Tensile test device for methane hydrate-containing sediments and test method thereof

Abstract

The present invention provides a tensile test device for methane hydrate-containing sediments and a test method thereof, including a pressure-bearing chamber, a constant temperature box, a gas supply system, a tensile system and a data acquisition system. In the tensile test device for methane hydrate-containing sediments of the present invention, by setting the pressure-bearing chamber and the constant temperature box, the low temperature and high pressure environment required for the formation of methane hydrate sediments on the seabed can be simulated. Methane is injected into the soil sample with a certain water content through the gas supply system, so that methane combines with water to form methane hydrate in the soil pores under certain gas pressure and temperature conditions, realizing the rapid and accurate simulation of the preparation of in-situ methane hydrate-containing soil in the marine environment in the laboratory, thereby reducing the difficulty and cost of obtaining test samples of methane hydrate sediments.

Description

Technical Field

[0001] The present invention relates to the technical field of physical property testing of materials, and particularly to a tensile test device for methane hydrate-containing sediments. Background Art

[0002] Methane hydrate (commonly known as combustible ice) is a kind of ice-like, non-stoichiometric cage-shaped crystalline compound formed by gas molecules such as methane being inhaled into the voids of cage-shaped water molecule clusters under certain pressure and temperature conditions. It is widely distributed in the submarine sediments of the continental margin slope area and the permafrost zone, and has the characteristics of high calorific value, large energy, and clean and pollution-free.

[0003] At present, the related research on the mechanical properties of methane hydrate-containing sediments is still in the initial stage of exploration. Most laboratories use triaxial tests to simulate the mechanical properties of methane hydrate-containing sediments in the actual geotechnical environment. The triaxial test is one of the most commonly used test methods in laboratory soil testing. However, when applied to the testing of methane hydrate-containing sediments, there are mainly the following defects: First, methane hydrate-containing sediments generally exist stably in deep-sea sediment areas and permafrost zones on land, resulting in difficult and costly acquisition of test samples; Second, the current triaxial test device can only apply confining pressure and axial pressure, and cannot apply other types of forces, thus resulting in a relatively limited scope of mechanical research on methane hydrate-containing sediments and restricting the development of its constitutive model. Summary of the Invention

[0004] In order to solve the technical problems in the prior art that the mechanical test device for methane hydrate-containing sediments has high sample acquisition cost and relatively limited mechanical research scope, the technical solution of the present invention is as follows:

[0005] On the one hand, the present invention provides a tensile test device for methane hydrate-containing sediments, including a pressure-bearing chamber, a constant-temperature box, a gas supply system, a tensile system, and a data acquisition system.

[0006] A dumbbell-shaped specimen frame is arranged inside the pressure-bearing chamber for clamping the specimen to be tested. The specimen frame is spliced by a movable part and a fixed part. The fixed part is fixed inside the pressure-bearing chamber. The pressure-bearing chamber is also provided with a piston hole communicating with the outside. A tensile piston is inserted into the piston hole. The movable part is connected to the tensile piston and moves away from the fixed part under the drive of the tensile piston.

[0007] The constant-temperature box is arranged outside the pressure-bearing chamber.

[0008] The gas supply system includes a methane gas cylinder, a gas booster pump, and a vacuum pump. The methane gas cylinder is connected to the gas booster pump, and the gas booster pump and the vacuum pump are respectively connected to the pressure-bearing chamber.

[0009] The stretching system includes a loading pump, a hydraulic loading cylinder and a loading piston. The loading pump is connected to the hydraulic loading cylinder to drive the movement of the loading piston in the hydraulic loading cylinder.

[0010] The data acquisition system includes a processor, and a tensile force sensor, a displacement sensor, a temperature sensor and a first pressure sensor electrically connected to the processor. The tensile force sensor is connected between the loading piston and the stretching piston. The displacement sensor is arranged on the stretching piston. The temperature sensor and the first pressure sensor are arranged on the pressure-bearing chamber.

[0011] In the tensile test device for methane hydrate-containing sediment of the present invention, by providing a pressure-bearing chamber and a constant temperature box, the low temperature and high pressure environment required for the formation of methane hydrate sediment on the seabed can be simulated. Methane is injected into the soil sample with a certain water content through the gas supply system, so that methane combines with water to form methane hydrate in the soil sample pores under certain gas pressure and temperature conditions, realizing the rapid and accurate simulation of the preparation of in-situ methane hydrate-containing soil in the marine environment in the laboratory, thereby reducing the difficulty and cost of obtaining test samples of methane hydrate sediment; by providing a stretching system and a data acquisition system, tensile tests can be carried out according to different geological working conditions, so as to obtain various mechanical indexes such as tensile strength, modulus and reduction of area. The tensile test device for methane hydrate-containing sediment in the present invention has a working principle that conforms to the in-situ hydrate formation mode and mining working condition, has a relatively simple structure and low cost, and can be equipped for most scientific research and survey and design units.

