Experimental device for achieving oil and gas well plugging by simulating underground thermite to melt bismuth alloy

Abstract

The invention discloses an experimental device for realizing oil and gas well plugging by simulating an underground thermite to melt bismuth alloy, which comprises a pressure container, a combustion system, a data acquisition system, a gas supply system and a power supply system, and is characterized in that the combustion system is arranged in the pressure container and comprises an electric ignition experiment table, an experimental sleeve and an electric ignition wire; the outer surface of the experiment sleeve is coated with bismuth alloy, the experiment sleeve is placed on the electric ignition experiment table, the electric ignition wire extends into the experiment sleeve in the using state, the power supply system is connected with the electric ignition wire, the gas supply system is communicated with the pressure container, and a heating device is arranged in the pressure container. The data acquisition system comprises a high-speed camera and a thermocouple signal collector, and the thermocouple signal collector is connected with the thermocouple through a signal line penetrating through the pressure container. According to the invention, by adding the pressure container, the gas supply system and the heating device, the experiment of melting the bismuth alloy by the thermite in the underground environment is simulated, and data support is provided for oil-gas well plugging.

Description

Technical Field

[0001] The invention relates to an experimental device for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging, belonging to the technical field of electric ignition. Background Art

[0002] Since rotary drilling technology became the industry standard in 1859, more than 65,000 oil and gas fields have been discovered worldwide, ranging from conventional pressure formations to ultra-deep formations, high-temperature and high-pressure wells. Despite continuous advancements in drilling and completion technologies, the early industry regulatory system lacked systematic definitions and standards for the management of oil and gas wells after their lifecycles ended, leading many operators to view permanent plugging and abandonment (P&A) as an uneconomical burden. The resulting large number of abandoned wells and observation wells has become an environmental risk, primarily manifested in problems such as continued hydrocarbon leakage, water layer contamination, and wellbore gas migration. The primary goal of P&A operations is to restore the integrity of formations damaged by drilling and production disturbances by establishing an effective barrier system, thereby permanently isolating oil and gas reservoirs from the surface and other formations.

[0003] Portland cement has long been widely used in oil well plugging operations due to its low cost, easy operation and mature industrial base. However, this material has many limitations under long-term downhole service conditions, such as high brittleness, significant chemical shrinkage, poor thermal stability, easy cracking, and insufficient durability in acidic or high CO2 concentration environments. These factors together affect its reliability under complex working conditions. To solve the above problems, researchers have developed a variety of new sealing materials. Among them, Khalifeh et al. proposed a technical path for modified geopolymers, by regulating their chemical composition to improve compressive strength, ductility and resistance to chemical corrosion, thereby forming a dense and stable sealing structure. In addition, thermosetting polymers, thermoplastic polymers, elastomers and metal materials have also been gradually introduced to meet the high-performance sealing needs in complex downhole environments.

[0004] Among the many candidate materials, bismuth-based alloys have attracted particular attention due to their low melting point, high fluidity, and excellent corrosion resistance. Liquid bismuth can achieve complete filling and deformation matching in the wellbore, potentially forming a tight, sealed plugging structure. However, achieving bismuth melting downhole still faces significant energy input challenges. To overcome this issue, researchers have proposed using thermite reaction as an in-situ heat source. This reaction utilizes the high-temperature, exothermic reaction between aluminum powder and iron oxide to release a large amount of heat, sufficient to drive the melting and expansion of the bismuth material downhole.

