Patent Publication Number: US-9422797-B2

Title: Method of recovering hydrocarbons from a reservoir

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/768,872, filed Feb. 15, 2013, which is a continuation of U.S. application Ser. No. 12/836,992, filed Jul. 15, 2010, now U.S. Pat. No. 8,387,692, which claims benefit of U.S. Application Ser. No. 61/226,642, filed Jul. 17, 2009, and U.S. Application Ser. No. 61/226,650, filed Jul. 17, 2009, which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate to downhole steam generators. 
     2. Description of the Related Art 
     There are extensive viscous hydrocarbon reservoirs throughout the world. These reservoirs contain a very viscous hydrocarbon, often called “bitumen,” “tar,” “heavy oil,” or “ultra heavy oil,” (collectively referred to herein as “heavy oil”) which typically has viscosities in the range from 3,000 to over 1,000,000 centipoise. The high viscosity makes it difficult and expensive to recover the hydrocarbon. 
     Each oil reservoir is unique and responds differently to the variety of methods employed to recover the hydrocarbons therein. Generally, heating the heavy oil in situ to lower the viscosity has been employed. Normally reservoirs as viscous as these would be produced with methods such as cyclic steam stimulation (CSS), steam drive (Drive), and steam assisted gravity drainage (SAGD), where steam is injected from the surface into the reservoir to heat the oil and reduce its viscosity enough for production. However, some of these viscous hydrocarbon reservoirs are located under a permafrost layer that may extend as deep as 1800 feet. Steam cannot be injected though the permafrost layer because the heat could potentially expand the permafrost, causing wellbore stability issues and significant environmental problems with melting permafrost. 
     Additionally, the current methods of producing heavy oil reservoirs face other limitations. One such problem is wellbore heat loss of the steam, as the steams travels from the surface to the reservoir. This problem is worsened as the depth of the reservoir increases. Similarly, the quality of steam available for injection into the reservoir also decreases with increasing depth, and the steam quality available downhole at the point of injection is much lower than that generated at the surface. This situation lowers the energy efficiency of the oil recovery process. 
     To address the shortcomings of injecting steam from the surface, the use of downhole steam generators (DHSG) has been employed. DHSGs provide the ability to heat steam downhole, prior to injection into the reservoir. DHSGs, however, also present numerous challenges, including excessive temperatures, corrosion issues, and combustion instabilities. These challenges often result in material failures and thermal instabilities and inefficiencies. 
     Therefore, there is a continuous need for new and improved downhole steam generator designs. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention relate to a downhole steam generation apparatus. In one embodiment, a downhole steam generation apparatus for injecting a heated fluid mixture into a reservoir may include an injection section including a housing, an injector element disposed in the housing, and an injector plate coupled to the housing. The apparatus may include a combustion section including a body coupled to the housing and forming a combustion chamber, wherein the body includes a unitary annulus disposed therethrough. The apparatus may further include an evaporation section including a nozzle coupled to the body, wherein the nozzle is operable to inject fluid droplets into the combustion chamber in a direction away from the injection section. 
     In one embodiment, a method for injecting a heated fluid mixture into a reservoir may include positioning an apparatus in a wellbore, wherein the apparatus includes a liner having a chamber; supplying a fuel, an oxidant, and a fluid to the apparatus; combusting the fuel and the oxidant in the chamber while flowing the fluid through an annulus disposed through the liner, thereby heating the fluid and cooling the liner; injecting droplets of the heated fluid into the chamber co-flow to injection of the fuel and oxidant into the chamber; and evaporating the droplets by combustion of the fuel and the oxidant to produce steam. 
     In one embodiment, a method for injecting a heated fluid mixture into a reservoir may include supplying a first fluid and a second fluid to an injector body; injecting the first fluid and the second fluid from the injector body to a combustion chamber for combustion of the first and second fluids, wherein the combustion section includes a chamber, a liner surrounding the chamber, and a unitary annulus disposed through the liner; supplying a third fluid through the unitary annulus of the liner, thereby cooling the liner; heating the fluid supplied through the unitary annulus by combustion of the first and second fluids in the combustion chamber; injecting droplets of the heated fluid from the unitary annulus into the combustion chamber in a direction parallel to the flow of the first and second fluids, thereby evaporating the droplets; injecting the combusted first and second fluids and the evaporated droplets into the reservoir; and injecting a nanocatalyst into the reservoir. 
     In one embodiment, a downhole steam generation apparatus for injecting a heated fluid mixture into a reservoir may include an injection section having a housing, an injector element disposed in the housing, and an injector plate coupled to the housing. The apparatus may include a combustion section having a body coupled to the housing that forms a combustion chamber. The body may include a unitary annulus disposed therethrough. The apparatus may include an evaporation section having a nozzle coupled to the body. The nozzle is operable to inject fluid droplets into the combustion chamber in a direction away from the injection section. 
     The unitary annulus may be in fluid communication with the nozzle. The evaporation section may further include a conduit coupled to the nozzle and the body. The unitary annulus may be in fluid communication with the nozzle via the conduit. The nozzle may be operable to inject fluid droplets into the combustion chamber in a direction radially outward toward the body. 
     In one embodiment, a method for injecting a heated fluid mixture into a reservoir may comprise positioning an apparatus in a wellbore, wherein the apparatus includes a liner having a chamber; supplying a fuel, an oxidant, and a fluid to the apparatus; combusting the fuel and the oxidant in the chamber while flowing the fluid through an annulus disposed through the liner, thereby heating the fluid and cooling the liner; injecting droplets of the heated fluid into the chamber co-flow to injection of the fuel and oxidant into the chamber; and evaporating the droplets by combustion of the fuel and the oxidant to produce steam. 
     The fuel may include at least one of synthesis gas and hydrogen, and the oxidant may include at least one of dioxide, pure oxygen, and enriched air. The method may further comprise flowing the heated fluid through a conduit that radially extends into the chamber. The method may further comprise injecting droplets of the heated fluid into the chamber using a nozzle coupled to the conduit. The steam may include superheated steam. 
     In one embodiment, a method for injecting a heated fluid mixture into a reservoir may comprise supplying a first fluid and a second fluid to an injector body; injecting the first fluid and the second fluid from the injector body to a combustion chamber for combustion of the first and second fluids, wherein the combustion section includes a chamber, a liner surrounding the chamber, and a unitary annulus disposed through the liner; supplying a third fluid through the unitary annulus of the liner, thereby cooling the liner; heating the fluid supplied through the unitary annulus by combustion of the first and second fluids in the combustion chamber; injecting droplets of the heated fluid from the unitary annulus into the combustion chamber in a direction parallel to the flow of the first and second fluids, thereby evaporating the droplets; injecting the combusted first and second fluids and the evaporated droplets into the reservoir; and injecting a nanocatalyst into the reservoir. 
     The first fluid may be an oxidant comprising at least one of dioxide, pure oxygen, and enriched air. The second fluid may be a fuel comprising at least one of synthesis gas and hydrogen. The method may further comprise generating superheated steam by evaporation of the droplets. The method may further comprise recovering gas hydrates from the reservoir. The method may further comprise upgrading hydrocarbons disposed in the reservoir using the combusted first and second fluids, the evaporated droplets, and the nanocatalyst injected into the reservoir. The nanocatalyst may be injected into the reservoir simultaneously with the combusted first and second fluids and the evaporated droplets. 
