Simulation experiment system for interaction between natural gas hydrate formation and wellbore working fluid

Abstract

The application discloses a natural gas hydrate stratum and wellbore working fluid interaction simulation experiment system, and relates to the field of experimental instruments, which comprises a high-pressure kettle, a gas injection unit, a liquid injection unit, a wellbore working fluid circulation unit, a vacuum preparation module and a monitoring unit; the high-pressure kettle is internally provided with a simulated stratum and a vertical simulated wellbore with a liquid permeation hole; the gas injection unit and the liquid injection unit are respectively used for injecting methane gas and working fluid into the high-pressure kettle; the wellbore working fluid circulation unit comprises a magnetic circulation pump and a high-pressure filter and is used for driving the working fluid to circulate in the simulated wellbore; the vacuum preparation module is used for preparing an initial experimental environment; and the monitoring unit comprises temperature, pressure and displacement sensors, 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 application can simulate a wellbore working fluid circulation invasion process and comprehensively evaluate the influence of the working fluid on the stability of a natural gas hydrate stratum and the phase change of hydrates.

Description

Simulation Experimental System for the Interaction between Natural Gas Hydrate Formation and Wellbore Working Fluid Technical Field

[0001] This invention relates to the field of experimental equipment technology, and in particular to an experimental system for simulating the interaction between natural gas hydrate formations and wellbore working fluids. Background Technology

[0002] Natural gas hydrate is a cage-like crystalline substance formed when natural gas and water react under certain temperature and pressure. It is flammable and commonly known as "combustible ice." Natural gas hydrate can exist in nature in various forms. Due to its characteristics, the development of natural gas hydrate differs from that of conventional energy sources. Specifically, natural gas hydrate is a solid when buried on the ocean floor, but its molecular structure changes during extraction, transforming it from a solid to a gas.

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

[0004] During the circulation of the working fluid in the wellbore, the working fluid intrudes into the formation, affecting both the phase change and decomposition of natural gas hydrates, which in turn reduces formation strength. Furthermore, the working fluid also hydrates clay minerals in the formation, impacting the wellbore stability of hydrated formations. In this process, hydrates and mineral particles from the formation circulate with the working fluid, affecting its density, viscosity, and other properties.

[0005] Currently, existing natural gas hydrate formation simulation experimental devices can only simulate the decomposition of natural gas hydrates during the process of working fluid intruding into the natural gas hydrate formation from the end face. They lack research methods to simulate the interaction mechanism between working fluid and natural gas hydrate formation during wellbore circulation. Furthermore, existing natural gas hydrate formation simulation sample preparation technology is also difficult to simulate actual natural gas hydrate formation conditions, resulting in the inability of existing natural gas hydrate formation simulation experimental devices to simulate the impact of working fluid on natural gas hydrate formations. Summary of the Invention

[0006] The purpose of this invention is to provide a simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids, in order 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 formations.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides an experimental system for simulating the interaction between natural gas hydrate formations and wellbore working fluids, comprising:

[0009] The high-pressure vessel contains a simulated formation of the natural gas hydrate extraction site to be simulated. A simulated wellbore is vertically installed at the center of the simulated formation, and multiple liquid permeation holes are distributed on the sidewalls of the simulated wellbore.

[0010] The gas injection unit includes a methane gas source and an air compressor. The outlet of the methane gas source is connected to the inlet of the air compressor, and the outlet of the air compressor is connected to the autoclave.

[0011] The injection unit includes a constant speed and constant pressure pump and a stirring container. The outlet of the constant speed and constant pressure pump is connected to the top of the stirring container. The stirring container is used to hold the working fluid in the wellbore. The outlet of the stirring container is connected to the bottom of the high pressure vessel.

[0012] The wellbore working fluid circulation unit includes a magnetic circulation pump and a high-pressure filter. The inlet of the high-pressure filter is connected to the top of the simulated wellbore through a first pipeline. The outlet of the high-pressure filter is connected to the inlet of the magnetic circulation pump. The outlet of the magnetic circulation pump is connected to the bottom of the simulated wellbore.

