Supercritical hydrothermal combustion type downhole multi-element heat fluid generating method and device

Abstract

The application discloses a supercritical hydrothermal combustion type downhole multi-element heat fluid generating method and device; a first-stage combustion zone, a second-stage combustion zone, a third-stage reaction zone, a fourth-stage reaction zone and a fifth-stage mixing zone are arranged, a hot surface forced ignition mode is adopted, cold fuel injection stable ignition in a starting stage is realized, and cold fuel ignition requirements of a downhole device are met; large-flow material is axially graded, upper combustion / reaction provides heat for lower reaction, stable supercritical hydrothermal combustion and rapid oxidation of material at each stage are ensured in the downhole device with limited radial space, and large-flow of the downhole multi-element heat fluid generating device is realized; a hydraulic turbine is installed at the bottom of the multi-element heat fluid generating device, pressure potential energy of generated supercritical fluid is effectively utilized, and parameter self-adjustment of the multi-element heat fluid is realized; and the application can provide a feasible scheme and technical guidance for efficient and clean heavy oil thermal recovery technology.

Description

Technical Field

[0001] This invention belongs to the field of heavy oil extraction technology, specifically relating to a supercritical hydrothermal combustion type downhole multi-element thermal fluid generation method and apparatus. Background Technology

[0002] Of the discovered heavy oil reservoirs, those with a depth greater than 800m account for approximately 80% of the proven reserves, with about half of the reservoirs located at depths of 1300–1700m. Compared to conventional oil and gas, heavy oil not only has higher contents of resins and asphaltenes but also higher viscosity and pour point, resulting in poorer fluidity. Therefore, its extraction technology is much more complex than that of conventional oil and gas development, and the recovery rate is relatively lower. However, heavy oil is extremely sensitive to temperature; for every 10°C increase, its viscosity decreases by half. Currently, oilfields mainly extract heavy oil by injecting steam generated from surface steam injection boilers into downhole wells, combined with steam huff and puff, steam drive, and steam-assisted gravity drainage thermal recovery technologies. However, existing extraction methods suffer from problems such as high heat loss (heat loss from surface equipment and pipelines, and heat loss from steam injection wellbore), limited reservoir depth, and large footprint of surface equipment.

[0003] Multi-component thermal fluid technology is an oil extraction technology that utilizes the synergistic effect of gases (N2, CO2) and steam to form foam oil underground, increasing the oil's expansion coefficient and fluidity. Specifically: 1) High-temperature multi-component thermal fluid heats the oil reservoir, significantly reducing the viscosity of heavy oil; 2) The multi-component thermal fluid contains large amounts of N2 and CO2, which dissolve in the crude oil under high pressure, further reducing viscosity and increasing the expansion coefficient, interacting with the crude oil to form foam oil and increasing fluidity; 3) The multi-component fluid has a significant pressurizing effect; 4) It expands the swept volume; after injection of the multi-component thermal fluid, the high-pressure zone formed by gas diffusion is significantly larger than the high-pressure zone formed by steam injection, resulting in a very significant pressurizing effect; 5) It reduces heat loss from the oil reservoir; the N2 and CO2 in the multi-component thermal fluid are suspended above the oil reservoir, maintaining the reservoir temperature and reducing heat loss. In summary, the generated multi-component thermal fluid (steam, N2, CO2, etc.) has both thermal viscosity-reducing and gas miscibility-reducing effects, thus effectively improving the recovery rate of heavy oil. Supercritical hydrothermal combustion refers to the combustion of fuel compounds at a certain concentration in a supercritical water environment (T > 374.1℃, P > 22.1MPa). When the temperature exceeds the auto-ignition temperature, the fuel compounds, when mixed with an oxidant, ignite in the supercritical water, releasing a large amount of heat and forming a hydrothermal flame. Supercritical hydrothermal combustion has a fast reaction rate and a high hydrothermal flame temperature, reaching 700–1100℃, resulting in high fuel combustion efficiency and making it a highly efficient energy source. Furthermore, the combustion process in supercritical water involves direct heat transfer between molecules, resulting in high heat exchange efficiency, thus allowing for a compact structure in supercritical hydrothermal combustion reactors.

[0004] Combining supercritical hydrothermal combustion with multi-component thermal fluid injection technology, a low-temperature, high-pressure fuel solution and oxidant are injected into a combustion device to ignite the fuel and generate a supercritical hydrothermal flame. The reaction produces a multi-component thermal fluid containing CO2, H2O, and N2, which is directly injected into the oil reservoir for heavy oil thermal recovery. This achieves the following: 1) The generator device has a compact geometry, meeting the requirements of limited downhole space; 2) The downhole device is not limited by well depth and is suitable for deep and ultra-deep heavy oil development; 3) The supercritical hydrothermal combustion device has no smoke loss and avoids surface heat loss and wellbore heat loss, improving energy utilization efficiency and reducing fuel consumption.

