PRODUCTION OF HYDROCARBON USING DIRECT-CONTACT STEAM GENERATION

Abstract

A process for in situ thermal recovery of hydrocarbons from a reservoir is provided. The process includes: providing an oxygen-enriched mixture, fuel, feedwater and an additive including at least one of ammonia, urea and a volatile amine to a Direct-Contact Steam Generator (DCSG); operating the DCSG, including contacting the feedwater and the additive with hot combustion gas to obtain a steam-based mixture including steam, CO.sub.2 and the additive; injecting the steam-based mixture or a stream derived from the steam-based mixture into the reservoir to mobilize the hydrocarbons therein; and producing a produced fluid including the hydrocarbons.

Claims

1. A process for in situ thermal recovery of hydrocarbons from a reservoir, comprising: providing an oxygen-enriched mixture, fuel, feedwater and an additive to a direct-contact steam generator (DCSG), the additive being carried by a heat carrier gas; operating the DCSG, comprising contacting the feedwater and the additive with hot combustion gas to obtain a steam-based mixture comprising steam, CO.sub.2 and the additive, the heat carrier gas providing stability to the additive during operation of the DCSG; injecting the steam-based mixture or a stream derived from the steam-based mixture into the reservoir to mobilize the hydrocarbons therein; and producing a produced fluid comprising the hydrocarbons.

2. The process of claim 1, wherein the additive comprises at least one of a viscosity reduction agent or a well integrity agent.

3. The process of claim 1, wherein the additive comprises at least one of a viscosity reduction agent, an anticorrosive agent, an antifouling agent, a scale inhibitor or a thermally stable cement.

4. The process of claim 1, wherein the heat carrier gas comprises CO.sub.2 or nitrogen.

5. The process of claim 1, wherein the heat carrier gas comprises steam at a lower temperature than outgoing steam.

6. A process for steam-assisted gravity drainage (SAGD) recovery of hydrocarbons from a reservoir, comprising: providing an oxygen-enriched mixture, fuel, feedwater and an additive to a direct-contact steam generator (DCSG), the additive comprising a well integrity agent chosen from the group consisting of an anticorrosive agent, an antifouling agent, a scale inhibitor and a thermally stable cement; operating the DCSG, comprising contacting the feedwater and the additive with hot combustion gas to obtain a steam-based mixture comprising steam, CO.sub.2 and the additive; injecting the steam-based mixture or a stream derived from the steam-based mixture into the reservoir via a SAGD injection well to mobilize hydrocarbons therein; and recovering the hydrocarbons as produced fluids from a SAGD production well.

7. The process of claim 6, wherein the concentration of the additive in the steam-based mixture is between about 0.1 wt % and about 30 wt %.

8. The process of claim 6, wherein the additive further comprises at least one of a viscosity reduction agent.

9. The process of claim 6, wherein the additive is in a dispersed state.

10. The process of claim 6, wherein the feedwater is provided as a feedwater stream and the additive is provided as a separate additive stream, to the DCSG.

11. The process of claim 10, wherein the feedwater stream is contacted with the hot combustion gas for a longer time period than the additive stream.

12. The process of claim 6, wherein the feedwater comprises at least part of the produced water and the fuel comprises at least part of the produced gas.

13. The process of claim 6, wherein the feedwater further comprises makeup water and the concentration of the makeup water in the feedwater is of up to about 5 wt % of the feedwater.

14. A process for in situ thermal recovery of hydrocarbons from a reservoir, comprising: providing an oxygen-enriched mixture, fuel, feedwater and an additive in liquid state to a DCSG; operating the DCSG, comprising contacting the feedwater and the additive with hot combustion gas to obtain a steam-based mixture comprising steam, CO.sub.2 and the additive in a gaseous state and/or a dispersed state; injecting the steam-based mixture or a stream derived from the steam-based mixture into the reservoir to mobilize the hydrocarbons therein; and producing a produced fluid comprising the hydrocarbons.