     In one embodiment, a method of optimizing a burner located in a wellbore may comprise supplying a fuel and an oxidant to the burner; combusting the fuel and the oxidant, thereby forming a combustion flame; and controlling a size, a shape, and an intensity of the flame to optimize the burner based on wellbore conditions. 
     In one embodiment, a method of selecting combustion chamber parameters including but not limited to length, diameter and number may be provided to optimize heat transfer to the walls and optimize complete combustion. 
     In one embodiment, a method of selecting water injector parameters including the number, design, droplet size distribution and spray geometry may be provided to avoid flame quenching, complete evaporation in a distance commensurate with the application requirements, provide wall wetting to avoid overheating and minimize deposit formations on the walls of the combustion chamber and downstream components. 
     In one embodiment, a method of controlling heat transfer in a burner may comprise providing a burner having an injector head and a combustion chamber; combusting reactants in the combustion chamber; supplying water through one or more cooling passages disposed in the walls of the combustion chamber; and varying one or more of: reactants in the burner, injector head design, combustion chamber geometry, water flow rate, fluid velocity swirl and turbulence, cooling passage geometry, number of cooling passages, wall characteristics to induce turbulence, inserts in the cooling passages, and direction of flow within the cooling passages, to thereby minimize the formation of at least one of steam and gas bubbles in the cooling passages of the combustion chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  illustrates a side view of a downhole steam generator according to one embodiment of the invention. 
         FIG. 2  illustrates a cross sectional view of the downhole steam generator according to one embodiment of the invention. 
         FIG. 3  illustrates a cross sectional view of an injector body according to one embodiment of the invention. 
         FIG. 4  illustrates a bottom view of an injector plate according to one embodiment of the invention. 
         FIG. 5  illustrates a cross sectional view of an injector element according to one embodiment of the invention. 
         FIG. 5A  illustrates a cross sectional top view of the injector element according to one embodiment of the invention. 
         FIG. 6  illustrates a perspective view of an evaporation section according to one embodiment of the invention. 
         FIG. 7  illustrates a top view of the evaporation section according to one embodiment of the invention. 
         FIG. 8  illustrates an isometric view of a downhole steam generator according to one embodiment of the invention. 
         FIG. 9  illustrates a cross sectional view of the downhole steam generator according to one embodiment of the invention. 
         FIGS. 10 and 11  illustrate a side view and a cross sectional view of the downhole steam generator according to one embodiment of the invention. 
         FIG. 12  illustrates an upper end isometric view of an injection section according to one embodiment of the invention. 
         FIG. 13  illustrates a lower end isometric view of the injection section according to one embodiment of the invention. 
         FIG. 14  illustrates a side view of the injection section according to one embodiment of the invention. 
         FIGS. 15, 16, and 17  illustrate cross sectional views of the injection section according to one embodiment of the invention. 
         FIG. 18  illustrates a cross sectional view of an injector element according to one embodiment of the invention. 
         FIGS. 19, 20, and 21  illustrate isometric and cross sectional views of a combustion section and an evaporation section according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention generally relate to an apparatus and method of use of a downhole steam generator (DHSG). As set forth herein, embodiments of the invention will be described as they relate to a DHSG and heavy oil reservoirs. It is to be noted, however, that aspects of the invention are not limited to use with a DHSG, but are applicable to other types of systems, such as other downhole mixing devices. It is to be further noted, however, that aspects of the invention are not limited to use in the recovery of heavy oil, but are applicable to use in the recovery of other types of products, such as gas hydrates. To better understand the novelty of the apparatus of the invention and the methods of use thereof, reference is hereafter made to the accompanying drawings. 
       FIG. 1  illustrates a DHSG  10  according to one embodiment. The DHSG  10  may be utilized with various and multiple wellbore configurations, including vertical, horizontal, or combinations thereof. In addition, the DHSG  10  may be operable with various enhanced oil recovery methods, including cyclic steam stimulation (CSS), steam drive (Drive), steam assisted gravity drainage (SAGD), carbon dioxide (CO 2 ) flooding, or combinations thereof. The DHSG  10  may be configured to produce a range of products so as to optimize recovery of hydrocarbons and gas hydrates based on the specific wellbore and reservoir characteristics for one or more reservoirs. The DHSG  10  may be operable at wellbore depths of about 100 feet to about 500 feet; 500 feet to about 2500 feet; about 2500 feet to about 5000 feet; and/or about 5000 feet to greater than about 8000 feet. 
     In operation, the DHSG  10  is operable to generate heat within a heavy oil reservoir by burning a fuel and an oxidant supplied from the surface. The viscosity of heavy oil in the reservoir may be reduced by injecting one or more fluids and/or solvents, including but not limited to, water, partially or fully saturated steam, superheated steam, oxygen, air, rich air, natural gas, carbon dioxide, carbon monoxide, methane, nitrogen, hydrogen, hydrocarbons, oxygenated-hydrocarbons, or combinations thereof, using the DHSG  10  or separately from the DHSG  10 , into the reservoir. In one embodiment, one or more of these fluids may be combusted in the DHSG  10  to produce a stream of heated water, partially or fully saturated steam, or superheated steam, which may also include carbon dioxide, carbon monoxide, natural gas, methane, nitrogen, hydrogen, hydrocarbons, oxygenated-hydrocarbons, air, rich air, and/or oxygen, and which will be injected into the reservoir. In one embodiment, nanocatalysts may also be dispersed into the reservoir independently or in combination with the combustion products injected into the reservoir using the DHSG to further facilitate recovery of hydrocarbons. In one embodiment, nanocatalysts may be injected into the reservoir with the combustion products using the DHSG to further facilitate recovery of hydrocarbons. U.S. Pat. No. 7,712,528 and co-pending U.S. patent application Ser. No. 12/767,466 are herein incorporated by reference and describe exemplary embodiments of utilizing nanocatalysts for the recovery of hydrocarbons which may be used with the embodiments described herein. The heavy oil in the reservoir may then be recovered by a variety of ways known in the art, such as by gas lift. 
     To generate combustion, the DHSG  10  may utilize natural gas as a fuel. In one embodiment, the DHSG  10  may utilize an oxygen and carbon dioxide mixture as an oxidant. In one embodiment, the oxidant stream may include a small percentage of nitrogen, such as about 5 percent. In one embodiment, synthesis gas may be used as the fuel. In one embodiment, the oxidant may include dioxide. In one embodiment, a mixture of oxygen and nitrogen may be used as the oxidant. In one embodiment, any gaseous or liquid fuel may be used, which may include natural gas, synthesis gas, low BTU gas derived from coal or other fuels, such as hydrogen, etc. In one embodiment, the oxidant may be pure oxygen or oxygen diluted with other fluids, such as carbon dioxide, carbon monoxide, hydrogen, nitrogen, and/or steam. In one embodiment, the oxidant may be air or enriched air. 
     In one embodiment, the oxygen and carbon dioxide mixture may be used to help control combustion, particularly to control flame temperature and to avoid extremely high flame temperatures. This mixture may be mixed at the surface and supplied in a single conduit to the DHSG  10 . In one embodiment, the fuel, the oxidant, and/or any other fluids, such as water, may be supplied by separate conduits to the DHSG  10  as will be further described below. 
     The DHSG  10  may be operable to adjust flame temperature by changing the concentration of diluents supplied to the flame. Any non-reacting diluent may be used to facilitate adjustment of the flame temperature when supplied separately to the DHSG  10  and/or mixed with either the fuel or oxidant streams or both. In one embodiment, the carbon dioxide flow rate to the DHSG  10  can be adjusted to control flame temperature. The carbon dioxide may be mixed with the fuel, the oxidant, or both. In one embodiment, a diluent such as argon may be supplied to the DHSG  10  separately and/or mixed with either the fuel or oxidant streams or both. 