[0005] Supercritical hydrothermal combustion-type downhole multi-element thermal fluid steam injection technology meets the needs of energy conservation, emission reduction, and ensuring energy security. The design focus of industrial-scale supercritical hydrothermal combustion-type multi-element thermal fluid generators is on cold-state fuel ignition and stable combustion of large-flow-rate materials, generating multi-element thermal fluids with target parameters. This invention provides a supercritical hydrothermal combustion-type downhole multi-element thermal fluid generator that meets the above requirements, offering a feasible solution for heavy oil extraction in medium and deep oil reservoirs. Summary of the Invention

[0006] The purpose of this invention is to overcome the difficulty of existing steam injection technology in meeting the requirements of downhole equipment, and to provide a method and device for generating a supercritical hydrothermal combustion type multi-element thermal fluid. During startup, cold ignition of downhole fuel is achieved by forced ignition with a small flow rate. During operation, stable oxidation and heat release of each stage of fuel are maintained by axial grading of a large flow rate of material. Cooling and temperature-regulating water is introduced at the bottom of the device and a pressure-reducing turbine is set up to achieve self-adjustment of outlet fluid parameters, thereby obtaining a multi-element thermal fluid with target parameters.

[0007] To achieve the above objectives, this invention provides a method for generating a supercritical hydrothermal combustion-type downhole multi-element thermal fluid. The method comprises a first-stage combustion zone, a second-stage combustion zone, a third-stage reaction zone, a fourth-stage reaction zone, and a fifth-stage mixing zone. First-stage fuel at room temperature is injected into the first-stage combustion zone A1, where a supercritical hydrothermal combustion reaction occurs with the assistance of an oxidant. Second-stage fuel is spirally injected into the second-stage combustion zone A2, where it rapidly mixes with the high-temperature combustion products of the first-stage fuel and the remaining oxidant, resulting in a supercritical hydrothermal combustion reaction with the assistance of an oxidant. Third-stage fuel is injected into the third-stage reaction zone A3. The fuel is mixed with the high-temperature combustion products of upstream Stage II fuel and heated to the required preheating temperature. Under the assistance of an oxidant, a rapid supercritical water oxidation reaction occurs, resulting in a rapid temperature rise. Stage IV fuel is injected into Stage IV reaction zone A4 and mixed with the high-temperature combustion products of upstream Stage III fuel and the remaining oxidant. It is then heated to the required preheating temperature and undergoes a rapid supercritical water oxidation reaction under the assistance of an oxidant, resulting in a rapid temperature rise. Stage V blended water is injected into Stage V blending zone A5 and mixed with the high-temperature products of rapid supercritical water oxidation of upstream Stage IV fuel, generating a high-temperature and high-pressure supercritical multi-element thermal fluid.

[0008] In the first-stage combustion zone A1, combustion is initiated by forced ignition, generating high-temperature supercritical water, which then heats the downstream reaction zones. Once the first-stage combustion zone A1, second-stage combustion zone A2, third-stage reaction zone A3, and fourth-stage reaction zone A4 are filled with supercritical water, establishing the initial conditions for stable reactions of each fuel stage, the reaction fuels and oxidants of each stage are injected, resulting in supercritical hydrothermal combustion and rapid supercritical water oxidation reactions, until the first-stage combustion zone A1, second-stage combustion zone A2, third-stage reaction zone A3, and fourth-stage reaction zone A4 reach normal operating conditions. The fifth-stage blended water flows into the fifth-stage blending zone A5, mixing with the upstream high-temperature reaction fluid to generate a supercritical multi-element thermal fluid. After stable operation, the first-stage fuel is cooled and injected for stable combustion through thermal auto-ignition, while maintaining the stable reaction process of each fuel stage and continuously generating a large flow of multi-element thermal fluid.

[0009] The pressure of the supercritical multi-component thermofluid in the reaction zone is reduced by using a hydraulic turbine, which drives a scraper device to rotate and scour the inner wall of the reaction chamber.

[0010] Simultaneously, a supercritical hydrothermal combustion type downhole multi-element thermal fluid generator is provided, comprising a top end cover, an upper end cover, a pressure-bearing wall, and a bottom end cover connected in sequence. The top end cover houses a stage I fuel igniter. The inner side of the upper end cover, from the outside in, is arranged with a three-stage spiral wall of the reaction chamber and a stage I combustion chamber spiral cooling wall, located inside the pressure-bearing wall. The area enclosed by the stage I combustion chamber spiral cooling wall is the stage I combustion zone A1. Below stage I combustion zone A1 are, in sequence, stage II combustion zone A2, stage III reaction zone A3, stage IV reaction zone A4, and stage V mixing zone A5. The three-stage spiral wall of the reaction chamber has three spiral channels corresponding to and connecting stage III reaction zone A3, stage IV reaction zone A4, and stage V mixing zone A5, respectively. The top end cover has a stage I fuel channel and stage I and II oxidant channels connecting to stage I combustion zone A1. Fuel inlets corresponding to and connecting the three spiral channels are opened on the upper end cover. The bottom end cover has a multi-element thermal fluid outlet.