15. The process of claim 14, wherein the additive is provided as a liquid in pure form to the DCSG.

16. The process of claim 14, wherein the additive is provided in solution in a solvent.

17. The process of claim 16, wherein the solvent is water.

18. The process of claim 14, wherein the additive is in a gaseous state in the steam-based mixture.

19. The process of claim 14, wherein the additive comprises at least one of ammonia, urea or a volatile amine.

20. The process of claim 14, wherein the additive comprises ammonia provided as an ammonium hydroxide solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] FIG. 1 is a process flow diagram of a hydrocarbon recovery operation, showing possible additive injection points;

[0092] FIG. 2A is a process flow diagram of a hydrocarbon recovery operation, showing possible additive injection points and featuring a steam/CO.sub.2 separation step;

[0093] FIG. 2B is a process flow diagram of a hydrocarbon recovery operation, showing possible additive injection points and featuring a steam/CO.sub.2 membrane separation step; and

[0094] FIG. 3 is a top schematic view of a hydrocarbon recovery system with steam generation, water recycling and additive delivery at remote hydrocarbon recovery facilities.

DETAILED DESCRIPTION

[0095] Various techniques that are described herein enable thermal in situ recovery operations of hydrocarbons, such as steam-assisted gravity drainage (SAGD), including the use of a direct-contact steam generator (DCSG) for generating steam. The outlet stream generated by the DCSG typically includes steam and CO.sub.2 and may be referred to as a combustion mixture or a steam-based mixture. While the combustion mixture can be directly injected into a reservoir to mobilize the hydrocarbons therein, in some scenarios it can be desirable to co-inject an additive into the reservoir along with the combustion mixture. In some scenarios, co-injection of an additive can improve bitumen recovery, can provide a certain benefit to existing tubing or downhole tools including electric submersible pumps (ESPs), enhance conformance, or provide solutions to formation damage. The additive can be mixed with the combustion mixture downstream of the DCSG, or can alternatively be injected into the DCSG along with feedwater so that the additive is incorporated into the steam-based mixture as the steam-based mixture is generated.

[0096] A DCSG generates steam by directly contacting feedwater with a hot combustion gas which is produced using fuel (for example, natural gas) and an oxidizing gas (for example, an oxygen-enriched gas mixture, such as purified oxygen). Depending on the oxidizing gas and fuel that are used, the combustion gas can include various amounts of carbon dioxide (CO.sub.2) as well as other gases such as carbon monoxide (CO), hydrogen (H.sub.2), nitrogen based compounds (NO.sub.x) such as nitric oxide (NO) and nitrogen dioxide (NO.sub.2), and/or sulfur based compounds (SO.sub.x) such as sulfur oxides. The fuel and oxidizing gas can be premixed prior to reaching a burner, and a flame is generated in a combustion chamber, thereby forming the hot combustion gas. The feedwater is typically run down the combustion chamber in jacketed pipes and into an evaporation chamber, and the hot combustion gas evaporates the feedwater in the evaporation chamber, thereby generating the outlet stream which includes steam and combustion gas, which typically mostly includes CO.sub.2.

[0097] There are several types of additives that can be incorporated into the steam-based mixture, depending for example on the nature of the reservoir, production stage (start-up, ramp up, plateau, decline, wind down), the configuration of the hydrocarbon recovery operation, economic and/or environmental parameters. In some implementations, the additive can be a liquid additive which is vaporizable and/or dispersible into the combustion mixture, such as ammonia or a volatile amine, or any other additive desired. In some scenarios, injecting the additive into the DCSG for vaporizing and/or dispersing into the combustion mixture can reduce costs and/or increase safety compared to having to vaporize the additive prior to injecting the additive into the combustion mixture.

[0098] DCSGs can be located at remote hydrocarbon recovery facilities due to their small size and scalability, and steam can thereby be generated proximate to the well pads as opposed to being generated at a distant processing facility and conveyed to the well pad. The CO.sub.2 included in the combustion gas can either be co-injected with the steam into the injection well (in whole or in part), or separated prior to the injection. In some scenarios, the additives to be co-injected can be stored proximate to the well pads, at each remote hydrocarbon recovery facility, or dissolved in the feedwater thereby potentially reducing the costs and/or safety considerations. In some scenarios, using DCSGs at remote hydrocarbon recovery facilities can allow for eliminating chemical skids.

[0099] Some implementations of the technology are described in greater detail below.

[0100] Steam Generation Implementations

[0101] Referring to FIG. 1, a hydrocarbon recovery operation using steam-assisted gravity drainage is shown. It should be understood that throughout the present description, hydrocarbon recovery using SAGD is used to illustrate the various implementations. It should be understood that the processes and techniques of the present description can also be implemented using other hydrocarbon recovery processes. Non-limiting examples of such other hydrocarbon recovery processes include cyclic steam stimulation (CSS) and Vapor Extraction (VAPEX), among others. It should also be understood that the techniques of the present description can also be implemented with processes utilizing co-injection of steam and solvent.