[0013] A vacuum preparation module includes a vacuum device and a sealed intermediate container. The middle part of the first pipeline is connected to one end of the second pipeline, and the other end of the second pipeline extends into the top of the intermediate container. The suction port of the vacuum device is connected to the top of the intermediate container. A first discharge pipe is provided at the bottom of the intermediate container, and a first vent valve is provided on the first discharge pipe.

[0014] The monitoring unit includes a computer, temperature sensors, pressure sensors, displacement sensors, and a first data acquisition system. There are multiple temperature sensors, pressure sensors, and displacement sensors. All temperature sensors are distributed in several layers vertically within the simulated geological formation. All pressure sensors are also distributed in several layers vertically within the simulated geological formation. The displacement sensors are distributed on the inner top and side walls of the autoclave. All temperature sensors, pressure sensors, and displacement sensors are connected to the first data acquisition system, which is connected to the computer.

[0015] Preferably, the monitoring unit further includes an ultrasonic detection system, which includes three pairs of ultrasonic probes, each pair of ultrasonic probes including a transmitting probe and a receiving probe arranged opposite to the transmitting probe;

[0016] In the first pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the first side wall and the second side wall of the autoclave; in the second pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the third side wall and the fourth side wall of the autoclave; in the third pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the top wall and the bottom wall of the autoclave.

[0017] Preferably, the monitoring unit further includes a resistivity imaging system, which includes a ring electrode array and a resistivity inspection instrument. The ring electrode array is inserted into the simulated stratum, and the ring motor array is signal-connected to the resistivity inspection instrument.

[0018] Preferably, the monitoring unit further includes a microscopic imaging system, which includes a microscopic imaging lens and a second data acquisition system. The microscopic imaging lens is fixed on the outside of the autoclave and faces the observation window on the autoclave. The microscopic imaging lens is connected to the computer signal through the second data acquisition system.

[0019] Preferably, the device further includes a movable support, the bottom of which is provided with at least three casters. A first tilting shaft and a second tilting shaft are rotatably connected to the movable support. The second tilting shaft is coaxial with the first tilting shaft. The first tilting shaft and the second tilting shaft are respectively fixedly connected to the autoclave. A speed reducer is fixedly installed on the movable support. The speed reducer is a worm gear reducer with a self-locking function. The output shaft of the speed reducer is coaxial with and fixedly connected to the second tilting shaft. A handwheel is fixedly installed on the input shaft of the speed reducer.

[0020] Preferably, the autoclave includes a cylinder, a top cover, and a bottom cover. The top cover is detachably connected to the top end of the cylinder, and the bottom cover is detachably connected to the bottom end of the cylinder. Sealing rings are respectively sandwiched between the top cover and the cylinder, and between the bottom cover and the cylinder. The top cover and the bottom cover are respectively provided with through holes corresponding to the simulated well shaft, and the simulated well shaft passes through the through holes on the top cover and the bottom cover.

[0021] Preferably, the system further includes a liquid extraction unit, which comprises a solid-liquid separator, a first storage tank, a second storage tank, and a gas-liquid separator. The inlet of the solid-liquid separator is connected to the second pipeline, the solid outlet of the solid-liquid separator is connected to the first storage tank, the liquid outlet of the solid-liquid separator is connected to the inlet of the gas-liquid separator via a third pipeline, the liquid outlet of the gas-liquid separator is connected to the second storage tank, and the gas outlet of the gas-liquid separator is connected to an exhaust pipe.

[0022] Preferably, a first filter is provided on the third pipeline, and a dryer and a gas flow meter are provided on the exhaust pipe.

[0023] Preferably, it also includes a temperature control unit, which includes a constant temperature bath and a jacket fixedly sleeved on the outside of the autoclave. The outlet of the constant temperature bath is connected to the inlet of the jacket, and the outlet of the jacket is connected to the return port of the constant temperature bath.

