Device and test method for simulating brine-sediment migration characteristics of salt cavern gas storage under action of air pressure rise and fall

Abstract

The invention provides a device for simulating brine-sediment migration characteristics of a salt-cavern gas storage under the action of air pressure rise and fall and a test method. The simulation test device comprises a gas injection system, a simulation salt cavity, a gas production system, a brine discharge system, a temperature regulation and control system and a pore pressure measurement system. The gas injection system is connected with the simulated salt cavity through a gas injection pipe; the gas production system is connected with the simulated salt cavity through an exhaust pipe; the simulated salt cavity and the brine recovery device are connected through a simulated brine discharging pipe and a water discharging pipe; and the temperature regulation and control system and the pore pressure measurement system are connected with the simulated salt cavity through pipelines. The test device is reasonable in design, through an indoor simulation test, the brine and sediment migration rule under the free sinking condition, the sediment gap structure evolution rule under the self-weight compaction effect and the brine and sediment secondary migration rule under gas injection and production can be researched, and reference is provided for reasonable setting of injection and production operation parameters of the salt cavern gas storage.

Description

Technical Field

[0001] This invention relates to the field of simulation technology for the injection and production process of salt cavern gas storage, and in particular to a device and test method for simulating the brine-sediment transport characteristics of salt cavern gas storage under the action of gas pressure rise and fall. Background Technology

[0002] In recent years, scholars both domestically and internationally have conducted extensive research on sediment in salt cavern gas storage facilities, including sediment formation processes, physicochemical properties, stacking forms, stress states, space utilization, and their impact on the stability of the gas storage facility. Studies have shown that the void space within the sediment possesses a certain gas storage capacity, and utilizing the effective void space of the sediment for gas storage is a future trend. However, current research on sediment-brine transport characteristics is relatively limited and focuses on a limited range of topics. For high-impurity salt cavern gas storage facilities, sediment occupies most of the salt cavity volume, and the transport of sediment and brine significantly affects the dynamic internal boundary conditions of the gas storage facility. The resulting changes in the gas-water interface position also affect the depth of tubing subsidence, threatening the safe and stable operation of the gas storage facility.

[0003] CN117780340A develops a simulation test device and method for gas-driven brine discharge from salt cavern sediment. The simulation test device includes an injection device, a salt cavern simulation device, and a recovery device. The injection device is connected to the salt cavern simulation device via an injection pipe. The salt cavern simulation device contains a simulated brine discharge column, which is connected to the recovery device via a drain pipe. By injecting air into the simulated salt cavern through the injection device, residual particles and brine are discharged from the simulated brine discharge pipe and enter the recovery device, thereby studying the flow law of gas-driven brine discharge from the salt cavern sediment. Furthermore, by setting up control experiments with mechanical sand fixation and the addition of chemical sand-fixing agents, the clogging law of sediment particles and the clogging law of salt crystallization in the brine discharge column are further studied.

[0004] CN116413394A develops a device and method for evaluating the utilization capacity of voids in the bottom sediment of a salt cavern gas storage facility. The device includes: a simulated salt cavity, a gas pressurization system, a top air inlet valve, a top liquid inlet valve, a bottom air inlet valve, a bottom vent valve, a water injection pump, and a water tank. The top of the simulated salt cavity is connected to the top air inlet valve and the top liquid inlet valve via pipelines; similarly, the bottom of the simulated salt cavity is connected to the bottom vent valve and the bottom air inlet valve via pipelines. The gas pressurization system, the top air inlet valve, and the bottom air inlet valve are connected together via pipelines. The gas pressurization system and the bottom liquid inlet valve are connected to the water injection pump via pipelines, and the water tank is connected to the water injection pump. The sediment is placed at the bottom of the simulated salt cavity, and the brine is stored in the water tank. A method for evaluating the utilization capacity of the sediment voids at the bottom of a salt cavern gas storage tank is proposed. By injecting gas and draining brine, a portion of the brine in the sediment void space is discharged to assess the gas storage capacity of the sediment void space.

