Underground gas-steam generator for heavy oil thermal recovery and medium flow calculation method

Abstract

The invention provides an underground gas-steam generator for heavy oil thermal recovery and a medium flow calculation method.The generator comprises a combustion system and a water vapor system and mainly comprises a gas inlet device, a mixer, an ignition device, a combustion chamber, a vaporizing chamber, a cooling device, a mixed gas outlet and the like. The gas-steam generator is arranged underground, water is directly sprayed into smoke generated by combustion of fuel and a combustion improver through a ground pipeline at the well bottom, the fuel and the combustion improver are input underground through the ground pipeline, and smoke exhaust heat loss and transmission heat loss generated in the steam injection process of a conventional ground boiler are eliminated; the ceramic layer with the heat insulation effect is arranged on the outer wall face of the combustion chamber, cooling water enters from the rear end of the combustion chamber, a cooling water film is formed on the outer wall face of the ceramic layer and used for cooling the combustion chamber of the gas-steam generator, and safe operation of the gas-steam generator is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of heavy oil thermal recovery in petroleum engineering, and particularly to a downhole gas-steam generator for heavy oil thermal recovery and a method for calculating the medium flow rate. Background Art

[0002] At present, the main heavy oil thermal recovery methods are steam soaking, steam flooding and SAGD. All three methods require the construction of a steam station on the ground. The steam generated by the steam station is transported through the ground steam transmission pipeline to each injection well, and then through the tubing in each injection well to the target oil layer underground. The high-temperature steam is used to reduce the viscosity of the crude oil for exploitation or displacement. The traditional ground steam injection thermal recovery technology has the following disadvantages:

[0003] (1) Environmental pollution: A large amount of heat is carried away when the ground steam generating equipment burns fossil fuels, generating SO X , NO X , particulate matter, polluting the surrounding environment.

[0004] (2) Poor equipment mobility: The ground steam generating equipment and its auxiliary supporting devices are large in volume and have poor mobility, which is not suitable for the operation requirements of dispersed oil wells.

[0005] (3) Low downhole steam dryness: The steam dryness at the outlet of the ground steam generating equipment is 75%. After being transmitted through the ground steam transmission pipeline and the injection wellbore, the steam dryness reaching the downhole is low, only 40%. It cannot meet the requirements of the thermal recovery process.

[0006] (4) Large heat loss and low energy efficiency utilization rate: The heat loss generated by the ground steam generating equipment is about 15%-20%, the heat loss from the steam station to the injection wellhead is about 5%-10%, and the heat loss from the wellhead to the target oil layer is about 20%. The overall energy efficiency utilization rate is low.

[0007] (5) Limited reservoir depth: Except that the application depth of steam soaking reaches 1800 meters, the steam flooding with higher recovery rate is mainly applied to reservoirs with a depth within 1200 meters. The use depth of the reservoir is limited.

[0008] (6) Increased wellbore input cost: The wellbore of the steam injection well needs to adopt special cementing techniques, such as heat-insulating casing, etc., and high temperature is likely to cause casing damage, resulting in an increase in workover costs.

[0009] To overcome the above deficiencies, a downhole gas-steam generator for heavy oil thermal recovery is provided, which provides a new choice of development tool for heavy oil development and has far-reaching significance. Summary of the Invention

[0010] To solve the above problems, the present disclosure provides a downhole gas-steam generator for heavy oil thermal recovery and a method for calculating the medium flow rate, aiming to solve the problems of low thermal energy utilization rate, serious dryness loss, and environmental pollution during the steam injection process of conventional heavy oil thermal recovery steam injection boilers. Water, fuel, and combustion improver are input into the downhole gas-steam generator from the ground through three sets of supporting systems on the ground by three groups of process pipe strings, directly generating a mixture of steam and flue gas at the bottom of the well, eliminating the heat and dryness losses during the steam transmission process. At the same time, the flue gas supplements the formation energy, increases the fluidity of crude oil, and improves the recovery rate, which is a more efficient, energy-saving, low-carbon, and emission-reducing new way for heavy oil thermal recovery.

