-2 at 112.

Injecting the second mobilizing agent stream at 314 may include injecting the second mobilizing agent stream into a second mobilizing agent chamber with, via, and/or utilizing the second horizontal well system. The second mobilizing agent chamber may extend within the subterranean formation, and an example of the second mobilizing agent chamber is illustrated in Fig. 1 at 220. The injecting at 314 may be performed concurrently, or at least partially concurrently, with the injecting at 312. An example of the second mobilizing agent stream is illustrated in Fig. 1 at 212.
Producing bitumen at 316 may include producing bitumen from the subterranean formation with, via, and/or utilizing both the first horizontal well system and the second horizontal well system. The producing at 316 may be performed concurrently, or at least partially concurrently, with the injecting at 312 and/or with the injecting at 314.
Cyclic sweep stage 320 may be performed subsequent to mobilizing agent chamber development stage 310. Additionally or alternatively, cyclic sweep stage 320 may be performed prior to harvesting stage 330. Cyclic stage 320 may include repeatedly, cyclically, and/or sequentially performing the reducing at 322 and the increasing at 324. As an example, cyclic stage 320 may include perfon-ning the reducing at 322 and subsequently performing the increasing at 324 a plurality of times, or over a plurality of cycles.
During cyclic stage 320, the first mobilizing agent stream and/or the second mobilizing agent stream may also include, consist of, and/or consist essentially of one or more of steam, hot water, a solvent, a diluent, and/or mixtures thereof at any suitable concentration, or relative concentration. Examples of suitable concentrations include at least 0 mole percent, at least 5 mole percent, at least 10 mole percent, at least 20 mole percent, at least 30 mole percent, at least 40 mole percent, at least 50 mole percent, at least 60 mole percent, at least 70 mole percent, at least 80 mole percent, at least 90 mole percent, at least 95 mole percent, 100 mole percent, at most 100 mole percent, at most 95 mole percent, at most 90 mole percent, at most 80 mole percent, at most 70 mole percent, at most 60 mole percent, at most 50 mole percent, at most 40 mole percent, at most 30 mole percent, at most 20 mole percent, at most 10 mole percent, at most 5 mole percent, and/or 0 mole percent steam, hot water, solvent, and/or diluent.
Examples of suitable diluents and/or solvents include alkanes, alkenes, naphthenes, aromatic hydrocarbons, gas plant condensates, catalytically converted light gas, and/or mixtures thereof Such diluents may include any suitable number of carbon atoms, such as at least 2, at least 3, at least 4, at least 6, at least 8, at least 10, at least 15, at least 20, at least 25, at least 30, at most 35, at most 30, at most 25, at most 20, at most 15, and/or at most 10 carbon atoms.
During cyclic stage 320, the first mobilizing agent stream and/or the second mobilizing agent may include mobilizing agent comprising a diluent- steam mixture, the composition of which may be the same as or different from that in the mobilizing agent chamber development stage. For example, the mobilizing agent in the chamber development stage of a steam-dominated process such as SAGD, ES-SAGD, SA-SAGD, CSS, LASER, may include at least one of: (i) essentially of 100 mole percent steam; (ii) at least 97 mole percent steam; or (iii) at least 88 mole percent steam. During the cyclic sweep stage of the above-mentioned steam-dominated processes, at least one of the first mobilizing agent stream and the second mobilizing agent stream may include at least one of: (i) at least five mole percent more diluent when compared to a corresponding stream during the mobilizing agent chamber development stage;
(ii) at least 10 mole percent more diluent when compared to the corresponding stream during the mobilizing agent chamber development stage; (iii) at least 50 mole percent more diluent when compared to the corresponding stream during the mobilizing agent chamber development stage;