[0005] The aforementioned inventions primarily focus on studying the gas-driven brine discharge patterns within sediment and evaluating the gas storage capacity of sediment voids. This invention, however, focuses on studying the transport patterns of sediment and brine under temperature and pressure loads. Therefore, this invention develops a device and experimental method for simulating the brine-sediment transport characteristics in salt cavern gas storage tanks under pressure fluctuations. Summary of the Invention

[0006] The technical solution of this invention is as follows: A device for simulating the brine-sludge transport characteristics of a salt cavern gas storage tank under pressure fluctuations is developed, comprising an injection system, a gas sampling system, a brine discharge system, a simulated salt chamber, a temperature control system, and a pore pressure measurement system. The injection system consists of a nitrogen cylinder, a buffer bottle, an injection pipe, a first pressure gauge, a first control valve, a second control valve, a third control valve, and a fourth control valve. The injection pipe can be connected to the injection hole on the cover plate of the simulated salt chamber. The simulated salt chamber includes a graduated simulated salt chamber sidewall, a cover plate, and a base. During the experiment, the base is connected to the pressure chamber sidewall with fixing bolts, and the simulated salt chamber sidewall is installed, then sludge and brine are added. The gas sampling system consists of a gas cylinder, an exhaust pipe, and a fifth control valve. The exhaust pipe can be connected to the exhaust hole on the cover plate. The brine discharge system includes a simulated brine discharge pipe, a drain pipe, a sixth control valve, a seventh control valve, and a measuring cup. Similarly, the brine discharge pipe can be connected to the brine discharge hole on the cover plate. The temperature control system includes the pressure chamber sidewall, the pressure chamber semi-cylindrical heating plate, the pressure chamber thermocouple, the pressure chamber temperature controller, the water container sidewall, the water container heating plate, the water container thermocouple, the water container base, and the water container temperature controller. The pore pressure measurement system includes a permeable stone, a pore water pressure measuring hole, a pore water pressure measuring tube, a pore pressure sensor, a data acquisition unit, and a result display terminal.

[0007] The sediment used in this invention can be actual sediment samples or artificially prepared sediment based on the results of on-site sediment property tests.

[0008] Slag test sample.

[0009] The brine used in this invention is artificially prepared saturated brine.

[0010] The simulated salt chamber of this invention includes a simulated salt chamber cover, a simulated salt chamber sidewall, and a base.

[0011] This invention simulates the sidewalls of a salt chamber using a transparent acrylic cylindrical tube (with graduations).

[0012] The cover plate of the present invention is provided with an injection pipe through hole, an exhaust pipe through hole, a liquid level measuring hole, a brine discharge hole, and a thermocouple.

[0013] Insertion hole.

[0014] The cover plate is equipped with a liquid level sensor, which can monitor changes in the brine level.

[0015] The cover plate is connected to the side wall of the pressure chamber by bolts.

[0016] The simulated brine drain pipe is made of stainless steel.

[0017] The inlet of the simulated brine drain pipe is equipped with a sieve with a diameter of 2mm.

[0018] The simulated brine discharge pipe is sealed at the bottom, with a liquid inlet located on the lower right side. The pipe inlet is treated to prevent sand from entering, which can be achieved mechanically.

[0019] Sand control (setting up sand control belts), chemical sand control (sand fixing agent: epoxy resin and phenolic resin foam solution).

[0020] The gas injection pipe is equipped with a first control valve, a second control valve, a third control valve, a fourth control valve, and a fifth control valve.

[0021] The system includes a first pressure gauge and a second pressure gauge. A second and third control valve control the air intake of the buffer bottle, while the first pressure gauge monitors the pressure in the buffer bottle in real time. A fourth control valve controls the air injection into the chamber, and the second pressure gauge monitors the chamber pressure in real time. This allows for adjustment of different injection pressures during simulation experiments. All the valves and pressure gauges work together to measure the porosity of the sediment.

[0022] The gas extraction pipe is equipped with a fifth control valve.

[0023] The drain pipe is equipped with a sixth control valve and a seventh control valve, which can control the amount of water discharged.

[0024] The pore water pressure measuring tube is equipped with an eighth control valve.