[0005] Chinese invention patent CN119914897A discloses an electrically started thermite ignition device and its use method. The handheld stun gun includes two handheld stun gun electrode posts, a power supply, and a stun gun housing. One end of one handheld stun gun electrode post is electrically connected to the positive pole of the power supply, and one end of the other handheld stun gun electrode post is electrically connected to the negative pole of the power supply. The other ends of the two handheld stun gun electrode posts extend out of the stun gun housing respectively. The filling bucket includes two filling bucket electrode posts, a filling bucket housing, a tungsten filament, and thermite. One end of one filling bucket electrode post is connected to one end of the tungsten filament, and one end of the other filling bucket electrode post is connected to the other end of the tungsten filament. The other ends of the two filling bucket electrode posts are respectively in contact with the other ends of the two handheld stun gun electrode posts. Chinese invention patent CN115236264A provides an experimental device and experimental method for synchronously testing multiple combustion characteristics of thermite reaction, including a closed constant volume combustion system, an ignition system, a test system, and a data acquisition system; wherein the closed constant volume combustion system includes a closed constant volume burner body, a first plug, a second plug and a pressure relief valve, a combustion table, and a combustion plate; the ignition system includes an electrode rod, an insulating tube, a heating wire, a DC power supply, and a power cord arranged on the first plug; the test system includes a high-speed camera, an infrared temperature camera, a pressure sensor, and a data cable; the data acquisition system includes a computer for collecting high-speed camera image data, a computer for collecting infrared temperature and infrared image data, and a data collector and a computer for collecting pressure data from the pressure sensor.

[0006] Although the above patent can realize the convenient ignition and in-depth analysis of thermite, it cannot simulate the temperature and pressure conditions in underground oil and gas wells, and cannot achieve the purpose of melting bismuth alloy with thermite. Summary of the Invention

[0007] The purpose of the present invention is to provide an experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging, thereby resolving the technical defects of the prior art in that the temperature and pressure conditions in underground oil and gas wells cannot be simulated, and that thermite melting of bismuth alloy cannot be solved.

[0008] To solve the above problems, the technical solution adopted by the present invention is: an experimental device for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging, comprising a pressure vessel, a combustion system, a data acquisition system, a gas supply system and a power supply system. The combustion system is arranged in the pressure vessel, and includes an electric ignition test bench, an experimental sleeve and an electric ignition wire. The outer surface of the experimental sleeve is coated with bismuth alloy. When in use, the experimental sleeve is placed on the electric ignition test bench, and the thermite is placed therein. The electric ignition wire is inserted into the experimental sleeve when in use to ignite the thermite. The power supply system and the electric point are connected. The ignition wire connection is used to provide electrical energy to the electric ignition wire. The gas supply system is connected to the pressure vessel and is used to introduce nitrogen into the pressure vessel to simulate the underground pressure environment. A heating device is installed in the pressure vessel to heat the pressure vessel to simulate the underground temperature environment. The data acquisition system includes a high-speed camera and a thermocouple signal collector. The thermocouple signal collector is connected to the thermocouple installed on the experimental sleeve using a signal line passing through the pressure vessel to collect the temperature of the thermite. The pressure vessel is made of a transparent material. The high-speed camera is used to observe the melting and solidification process of the bismuth alloy.

[0009] As a further improvement of the present invention, a quartz tube is further included. The quartz tube is sleeved on the experimental sleeve and is used to collect the high-temperature melted bismuth alloy.

[0010] As a further improvement of the present invention, a notch is provided along the axial direction of the quartz tube, and fixing portions are provided on both sides of the notch toward the centerline of the quartz tube. Two slots are provided along the axis of the experimental sleeve, and the two slots respectively cooperate with the two fixing portions of the quartz tube. The outer surface of the experimental sleeve is coated with a bismuth alloy only on one side of the quartz tube between the two slots, and the thermocouple is provided on a portion of the experimental sleeve that is not coated with the bismuth alloy.

[0011] As a further improvement of the present invention, the electric ignition test bench includes a base, a support platform arranged on the base and two terminal posts arranged on the base. The two terminal posts are symmetrically distributed on both sides of the support platform. The support platform is used to support the experimental sleeve when in use. The two terminal posts are used to connect to the power supply system and are used to connect and support the electric ignition wire when in use.

[0012] As a further improvement of the present invention, it also includes a spring and a sleeve, both of which are sleeved on the terminal, and the sleeve is located above the spring and supported by the spring. A compression sleeve is provided on the terminal and is threadedly matched with the compression sleeve. The compression sleeve presses the two ends of the electric ignition wire between it and the sleeve and contacts the terminal.

[0013] As a further improvement of the present invention, a closing mechanism is provided at the bottom of the pressure vessel, the closing mechanism is sealed and fixed to the pressure vessel, and the bottom of the electric ignition test bench is threadedly matched with the closing mechanism.

