Simulation experiment system for interaction of natural gas hydrate stratum and wellbore working fluid

Abstract

The invention discloses a natural gas hydrate stratum and wellbore working fluid interaction simulation experiment system, and relates to the field of experiment instruments, the system comprises: an autoclave in which a simulation stratum and a vertical simulation wellbore with a liquid permeable hole are arranged; the gas injection unit and the liquid injection unit are respectively used for injecting methane gas and working liquid into the autoclave; the shaft working fluid circulating unit comprises a magnetic circulating pump and a high-pressure filter and is used for driving the working fluid to circulate in the simulation shaft; the vacuum preparation module is used for preparing an experiment initial environment; and the monitoring unit comprises a temperature sensor, a pressure sensor, a displacement sensor, an ultrasonic detection system, a resistivity imaging system and a microscopic imaging system, and is used for monitoring and collecting parameter changes of the simulated stratum under the action of multiple physical fields in real time. The device can truly simulate the circulation invasion process of the shaft working fluid, and comprehensively evaluate the influence on the formation stability of the natural gas hydrate and the phase change of the hydrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of experimental apparatus, in particular to a natural gas hydrate formation and wellbore working fluid interaction simulation experiment system. BACKGROUND

[0002] Natural gas hydrate refers to a kind of cage-shaped crystal substance generated by natural gas and water under certain temperature and pressure, which can burn when meeting fire, commonly known as "flammable ice". Natural gas hydrate can exist in nature in many ways. Based on the characteristics of natural gas hydrate, it is different from the development of conventional energy. It is shown that natural gas hydrate is buried in the ocean floor as a solid, and the molecular structure changes from solid to gas during the exploitation process.

[0003] Wellbore stability is the core of safe and efficient drilling of natural gas hydrate, and high-performance wellbore working fluid is the key to maintaining wellbore stability. Wellbore working fluid is the general term for all working fluids in the process of oil and gas well operation, including drilling fluid, completion fluid, cement slurry, perforating fluid, spacer fluid, packer fluid, gravel packing fluid, workover fluid, fracturing fluid, acid fluid, displacement fluid, etc.

[0004] During the circulation of wellbore working fluid, the working fluid will invade the formation, on the one hand, affecting the phase change and decomposition of natural gas hydrate, and the decomposition of natural gas hydrate will cause the reduction of formation strength; on the other hand, the working fluid will also cause hydration with clay minerals in the formation, affecting the wellbore stability of the hydrate formation. During this process, hydrate and mineral particles in the formation will circulate with the working fluid, thereby affecting the density and viscosity of the working fluid.

[0005] At present, the existing natural gas hydrate formation simulation experiment device can only simulate the decomposition of natural gas hydrate during the process of working fluid invading the natural gas hydrate formation from the end face, lacks research means for simulating the interaction mechanism of working fluid and natural gas hydrate formation during wellbore circulation, and the existing natural gas hydrate formation simulation sample preparation technology also cannot simulate the actual natural gas hydrate formation conditions, resulting in that the existing natural gas hydrate formation simulation experiment device cannot simulate the influence of working fluid on natural gas hydrate formation. SUMMARY

[0006] The purpose of the present application is to provide a natural gas hydrate formation and wellbore working fluid interaction simulation experiment system to solve the problems existing in the prior art and realize the simulation test of the influence of drilling fluid on the wellbore stability of natural gas hydrate formation.

[0007] To achieve the above purpose, the present application provides the following scheme: The present application provides a natural gas hydrate formation and wellbore working fluid interaction simulation experiment system, comprising: A high-pressure kettle, wherein a simulated formation of a formation where natural gas hydrate exploitation is simulated is arranged in the high-pressure kettle, a center of the simulated formation is vertically provided with a simulated wellbore, and a side wall of the simulated wellbore is provided with a plurality of liquid-permeable holes; An air injection unit, wherein the air injection unit comprises a methane gas source and an air compressor, an air outlet of the methane gas source is communicated with an air inlet of the air compressor, and an air outlet of the air compressor is communicated with the high-pressure kettle; A liquid injection unit, wherein the liquid injection unit comprises a constant-speed constant-pressure pump and a stirring container, a liquid outlet of the constant-speed constant-pressure pump is communicated with a top end of the stirring container, the stirring container is used for containing wellbore working fluid, and a liquid outlet of the stirring container is communicated with a bottom end of the high-pressure kettle; A wellbore working fluid circulating unit, wherein the wellbore working fluid circulating unit comprises a magnetic circulating pump and a high-pressure filter, a liquid inlet of the high-pressure filter is communicated with a top end of the simulated wellbore through a first pipeline, a liquid outlet of the high-pressure filter is communicated with a liquid inlet of the magnetic circulating pump, and a liquid outlet of the magnetic circulating pump is communicated with a bottom end of the simulated wellbore; A vacuum preparation module, wherein the vacuum preparation module comprises a vacuum device and a sealed intermediate container, a middle part of the first pipeline is communicated with one end of a second pipeline, the other end of the second pipeline extends into a top part of the intermediate container, a suction port of the vacuum device is communicated with a top end of the intermediate container, and a bottom end of the intermediate container is provided with a first discharge pipe, and the first discharge pipe is provided with a first vent valve; A monitoring unit, wherein the monitoring unit comprises a computer, a plurality of temperature sensors, a plurality of pressure sensors, a plurality of displacement sensors, and a first data acquisition system, all the temperature sensors are distributed in the simulated formation in a plurality of layers along a vertical direction, all the pressure sensors are distributed in the simulated formation in a plurality of layers along the vertical direction, and the displacement sensors are distributed on a top end inner wall and a side inner wall of the high-pressure kettle; the temperature sensors, the pressure sensors, and the displacement sensors are signal-connected with the first data acquisition system, and the first data acquisition system is signal-connected with the computer.