[0011] For this reason, the present invention proposes a downhole gas-steam generator for heavy oil thermal recovery, including:

[0012] An air intake device having an air intake passage and a natural gas intake passage;

[0013] A mixing device having a mixing chamber, and the mixing chamber is respectively communicated with the air intake passage and the natural gas intake passage;

[0014] A combustion chamber is arranged at the outlet end of the mixing device, and a slender central injection section is arranged between the combustion chamber and the mixing device;

[0015] An ignition device is radially arranged on the side wall of the combustion chamber and communicated with it;

[0016] A vaporization chamber is located at the rear end of the combustion chamber and communicated with it;

[0017] Water injection nozzles are circumferentially and uniformly distributed outside the vaporization chamber, and several of the water injection nozzles are respectively communicated with the water inlet, and

[0018] A mixture gas outlet is arranged at the end of the vaporization chamber.

[0019] Furthermore, a ceramic heat insulation layer is provided on the outer side wall of the cylinder corresponding to the combustion chamber.

[0020] Furthermore, a ceramic heat insulation layer is provided on the outer side wall of the cylinder corresponding to the vaporization chamber.

[0021] Furthermore, a cooling water ring is provided outside the ceramic heat insulation layer corresponding to the combustion chamber.

[0022] Furthermore, the cooling water ring is communicated with the water inlet.

[0023] Furthermore, the water inlet is located at the rear end position of the combustion chamber.

[0024] Furthermore, a pressure-bearing device is provided on the outer side of the cylinder corresponding to the combustion chamber.

[0025] Furthermore, a pressure-bearing device is provided on the outer side of the cylinder corresponding to the vaporization chamber.

[0026] Furthermore, a swirler is provided at the front side inside the combustion chamber.

[0027] Furthermore, a gas pipe joint is provided at the outer end of the natural gas intake passage, and the gas pipe joint is connected to a natural gas pipe.

[0028] Furthermore, the ignition device is an electric spark plug.

[0029] Furthermore, the ignition device is radially arranged on the side wall of the combustion chamber.

[0030] Furthermore, the mixture outlet is connected to the end of the vaporization chamber through a tail necking structure.

[0031] The present invention also proposes a usage method of an underground gas-vapor generator for heavy oil thermal recovery, including the following steps:

[0032] Step 1: Natural gas enters the mixer through the natural gas intake passage, and air enters the mixer through the air intake passage. After being mixed in the mixer, the two form a uniform mixture.

[0033] Step 2: The first path of the mixture is sprayed into the combustion chamber through the central injection section. After the second path of the mixture is swirled by the swirler provided on both sides at the inlet of the combustion chamber, it changes from axial movement to rotational movement and enters the front end of the combustion chamber through the swirler to form a primary recirculation. The second path of the mixture at the rear end of the combustion chamber and part of the high-temperature flue gas flow backward to the central area of the combustion chamber to form a secondary recirculation.

[0034] Step 3: The ignition device first ignites the second path of the mixture at the outer edge, and then the flame quickly propagates from the outside to the deep layer of the inner-side airflow, igniting the first path of the mixture to form a main combustion zone.

[0035] Step 4: The second path of the mixture is first ignited for lean-oxygen combustion under a low oxygen concentration. The combustion under oxygen-deficient conditions effectively inhibits the formation of nitrogen oxides, reduces the corrosion of the flue gas formed by nitrogen oxides and steam, and the flame propagates inward.

[0036] Step 5: Rich-oxygen combustion involving the first path of the mixture is carried out inside the combustion chamber. The oxygen in the air is exhausted under two-stage combustion, effectively avoiding residual oxygen corrosion and generating high-temperature and high-pressure flue gas.