[0025] In this embodiment of the invention, the height of the simulated salt chamber sidewall is 30cm, and its diameter is 20cm. The diameters of the air injection hole, air sampling hole, liquid level measuring hole, brine discharge hole, and temperature measuring hole are all 2cm, and the intervals between the air injection hole, air sampling hole, liquid level measuring hole, brine discharge hole, and temperature measuring hole are also 2cm. The heights of the air injection pipe, air sampling pipe, liquid level measuring pipe, brine discharge pipe, and temperature measuring pipe are all 4cm, and they are spaced 0.5cm apart.

[0026] The pressure chamber sidewall of the present invention is made of stainless steel, and the semi-cylindrical electric heating plate of the pressure chamber is embedded in the pressure chamber sidewall.

[0027] The two ends of its resistance wire are connected to the temperature controller, and the outside of the heating plate is filled with heat-insulating asbestos.

[0028] Because the aeration and brine discharge systems are at room temperature (e.g., 25°C), while the temperature of the brine in the simulated salt chamber is at the set temperature...

[0029] Temperature variations (e.g., 50.5℃) cause a temperature gradient in the water within the drain pipe, affecting measurement accuracy. Therefore, placing the drain pipe and pore water pressure measuring tube in a water container with a constant temperature ensures that temperature changes within the simulated brine chamber do not affect the measurement of water volume, thus enabling accurate measurement of pore water pressure in the sediment and the volume of brine discharged.

[0030] Because plastic drainage pipes and pore water pressure measuring tubes have a large coefficient of thermal expansion, they can introduce significant errors into the test results.

[0031] Therefore, the drainage pipe and pore water pressure measuring pipe of this invention are made of stainless steel, with a spiral structure in the middle section. The spiral section is located in a room temperature water container and can exchange heat with the water.

[0032] An airtightness check should be performed on the testing apparatus before use. The steps for checking the airtightness of the apparatus include opening the first control valve and the second...

[0033] Four control valves: close other control valves, start the nitrogen cylinder, adjust the injection pressure, slowly increase the pressure to the test pressure, and check whether there is any leakage in the test system; after the test, stop the injection, open the fifth control valve, and release the pressure.

[0034] This invention also provides an experimental method for simulating the transport characteristics of brine and sediment in a salt cavern gas storage facility under pressure fluctuations, using the aforementioned simulation experimental apparatus. The simulation experimental method includes methods for simulating the transport laws of brine and sediment under free settling conditions, methods for simulating the evolution of sediment pore structure under self-weight compaction, and methods for simulating the secondary transport laws of brine and sediment under gas injection and production conditions. Figure 3 As shown.

[0035] (1) The simulation test method for the transport law of brine and sediment under free sinking conditions includes the following steps:

[0036] Step 1: Connect the pressure chamber sidewall to the simulated salt chamber base using fixing bolts and O-rings, then install the simulated salt chamber sidewall. Prepare saturated brine and sediment particle samples of different particle sizes (add some tracer sand to the sediment particles). First, pour the brine into the simulated salt chamber.

[0037] Step 2: Activate the temperature control device and set the temperature at 50.5℃ to simulate the actual salt chamber temperature. At the same time, set up multiple control experiments and set the sediment drop height and sediment particle size range as variables.

[0038] Step 3: Pour a set of sediment into an open container at a constant speed from a certain height until the brine level is 2-3 cm above the sediment surface.

[0039] Step 4: Allow the static test apparatus to settle fully, sealing the simulated salt chamber with a cover plate during this process. Observe the flow pattern of the tracer sand within the sealed container, photograph and record the migration patterns of the brine and sediment particles, and record the changes in pore pressure in the sediment. After the sediment has stabilized, photograph and record the stratified settling state of the sediment.

[0040] Step 5: Change the particle size range or the settling height of the sediment particles, prepare a new open container filled with saturated brine, and repeat steps 3-4 of the experiment to analyze the transport law of brine and sediment particles under different particle size ranges and settling heights.

[0041] (2) The simulation test method for the transport law of brine and sediment under self-weight compaction includes the following steps:

[0042] Step 1: Following step 4 of the previous experiment, continue to allow the sediment to settle for 3 hours. Start the pore pressure measurement system. Record the pore water pressure of the sediment and the brine height every 30 minutes.

