A hydrate sediment fracture toughness testing system

Abstract

The present invention discloses a hydrate sediment fracture toughness testing system, which belongs to the technical field of hydrate sediment fracture toughness testing. The system includes a sample synthesis unit, a three-point bending test unit and a direct shear test unit. The three-point bending test unit can be detachably connected to the sample synthesis unit and is used to measure the type I fracture toughness of the hydrate sediment; the direct shear test unit can be detachably replaced by the three-point bending test unit and connected to the sample synthesis unit to measure the type II fracture toughness of the hydrate sediment. During the test, horizontal loading is adopted to eliminate the influence of gravity on fracture toughness. In order to reduce the influence of friction on fracture toughness, the system adopts a design scheme of a three-point bending bracket, a sliding base and a guide rail. In addition, hydrates are easy to decompose at room temperature and pressure. The sample synthesis unit can realize the synthesis of hydrates and ensure that the hydrates do not decompose during the test.

Description

Technical Field

[0001] The invention discloses a hydrate sediment fracture toughness testing system, belonging to the technical field of hydrate sediment fracture toughness testing. Background Art

[0002] Natural gas hydrates, with their high energy density, low carbon footprint, and clean character, are considered a promising alternative to traditional fossil fuels. Improving gas production rates and ensuring stable production over the long term are key challenges facing the commercialization of natural gas hydrates. Improving the permeability of hydrate sediment reservoirs is crucial for increasing hydrate decomposition capacity, gas production efficiency, and gas production rates. Hydraulic fracturing is a key technology for improving reservoir permeability in unconventional gas reservoirs, such as ultra-low permeability shale gas and tight gas reservoirs, and is a highly promising technology for increasing production in hydrate reservoirs.

[0003] The fracture mechanics properties of hydrate sediments are a key foundation for the theory and technology of hydrate reservoir fracturing. They play a crucial role in studying the initiation and propagation behavior of hydrate reservoir fractures, fracture propagation morphology, and production stimulation. Due to the unique properties of hydrate sediments, such as low mechanical strength and easy decomposition at room temperature and pressure, there is currently no testing system capable of measuring the Type I and Type II fracture toughness of hydrate sediments. Therefore, a new technical solution is urgently needed to address this issue. Summary of the Invention

[0004] To address the problems of the prior art, the present invention aims to provide a hydrate sediment fracture toughness testing system. During the test, horizontal loading is employed to eliminate the influence of gravity on fracture toughness. To reduce the effects of friction on fracture toughness, the hydrate sediment fracture toughness testing system utilizes a three-point bending bracket, a sliding base, and guide rails. Furthermore, hydrates readily decompose at room temperature and pressure. The sample synthesis unit is capable of synthesizing hydrates and ensuring that they do not decompose during testing, thus avoiding the impact of hydrate decomposition on the mechanical properties of the hydrate sediment.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a hydrate sediment fracture toughness testing system, comprising a sample synthesis unit, the sample synthesis unit comprising a reactor, the system further comprising a three-point bending test unit and a direct shear test unit interchangeably connected to the sample synthesis unit; the three-point bending test unit comprises a three-point bending bracket, a triangular base plate, a steel rod, a first top cover, a first horizontal loading mechanism, a first data acquisition instrument and a screw; a ball-and-socket connection groove is provided at the bottom of the three-point bending bracket, and a ball pulley is installed in the ball-and-socket connection groove, the number of the three-point bending brackets is two and they are symmetrically arranged, the two three-point bending brackets form an integrated structure, the side surfaces of the three-point bending brackets correspond to the positions of the fixed brackets to achieve positioning; the triangular base plate is arranged between the two three-point bending brackets, and cooperates with the base plate of the three-point bending bracket to form a long Square bottom plate; the steel rod passes through the side wall of the reactor and locks the triangular bottom plate to the three-point bending bracket; the screw passes through the top of the reactor and the first top cover and cooperates with the bearing on the top of the three-point bending bracket; the first horizontal loading mechanism is horizontally arranged and abuts the side baffle of the first top cover; the first data acquisition instrument is communicatively connected to the first horizontal loading mechanism; the direct shear test unit includes a second base, a cube shear box, a second top cover, a second horizontal loading mechanism and a second data acquisition instrument, the cube shear box is formed by a fixed base and a sliding base, the fixed base is fixed to the second base, and the sliding base is slidably connected to the second base through a guide rail; the second top cover is a split structure, which is respectively fixed above the fixed base and the sliding base; the second horizontal loading mechanism is horizontally arranged and abuts the sliding base; the second data acquisition instrument is communicatively connected to the second horizontal loading mechanism.