[0024] Preferably, the injection unit further includes a condenser and a preheater arranged in parallel. The wellbore working fluid flowing out of the outlet of the stirring container flows through the condenser or the preheater and then enters the autoclave. The condenser is used to cool the wellbore working fluid flowing out of the outlet of the stirring container to a set temperature, and the preheater is used to heat the wellbore working fluid flowing out of the outlet of the stirring container to a set temperature.

[0025] The present invention achieves the following technical effects compared to the prior art:

[0026] This invention presents a simulation experiment system for the interaction between natural gas hydrate formations and wellbore working fluids. By simulating the extraction process of natural gas hydrates, it monitors temperature, pressure, and displacement parameters in the simulated formation. Through ultrasonic testing, resistivity imaging, and microscopic imaging of the simulated formation, it investigates the impact of the simulated wellbore working fluid on the formation during natural gas hydrate extraction. By setting up a simulated wellbore with permeable holes and establishing a wellbore working fluid circulation unit, it simulates the dynamic circulation process of the working fluid within the simulated wellbore. This overcomes the limitations of existing technologies that can only simulate static end-face invasion, and more realistically reflects the complex working conditions of working fluid interaction with the formation during drilling and completion operations, including annular flow, filtration, invasion, and the formation itself. The system integrates in-situ monitoring units for multiple parameters and scales, including temperature, pressure, displacement, ultrasonic waves, resistivity, and microscopic imaging. It can simultaneously and in real-time capture information on the entire process of hydrate decomposition, formation strength degradation, particle migration, and wellbore instability induced by working fluid invasion, from macroscopic mechanical deformation and changes in state of matter to microscopic structural evolution, providing rich data support for mechanistic research. This system organically integrates functional modules such as simulated formation preparation, hydrate synthesis, working fluid circulation, multi-parameter monitoring, and product separation, collection, and post-processing (e.g., rock sample overturning and unloading) to form a complete experimental research platform. It can not only assess the impact of the working fluid on the stability of hydrate formations but also simultaneously study the reaction of hydrate decomposition to working fluid properties (e.g., solid content, rheology), providing direct experimental evidence for optimizing working fluid formulations and drilling process parameters. The system employs a high-pressure reactor design and is equipped with a safety valve, a high-precision constant temperature and pressure control unit, and a vacuum preparation module. This allows for accurate replication of the high-pressure, low-temperature environment of hydrate formations in deep-sea or permafrost layers, enabling experiments to be conducted within safe limits. A multi-channel data acquisition system ensures the synchronization and accuracy of monitoring data, improving the reliability of experimental results. Attached Figure Description

[0027] 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.

[0028] Figure 1 is a schematic diagram of the experimental system for simulating the interaction between natural gas hydrate formations and wellbore working fluid according to the present invention.

[0029] 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

[0030] 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.

[0031] The purpose of this invention is to provide a simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids, in order 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 formations.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] As shown in Figure 1, this embodiment provides a simulation experimental system 100 for the interaction between natural gas hydrate formations and wellbore working fluids, including:

[0034] High-pressure vessel 1, which contains a simulated formation of the natural gas hydrate extraction site to be simulated. A simulated wellbore 9 is vertically installed in the center of the simulated formation, and multiple liquid permeation holes are distributed on the sidewalls of the simulated wellbore 9.

[0035] Gas injection unit 2, which includes methane gas source 19 and air compressor 20, the outlet of methane gas source 19 is connected to the inlet of air compressor 20, and the outlet of air compressor 20 is connected to autoclave 1.

[0036] The injection unit 3 includes a constant speed and constant pressure pump 21 and a stirring container 22. The outlet of the constant speed and constant pressure pump 21 is connected to the top of the stirring container 22. The stirring container 22 is used to hold the wellbore working fluid. The outlet of the stirring container 22 is connected to the bottom of the high pressure vessel 1. The stirring container 22 has a piston. The space below the piston in the stirring container 22 holds the wellbore working fluid. The stirring speed of the stirring blades in the stirring container 22 can be controlled by a motor. The upper space in the stirring container 22 is connected to the outlet of the constant speed and constant pressure pump 21. When the constant speed and constant pressure pump 21 is working, the working fluid is injected into the high pressure vessel 1 through the piston.