and (iv) at least 100 mole percent more diluent when compared to the corresponding stream during the mobilizing agent chamber development stage.
As another example, the mobilizing agent in the chamber development stage of a diluent-dominated process, such as VAPEX, H-VAPEX, or CSP, may include at least one of: (i) essentially of 100 mole percent diluent; (ii) at least 80 mole percent diluent; or (iii) at least 40 mole percent diluent. During the cyclic sweep stage of a diluent-dominated mobilizing agent chamber development stage, at least one of the first mobilizing agent stream and the second mobilizing agent stream may include at least one of: (i) at least 10 mole percent more steam when compared to a corresponding stream during the mobilizing agent chamber development stage; (ii) at least 30 mole percent more steam when compared to the corresponding stream during the mobilizing agent chamber development stage; (iii) at least 50 mole percent more steam when compared to the corresponding stream during the mobilizing agent chamber development stage; and (iv) at least 70 mole percent more steam when compared to the corresponding stream during the mobilizing agent chamber development stage.
In yet another embodiment, during cyclic stage 320, regardless of the mobilizing agent composition used in the mobilizing agent chamber stage and/or of the recovery process used in that stage, the mobilizing agent in the cyclic sweep stage may be a diluent-dominated mixture containing at least one of: (i) at least 10 mole percent steam; (ii) at least 30 mole percent steam;
(iii) at least 50 mole percent steam; or (iv) at least 70 mole percent more steam. Such diluent-dominated mixtures with the stated concentrations of steam are found to be more potent in accessing bitumen in the bypassed regions.
Reducing the relative injection of the second mobilizing agent stream at 322 may include reducing injection of the second mobilizing agent stream into the second mobilizing agent =
chamber relative to injection of the first mobilizing agent stream into the first mobilizing agent chamber. This may include decreasing a flow rate of the second mobilizing agent stream into the second mobilizing agent chamber, reducing an injection pressure of the second mobilizing agent stream, and/or reducing a pressure within the second mobilizing agent chamber.
Additionally or alternatively, the reducing at 322 may include increasing a flow rate of the first mobilizing agent stream into the first mobilizing agent chamber, increasing an injection pressure of the first mobilizing agent stream, and/or increasing a pressure within the first mobilizing agent chamber.
The reducing at 322 may include reducing to produce and/or facilitate flow of bitumen from the first mobilizing agent chamber, away from the first horizontal well system, toward the second horizontal well system, toward the second mobilizing agent chamber, and/or into the second horizontal well system. Stated another way, the reducing at 322 may include producing and/or generating a motive force for flow of mobilizing agent and/or bitumen, within the subterranean fon-nation, generally away from the first mobilizing agent chamber, and/or toward the second mobilizing agent chamber.
The reducing at 322 may include reducing such that a second injection pressure of the second mobilizing agent stream to a threshold percent of a first injection pressure of the first mobilizing agent stream. Examples of the threshold fraction of the first injection pressure include threshold fractions of at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at most 95, at most 90, at most 80, at most 70, at most 60, at most 50, at most 40, at most 30, at most 20, and/or at most 10 percent of the first injection pressure.
The reducing at 322 additionally or alternatively may include reducing such that a pressure difference between the first injection pressure and the second injection pressure is equal to a maximum pressure difference between a maximum mobilizing agent chamber pressure and a virgin reservoir pressure of the subterranean formation. Additionally or alternatively, the pressure differential may be at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at most 95, at most 90, at most 80, at most 70, at most 60, at most 50, at most 40, at most 30, at most 20, and/or at most 10 percent of the maximum pressure difference. The maximum pressure difference also may be referred to herein as a maximum permissible pressure difference, a maximum pressure difference that is achievable by bitumen production system 10, and/or a maximum pressure difference before fracture of the subterranean formation.
The reducing at 322 additionally or alternatively may include reducing such that a second injection rate of the second mobilizing agent stream is a threshold percent of a first injection rate of the first mobilizing agent stream. Examples of the threshold fraction of the first injection rate include threshold fractions of at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at most 95, at most 90, at most 80, at most 70, at most 60, at most 50, at most 40, at most 30, at most 20, and/or at most 10 percent of the first injection rate.
Increasing the relative injection of the second mobilizing agent stream at 324 may be performed subsequent to the reducing at 322. The increasing at 324 may include increasing injection of the second mobilizing agent stream into the second mobilizing agent chamber relative to injection of the first mobilizing agent stream into the first mobilizing agent chamber.
This may include increasing a flow rate of the second mobilizing agent stream into the second mobilizing agent chamber, increasing an injection pressure of the second mobilizing agent stream, and/or increasing a pressure within the second mobilizing agent chamber. Additionally or alternatively, the increasing at 324 may include decreasing a flow rate of the first mobilizing agent stream into the first mobilizing agent chamber, decreasing an injection pressure of the first mobilizing agent stream, and/or decreasing a pressure within the first mobilizing agent chamber.
The increasing at 324 may include increasing to produce and/or facilitate flow of bitumen from the second mobilizing agent chamber, away from the second horizontal well system, toward the first horizontal well system, toward the first mobilizing agent chamber, and/or into the first horizontal well system. Stated another way, the reducing at 322 may include producing and/or generating a motive force for flow of mobilizing agent and/or bitumen, within the subterranean for-nation, generally away from the first mobilizing agent chamber, and/or toward the second mobilizing agent chamber.
The increasing at 324 may include increasing such that the first injection pressure is a threshold percent of the second injection pressure. Examples of the threshold percent of the second injection pressure include threshold fractions of at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at most 95, at most 90, at most 80, at most 70, at most 60, at most 50, at most 40, at most 30, at most 20, and/or at most 10 percent of the first injection pressure.
The increasing at 324 additionally or alternatively may include increasing such that a third injection rate of the first mobilizing agent stream is a threshold percent of a fourth injection rate of the second mobilizing agent stream. Examples of the threshold percent of the second injection rate include threshold fractions of at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at most 95, at most 90, at most 80, at most 70, at most 60, at most 50, at most 40, at most 30, at most 20, and/or at most 10 percent of the fourth injection rate.