[0037] Step 6: A ceramic heat insulation layer is provided on the outer wall of the combustion chamber. Water enters in two paths. The first path enters from the water inlet and swirls along the spiral channel on the outer wall surface of the ceramic heat insulation layer to avoid cooling the outside of the combustion chamber. Under the dual cooling and heat insulation of water and the ceramic heat insulation layer, the combustion chamber is effectively prevented from being scoured by high-temperature and high-pressure flue gas, causing material oxidation and ablation problems, and ensuring the service life of the combustion chamber.

[0038] Step 7: Another stream of water directly enters from the water inlet at the rear end of the combustion chamber, converges with the first stream of cooling water, is atomized by the water supply nozzle and then enters the vaporization chamber, where it vaporizes in the high-temperature flue gas.

[0039] Step 8: To prevent the influence of bottom-hole backpressure, the generated steam and flue gas mixture is accelerated by the bottom necking structure and then sprayed into the target layer through the mixture outlet.

[0040] The present invention also proposes a method for calculating the medium flow rate in a downhole gas-steam generator for heavy oil thermal recovery, including the following steps:

[0041] S1: Select relevant parameters at the outlet of the downhole gas-steam generator according to the injection pressure and displacement requirements of the steam flooding injection well.

[0042] S2: Determine the theoretical flow rate of natural gas according to the natural gas composition and calorific value.

[0043] S3: Determine the theoretical flow rate of air according to the volume ratio of nitrogen to oxygen in dry air and the gas composition.

[0044] S4: Determine the theoretical supply and demand quantity of water according to the steam generation amount of the gas-steam generator.

[0045] Compared with the prior art, the present disclosure has the following advantages:

[0046] (1) High thermal energy utilization rate: The gas-steam generator is placed downhole, and water is directly sprayed into the flue gas generated by the combustion of fuel and combustion-supporting agent at the bottom of the well through the surface pipeline, eliminating the exhaust heat loss and transmission heat loss generated during the steam injection process of a conventional surface boiler.

[0047] (2) High steam dryness: The steam at the outlet of the downhole gas-steam generator avoids the dryness loss of the surface transmission pipeline and the downhole transmission string, and has a high dryness when injected into the oil layer.

[0048] (3) Good safety performance: A ceramic layer with heat insulation effect is arranged on the outer wall surface of the combustion chamber. Cooling water enters from the rear end of the combustion chamber and forms a layer of cooling water film on the outer wall surface of the ceramic layer to cool the combustion chamber of the gas-steam generator and ensure the safe operation of the gas-steam generator.

[0049] (4) Good combustion stability: The downhole gas-steam generator designed by the present invention adopts a two-stage recirculation combustion model to ensure continuous and stable combustion without extinguishing or backfiring.

[0050] (5) Not easily corroded; Adopting two-stage combustion of lean oxygen and rich oxygen can effectively inhibit the formation of nitrogen oxides, reduce flue gas corrosion, burn out the oxygen in the air, and reduce residual oxygen corrosion.

[0051] Other features and advantages of the present invention will be described in the following specification, and in part will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structures pointed out in the specification, the claims and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 The structural schematic diagram of the downhole gas-steam generator of the present invention is shown;

[0054] Figure 2 The flow chart of the medium flow calculation method in the downhole gas-steam generator of the present invention is shown.

[0055] Reference numerals: 1, natural gas intake channel; 2, mixing chamber; 3, central injection section; 4, mixer; 5, cyclone; 6, ignition device; 7, combustion chamber; 8, pressure-bearing device; 9, ceramic heat insulation layer; 10, water inlet; 11, vaporization chamber; 12, water supply nozzle; 13, mixture gas outlet; 14, air intake channel; 15, cooling water ring. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0057] Refer to Figure 1 As shown, the downhole gas-steam generator involved in the present invention is a gas-fired gas-steam generator, mainly including two parts: a combustion system and a water-vapor system. Air is selected as the combustion-supporting agent and natural gas is used as the fuel. The combustion system includes three processes: mixing, ignition, and combustion; the water-vapor system includes three processes: cooling, vaporization, and ejection. The main components include an intake device, a mixer 4, an ignition device 6, a combustion chamber 7, a vaporization chamber 11, a cooling device, a mixture gas outlet 13, etc.