[0008] Preferably, the monitoring unit further comprises an ultrasonic detection system, and the ultrasonic detection system comprises three pairs of ultrasonic probes, each pair of the ultrasonic probes comprises one transmitting probe and one receiving probe which is oppositely arranged with the transmitting probe; The first pair of the transmitting probe and the receiving probe of the ultrasonic probes are arranged on the first side wall and the second side wall of the autoclave respectively; the second pair of the transmitting probe and the receiving probe of the ultrasonic probes are arranged on the third side wall and the fourth side wall of the autoclave respectively; and the third pair of the transmitting probe and the receiving probe of the ultrasonic probes are arranged on the top wall and the bottom wall of the autoclave respectively.

[0009] Preferably, the monitoring unit further comprises a resistivity imaging system, the resistivity imaging system comprising a loop electrode array and a resistivity inspection instrument, the loop electrode array being inserted in the simulated formation, and the loop electrode array being signal connected with the resistivity inspection instrument.

[0010] Preferably, the monitoring unit further comprises a microscopic imaging system, the microscopic imaging system comprising a microscopic imaging lens and a second data acquisition system, the microscopic imaging lens being fixedly arranged outside the autoclave, the microscopic imaging lens being opposite to an observation window on the autoclave, and the microscopic imaging lens being signal connected with the computer through the second data acquisition system.

[0011] Preferably, the mobile support further comprises at least three casters arranged at the bottom end of the mobile support, a first overturning shaft and a second overturning shaft being rotatably connected to the mobile support, the second overturning shaft being coaxial with the first overturning shaft, the first overturning shaft and the second overturning shaft being fixedly connected with the autoclave respectively, a speed reducer being fixedly arranged on the mobile support, the speed reducer being a worm and gear speed reducer with self-locking function, an output shaft of the speed reducer being coaxial with and fixedly connected with the second overturning shaft, and a hand wheel being fixedly arranged on an input shaft of the speed reducer.

[0012] Preferably, the autoclave comprises a barrel, a top cover and a bottom cover, the top cover being detachably connected with the top end of the barrel, the bottom cover being detachably connected with the bottom end of the barrel, a sealing ring being arranged between the top cover and the barrel and between the bottom cover and the barrel respectively, the top cover and the bottom cover being respectively provided with through holes corresponding to the simulated wellbore, and the simulated wellbore passing through the through holes of the top cover and the bottom cover.

[0013] Preferably, the liquid extraction unit comprises a solid-liquid separator, a first storage tank, a second storage tank and a gas-liquid separator, the feed inlet of the solid-liquid separator being communicated with the second pipeline, the solid outlet of the solid-liquid separator being communicated with the first storage tank, the liquid outlet of the solid-liquid separator being communicated with the feed inlet of the gas-liquid separator through a third pipeline, the liquid outlet of the gas-liquid separator being communicated with the second storage tank, and the gas outlet of the gas-liquid separator being connected with an exhaust pipe.

[0014] Preferably, a first filter is arranged on the third pipeline, and a dryer and a gas flow meter are arranged on the exhaust pipe.

[0015] Preferably, the temperature control unit comprises a thermostat tank and a jacket fixedly sleeved outside the autoclave, a liquid outlet of the thermostat tank is communicated with a liquid inlet of the jacket, and a liquid outlet of the jacket is communicated with a liquid return port of the thermostat tank.

[0016] Preferably, the liquid injection unit further comprises a condenser and a preheater arranged in parallel, wellbore working fluid flowing out of the liquid outlet of the stirring container enters the autoclave after passing through the condenser or the preheater; the condenser is used for cooling the wellbore working fluid flowing out of the liquid outlet of the stirring container to a set temperature, and the preheater is used for heating the wellbore working fluid flowing out of the liquid outlet of the stirring container to a set temperature.