[0012] In a possible design, the pressure-bearing chamber includes a chamber cover plate and a chamber body. The chamber cover plate is detachably covered on the chamber opening of the chamber body, and the bottom of the chamber body is fixed on the test platform.

[0013] In a possible design, the gas supply system further includes an air compressor, and the air compressor is connected to the gas booster pump to provide a driving gas source for the gas booster pump.

[0014] In a possible design, a traveling trolley is further arranged inside the pressure-bearing chamber. The traveling trolley includes a support platform and pulleys, and the specimen frame is placed on the support platform.

[0015] In a possible design, the gas supply system further includes a gas buffer tank, a pressure regulating valve, a gas flow controller and a check valve. The gas buffer tank is connected between the gas booster pump and the pressure-bearing chamber, and the pressure regulating valve, the gas flow controller and the check valve are connected between the gas buffer tank and the pressure-bearing chamber.

[0016] In a possible design, a safety valve and a second pressure sensor are further provided on the buffer tank, and the second pressure sensor is electrically connected to the processor.

[0017] In a possible design, the tensile test device for methane hydrate-containing sediment in the present invention further includes: a gas recovery device connected to the pressure-bearing chamber.

[0018] In a possible design, the interior of the hydraulic loading cylinder is divided into a left chamber and a right chamber by the loading piston, and the left chamber and the right chamber are respectively connected to the loading pump; a third pressure sensor is further provided between the loading pump and the right chamber, and the third pressure sensor is electrically connected to the processor.

[0019] On the other hand, the present invention also provides a tensile test method for methane hydrate-containing sediment. The test method is based on the above-mentioned tensile test device for methane hydrate-containing sediment and includes the following steps:

[0020] Step 1, soil sample forming: Press the soil sample into a sample with a jack according to the set density, and after pressing, put it into the refrigerator together with the mold and then take out the soil sample.

[0021] Step 2, soil sample installation: Install the formed soil sample in the sample frame in the chamber body and cover the chamber cover plate.

[0022] Step 3, vacuum pumping: Start the vacuum pump to pump vacuum on the pressure-bearing chamber and its connecting pipelines to remove internal impurities.

[0023] Step 4, gas application: Open the methane gas cylinder and the gas booster pump, adjust the pressure regulating valve to adjust the pressure to the set pressure value of 6 Mpa to 10 Mpa, then close the methane gas cylinder and the gas booster pump, and at the same time close the air inlet of the pressure-bearing chamber.

[0024] Step 5, airtightness inspection: Start the data acquisition system and turn on the thermostat, set the temperature to 18°C to 20°C, maintain the internal temperature of the pressure-bearing chamber stable, and determine the airtightness of the pressure-bearing chamber through the monitoring data changes of the temperature sensor and the pressure sensor.

[0025] Step 6, synthesis of hydrate sample: Set the temperature of the thermostat to -2°C to 2°C to lower the internal temperature of the pressure-bearing chamber, thereby lowering the temperature of the soil sample to reach the hydrate synthesis condition, and start to form hydrates in the soil sample.

[0026] Step 7, determination of completion of hydrate synthesis: When the pressure value displayed by the first pressure sensor remains stable within the range of 3 Mpa to 6 Mpa and the temperature value displayed by the temperature sensor remains constant within the range of -2°C to 2°C, the hydrate synthesis in the soil sample inside the pressure-bearing chamber is completed and the sample preparation is completed.

[0027] Step 8: Tensile test. Start the loading pump to drive the tensile piston and the movable part to move by the loading piston. The movable part conducts tensile test on the specimen. The force sensor collects the force exerted by the loading piston on the tensile piston, and the displacement sensor collects the lateral strain displacement data of the tensile piston.

[0028] Step 9: Gas collection and specimen disassembly. After the tensile test is completed, turn off the loading pump, raise the temperature of the constant temperature box to 20°C. The hydrate of the specimen decomposes, and the released methane is collected through the gas recovery device. Calculate the hydrate saturation of the specimen according to the collected amount. Finally, remove the specimen from the specimen frame.