[0014] As a further improvement of the present invention, the heating device includes a cover body and a heating wire. The cover body is arranged on the top of the pressure vessel to seal the top of the pressure vessel. The heating wire is arranged on the side of the cover body facing the inside of the pressure vessel. The heating wire is energized to heat the gas in the pressure vessel.

[0015] As a further improvement of the present invention, the gas supply system includes at least one high-pressure gas tank, which is connected to the pressure vessel by a gas inlet pipe. A gas valve is provided at the gas outlet of the high-pressure gas tank. The gas valve is opened to pass gas from the high-pressure gas tank into the pressure vessel to increase the pressure inside the pressure vessel, and the gas valve is closed to stop passing gas to the pressure vessel.

[0016] As a further improvement of the present invention, the pressure vessel is provided with a pressure gauge and a thermometer for detecting the pressure and temperature of the gas in the pressure vessel respectively.

[0017] As a further improvement of the present invention, the data acquisition system further includes a computer, which is signal-connected to the high-speed camera and the thermocouple signal collector and is used to collect data collected by the high-speed camera and the thermocouple signal collector.

[0018] In summary, the beneficial effects of the present invention are: 1. By adding a pressure vessel, using a gas supply system and a heating device, the present invention simulates the pressure and temperature environment of underground oil and gas wells, making experimental exploration more instructive for engineering practice. The combustion system ignites the thermite, which melts the bismuth alloy coated on the experimental casing. After combustion is complete, the melted bismuth alloy solidifies, thereby simulating the thermite melting bismuth alloy experiment in an underground environment and providing data support for oil and gas well plugging.

[0019] 2. The present invention provides a quartz tube outside the experimental casing to facilitate the collection of melted bismuth alloy. A high-speed camera can be used to clearly observe the melting of the bismuth alloy under different thermite formulations, thereby selecting a thermite formulation that is more suitable for practice.

[0020] 3. The present invention can observe the temperature changes of various thermite formulations in a simulated underground oil and gas well environment through the data acquisition system, providing strong data support for the adjustment and improvement of the thermite formulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention.

[0022] Figure 2 It is a structural schematic diagram of the combustion system in the present invention.

[0023] Figure 3 It is a rear view of the experimental sleeve and the quartz tube in the present invention.

[0024] Figure 4 It is a front view of the experimental sleeve and the quartz tube in the present invention.

[0025] Figure 5 It is a bottom view of the heating device of the present invention.

[0026] Figure 6 It is a structural schematic diagram of the connecting piece in the present invention.

[0027] Figure 7 It is a schematic diagram of the three-dimensional structure of the closing mechanism in the present invention.

[0028] Figure 8 It is a temperature-time curve diagram of the experiment of the present invention.

[0029] Among them: 1. Pressure vessel; 2. Combustion system; 3. Data acquisition system; 4. Gas supply system; 5. Power supply system; 6. Electric ignition test bench; 7. Experimental sleeve; 8. Electric ignition wire; 9. High-speed camera; 10. Thermocouple signal collector; 11. Thermocouple temperature measuring point; 12. Quartz tube; 13. Notch; 14. Fixing part; 15. Base; 16. Support platform; 17. Terminal; 18. Spring; 19. Sleeve; 20. Compression sleeve; 21. Closing mechanism; 22. Cover; 23. Heating wire; 24. High-pressure gas tank; 25. Pressure gauge; 26. Thermometer; 27. Computer; 28. Connector; 29. ​​Threaded hole. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0031] like Figure 1 The experimental device for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging shown in the figure includes a pressure vessel 1, a combustion system 2, a data acquisition system 3, a gas supply system 4 and a power supply system 5. The pressure vessel 1 is a cylindrical shell. When in use, the top and bottom ends of the pressure vessel 1 are closed and sealed to ensure the internal pressure. The combustion system 2 is set in the pressure vessel 1. Figure 1 and Figure 2 As shown, the combustion system 2 includes an electric ignition test bench 6, a test sleeve 7 and an electric ignition wire 8. The electric ignition test bench 6 is located inside the pressure vessel 1 and at the bottom of the pressure vessel 1. The outer surface of the test sleeve 7 is coated with a bismuth alloy, wherein the bismuth alloy can melt at high temperature and solidify when the temperature drops.