[0011] The outer side of the Stage I fuel igniter is provided with a core tube and an inner sleeve. The inner sleeve is connected to the top end cap. The spiral cooling wall of the Stage I combustion chamber is connected to the inner sleeve. A ring of oblique holes is opened along the circumferential direction on the lower side wall of the core tube. A circular hole with a diameter larger than the diameter of the igniter terminal is opened at the bottom closed end of the core tube. The oblique holes and the annular hole on the bottom closed end serve as the Stage I fuel injection port for injecting Stage I fuel into the Stage I combustion zone A1. The top end cap is provided with Stage I fuel inlet N1 and Stage I and Stage II oxidant inlets N2, respectively. The annular gap between the inner wall of the core tube and the outer wall of the igniter terminal forms the Stage I fuel channel. The annular gap between the outer wall of the core tube and the inner wall of the inner sleeve forms the Stage I and Stage II oxidant channels.

[0012] The outer side of the three-stage spiral wall of the reaction chamber is provided with three independent spiral channels as the stage III fuel and oxidant spiral channel, the stage IV fuel spiral channel, and the stage V mixed water spiral channel. The upper end cover is provided with stage II fuel inlet N3, stage III fuel and oxidant inlet N4, stage IV fuel inlet N5, and stage V mixed water inlet N6. Stage II fuel inlet N3 is connected to the spiral channel on the outer wall of the stage I combustion chamber spiral cooling wall, and the spiral channel on the outer wall of the stage I combustion chamber spiral cooling wall forms the stage II fuel channel. Stage III fuel and oxidant inlet N4 is connected to the stage III fuel and oxidant spiral channel, stage IV fuel inlet N5 is connected to the stage IV fuel spiral channel, and stage V mixed water inlet N6 is connected to the stage V mixed water spiral channel.

[0013] Several through holes are formed on the last turn of the Stage III fuel and oxidizer spiral channel, serving as Stage III fuel and oxidizer inlets. The Stage III fuel and oxidizer spiral channel stops at the Stage III fuel and oxidizer inlets. The area between the Stage I combustion chamber spiral cooling wall outlet and the Stage III fuel and oxidizer inlet is the Stage II combustion zone A2. Several through holes are formed on the last turn of the Stage IV fuel spiral channel, serving as Stage IV fuel inlets. The Stage IV fuel spiral channel stops at the Stage IV fuel inlets. The area between the Stage III fuel and oxidizer inlets and the Stage IV fuel inlets is the Stage III reaction zone A3. Several arrayed small holes are formed at the bottom of the Stage V mixed water spiral channel, serving as Stage V mixed water inlets. The area between the Stage IV fuel inlets and the Stage V mixed water inlets forms the Stage IV reaction zone A4. The area between the Stage V mixed water inlet area and the hydraulic turbine inlet cover is the Stage V mixing zone A5.

[0014] The lower part of the pressure wall is equipped with a rotating shaft and a hydraulic turbine inlet cover; the rotating shaft passes through the center of the bottom end cover, the middle part of the rotating shaft passes through the hydraulic turbine inlet cover, the hydraulic turbine is installed at the lower part of the rotating shaft, and the hydraulic turbine fluid inlet N7 is provided on the hydraulic turbine inlet cover. The rotating shaft is rotatably connected to the hydraulic turbine inlet cover and the bottom end cover respectively through thrust bearings.

[0015] A rotating scraper is installed on the upper part of the rotating shaft.

[0016] The fuel supplied to the Class I combustion zone A1, Class II combustion zone A2, Class III reaction zone A3, and Class IV reaction zone A4 is any one of methanol or methanol solution, ethanol or ethanol solution, and crude oil or crude oil / water mixture. The fuel supplied to the Class I combustion zone A1, Class II combustion zone A2, Class III reaction zone A3, and Class IV reaction zone A4 is the same. The blended water supplied to the Class V blended water inlet N6 is oilfield wastewater or softened water.

[0017] Compared with the prior art, the advantages of the device of the present invention are specifically manifested in the following aspects:

[0018] 1) By using hot-surface forced ignition of the Class I fuel, stable cold-state injection ignition of the fuel can be achieved during the start-up phase. The purpose is to establish a supercritical water environment in each reaction zone to achieve stable combustion and initial oxidation conditions for normal operation. This ignition method does not require additional heating devices, overcomes the fuel critical preheating temperature limitation in the hydrothermal combustion process of thermal auto-ignition, and meets the cold-state fuel ignition requirements of downhole equipment.