It is within the scope of the present disclosure that methods 300 may include transitioning from mobilizing agent chamber development stage 310 to cyclic sweep stage 320 based upon and/or responsive to any suitable criteria. As an example, methods 300 may include transitioning responsive to a temperature within the subterranean formation.
Examples of the temperature within the subterranean formation include a temperature within the first mobilizing agent chamber, a temperature within the second mobilizing agent chamber, a temperature between the first mobilizing agent chamber and the second mobilizing agent chamber, and/or a temperature at a location on a vertical plane mid-way between the first horizontal well system and the second horizontal well system. Example values for the temperature include temperatures of at least 20 C, at least 30 C, at least 40 C, at 50 C, at least 60 C, and/or at least 70 C.
As discussed, cyclic sweep stage 320 may include repeatedly, cyclically, and/or sequentially performing the reducing at 322 and the increasing at 324, and it is within the scope of the present disclosure that cyclic sweep stage 320 may include any suitable number, or a selected number, of cycles of the reducing at 322 and the increasing at 324.
As examples, the selected number of cycles may include, or be, at least 1, at least 2, at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at most 150, at most 100, at most 80, at most 60, at most 50, at most 40, and/or at most 30 cycles.
Each cycle may include performing the reducing at 322 for a first time period and subsequently performing the increasing at 324 for a second time period. Under these conditions, a total time period for cyclic stage 320 may be a product of the selected number of cycles and a sum of the first time period and the second time period.
The first time period and the second time period may have any suitable duration. As examples, the first time period and/or the second time period may be at least 7 days, at least 14 =
days, at least 21 days, at least 30 days, at least 60 days, at least 90 days, at least 120 days, at least 150 days, at most 730 days, at most 365 days, at most 300 days, at most 240 days, at most 180 days, at most 150 days, at most 120 days, at most 90 days and/or at most 60 days. The first time period may be the same as, or different from, the second time period.
The total time period may include an initial time period and a subsequent time period.
The initial time period and the subsequent time period may have any suitable duration and/or relative duration, and the initial time period may be equal to, or may differ from, the subsequent time period.
It is within the scope of the present disclosure that a composition of the first mobilizing agent stream and/or of the second mobilizing agent stream may differ between the initial time period and the subsequent time period. As an example, and during the initial time period, the first mobilizing agent stream and/or the second mobilizing agent stream may include a diluent-steam mixture. Examples of concentrations of diluent and/or steam in the diluent-steam mixture are disclosed herein.
During the subsequent time period, the first mobilizing agent stream and/or the second mobilizing agent stream may consist essentially of steam or may include, or be, a mixture of steam and a non-condensable gas. Examples of the non-condensable gas include methane, nitrogen, air, carbon dioxide, and/or flue gas. Examples of concentrations of steam and/or of non-condensable gas in the mixture of steam and non-condensable gas include concentrations of at least 1 mole percent, at least 2 mole percent, at least 4 mole percent, at least 6 mole percent, at least 8 mole percent, at least 10 mole percent, at least 15 mole percent, at least 20 mole percent, at least 25 mole percent, at most 50 mole percent, at most 40 mole percent, at most 30 mole percent, at most 25 mole percent, at most 20 mole percent, and/or at most 15 mole percent steam and/or non-condensable gas.
Harvesting stage 330 may be performed subsequent to cyclic sweep stage 320 The harvesting stage harvests residual diluent and bitumen to improve the economics of the MCH
method by progressively increasing the concentration of a non-condensable gas and progressively decreasing the concentrations of the mobilizing agents in the first or the second mobilizing stream.
Reducing the injection at 332 in the harvesting stage may be similar to the reducing at 322 of the cyclic sweep stage, and may include decreasing a flow rate of the first mobilizing agent stream or the second mobilizing agent stream, reducing an injection pressure of the first mobilizing agent stream or the second mobilizing agent stream, and/or reducing a pressure within the first mobilizing agent chamber or the second mobilizing agent chamber. The reducing injection at step 332 allows flooding of the subterranean formation from the higher rate horizontal well system or the higher pressure mobilizing agent chamber to the lower rate horizontal well system or lower pressure mobilizing agent chamber. The reducing injection at step 332 additionally or alternatively may be referred to as a drive stage of the harvesting stage.
Increasing the injection at 334 in the harvesting stage may be similar to the reducing at 322 of the cyclic sweep stage, and may include decreasing a flow rate of the first mobilizing agent stream or the second mobilizing agent stream, reducing an injection pressure of the first mobilizing agent stream or the second mobilizing agent stream, and/or reducing a pressure within the first mobilizing agent chamber or the second mobilizing agent chamber. The increasing injection step 334 allows flooding of the subterranean formation from the higher rate horizontal well system or the higher pressure mobilizing agent chamber to the lower rate horizontal well system or lower pressure mobilizing agent chamber.
Progressively increasing the fraction of non-condensable gas at 336 may include increasing the concentration of a non-condensable gas and progressively decreasing the concentrations of the mobilizing agents in the first or the second mobilizing stream. Examples of the condensable gas are disclosed herein.
As discussed herein, the first horizontal well system may include a single well, such as well 101 of Figs. 1-2, and the second horizontal well system may include a single well, such as well 201 of Fig. 1. The single well of the first horizontal well system also may be referred to herein as a first well, while the single well of the second horizontal well system also may be referred to herein as a second well.
Under these conditions, the injecting at 312 in Fig. 12 may include injecting the first mobilizing agent stream into the first mobilizing agent chamber via the first well. Similarly, the injecting at 314 in Fig. 12 may include injecting the second mobilizing agent stream into the second mobilizing agent chamber via the second well. In addition, the producing at 316 in Fig.
12 may include producing bitumen from the subterranean for-nation via the first well and/or via the second well. In such a configuration, the first well and/or the second well may be configured to be an injector or a producer for a cyclic process, such as CSS and/or CSP.
When the first and second horizontal well systems include corresponding single wells, cyclic stage 320 may include perfonning a plurality of cycles in which both the first mobilizing agent stream and the second mobilizing agent stream consist essentially of steam followed by at least one cycle in which the first mobilizing agent stream and/or the second mobilizing agent stream is a diluent-steam mixture. Additionally or alternatively, cyclic stage 320 may include perfoiming a plurality of cycles in which both the first mobilizing agent stream and the second mobilizing agent stream consist essentially of a solvent followed by at least one cycle in which the first mobilizing agent stream and/or the second mobilizing agent stream is a solvent-steam mixture.
As also discussed herein, the first horizontal well system may include a pair of wells, such as lower well 101 and upper well 102 of Figs. 1-2, and the second horizontal well system may include a pair of wells, such as lower well 201 and upper well 202 of Fig.
1. Under these conditions, the injecting at 312 may include injecting via the first upper well, the injecting at 314 may include injecting via the second upper well, and the producing at 316 may include producing via both the first lower well and the second lower well.
Fig. 13 is a flowchart depicting methods 400, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process. The bitumen recovery process utilizes a horizontal well system, such as horizontal well system 100 of Figs. 1-2, that extends within a subterranean formation to mobilize and produce bitumen from the subterranean formation. Methods 400 include a mobilizing agent chamber development stage 410 and a modified stage 420. Mobilizing agent chamber development stage 410 includes injecting a mobilizing agent stream at 412 and producing bitumen at 414. Modified stage 420 includes injecting a modified mobilizing agent stream at 422 and producing bitumen at 424.
Injecting the mobilizing agent stream at 412 may include injecting a mobilizing agent stream, such as mobilizing agent stream 112 of Figs. 1-2, into a mobilizing agent chamber, such as mobilizing agent chamber 120 of Figs. 1-2, with, via, and/or utilizing the horizontal well system.