[0102] Still referring to FIG. 1, in some implementations, an oxygen-enriched mixture 10, fuel 12 and feedwater 14 are fed to a DCSG 16. The oxygen-enriched mixture 10 can be oxygen-enriched air, or oxygen at different levels of purity. Optionally, high purity oxygen can be used. In some implementations, the oxygen-enriched mixture 10 can be generated using an oxygen module 36 which can separate an incoming air stream 38 into the oxygen-enriched mixture 10 and oxygen-lean air 40.

[0103] Still referring to FIG. 1, the DCSG 16 can be operated to obtain a steam-based mixture 18 which includes steam and CO.sub.2. Depending on the type of fuel 12 and oxygen-enriched mixture 10, the steam-based mixture 18 can also include various amounts of other gases, as explained above. It is noteworthy that the concentration of CO.sub.2 in an outlet stream of a DCSG which is not subjected to steam-CO.sub.2 separation can be up to 12 wt %, typically between 6 wt % and 12 wt %. In some scenarios, depending for example on the properties and geological layout of the reservoir, it can be desirable to incorporate an additive into the steam-based mixture 18 and co-inject the additive into the reservoir along with the steam-based mixture 18, as will be explained in further detail herein.

[0104] Still referring to FIG. 1, the steam-based mixture 18 is injected into a hydrocarbon-bearing reservoir via an injection well 20, and produced fluids 24 are recovered from a production well 22. In some implementations, the injection well and the production well are located on a well pad 23 that is part of the hydrocarbon recovery operation. The produced fluids 24 can be separated in separator 26 into a produced gas component 28, produced non-gaseous hydrocarbons 30 and produced water 32. The produced water 32 can be oily water which can contain some solid materials.

[0105] In some implementations, the DCSG 16 can operate effectively with low feedwater quality, and in some scenarios with feedwater quality that is considered unacceptable for steam generation using a once through steam generator OTSG or drum boiler. The feedwater 14 can include fresh water, recycled produced water from a steam-assisted hydrocarbon recovery process or a mixture thereof. Recycled produced water can include high levels of contaminants and impurities (such as volatile organic compounds, residual hydrocarbons, inorganic compounds and/or suspended solids), which can be flared in the DCSG.

[0106] In some implementations, all or part of the produced gas 28 can be sent back to a processing facility for separating light hydrocarbons from unwanted compounds, and/or all or part of the produced gas 28 can directly be used as part of the fuel 12 for the DCSG 16. In some implementations, the fuel 12 used for the DCSG can be a mixture including at least a portion of the produced gas 28 and makeup fuel 34. The DCSG 16 can operate using different types of fuel 12, such as be natural gas, syngas, refinery fuel gas, coke, asphaltenes or mixtures thereof. The flexibility in the types of fuel that can be used provides an advantage against escalating natural gas prices or natural gas supply interruptions.

[0107] In some implementations, the produced non-gaseous hydrocarbons 30 can include heavy oil and/or bitumen and are typically further processed or upgraded in a processing facility. At least part of the produced water 32 can be recycled back to the DCSG 16 to be used as feedwater. In some implementations, makeup water 42 can be added to the produced water 32 for use as DCSG feedwater. As there is little to no produced gas 28 and produced water 32 during SAGD startup operations, the feedwater 14 and the fuel 12 mainly consist of the makeup water 40 and an external source of fuel supplied to the DCSG 16, respectively. As production from the SAGD operation begins to ramp up, produced gas 28 and produced water 32 can be obtained from the separator 26 and respectively used as part of the fuel 12 and feedwater 14, thereby requiring less makeup water 42 and makeup fuel 34. When the SAGD operation reaches a normal operating stage, the feedwater 14 can mainly include produced water 32, with a varying amount of makeup water 42 added as required. In some implementations, very little makeup water 42 is required when the SAGD operation reaches a ramped-up continuous regime. When the reservoir retains water, as is often the case in SAGD startup, the proportion of makeup water 42 to total feedwater 14 is higher. When more water is recovered from the produced fluids 24, the proportion of makeup water 42 to total feedwater 14 is lower. In some scenarios, more water is released from the reservoir than is injected. In such cases, no makeup water is needed and the excess water recovered can be stored for later use. In some implementations when SAGD is used, high water production can sometimes be observed as a result of prolonged interruptions (e.g., due to phase separation in the reservoir), such as after unplanned events (e.g., fires). In some implementations, other operational events including infill well when in production can lead to different water/oil cuts in produced pad fluids.