[0019] 2) In this invention, the fuel solution and oxidant are axially graded. In a reaction chamber with limited radial dimensions: (1) the flow rate of the I and II grade materials is lower than the flame wave velocity of supercritical hydrothermal combustion, and high-concentration fuel is used to ensure stable combustion of cold-injected fuel during operation; (2) the III and IV grade materials are mixed with the high-temperature products after the reaction of the previous stage and heated to the critical preheating temperature of the rapid supercritical water oxidation reaction, and the flow rate of the III and IV grade materials after mixing meets the flow rate limit, so that the rapid supercritical water oxidation reaction occurs and heat is released to generate high-temperature supercritical fluid. Therefore, axially classifying the reactants not only ensures that each stage of material meets the flow rate limits for maintaining a stable supercritical water rapid exothermic reaction in the space-constrained downhole device, but also ensures that each stage of material meets the initial temperature requirements of the corresponding reaction through stepwise preheating. This guarantees stable hydrothermal combustion and oxidation of the fuel solution, enabling high-flow-rate operation of the downhole supercritical hydrothermal combustion type multi-element thermal fluid generator. It also ensures stable hydrothermal flame combustion during normal operation, with the flow rate of unburned materials lower than the flame wave velocity under supercritical pressure conditions. The flame wave velocity of supercritical hydrothermal combustion is in the range of 0.01–0.1 m / s, while the flameless rapid supercritical water oxidation reaction requires the flow rate of reactants to be in the range of 0.2–1 m / s.

[0020] 3) By introducing mixed water at the bottom of the generator and equipping it with a pressure-reducing turbine, the outlet mixed medium is sequentially cooled and depressurized to the target parameters, achieving self-regulation of the parameters of the multi-component thermofluid. In addition, by utilizing the energy conversion characteristics of the pressure-reducing turbine, the pressure energy of the high-pressure reaction products is converted into the kinetic energy to drive the rotating scraper, eliminating the need for additional drive equipment and overcoming the energy loss caused by valve pressure reduction, thus improving energy utilization efficiency. Attached Figure Description

[0021] Figure 1a This is a cross-sectional schematic diagram of the device structure described in this invention.

[0022] Figure 1b This is a top view schematic diagram of the device structure described in this invention.

[0023] Figure 2a This is a cross-sectional schematic diagram of the three-stage spiral wall structure of the reaction chamber of the present invention.

[0024] Figure 2b for Figure 2aA top-down view.

[0025] Figure 3 This is a partial enlarged view of the upper part of the device of the present invention.

[0026] Figure 4 This is a partial enlarged view of the lower part of the device of the present invention.

[0027] The labels in the diagram represent: A1. Stage I combustion zone, A2. Stage II combustion zone, A3. Stage III reaction zone, A4. Stage IV reaction zone, A5. Stage V blending zone, 1. Top end cap, 2. Core tube, 3. Inner sleeve, 4. Top end cap, 5. Stage I combustion chamber spiral cooling wall, 6. Three-stage spiral wall of the reaction chamber, 6-1. Stage III fuel and oxidizer spiral channel, 6-2. Stage IV fuel spiral channel, 6-3. Stage V blending water spiral channel, 7. Pressure wall, 8. Rotating scraper, 9. Hydraulic turbine inlet cover, 10. Hydraulic turbine, 11. Bottom end cap, 12. Rotating shaft, 1 3. First double-ended stud, 14. Ignition terminal, 15. Second double-ended stud, 16. Class I fuel inlet, 17. Hot-face igniter, 18. Class III fuel and oxidizer inlet, 19. Class IV fuel inlet, 20. Class V mixed water inlet, 21. Thrust bearing, 22. Thrust bearing, N1. Class I fuel inlet, N2. Class I and II oxidizer inlets, N3. Class II fuel inlet, N4. Class III fuel and oxidizer inlet, N5. Class IV fuel inlet, N6. Class V mixed water inlet, N7. Hydraulic turbine fluid inlet, N8. Multi-component hot fluid outlet. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] refer to Figure 1a , Figure 1b , Figure 2a , Figure 2b The present invention is a supercritical hydrothermal combustion type downhole multi-element thermal fluid generator, including a top end cover 1, an upper end cover 4, a pressure-bearing wall 7 and a bottom end cover 11, which are connected and assembled in sequence.

[0030] In this invention, the top end cap 1 and the upper end cap 4 are connected and fastened by a first double-ended stud 13, and the upper end cap 4 and the pressure-bearing wall 7 are connected and fastened by a second double-ended stud 15. A core tube 2 and an inner sleeve 3 are provided in the top end cap 1. The inner sleeve 3 is located outside the core tube 2 and is threadedly connected to the top end cap 1. The spiral cooling wall 5 of the first-stage combustion chamber is threadedly connected to the inner sleeve 3. The area enclosed by the spiral cooling wall 5 of the first-stage combustion chamber is the first-stage combustion zone A1. A first-stage fuel igniter is inserted into the center of the core tube 2. The first-stage fuel igniter is composed of an igniter terminal 14 and a hot-face igniter 17. The hot-face igniter 17 is a spiral igniter made of coiled resistance wire. The coil has a ring of oblique holes on the circumference of the lower side wall of the core tube 2, and a circular hole with a diameter larger than the diameter of the igniter terminal 14 on the closed bottom end of the core tube 2. The oblique holes arranged in the circumferential direction at the lower part of the core tube 2 and the annular hole on the closed bottom end together serve as the first-stage fuel inlet 16. The top end cap 1 is provided with a first-stage fuel inlet N1 and a first- and second-stage oxidant inlet N2. The annular gap between the inner wall of the core tube 2 and the outer wall of the igniter terminal 14 forms the first-stage fuel channel, and the annular gap between the outer wall of the core tube 2 and the inner wall of the inner sleeve 3 forms the first- and second-stage oxidant channels. The first- and second-stage oxidant inlet N2 is connected to the first- and second-stage oxidant channels.