[0029] In a possible design, in the said Step 1, the set density of the soil sample is 1.5 g / cm 3 ~2.5 g / cm 3 , and the water content is 2% - 40%.

[0030] The test method provided by the present invention can preferably reproduce the methane hydrate formation environment in the laboratory, simulate the growth habit of hydrates in the natural state, and conduct tensile strength tests, providing technical guarantee and support for exploring the mechanical behavior laws of methane hydrate-bearing sediments and improving the corresponding constitutive models, and also playing a positive role in promoting the commercial exploitation of methane hydrates in China. Description of the Drawings

[0031] Figure 1 is a schematic diagram of a tensile test device for methane hydrate-bearing sediments provided by an embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of a tensile system and a pressure-bearing chamber provided by an embodiment of the present invention;

[0033] Figure 3 is Figure 2 a top view of the pressure-bearing chamber without the chamber cover plate assembled in

[0034] Figure 4 is a schematic diagram of a specimen provided by an embodiment of the present invention.

[0035] Reference numerals: 10, pressure-bearing chamber; 11, specimen frame; 111, movable part; 112, fixed part; 12, piston hole; 13, tensile piston; 14, support platform; 15, pulley; 16, chamber cover plate; 161, air inlet; 162, temperature measurement hole; 163, air outlet; 17, chamber body; 20, constant temperature box; 31, methane gas cylinder; 32, gas booster pump; 33, vacuum pump; 34, gas buffer tank; 341, safety valve; 342, pressure sensor II; 35, pressure regulating valve; 36, gas flow controller; 37, check valve; 38, air compressor; 41, loading pump; 42, hydraulic loading cylinder; 43, loading piston; 44, pressure sensor III; 51, processor; 52, tensile force sensor; 53, displacement sensor; 54, temperature sensor; 55, pressure sensor I; 60, gas recovery device; 70, specimen; 80, solenoid valve X; 81, solenoid valve I; 82, solenoid valve II; 83, solenoid valve III; 84, solenoid valve IV; 85, solenoid valve V; 86, solenoid valve VI; 87, solenoid valve VII; 88, solenoid valve VIII; 89, solenoid valve IX; 90, test platform. Detailed implementation mode

[0036] The technical solutions in the present invention will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0037] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a connection that can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "side", "inner", "outer", "top", "bottom", etc. is based on the installed orientation or positional relationship, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0039] It should also be noted that in the embodiments of the present invention, the same reference numerals are used to represent the same component or the same part. For the same parts in the embodiments of the present invention, only one of the parts or components may be marked with the reference numeral in the figure. It should be understood that for other identical parts or components, the reference numerals are equally applicable.

[0040] Hereinafter, terms such as "first", "second", etc. are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features.

[0041] Currently, there is a lack of a complete set of devices and methods for testing the tensile strength of methane hydrate-bearing sediments. Most of the known devices for testing tensile strength are modified based on conventional tensile testers, and to a certain extent, they cannot meet the working conditions of simulating subsea methane hydrate sediments. In addition, the lack of data on the tensile strength of methane hydrate-bearing sediments restricts the development of constitutive models for methane hydrate-bearing sediments. The present invention can better reproduce the methane hydrate formation environment in the laboratory, simulate the growth habits of hydrates in the natural state, and conduct tensile strength tests, providing technical guarantees and support for clarifying the mechanical behavior laws of methane hydrate-bearing sediments and improving the corresponding constitutive models, and also playing a positive role in promoting the commercial exploitation of methane hydrates in China.

[0042] As Figures 1-3 shown, an embodiment of the present invention provides a tensile test device for methane hydrate-bearing sediments, including a pressure-bearing chamber 10, a constant temperature chamber 20, a gas supply system, a tensile system, and a data acquisition system. The constant temperature chamber 20 provides a low-temperature environment for the pressure-bearing chamber 10 to simulate the subsea environmental state. The gas supply system injects methane into the pressure-bearing chamber 10 so that it combines with water in the pores of the soil sample to form a specimen 70 - methane hydrate sediment. The tensile system performs a tensile action on the specimen 70, and during the tensile process, the data acquisition system collects test data. Among them, the specific designs of each component are as follows.