[0006] Furthermore, the first horizontal loading mechanism includes a first hydraulic cylinder, a first force sensor and a pressure head connected in sequence. The pressure head is horizontally arranged and abuts against the lateral baffle of the first top cover; the first force sensor is communicatively connected to the first data acquisition instrument.

[0007] Furthermore, the number of the fixed brackets is the same as the number of the three-point bending brackets and corresponds one to one. The fixed brackets are welded to the first base to form a rigid support structure; the first base is detachably fixed to the bottom of the reactor; the side baffles of the three-point bending brackets form a positioning matching surface with the fixed brackets; the triangular bottom plate and the bottom plates of the three-point bending brackets on both sides are spliced ​​into a complete bearing surface; the first top cover realizes vertical displacement control through a threaded screw.

[0008] Furthermore, threaded holes are provided at both ends of the triangular bottom plate, and corresponding circular holes are provided on the bottom plate of the three-point bending bracket. The steel rod passes through the side wall of the reactor, the threaded holes of the triangular bottom plate and the circular holes on the bottom plate of the three-point bending bracket in sequence to achieve locking.

[0009] Furthermore, the second horizontal loading mechanism includes a second force sensor and a second hydraulic cylinder connected in sequence, the second force sensor is horizontally arranged and abuts against the sliding base, and the second force sensor is communicatively connected to the second data acquisition instrument.

[0010] Furthermore, a thermometer and a pressure gauge are connected to the top of the reactor.

[0011] Furthermore, the second base is detachably fixed to the bottom of the reactor.

[0012] Furthermore, the sample synthesis unit further includes a gas supply module, a vacuum module, a constant temperature control module and an exhaust metering module:

[0013] The gas supply module includes a high-pressure gas cylinder, a gas booster pump, a first gas flow meter, a first valve, a second valve, and an intermediate storage tank, wherein the high-pressure gas cylinder, the gas booster pump, the first gas flow meter, the first valve, and the intermediate storage tank are sequentially connected through pipelines, and the intermediate storage tank is connected to the reactor through the second valve;

[0014] The vacuum pump module includes a third valve and a vacuum pump, and the third valve is installed on the connecting pipe between the reactor and the vacuum pump;

[0015] The constant temperature control module includes a constant temperature water bath covering the intermediate storage tank and the reactor;

[0016] The exhaust metering module includes a fourth valve, a pneumatic back pressure valve, a gas-water separator, a second gas flow meter and a gas collecting bottle. The fourth valve is arranged at the gas outlet end of the reactor. The fourth valve, the pneumatic back pressure valve, the gas-water separator, the second gas flow meter and the gas collecting bottle are connected in sequence through pipelines.

[0017] Furthermore, the first hydraulic cylinder is connected to a first hydraulic system.

[0018] Furthermore, the second hydraulic cylinder is connected to a second hydraulic system.

[0019] The beneficial effect of the hydrate sediment fracture toughness test system provided by the present invention is that: the present invention is different from the traditional fracture toughness test system. Hydrate sediments have low strength, which leads to the non-negligible influence of gravity on fracture toughness. The horizontal loading method is adopted to eliminate the influence of gravity. In order to reduce friction, a ball pulley is designed in the three-point bending test unit. After the hydrate sediment sample is synthesized, the triangular base plate and the base plate of the three-point bending bracket can be separated by pulling the steel rod, and then the horizontal load is applied by the first horizontal loading mechanism. The fixed bracket and the three-point bending bracket are only close together and not connected. The fixed bracket can act as a reaction force. Due to the one-piece structure formed by the two three-point bending brackets arranged symmetrically on the left and right, the sample bends under the action of force. The three-point bending bracket uses the contact point between the vertex of the triangular base plate and the base plate of the three-point bending bracket as the center of the circle. Under the action of the ball pulley, the two ends of the three-point bending bracket rotate, which plays a role in reducing friction. The direct shear test unit adopts the solution of sliding base and guide rail. In addition, hydrates are easy to decompose under normal pressure and temperature conditions, and hydrates have a significant impact on the mechanical properties of hydrate sediments. The sample synthesis unit can realize the synthesis of hydrates and ensure that hydrates do not decompose during the test process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the hydrate sediment fracture toughness testing system proposed in an embodiment of the present invention applied to a Type I fracture toughness test;