[0058] Specifically, the intake device includes an air intake passage 14 and a natural gas intake passage 1. A gas pipe joint is provided at the outer end of the natural gas intake passage 1, and the gas pipe joint is connected to the natural gas pipe to ensure that the two gases enter the mixing chamber 2 at the front end of the downhole gas-steam generator. The mixer 4 ensures that the two gases are fully premixed in the mixing chamber to form a continuous and stable combustible gas source. The combustion chamber 7 completes the full combustion after the ignition of the combustible gas source, and finally forms high-temperature flue gas that meets the requirements. The ignition device 6 provides an ignition source, is radially arranged on the side wall of the combustion chamber 7 and is communicated with it. The ignition device 6 of the present invention is an electric spark plug, and the ignition method is electric ignition.

[0059] The vaporization chamber 11 uses circumferentially evenly distributed water injection nozzles 12 to radially inject water into the combustion airflow to complete the vaporization process of water underground and form a flue gas-steam mixture that meets the requirements. The mixture outlet 13 ensures that the steam and flue gas mixture is sprayed into the oil layer after accelerating through the tail necking structure. The cooling device mainly includes a cooling water ring 15 and a ceramic heat insulation layer 9, and ensures the service life of the combustion chamber 7 through double protection of cooling and heat insulation. Among them, the input end of the cooling water ring 15 is connected to the water inlet 10, and the water inlet 10 is located at the rear end of the combustion chamber 7, so that the cooling water enters from the rear end of the combustion chamber 7 and forms a layer of cooling water film on the outer wall surface of the ceramic layer.

[0060] In addition, a pressure-bearing device 8 is provided on the outer side of the cylinder corresponding to the combustion chamber 7 and the vaporization chamber 11.

[0061] As Figure 2 shown, the present application also proposes a calculation method for the theoretical flow rates of three media under the required dryness and displacement of the downhole gas-steam generator, including the following steps:

[0062] S1: According to the injection pressure and displacement requirements of the steam injection well in steam flooding, select the relevant parameters at the outlet of the downhole gas-steam generator;

[0063] S2: Determine the theoretical flow rate of natural gas according to the natural gas composition and calorific value;

[0064] S3: Determine the theoretical flow rate of air according to the volume ratio of nitrogen and oxygen in dry air and the gas composition;

[0065] S4: Determine the theoretical supply and demand of water according to the steam generation amount of the gas-steam generator.

[0066] Specifically, according to the injection pressure and displacement requirements of the steam injection well in steam flooding on site, the relevant parameters at the outlet of the downhole gas-steam generator are selected as follows:

[0067] Table 1 Parameters at the outlet of the gas-steam generator

[0068] Index Pressure Steam generation rate Steam temperature Parameter value 8 MPa 5 t / h to 9 t / h 294℃

[0069] (1) Determination of the theoretical flow rate of natural gas

[0070] The natural gas components and calorific values are selected as follows:

[0071] Table 2 Analysis of Gas Components

[0072] Gas composition <![CDATA[CH4]]> <![CDATA[C3H8]]> <![CDATA[C4H 10 > <![CDATA[C5 + > <![CDATA[N2]]> Percentage % 98 0.3 0.3 0.4 1

[0073] The corresponding higher calorific value H of natural gas h is 40403 KJ / Nm 3 , and the lower calorific value H l is 36442 KJ / Nm 3 (8705.9 Kcal / Nm 3 ).