[0043] The pressure-bearing chamber 10 is a cuboid mechanism, and a dumbbell-shaped specimen 70 frame 11 is arranged inside it for clamping the specimen 70 to be tested. The specimen 70 frame 11 is composed of two symmetrically arranged frame-shaped parts spliced together, namely a movable part 111 and a fixed part 112. The fixed part 112 is fixed inside the pressure-bearing chamber 10. When the tensile system performs a tensile action, the fixed part 112 always remains stationary to fix one end of the specimen 70. The pressure-bearing chamber 10 is also provided with a piston hole 12 communicating with the outside. A tensile piston 13 is inserted into the piston hole 12. The movable part 111 is connected to the tensile piston 13, and the tensile piston 13 can axially move along the inner wall of the piston hole 12, thereby driving the movable part 111 to move together, and thus stretching the other end of the specimen 70.

[0044] The thermostat 20 is arranged outside the pressure-bearing chamber 10 and can adjust the temperature of the pressure-bearing chamber 10 to simulate the low-temperature environment of the seabed. During the methane hydrate sediment formation stage, the thermostat 20 needs to provide a low-temperature environment of -2°C to 2°C for the pressure-bearing chamber 10 and maintain it until the end of the tensile test. When the test needs to be ended and methane is decomposed from the soil sample, the thermostat 20 needs to provide a temperature environment of 18°C to 20°C for the pressure-bearing chamber 10.

[0045] The gas supply system includes a methane gas cylinder 31, a gas booster pump 32 and a vacuum pump 33. The methane gas cylinder 31 is connected to the gas booster pump 32, and the gas booster pump 32 and the vacuum pump 33 are respectively connected to the pressure-bearing chamber 10. The gas booster pump 32 pumps the methane in the methane gas cylinder 31 into the pressure-bearing chamber 10, so that the methane gas in the pressure-bearing chamber 10 reaches 6 Mpa - 10 Mpa to simulate the high-pressure environment of the seabed. Before pumping methane into the pressure-bearing chamber 10, it is necessary to use the vacuum pump 33 to evacuate the impurities in the pipeline and the pressure-bearing chamber 10 to avoid impurities affecting the test data.

[0046] The tensile system includes a loading pump 41, a hydraulic loading cylinder 42 and a loading piston 43. The loading pump 41 is connected to the hydraulic loading cylinder 42 to drive the loading piston 43 in the hydraulic loading cylinder 42 to move. The loading piston 43 divides the interior of the hydraulic loading cylinder 42 into a left chamber and a right chamber. The loading pump 41 is respectively connected to the left chamber and the right chamber. When the loading pump 41 pumps liquid into the right chamber, it can push the loading piston 43 to move leftward. The loading piston 43 drives the tensile force sensor 52, the tensile piston 13 and the movable part 111 to move together, so that the tensile system performs a tensile action on the specimen 70.

[0047] Data acquisition system, including a processor 51 and a tensile sensor 52, a displacement sensor 53, a temperature sensor 54, and a pressure sensor 55 electrically connected to the processor 51. The tensile sensor 52 is connected between the loading piston 43 and the stretching piston 13. The displacement sensor 53 is arranged on the stretching piston 13. The temperature sensor 54 and the pressure sensor are arranged on the pressure-bearing chamber 10. The tensile sensor 52 is connected between the loading piston 43 and the stretching piston 13. When the loading pump 41 drives the loading piston 43 to move leftward, the tensile force received by the stretching piston 13 is monitored through the tensile sensor 52, and the displacement of the stretching piston 13 is monitored through the displacement sensor 53. Since the stretching piston 13, the movable part 111, and the specimen 70 are all in a linkage relationship, the tensile sensor 52 and the displacement sensor 53 also synchronously monitor the tensile force received by the specimen 70 and the strain displacement data. The temperature sensor 54 and the pressure sensor 55 are both arranged on the pressure-bearing chamber 10 to monitor the temperature and gas pressure inside the pressure-bearing chamber 10. Among them, the temperature sensor 54 can be arranged inside the pressure-bearing chamber 10 or in the temperature measurement hole 162, and the temperature measurement hole 162 is opened on the chamber cover plate 16. The displacement sensor 53, the temperature sensor 54, the pressure sensor 55, and the tensile sensor 52 are all connected to the processor 51 through ordinary signal lines, and the processor 51 is also connected to the computer through a signal line. The real-time control and acquisition of data are generally realized through the computer.

[0048] In this device, specimens 70 with different hydrate contents are prepared by injecting methane into specimens 70 with different initial water contents and then cooling. After the specimens 70 are formed, tensile tests can be carried out on the specimens 70 under certain temperature and pressure conditions to determine their mechanical parameters. Based on the device, a set of methods for testing the tensile mechanical parameters of methane hydrate-containing sediments is formed, and the mechanical parameters measured by this method are relatively close to the natural state.