[0108] Additive Implementations

[0109] Still referring to FIG. 1, in some implementations, an additive 44a, 44b, 44c (or a plurality of additives) can be provided to the DCSG 16 and/or to the steam-based mixture 18 of the DCSG 16. The nature and purpose of the additive can vary. In some scenarios, the additive can be added with the goal of improving hydrocarbon recovery. In other scenarios, the additive can be added with the goal of improving well integrity. In some implementations, the temperature and pressure conditions within the main chamber of the DCSG 16 and/or within the steam-based mixture 18 can condition and/or chemically transform the additive in order to impart certain properties to the additive. For example, an additive in liquid state can be provided to the DCSG 16 and contacted with hot combustion gas originating from combustion of the fuel 12 and the oxygen-enriched mixture 10, in order to be vaporised and/or dispersed into the steam-based mixture 18. After contacting the hot combustion gas, the additive can be present in a gaseous state and/or as a dispersed liquid in the steam-based mixture 18.

[0110] It should be understood that the expression in a liquid state, as used herein, refers to the additive being injected into the DCSG as a liquid in pure form, as a mixture with other liquids, or in solution in a solvent such as water. It should also be understood that the expression in a gaseous state, as used herein, refers to the additive being present as a gas/vapor in the steam-based mixture. It should also be understood that the expression in a dispersed state, as used herein, refers to the additive being dispersed into the steam-based mixture of the DCSG as gas particles (e.g., a gas mixture) and/or liquid particles (e.g., an aerosol-like phase). In some implementations, the additive is stable under DCSG operating conditions; i.e., the additive can undergo phase transition, but most of the additive does not undergo chemical degradation or chemical reaction(s), which can change its molecular nature. In some implementations, the additive is vaporizable so that a mixture of steam with the additive in gaseous state and/or dispersed state is obtained as the output stream of the DCSG.

[0111] In some implementations, the additive can include ammonia in order to obtain a steam/CO.sub.2/ammonia mixture as the output stream of the DCSG. In some implementations, the additive can include a volatile amine, in order to obtain a steam/CO.sub.2/volatile amine mixture as the output stream of the DCSG. In some implementations, the additive can include urea (e.g., a urea solution such as a urea aqueous solution), in order to obtain a steam/CO.sub.2/volatile amine mixture as the output stream of the DCSG. It should be understood that the term ammonia, as used herein, refers to either gaseous ammonia or ammonia in solution (in water or another solvent). For example, the ammonia can be an ammonium hydroxide aqueous solution. Co-injection of steam with ammonia, urea and/or volatile amine will be discussed in further detail below.

[0112] In some implementations, the additive can include at least one of a surfactant, a viscosity reduction agent or a well integrity agent.

[0113] It should be understood that the term surfactant, as used herein refers to amphiphilic compounds (i.e., compounds containing both hydrophobic groups and hydrophilic groups). The surfactant can be nonionic, cationic, anionic or amphoteric. As non-limiting examples, the hydrophobic tail of the surfactant can include a hydrocarbon chain (which can be branched, linear or aromatic), a fluorocarbon chain, a siloxane chain or a polyethylene-like chain (such as polyethylene oxide and/or polypropylene oxide chains). Non-limiting examples of anionic surfactants have anionic functional groups at their heads, such as sulfate, sulfonate, phosphate and carboxylates. Non-limiting examples of cationic surfactants have cationic functional groups at their heads, such as primary, secondary, tertiary ammonium salts (which are pH dependent), quaternary ammonium salts (which are pH independent). Amphoteric surfactants have both cationic and anionic centers at their head (or at two opposed heads). Non-limiting examples of nonionic surfactants include fatty alcohols, polyethylene glycol alkyl ethers, polypropylene glucol alkyl ethers, glucoside alkyl ethers, glycerol alkyl esters, block copolymers of polyethylene glycol and polypropylene glycol, among others.