     As illustrated in  FIG. 1 , the DHSG  10  includes a housing  15  defining a hollow sleeve that surrounds an injection section  20  at one end, an evaporation section  40  at an opposite end, a combustion section  30  disposed between the injection section  20  and the evaporation section  40 . In one embodiment, the DHSG  10  may include a tailpipe  50  adjacent the evaporation section  40  (shown in  FIG. 2 ). The DHSG  10  may be dimensioned to fit within standard wellbore casing. A length  13  of the DHSG  10  may include a range of about 72 inches to about 360 inches or longer. In one embodiment, the length  13  of the DHSG  10  is about 180 inches. An outer diameter  17  of the housing  15  of the DHSG  10  may include a range of about 4 inches to about 10 inches. In one embodiment, the outer diameter  17  of the housing  15  of the DHSG  10  is about 6 inches. 
     The DHSG  10  may be formed from corrosion resistant materials, for example, to avoid corrosion by sulfur compounds for the components exposed to flame and combustion products. Particular components of the DHSG  10  may be formed from metals, such as steel, copper, and cobalt, from metal alloys, such as stainless steel, nickel-copper, and ceramic dispersion coppers, and metal alloys from brands such as Monel, Inconel, and Haynes alloys. In one embodiment, Monel 400 or 500 may be used for the DHSG components exposed to gaseous oxygen. In one embodiment, Haynes 188, 230, and/or 556 may be used for the DHSG  10  components subjected to a corrosive environment. In one embodiment, the water exposed components of the DHSG  10  may be formed from copper alloys, OFHC, GlidCop, GRCop84, AMZirc, beryllium copper, high thermally conductive materials, and/or ductile materials. In one embodiment, the combustion and/or evaporation sections  30  and  40  of the DHSG  10  may be formed from cobalt alloys, Haynes 188, Alloy 25, creep resistant materials, corrosion resistant materials, and/or materials having high strength at high temperatures. Higher temperature metals may facilitate cooling of the DHSG  10 , and increase its thermal control and efficiency, thereby reducing stresses in the DHSG  10  components caused by extreme temperatures and increasing conduction paths from the heated surfaces to the cooling channels, as described herein. 
       FIG. 2  illustrates a sectional view of the DHSG  10 . As illustrated, the injection section  20  includes an injector body  25 , such as a housing and further described with respect to  FIG. 3 , an igniter port  24 , one or more injector elements  27 , and one or more injector ports  21  located in an injector plate  29 . The fuel and oxidant are supplied to the injector body  25 , directed through the injector elements  27 , and ignited by an igniter (not shown) as they exit the injector plate  29  into the combustion chamber  35 . The igniter may provide the ignition necessary for combustion of the products injected into the combustion chamber  35  via the igniter port  24 . The igniter may have the ability to ignite under startup conditions and provide repeat ignitions. In one embodiment, the ignition of the igniter may be provided with a pyrophoric material. In one embodiment, the ignition of the igniter may be by spark with a pyrophoric backup. In one embodiment, the DHSG  10  may alternatively include hot surface ignition to ignite the combustion products supplied to the DHSG  10 . In one embodiment, the injection section  20  may be operable to maintain an adiabatic flame temperature in a range of about 3,200 degrees Fahrenheit to about 3,450 degrees Fahrenheit. In one embodiment, the injection section  20  may be operable to maintain an adiabatic flame temperature in a range of about 2,500 degrees Fahrenheit to about 5,500 degrees Fahrenheit. In one embodiment, the injection section  20  may be operable to maintain an adiabatic flame temperature in a range of about 3,000 degrees Fahrenheit to about 6,000 degrees Fahrenheit. In one embodiment, the injection section  20  may be operable to maintain an adiabatic flame temperature in a range of about 1,500 degrees Fahrenheit to about 7,000 degrees Fahrenheit. 
     The injector body  25  and the injector plate  29  are surrounded by the housing  15 . The injector body  25  and/or the injector plate  29  may be coupled to a liner  33 , such as a housing or body, of the combustion section  30 . An annulus  19  may be formed between the housing  15  and the liner  33 . The liner  33  may be formed from a single structural component. In one embodiment, the liner  33  may include multiple segments coupled together to form a single structure. In one embodiment, the liner  33  may include an inner diameter of about 3 inches. In one embodiment, the liner  33  may include an inner diameter in a range of about 2 inches to about 8 inches. At a first end, the liner  33  has a flanged end that is adapted to sealingly engage a lower portion of the injector body  25 , such that fluids flowing through the injector elements  27  exit into the combustion chamber  35  of the liner  33 . At a second end, the liner  33  may also have a flanged end that is in fluid communication with the evaporation section  40  and may be coupled to a tailpipe  50 . In alternative embodiments, the ends of the liner  33  may include other means of connection to secure the components of the DHSG  10  together and with other downhole components to facilitate insertion into the wellbore. In one embodiment, the tailpipe  50  is integral with the housing  15 . In one embodiment, the tailpipe  50  may be adapted to engage a downhole tool, such as a packer. 
     The liner  33  may further include an annular structure with a hollow body that forms the combustion chamber  35 . The annular structure may have one or more holes or channels  37  circumferentially located about the wall of the annular structure, also surrounding the combustion chamber  35 . The channels  37  extend the longitudinal length of the liner  33 . In an alternative embodiment, the liner  33  may include a unitary annulus disposed through the body of the liner  33 , surrounding the combustion chamber  35 , and in fluid communication with the injection section  20  and the evaporation section  40 , through which fluid may be directed. In an alternative embodiment, the liner  33  may include a narrow annulus having a spider portion or other similar device to help direct flow of fluids through the annulus. The spider portion may be placed over the inner wall of the liner and then the outer wall of the liner may be placed over the assembled inner wall and the spider portion, thereby forming one or more channels through the liner. In one embodiment, the channels  37  may include a circular shape. A fluid may enter an upper manifold in fluid communication with the channels  37  near the first end of the liner  33  adjacent the injection section  20  and may exit the channels  37  near the second end of the liner  33  adjacent the evaporation section  40 . The channels  37  may empty into a lower manifold  39  disposed in the second end of the liner  33 , which supplies the fluid to the evaporation section  40 . In one embodiment, the lower manifold  39  may be disposed within the flanged end of the liner  33 . As stated above, a similar manifold may be disposed in the first end of the liner  33 , which supplies the fluid to the channels  37 . In one embodiment, liquid water is supplied to the channels  37  of the liner  33 , wherein the water is purified to less than one part per million of total dissolved solids. The chemistry of the liquid water may be controlled to prevent scaling in the channels  37  of the liner  33 . 
     As energy or heat is generated and is released from the combustion reactions generated in the combustion chamber  35 , the fluid supplied through the channels  37  of the liner  33  may act as a cooling agent and a heat transfer mechanism, to control and reduce the temperature of the liner  33 . Fluids may be introduced into the channels  37  at its coolest temperature nearest the injection section  20  and the energy generated by the combustion reaction in the combustion chamber  35  may be used to heat the fluid as it travels through the channels  37  along the length of the liner  33  away from the injection section  20 . In one embodiment, a fluid directed through the channels  37  of the liner  33  may be heated to a temperature below the boiling temperature of the fluid. In one embodiment, the DHSG  10  may be configured to heat fluid as it is directed through the channels  37  of the liner  33 , while preventing steam generation in the channels  37 . In one embodiment, fluid may alternately flow from a point furthest away from the injection section  20  to a point closest to the injection section to maintain temperature control of the liner  33 . 