[0049] In a preferred embodiment of the present invention, in order to be able to conveniently open and close the pressure-bearing chamber 10 so as to place the compacted soil sample in the specimen 70 frame 11, the pressure-bearing chamber 10 is designed as a structure that can be opened and closed. Specifically, the pressure-bearing chamber 10 includes a chamber cover plate 16 and a chamber body 17. The chamber body 17 is in a cuboid structure, with the top being the chamber opening. The chamber cover plate 16 is detachably covered on the chamber opening of the chamber body 17. The bottom of the chamber body 17 is fixed to the test platform 90. Among them, the chamber cover plate 16 and the chamber body 17 can be connected by bolts, and the connection part is also sealed, such as by laying a sealing ring. The chamber body 17 is also fixed to the test platform 90 by bolts. The constant temperature box 20 covers the pressure-bearing chamber 10 and the test platform 90 together to adjust the temperature of the pressure-bearing chamber 10 and the test platform 90 together. Among them, the chamber cover plate 16 is also provided with an air inlet 161, which is connected to the gas supply system to introduce methane.

[0050] In a preferred embodiment of the present invention, since methane is a combustible gas, there are more stringent explosion-proof requirements during its pressurization process. Therefore, the gas supply system further includes an air compressor 38, which is connected to the gas booster pump 32 to provide a driving gas source for the gas booster pump 32. Among them, the air compressor 38 can be designed at a place far from the methane gas cylinder 31 and the gas booster pump 32. The high-pressure air generated by the air compressor 38 is supplied to the gas booster pump 32 through a long pipeline as the driving gas source of the gas booster pump 32 to make the gas booster pump 32 work.

[0051] In a preferred embodiment of the present invention, during the tensile test, the specimen 70 is horizontally placed in the pressure-bearing chamber 10 through the specimen 70 frame 11. In order to prevent the specimen 70 from collapsing, a support structure is required at the bottom of the specimen 70. At the same time, when the specimen 70 is stretched, a frictional force will be generated between the specimen 70 and the support structure, which will affect the test data. Therefore, a traveling trolley is needed to support the specimen 70 and be able to move with the specimen 70 at the same time to minimize the frictional force. Specifically, a traveling trolley is further provided inside the pressure-bearing chamber 10. The traveling trolley includes a support table 14 and pulleys 15, and the specimen 70 frame 11 is placed on the support table 14.

[0052] In a preferred embodiment of the present invention, in order to make the gas supply system operate stably and safely, the gas supply system further includes a gas buffer tank 34, a pressure regulating valve 35, a gas flow controller 36 and a check valve 37. The gas buffer tank 34 is connected between the gas booster pump 32 and the pressure-bearing chamber 10, and the pressure regulating valve 35, the gas flow controller 36 and the check valve 37 are connected between the gas buffer tank 34 and the pressure-bearing chamber 10.

[0053] Among them, the buffer tank is mainly used to buffer the pressure fluctuations of the system in various systems to make the system work more smoothly. The buffering performance of the buffer tank is mainly achieved by compressing the gas in the tank. In this embodiment, the gas buffer tank 34 is used to buffer the air pressure fluctuations between the gas booster pump 32 and the pressure-bearing chamber 10 to make the methane pressure entering the pressure-bearing chamber 10 stable; the pressure regulating valve 35 is used to adjust the methane pressure entering the pressure-bearing chamber 10; the gas flow controller 36 is used to control the gas flow of methane and further control the methane intake volume in the pressure-bearing chamber 10; the check valve 37 is used to prevent the methane in the pressure-bearing chamber 10 from flowing back.

[0054] In a preferred embodiment of the present invention, in order to improve the safety of the gas buffer tank 34 and prevent the risk of explosion due to excessive gas pressure in the buffer pipe, the gas buffer tank 34 is further provided with a safety valve 341 and a second pressure sensor 342. The second pressure sensor 342 is electrically connected to the processor 51. The safety valve 341 has a pressure threshold. When the air pressure in the gas buffer tank 34 is too high, the safety valve 341 automatically opens to relieve pressure. The second pressure sensor 342 sends the pressure information in the gas buffer tank 34 to the processor 51 to monitor the air pressure condition of the gas buffer tank 34 in real time. If it exceeds the set preset value, the processor 51 sends an alarm message outward.