[0074] By querying the thermodynamic parameter table of saturated steam, the corresponding enthalpy values of saturated water and saturated steam in saturated steam at 8 MPa can be obtained:

[0075] Table 3 Enthalpy Values of Saturated Steam

[0076] Pressure Enthalpy value of saturated water Enthalpy value of saturated steam 8 MPa 313.3 Kcal / kg 659.2 Kcal / kg

[0077] Therefore, the steam enthalpy value is H S = X GS H GS +(1 - X GS )H WS , where X GS is the steam dryness, H GS is the enthalpy value of saturated steam, and H WS is the enthalpy value of saturated water.

[0078] The required amount of natural gas is

[0079] (2) Determination of the Theoretical Air Flow

[0080] The combustion of gas requires an appropriate amount of oxygen to be supplied. The oxygen required by the downhole gas-steam generator of the present invention is obtained from the air. Without considering the small amounts of carbon dioxide and other rare gases contained in dry air, the volumetric composition of dry air can be calculated as 21% oxygen and 79% nitrogen. Then the volume ratio of nitrogen to oxygen in dry air is:

[0081]

[0082] The combustion reaction formula of any form of hydrocarbon can be represented by the following general formula:

[0083]

[0084] Considering that oxygen is provided by air, the combustion reaction formula involving air is:

[0085]

[0086] According to the above formula, when the gas composition is determined, the theoretical air required for gas combustion is:

[0087]

[0088] In the formula, V 空气 — theoretical air volume (Nm 3 / h dry air / Nm 3 / h dry gas);

[0089] H2, CO, C m H n , H2O — volume fractions of each combustible component in the gas;

[0090] 02 — volume fraction of oxygen in the gas.

[0091] (3) Determination of the theoretical water flow rate

[0092] The theoretical supply and demand quantity of water is equal to the steam generation quantity.

[0093] Taking the required steam generation quantity of 5 t / h and dryness of 70% as an example, the theoretical flow rates of the three media required are calculated as follows:

[0094] The enthalpy value of the steam is:

[0095] H S =(659.2×70% + 313.3×30%)×5×10 3 =2762.15×10 3 Kcal / h

[0096] The required theoretical natural gas quantity is

[0097] The required theoretical air quantity is:

[0098]

[0099] V 空气 =9.59×317.2 = 3041.9 Nm 3 / h

[0100] The required theoretical water supply quantity is V 水 =5 t / h.

[0101] The present invention also provides a method for using a downhole gas-steam generator for heavy oil thermal recovery, including the following steps:

[0102] Step 1: Natural gas enters the mixer 4 through the natural gas inlet channel 1, and air enters the mixer 4 through the air inlet channel 14. After being mixed in the mixer 4, they form a uniform mixture gas;

[0103] Step 2: The first path of the mixed gas is injected into the combustion chamber 7 through the central injection section 3. After the second path of the mixed gas is swirled by the swirlers 5 arranged on both sides of the inlet of the combustion chamber 7, its axial movement changes to rotational movement, and it enters the front end of the combustion chamber 7 through the swirlers 5 to form a primary recirculation. At the rear end of the combustion chamber 7, the second path of the mixed gas and part of the high-temperature gas flow backward to the central area of the combustion chamber 7 to form a secondary recirculation.

[0104] Step 3: The ignition device 6 first ignites the second path of the mixed gas at the outer edge, and then the flame quickly propagates from the outside to the deep layer of the inner-side airflow, igniting the first path of the mixed gas to form the main combustion zone.

[0105] Step 4: The second path of the mixed gas is first ignited to carry out lean-oxygen combustion under a low oxygen concentration.

[0106] Step 5: Rich-oxygen combustion involving the first path of the mixed gas is carried out inside the combustion chamber 7.

[0107] Step 6: A ceramic heat insulation layer 9 is provided on the outer wall of the combustion chamber 7. Water enters in two paths. The first path enters from the water inlet 10 and swirls along the spiral channel on the outer wall surface of the ceramic heat insulation layer 9.

[0108] Step 7: The other path of water directly enters from the water inlet 10 at the rear end of the combustion chamber 7, converges with the first path of cooling water, is atomized by the water supply nozzle 12 and then enters the vaporization chamber 11 to vaporize in the high-temperature flue gas.