     The channels  37  of the liner  33  may be in communication with the evaporation section  40  via the lower manifold  39 . The evaporation section  40  may include one or more conduits  43  that are in fluid communication with the manifold  39  of the liner  33 . The conduits  43  may radially extend from the liner  33  and intersect at a compartment  47 , which may be centrally located within the combustion chamber  35 . The compartment  47  may be coupled to one or more nozzles  45  (shown in  FIGS. 6 and 7 ) that are adapted to convert the fluid communicated to the compartment  47  from the lower manifold  39  into droplets of the fluid, for example, and inject these fluid droplets into the combustion chamber  35  in a direction that is counterflow to the flow of the combustion products. These fluid droplets may be evaporated by the combustion products in the combustion chamber  35  and exhausted from the DHSG  10  along with the combustion products into the heavy oil reservoir. In one embodiment, the evaporation section  40  may be coupled to the injection section  20  and/or the combustion section  30  in manner that the injection of the fluid droplets is into and/or downstream of the combustion chamber  35 . In one embodiment, evaporation section  40  may be coupled to the injection section  20  and/or combustion section  30  in a manner that the injection of the fluid droplets may be counterflow, co-flow, and/or radial to the flow of the combustion products. In one embodiment, the evaporation section  40  may be operable to inject fluid droplets radially outward from the center of the combustion chamber  35  to the walls of the combustion chamber  35 . The droplet injection parameters, including direction, velocity, size distribution, etc. may be optimized to produce the best balance of performance considering impacts on the combustion flame, liner wall wetting, evaporation distance, and liner wall cooling. 
       FIG. 3  illustrates one embodiment of the injector body  25 . The injector body  25  may include a housing that is in fluid communication with the one or more supply lines for supplying combustion fluids to the DHSG  10  and is operable to direct the combustion fluids to the combustion chamber  35 . The injector body  25  may also be operable to house the igniter and align the igniter with the igniter port  24 . The injector body  25  includes an oxidant supply line  22 A, a fuel supply line  22 B, a top cover  23 , and an inner plate  26 . The oxidant may be supplied to a top plenum of the injection section  20 , via the oxidant supply line  22 A, through an opening in the top cover  23 . The top cover  23  may include an arcuate roof having a substantially flat top surface, a flanged base, and a conduit extending from the roof to the base, thereby defining the igniter port  24 . The igniter port  24  is disposed through the top cover  23  and extends through the injector body  25 . The top cover  23  may sealingly engage the inner plate  26  as the top cover  23  is coupled to the injector body  25 , thereby enclosing the top plenum. In one embodiment, the inner plate  26  may be integral with the top cover  23 . In one embodiment, the flanged base of the top cover  23  may be bolted to the injector body  25 . In one embodiment, injector body  25  may be cooled by passing a portion or all of a cooling fluid, such as liquid water, through passages in the injector body  25 . 
     An intermediate plenum may be formed within the injector body  25  for receiving the fuel supplied from the fuel supply line  22 B. The top cover  23  and the inner plate  26  may sealingly enclose the intermediate plenum. The fuel may be supplied to the intermediate plenum of the injector body  25 , via the fuel supply line  22 B, through an opening in the injector body  25 . In an optional embodiment, a bottom plenum may optionally be formed within the injector body  25  for receiving one or more fluids, such as partially or fully saturated steam, water, carbon dioxide, or combinations thereof via one or more feed ports  28  for mixing with the fuel. In one embodiment, the one or more fluids may be used as cooling fluids to cool the components of the DHSG  10 , such as the injection section  20  and/or combustion section  30 . The injector plate  29  may be coupled to the base of the injector body  25 , thereby sealingly enclosing the bottom plenum. In one embodiment, the injector plate  29  may be bolted to the injector body  25 , as shown in  FIG. 4 . 
     The injector elements  27  may extend from the top plenum, through the intermediate and bottom plenums, and through the injector plate  29 , such that the plenums are in fluid communication with the combustion chamber  35 . The injector elements  27  may be coupled to the inner plate  26 , the injector body  25 , and the injector plate  29 . The injector elements  27  may be configured to control mixing of the fuel, the oxidant, and/or any other fluid supplied through the injector elements  27  to control flame shape while achieving essentially complete combustion. The fluid mixing rates may be adjusted to control the size of the combustion flame. 
       FIG. 4  illustrates a bottom view of the injector plate  29 . As illustrated, the injector elements  27  are disposed in concentric patterns around the igniter port  24  and extend through the injector ports  21  of the injector plate  29 . The injector elements  27  may be positioned within a diameter  25   a , as indicated by the dashed reference circle, which may define the inner diameter of the injector body  25 . In one embodiment, the diameter  25   a  may be in a range of about 2 inches to about 5 inches. In one embodiment, the diameter  25   a  may be about 3 inches. In one embodiment, only a single injector element  27  may be configured for use with the DHSG  10 . 
       FIG. 5  illustrates a cross sectional view of an injector element  27 . The injector element  27  includes a body  27   a  and a sleeve  27   c . The body  27   a  includes a top section that is coupled to the inner plate  26  (as shown in  FIG. 3 ), and a channel  27   b  longitudinally disposed through the body  27   a  that exits at the injector plate  29  and is in fluid communication with the combustion chamber  35 . The body  27   a  is coupled to the inner plate  26  so that the channel  27   b  is in fluid communication with the top plenum of the injector body  25 . The sleeve  27   c  is coupled to and surrounds a portion of the body  27   a , forming an annulus between the sleeve  27   c  and the body  27   a  that exits at the injector plate  29  and is in fluid communication with the combustion chamber  35 . The sleeve  27   c  further includes one or more first ports  27   d  and optionally one or more second ports  27   e  if a bottom plenum is utilized. Both sets of ports  27   d  and  27   e  are disposed through the sleeve  27   c  and are in communication with the annulus formed between the sleeve  27   c  and the body  27   a  of the injector element  27 . The first ports  27   d  are provided with an angled entrance, relative to the longitudinal axis of the injector element  27 , into the annulus. The second ports  27   e  are provided with a tangential entrance, relative to the wall of the sleeve  27   c  (as shown in  FIG. 5A ) to generate a swirling effect of the entering fluids to facilitate efficient mixing of the reactants. The sleeve  27   c  is coupled to the injector body  25  so that the first ports  27   d  are in direct fluid communication with the intermediate plenum and the second ports  27   e  are in direct fluid communication with the third plenum (as shown in  FIG. 3 ). 