[0043] Step 2: Plot the curves of pore water pressure and brine height in the sediment as a function of compaction time. After 3 hours, connect the air injection system and measure the porosity of the sediment every 30 minutes. The air injection pressure is 0.3 MPa. Record the changes in the porosity of the sediment.

[0044] Step 3: Change the particle size range of the sediment and repeat steps 1-2. Analyze the migration characteristics of brine and sediment under different self-weight compaction times and different sediment particle size ranges.

[0045] (3) The experimental method for simulating the secondary transport of brine and sediment under gas injection and production includes the following steps:

[0046] Step 1: Following Step 2 of the previous experiment, the simulated gas injection process begins. Gas is injected and pressurized, and changes in brine level and sediment height are observed and recorded. Simultaneously, changes in brine temperature and sediment pore water pressure over time are recorded.

[0047] Step 2: Simulate the gas extraction process. Connect the gas extraction system, extract gas, and observe and record changes in brine level and sediment height. Similarly, record changes in brine temperature and sediment pore water pressure over time.

[0048] Step 3: Measure the effective porosity of the sediment. Connect the brine discharge system, inject air to discharge the brine, and record the volume of discharged brine. This volume is the porosity of the sediment that can be used for air storage.

[0049] Step 4: Change the particle size range of the sediment and repeat steps 1-2. Analyze the secondary migration patterns of brine and sediment under the influence of air pressure fluctuations.

[0050] The present invention lays 1 to 3 layers of colored tracer sand inside the sediment particles to analyze the flow pattern of brine and sediment particles in the sediment during the experiment.

[0051] The principle of the device for measuring the porosity of sediment particles described in this invention is as follows:

[0052] The porosity of sediment particles is measured using the principle of isothermal gas expansion. Specifically, a gas of known volume and pressure is isothermally expanded into a container of unknown volume, and the equilibrium pressure of the gas after expansion is measured. From the ideal gas law, we have:

[0053] P b V b =Z1n1RT1 (1)

[0054] P a (V w +V v )=Z2n2RT2 (2)

[0055] P e (V b +V w +V v )=Z3(n1+n2)RT3 (3)

[0056] In the formula, P b The pressure of the buffer bottle is Pa; P a The local standard atmospheric pressure is Pa; P e To balance the pressure, Pa; V b Let m be the volume of the buffer bottle. 3 V w V is the volume of the net brine above the sediment; vLet be the pore volume of the sediment; R be the molar gas constant, taken as 8.314 J / (mol·K); Z1, Z2, and Z3 be the gas compressibility coefficients in the buffer bottle, pressure chamber, and after expansion, respectively; T1, T2, and T3 be the temperatures (K) in the buffer bottle, pressure chamber, and after expansion, respectively; n1 and n2 be the number of moles of gas in the buffer bottle and pressure chamber, respectively. During the gas expansion, the pressure in the pressure chamber is standard atmospheric pressure, and the room temperature is 25℃. If the effect of gas pressure on the sediment particle volume and the change in gas compressibility factor are ignored, then:

[0057] Z1=Z2=Z3 (4)

[0058] T1=T2=T3 (5)

[0059] Combining equations (1)-(5), we get:

[0060] P e (V b +V w +V v ) = P b V b +P a (V w +V v (6)

[0061] Furthermore, from the formula for the porosity of sediment:

[0062]

[0063] In the formula, V s denoted as , where is the total volume of the sediment accumulation at the bottom of the pressure chamber; and is the porosity of the sediment.

[0064] Combining equations (6) and (7), the formula for calculating the porosity of sediment particles is obtained as follows:

[0065] Attached Figure Description

[0066] Figure 1 The present invention provides a device for simulating the brine-sediment transport characteristics of a salt cavern gas storage tank under the action of air pressure rise and fall.

[0067] Figure 2 This is a schematic diagram of the simulated brine drain pipe and sandproof belt provided by the present invention.

[0068] Figure 3 This is a schematic diagram of the experimental design for simulating the transport characteristics of brine and sediment in a salt cavern gas storage tank under simulated air pressure rise and fall, as provided by the present invention.