[0109] Step 8: To prevent being affected by the bottom-hole back pressure, the generated steam and flue gas mixture is accelerated through the bottom necking structure and then sprayed into the target layer through the mixed gas outlet 13.

[0110] The working principle and process of the downhole gas-steam generator for heavy oil thermal recovery according to the present invention are briefly described below with reference to the accompanying drawings.

[0111] Mixing process: Natural gas enters the mixer 4 through the natural gas inlet channel 1, and air enters the mixer 4 through the air inlet channel 14. The two are mixed in the mixer 4 to form a uniform mixed gas. The first path of the mixed gas is injected into the combustion chamber 7 through the central injection section 3. After the second path of the mixed gas is swirled by the swirlers 5 arranged on both sides of the inlet of the combustion chamber 7, its axial movement changes to rotational movement and a primary recirculation is formed at the front end of the combustion chamber 7. At the rear end of the combustion chamber 7, the second path of the mixed gas and part of the high-temperature gas flow backward to the central area of the combustion chamber 7 to form a secondary recirculation.

[0112] Ignition process: The ignition device 6 first ignites the second path of the mixed gas at the outer edge, and then the flame quickly propagates from the outside to the deep layer of the inner-side airflow, igniting the first path of the mixed gas to form the main combustion zone.

[0113] Combustion process: The second mixture is first ignited for lean combustion under a low oxygen concentration to reduce the corrosion of the flue gas formed by nitrogen oxides and steam. Then the flame propagates inward to carry out oxygen-rich combustion with the participation of the first mixture inside the combustion chamber 7. The oxygen in the air is exhausted under two-stage combustion, effectively avoiding residual oxygen corrosion and generating high-temperature and high-pressure flue gas.

[0114] Cooling process: A ceramic heat insulation layer 9 is provided on the outer wall of the combustion chamber 7. Water enters in two paths. The first path enters from the water inlet 10 and swirls along the outer wall surface of the ceramic heat insulation layer 9 in a spiral channel to cool the outer wall surface of the combustion chamber 7. Under the dual cooling and heat insulation of water and the ceramic heat insulation layer 9, it effectively avoids the problems of material oxidation and ablation caused by the erosion of the high-temperature and high-pressure flue gas on the combustion chamber 7, and ensures the service life of the combustion chamber 7.

[0115] Vaporization process: The other path of water directly enters from the water inlet 10 at the rear end of the combustion chamber 7, converges with the first path of cooling water, is atomized by the feed water nozzle 12 and then enters the vaporization chamber 11 to be vaporized in the high-temperature flue gas.

[0116] Ejection process: To prevent the influence of bottom hole back pressure, the generated steam and flue gas mixture is accelerated by the bottom necking structure and then sprayed into the target layer through the mixture outlet 13.

[0117] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A downhole gas-steam generator for heavy oil thermal recovery, characterized in that, Comprising: An intake device having an air intake passage (14) and a natural gas intake passage (1); A mixer (4) having a mixing chamber (2), the mixing chamber (2) being in communication with the air intake passage (14) and the natural gas intake passage (1) respectively; A combustion chamber (7) provided at the outlet end of the mixer (4), and a slender central injection section (3) is provided between the combustion chamber (7) and the mixer (4); An ignition device (6) radially provided on the side wall of the combustion chamber (7) and in communication therewith; A vaporization chamber (11) located at the rear end of the combustion chamber (7) and in communication therewith; Water supply nozzles (12) are circumferentially and uniformly distributed on the outer circumference of the vaporization chamber (11), and several of the water supply nozzles (12) are respectively in communication with a water inlet (10), and A mixture gas outlet (13) is provided at the end of the vaporization chamber (11).

2. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, wherein A ceramic heat insulation layer (9) is provided on the outer side wall of the cylinder corresponding to the combustion chamber (7).