Producing bitumen at 414 may include producing bitumen from the subterranean formation with, via, and/or utilizing the horizontal well system. The producing at 414 may be performed concurrently, or at least substantially concurrently, with the injecting at 412.
Modified stage 420 may be subsequent to chamber development stage 410.
However, this is not required to all embodiments, and it is within the scope of the present disclosure that mobilizing agent chamber development stage 410 may follow, or be subsequent to modified stage 420 and/or that methods 400 may include sequentially performing a plurality of chamber development stages 410 followed by a plurality of modified stages 420.
Injecting the modified mobilizing agent stream at 422 may include injecting the modified mobilizing agent stream into the mobilizing agent chamber with, via, and/or utilizing the horizontal well system.
A composition of the modified mobilizing agent stream differs from a composition of the mobilizing agent stream. As an example, chamber development stage 410 may include performing a SAGD process, in which the mobilizing agent stream may include, be, and/or consist essentially of steam. Under these conditions, the modified mobilizing agent stream may include, be, and/or consist essentially of a diluent-steam mixture. As another example, mobilizing agent chamber development stage 410 may include performing a SA-SAGD process, in which the mobilizing agent stream may include, be, and/or consist essentially of a diluent-steam mixture. Under these conditions, the modified mobilizing agent stream may include a greater mole fraction of diluent than that in the mobilizing agent stream of mobilizing agent chamber development stage 410.
As yet another example, the chamber development stage may include performing an H-VAPEX process in which the mobilizing agent stream may include, be, and/or consist essentially =
of a diluent, or a heated diluent. Under these conditions, the modified mobilizing agent stream may include a diluent-steam mixture.
Producing bitumen at 424 may include producing bitumen from the subterranean formation with, via, and/or utilizing the horizontal well system. The producing at 424 may be performed concurrently, or at least substantially concurrently, with the injecting at 422.
Fig. 14 is a flowchart depicting methods 500, according to the present disclosure, of improving sweep efficiency in an in-situ bitumen recovery process. The in-situ bitumen recovery process utilizes a first horizontal well system, such as first horizontal well system 100 of Figs. 1-2, and a second horizontal well system, such as second horizontal well system 200 of Fig. 1, to mobilize and produce bitumen from the subterranean formation. The second horizontal well system is horizontally spaced apart from the first horizontal well system within a subterranean formation.
Methods 500 comprise a cyclic sweep stage 520 that includes injecting a first mobilizing agent stream at 522 and injecting a second mobilizing agent stream at 524. The injecting at 522 may include injecting into a first mobilizing agent chamber via the first horizontal well system, such as to generate a first pressure within the first mobilizing agent chamber. The injecting at 524 may include injecting a second mobilizing agent stream into a second mobilizing agent chamber via the second horizontal well system, such as to generate a second pressure within the second mobilizing agent chamber.
During cyclic sweep stage 520, a pressure differential between the first pressure and the second pressure provides a motive force for flow of mobilizing agent away from the first mobilizing agent chamber, through the bypassed region, toward the second mobilizing agent chamber, and into the second horizontal well system.

Cyclic sweep stage 520 also includes step 526 to lower first pressure to PL
and step 528 to increase second pressure to PH so as to reverse the flow direction of the mobilizing agent away from the second mobilizing agent chamber, through the bypassed region, toward the first mobilizing agent chamber, and into the first horizontal well system. At least one cycle of ___________________________________________________________________________ forward flow followed by reverse flow is perfoi Hied to help access the entire bypassed region, thereby improving the sweep efficiency of the subterranean formation by conventional recovery processes.
Methods 500 may include optional stage 510 preceding cyclic sweep stage 520, which when performed, may be similar, or at least substantially similar, to mobilizing agent chamber development stage 310 of methods 300. Methods 500 may also include optional stage 530 subsequent to cyclic sweep stage 520, which when performed, may be similar, or at least substantially similar, to mobilizing agent chamber development stage 310 of methods 300.
Methods 500 may yet include a harvesting stage 540, subsequent to cyclic sweep stage 520 and/or stage 530, which when performed, may be similar, or at least substantially similar, to harvesting stage 330 of methods 300.
In the present disclosure, a plurality of distinct streams, including the mobilizing agent stream, the first mobilizing agent stream, the second mobilizing agent stream, and/or the modified mobilizing agent stream may be injected into the subterranean formation during a variety of different, or distinct, steps of methods 300, 400, and/or 500. It is within the scope of the present disclosure that a given stream may have a corresponding composition that is constant, or at least substantially constant, during the various steps that utilize the stream. As an example, and with reference to methods 300 of Fig. 12, a composition of the first mobilizing agent stream may be constant, or at least substantially constant, during the chamber development stage, during the cyclic sweep stage, and also during the harvesting stage. Stated another way, the composition of the first mobilizing agent stream may be fixed, may be at least substantially fixed, may not change, and/or may not be purposefully changed while methods 300 are performed.
Additionally or alternatively, it is also within the scope of the present disclosure that the corresponding composition of the given stream may vary, may be purposefully varied, and/or may be systematically varied during the steps that utilize the stream. As an example, and with continued reference to methods 300 of Fig. 12, the composition of the first mobilizing agent stream during mobilizing agent chamber development stage 310 may differ from the composition of the first mobilizing agent stream during cyclic sweep stage 320 and/or during harvesting stage 330. As another example, the composition of the first mobilizing agent stream may vary during mobilizing agent chamber development stage 310, may vary during cyclic sweep stage 320, and/or may vary during harvesting stage 330. Stated another way, an initial composition of the first mobilizing agent stream at an initial time period during methods 300 may differ from a subsequent, or later composition of the first mobilizing agent stream at a subsequent, or later, time during methods 300.
In the present disclosure, several of the illustrative, non-exclusive examples have been discussed and/or presented in the context of flow diagrams, or flow charts, in which the methods are shown and described as a series of blocks, or steps. Unless specifically set forth in the accompanying description, it is within the scope of the present disclosure that the order of the blocks may vary from the illustrated order in the flow diagram, including with two or more of the blocks (or steps) occurring in a different order and/or concurrently.