[0031] refer to Figure 1a Sealing elements are provided at the end face connection between the top end cover 1 and the inner sleeve 3, the end face connection between the upper end cover 4 and the three-stage spiral wall 6 of the reaction chamber, and the end face connection between the upper end cover 4 and the pressure wall 7.

[0032] In this invention, the upper end cover 4 is provided with a Class II fuel inlet N3, a Class III fuel and oxidant inlet N4, a Class IV fuel inlet N5, and a Class V mixed water inlet N6. A spiral channel is opened on the outer wall of the Class I combustion chamber spiral cooling wall 5. The Class II fuel inlet N3 is connected to the spiral channel on the outer wall of the Class I combustion chamber spiral cooling wall 5. The spiral channel on the outer wall of the Class I combustion chamber spiral cooling wall 5 forms a channel for Class II fuel.

[0033] In this invention, a three-stage spiral wall 6 for the reaction chamber is installed inside the pressure-bearing wall 7. The outer wall of the three-stage spiral wall 6 has three independent threaded channels. Adjacent threads and the inner wall of the pressure-bearing wall 7 sequentially form a Class III fuel and oxidant spiral channel 6-1, a Class IV fuel spiral channel 6-2, and a Class V mixed water spiral channel 6-3. The Class III fuel and oxidant inlet N4 communicates with the Class III fuel and oxidant spiral channel 6-1, the Class IV fuel inlet N5 communicates with the Class IV fuel spiral channel 6-2, and the Class V mixed water inlet N6 communicates with the Class V mixed water spiral channel 6-3. A small hole is formed on the last turn of the Class III fuel and oxidant spiral channel 6-1 as the Class III fuel and oxidant injection port 18. The area between the outlet of the spiral cooling wall 5 of the stage I combustion chamber and the stage III fuel and oxidizer inlet 18 is the stage II combustion zone A2. A small hole is opened on the last turn of the stage IV fuel spiral channel 6-2 as the stage IV fuel inlet 19. The stage IV fuel spiral channel 6-2 stops here. The area between the stage III fuel and oxidizer inlet 18 and the stage IV fuel inlet 19 is the stage III reaction zone A3. Several arrayed small holes are opened at the bottom of the stage V mixed water spiral channel 6-3 as the stage V mixed water inlet 20. The area between the stage IV fuel inlet 19 and the stage V mixed water inlet 20 is the stage IV reaction zone A4. The area from the stage V mixed water inlet 20 to the hydraulic turbine inlet cover 9 is the stage V mixing zone A5.

[0034] In this invention, the bottom end cap 11 is tightly connected to the inner side of the pressure-bearing wall 7. A rotating shaft 12 is provided, passing through the center of the bottom end cap 11. A rotating scraper 8 is installed on the upper part of the rotating shaft 12. The working surface of the rotating scraper 8 contacts the inner wall of the V-level mixing zone A5. The middle part of the rotating shaft 12 passes through the hydraulic turbine inlet cover 9. A hydraulic turbine 10 is installed on the lower part of the rotating shaft 12. A hydraulic turbine fluid inlet N7 is provided on the hydraulic turbine inlet cover 9. A multi-element hot fluid outlet N8 is provided on the bottom end cap 11. The rotating shaft 12 is rotatably connected to the hydraulic turbine inlet cover 9 and the bottom end cap 11 through a first thrust bearing 21 and a second thrust bearing 22, respectively.

[0035] The lower inner wall of the pressure-bearing wall 7 is provided with a step, and the bottom end cap 11 is axially limited by the step on its outer wall and the step on the inner wall of the pressure-bearing wall 7. The bottom end of the three-stage spiral wall 6 of the reaction chamber contacts the upper end face of the bottom end cap 11, thereby keeping the overall axial position unchanged.

[0036] In this invention, the fuel supplied to the first-stage combustion zone A1, the second-stage combustion zone A2, the third-stage reaction zone A3, and the fourth-stage reaction zone A4 is any one of methanol or methanol solution, ethanol or ethanol solution, and crude oil or crude oil / water mixture; as a preferred embodiment, the fuel supplied to the first-stage combustion zone A1, the second-stage combustion zone A2, the third-stage reaction zone A3, and the fourth-stage reaction zone A4 is the same, and the blended water supplied to the fifth-stage blended water inlet N6 is oilfield wastewater or softened water.