[0017] The present application has the following technical effects relative to the prior art: The natural gas hydrate formation and wellbore working fluid interaction simulation experiment system simulates the exploitation process of natural gas hydrate, monitors the temperature, pressure and displacement parameters in the simulated formation, and explores the influence of the simulated wellbore working fluid on the formation in the exploitation process of natural gas hydrate by ultrasonic testing, resistivity imaging and microscopic imaging of the simulated formation. By arranging a simulated wellbore with a liquid permeable hole and establishing a wellbore working fluid circulation unit, the dynamic circulation process simulation of the wellbore working fluid in the simulated wellbore is realized, overcoming the limitation of the prior art that can only simulate static end face invasion, and more truly reflecting the complex working conditions of the interaction between the working fluid and the formation in annular flow, filtration invasion and the like in the drilling and completion operation process. The system integrates in-situ monitoring units of multiple parameters and multiple scales such as temperature, pressure, displacement, ultrasonic wave, resistivity and microscopic imaging, can synchronously and real-timely capture the whole process information of hydrate decomposition, formation strength deterioration, particle migration and wellbore instability induced by working fluid invasion from multiple dimensions such as macroscopic mechanical deformation and material state change to microscopic structure evolution, and provides rich data support for mechanism research. The simulated formation preparation, hydrate synthesis, working fluid circulation, multi-parameter monitoring, product separation and collection and post-processing (such as rock sample overturning and unloading) and other functional modules are organically integrated, forming a complete experimental research platform. Not only can the influence of the working fluid on the stability of the hydrate formation be evaluated, but also the reaction of hydrate decomposition on the performance (such as solid content and rheological property) of the working fluid can be synchronously studied, providing direct experimental basis for optimizing the working fluid formula and drilling process parameters. The system adopts an autoclave design and is equipped with a safety valve, a high-precision constant temperature and pressure control unit and a vacuum preparation module, can accurately reproduce the high-pressure and low-temperature environment of hydrate occurrence in deep sea or permafrost layer, and perform experiments within a safe range. A multi-channel data acquisition system ensures the synchronicity and accuracy of the monitoring data, and improves the reliability of the experimental results. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the experimental system for simulating the interaction between natural gas hydrate formations and wellbore working fluids according to the present invention. Figure: 100. Simulation Experimental System for Interaction between Natural Gas Hydrate Formation and Wellbore Working Fluid; 1. High-Pressure Vessel; 2. Gas Injection Unit; 3. Liquid Injection Unit; 4. Liquid Extraction Unit; 5. Vacuum Preparation Module; 6. Integrated Temperature and Pressure Sensor; 7. Ring Electrode Array; 8. Observation Window; 9. Simulated Wellbore; 10. Displacement Sensor; 11. Jacket; 12. Ultrasonic Probe; 13. Magnetic Circulation Pump; 14. Second Vent Valve; 15. Gas Injection Pressure Gauge; 16. Safety Valve; 17. Circulation Pressure Gauge; 18. High-Pressure Filter; 19. Methane Gas Source; 20. Air Compressor; 21. Constant Speed ​​and Constant Pressure Pump; 22. Stirring Container; 23. Preheater; 24. Condenser; 25. Second Temperature Detector; 26. Liquid Injection Pressure Gauge; 27. Solid-Liquid Separator; 2 8. First storage tank; 29. ​​Gas-liquid separator; 30. Second storage tank; 31. First filter; 32. Eighth control valve; 33. Dryer; 34. Gas flow meter; 35. First vent valve; 36. Intermediate container; 37. Vacuum pressure gauge; 38. Vacuum device; 39. Tenth control valve; 40. Third storage tank; 41. Movable support; 42. Casters; 43. First control valve; 44. Fourth control valve; 45. First temperature detector; 46. Seventh pressure valve; 47. Fifth control valve; 48. Eleventh control valve; 49. Twelfth control valve; 50. Ninth control valve; 51. Second control valve; 52. Third control valve; 53. Sixth control valve; 54. First tilting shaft; 55. Second tilting shaft; 57. Handwheel; 58. Reducer. Detailed Implementation

[0020] 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 embodiments of the present invention, and not all embodiments. 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.

[0021] The purpose of the present application is to provide a natural gas hydrate formation and wellbore working fluid interaction simulation experiment system to solve the above-mentioned problems existing in the prior art and realize the simulation test of the influence of drilling fluid on the wellbore stability of natural gas hydrate formation.

[0022] In order to make the above-mentioned purposes, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0023] As shown in the Figure 1 The present embodiment provides a natural gas hydrate formation and wellbore working fluid interaction simulation experiment system 100, which comprises: A high-pressure kettle 1, a simulated formation of the formation where natural gas hydrate exploitation is needed to be simulated is arranged in the high-pressure kettle 1, a simulated wellbore 9 is vertically arranged at the center of the simulated formation, and a plurality of liquid-permeable holes are distributed on the sidewall of the simulated wellbore 9; A gas injection unit 2, the gas injection unit 2 comprises a methane gas source 19 and an air compressor 20, the gas outlet of the methane gas source 19 is in communication with the gas inlet of the air compressor 20, and the gas outlet of the air compressor 20 is in communication with the high-pressure kettle 1; A liquid injection unit 3, the liquid injection unit 3 comprises a constant-speed constant-pressure pump 21 and a stirring container 22, the liquid outlet of the constant-speed constant-pressure pump 21 is in communication with the top end of the stirring container 22, the stirring container 22 is used for containing wellbore working fluid, and the liquid outlet of the stirring container 22 is in communication with the bottom end of the high-pressure kettle 1; the stirring container 22 has a piston therein, the lower space of the piston in the stirring container 22 contains wellbore working fluid, and the stirring rate of the stirring blade in the stirring container 22 can be controlled by a motor, the upper space in the stirring container 22 is connected with the liquid outlet of the constant-speed constant-pressure pump 21, and the working fluid is injected into the high-pressure kettle 1 through the piston when the constant-speed constant-pressure pump 21 is working.