[0037] The wellbore working fluid circulation unit includes a magnetic circulation pump 13 and a high-pressure filter 18. The inlet of the high-pressure filter 18 is connected to the top of the simulated wellbore 9 through a first pipeline, and the outlet of the high-pressure filter 18 is connected to the inlet of the magnetic circulation pump 13. The outlet of the magnetic circulation pump 13 is connected to the bottom of the simulated wellbore 9. The high-pressure filter 18 has a screen inside, which can remove useless solid phases (i.e., solid particles and other solid impurities) from the wellbore working fluid.

[0038] Vacuum preparation module 5 includes a vacuum device 38 and a sealed intermediate container 36. The middle part of the first pipeline is connected to one end of the second pipeline, and the other end of the second pipeline extends into the top of the intermediate container 36. The suction port of the vacuum device 38 is connected to the top of the intermediate container 36. A first discharge pipe is provided at the bottom of the intermediate container 36, and a first vent valve 35 is provided on the first discharge pipe.

[0039] The monitoring unit includes a computer, temperature sensors, pressure sensors, displacement sensors 10, and a first data acquisition system. There are multiple temperature sensors, pressure sensors, and displacement sensors 10. All temperature sensors are distributed in several layers vertically within the simulated geological formation, as are all pressure sensors. The displacement sensors 10 are located on the inner top and side walls of the autoclave 1. All temperature sensors, pressure sensors, and displacement sensors 10 are connected to the first data acquisition system, which is connected to the computer. In this embodiment, an integrated temperature and pressure sensor 6 is used as both the temperature and pressure sensors to save installation space, reduce the number of openings in the autoclave 1, lower sealing risks, and ensure that the measurement points for temperature and pressure are at the same height.

[0040] In this embodiment, a third storage tank 40 is provided below the high-pressure filter 18. The solid discharge port of the high-pressure filter 18 is connected to the third storage tank 40. The third storage tank 40 is used to store the useless solid phase (i.e., solid particulate matter and other solid impurities) filtered by the high-pressure filter 18. A tenth control valve 39 is provided on the connecting pipe between the third storage tank 40 and the high-pressure filter 18. In this embodiment, the first pipeline in the wellbore working fluid circulation unit is also connected to a safety valve 16 through a first connecting pipe. The safety valve 16 is adjustable with a pressure resistance of 25~31.5MPa. When the pressure in the system exceeds the set pressure, gas and liquid can be directly discharged from the system through the overflow hole to reduce the internal pressure of the system, thereby protecting the system safety and ensuring the stability of the wellbore working fluid circulation process. The outlet of the magnetic circulation pump 13 is connected to the bottom of the simulated wellbore 9 through the fourth pipeline; the fourth pipeline is connected to the second discharge pipe, and the second discharge pipe is equipped with a second vent valve 14. By opening the second vent valve 14, the working fluid in the simulated wellbore 9 can be discharged through the fourth pipeline and the second discharge pipe.

[0041] In this embodiment, an injection pressure gauge 15 and a first control valve 43 are provided on the connecting pipe between the air outlet of the air compressor 20 and the high pressure vessel 1. The first control valve 43 is closer to the high pressure vessel 1 than the injection pressure gauge 15. The injection pressure can be directly detected by the injection pressure gauge 15, and the injection can be controlled by the first control valve 43.

[0042] In the optional embodiments of this example, the monitoring unit further includes an ultrasonic detection system, which includes three pairs of ultrasonic probes 12, each pair of ultrasonic probes 12 including a transmitting probe and a receiving probe arranged opposite to the transmitting probe.

[0043] The transmitting and receiving probes of the first pair of ultrasonic probes 12 are respectively located on the first and second side walls of the autoclave 1; the transmitting and receiving probes of the second pair of ultrasonic probes 12 are respectively located on the third and fourth side walls of the autoclave 1; and the transmitting and receiving probes of the third pair of ultrasonic probes 12 are respectively located on the top and bottom walls of the autoclave 1.