       FIG. 6  illustrates a perspective view of the evaporation section  40 , and  FIG. 7  illustrates a top view of the evaporation section  40 . As illustrated, the conduits  43  are coupled to the liner  33  so that the channels  37  are in fluid communication with the conduits  43  via the manifold  39 . The conduits  43  may include cylindrical housings having channels disposed through the housings. The conduits  43  may be coupled at the opposite end to the compartment  47 . The compartment  47  may include a spherical housing having a cavity disposed within the housing. The cavity of the compartment  47  may be in fluid communication with the channels of the conduits  43 , and may be further coupled to the nozzle  45 . The nozzle  45  may be adapted to inject fluid droplets, for example, from the fluid communicated to the compartment  47  into the combustion chamber  35 . These fluid droplets may be injected into the combustion products generated in the combustion chamber  35 , evaporated by the heated combustion products, and exhausted along with the combustion products from the DHSG  10 , through the tailpipe  50  for example, and into the oil reservoir. In one embodiment, the heat generated by combustion is used to evaporate the fluid injected as droplets near the end of the combustion chamber  35 . The fluid may be preheated as it flows through the liner  33 . The droplet injection is configured to cool the components downstream of the combustion chamber  35 , evaporate the droplets downstream of the combustion chamber  35  at a distance commensurate with the specific application, avoid adverse impacts on the combustion flame such as quenching, avoid plugging of the nozzle(s)  45 , and avoid deposition of solids on the liner walls. In one embodiment, the nozzle  45  may be adapted to generate multiple fluid droplets of multiple sizes in a range of about 10 microns to about 150 microns. In one embodiment, the fluid droplets may impinge on the tailpipe  50  located downstream of the injection section  20 . In one embodiment, the fluid droplets may be injected into and/or downstream of the combustion chamber  35 , evaporated by the combustion products, and injected into the heavy oil reservoir. 
     In one embodiment, the conduits may include eight conduits  43  radially disposed around the compartment  47 . In one embodiment, liquid water may be heated by heat generated from the combustion flame as it travels through the channels  37  and may exit the channels  37  of the liner  33  into the conduits  43 . In one embodiment, liquid water may be injected at a high velocity into the heated combustor exhaust and boiled via droplet evaporation, thereby providing partially or fully saturated steam or superheated steam generation. In one embodiment, liquid water may be evaporated to about a range of 90 percent to 95 percent steam quality at the point of injection into the oil reservoir. In one embodiment, liquid water may be evaporated to about a range of 80 percent to 100 percent steam quality at the point of injection into the oil reservoir. In one embodiment, liquid water may be evaporated to about a range of about 95 percent to about 99 percent steam quality at the point of injection into the heavy oil reservoir. 
     In one embodiment, the number of droplet injectors, type of droplet injectors, spray pattern, and direction of spray of the evaporation section may be adjusted to provide rapid droplet evaporation and combustion product cooling. The evaporation section facilitates an equilibrium steam quality of the combustion products. In one embodiment, the evaporation section may facilitate fluid droplets impinging on the walls of the combustion section downstream of the injection section so that the wall temperature of the combustion section remains close to the fluid droplet temperature. 
     In an alternative embodiment, the DHSG  10  may include an injection section that supplies the fuel and the oxidant in such a manner that the fluids mix in the combustion chamber and provides a stable combustion flame having a shape that fits within the combustion chamber volume, during the startup and shutdown of the DHSG  10 , as well as during the full operating range of pressures and stoichiometry. The DHSG  10  may include a number of alternate injection sections that produce diffusion flames, partially premixed diffusion flames, and premixed flames. Each of these flame types may be utilized with the DHSG  10 , including stable flames of adequate size during the operation of the DHSG  10 . 
     In one embodiment, the DHSG  10  may include a diffusion flame injection section. The fuel and the oxidant are injected into the combustion chamber as separate fluid streams. The diffusion flame injection section includes injector elements that are operable and arranged to provide controlled mixing of the fluids into the combustion chamber, thereby producing a combustible mixture. The diffusion flame injection section provides a combustion flame that is stabilized by controlling the injection velocities of the fluids into the combustion chamber, such as maintaining low injection velocities of the fluids relative to the flame speed, and/or by recirculating hot combustion products back to the base of the flame, such as by injecting the fuel and/or the oxidant with a swirl that produces an axisymmetric recirculation zone or by generating a recirculation zone in the wake behind a bluff body or the walls of the injectors themselves. The combustion flame shape may be adjusted by controlling the rate of the fuel/oxidant mixing. In general, rapid mixing produces a compact high intensity combustion flame with high radiative heat transfer in contrast to slow mixing which produces a larger low intensity combustion flame with lower radiative heat transfer. By varying the swirl and the injection velocities, the combustion flame shape can be adjusted to fit the combustion chamber. In one embodiment, the DHSG  10  may include one or more injection sections/elements to provide additional combustion flame shaping flexibility, such as by operating less than all of the injection sections/elements during lower operating ranges or by reducing the range of firing rates for each individual injection section/elements to provide enhanced combustion flame stability and control. 
     A method of utilizing the DHSG  10  may include supplying natural gas and an oxygen and carbon dioxide mixture to an injector body of the DHSG  10 . The mixture may be mixed at the surface and supplied to the DHSG  10  in a single conduit and the fluids may be mixed in the injector body. The DHSG  10  may be positioned in a first well for use as an injection well. The method may further include directing the fluids through one or more injector elements that are in fluid communication with the combustion chamber. The injector elements may be coupled to the injector body and disposed in a circular array. The injector elements may include a body and a sleeve surrounding the body. The method may further include directing the mixture from a first plenum of the injector body, through a channel of the body of an injector element, and injecting the mixture into the combustion chamber. The method may further include directing the natural gas from a second plenum of the injector body, and optionally directing a diluting or cooling fluid, such as water, partially or fully saturated steam, oxygen, air, enriched air, nitrogen, hydrogen, and/or carbon dioxide, from an optional third plenum of the injector body, through the sleeve of the injector element, such that the fluids form a swirling pattern as they are directed through the sleeve. The method may further include injecting the fluids into the combustion chamber with the mixture. The method may further include providing an ignition flame from an igniter through an igniter port disposed through the injector body to combust the mixture of fluids injected into the combustion chamber. The method may further include igniting the mixture of fluids in the combustion chamber, thereby generating a combustion flame and combustion products. The swirling pattern may help maintain a stabilized combustion flame within the combustion chamber. The fluids flowing through the combustion section may provide cooling of the DHSG  10 , and the temperature of the DHSG  10  may be controlled by carbon dioxide dilution. In one embodiment, additional cooling passages may be provided in the combustion section. The method may further include supplying a fluid, such as water, through one or more channels of a liner, wherein the liner surrounds the combustion chamber. The method may further include heating the fluid as it travels through the channels by the combustion reactions in the combustion chamber, wherein the fluid cools the liner. The combustion flame may transfer heat to the liner walls by radiative and convective heat transfer. The method may further include injecting the heated fluid from the channels into the combustion chamber, in a droplet form, via one or more conduits in fluid communication with the channels, and boiling the heated fluid via droplet evaporation, wherein the combustion flame and products evaporate fluid droplets of the heated fluid injected into the combustion chamber. The fluid may cool the combustion products. The method may further include injecting the combustion products and the evaporated fluid droplets into an oil reservoir to upgrade and/or reduce the viscosity of hydrocarbons in the oil reservoir. The method may further include recovering at least the upgraded and/or less viscous hydrocarbons from a second well that is located adjacent to the first well in which the DHSG is located. The second well may be utilized as a production well. The production well may include one or more pressure control devices located at the surface to control the back pressure on the oil reservoir. In one embodiment, a choke valve may be used to maintain and/or control the pressure and/or flow of fluids recovered from the oil reservoir via the production well. 