[0069] Figure 4The experimental procedure diagram provided by this invention illustrates the characteristics of brine-sediment transport in a salt cavern gas storage tank under simulated pressure rise and fall.

[0070] In the diagram: 1-Fixing bolt; 2-Injection pipe; 3-Gas sampling pipe; 4-Brine discharge pipe; 5-Injection hole; 6-Gas sampling hole; 7-Brine discharge hole; 8-Temperature measuring hole; 9-Liquid level measuring hole; 10-Pressure chamber thermocouple; 11-Pressure chamber temperature controller; 12-Simulated salt chamber sidewall; 13-Scale; 14-Pressure chamber sidewall; 15-Pressure chamber semi-cylindrical heating plate; 16-Saturated brine; 17-Sediment particles; 18-O-ring; 19-Permeable stone; 20-Pressure chamber base; 21-Nitrogen cylinder; 22-First control valve; 23-Second control valve; 24-Third control valve; 25-First pressure gauge; 26-Buffer bottle; 27-Injection pipeline; 2 8-Fourth control valve; 29-Second pressure gauge; 30-Fifth control valve; 31-Gas sampling pipeline; 32-Gas storage cylinder; 33-Pore water pressure measuring hole; 34-Water container sidewall; 35-Water container heating plate; 36-Water container thermocouple; 37-Support; 38-Water container temperature controller; 39-Water container base; 40-Eighth control valve; 41-Pore pressure sensor; 42-Data acquisition unit; 43-Result display terminal; 44-Simulated brine discharge pipe; 45-Sixth control valve; 46-Drain pipe; 47-Seventh control valve; 48-Measuring cup; 49-Sieve hole; 50-Sandproof belt; 51-Gravel; 52-Liquid level measuring tube; 53-Temperature measuring tube. Detailed Implementation

[0071] like Figure 4 As shown, an experimental method for simulating the brine-sediment transport characteristics of a salt cavern gas storage facility under pressure fluctuations includes a simulation experiment method for the transport law of brine and sediment under free sinking conditions, a simulation experiment method for the evolution law of sediment pore structure under self-weight compaction, and a simulation experiment method for the secondary transport law of brine and sediment under gas injection and production conditions.

[0072] (1) The specific implementation steps of the simulation experiment method for the transport law of brine and sediment under free sinking conditions are as follows:

[0073] 1) Sample and apparatus preparation: Sediment particles of different size ranges were obtained using a sieving method, and saturated brine was prepared. The current experiment requires a simulated salt chamber test apparatus, a temperature control system, and a pore pressure measurement system. The pressure chamber sidewall was connected to the simulated salt chamber base with bolts. The temperature control system and pore pressure measurement system were then installed. The saturated brine was poured into an open container, and the temperature was controlled at 50.5℃.

[0074] 2) Set up multiple control tests: Set different sediment drop heights and sediment particle size ranges.

[0075] 3) Simulate the process of sludge peeling and soaking: Pour sludge particles of a certain size range into the simulated salt chamber at a predetermined height at a uniform speed until the brine surface is 2-3 cm higher than the sludge surface.

[0076] 4) Simulated Free Settling: Seal the open container with a cover plate and place the test device in a static position to allow the sediment particles to settle fully. Observe the flow pattern of the tracer sand in the closed container, take photos to record the migration patterns of the sediment particles and brine, and simultaneously record the changes in pore pressure in the sediment. After the sediment has stabilized, take photos to record the stratified settling state of the sediment.

[0077] 5) Conduct control experiments and summarize the results: Remove the lid and pore pressure measurement system from the sealed container, pour out the brine, remove the sediment, air-dry or oven-dry the sediment, wash away the sediment and brine remaining in the simulated salt chamber, and then pour in brine again. Repeat steps 3-4 to analyze the transport patterns of brine and sediment particles under different sediment particle size ranges and different falling heights.

[0078] (2) The specific implementation steps of the simulation experiment method for the evolution law of sediment pore structure under self-weight compaction are as follows:

[0079] 1) Self-weight stacking: Following step 4 of the previous experiment, continue stacking for 3 hours. Take photos every 30 minutes to record the pore pressure of the sediment and the brine height. Plot the curves of pore pressure of the sediment and brine height as a function of compaction time.