[0032] like Figure 1 and Figure 2As shown, in the use state, the experimental sleeve 7 is placed on the electric ignition test table 6, and its end is supported by the electric ignition test table 6. The experimental sleeve 7 contains thermite, and the electric ignition wire 8 extends into the experimental sleeve 7 in the use state. The electric ignition wire 8 is energized to ignite the thermite. The combustion of the thermite generates heat to melt the bismuth alloy.

[0033] like Figure 1 As shown, the power supply system 5 is connected to the electric ignition wire 8 for providing electrical energy to the electric ignition wire 8, wherein the power supply system 5 is arranged on the outside of the pressure vessel 1, and is connected to the electric ignition wire 8 by a wire extending into the pressure vessel 1, and the gas supply system 4 is located on the outside of the pressure vessel 1 and is connected to the pressure vessel 1, and is used to introduce nitrogen into the pressure vessel 1 to simulate the underground pressure environment. The present invention introduces nitrogen into the pressure vessel 1 to increase the pressure in the pressure vessel 1 so that the pressure in the pressure vessel 1 is equivalent to the underground pressure. The present invention is provided with a heating device in the pressure vessel 1, and the heating device is used to heat the gas in the pressure vessel 1 to simulate the underground temperature environment.

[0034] like Figure 1 As shown, the data acquisition system 3 in the present invention includes a high-speed camera 9 and a thermocouple signal collector 10. The thermocouple signal collector 10 is connected to the thermocouple provided on the experimental sleeve 7 by a signal line passing through the pressure vessel 1 to collect the temperature of the thermite. The pressure vessel 1 is made of a transparent material. In the present invention, the pressure vessel 1 is preferably made of quartz. The high-speed camera 9 is disposed outside the pressure vessel 1 and is disposed in the direction of the pressure vessel 1 to observe the melting and solidification process of the bismuth alloy.

[0035] like Figure 1 and Figure 2 As shown, in order to facilitate the collection of melted bismuth alloy and the observation of its melting and solidification conditions, the present invention is provided with a quartz tube 12, which is sleeved on the experimental sleeve 7. When the bismuth alloy melts at high temperature, it flows to the lower part of the experimental sleeve 7 and flows between the experimental sleeve 7 and the quartz tube 12. The quartz tube 12 collects the high-temperature melted bismuth alloy. Figure 4 and Figure 4As shown, the best embodiment of the present invention is provided with a notch 13 along the axial direction of the quartz tube 12, that is, the cross-sectional profile of the quartz tube 12 is not a perfect circle, wherein the central angle corresponding to the cross-sectional profile of the quartz tube 12 is greater than 180 degrees, and a fixing portion 14 is provided on both sides of the notch 13 toward the center line direction of the quartz tube 12. The fixing portion 14 is made of the same material as the quartz tube 12, both made of transparent quartz material, and the quartz tube 12 and the fixing portion 14 are integrally formed. The present invention has two card grooves along the axis on the outer surface of the experimental sleeve 7, the width of the card groove is slightly larger than the thickness of the fixing portion 14, and the two card grooves are respectively matched with the two fixing portions 14 of the quartz tube 12. In use, the quartz tube 12 is put on the experimental sleeve and tube 7 from one end, and the two fixing portions 14 are separated. The quartz tube 12 is pushed axially to fit over the experimental sleeve 7, corresponding to the two slots. During this process, the two fixing portions 14 slide within the two slots, respectively. In the present invention, the height of the quartz tube 12 is equal to the height of the two fixing portions 14 and slightly less than the height of the experimental sleeve 7. The outer surface of the experimental sleeve 7 in the present invention is coated with a bismuth alloy only on the side of the quartz tube 12 between the two slots, while the side of the experimental sleeve 7 away from the quartz tube 12 is not coated with a bismuth alloy. A thermocouple is disposed on the portion of the experimental sleeve 7 not coated with the bismuth alloy. The number of thermocouples in the present invention is at least one. If the number of thermocouples exceeds one, they are evenly spaced from top to bottom on the experimental sleeve 7, thereby enabling detection of the temperature of the thermite at different heights.