     The DHSG  10  may be operable under pressure conditions in a range of about 800 psi to about 1,600 psi. The DHSG  10  may be operable under pressure conditions in a range of about 500 psi to about 2,000 psi. In one embodiment, the DHSG  10  is operable under a pressure range of about 800 psi to about 2,000 psi. In one embodiment, the DHSG  10  may be operable under pressure conditions in a range of about 100 psi to about 4,000 psi. In one embodiment, the DHSG  10  may be operable under pressure conditions up to about 10,000 psi. In one embodiment, the DHSG  10  may also be operable under a nominal flame temperature in a range of about 3,200 degrees Fahrenheit to about 3,450 degrees Fahrenheit. In one embodiment, the DHSG  10  may also be operable under a nominal flame temperature in a range of about 2,500 degrees Fahrenheit to about 5,500 degrees Fahrenheit. In one embodiment, the DHSG  10  is operable under a nominal flame temperature in a range of about 3,000 degrees Fahrenheit to about 3,500 degrees Fahrenheit. In one embodiment, the DHSG  10  may be operable at internal pressures up to 1,800 psi and exhaust a heated fluid mixture at up to 600 degrees Fahrenheit. In one embodiment, the DHSG  10  may be operable to exhaust a heated fluid mixture at a temperature within a range of about 500 degrees Fahrenheit to about 800 degrees Fahrenheit. In one embodiment, the DHSG  10  may be operable to exhaust a heated fluid mixture at a temperature within a range of about 250 degrees Fahrenheit to about 800 degrees Fahrenheit. In one embodiment, the DHSG  10  may be operable to exhaust a heated fluid mixture at a temperature of about 600 degrees Fahrenheit. In one embodiment, the DHSG  10  may be operable to limit metal temperatures to below 1,000 degrees Fahrenheit. 
     The DHSG  10  may be configured to generate a fluid having a steam quality in a range of about 75 percent to about 100 percent. In one embodiment, the DHSG  10  may be configured to generate a fluid having about a 90 percent to about a 95 percent steam quality. The DHSG  10  may also be configured to provide a mass flow rate of a fluid, such as partially saturated, fully saturated, or superheated steam, in a range of about 400 barrels per day (bbd) to about 1500 barrels per day. In one embodiment, the DHSG  10  may be configured to provide a mass flow rate of a fluid, such as partially saturated, fully saturated, or superheated steam, at about 1500 bbd under a pressure condition of about 1600 psi. Finally, the DHSG  10  may be configured to have a minimum operating life of about 3 years. 
     The DHSG  10  may be configured to inject a mixture of fluids into a formation to heat the formation and to facilitate the recovery of hydrocarbons from the formation, such as by reducing the viscosity of heavy oil located in the formation. In one embodiment, the mixture may comprise from about 18 percent to about 29 percent of carbon dioxide by volume. In one embodiment, the mixture may comprise from about 10 percent to about 30 percent of carbon dioxide by volume. In one embodiment, the mixture may comprise from about 1 percent to about 40 percent of carbon dioxide by volume. In one embodiment, the mixture may comprise about 0.5 percent or about 5 percent of oxygen by volume. In one embodiment, the mixture may comprise from about 0.5 percent to about 5 percent of oxygen by volume. The mixture may be injected into the formation at a pressure of about 900 psi, 1200 psi, or 1600 psi. The mixture may be injected into the formation at a mass flow rate of about 400 bbd, 800 bbd, 1200 bbd, or 1500 bbd. 
       FIG. 8  illustrates an isometric view of a DHSG  100  according to one embodiment of the invention. The DHSG  100  includes an injection section  110 , a combustion section  120 , and an evaporation section  130 . The injection section  110 , the combustion section  120 , and the evaporation section  130  may operate similarly to the injection section  20 , the combustion section  30 , and the evaporation section  40  of the DHSG  10  described above, with some additional modifications as will be described below. The same embodiments described above with respect to the DHSG  10  may be used with the DHSG  100  described herein, and vice versa. In addition, the DHSG  100  may also be configured to operate under the same operating conditions recited above with respect to the DHSG  10 . As illustrated, the injection section  110  is in fluid communication with feed tubes  140  for supplying one or more fluids to the injection section  110 , some of which are supplied to injection manifolds (further described below) of the injection section  110  for combustion and injection into a hydrocarbon-bearing formation, such as a heavy oil reservoir. The combustion section  120  may be coupled at its upper end to the injection section  110  by a bolted connection. The combustion section  120  may include a plurality of pressure relief ports to facilitate operation of the DHSG  100 . The evaporation section  130  may be disposed within the lower end of the combustion section  120  for injection of a cooling fluid, such as H 2 O, into the combustion section  120 . 
       FIG. 9  illustrates a cross section view of the DHSG  100 . The DHSG  100  is enclosed by a housing  150 , such as a casing. The housing  150  may include a metallic cylindrical body having a hollow internal chamber for supporting the injection section  110 , the combustion section  120 , the evaporation section  130 , and the feed tubes  140 . The feed tubes  140  may be configured for supplying fluids to the injection section  110  and may include one or more bellows  141  to compensate for expansion, contraction, and/or movement of the feed tubes  140  due to thermal, pressure, or mechanical stresses experienced by the feed tubes  140 . In one embodiment, four or five feed tubes  140  are included in the DHSG  100 . One or more of the fluids supplied to the injection section  110  may then be mixed and injected into a combustion chamber  121  of the combustion section  120  for combustion. A fluid may also be injected into the combustion chamber  121  and/or downstream of the combustion chamber  121  by an injector  131  of the evaporation section  130  and combined with the combustion products. The injector  131  may be operable to inject liquid water droplets, for example, into the combustion chamber  121  and/or downstream of the combustion chamber  121 , which are evaporated when combined with the combustion products, thereby forming partially saturated, fully saturated, or superheated steam. The bottom end of the housing  150  may have a nozzle  151  for exhausting the combustion products and the steam out of the DHSG  100  and injecting them into a hydrocarbon-bearing formation. 
       FIGS. 10 and 11  illustrate a side view and a cross section view of the DHSG  100 . As shown, the DHSG  100  may include an overall length of less than about 30 feet, may operate within wellbore conditions having a pressure range of about 800 psi to about 1600 psi, may be operable to receive combustion fluids at a maximum pressure of about 3000 psi and at a temperature range of about 75 degrees Fahrenheit to about 180 degrees Fahrenheit. In one embodiment, the DHSG  100  may be operable to receive combustion fluids at a temperature range of about 32 degrees Fahrenheit to about 210 degrees Fahrenheit. The combustion section  120  may include an internal diameter of about 3 inches and the DHSG  100  may include a maximum outer diameter of about 6 inches. The DHSG  100  may be operable to inject combustion fluids at a pressure of about 1800 psi and a temperature of about 600 degrees Fahrenheit into a hydrocarbon-bearing formation. In one embodiment, the DHSG  100  may include a turndown ratio of about 4:1 with a flow rate of about 1,500 bbd. In one embodiment, the DHSG  100  may include a pressure turndown ratio of about 2:1 within a wellbore pressure environment of about 1600 psi. In one embodiment, the DHSG  100  may be configured to include a mass flow rate turndown ratio of about 4:1. In one embodiment, the DHSG  100  may be configured to include an internal fluid velocity flow rate turndown ratio of about 8:1. 
       FIG. 12  illustrates an upper end isometric view of the injection section  110  coupled to the feed tubes  140 . The injection section  110  includes a housing having a flanged end  111  for connection to the combustion section  120 . The injection section  110  also includes an upper manifold  112  and a lower manifold  113  circumscribing the housing of the injection section  110  for supplying a fluid, such as a fuel, such as methane, to the injection section  110 . The manifolds  112  and  113  may comprise cylindrical conduits surrounding the housing of the injection section  110  and having a circular, such as a ring or halo-type, shape. A first feed tube  142  is coupled to the upper manifold  112  for supplying a fluid from the surface of a wellbore to the DHSG  100 . In one embodiment, the feed tube  142  may also be coupled to the lower manifold  113 . In one embodiment, a separate feed tube may be coupled to the lower manifold  113  for supplying a fluid to the injection section  110 , such that the fluid may be the same or a different fluid supplied to the upper manifold. Also illustrated are feed tubes  143  and  144  coupled to the injection section  110  (further described below). 