[0080] 2) Measure the change in sediment porosity: After 3 hours, connect the gas injection system (connect the nitrogen cylinder, the first control valve, the second control valve, the buffer bottle, the first pressure gauge, the third control valve, the fourth control valve, the second pressure gauge, and the simulated salt chamber cover plate in sequence with the gas injection pipe), measure the porosity of sediment particles every 30 minutes, and record the change in sediment porosity.

[0081] 3) Conduct control experiments and summarize the results: Repeat steps 1-2 by changing the particle size range of the sediment. Analyze the migration characteristics of brine and sediment under different self-weight compaction times and different sediment particle size ranges.

[0082] (3) The specific implementation steps of the simulation experiment method for the secondary transport law of brine and sediment under gas injection and production are as follows:

[0083] 1) Setting up the gas injection and collection device: Following the previous test step 2, connect the gas collection system (connect the simulated salt chamber cover, the fifth control valve and the gas storage cylinder in sequence with the exhaust pipe) to prepare for simulating the gas injection and collection process.

[0084] 2) First, simulate the gas injection process: inject gas and pressurize (0.005-0.2MPa), take pictures to record the changes in sediment height, record the changes in brine level and brine temperature, and draw curves showing the changes in brine level, brine temperature and sediment pore pressure over time.

[0085] 3) Simulate the gas extraction process: reduce the gas pressure (0.005-0.2MPa), take pictures to record the changes in sediment height, record the changes in brine level and temperature, and plot the curves of brine level, brine temperature and sediment pore pressure over time.

[0086] 4) Measure the effective void volume of the sediment: Connect the brine discharge system, inject air to discharge the brine, and record the volume of discharged brine. This volume is the void volume in the sediment that can be used for air storage.

[0087] 5) Conduct control experiments and summarize the results: Change the particle size range of the sediment and repeat steps 1 to 4. Summarize the secondary migration patterns of brine and sediment during gas injection and production.

Claims

1. A device for simulating the brine-sediment migration characteristics of a salt cavern gas storage under the action of simulated gas pressure cycling, characterized in that, The simulation test device comprises a gas injection system, a simulated salt cavity, a gas production system, a brine discharge system, a temperature control system and a pore pressure measurement system; the gas injection system and the simulated salt cavity are connected through a gas injection pipe; the gas production system and the simulated salt cavity are connected through a gas discharge pipe; the simulated salt cavity and the brine recovery device are connected through a simulated brine discharge pipe and a drain pipe; the temperature control system and the pore pressure measurement system are connected with the simulated salt cavity through pipelines.

2. The simulation test device according to claim 1, characterized in that The gas injection system comprises a nitrogen cylinder, a buffer bottle, a first control valve, a second control valve, a third control valve, a fourth control valve, a first pressure gauge, a second pressure gauge and a gas injection pipe; the gas production system comprises a gas production pipe, a gas storage bottle and a fifth control valve; the buffer bottle is a stainless steel pressure vessel; the pressure gauge is a digital pressure gauge with an RS485 interface.

3. The simulation test device according to claim 1, characterized in that, The simulated salt cavity comprises a transparent cylindrical container, a transparent cubic container or a transparent cuboid container; the transparent cylindrical container comprises a cover plate, a simulated salt cavity side wall and a simulated salt cavity base; the cover plate and the simulated salt cavity side wall are connected through flanges; the simulated salt cavity side wall is made of transparent acrylic cylinder and has scales on the upper surface; the cover plate is provided with a liquid level sensor, and the reference is a MIK-MP ultrasonic liquid level meter.

4. The simulation apparatus according to claim 1, wherein The brine discharge system comprises a simulated brine discharge pipe, a drain pipe, a sixth control valve, an eighth control valve, a water container and a measuring cup; the valves are one-way valves, which can prevent liquid and gas from flowing back, improve the stability and reliability of the device; the simulated brine discharge pipe and the drain pipe are made of stainless steel hoses; the water container comprises a water container side wall, a water container electric heating plate, a water container base, a water container electric thermocouple, a support and a water container temperature control system.