[0024] A wellbore working fluid circulating unit, the wellbore working fluid circulating unit comprises a magnetic circulating pump 13 and a high-pressure filter 18, the liquid inlet of the high-pressure filter 18 is in communication with the top end of the simulated wellbore 9 through a first pipeline, the liquid outlet of the high-pressure filter 18 is in communication with the liquid inlet of the magnetic circulating pump 13, and the liquid outlet of the magnetic circulating pump 13 is in communication with the bottom end of the simulated wellbore 9; the high-pressure filter 18 has a screen therein, and the high-pressure filter 18 can remove useless solid phases (i.e. solid particles and other solid impurities) in the wellbore working fluid; A vacuum preparation module 5, the vacuum preparation module 5 comprises a vacuum device 38 and a sealed intermediate container 36, the middle part of the first pipeline is in communication with one end of a second pipeline, the other end of the second pipeline extends into the top of the intermediate container 36, the air suction port of the vacuum device 38 is in communication with the top end of the intermediate container 36, and the bottom end of the intermediate container 36 is provided with a first discharge pipe, and the first discharge pipe is provided with a first vent valve 35; The monitoring unit comprises a computer, temperature sensors, pressure sensors, displacement sensors 10 and a first data acquisition system. The temperature sensors, the pressure sensors and the displacement sensors 10 are all multiple. All the temperature sensors are distributed in the simulated formation in several layers along the vertical direction. All the pressure sensors are distributed in the simulated formation in several layers along the vertical direction. The displacement sensors 10 are distributed on the top end inner wall and the side inner wall of the autoclave 1. The temperature sensors, the pressure sensors and the displacement sensors 10 are all signal connected with the first data acquisition system, and the first data acquisition system is signal connected with the computer. In the embodiment, the integrated temperature and pressure sensor 6 is used as the temperature sensor and the pressure sensor, so as to save the installation space, reduce the opening of the autoclave 1, reduce the sealing risk and ensure that the positions of the measurement points of the temperature and the pressure are consistent in height.

[0025] In the embodiment, a third storage tank 40 is arranged below the high-pressure filter 18. The solid discharge port of the high-pressure filter 18 is in communication with the third storage tank 40. The third storage tank 40 is used for storing the useless solid phase (i.e. solid particulate matter and other solid impurities) filtered by the high-pressure filter 18. The tenth control valve 39 is arranged on the communication pipe of the third storage tank 40 and the high-pressure filter 18. In the embodiment, the first pipeline in the wellbore working fluid circulating unit is further connected with a safety valve 16 through a first connecting pipe. The safety valve 16 is adjustable in pressure of 25-31.5 MPa. When the pressure in the system exceeds the set pressure, the gas and liquid can be directly discharged from the system through the overflow hole to reduce the internal pressure of the system, so as to protect the system and ensure the stability of the wellbore working fluid circulating process. The liquid outlet of the magnetic circulating pump 13 is in communication with the bottom end of the simulated wellbore 9 through a fourth pipeline. The fourth pipeline is connected with a second discharge pipe. The second discharge pipe is provided with a second vent valve 14. By opening the second vent valve 14, the wellbore working fluid in the simulated wellbore 9 can be discharged through the fourth pipeline and the second discharge pipe.

[0026] In the embodiment, an air injection pressure gauge 15 and a first control valve 43 are arranged on the communication pipe between the air outlet of the air compressor 20 and the autoclave 1. The first control valve 43 is closer to the autoclave 1 than the air injection pressure gauge 15. The air injection pressure can be directly detected through the air injection pressure gauge 15. The opening and closing of the air injection can be controlled through the first control valve 43.

[0027] In the optional scheme of the embodiment, preferably, the monitoring unit further comprises an ultrasonic detection system. The ultrasonic detection system comprises three pairs of ultrasonic probes 12. Each pair of ultrasonic probes 12 comprises a transmitting probe and a receiving probe which is oppositely arranged relative to the transmitting probe. The transmitting probe and the receiving probe in the first pair of ultrasonic probes 12 are arranged on the first side wall and the second side wall of the autoclave 1 respectively; the transmitting probe and the receiving probe in the second pair of ultrasonic probes 12 are arranged on the third side wall and the fourth side wall of the autoclave 1 respectively; and the transmitting probe and the receiving probe in the third pair of ultrasonic probes 12 are arranged on the top wall and the bottom wall of the autoclave 1 respectively.

[0028] In an optional scheme of the embodiment, preferably, the monitoring unit further comprises a resistivity imaging system, the resistivity imaging system comprising a loop electrode array 7 and a resistivity inspection instrument, the loop electrode array 7 being inserted in the simulated formation, and the loop electrode array being signal-connected with the resistivity inspection instrument.

[0029] In an optional scheme of the embodiment, preferably, the monitoring unit further comprises a microscopic imaging system, the microscopic imaging system comprising a microscopic imaging lens and a second data acquisition system, the microscopic imaging lens being fixedly arranged outside the autoclave 1, the microscopic imaging lens facing the observation window 8 on the autoclave 1, and the microscopic imaging lens being signal-connected with the computer through the second data acquisition system.

[0030] In an optional scheme of the embodiment, preferably, the device further comprises a mobile support 41, the bottom end of the mobile support 41 being provided with at least three casters 42, the mobile support 41 being rotatably connected with a first overturning shaft 54 and a second overturning shaft 55, the second overturning shaft 55 being coaxial with the first overturning shaft 54, and the first overturning shaft 54 and the second overturning shaft 55 being fixedly connected with the autoclave 1 respectively; a speed reducer 58 being fixedly arranged on the mobile support 41, the speed reducer 58 being a worm and gear speed reducer with self-locking function, an output shaft of the speed reducer 58 being coaxial with and fixedly connected with the second overturning shaft 55, and a hand wheel 57 being fixedly arranged on an input shaft of the speed reducer 58.

[0031] In an optional scheme of the embodiment, preferably, the autoclave 1 comprises a barrel, a top cover and a bottom cover, the top cover being detachably connected with the top end of the barrel, the bottom cover being detachably connected with the bottom end of the barrel, and a sealing ring being arranged between the top cover and the barrel and between the bottom cover and the barrel respectively; the top cover and the bottom cover being respectively provided with through holes corresponding to the simulated wellbore 9, and the simulated wellbore 9 passing through the through hole on the top cover and the through hole on the bottom cover.