As used herein, the term "and/or" placed between a first entity and a second entity means one of (1) the first entity, (2) the second entity, and (3) the first entity and the second entity.
Multiple entities listed with "and/or" should be construed in the same manner, i.e., "one or more"
of the entities so conjoined. Other entities may optionally be present other than the entities specifically identified by the "and/or" clause, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, a reference to "A
and/or B," when used in conjunction with open-ended language such as "comprising" may refer, in one embodiment, to A only (optionally including entities other than B); in another embodiment, to B only (optionally including entities other than A); in yet another embodiment, to both A and B
(optionally including other entities). These entities may refer to elements, actions, structures, steps, operations, values, and the like.
As used herein, the phrase "at least one," in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entity in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase "at least one" refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") may refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other entities). In other words, the phrases "at least one," "one or more," and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions "at least one of A, B and C," "at least one of A, B, or C," "one or more of A, B, and C," "one or more of A, B, or C" and "A, B, and/or C" may mean A alone, B
alone, C alone, A
and B together, A and C together, B and C together, A, B and C together, and optionally any of the above in combination with at least one other entity.
In the event that any patents, patent applications, or other references are incorporated by reference herein and (1) define a term in a manner that is inconsistent with and/or (2) are otherwise inconsistent with, either the non-incorporated portion of the present disclosure or any of the other incorporated references, the non-incorporated portion of the present disclosure shall control, and the term or incorporated disclosure therein shall only control with respect to the reference in which the term is defined and/or the incorporated disclosure was present originally.
As used herein the terms "adapted" and "configured" mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms "adapted" and "configured" should not be construed to mean that a given element, component, or other subject matter is simply "capable of' performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function.
It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa.

As used herein, the phrase, "for example," the phrase, "as an example," and/or simply the term "example," when used with reference to one or more components, features, details, structures, embodiments, and/or methods according to the present disclosure, are intended to convey that the described component, feature, detail, structure, embodiment, and/or method is an illustrative, non-exclusive example of components, features, details, structures, embodiments, and/or methods according to the present disclosure. Thus, the described component, feature, detail, structure, embodiment, and/or method is not intended to be limiting, required, or exclusive/exhaustive; and other components, features, details, structures, embodiments, and/or methods, including structurally and/or functionally similar and/or equivalent components, features, details, structures, embodiments, and/or methods, are also within the scope of the present disclosure.
Industrial Applicability The systems and methods disclosed herein are applicable to the oil and gas industry.
It is believed that the disclosure set forth above encompasses multiple embodiments of the invention described herein which embodiments may possess independent utility. While each of these embodiments has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite "a" or "a first" element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower, or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.

Claims

1. A method of improving sweep efficiency in an in-situ bitumen recovery process, utilizing a first horizontal well system and a second horizontal well system horizontally spaced apart from the first horizontal well system within a subterranean formation, the method comprising:
during a mobilizing agent chamber development stage:
(i) injecting a first mobilizing agent stream into a first mobilizing agent chamber via the first horizontal well system;
(ii) injecting a second mobilizing agent stream into a second mobilizing agent chamber via the second horizontal well system; and (iii) producing bitumen from the subterranean formation via both the first horizontal well system and the second horizontal well system; and during a cyclic sweep stage, which is subsequent to the mobilizing agent chamber development stage:
(iv) reducing an injection pressure of the second mobilizing agent stream into the second mobilizing agent chamber, relative to an injection pressure of the first mobilizing agent stream into the first mobilizing agent chamber;
(v) driving the first mobilizing agent stream from the first mobilizing agent chamber through a first side of a bypassed region created in the mobilizing agent chamber development stage, and producing mobilized bitumen through the second horizontal well system;
(vi) subsequent to step (v), increasing the injection pressure of the second mobilizing agent stream into the second mobilizing agent chamber, relative to the injection pressure of the first mobilizing agent stream into the first mobilizing agent chamber;
(vii) driving the second mobilizing agent stream from the second mobilizing agent chamber through a second side of the bypassed region, and producing mobilized bitumen through the first horizontal well system; and (viii) repeating steps (iv) through (vii), for a plurality of cycles, to reverse the direction of flow of the first mobilizing agent stream and the second mobilizing agent stream through the first side and the second side of the bypassed region, thereby improving the sweep efficiency of the bypassed region by the first and second mobilizing agent streams.