5. The simulation apparatus according to claim 1, wherein The temperature control system comprises a pressure chamber side wall, a pressure chamber semi-cylindrical electric heating plate, a pressure chamber electric thermocouple, a pressure chamber temperature controller and a water container.

6. The simulation test device of claim 1, wherein The pore pressure measurement system comprises a water permeable stone, a pore water pressure measuring hole, a pore water pressure measuring pipe and a pore pressure sensor, a data collector and a result display terminal; the pore water pressure measuring pipe needs to pass through the water container and then be connected with the pore pressure sensor.

7. A test method for simulating the brine-sediment migration characteristics of a salt cavern gas storage under the action of simulated gas pressure lift, characterized in that, A device for simulating the brine-sediment migration law characteristics of a salt cavern gas storage under the action of gas pressure lifting according to any one of the above claims 1 to 6, and a test method thereof, which comprises: a simulation test method of brine and sediment migration law under free falling conditions, a simulation test method of sediment void structure evolution law under self-weight compaction, and a simulation test method of secondary migration law of brine and sediment under gas injection and production.

8. The simulation test method according to claim 7, characterized by, The simulation test method of brine and sediment migration law under free falling conditions comprises the following steps: Step 1: connect the pressure chamber side wall and the simulated salt cavity base with fixed bolts and O-rings, then install the simulated salt cavity side wall, prepare saturated brine and sediment particle samples of different particle size ranges (add some tracer sand to the sediment particles), and first pour the brine into the simulated salt cavity; Step 2: start the temperature control device, control the temperature at 50.5℃ to simulate the temperature of the real salt cavity, and set multiple groups of control tests with the sediment falling height and the sediment particle size range as variables; Step 3: uniformly pour a group of sediments from a certain height into the open container until the brine liquid surface is 2-3 cm higher than the sediment surface. Step 4: The test device is left to stand so that the sediment particles can settle down, and in this process, the simulated salt cavity device is sealed with a cover plate, the flow pattern of the tracer sand in the closed container is observed, the migration law of the brine and the sediment particles is recorded by taking pictures, the change of the sediment void pressure is recorded, and after the sediment settles down stably, the layered sedimentation state is recorded by taking pictures; Step 5: The particle size range of the sediment particles or the sediment falling height is changed, a new open container filled with saturated brine is prepared, and the experimental steps 3-4 are repeated to analyze the migration law of the brine and the sediment particles under the conditions of different particle size ranges of the sediment particles and different falling heights.

9. The simulation test method according to claim 7 or 8, characterized in that, The brine and sediment migration law simulation test method under the self-weight compaction condition comprises the following steps: Step 1: After the previous test step 4, continue to stand and accumulate, and record the sediment pore water pressure and the brine height every 30 minutes for 3 hours; Step 2: Draw a curve of the sediment pore water pressure and the brine height changing with the compaction time, after 3 hours, connect the gas injection system, measure the sediment void ratio every 30 minutes, the gas injection pressure is 0.3 MPa, and the change of the sediment void ratio is recorded; Step 3: Change the particle size range of the sediment particles, repeat steps 1-2, and analyze the migration characteristics of the brine and the sediment under the conditions of different self-weight compaction times and different particle size ranges of the sediment particles.

10. The simulation test method according to any one of claims 7 to 9, characterized in that, The brine and sediment secondary migration law simulation test method under the injection and production conditions comprises the following steps: Step 1: After the previous test step 2, start the simulation of the gas injection process, inject gas and pressurize, observe and record the change of the brine level and the sediment height, and record the change of the brine temperature and the sediment pore water pressure with time; Step 2: Simulate the gas production process, connect the gas production system, produce gas, observe and record the change of the brine level and the sediment height, and also record the change of the brine temperature and the sediment pore water pressure with time; Step 3: Measure the effective void ratio of the sediment, connect the brine discharge system, inject gas and discharge brine, and record the discharged brine amount; Step 4: Change the particle size range of the sediment particles, repeat steps 1-3, and analyze the secondary migration law of the brine and the sediment under the action of the gas pressure rising and falling.

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