       FIG. 13  illustrates a lower end isometric view of the injection section  110 . The housing of the injection section  110  includes an upper section  117  and a lower section  116 , each comprising cylindrical bodies having flow bores therethrough. The upper section  117  may include a dome or hemispherical shaped top end. The manifolds  112  and  113  each include one or more supply tubes  114  and  115 , respectively, that extend from the manifolds to the lower section  116  of the housing, The supply tubes  114  and  115  may be coupled to the bottoms of the manifolds and the side of the housing, thereby establishing fluid communication therebetween. The supply tubes  114  and  115  may be equally spaced around the circumference of the manifolds and/or the housing of the injection section  110 . 
     Also illustrated is an injector plate  118  coupled to and sealingly engaged with the flanged end  111  of the housing for directing the combustion fluids into the combustion section  120  of the DHSG  100 . The injector plate  118  may also be operable for supporting one or more injector elements and an igniter (further described below). The injector plate  118  may include first injector element ports  161 , second injector element ports  162 , and an igniter port  171 . The first injector element ports  161  may be equally spaced apart forming a circular pattern adjacent the outer diameter of the injector plate  118 . The second injector element ports  162  may also be equally spaced apart forming a circular pattern adjacent the center of the injector plate  118 , surrounded by the first injector element ports  161 . The igniter port  171  may be disposed in the center of the injector plate  118  and surrounded by the first and second injector element ports  161  and  162 . 
       FIG. 14  illustrates a side view of the injection section  110 . The supply tubes  114  and  115  may be coupled to the manifolds  112  and  113  by a fitting, such as a JIC fitting, and may be coupled to the lower section  116  of the housing by a weld, such as a braze or electronic beam weld. A non-conductive coating may be applied to the bottom of the flanged end  111  to mitigate corrosion of the housing and the connection to the combustion section  120 . 
       FIG. 15  illustrates a cross section view of the injection section  110 . The injection section  110  further includes an igniter housing  170  for supporting an igniter as described above. The upper section  117  may be coupled to the lower section  116  by a welded or bolted connection. A housing plate  119  may be sealingly disposed between the upper and lower sections  117  and  116 . In one embodiment, the housing plate  119  may be disposed upon an inner edge of the lower section  116 . The upper section  117  of the housing further includes an inner chamber  181  through which the igniter housing  170  is disposed and an outer chamber  182  surrounding and sealingly isolated from the inner chamber  181 . The outer chamber  182  may include one or more conduits forming circular flow paths disposed around the inner chamber  181 . The lower section  116  of the housing similarly includes an inner chamber  183  through which the igniter housing  170  is disposed and an outer chamber  184  surrounding and sealingly isolated from the inner chamber  183 . The outer chamber  184  supports injector elements  160  and the inner chamber  183  supports injector elements  165 , the upper ends of which extend into the outer and inner chambers  182  and  181 , respectively of the upper section  117 . The injector elements  160  and  165  may operate in a similar manner as the injector elements  27  described above with respect to the DHSG  10 . 
     Illustrated in  FIGS. 15 and 16  is the second feed tube  143  in fluid communication with the inner chamber  181  of the upper section  117 . The second feed tube  143  may comprise one or more flow paths for supplying a fluid, such as an oxidant, for example an oxygen and carbon dioxide mixture or an oxygen and carbon dioxide mixture having a small percentage of nitrogen, at an increased amount to the inner chamber  181 . The fluid is directed from the inner chamber  181  to the injector elements  165 . The fluid may then be mixed within the injector elements  165  with another fluid, such as a fuel, that is supplied to the injector elements  165  via the lower manifold  113 . The supply tubes  115  extend from the lower manifold  113  to the inner chamber  183  of the lower section  116  and into the injector elements  165 . The combined fluids are then injected into the combustion section  120  and ignited by the igniter. 
     Illustrated in  FIGS. 15 and 17  is the third feed tube  144  in fluid communication with the outer chamber  182  of the upper section  117  of the housing. The third feed tube  144  may comprise one or more flow paths for supplying a fluid, such as an oxidant, for example an oxygen and carbon dioxide mixture or an oxygen and carbon dioxide mixture having a small percentage of nitrogen, at an increased amount to the outer chamber  182 . The fluid is directed from the outer chamber  182  to the injector elements  160 . The fluid may then be mixed within the injector elements  160  with another fluid, such as a fuel, that is supplied to the injector elements  160  via the upper manifold  112 . The supply tubes  114  extend from the upper manifold  112  to the outer chamber  184  of the lower section  116  and into the injector elements  160 . The combined combustion product is then injected into the combustion section  120  and ignited by the igniter. 
     In one embodiment, the feed tubes  140  and/or the igniter housing  170  may be formed from a metallic material, such as a nickel-copper alloy, such as Monel. In one embodiment, the manifolds  112  and  113  may be formed from a metallic material, such as a nickel-cobalt alloy, such as Haynes 188. In one embodiment, the upper section  117  of the housing may be formed from a metallic material, such as a nickel-copper alloy, such as Monel. In one embodiment, the lower section  116  of the housing may be formed from a metallic material, such as a nickel-cobalt alloy, such as Haynes 188. In one embodiment, the injector elements  160  and  165  may be formed from a metallic material, such as a nickel-copper alloy, such as Monel. 
       FIG. 18  illustrates a cross sectional view of an injector element  160 . Injector element  160  may be the same as injector element  165  disclosed above. The injector element  160  has an upper end in fluid communication with a chamber of the upper section  117  via an inner flow bore  166  disposed through the body  167  of the injector element. The inner flow bore  166  directs a fluid into the combustion section  120 . The injector element has a middle or lower section in fluid communication with a chamber of the lower section  116  via an outer flow bore  168  disposed through a sleeve  164  surrounding the body  167  and the inner flow bore  166  of the injector element. The outer flow bore  168  directs a fluid into the combustion section  120 . The sleeve  164  may include one or more ports  169  that are angled relative to the outer flow bore  168  to introduce a swirling effect of the fluid flowing therethrough. The swirling effect facilitates mixing of the fluid with the other fluids that are injected into the combustion chamber  120 . 
       FIGS. 19, 20, and 21  illustrate isometric and cross sectional views of the combustion section  120  and the evaporation section  130 . The combustion section  120  includes a liner  121  forming a combustion chamber and a pair of flanged ends  122  and  123 , each end having a manifold  126  and  127  disposed therein. The combustion section  120  and the evaporation section  130  are formed and operate in a similar manner as the combustion section  30  and the evaporation section  40  described above with respect to the DHSG  10 , which will not be repeated for brevity. Also illustrated is a feed tube  145  coupled to the flanged end  122  of the liner  121  for supplying a fluid, such as a cooling fluid, such as liquid water, to the manifold  126 , then to one or more cooling channels  125  disposed along the longitudinal length of the walls of the liner  121 , then to the manifold  127  (which is in fluid communication with the evaporation section) to facilitate thermal control of the DHSG  100  and the production of partially saturated, fully saturated, or superheated steam via the injector  131  of the evaporation section  130 . In one embodiment, the feed tube  145  may be formed from a metallic material, such as a nickel-cobalt alloy, such as Haynes 230. In one embodiment, components of the injection section  110 , the combustion section  120 , and the evaporation section  130  may be formed from a metallic material, such as a beryllium-copper alloy. In one embodiment, the injector  131  may be formed from a metallic material, such as a nickel-cobalt alloy, such as Haynes 230. 