2. The method of claim 1, further comprising:
a harvesting stage, which is subsequent to the cyclic sweep stage, wherein the harvesting stage includes a drive stage in which the injection pressure of one of the first mobilizing agent stream and the second mobilizing agent stream is reduced relative to the injection pressure of the other of the first mobilizing agent stream and the second mobilizing agent stream, wherein the harvesting stage includes replacing at least one component of one of the first mobilizing agent stream and the second mobilizing agent stream with a non-condensable gas, and further wherein the harvesting stage includes producing the other of the first mobilizing agent stream and the second mobilizing agent stream, and residual bitumen, from the subterranean formation.

3. The method of claim 1 or 2, wherein, during the mobilizing agent chamber development stage, the injecting the first mobilizing agent stream and the injecting the second mobilizing agent stream are performed continuously and at least partially concurrently.

4. The method of any one of claims 1-3, wherein, during the mobilizing agent chamber development stage, the producing bitumen from both the first horizontal well system and the second horizontal well system is performed continuously and at least partially concurrently.

5. The method of claim 1 or 2, wherein, during the mobilizing agent chamber development stage, the injecting the first mobilizing agent stream and the injecting the second mobilizing agent stream are performed cyclically and at least partially concurrently.

6. The method of any one of claims 1, 2 or 5, wherein, during the mobilizing agent chamber development stage, the producing bitumen from both the first horizontal well system and the second horizontal well system is performed cyclically and at least partially concurrently.

7. The method of any one of claims1-6, wherein the reducing the injection pressure of the second mobilizing agent stream includes reducing a second injection pressure of the second mobilizing agent stream to at least 10 and at most 90 percent of a first injection pressure of the first mobilizing agent stream.

8. The method of claim 7, wherein the increasing the injection pressure of the second mobilizing agent stream includes increasing the second injection pressure of the second mobilizing agent stream to from between 110 to 300 percent of the first injection pressure of the first mobilizing agent stream.

9. The method of any one of claims 1-6 wherein the reducing the injection pressure of the second mobilizing agent stream includes reducing a second injection pressure of the second mobilizing agent stream relative to a first injection pressure of the first mobilizing agent stream such that a pressure difference between the first injection pressure and the second injection pressure is at least one of:
equal to a maximum pressure difference between a maximum mobilizing agent chamber pressure and a virgin reservoir pressure; and (ii) at least 10 and at most 100 percent of the maximum pressure difference between the maximum mobilizing agent chamber pressure and the virgin reservoir pressure.

10. The method of claim 9, wherein the increasing the injection pressure of the second mobilizing agent stream includes increasing the second injection pressure of the second mobilizing agent stream relative to the first injection pressure of the first mobilizing agent stream such that the pressure difference between the second injection pressure of the second mobilizing agent stream and the first injection pressure of the first mobilizing agent stream is at least one of:
equal to the maximum pressure difference between the maximum mobilizing agent chamber pressure and the virgin reservoir pressure; and (ii) at least 10 and at most 100 percent of the maximum pressure difference between the maximum mobilizing agent chamber pressure and the virgin reservoir pressure.

11. The method of any one of claims 1-10, wherein injection pressures of the mobilizing agent streams in each of the horizontal well systems are the same in each cycle of the plurality of cycles.

12. The method of any one of claims 1-11, wherein reduced injection pressures of the mobilizing agent streams in each of the horizontal well systems are the same in each cycle of the plurality of cycles.

13. The method of any one of claims 1-10, wherein the increased injection pressures of the mobilizing agent streams in each of the horizontal well systems are different in each cycle of the plurality of cycles.

14. The method of any one of claims 1-10 and 13, wherein reduced injection pressures of the mobilizing agent streams in each of the horizontal well systems are different in each cycle of the plurality of cycles.

15. The method of any one of claims 1-14, wherein, at least one of the first mobilizing agent stream and the second mobilizing agent stream includes a diluent-steam mixture.

16. The method of any one of claims 1-15, wherein, the mobilizing agent chamber development stage includes a steam-dominated process.

17. The method of claim 16, wherein, during the mobilizing agent chamber development stage, both the first mobilizing agent stream and the second mobilizing agent stream at least one of:
(i) consist essentially of steam;
(ii) are at least 95 mole percent steam; and (iii) are at least 70 mole percent steam.

18. The method of any one of claims 1-15, wherein, the mobilizing agent chamber development stage includes a diluent-dominated process.

19. The method of claim 18, wherein both the first mobilizing agent stream and the second mobilizing agent stream at least one of:
(i) consist essentially of diluent;
(ii) are at least 95 mole percent diluent; and (iii) are at least 70 mole percent diluent.

20. The method of any one of claims 15, 18, and 19, wherein, during the cyclic sweep stage, at least one of the first mobilizing agent stream and the second mobilizing agent stream includes at least one of:

(i) at least five mole percent more diluent when compared to a corresponding mobilizing agent stream during the mobilizing agent chamber development stage;
(ii) at least 10 mole percent more diluent when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage;
(iii) at least 50 mole percent more diluent when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage;
and (iv) at least 100 mole percent more diluent when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage.

21. The method of any one of claims 1, 15, 18, and 19, wherein, during the cyclic sweep stage at least one of the first mobilizing agent stream and the second mobilizing agent stream includes at least one of:
(i) at least five mole percent more steam when compared to a corresponding mobilizing agent stream during the mobilizing agent chamber development stage;
(ii) at least 10 mole percent more steam when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage;
(iii) at least 50 mole percent more steam when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage;

and (iv) at least 100 mole percent more steam when compared to the corresponding mobilizing agent stream during the mobilizing agent chamber development stage.

22. The method of any one of claims 15 and 18-20, wherein the diluent includes at least one of an alkane, an alkene, a naphthene, an aromatic hydrocarbon, a gas plant condensate, and a catalytically converted light gas oil.