[0032] In a preferred embodiment, the liquid extraction unit 4 is further included. The liquid extraction unit 4 includes a solid-liquid separator 27, a first storage tank 28, a second storage tank 30, and a gas-liquid separator 29. The inlet of the solid-liquid separator 27 is connected to a second pipeline, the solid outlet of the solid-liquid separator 27 is connected to the first storage tank 28, the liquid outlet of the solid-liquid separator 27 is connected to the inlet of the gas-liquid separator 29 via a third pipeline, the liquid outlet of the gas-liquid separator 29 is connected to the second storage tank 30, and the gas outlet of the gas-liquid separator 29 is connected to an exhaust pipe. In this embodiment, an eleventh control valve 48 is provided on the connecting pipe between the solid outlet of the solid-liquid separator 27 and the first storage tank 28, and a twelfth control valve 49 is provided on the connecting pipe between the liquid outlet of the gas-liquid separator 29 and the second storage tank 30.

[0033] In the optional scheme of this embodiment, a more preferred embodiment is that a first filter 31 and an eighth control valve 32 are provided on the third pipeline, the eighth control valve 32 is located between the first filter 31 and the gas-liquid separator 29, and a dryer 33, a ninth control valve 50 and a gas flow meter 34 are provided on the exhaust pipe, the ninth control valve 50 is located between the dryer 33 and the gas flow meter 34, and the dryer 33 is closer to the gas-liquid separator 29 than the ninth control valve 50.

[0034] In the optional solutions of this embodiment, a more preferred option is to further include a temperature control unit. The temperature control unit includes a constant temperature bath and a jacket 11 fixedly sleeved on the outside of the high pressure vessel 1. The liquid outlet of the constant temperature bath is connected to the liquid inlet of the jacket 11, and the liquid outlet of the jacket 11 is connected to the liquid return port of the constant temperature bath.

[0035] In an optional embodiment, more preferably, the injection unit 3 further includes a condenser 24 and a preheater 23 arranged in parallel. The working fluid flowing out of the outlet of the stirring container 22 flows through the condenser 24 or the preheater 23 and then enters the autoclave 1. The condenser 24 is used to cool the working fluid flowing out of the outlet of the stirring container 22 to a set temperature, and the preheater 23 is used to heat the working fluid flowing out of the outlet of the stirring container 22 to a set temperature.

[0036] In this embodiment, the inlet pipe of the condenser 24 and the inlet pipe of the preheater 23 are respectively connected to the outlet pipe at the outlet of the stirring container 22. A second control valve 51 is provided on the inlet pipe of the condenser 24, and a third control valve 52 is provided at the inlet pipe of the preheater 23. By opening the second control valve 51 and closing the third control valve 52, the well working fluid flowing out of the outlet of the stirring container 22 flows through the condenser 24 and enters the high pressure vessel 1. By closing the second control valve 51 and opening the third control valve 52, the well working fluid flowing out of the outlet of the stirring container 22 flows through the condenser 24 and enters the high pressure vessel 1. The outlet pipe of the condenser 24 and the outlet pipe of the preheater 23 are respectively connected to the inlet pipe at the bottom of the high pressure vessel 1. A liquid injection pressure gauge 26 and a fourth control valve 44 are provided on the inlet pipe at the bottom of the high pressure vessel 1. The liquid injection pressure can be directly detected by the liquid injection pressure gauge 26, and the opening and closing of the liquid injection can be controlled by the fourth control valve 44. In addition, a first temperature detector 45 is installed on the condenser 24, and a second temperature detector 25 is installed on the preheater 23. The condenser 24 and the preheater 23 are respectively connected to a computer control system. The computer obtains the real-time temperature of the liquid in the condenser 24 and the preheater 23 through the first temperature detector 45 and the second temperature detector 25. The temperature can be controlled by software, and the temperature of the liquid in the condenser 24 and the preheater 23 can be adjusted.

[0037] In this embodiment, the circulating working fluid used in the constant temperature bath is a mixture of ethylene glycol and water, and the mass ratio of ethylene glycol to water in the mixture is 1:1.

[0038] It is worth noting that the simulated formation should ideally be identical to the formation at the natural gas hydrate extraction site in terms of porosity, clay content, and mineral content. If complete identicality is not possible, they should be as close as possible. Resistivity imaging systems are existing technologies familiar to those skilled in the art; therefore, their specific working principles will not be elaborated upon in this embodiment.

[0039] Vacuum preparation module 5 is used to evacuate the autoclave 1. By evacuating the autoclave 1 and removing the original air, the vacuum device 38 is shut off, and the system is allowed to stand for a period of time (e.g., 1-2 hours). The reading on the vacuum pressure gauge 37 is observed. If the reading on the vacuum pressure gauge 37 indicates an increase in system pressure after standing, it indicates a problem with the system's sealing, suggesting a leak. The leak needs to be located and repaired, and the above operation is repeated until the reading on the vacuum pressure gauge 37 indicates that the system pressure remains constant, proving that the system's sealing is good. Then, methane gas is injected into the autoclave 1 using the gas pressurization system in the pressure control unit until the gas pressure in the autoclave 1 reaches 2 MPa. In this embodiment, the vacuum device 38 specifically uses a vacuum pump. A vacuum pressure gauge 37 and a fifth control valve 47 are installed on the connecting pipe between the vacuum device 38 and the intermediate container 36. The vacuum pressure gauge 37 can directly detect the real-time vacuum level, and the fourth control valve 44 can control the opening and closing of the vacuum process. A circulating pressure gauge 17, a sixth control valve 53, and a seventh pressure valve 46 are installed on the second pipeline. The circulating pressure gauge 17 and the sixth control valve 53 are located between the connection port of the second pipeline and the first pipeline and between the connection port of the solid-liquid separator 27 and the second pipeline. The seventh control valve is located between the connection port of the solid-liquid separator 27 and the second pipeline and the intermediate container 36. The circulating pressure of the wellbore working fluid can be detected in real time through the circulating pressure gauge 17.