     The DHSG  10  and  100  described above may include multiple combustion chambers. In one embodiment, the multiple combustion chambers may be positioned in series or in a parallel configuration. Each combustion chamber may share a liner with one or more other combustion chambers and/or may include a single liner. In one embodiment, the DHSG  10  and  100  may include a variety of multiple injection, combustion, and evaporation section configurations described above. 
     In one embodiment, one or more fluids, including but not limited to water, natural gas, oxygen, air, rich air, carbon dioxide, nitrogen, hydrogen, inert gases, hydrocarbons, oxygenated-hydrocarbons, and combinations thereof may be supplied from the surface to the DHSG via one or more tubular members, such as umbilicals. The one or more fluids may be supplied to the DHSG simultaneously and/or in a staged fashion depending on the desired operation. In one embodiment, the one or more fluids, including but not limited to carbon dioxide, nitrogen, hydrogen, and/or inert gases may be used to control (lower) the temperature of the DHSG or a liner/combustion chamber of the DHSG, transmit incremental heat from the DHSG to an oil reservoir, and improve oil recovery by dissolving into the oil, thereby upgrading the oil and decreasing its viscosity. In one embodiment, carbon dioxide, nitrogen, and/or other inert gases may be simultaneously injected with steam using the DHSG. In one embodiment, hydrogen may be simultaneously injected with steam using the DHSG. In one embodiment, the DHSG may be configured to inject other materials (liquids, gases, solids) that complement steam and provide in-situ upgrading. In one embodiment, the other materials may include nanocatalysts, surfactants, solvents, etc. In one embodiment, the DHSG may be operable to maintain and/or adjust the pressure and flow rates of fluids/materials flowing through the DHSG in real time to optimize reservoir production and process economics. 
     In one embodiment, steam, excess oxygen (including air or enriched air), carbon dioxide, nitrogen, and/or hydrogen may be simultaneously injected into the oil reservoir via the DHSG to generate incremental heat and a controlled independent steam front. In-situ oxidation (combustion) of the oil reservoir&#39;s bypassed residual oil may generate more heat and more steam downhole. The DHSG may be configured to generate and manage stable in-situ oxidation through the addition of surplus oxygen and external high pressure steam. The large, stable incremental steam front may yield more heat for more oil combustion. In one embodiment, surplus pressurized oxygen and high quality steam may be injected directly to the oil reservoir using the DHSG. Residual oil that may be left behind the initial steam front may support and accelerate combustion of the surplus oxygen, thereby creating a combustion front. The combustion front may increase the temperature of the steam front, and may heat and/or vaporize water present in the reservoir to generate another large, stable steam front which can accelerate oil production. In one embodiment, the initial steam front may heat the oil ahead of the in-situ combustion to ensure that all surplus oxygen reacts in the reservoir and prevent non-combusted oxygen breakthrough into the production wells, thereby improving safety and decreasing potential corrosive effects to infrastructure. 
     In one embodiment, the DHSG may be used to combust natural gas and thereby produce carbon dioxide, which is injected into and remains in the oil reservoir (sequestration). In one embodiment, the carbon dioxide produced from a production well may be recycled and reused for DHSG cooling and/or enhanced reservoir production. In one embodiment, the carbon dioxide produced from a production well may be sold and/or used for other types of operations. 
     In one embodiment, the reservoir pressure may be maintained and controlled at the production well using a pressure control device to “throttle” the produced fluid stream to maintain “back pressure”. The reservoir pressure may also be maintained and controlled using the DHSG by injecting fluids at the injection well. The use of two pressure control points may provide better reservoir management, promote gas solubility in the oil for less viscous oil and accelerated recovery, improve the gas-oil-ratio (GOR) which in turn reduces the oil&#39;s viscosity ahead of the steam front and accelerates production, prevents premature gas production, which detracts from oil production and may increase operating costs if not managed. In addition, gas injection reduces the partial pressure of steam and causes it to condense deeper in the oil reservoir, so that heat transfer improves and oil production increases. In one embodiment, the recovered fluids at the production well may be controlled (e.g. limited) so that the injection pressure is maximized within the oil reservoir formation. Maintaining a high reservoir pressure may provide high-flowing back pressure on the production well, high solubility of carbon dioxide in the cold oil ahead of the steam front, and high condensation temperature of the steam which in turn assures high solubility of water in the hot oil. This combination of effects reduces the oil&#39;s viscosity, limits or prohibits oxygen breakthrough, and increases pyrolysis of the oil in the reservoir thereby increasing its API gravity and reducing its sulfur content. 
     In one embodiment, one or more tubular members or bundled conduits, such as umbilicals, may be used to transmit electric power, fluids, gases and/or communication signals from surface equipment to one or more components of the DHSG. In one embodiment, the tubular members may include wires and/or pipes bundled within a larger reinforced encasement, including insulation. In one embodiment, one or more umbilicals may be used to deliver water, oxygen, nitrogen, carbon dioxide, fuel, and/or other gases and fluids from surface equipment to the DHSG. In one embodiment, the umbilicals may include control lines from surface equipment to the DHSG. 
     In one embodiment, one or more (automated) control systems and/or sensors may be used to provide real time control/monitoring of the DHSG and the reservoir production. A control system may be operable to reduce the effects of lag times, and monitoring and managing DHSG operations several hundreds and/or thousands of feet below the surface control elements. The control system may include all aspects of safe, reliable operations across all potential operating conditions and anomalies, including automatic shut down of the DHSG as required. In one embodiment, one or more components including flowmeters, high temperature fiber optic monitoring (to monitor steam distribution in real time), high temperature gauges and valves for downhole monitoring, and high pressure and temperature sensors, thermocouples, and transducers may be used with the DHSG to measure and monitor one or more operational characteristics. 
     In one embodiment, one or more support devices, such as packers, may be used to support DHSG equipment to a specified position in the wellbore casing or tubular and to provide a pressure seal. The packers may have a mandrel so that tubing can be run within the length of the packer. In one embodiment, one or more packers may be used to support the weight of the DHSG, tubulars and the tailpipe. The output from the tailpipe of the DHSG may be disposed through the mandrel in the packer to be injected into the oil reservoir. In one embodiment, the packer may be operable at high temperatures of up to 680 degrees Fahrenheit. 
     In one embodiment, one or more artificial lift systems may be used with the DHSG system to provide incremental pumping power to lift fluids from the reservoir, including oil, water, sand, etc. to the surface for separation. An artificial lift system may be used with a light oil diluent stream (which is pumped into the production well, resulting in a lower viscosity blended oil mixture) for easier pumping. Artificial lift systems may include progressive cavity pumps and electrical submersible pumps. 
     In one embodiment, a variety of other fit-for-purpose equipment and services may be used with the DHSG system, including but not limited to specific drilling fluids (SAGD drilling fluids), well placement devices (inclination and gamma ray, high temperature logging tools, measuring while drilling tools, logging while drilling tools, sand screens (to improve tolerance of ESP pumps), and equalizer technology for more efficient sweep of the formation by the injected steam, high temperature valves, and high temperature thermocouple systems. 
     While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.