[0055] In a preferred embodiment of the present invention, since methane is a combustible gas, in order to ensure safety, it is recovered and centrally processed after the test is completed, and at the same time, parameters are provided for calculating the saturation of the specimen 70. Specifically, the tensile test device for methane hydrate sediments in this embodiment further includes: a gas recovery device 60, which is connected to the pressure-bearing chamber 10. The gas recovery device 60 is communicated with the pressure-bearing chamber 10 through a pipeline. Specifically, an air outlet 163 can be opened on the chamber cover plate 16, and then the air outlet 163 is connected to the gas recovery device 60. The gas recovery device 60 is a graduated container that collects the decomposed gas and also provides parameters for estimating the saturation.

[0056] In a preferred embodiment of the present invention, the interior of the hydraulic loading cylinder 42 is divided into a left chamber and a right chamber by a loading piston 43. The left chamber and the right chamber are respectively connected to a loading pump 41. A third pressure sensor 44 is further provided between the loading pump 41 and the right chamber. The third pressure sensor 44 is electrically connected to the processor 51. The third pressure sensor 44 monitors the hydraulic pressure in the right chamber and measures the pressure value of the loading pump 41.

[0057] The left chamber of the hydraulic loading cylinder 42 is connected to the loading pump 41 through a three-way pipe. An electromagnetic valve five 85 and an electromagnetic valve six 86 are provided on the three-way pipe. The electromagnetic valve five 85 controls the drainage, and the electromagnetic valve six 86 controls the liquid inlet. Correspondingly, the right chamber of the hydraulic loading cylinder 42 is also connected to the loading pump 41 through a three-way pipe. An electromagnetic valve seven 87 and an electromagnetic valve eight 88 are provided on the three-way pipe. The electromagnetic valve eight 88 controls the drainage, and the electromagnetic valve seven 87 controls the liquid inlet.

[0058] Among them, select modes such as constant pressure, stress type, and strain type for loading, and turn on the loading pump 41 to conduct a tensile test on the specimen 70.

[0059] Specifically, electromagnetic valve one 81, electromagnetic valve two 82, electromagnetic valve three 83, and electromagnetic valve four 84 are sequentially arranged on the connecting pipelines between the methane gas cylinder 31, the gas booster pump 32, the gas buffer tank 34, the pressure regulating valve 35, the one-way valve 37, and the pressure-bearing chamber 10. An electromagnetic valve ten 80 is arranged on the connecting pipeline between the vacuum pump 33 and the pressure-bearing chamber 10. Electromagnetic valve six 86 and electromagnetic valve seven 87 are arranged on the connecting pipelines between the loading pump 41 and the left and right chambers of the hydraulic loading cylinder 42. Electromagnetic valve five 85 and electromagnetic valve eight 88 are arranged on the air outlet pipelines of the left and right chambers. An electromagnetic valve nine 89 is arranged on the connecting pipeline between the pressure-bearing chamber 10 and the gas recovery device 60. The gas flow controller 36, electromagnetic valve one 81 to electromagnetic valve ten 80 are all electrically connected to the processor 51, and then the opening and closing conditions of each pipeline are controlled in real time through a computer.

[0060] The present invention also provides a tensile test method for methane hydrate-containing sediments, and this test method is based on the above-mentioned tensile test device for methane hydrate-containing sediments.

[0061] In a preferred embodiment of the present invention, the test method includes the following steps:

[0062] Step one, forming the soil sample. The soil sample is molded into a shape with a jack according to the set density. The shape of the mold is dumbbell-shaped. After molding, it is placed in a refrigerator together with the mold and then the soil sample is taken out; wherein, the set density is to simulate the soil density of the methane hydrate stable layer on the seabed, and the value is 1.5 - 2.5 g / cm 3 , and the water content is 2% - 40%.

[0063] Step two, installing the soil sample. The formed soil sample is installed in the sample 70 frame 11 in the chamber body 17. The movable part 111 and the fixed part 112 respectively fix the two ends of the soil sample. The chamber cover plate 16 is connected to the chamber body 17 by bolts, and the connection is sealed with a sealing ring.

[0064] Step three, evacuating. Close electromagnetic valve four 84 and electromagnetic valve nine 89, turn on the vacuum pump 33 and electromagnetic valve ten 80, evacuate the pressure-bearing chamber 10 and its connecting pipelines to remove internal impurities.

[0065] Step four, applying gas. Turn on the methane gas cylinder 31, the gas booster pump 32, electromagnetic valve one 81 to electromagnetic valve four 84. After adjusting the pressure regulating valve 35 to the set pressure value of 6 Mpa - 10 Mpa, turn off the methane gas cylinder 31, the gas booster pump 32, electromagnetic valve one 81 to electromagnetic valve three 83, and at the same time close the air inlet 161 of the pressure-bearing chamber 10, that is, close electromagnetic valve four 84.