[0114] It should be understood that the term viscosity reducing agent, as used herein, refers to an agent that, when injected into the reservoir along with the steam-based mixture, reduces the viscosity of the produced fluids compared to the viscosity of produced fluids obtained when no viscosity reducing agent is used. In some scenarios, the viscosity reducing agent can reduce the viscosity of the produced fluids by at least 10%. Non-limiting example of viscosity reducing agents may include alkane-based formulations such as paraffinic oil, diethyl sebacate, diethylene glycol monoethyl ether, ethyl alcohol, ethyl oleate (EO), isopropyl alcohol (IPA), isopropyl myristate, linoleic acid, propionic acid, triethyl citrate, propylene glycol, ethanol, propanol, isopropanol, polyethylene glycol, polyperfluoroethers, fluorocarbon (halothane, methoxyflurane, enflurane, isoflurane, sevoflurane and desflurane, etc.), fluorinated ketone, perfluorodecalin, perfluoroacrylate, perfluoromethacrylate, benzyl alcohol, lauryl alcohol, perfluorodecalin, N-Methyl-2-pyrrolidone, glycofurol, polyethylene glygol (PEG), alkyl ketone, lower alkyl ester of citric acid, benzyl benzoate, methyl benzoate, ethyl benzoate, n-propyl benzoate, isopropyl benzoate, butyl benzoate, isobutyl benzoate, sec-butyl benzoate, tert-butyl benzoate, and isoamyl benzoate, or mixtures thereof.

[0115] It should be understood that the term well integrity agents, as used herein, refers to compounds that can promote structural integrity of the tubing/annulus of an injection or production well, downhole tools (e.g., ESP, instrumentation) and/or structural integrity of the reservoir, if damaged. Non-limiting examples of well integrity agents include anticorrosive agents, antifouling agents, scale inhibitors and thermally stable cements that can block areas of a well that are permeable to steam.

[0116] As shown in FIG. 1, in some implementations, additive 44a can be added as part of the feedstream of the DCSG 16, along with the feedwater 14. For example, the additive 44a and the feedwater 14 can be mixed prior to being provided to the DCSG 16. In some implementations, the feedwater 14 can be provided as a feedwater stream and additive 44b can be provided to the DCSG 16 as a separate additive stream. In some implementations, additive 44c can be provided to the output stream 18 of the DCSG 16. In some implementations, the feedwater 14 can be contacted with the hot combustion gas for a longer time period than the additive 44b. In other words, the additive 44b can be provided to the DCSG 16 at an inlet which is distant from the feedwater inlet, so that the additive 44b is not subjected to DCSG temperature and pressure conditions for a time period as long as the feedwater 14.

[0117] Ammonia/volatile Amine Implementations

[0118] Still referring to FIG. 1, in some implementations, the additive can include at least one of ammonia, urea and a volatile amine. In such case, a steam/CO.sub.2/ammonia mixture, a steam/CO.sub.2/volatile amine, steam/CO.sub.2/urea, a steam/CO.sub.2/ammonia/volatile amine or a steam/CO.sub.2/urea/ammonia/volatile amine mixture is obtained as the steam-based mixture 18. In some implementations, ammonia can be generated using the DCSG by reaction of urea and/or of the ammonium hydroxide solution.

[0119] It should be understood that the term volatile amine, as used herein, refers to a single amine or a mixture of amines. In some implementations, such volatile amine can have a boiling point at atmospheric pressure of 150 C. or less, and/or a pKa of 5.0 or more. Non-limiting examples of volatile amine include C.sub.3-C.sub.8 amines, such as methyl amine, dimethyl amine, trimethyl amine, diethyl amine, ethyl amine, isopropyl amine, n-propyl amine, diethyl amine, 1,1-dimethyl hydrazine, isobutyl amine, n-butyl amine, pyrrolidone, triethylamine, methyl hydrazine, piperidine, dipropylamine, hydrazine, pyridine, ethylenediamine, 3-methoxypropylamine, N,N-diethylhydroxylamine, morpholine, pyrrole, cyclohexylamine or a mixture thereof.

[0120] In some embodiments, the ammonia and/or the volatile amine can be provided to the DCSG 16 with the feedwater 14. The ammonia and/or the volatile amine can be mixed with the feedwater 14 prior to being injected into the DCSG 16, or injected into the DCSG 16 separately. In some scenarios, the ammonia can be injected into the DCSG 16 as an aqueous ammonium hydroxide solution. In some scenarios, the volatile amine can be injected into the DCSG 16 as an aqueous solution. In what follows, the term NH.sub.2-containing compound is used to refer to ammonia or volatile amine. The feedwater 14 and the NH.sub.2-containing compound feedstream can be contacted with hot combustion gases of the DCSG 16 such that a steam-based mixture 18 including steam, CO.sub.2 and the NH.sub.2-containing compound is obtained. In some scenarios, the NH.sub.2-containing compound is in a gaseous state and/or in a dispersed state within the steam-based mixture 18.