[0036] like Figure 1 and Figure 2As shown, the electric ignition test bench 6 in the present invention includes a base 15, a support platform 16 arranged on the base 15 and two terminal posts 17 arranged on the base 15. The two terminal posts 17 in the present invention are symmetrically distributed on both sides of the support platform 16, and the height of the terminal posts 17 is greater than the height of the support platform 16. The support platform 16 is used to support the experimental sleeve 7 when in use. The two terminal posts 17 are used to connect to the power supply system 5. The two ends of the electric ignition wire 8 are respectively connected to the two terminal posts 17. When in use, the electric ignition wire 8 is supported by the two terminal posts 17. The present invention is preferably provided with two springs 18 and two sleeves 19, and the two springs 18 and the two sleeves 19 are respectively sleeved on the terminal 17, that is, each terminal 17 is sleeved with a spring 18 and a sleeve 19, and the sleeve 19 is located above the spring 18 and supported by the spring 18, and the bottom end of the spring 18 is supported by the base 15, and the top end of the spring 18 contacts the bottom end of the sleeve 19, so that the spring 18 supports the sleeve 19 upward. The spring 18 in the present invention is in a compressed state and pushes the sleeve 19 upward. A compression sleeve 20 is provided on the terminal 17 and is threadedly matched with it. The compression sleeve 20 is located on the sleeve 1 9, the compression sleeve 20 compresses the two ends of the electric ignition wire 8 between it and the sleeve 19 and contacts the terminal 17. When the present invention is in use, the compression sleeve 20 can be twisted according to the height of the experimental sleeve 7. When the compression sleeve 20 moves downward, the compression sleeve 20 pushes the compression spring 18 to further contract through the sleeve 19, and when the compression sleeve 20 moves upward, the spring 18 pushes the sleeve 19 to move upward, so that the electric ignition wire 8 is always clamped between the sleeve 19 and the compression sleeve 20. The present invention can adjust the height of the electric ignition wire 8 according to the height of the experimental sleeve 7 by adjusting the position of the compression sleeve 20 on the terminal 17.

[0037] like Figure 1 、 Figure 2 、 Figure 6 and Figure 7 As shown, in order to ensure the pressure in the pressure vessel 1 and avoid the reduction of the air pressure in the pressure vessel 1 due to leakage, the present invention is provided with a closing mechanism 21 at the bottom of the pressure vessel 1, and the closing mechanism 21 is sealed and fixed to the pressure vessel 1. The bottom of the electric ignition test bench 6 is threadedly matched with the closing mechanism 21. The present invention is provided with a connecting piece 28 at the bottom of the base 15 of the electric ignition test bench 6. The electric ignition test bench 6 and the connecting piece 28 can be detachably connected by multiple bolts. The lower part of the connecting piece 28 is provided with an external thread, and a threaded hole 29 is provided on the closing mechanism 21. The threaded portion of the connecting piece 28 extends into the threaded hole 29 and is threadedly matched with the closing mechanism 21, so that the electric ignition test bench 6 is detachably mounted on the closing mechanism 21.

[0038] like Figure 5As shown, the heating device in the present invention includes a heating wire 23 and a circular plate-shaped cover 22. The cover 22 is arranged on the top of the pressure vessel 1 to seal the top of the pressure vessel 1. The cover 22 in the present invention is fixedly connected to the top of the pressure vessel 1. The heating wire 23 is arranged on the side of the cover 22 facing the inside of the pressure vessel 1. The heating wire 23 is energized to heat the gas in the pressure vessel 1. The heating pink ribbon 23 in the present invention is powered by a separate power supply, which is not shown in the figure.