[0037] Based on the above structure, the operating principle of this invention is as follows:

[0038] Based on the structure of this invention, four stages of fuel and one stage of mixed water are configured, namely, Stage I fuel, Stage II fuel, Stage III fuel, Stage IV fuel, and Stage V mixed water. Stage I fuel at room temperature enters the device through Stage I fuel inlet 1, flows through core tube 2, and is injected into Stage I combustion zone A1 through Stage I fuel injection port 16, where a supercritical hydrothermal combustion reaction occurs. Stage II fuel enters the device through Stage II fuel inlet N3, flows through the external threaded channel of the spiral cooling wall 5 of the Stage I combustion chamber, and is spirally injected into Stage II combustion zone A2. The oxidant required for both Stage I and Stage II fuels enters the device through Stage I and Stage II oxidant inlets N2, flows through Stage I and Stage II oxidant channels, and sequentially enters Stage I combustion zone A1 and Stage II combustion zone A2, providing oxidant for the supercritical hydrothermal combustion of Stage I and Stage II fuels. After entering Stage II combustion zone A2, Stage II fuel rapidly mixes with the high-temperature combustion products and residual oxidant of Stage I fuel, resulting in a supercritical hydrothermal combustion reaction. Stage III fuel flows into the Stage III fuel and oxidant spiral channel 6-1 from the Stage III fuel and oxidant inlet N4, and is injected into the Stage III reaction zone A3 through the Stage III fuel and oxidant injection port 18. It mixes with the high-temperature combustion products of the upstream Stage II fuel and is heated to the required preheating temperature, undergoing a rapid supercritical water oxidation reaction and rapid temperature rise. Stage IV fuel flows into the Stage IV fuel spiral channel 6-2 from the Stage IV fuel inlet N5, and is injected into the Stage IV reaction zone A4 through the Stage IV fuel injection port 19. It mixes with the high-temperature combustion products of the upstream Stage III fuel and the remaining oxidant and is heated to the required preheating temperature, undergoing a rapid supercritical water oxidation reaction and rapid temperature rise. The oxidant required for both Stage III and Stage IV fuels enters the device from the Stage III fuel and oxidant inlet N4, flows through the Stage III fuel and oxidant spiral channel 6-1, and enters the reaction chamber through the Stage III fuel and oxidant injection port 18. It then passes sequentially through the Stage III reaction zone A3 and the Stage IV reaction zone A4, providing oxidant for the rapid supercritical water oxidation of both Stage III and Stage IV fuels. Grade V blended water flows into the Grade V blended water spiral channel 6-3 from Grade V blended water inlet N6, and is injected into the Grade V blending zone A5 from Grade V blended water injection port 20. It mixes with the high-temperature products of rapid supercritical water oxidation of upstream Grade IV fuel, generating a high-temperature, high-pressure supercritical multi-element thermofluid. This supercritical multi-element thermofluid flows into the hydraulic turbine zone from hydraulic turbine fluid inlet N7, driving the hydraulic turbine 10 to rotate, further driving the rotating shaft 12 and rotating scraper 8 to rotate, while simultaneously reducing the pressure of the supercritical multi-element thermofluid. During the rotation of the rotating scraper 8, it scours the bottom inner wall of the three-stage spiral wall 6 of the reaction chamber, preventing inorganic salt particles precipitated from the supercritical multi-element thermofluid from depositing at the bottom of the spiral wall 6 and causing equipment blockage. Finally, the generated multi-element thermofluid flows out from the multi-element thermofluid outlet N8 and is injected into the formation.

[0039] Based on the above structure, the startup method of this invention is as follows: The multi-element thermal fluid device is filled with supercritical pressure room temperature water. The hot-face igniter 17 is activated, and room temperature Stage I fuel enters the device. In Stage I combustion zone A1, it contacts the high-temperature surface of the hot-face igniter 17 and ignites through forced ignition, generating high-temperature supercritical water, which then heats the downstream reaction zones. After Stage I combustion zone A1, Stage II combustion zone A2, Stage III reaction zone A3, and Stage IV reaction zone A4 are filled with supercritical water, establishing the initial conditions for stable reactions of each stage of fuel, the Stage II fuel pump, Stage III fuel pump, Stage IV fuel pump, and corresponding oxidant pump are activated to inject the reactants into the device, causing supercritical hydrothermal combustion and rapid supercritical water oxidation reactions, until Stage I combustion zone A1, Stage II combustion zone A2, Stage III reaction zone A3, and Stage IV reaction zone A4 reach normal operating conditions. Start the stage V blending water pump to allow stage V blending water to flow into stage V blending zone A5, where it mixes with the upstream high-temperature reaction fluid to generate a supercritical multi-component thermal fluid. After the multi-component thermal fluid device stabilizes, the start-up phase is complete. Turn off the hot-face igniter 17 and achieve stable combustion of stage I fuel through thermal auto-ignition, while maintaining the stable reaction process of each stage of fuel, generating a large flow rate of multi-component thermal fluid.