[0066] Step 5: Check airtightness. Start the data acquisition system and turn on the thermostat 20. After setting the temperature value to 18°C - 20°C, control the internal temperature of the pressure-bearing chamber 10; monitor and record the data changes of the temperature sensor 54 and the pressure sensor 55 to determine the airtightness of the pressure-bearing chamber 10.

[0067] Step 6: Synthesize the hydrate sample. Set the temperature of the thermostat 20 to -2°C - 2°C to lower the internal temperature of the pressure-bearing chamber 10, thereby reducing the temperature of the soil sample to reach the hydrate synthesis condition, and start to form hydrates in the soil sample.

[0068] Step 7: Judge the completion of hydrate synthesis. When the pressure value displayed by the pressure sensor -55 remains stable at 3 Mpa - 6 Mpa and the temperature value displayed by the temperature sensor 54 remains constant at -2°C - 2°C, the hydrate synthesis in the soil sample inside the pressure-bearing chamber 10 is completed, and the sample 70 is prepared.

[0069] Step 8: Tensile test. Turn on the loading pump 41 to drive the tensile piston 13 and the movable part 111 to move by the loading piston 43. The movable part 111 stretches the sample 70. The force sensor 52 collects the force exerted by the loading piston 43 on the tensile piston 13, and the displacement sensor 53 collects the lateral strain displacement data of the tensile piston 13. Among them, modes such as constant pressure, stress type, and strain type can also be selected for loading, and the loading pump 41 is turned on to conduct a tensile test on the sample 70.

[0070] Step 9: Collect gas and disassemble the sample. After the tensile test is completed, turn off the loading pump 41, raise the temperature of the thermostat 20 to 20°C, the hydrate in the sample 70 decomposes, and the released methane is collected through the gas recovery device 60. Calculate the saturation of the hydrate according to the collected amount, and finally remove the sample 70 from the sample frame 11 of the sample 70.

[0071] As Figure 4 shown, in a preferred embodiment of the present invention, the sample 70 is dumbbell-shaped, with a length L1 of 240 mm, the distance L2 between the centers of the balls at both ends of the dumbbell is 150 mm, the ball diameter D is 90 mm, L3 in the middle of the dumbbell is 50 mm, and L4 is 50 mm. That is to say, when the sample 70 is subjected to a tensile test, the dimensions of the sample 70 are all the standard values.

[0072] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A tensile test device for methane hydrate-containing sediments, characterized in that Comprising: A pressure-bearing chamber (10) with a dumbbell-shaped specimen frame (11) disposed inside for clamping a specimen (70) to be tested. The specimen frame (11) is assembled by a movable part (111) and a fixed part (112). The fixed part (112) is fixed inside the pressure-bearing chamber (10). The pressure-bearing chamber (10) is also provided with a piston hole (12) communicating with the outside. A tensile piston (13) is inserted into the piston hole (12). The movable part (111) is connected to the tensile piston (13) and moves away from the fixed part (112) under the drive of the tensile piston (13). A constant temperature chamber (20) disposed outside the pressure-bearing chamber (10). A gas supply system including a methane gas cylinder (31), a gas booster pump (32) and a vacuum pump (33). The methane gas cylinder (31) is connected to the gas booster pump (32) and an electromagnetic valve I (81) is provided on the connecting pipeline. The gas booster pump (32) and the vacuum pump (33) are respectively connected to the pressure-bearing chamber (10). A tensile system including a loading pump (41), a hydraulic loading cylinder (42) and a loading piston (43). The loading pump (41) is connected to the hydraulic loading cylinder (42) to drive the loading piston (43) inside the hydraulic loading cylinder (42) to make a reciprocating motion. A data acquisition system including a processor (51) and a tensile force sensor (52), a displacement sensor (53), a temperature sensor (54) and a pressure sensor I (55) electrically connected to the processor (51). The tensile force sensor (52) is connected between the loading piston (43) and the tensile piston (13). The displacement sensor (53) is disposed on the tensile piston (13). The temperature sensor (54) and the pressure sensor I (55) are both disposed on the pressure-bearing chamber (10).

2. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that The pressure-bearing chamber (10) includes a chamber cover plate (16) and a chamber body (17). The chamber cover plate (16) is detachably covered on the chamber opening of the chamber body (17). The bottom of the chamber body (17) is fixed to a test platform (90).

3. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that The gas supply system further includes an air compressor (38) connected to the gas booster pump (32) for providing a driving gas source for the gas booster pump (32).

4. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that A walking trolley is further disposed inside the pressure-bearing chamber (10). The walking trolley includes a support platform (14) and pulleys (15). The specimen frame (11) is placed on the support platform (14).

5. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that The gas supply system further includes a gas buffer tank (34), a pressure regulating valve (35), a gas flow controller (36) and a check valve (37). The gas buffer tank (34) is connected between the gas booster pump (32) and the pressure-bearing chamber (10). The pressure regulating valve (35), the gas flow controller (36) and the check valve (37) are connected between the gas buffer tank (34) and the pressure-bearing chamber (10).

6. The tensile test device for methane hydrate-containing sediments according to claim 5, characterized in that The buffer tank is also provided with a safety valve (341) and a second pressure sensor (342), and the second pressure sensor (342) is electrically connected to the processor (51).

7. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that It further includes: a gas recovery device (60), and the gas recovery device (60) is connected to the pressure-bearing chamber (10).

8. The tensile test device for methane hydrate-containing sediments according to claim 1, characterized in that The interior of the hydraulic loading cylinder (42) is divided into a left chamber and a right chamber by a loading piston (43), and the left chamber and the right chamber are respectively connected to the loading pump (41); a third pressure sensor (44) is further arranged between the loading pump (41) and the right chamber, and the third pressure sensor (44) is electrically connected to the processor (51).

9. A tensile test method for methane hydrate-containing sediments, characterized in that The tensile test method is based on the tensile test device for methane hydrate-containing sediment according to any one of claims 1-8, and includes the following steps: Step 1, forming the soil sample. Press the soil sample into a sample with a jack according to the set density, and after pressing, put the sample together with the mold into the refrigerator for freezing and then take out the soil sample; Step 2, installing the soil sample. Install the formed soil sample into the sample frame (11) in the chamber body (17), and cover the chamber cover plate (16); Step 3, evacuating. Turn on the vacuum pump (33) to evacuate the pressure-bearing chamber (10) and its connecting pipelines to remove internal impurities; Step 4, applying gas. Turn on the methane gas cylinder (31) and the gas booster pump (32), adjust the pressure regulating valve (35) to set the pressure value to 6 Mpa - 10 Mpa, then turn off the methane gas cylinder (31) and the gas booster pump (32), and at the same time close the air inlet (161) of the pressure-bearing chamber (10); Step 5, checking airtightness. Start the data acquisition system and turn on the thermostat (20), set the temperature to 18°C - 20°C, maintain the internal temperature of the pressure-bearing chamber (10) stable, and determine the airtightness of the pressure-bearing chamber (10) through the monitoring data changes of the temperature sensor (54) and the first pressure sensor (55); Step 6, synthesizing the hydrate sample. Set the temperature of the thermostat (20) to -2°C - 2°C to lower the internal temperature of the pressure-bearing chamber (10), thereby lowering the temperature of the soil sample to reach the hydrate synthesis condition, and start to form hydrates in the soil sample; Step 7, judging that the hydrate synthesis is completed. When the pressure value displayed by the first pressure sensor (55) remains stable within the range of 3 Mpa - 6 Mpa and the temperature value displayed by the temperature sensor (54) remains constant within the range of -2°C - 2°C, the hydrate synthesis in the soil sample inside the pressure-bearing chamber (10) is completed, and the sample (70) is prepared; Step 8, tensile test. Turn on the loading pump (41) to drive the loading piston (43) to drive the tensile piston (13) and the movable part (111) to move, the movable part (111) stretches the sample (70), the force sensor (52) collects the force exerted by the loading piston (43) on the tensile piston (13), and the displacement sensor (53) collects the lateral strain displacement data of the tensile piston (13); Step 9: Collect gas and disassemble the sample. After the tensile test is completed, turn off the loading pump (41), raise the temperature of the thermostat (20) to 20°C. The hydrate of the sample (70) decomposes, and the released methane is collected through the gas recovery device (60). Calculate the hydrate saturation of the sample (70) based on the collected amount. Finally, remove the sample (70) from the sample frame (11).

10. The tensile test method for methane hydrate-containing sediments according to claim 9, characterized in that In the first step, the set density of the soil sample is 1.5 g / cm 3 ~2.5 g / cm 3 , and the water content is 2% - 40%.

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