[0044] In the optional embodiments of this example, more preferably, the monitoring unit further includes a resistivity imaging system, which includes a ring electrode array 7 and a resistivity inspection instrument. The ring electrode array 7 is inserted into the simulated strata, and the ring motor array is connected to the resistivity inspection instrument for signal transmission.

[0045] In the optional scheme of this embodiment, more preferably, the monitoring unit further includes a microscopic imaging system, which includes a microscopic imaging lens and a second data acquisition system. The microscopic imaging lens is fixed on the outside of the autoclave 1 and faces the observation window 8 on the autoclave 1. The microscopic imaging lens is connected to the computer signal through the second data acquisition system.

[0046] In the optional embodiments of this example, a more preferred option is to include a movable support 41. The bottom of the movable support 41 is provided with at least three casters 42. A first tilting shaft 54 ​​and a second tilting shaft 55 are rotatably connected to the movable support 41. The second tilting shaft 55 is coaxial with the first tilting shaft 54. The first tilting shaft 54 ​​and the second tilting shaft 55 are respectively fixedly connected to the high-pressure reactor 1. A reducer 58 is fixedly installed on the movable support 41. The reducer 58 is a worm gear reducer with a self-locking function. The output shaft of the reducer 58 is coaxial with and fixedly connected to the second tilting shaft 55. A handwheel 57 is fixedly installed on the input shaft of the reducer 58.

[0047] In the optional scheme of this embodiment, the preferred embodiment is that the autoclave 1 includes a cylinder, a top cover and a bottom cover. The top cover is detachably connected to the top end of the cylinder, and the bottom cover is detachably connected to the bottom end of the cylinder. Sealing rings are respectively sandwiched between the top cover and the cylinder and between the bottom cover and the cylinder. The top cover and the bottom cover are respectively provided with through holes corresponding to the simulated well 9. The simulated well 9 passes through the through holes on the top cover and the bottom cover.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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:

[0057] 1. Simulated formation preparation and loading:

[0058] 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.

[0059] 2. System sealing and air injection:

[0060] 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).

[0061] 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.

[0062] 3. Synthesis of natural gas hydrates:

[0063] 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.

[0064] 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.

[0065] 4. Wellbore working fluid circulation simulation experiment:

[0066] 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.

[0067] 5. Dynamic monitoring and data collection:

[0068] The monitoring unit operates continuously throughout the entire cyclic experiment:

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 6. Product processing and analysis:

[0076] 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.

[0077] 7. Post-experiment processing:

[0078] 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.

[0079] 8. This system allows for convenient conduct of a series of comparative experiments, for example:

[0080] 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.

[0081] 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).

[0082] 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.

[0083] 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.