[0039] like Figure 1 As shown, the gas supply system 4 in the present invention includes at least one high-pressure gas tank 24, which is connected to the pressure vessel 1 by a gas inlet pipe. A gas valve is provided at the gas outlet of the high-pressure gas tank 24. The gas valve is opened to allow gas to be passed from the high-pressure gas tank 24 to the pressure vessel 1 to increase the pressure in the pressure vessel 1. The gas valve is closed to stop the flow of gas to the pressure vessel 1. When there are multiple high-pressure gas tanks 14, each high-pressure gas tank 14 is connected to a gas pipe, and all the gas pipes are connected to the pressure vessel 1 through the same gas inlet pipe.

[0040] like Figure 1 As shown, the present invention is provided with a pressure gauge 25 and a thermometer 26 on the pressure vessel 1, which are used to detect the pressure and temperature of the gas in the pressure vessel 1, respectively. When the pressure and temperature in the pressure vessel 1 reach the pressure and temperature corresponding to the underground environment, the thermite is ignited to melt the bismuth alloy closer to the underground environment.

[0041] like Figure 1 As shown, the data acquisition system 3 of the present invention is provided with a computer 27, which is signal-connected to the high-speed camera 9 and the thermocouple signal collector 10, and is used to collect data collected by the high-speed camera 9 and the thermocouple signal collector. The power supply system 5 of the present invention is connected to a transformer, which can adjust the operating voltage of the electric ignition wire 8.

[0042] The experiment of the present invention for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging includes the following steps: Step 1: Weigh a certain mass of thermite, place it into the experimental casing 7 and compact it.

[0043] Step 2: Place the experimental sleeve 7 on the support platform 16 of the electric ignition test bench 6, where the corresponding position on the experimental sleeve 7 is coated with bismuth alloy. Put the quartz tube 12 on the experimental sleeve 7, and install the connector 28 on the sealing mechanism 21 and tighten it to prevent pressure leakage.

[0044] Step 3: Open the valve of the high-pressure gas tank 24 , adjust the pressure in the pressure vessel 1 to the set pressure, and then close the valve of the high-pressure gas tank 24 .

[0045] Step 4: Turn on the heating device, adjust the temperature in the pressure vessel 1 to the set temperature and turn off the heating device.

[0046] Step 5: Adjust the transformer to the required voltage.

[0047] Step 6: Synchronously start the high-speed motor and high-speed camera 9 and the thermocouple signal collector 10.

[0048] Step 7. Turn on the transformer power supply and disconnect the transformer power supply after the thermite burns.

[0049] Step 8: Collect experimental data using the data acquisition system 3.

[0050] The present invention provides the following specific application example: first weigh 2.5g of thermite (wherein the aluminum powder particle size is 1µm, and the mass ratio of Al to Fe2O3 is 1:3), and add SiO2 as a flame retardant. The present invention sets up five groups of parallel experiments, in which the mass fractions of SiO2 are 15%, 20%, 25%, 30% and 35% of the total mass, respectively.

[0051] After dry grinding and uniform mixing, the above powders are filled into the experimental sleeve 7, which is made of stainless steel and has an inner diameter of 5 mm. The powders are then compacted layer by layer to a height of 2 mm from the mouth of the experimental sleeve 7.

[0052] Put the quartz tube 12 on the experimental sleeve 7, and place the experimental sleeve 7 in the pressure vessel 1. Connect a thermocouple (where the accuracy of the thermocouple is ±1.5%), then seal the pressure vessel 1, and use a heating device to heat the gas in the pressure vessel 1 to 25°C (temperature control accuracy is ±0.5°C). Then, introduce high-purity nitrogen into the pressure vessel 1, adjust the initial pressure of the pressure vessel 1 to 1.01325 bar, close the gas valve of the high-pressure gas tank 24, and maintain the pressure for 5 minutes to test the air tightness.

[0053] The DC transformer output was set to 8V, and the high-speed camera (10,000 fps) and the thermocouple signal collector (sampling rate 1 kHz) were triggered synchronously. The transformer power supply was also started to ignite the reaction.

[0054] The whole process of combustion is recorded and the computer 27 is used to generate the temperature-time curve. Figure 8 The temperature distribution data shown is obtained, and the residue is collected for microscopic characterization. Collecting the residue for microscopic characterization is a prior art and is not an improvement of the present invention, so it will not be described in detail in the present invention.