23. The method of any one of claims 15 and 18-20, wherein the diluent includes a hydrocarbon with at least 2 and at most 35 carbon atoms.

24 The method of any one of claims 1-23, wherein the method includes transitioning from the mobilizing agent chamber development stage to the cyclic sweep stage responsive to a temperature at a location, on a vertical plane mid-way between the first horizontal well system and the second horizontal well system, reaching at least one of:
at least 30 °C; and (ii) at least 50 °C.

25. The method of any one of claims 1-24, wherein, during the cyclic sweep stage, the method includes performing a selected number of cycles, wherein each cycle in the selected number of cycles includes performing the reducing the injection pressure of the second mobilizing agent stream for a first time period and performing the subsequently increasing the injection pressure of the second mobilizing agent stream for a second time period.

26. The method of claim 25, wherein the first time period is at least one of:
(i) at least 7 and at most 365 days; and (ii) at least 30 and at most 120 days.

27. The method of any one of claims 25-26, wherein the second time period is at least one of:
(i) at least 7 and at most 365 days; and (ii) at least 30 and at most 120 days.

28. The method of any one of claims 25-27, wherein the first time period is at least one of:
the same as the second time period; and (ii) different from the second time period.

29. The method of any one of claims 25-28, wherein the selected number of cycles is at least one of:
at least 1 and at most 100 cycles; and (ii) at least 5 and at most 50 cycles.

30. The method of any one of claims 25-29, wherein a total time period for the cyclic sweep stage is a product of the selected number of cycles and a sum of the first time period and the second time period.

31. The method of claim 30, wherein the total time period includes an initial time period and a subsequent time period.

32. The method of claim 31, wherein at least one of:
the initial time period is equal to the subsequent time period; and (ii) the initial time period differs from the subsequent time period.

33. The method of any one of claims 31-32, wherein, during the initial time period, at least one of the first mobilizing agent stream and the second mobilizing agent stream includes at least one of:
(i) at least 20 and at most 100 mole percent diluent in a/the diluent-steam mixture;
and (ii) at least 30 and at most 80 mole percent diluent in the diluent-steam mixture.

34. The method of any one of claims 31-33, wherein, during the initial time period, at least one of the first mobilizing agent stream and the second mobilizing agent stream in the cyclic sweep stage is a diluent-dominated mixture containing at least one of:
(i) at least 10 mole percent steam;
(ii) at least 30 mole percent steam;
(iii) at least 50 mole percent steam; and (iv) at least 70 mole percent steam.

35. The method of any one of claims 31-34, wherein, during the subsequent time period, at least one of the first mobilizing agent stream and the second mobilizing agent stream consists essentially of at least one of:
steam;

(ii) a mixture of steam and a/the diluent; and (iii) the diluent.

36. The method of any one of claims 2-35, wherein, during the harvesting stage, the method further includes increasing, with increasing time, a fraction of a/the non-condensable gas in at least one of the first mobilizing agent stream and the second mobilizing agent stream.

37. The method of claim 36, wherein the non-condensable gas includes at least one of:
(i) methane;
(ii) nitrogen;
(iii) air;
(iv) carbon dioxide; and (v) flue gas.

38. The method of any one of claims 36-37, wherein at least one of the first mobilizing agent stream and the second mobilizing agent stream contains from 1 to 100 mole percent of the non-condensable gas.

39. The method of any one of claims 1-38, wherein the in-situ bitumen recovery process includes at least one of:
(i) a steam-assisted gravity drainage (SAGD) process;
(ii) a solvent-assisted SAGD (SA-SAGD) process;
(iii) an expanding solvent SAGD (ES-SAGD) process;

(iv) a vapor extraction (VAPEX) process;
(v) a heated VAPEX (H-VAPEX) process;
(vi) cyclic steam stimulation (CSS); and (vii) cyclic solvent processes (CSP).

40. The method of any one of claims 1-39, wherein the first horizontal well system includes a first upper well, which extends within the first mobilizing agent chamber, and a first lower well, which extends vertically below the first upper well within the first mobilizing agent chamber.

41. The method of claim 40, wherein the injecting the first mobilizing agent stream into the first mobilizing agent chamber includes injecting the first mobilizing agent stream via the first upper well.

42. The method of any one of claims 40-41, wherein the producing bitumen from the subterranean formation via the first horizontal well system includes producing bitumen from the subterranean formation via the first lower well.

43. The method of any one of claims 1-42, wherein the second horizontal well system includes a second upper well, which extends within the second mobilizing agent chamber, and a second lower well, which extends vertically below the second upper well within the second mobilizing agent chamber.

44. The method of claim 43, wherein the injecting the second mobilizing agent stream into the second mobilizing agent chamber includes injecting the second mobilizing agent stream via the second upper well.

45. The method of any one of claims 43-44, wherein the producing bitumen from the subterranean formation via the second horizontal well system includes producing bitumen from the subterranean formation via the second lower well.

46. The method of any one of claims 40-45, wherein the first horizontal well system and the second horizontal well system are configured for at least one of:
(i) a steam-assisted gravity drainage (SAGD) process;
(ii) a solvent-assisted SAGD (SA-SAGD) process;
(iii) an expanding solvent SAGD (ES-SAGD) process;
(iv) a vapor extraction (VAPEX) process;
(v) a heated VAPEX (H-VAPEX) process;

47. The method of any one of claims 1-38, wherein the first horizontal well system includes a first well, wherein the injecting the first mobilizing agent stream into the first mobilizing agent chamber includes injecting the first mobilizing agent stream via the first well, and further, wherein the producing bitumen from the subterranean formation via the first horizontal well system includes producing bitumen from the subterranean formation via the first well.