[0040] In summary, addressing the issues of high heat loss, limited reservoir depth, and large footprint of surface equipment in heavy oil thermal recovery processes based on surface steam injection boilers, this invention proposes a supercritical hydrothermal combustion-type downhole multi-element thermal fluid generator. The equipment has a compact structure, meeting the requirements of wellbore radial dimension limitations. During startup, cold ignition of downhole fuel is achieved through forced ignition at a low flow rate. During operation, stable oxidation and heat release at each stage of fuel are maintained through axial grading of a large flow rate, meeting the cold-injection ignition requirements of downhole equipment, ensuring stable supercritical hydrothermal combustion of large flow rates of fuel, realizing high-flow-rate operation of the downhole multi-element thermal fluid generator, and achieving self-regulation of multi-element thermal fluid parameters, thereby improving energy utilization efficiency.

[0041] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A supercritical hydrothermal combustion type downhole multi-element thermal fluid generator, characterized in that, The system includes a top end cap (1), an upper end cap (4), a pressure-bearing wall (7), and a bottom end cap (11) connected in sequence. The top end cap (1) is equipped with a Class I fuel igniter. The upper end cap (4) has a three-stage spiral wall (6) for the reaction chamber and a spiral cooling wall (5) for the Class I combustion chamber arranged from the outside to the inside. The three-stage spiral wall (6) for the reaction chamber is located inside the pressure-bearing wall (7). The area enclosed by the spiral cooling wall (5) for the Class I combustion chamber is the Class I combustion zone A1. Below the Class I combustion zone A1 are the Class II combustion zone A2, the Class III reaction zone A3, the Class IV reaction zone A4, and the Class V mixing zone A5. The three-stage spiral wall (6) for the reaction chamber has three spiral channels that are respectively connected to the bottom end cap. The system includes a Class III reaction zone A3, a Class IV reaction zone A4, and a Class V mixing zone A5. The top end cap (1) is equipped with a Class I fuel channel and Class I and II oxidant channels. The Class I and II oxidant channels are connected to the Class I combustion zone A1. The upper end cap (4) has fuel inlets that correspond to the three spiral channels. The bottom end cap (11) has a multi-element hot fluid outlet. The outside of the Class I fuel igniter is equipped with a core tube (2) and an inner sleeve (3). The inner sleeve (3) is connected to the top end cap (1). The Class I combustion chamber spiral cooling wall (5) is connected to the inner sleeve (3). The lower side wall of the core tube (2) has a ring of oblique holes along the circumferential direction. A large diameter hole is opened at the closed end of the bottom of the core tube (2). The circular hole of the igniter terminal (14) is a circular hole of the same diameter. The oblique hole and the circular hole on the bottom closed end serve as the Class I fuel injection port (16) for Class I fuel to be injected into the Class I combustion zone A1. The top end cap (1) is provided with Class I fuel inlet N1 and Class I and Class II oxidant inlet N2 respectively. The annular gap between the inner wall of the core tube (2) and the outer wall of the igniter terminal (14) forms the Class I fuel channel. The annular gap between the outer wall of the core tube (2) and the inner wall of the inner sleeve (3) forms the Class I and Class II oxidant channels. Three independent spiral channels are set on the outside of the three-stage spiral wall (6) of the reaction chamber as the Class III fuel and oxidant spiral channel (6-1) and the Class IV fuel spiral channel (6-1). 6-2) and V-level mixed water spiral channel (6-3); the upper end cover (4) is provided with II-level fuel inlet N3, III-level fuel and oxidant inlet N4, IV-level fuel inlet N5 and V-level mixed water inlet N6. II-level fuel inlet N3 is connected to the spiral channel on the outer wall of the I-level combustion chamber spiral cooling wall (5). The spiral channel on the outer wall of the I-level combustion chamber spiral cooling wall (5) forms the channel for II-level fuel. III-level fuel and oxidant inlet N4 is connected to III-level fuel and oxidant spiral channel (6-1). IV-level fuel inlet N5 is connected to IV-level fuel spiral channel (6-2). V-level mixed water inlet N6 is connected to V-level mixed water spiral channel (6-3).Several through holes are opened on the last turn of the Stage III fuel and oxidant spiral channel (6-1) as Stage III fuel and oxidant inlets (18). The Stage III fuel and oxidant spiral channel (6-1) stops at the Stage III fuel and oxidant inlet (18). The area between the outlet of the Stage I combustion chamber spiral cooling wall (5) and the Stage III fuel and oxidant inlet (18) is the Stage II combustion zone A2. Several through holes are opened on the last turn of the Stage IV fuel spiral channel (6-2) as Stage IV fuel inlets (19). The Stage IV fuel spiral channel (6-2) 6-2) The process stops at the Class IV fuel inlet (19). The area between the Class III fuel and oxidizer inlet (18) and the Class IV fuel inlet (19) is the Class III reaction zone A3. Several arrayed small holes are opened at the bottom of the Class V mixed water spiral channel (6-3) as the Class V mixed water inlet (20). The area between the Class IV fuel inlet (19) and the Class V mixed water inlet (20) forms the Class IV reaction zone A4. The area between the area where the Class V mixed water inlet (20) is located and the hydraulic turbine inlet cover (9) is the Class V mixing zone A5.