[0040] In practical operation, the simulation experiment system 100 for the interaction between natural gas hydrate formation and wellbore working fluid in this embodiment can be used to conduct experiments according to the following steps to more completely illustrate the usage of the simulation experiment system 100 for the interaction between natural gas hydrate formation and wellbore working fluid in this embodiment: 1. Simulated formation preparation and loading: Based on key parameters such as the actual lithology, porosity, water saturation, and clay mineral content of the target natural gas hydrate formation, core particles (such as quartz sand and clay minerals) and pore water are prepared, mixed evenly, and then loaded into the cylinder of the autoclave 1. During the loading process, temperature and pressure sensors can be simultaneously buried in layers within the simulated formation according to a pre-set sensor placement plan to ensure they can monitor temperature and pressure changes at different depths and radial locations. The simulated wellbore 9 is pre-fixed vertically at the center of the cylinder before loading, and its sidewall permeability holes are wrapped with filter screens to prevent formation particles from entering.

[0041] 2. System sealing and air injection: Install the top and bottom covers of the autoclave 1, ensuring all sealing rings are in place and tighten the connections to guarantee airtightness. Evacuate the autoclave 1 using the vacuum device 38 of the vacuum preparation module 5 to eliminate air interference. Then, close the vacuum passage and adjust the tilt angle of the autoclave 1 by turning the handwheel 57, ensuring the tilt angle of the simulated formation matches the actual tilt angle of the target natural gas hydrate formation. Next, inject methane gas into the autoclave 1 through the gas injection unit 2, monitoring the pressure using the gas injection pressure gauge 15 until the required formation pressure for the simulated formation is reached (e.g., 2-20 MPa range, set according to the simulation depth). Simultaneously, activate the temperature control unit, circulating ethylene glycol aqueous solution into the jacket 11 of the autoclave 1 through a constant temperature bath to control the temperature of the simulated formation within the stable temperature and pressure range of the target natural gas hydrate (e.g., 2-10°C).

[0042] To more realistically simulate underground overburden pressure, the simulated formation material can be compacted in layers during loading, or an independent axial loading piston (not shown in the figure) can be installed on top of the autoclave to apply a certain axial load to the simulated formation via external hydraulic or mechanical means to simulate the overburden pressure. This load can be kept constant throughout the experiment or varied during the wellbore stability test to study the effect of working fluid circulation on wellbore stability under different geostress conditions.

[0043] 3. Synthesis of natural gas hydrates: Under the established low temperature and high pressure conditions, a certain amount of deionized water or pre-prepared mineralized water is slowly injected into the simulated formation through injection unit 3, allowing it to fully contact with methane gas in the pores. The system is kept stable for a sufficiently long time (usually several hours to tens of hours), and pressure and temperature changes are observed in real time through the monitoring unit. Resistivity changes are monitored through the resistivity imaging system (hydrate formation leads to a significant increase in resistivity). Combined with the observation of crystal growth through the observation window 8 using the microscopic imaging system, it is determined that natural gas hydrate has been synthesized in the simulated formation, forming a simulated formation containing natural gas hydrate.

[0044] During the synthesis process, methane gas can be intermittently or continuously supplied through gas injection unit 2 to maintain system pressure and promote the increase of hydrate saturation. By monitoring multi-parameter data (such as the pressure drop becoming stable, the resistivity rising to a stable value, and the temperature curve showing an exothermic plateau followed by a drop), it can be comprehensively determined that the hydrate synthesis has reached equilibrium.

[0045] 4. Wellbore working fluid circulation simulation experiment: First, the pre-prepared wellbore working fluid is placed in the mixing container 22. Then, deionized water is pumped into the mixing container 22 by a constant speed and pressure pump 21, thereby displacing the wellbore working fluid in the mixing container 22. The wellbore working fluid (such as drilling fluid, completion fluid, etc.) is then pumped to the bottom of the high-pressure vessel 1 after being adjusted to the required temperature by the condenser 24 or preheater 23, and gradually fills the simulated formation and simulated wellbore 9. Then, the magnetic circulation pump 13 of the wellbore working fluid circulation unit is started, so that the wellbore working fluid enters from the bottom end of the simulated wellbore 9 and flows out from the top end according to the preset discharge rate and pressure. After being filtered by the high-pressure filter 18, it is then sucked into the magnetic circulation pump 13 to form a circulation. This process simulates the circulation of working fluid in an actual wellbore. The working fluid interacts with the simulated formation containing natural gas hydrates through permeable holes on the sidewall of the simulated wellbore 9. During circulation, the circulation rate and equivalent circulating density (ECD) of the working fluid in the simulated wellbore 9 can be precisely controlled by adjusting the frequency of the magnetic circulation pump 13 or the outlet valve. Simultaneously, the working fluid can be replenished or adjusted in the stirring container 22 through the filling port to supplement or adjust its performance during the simulation process. The high-pressure filter 18 can remove solid particles such as formation cuttings carried in the working fluid in real time, simulating the function of a solids control system. The degree of formation sand production can be analyzed by observing the pressure difference before and after the filter and the solid accumulation in the third storage tank 40.