3. The downhole gas-steam generator for heavy oil thermal recovery according to claim 2, wherein, A ceramic heat insulation layer (9) is provided on the outer side wall of the cylinder corresponding to the vaporization chamber (11).

4. The downhole gas-steam generator for heavy oil thermal recovery according to claim 2, wherein, A cooling water ring (15) is provided outside the ceramic heat insulation layer (9) corresponding to the combustion chamber (7).

5. The downhole gas-steam generator for heavy oil thermal recovery according to claim 4, characterized in that, The cooling water ring (15) is in communication with the water inlet (10).

6. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, The water inlet (10) is located at the rear end position of the combustion chamber (7).

7. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, wherein A pressure-bearing device (8) is provided outside the cylinder corresponding to the combustion chamber (7).

8. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, wherein, A pressure-bearing device (8) is provided outside the cylinder corresponding to the vaporization chamber (11).

9. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, A swirler (5) is provided at the front side inside the combustion chamber (7).

10. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, A pipe joint is provided at the outer end of the natural gas intake passage (1), and the pipe joint is connected to a natural gas pipe.

11. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, The ignition device (6) is an electric spark plug.

12. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, The ignition device (6) is radially provided on the side wall of the combustion chamber (7).

13. The downhole gas-steam generator for heavy oil thermal recovery according to claim 1, characterized in that, The mixture gas outlet (13) is connected to the end of the vaporization chamber (11) through a tail necking structure.

14. A method for using the downhole gas-steam generator for heavy oil thermal recovery according to any one of claims 1-13, characterized in that, Including the following steps: Step 1: Natural gas enters the mixer through the natural gas intake passage, air enters the mixer through the air intake passage, and the natural gas and air are mixed in the mixer to form a uniform mixture gas; Step 2: The first path of the mixture gas is sprayed into the combustion chamber through the central injection section, and the second path of the mixture gas is swirled by the swirler provided on both sides at the inlet of the combustion chamber, changes from axial movement to rotational movement, and enters the front end of the combustion chamber through the swirler to form a primary reflux, and the second path of the mixture gas at the rear end of the combustion chamber and part of the high-temperature flue gas flow backward to the central area of the combustion chamber to form a secondary reflux; Step 3: The ignition device first ignites the second path of the mixture gas at the outer edge, and then the flame quickly propagates from the outside to the deep layer of the inner side airflow, igniting the first path of the mixture gas to form a main combustion zone; Step 4: The second path of the mixture gas is ignited for lean oxygen combustion under a low oxygen concentration; Step 5: Rich oxygen combustion involving the first path of the mixture gas is carried out inside the combustion chamber, and the oxygen in the air is exhausted under two-stage combustion, effectively avoiding residual oxygen corrosion and generating high-temperature and high-pressure flue gas; Step 6: A ceramic heat insulation layer is provided on the outer wall of the combustion chamber, and water enters in two paths. The first path enters from the water inlet and swirls in a spiral channel on the outer wall surface of the ceramic heat insulation layer; Step 7: Another stream of water directly enters from the water inlet at the rear end of the combustion chamber, converges with the first stream of cooling water, is atomized by the water supply nozzle and then enters the vaporization chamber, where it vaporizes in the high-temperature flue gas. Step 8: To prevent being affected by the bottom-hole back pressure, the generated steam-gas mixture is accelerated by the bottom necking structure and then sprayed into the target layer through the mixture gas outlet.

15. A method for calculating the medium flow rate in the downhole gas-steam generator for heavy oil thermal recovery according to any one of claims 1-13, characterized in that, It includes the following steps: S1: Select relevant parameters at the outlet of the downhole gas-steam generator according to the steam injection pressure and displacement requirements of the steam drive injection well. S2: Determine the theoretical flow rate of natural gas according to the natural gas composition and calorific value. S3: Determine the theoretical flow rate of air according to the volume ratio of nitrogen to oxygen in dry air and the gas composition. S4: Determine the theoretical supply and demand of water according to the steam generation amount of the gas-steam generator.

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