[0121] Using the DCSG 16 to incorporate the NH.sub.2-containing compound into the steam-based mixture 18 can reduce the operating costs, for example, if no separate heating means are needed in order to volatilize the NH.sub.2-containing compound. Using the DCSG 16 to incorporate the NH.sub.2-containing compound into the steam-based mixture 18 can increase safety, as fewer personnel can be required to handle hazardous material. Using the DCSG 16 to incorporate the NH.sub.2-containing compound into the steam-based mixture 18 can also reduce the need to process the NH.sub.2-containing compound at a processing facility and the need for pipelining the heated NH.sub.2-containing compound from the processing facility to the injection well. The use of an NH.sub.2-containing compound can lower steam requirements, as the hydrocarbons in the reservoir can be more easily mobilized.

[0122] In some implementations, the concentration of the NH.sub.2-containing compound in the steam-based mixture can be between about 0.1 wt % and about 30 wt %, or between about 0.5 wt % and about 10 wt %, or between about 1 wt % and about 5 wt %. In some implementations, the additive includes ammonium hydroxide solution (e.g., 500-2000 ppm of ammonia in water) at a concentration in the steam-based mixture between about 20 and 30 wt %.

[0123] In some implementations, the steam-based mixture can have the following composition, which is given as a non-limiting example: [0124] Steam: about 75 wt % to 99.9 wt % [0125] Ammonia: about 0.1 wt % to 30 wt %; and [0126] CO.sub.2: about 2 wt % to 12 wt %.

[0127] In some implementations, the NH.sub.2-containing compound can be provided directly to the combustion mixture of the DCSG. As the temperature and pressure of the output stream of a DCSG are typically high, providing the NH.sub.2-containing compound to the output stream of the DCSG can heat up the NH.sub.2-containing compound to a temperature which is sufficient so that the NH.sub.2-containing compound is vaporized and/or dispersed into the combustion mixture.

[0128] Steam-CO.sub.2 Separation Implementations

[0129] In some scenarios, depending for example on the properties and geological layout of the reservoir, it can be desirable to lower the concentration of CO.sub.2 in the injection mixture to be injected into the reservoir. For example, the concentration of CO.sub.2 in the injection mixture can be desired to be at most about 4 wt % or at most about 2 wt %.

[0130] Now referring to FIG. 2A, a steam-CO.sub.2 separation unit 46 can be provided downstream of the DCSG 16. All or part of the CO.sub.2 can be separated from the combustion mixture 18 to obtain a CO.sub.2-depleted steam stream 48 and a CO.sub.2-rich stream 50. The CO.sub.2-depleted steam stream 48 can be injected into the reservoir through the injection well 20. In some implementations, the additive 44a, 44b, 44c can be added similarly as described above. In some implementations, the additive 44d can be added to the CO.sub.2-depleted steam stream 48, downstream of the steam-CO.sub.2 separation.

[0131] Now referring to FIG. 2B, in some implementations, the combustion mixture 18 can be split into at least two separate portions 48A and 48B. The first portion 48A can be supplied to a steam-CO.sub.2 separation unit 46. All or part of the CO.sub.2 can be separated from the first portion 48A in the steam-CO.sub.2 separation unit 46 in order to obtain a CO.sub.2-depleted steam stream 48 and a CO.sub.2-rich stream 50. In some implementations, the steam-CO.sub.2 separation unit 46 can include a membrane separation unit including at least one separation membrane suitable for separating at least part of the steam and at least part of the CO.sub.2 from a DCSG combustion mixture. Optionally, when a steam-CO.sub.2 membrane separation unit 46 is used, sweep gas 52 can be provided to the separation unit 46 for driving the separation. The sweep gas 52 can be composed of a combustible mixture which is suitable to (i) drive the separation of the steam and CO.sub.2 from the combustion mixture 18 and (ii) be used as fuel for a DCSG, for example when the CO.sub.2-depleted steam stream 48 is recycled back into the DCSG 16. When the sweep gas 52 is used as part of the fuel, the CO.sub.2-depleted steam stream 48 mainly includes steam and sweep gas 52, and can also include a residual amount of CO.sub.2. For example, the sweep gas 52 can include natural gas or other combustible fuel gases such as lower hydrocarbons (e.g., methane, ethane, propane and/or butane), a synthetic fuel gas such as syngas, or a refinery fuel gas. For example, the concentration of steam in the CO.sub.2-depleted steam stream 48 can be up to 90 wt %, and the concentration of sweep gas in the CO.sub.2-depleted steam stream 48 can be up to 10 wt %. The concentration of residual CO.sub.2 in the CO.sub.2-depleted steam stream 48 can be up to 1 wt %. It is understood that the composition of the CO.sub.2-depleted steam stream can vary when the additive is added at 44a, 44b and/or 44c, and that in such case, the nature and/or amount of sweep gas which is needed for the separation can also vary.