[0046] 5. Dynamic monitoring and data collection: The monitoring unit operates continuously throughout the entire cyclic experiment: Temperature and pressure: Temperature and pressure sensors are pre-embedded in the simulated strata to monitor and record temperature and pressure changes at different locations in the simulated strata in real time, and to analyze the advancement of the hydrate decomposition front.

[0047] Displacement and Deformation: The displacement sensor 10 installed on the inner wall of the autoclave 1 monitors the deformation of the simulated formation, such as well wall shrinkage, diameter expansion or collapse, that may occur during the intrusion of working fluid and decomposition of hydrates in the wellbore.

[0048] Ultrasound and Resistivity: Using several pairs of ultrasonic probes 12 of the ultrasonic detection system, the propagation speed and attenuation changes of ultrasonic waves in the simulated formation are measured, and the changes in the formation's mechanical properties (such as strength and elastic modulus) are inverted. Through the ring electrode array 7 of the resistivity imaging system, two-dimensional / three-dimensional distribution images of the simulated formation resistivity are acquired in real time, visually displaying the development dynamics of the hydrate decomposition zone and the working fluid invasion zone.

[0049] Microscopic imaging: Through the microscopic imaging system, continuous or timed image acquisition is performed on the interface between the simulated formation and the wellbore or a specific area through the observation window 8 to observe processes such as hydrate crystal decomposition, particle migration, and micro-crack generation.

[0050] All sensor data is collected by the first data acquisition system, the second data acquisition system, resistivity monitoring instruments, etc., and then processed, analyzed, and visualized by a computer.

[0051] Specifically, by comparing and analyzing ultrasonic wave velocity and amplitude data at different times before the start of the cycle (baseline state) and during the cycle, the dynamic decay process of simulated formation mechanical properties can be quantitatively assessed. The spatial distribution information provided by resistivity imaging can be coupled with temperature and pressure field data for analysis, accurately characterizing the spatiotemporal evolution of the hydrate decomposition front. Data from displacement sensor 10 can be used to assess the timing and severity of macroscopic instability phenomena such as wellbore enlargement, narrowing, or collapse.

[0052] 6. Product processing and analysis: During the circulation of the working fluid in the wellbore, the mixture generated, including formation water, decomposed gases, and potential formation sand, can be drawn out through the second pipeline. This mixture enters the liquid extraction unit 4, where it is processed successively by the solid-liquid separator 27 and the gas-liquid separator 29. The separated gas is metered by the dryer 33 and the gas flow meter 34 before being discharged or collected. The separated liquid and solid are stored in the second storage tank 30 and the first storage tank 28, respectively, for subsequent analysis of chemical composition and particle size. The liquid collected in the second storage tank 30 can be tested for ion concentration, pH value, viscosity, and other properties to analyze the performance and contamination of the working fluid after invading the formation and interacting with hydrates. The solid particles collected in the first storage tank 28 can be analyzed for particle size and mineral composition to study the characteristics of formation sand production. The real-time data from the gas flow meter 34 reflects the rate of gas production from hydrate decomposition and is one of the key indicators for assessing the degree of hydrate decomposition.

[0053] 7. Post-experiment processing: After the experiment, the magnetic circulation pump 13 and temperature control can be stopped. By driving the reducer 58 through the handwheel 57 on the movable support 41, the high-pressure vessel 1 is rotated as a whole, which facilitates the unloading of the simulated stratum rock sample after the experiment, and allows for offline analysis such as CT scanning and strength testing, and comparison and verification with online monitoring data.

[0054] 8. This system allows for convenient conduct of a series of comparative experiments, for example: Influence of working fluid type / performance: Repeat the above experimental steps by changing the wellbore working fluid with different formulations (such as inhibitor type and concentration, filtration control agent, etc.) and comparing the differences in their inhibitory effect on hydrate decomposition and wellbore stability maintenance capabilities.

[0055] Influence of engineering parameters: The effects of different circulation parameters on the interaction process were studied by changing the circulation flow rate, temperature, and pressure of the working fluid in the wellbore (adjusted through the injection unit and back pressure valve).

[0056] Influence of formation conditions: By changing the initial conditions of the simulated formation, such as hydrate saturation, formation lithology, porosity, and dip angle, the sensitivity of the interaction between the hydrate formation and the working fluid under different occurrence conditions is studied.

[0057] Through the above series of experiments, the key factors and their mechanisms of action affecting wellbore stability can be systematically obtained, providing a solid experimental basis and theoretical guidance for the design and optimization of drilling fluids for safe drilling of natural gas hydrates.