48. The method of any one of claims 1-38 and 47, wherein the second horizontal well system includes a second well, wherein the injecting the second mobilizing agent stream into the second mobilizing agent chamber includes injecting the second mobilizing agent stream via the second well, and further wherein the producing bitumen from the subterranean formation via the second horizontal well system includes producing bitumen from the subterranean formation via the second well.

49. The method of any one of claims 47-48, wherein the first well is configured for at least one of:
cyclic steam stimulation (CSS) of the subterranean formation; and (ii) a cyclic solvent process (CSP).

50. The method of any one of claims 48-49, wherein the second well is configured for at least one of:
cyclic steam stimulation (CSS) of the subterranean formation; and (ii) a cyclic solvent process (CSP).

51. The method of any one of claims 47-50, wherein, during the cyclic sweep stage, the method includes at least one of:
(i) performing a plurality of cycles in which both the first mobilizing agent stream and the second mobilizing agent stream consist essentially of steam followed by at least one cycle in which at least one of the first mobilizing agent stream and the second mobilizing agent stream is a diluent-steam mixture; and (ii) performing a plurality of cycles in which both the first mobilizing agent stream and the second mobilizing agent stream consist essentially of a solvent followed by at least one cycle in which at least one of the first mobilizing agent stream and the second mobilizing agent stream is a solvent-steam mixture.

52. A method of improving sweep efficiency in an in-situ bitumen recovery process that utilizes a horizontal well system extending within a subterranean formation, the method comprising:
during a mobilizing agent chamber development stage:
(1) injecting a mobilizing agent stream into a mobilizing agent chamber via the horizontal well system; and (ii) producing bitumen from the subterranean formation via the horizontal well system; and during a modified stage, which is subsequent to the mobilizing agent chamber development stage:
(iii) injecting a modified mobilizing agent stream into the mobilizing agent chamber via the horizontal well system, wherein a composition of the modified mobilizing agent stream differs from a composition of the mobilizing agent stream; and (iv) producing bitumen from the subterranean formation via the horizontal well system.

53. The method of claim 52, wherein the mobilizing agent chamber development stage includes performing a steam-assisted gravity drainage (SAGD) process, wherein the mobilizing agent stream consists essentially of steam, and further wherein the modified mobilizing agent stream comprises a diluent-steam mixture.

54. The method of claim 52, wherein the mobilizing agent chamber development stage includes performing a solvent-assisted steam-assisted gravity drainage (SA-SAGD) process, wherein the mobilizing agent stream includes a diluent-steam mixture, and further wherein the modified mobilizing agent stream includes a modified diluent-steam mixture including a greater mole fraction of diluent than a mole fraction of diluent in the mobilizing agent stream.

55. The method of claim 52, wherein the mobilizing agent chamber development stage includes performing a heated vapor extraction (H-VAPEX) process, wherein the mobilizing agent stream consists essentially of a diluent, and wherein the modified mobilizing agent stream comprises a diluent-steam mixture.

56. A method of improving sweep efficiency in an in-situ bitumen recovery process that utilizes a first horizontal well system and a second horizontal well system horizontally spaced-apart from the first horizontal well system within a subterranean formation, the method comprising:
during a cyclic sweep stage:
reducing an injection pressure of a second mobilizing agent stream into a second mobilizing agent chamber, relative to an injection pressure of a first mobilizing agent stream into a first mobilizing agent chamber, to drive the first mobilizing agent stream from the first mobilizing agent chamber through a first side of a bypassed region created in a mobilizing agent chamber development stage, and producing mobilized bitumen through the second horizontal well system;
(ii) subsequently, increasing the injection pressure of the second mobilizing agent stream into the second mobilizing agent chamber, relative to the injection pressure of the first mobilizing agent stream into the first mobilizing agent chamber, to drive the second mobilizing agent stream from the second mobilizing agent chamber through a second side of the bypassed region, and producing mobilized bitumen through the first horizontal well system; and (iii) repeating steps (i) and (ii), for a plurality of cycles, to reverse the direction of flow of the first mobilizing agent stream and the second mobilizing agent stream through the first side and the second side of the bypassed region, thereby improving the sweep efficiency of the bypassed region by the first and second mobilizing agent streams.

57. The method of claim 56, wherein the composition of the first mobilizing agent stream is different from the composition of the second mobilizing agent stream.

58. The method of claim 57, wherein, preceding the cyclic sweep stage, the method further includes performing the mobilizing agent chamber development stage, wherein the mobilizing agent chamber development stage includes:
(i) continuously injecting the first mobilizing agent stream into the first mobilizing agent chamber via the first horizontal well system;

(ii) continuously injecting the second mobilizing agent stream into the second mobilizing agent chamber via the second horizontal well system; and (iii) continuously producing bitumen from the subterranean formation via both the first horizontal well system and the second horizontal well system.

59. The method of any one of claims 56-58, further comprising:
a harvesting stage, which is subsequent to either the cyclic sweep stage and/or the mobilizing agent chamber development stage, wherein the harvesting stage includes reducing the injection pressure of one of the first mobilizing agent stream and the second mobilizing agent stream into the corresponding one of the first or second horizontal well system relative to the injection pressure of the other of the first mobilizing agent stream and the second mobilizing agent stream, and, wherein the harvesting stage includes replacing at least one component of at least one of the first mobilizing agent stream and the second mobilizing agent stream with a non-condensable gas to harvest at least one component of at least one of the first mobilizing agent stream and the second mobilizing agent stream and residual bitumen from the subterranean formation.