[0132] In some implementations, the CO.sub.2-rich stream 50 is mainly composed of CO.sub.2. For example, the concentration of CO.sub.2 in the CO.sub.2-rich stream 50 can be up to 90 wt %, and the concentration of steam in the CO.sub.2-rich stream 50 can be up to 10 wt %. It should be understood that the concentration of CO.sub.2 in the CO.sub.2-rich stream depends on the type of separation unit 46 used and can change depending on various operating factors, such as the concentration of CO.sub.2 in the combustion mixture 18, the temperature and pressure at which the separation is effected and the nature and concentration of sweep gas 52 used.

[0133] Still referring to FIG. 2B, in some implementations, the CO.sub.2-depleted steam stream 48 is recycled back to the DCSG 16. As the CO.sub.2-depleted steam stream 48 includes mainly steam and sweep gas, the CO.sub.2-depleted steam stream 48 can be suitable for use as part of the feedwater 14 and part of the fuel 12 for the DCSG 16. As the CO.sub.2-depleted steam stream 48 typically only includes a residual amount of CO.sub.2, recycling the CO.sub.2-depleted steam stream 48 back to the DCSG 16 can facilitate gradually lowering the concentration of CO.sub.2 in the combustion mixture 18 until steady-state or quasi steady-state concentrations are reached. The combustion mixture 18 is split (e.g., using a splitter 54) into the first portion 48A which is introduced into the steam-CO.sub.2 separation unit 46 and the second portion 48B which can be used for the desired application, such as injection into a hydrocarbon-bearing reservoir. The amount of the combustion mixture 18 supplied to the steam-CO.sub.2 separation unit 46 (i.e., the first portion 48A) depends on the desired concentration of CO.sub.2 in the combustion mixture 18 when the steady-state regime or quasi steady state regime is reached.

[0134] Still referring to FIG. 2B, in some implementations, the additive 44a, 44b, 44c can be added similarly as described above. In some implementations, the additive 44d can be added into the second portion 48B of the combustion mixture, after separation by the splitter 54, and before the second portion 48B is injected into the reservoir. In some implementations, the additive 44e can be added to the CO.sub.2-depleted steam stream 48 prior to the CO.sub.2-depleted steam stream 48 being recycled back to the DCSG 16. In some implementations, the additive 44f can be added to the sweep gas stream 52, for example in order to help drive the separation of the steam and the CO.sub.2. It is understood that not all additives can be added at any injection point. For example, an additive which is not stable under DCSG operating conditions is not to be added at 44a. Similarly, an additive which cannot act as a sweep gas is not to be added at 44f. In some implementations, the produced fluid 24 can include a portion of the additive injected into the reservoir. In some implementations, the separator 26 can separate the additive from the produced fluid 24 and the recovered additive can be re-used at any one of the injection points discussed herein.

[0135] Remote Injection Implementations

[0136] Referring to FIG. 3, a SAGD operation is shown, which includes several remote hydrocarbon recovery facilities 54 located at a remote distance from a processing facility 56 supporting the SAGD operation. Each of the remote hydrocarbon recovery facilities can include at least one steam generator 16, at least one well pad 23 for supporting the SAGD wells and associated equipment and piping, SAGD well pairs 21 extending from the well pad 23 into the reservoir, and at least one separator 26.

[0137] It should be understood that located at a distance means that the hydrocarbon recovery facilities 54 are not located in proximity to the processing facility 56. It is typical for the processing facility 56 to be located several kilometers from the remote hydrocarbon recovery facilities 54 being supported. It should also be understood that a remote hydrocarbon recovery facility is a facility that is located in a geographical area and includes at least one well pad 23 with corresponding SAGD well pairs 21, at least one steam generator 16 and at least one separator 26. The steam generator 16 and the separator 26 are installed in proximity to the at least one well pad 23. In this context, it should be understood that in proximity means that the steam generator 16 and separator 26 are located on the well pads 23 for supplying steam to the wells of the same well pad and treating production fluids retrieved from the same well pad; on an adjacent well pad 23 of the same hydrocarbon recovery facility 54; or in the general area as the well pads 23 of the given hydrocarbon recovery facility 54 and remote from the processing facility 56. Some examples of in proximity could mean that the steam generator 16 and separator 26 are located within about 200 meters, about 100 meters, about 50 meters, or even about 20 meters of the well pads 23.