[0058] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A system for modeling the interaction of a natural gas hydrate formation with a wellbore working fluid, comprising: The device comprises: a high-pressure kettle, a simulated formation of a formation where natural gas hydrate exploitation is needed to be simulated is arranged in the high-pressure kettle, a center of the simulated formation is vertically arranged with a simulated wellbore, and a side wall of the simulated wellbore is distributed with a plurality of liquid-permeable holes; an air injection unit, the air injection unit comprises a methane gas source and an air compressor, an air outlet of the methane gas source is communicated with an air inlet of the air compressor, and an air outlet of the air compressor is communicated with the high-pressure kettle; a liquid injection unit, the liquid injection unit comprises a constant-speed constant-pressure pump and a stirring container, an outlet of the constant-speed constant-pressure pump is communicated with a top end of the stirring container, the stirring container is used for containing wellbore working liquid, and an outlet of the stirring container is communicated with a bottom end of the high-pressure kettle; a wellbore working liquid circulating unit, the wellbore working liquid circulating unit comprises a magnetic circulating pump and a high-pressure filter, an inlet of the high-pressure filter is communicated with a top end of the simulated wellbore through a first pipeline, an outlet of the high-pressure filter is communicated with an inlet of the magnetic circulating pump, and an outlet of the magnetic circulating pump is communicated with a bottom end of the simulated wellbore; a vacuum preparation module, the vacuum preparation module comprises a vacuum device and a sealed intermediate container, a middle part of the first pipeline is communicated with one end of a second pipeline, the other end of the second pipeline extends into a top part of the intermediate container, a suction port of the vacuum device is communicated with a top end of the intermediate container, and a bottom end of the intermediate container is provided with a first discharge pipe, and a first vent valve is arranged on the first discharge pipe; a monitoring unit, the monitoring unit comprises a computer, a temperature sensor, a pressure sensor, a displacement sensor and a first data acquisition system, the temperature sensor, the pressure sensor and the displacement sensor are all multiple, all the temperature sensors are distributed in the simulated formation in a vertical direction and are divided into a plurality of layers, all the pressure sensors are distributed in the simulated formation in a vertical direction and are divided into a plurality of layers, and the displacement sensors are distributed on the top end inner wall and the side inner wall of the high-pressure kettle; the temperature sensor, the pressure sensor and the displacement sensor are all signal connected with the first data acquisition system, and the first data acquisition system is signal connected with the computer.

2. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: The monitoring unit further comprises an ultrasonic detection system, the ultrasonic detection system comprises three pairs of ultrasonic probes, each pair of the ultrasonic probes comprises a transmitting probe and a receiving probe which is oppositely arranged with the transmitting probe; wherein the transmitting probe and the receiving probe in the first pair of the ultrasonic probes are arranged on the first side wall and the second side wall of the high-pressure kettle respectively; the transmitting probe and the receiving probe in the second pair of the ultrasonic probes are arranged on the third side wall and the fourth side wall of the high-pressure kettle respectively; and the transmitting probe and the receiving probe in the third pair of the ultrasonic probes are arranged on the top wall and the bottom wall of the high-pressure kettle respectively.

3. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: The monitoring unit further comprises a resistivity imaging system, the resistivity imaging system comprises a ring electrode array and a resistivity inspection instrument, the ring electrode array is inserted in the simulated formation, and the ring electrode array is signal connected with the resistivity inspection instrument.

4. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: The monitoring unit further comprises a microscopic imaging system, the microscopic imaging system comprising a microscopic imaging lens and a second data acquisition system, the microscopic imaging lens being fixed outside the autoclave, the microscopic imaging lens being opposite to an observation window on the autoclave, the microscopic imaging lens being signal-connected with the computer through the second data acquisition system.

5. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: Further comprising a mobile support, the mobile support being provided with at least three casters at the bottom end, the mobile support being rotatably connected with a first overturning shaft and a second overturning shaft, the second overturning shaft being coaxial with the first overturning shaft, the first overturning shaft and the second overturning shaft being fixedly connected with the autoclave respectively; a speed reducer being fixedly arranged on the mobile support, the speed reducer being a worm and gear speed reducer with self-locking function, an output shaft of the speed reducer being coaxial with and fixedly connected with the second overturning shaft, a hand wheel being fixedly arranged on an input shaft of the speed reducer.

6. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: The autoclave comprises a barrel, a top cover and a bottom cover, the top cover being detachably connected with the top end of the barrel, the bottom cover being detachably connected with the bottom end of the barrel, a sealing ring being arranged between the top cover and the barrel and between the bottom cover and the barrel respectively; the top cover and the bottom cover being respectively provided with through holes corresponding to the simulated wellbore, the simulated wellbore passing through the through hole on the top cover and the through hole on the bottom cover.

7. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: Further comprising a liquid extraction unit, the liquid extraction unit comprising a solid-liquid separator, a first storage tank, a second storage tank and a gas-liquid separator, a feed inlet of the solid-liquid separator being communicated with the second pipeline, a solid discharge outlet of the solid-liquid separator being communicated with the first storage tank, a liquid discharge outlet of the solid-liquid separator being communicated with a feed inlet of the gas-liquid separator through a third pipeline, a liquid outlet of the gas-liquid separator being communicated with the second storage tank, and a gas outlet of the gas-liquid separator being connected with an exhaust pipe.

8. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 7, wherein: A first filter is arranged on the third pipeline, and a dryer and a gas flow meter are arranged on the exhaust pipe.

9. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: Further comprising a temperature control unit, the temperature control unit comprising a constant-temperature tank and a jacket fixedly arranged outside the autoclave, a liquid outlet of the constant-temperature tank being communicated with a liquid inlet of the jacket, and a liquid outlet of the jacket being communicated with a liquid return port of the constant-temperature tank.

10. The natural gas hydrate formation and wellbore working fluid interaction modeling laboratory system of claim 1, wherein: The liquid injection unit further comprises a condenser and a preheater arranged in parallel, the wellbore working fluid flowing out of the liquid outlet of the stirring container passing through the condenser or the preheater and then entering the autoclave; the condenser being used for cooling the wellbore working fluid flowing out of the liquid outlet of the stirring container to a set temperature, and the preheater being used for heating the wellbore working fluid flowing out of the liquid outlet of the stirring container to a set temperature.

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