[0084] 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 simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids, characterized in that, include: The high-pressure vessel contains a simulated formation of the natural gas hydrate extraction site to be simulated. A simulated wellbore is vertically installed at the center of the simulated formation, and multiple liquid permeation holes are distributed on the sidewalls of the simulated wellbore. The gas injection unit includes a methane gas source and an air compressor. The outlet of the methane gas source is connected to the inlet of the air compressor, and the outlet of the air compressor is connected to the autoclave. The liquid injection unit includes a constant-speed, constant-pressure pump and a stirring container. The outlet of the constant-speed, constant-pressure pump is connected to the top of the stirring container, which holds the wellbore working fluid. The outlet of the stirring container is connected to the bottom of the autoclave. The wellbore working fluid circulation unit includes a magnetic circulation pump and a high-pressure filter. The inlet of the high-pressure filter is connected to the top of the simulated wellbore via a first pipeline. The outlet is connected to the inlet of the magnetic circulation pump, and the outlet of the magnetic circulation pump is connected to the bottom of the simulated wellbore; a vacuum preparation module includes a vacuum device and a sealed intermediate container, the middle of the first pipeline is connected to one end of the second pipeline, the other end of the second pipeline extends into the top of the intermediate container, the suction port of the vacuum device is connected to the top of the intermediate container, a first discharge pipe is provided at the bottom of the intermediate container, and a first vent valve is provided on the first discharge pipe; a monitoring unit includes a computer, a temperature sensor, a pressure sensor, a displacement sensor, and a first data acquisition system, the temperature sensor, the pressure sensor, the displacement ... The system comprises multiple temperature sensors and pressure sensors, all distributed vertically in several layers within the simulated geological formation. The displacement sensors are distributed along the top and side inner walls of the autoclave. All temperature, pressure, and displacement sensors are connected to the first data acquisition system, which in turn is connected to the computer. The monitoring unit further includes an ultrasonic detection system comprising three pairs of ultrasonic probes. Each pair of probes includes a transmitting probe and a probe facing the transmitting probe. The monitoring unit includes a receiving probe; wherein, in the first pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the first side wall and the second side wall of the autoclave; in the second pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the third side wall and the fourth side wall of the autoclave; in the third pair of ultrasonic probes, the transmitting probe and the receiving probe are respectively disposed on the top wall and the bottom wall of the autoclave; the monitoring unit further includes a resistivity imaging system, which includes a ring electrode array and a resistivity measuring instrument, wherein the ring electrode array is inserted in the simulated stratum, and the ring electrode array is signal-connected to the resistivity measuring instrument;The monitoring unit also includes a microscopic imaging system, which comprises a microscopic imaging lens and a second data acquisition system. The microscopic imaging lens is fixed to the outside of the autoclave and faces the observation window on the autoclave. The microscopic imaging lens is connected to the computer signal via the second data acquisition system.

2. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 1, characterized in that: It also includes a movable support, the bottom of which is provided with at least three casters. A first tilting shaft and a second tilting shaft are rotatably connected to the movable support. The second tilting shaft is coaxial with the first tilting shaft. The first tilting shaft and the second tilting shaft are respectively fixedly connected to the autoclave. A speed reducer is fixedly installed on the movable support. The speed reducer is a worm gear reducer with a self-locking function. The output shaft of the speed reducer is coaxial with and fixedly connected to the second tilting shaft. A handwheel is fixedly installed on the input shaft of the speed reducer.

3. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 1, characterized in that: The autoclave includes a cylinder, a top cover, and a bottom cover. The top cover is detachably connected to the top end of the cylinder, and the bottom cover is detachably connected to the bottom end of the cylinder. Sealing rings are respectively sandwiched between the top cover and the cylinder, and between the bottom cover and the cylinder. The top cover and the bottom cover are respectively provided with through holes corresponding to the simulated well shaft, and the simulated well shaft passes through the through holes on the top cover and the bottom cover.

4. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 1, characterized in that: It also includes a liquid extraction unit, which comprises a solid-liquid separator, a first storage tank, a second storage tank, and a gas-liquid separator. The inlet of the solid-liquid separator is connected to the second pipeline, the solid outlet of the solid-liquid separator is connected to the first storage tank, the liquid outlet of the solid-liquid separator is connected to the inlet of the gas-liquid separator through a third pipeline, the liquid outlet of the gas-liquid separator is connected to the second storage tank, and the gas outlet of the gas-liquid separator is connected to an exhaust pipe.

5. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 4, characterized in that: The third pipeline is equipped with a first filter, and the exhaust pipe is equipped with a dryer and a gas flow meter.

6. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 1, characterized in that: It also includes a temperature control unit, which includes a constant temperature bath and a jacket fixedly sleeved on the outside of the autoclave. The outlet of the constant temperature bath is connected to the inlet of the jacket, and the outlet of the jacket is connected to the return port of the constant temperature bath.

7. The simulation experimental system for the interaction between natural gas hydrate formations and wellbore working fluids according to claim 1, characterized in that: The injection unit also includes a condenser and a preheater connected in parallel. The working fluid flowing out of the outlet of the stirring container flows through the condenser or the preheater and then enters the autoclave. The condenser is used to cool the working fluid flowing out of the outlet of the stirring container to a set temperature, and the preheater is used to heat the working fluid flowing out of the outlet of the stirring container to a set temperature.

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