2. The supercritical hydrothermal combustion type downhole multi-element thermal fluid generator according to claim 1, characterized in that, The lower part of the pressure wall (7) is provided with a rotating shaft (12) and a hydraulic turbine inlet cover (9); the rotating shaft (12) passes through the center of the bottom end cover (11), the middle part of the rotating shaft (12) passes through the hydraulic turbine inlet cover (9), the hydraulic turbine (10) is installed at the lower part of the rotating shaft (12), the hydraulic turbine fluid inlet N7 is provided on the hydraulic turbine inlet cover (9), and the rotating shaft (12) is rotatably connected to the hydraulic turbine inlet cover (9) and the bottom end cover (11) respectively through a thrust bearing.

3. The supercritical hydrothermal combustion type downhole multi-element thermal fluid generator according to claim 1, characterized in that, A rotating scraper (8) is installed on the upper part of the rotating shaft (12).

4. The supercritical hydrothermal combustion type downhole multi-element thermal fluid generator according to claim 1, characterized in that, The fuel supplied to the Class I combustion zone A1, Class II combustion zone A2, Class III reaction zone A3, and Class IV reaction zone A4 is the same, while the blended water supplied to the Class V blended water inlet N6 is oilfield wastewater or softened water.

5. A method for generating multi-element downhole thermal fluids using supercritical hydrothermal combustion, characterized in that, Based on the supercritical hydrothermal combustion type downhole multi-element thermal fluid generator according to any one of claims 1-4, a first-stage combustion zone, a second-stage combustion zone, a third-stage reaction zone, a fourth-stage reaction zone, and a fifth-stage mixing zone are set up. First-stage fuel at room temperature is injected into the first-stage combustion zone A1, where a supercritical hydrothermal combustion reaction occurs with the assistance of an oxidant. Second-stage fuel is spirally injected into the second-stage combustion zone A2, where it rapidly mixes with the high-temperature combustion products of the first-stage fuel and the remaining oxidant, undergoing a supercritical hydrothermal combustion reaction with the assistance of an oxidant. Third-stage fuel is injected into the third-stage reaction zone A3. The fuel is mixed with the high-temperature combustion products of upstream Stage II fuel and heated to the required preheating temperature. Under the assistance of an oxidant, a rapid supercritical water oxidation reaction occurs, resulting in a rapid temperature rise. Stage IV fuel is injected into Stage IV reaction zone A4 and mixed with the high-temperature combustion products of upstream Stage III fuel and the remaining oxidant. It is then heated to the required preheating temperature and undergoes a rapid supercritical water oxidation reaction under the assistance of an oxidant, resulting in a rapid temperature rise. Stage V blended water is injected into Stage V blending zone A5 and mixed with the high-temperature products of rapid supercritical water oxidation of upstream Stage IV fuel, generating a high-temperature and high-pressure supercritical multi-element thermal fluid.

6. The supercritical hydrothermal combustion type downhole multi-element thermal fluid generation method according to claim 5, characterized in that, In the first-stage combustion zone A1, combustion is initiated by forced ignition, generating high-temperature supercritical water, which then heats the downstream reaction zones. Once the first-stage combustion zone A1, second-stage combustion zone A2, third-stage reaction zone A3, and fourth-stage reaction zone A4 are filled with supercritical water, establishing the initial conditions for stable reactions of each fuel stage, the reaction fuels and oxidants of each stage are injected, resulting in supercritical hydrothermal combustion and rapid supercritical water oxidation reactions, until the first-stage combustion zone A1, second-stage combustion zone A2, third-stage reaction zone A3, and fourth-stage reaction zone A4 reach normal operating conditions. The fifth-stage blended water flows into the fifth-stage blending zone A5, mixing with the upstream high-temperature reaction fluid to generate a supercritical multi-element thermal fluid. After stable operation, the first-stage fuel is cooled and injected for stable combustion through thermal auto-ignition, while maintaining the stable reaction process of each fuel stage and continuously generating a large flow of multi-element thermal fluid.

7. The supercritical hydrothermal combustion type downhole multi-element thermal fluid generation method according to claim 5, characterized in that, The pressure of the supercritical multi-element thermofluid in the reaction zone is reduced by using a hydraulic turbine (10), and the hydraulic turbine (10) drives the scraper device to rotate and scour the inner wall of the reaction chamber.

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