[0138] Still referring to FIG. 3, each remote hydrocarbon recovery facility 54 can be provided with at least one water supply tank 58 and at least one additive supply tank 60. In some scenarios, a water supply tank 58 and/or an additive supply tank 60 provided at the remote hydrocarbon recovery facilities can remove or reduce the need for conveying water and/or additive from the distant processing facility 56, and can therefore reduce costs associated with pipelining or transporting the water and/or the additive. In some implementations, an additive tank can be provided at the remote hydrocarbon recovery facility 54 to reduce the transporting and/or handling of the additive over long distances.

[0139] Disposal of Volatile Organic Compounds (VOCs) Implementations

[0140] In some implementations, the DCSG can include a waste inlet for receiving a waste stream to be flared (i.e., destroyed). The waste stream can for example include volatile organic components (VOCs) which can originate from any stream of the hydrocarbon recovery operation which contains organic components. For example, waste streams originating from the separation of the produced fluids 24 into the produced gas 28 and/or non-gaseous hydrocarbon component 30 can be provided to the DCSG 16 and be injected along with the feedwater 14 or in conjunction with the feedwater 14 to be flared under DCSG operating conditions. In some implementations, the waste streams to be flared can originate from third parties.

[0141] Additives with Carrier Gas Implementations

[0142] In some implementations, the additive to be provided to the DCSG 16 can be carried by a heat carrier gas. The heat carrier gas can provide thermal stability to the additive during operation of the DCSG. This can be useful in scenarios where the additive is not stable under DCSG operating conditions, in order to improve the stability of the additive. In some scenarios, the heat carrier gas can absorb at least part of the heat instead of the additive, thereby allowing a higher proportion of the additive to exit the DCSG without being degraded and while retaining the properties of the additive. Non-limiting examples of carrier gases include non-condensable gases such as CO.sub.2 and nitrogen, steam at a lower temperature than outgoing steam.

[0143] System Implementations

[0144] In some implementations, there is provided a system for recovering hydrocarbons from a reservoir. The system includes a DCSG 16 for generating a combustion mixture 18. The DCSG 16 has an oxygen inlet, a fuel inlet and a feedwater inlet respectively connected to an oxygen supply line, a fuel supply line and a feedwater supply line. The DCSG can also have an additive inlet connected to an additive supply. In some implementations, the additive supply can be connected to the feedwater supply line, for providing the additive through the feedwater inlet. The DCSG 16 is provided with a combustion mixture outlet, and is in fluid communication with the injection well.

[0145] The production well 22 can allow for the recovery of the produced fluids 24 from the reservoir. The system can also include a separator 26 in fluid communication with the production well 22 to receive the produced fluids 24. The separator 26 can produce produced gas 28, produced non-gaseous hydrocarbons 30 and produced water 32. The separator 26 can be in fluid communication with the DCSG 16, for example to feed at least a portion of the produced water 32 as feedwater to the DCSG 16, or to feed at least a portion of the produced gas 28 as fuel to the DCSG 16.

[0146] In some implementations, a steam-CO.sub.2separation unit can be provided downstream of the DCSG and upstream of the injection well. The steam-CO.sub.2 separation unit 46 can be provided with a combustion mixture inlet, a sweep gas inlet, a CO.sub.2-rich stream outlet and a CO.sub.2-depleted steam stream outlet. In some implementations, the combustion mixture outlet of the DCSG 16 can be connected to the steam-CO.sub.2 separation unit 46 through a splitter 54, and the CO.sub.2-depleted steam stream outlet of the separation unit 46 can be connected to the fuel inlet (or another dedicated CO.sub.2-depleted steam stream inlet) of the DCSG 16. The splitter 54 separates the combustion mixture 18 into first and second portions 48A, 48B. The system also includes a well pad 23 supporting a well pair, the well pair including an injection well 20 and a SAGD production well 22.

[0147] Well-known methods, procedures and components have not been described in detail so as not to obscure the above description. The steps or operations in the flow charts and diagrams described herein are just for example and are not to be considered limiting. There may be variations to these steps or operations without departing from the principles discussed herein. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.

[0148] Although the above principles have been described with reference to certain specific examples and implementations, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.