[0055] Any portion of the above description not specifically described herein is prior art or can be implemented using prior art. Furthermore, the specific embodiments described herein are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. In other words, any equivalent variations and modifications made within the scope of the present invention should be considered within the technical scope of the present invention.

Claims

1. An experimental device simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging, characterized by: The device comprises a pressure vessel, a combustion system, a data acquisition system, a gas supply system and a power supply system. The combustion system is arranged in the pressure vessel and comprises an electric ignition test bench, an experimental sleeve and an electric ignition wire. The outer surface of the experimental sleeve is coated with a bismuth alloy. When in use, the experimental sleeve is placed on the electric ignition test bench and contains thermite. The electric ignition wire extends into the experimental sleeve when in use and is used to ignite the thermite. The power supply system is connected to the electric ignition wire and is used to provide electrical energy to the electric ignition wire. The gas supply system is connected to the pressure vessel and is used to pass nitrogen into the pressure vessel to simulate the underground pressure environment. A heating device is arranged in the pressure vessel and is used to heat the pressure vessel to simulate the underground temperature environment. The data acquisition system comprises a high-speed camera and a thermocouple signal collector. The thermocouple signal collector is connected to the thermocouple arranged on the experimental sleeve by a signal line passing through the pressure vessel and is used to collect the temperature of the thermite. The pressure vessel is made of a transparent material. The high-speed camera is used to observe the melting and solidification process of the bismuth alloy.

2. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The device also includes a quartz tube, which is sleeved on the experimental sleeve and is used for collecting the high-temperature melted bismuth alloy.

3. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 2, characterized in that: The quartz tube is provided with a notch along its axis, and fixing portions are provided on both sides of the notch toward the centerline of the quartz tube. Two slots are provided on the experimental sleeve along the axis, and the two slots respectively cooperate with the two fixing portions of the quartz tube. The outer surface of the experimental sleeve is coated with bismuth alloy only on one side of the quartz tube between the two slots. The thermocouple is provided on the portion of the experimental sleeve that is not coated with bismuth alloy.

4. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The electric ignition test bench includes a base, a support platform arranged on the base and two terminal posts arranged on the base. The two terminal posts are symmetrically distributed on both sides of the support platform. The support platform is used to support the experimental sleeve when in use. The two terminal posts are used to connect to the power supply system and are used to connect and support the electric ignition wire when in use.

5. The experimental device for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging according to claim 4, characterized in that: It also includes a spring and a sleeve, both of which are sleeved on the terminal, and the sleeve is located above the spring and supported by the spring. A compression sleeve is provided on the terminal to cooperate with its thread. The compression sleeve presses the two ends of the electric ignition wire between it and the sleeve and contacts the terminal.

6. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The bottom of the pressure vessel is provided with a closing mechanism, which is sealed and fixed to the pressure vessel, and the bottom of the electric ignition test bench is threadedly matched with the closing mechanism.

7. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The heating device includes a cover and a heating wire. The cover is arranged on the top of the pressure vessel to seal the top of the pressure vessel. The heating wire is arranged on the side of the cover facing the pressure vessel. The heating wire is energized to heat the gas in the pressure vessel.

8. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The gas supply system includes at least one high-pressure gas tank, which is connected to the pressure vessel by a gas inlet pipe. A gas valve is provided at the gas outlet of the high-pressure gas tank. The gas valve is opened to allow gas to flow from the high-pressure gas tank to the pressure vessel to increase the pressure inside the pressure vessel, and the gas valve is closed to stop the flow of gas to the pressure vessel.

9. The experimental device for simulating underground thermite melting of bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The pressure vessel is provided with a pressure gauge and a thermometer, which are used to detect the pressure and temperature of the gas in the pressure vessel respectively.

10. The experimental device for simulating underground thermite melting bismuth alloy to achieve oil and gas well plugging according to claim 1, characterized in that: The data acquisition system also includes a computer, which is connected to the high-speed camera and the thermocouple signal collector and is used to collect data collected by the high-speed camera and the thermocouple signal collector.

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