[0021] Figure 2 Schematic diagram of a combination of a three-point bending test unit and a reactor in a hydrate sediment fracture toughness testing system according to an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of a three-point bending test unit in a hydrate sediment fracture toughness testing system according to an embodiment of the present invention;

[0023] Figure 4 It is a partial assembly drawing of the three-point bending test unit;

[0024] Figure 5 yes Figure 4 A partial schematic diagram of

[0025] Figure 6 Schematic diagram of a direct shear test unit and a reactor combined in a hydrate sediment fracture toughness test system according to an embodiment of the present invention;

[0026] Figure 7 1. This is a schematic diagram of a direct shear test unit in a hydrate sediment fracture toughness test system according to an embodiment of the present invention, viewed from one perspective;

[0027] Figure 82. It is a schematic diagram of a direct shear test unit in a hydrate sediment fracture toughness test system according to an embodiment of the present invention from another perspective;

[0028] Figure 9 1 is a schematic diagram of the assembly of a sample synthesis unit in a hydrate sediment fracture toughness testing system according to an embodiment of the present invention;

[0029] Figure 10 This is a schematic diagram of the mechanical model for the three-point bending test of type I fracture toughness of hydrate sediments;

[0030] Figure 11 It is a schematic diagram of the mechanical model for the direct shear test of type II fracture toughness of hydrate sediments.

[0031] The marks in the figure are as follows: 1-fixed bracket, 2-first base, 3-three-point bending bracket, 4-pressing head, 5-first force sensor, 6-first hydraulic cylinder, 7-first data acquisition instrument, 8-first hydraulic system, 9-triangular base plate, 10-steel rod, 11-first top cover, 12-screw, 13-ball pulley, 14-second top cover, 15-fixed base, 16-second base, 17-sliding base, 18-second force sensor, 19-second hydraulic cylinder, 20-first Second data acquisition instrument, 21-second hydraulic system, 22-guide rail, 23-high-pressure gas cylinder, 24-gas booster pump, 25-first gas flow meter, 26-first valve, 27-second valve, 28-third valve, 29-vacuum pump, 30-thermometer, 31-fourth valve, 32-pneumatic back pressure valve, 33-gas-water separator, 34-second gas flow meter, 35-gas collecting bottle, 36-constant temperature water bath, 37-intermediate storage tank, 38-pressure gauge, 39-reactor. DETAILED DESCRIPTION

[0032] To more clearly illustrate the present invention, the present invention is further described below with reference to the accompanying drawings. Those skilled in the art should understand that the following detailed description is illustrative and non-restrictive and should not be used to limit the scope of protection of the present invention. Unless otherwise defined, technical or scientific terms used herein should have the same meaning as those having ordinary skill in the art to which the present invention belongs.

[0033] To avoid obscuring the essence of the present invention, well-known methods, procedures, flows, components and circuits have not been described in detail.

[0034] It should be understood that the terms "first", "second", "third" and "fourth" are used for descriptive purposes only, and the characteristics limited to "first", "second", "third" and "fourth" do not indicate any order, quantity or importance, but are only used to distinguish different components.

[0035] The present invention proposes a hydrate sediment fracture toughness testing system, such as Figures 1 to 11 As shown, the system includes a sample synthesis unit, a three-point bending test unit, and a direct shear test unit. The three-point bending test unit can be detachably connected to the sample synthesis unit to measure the Mode I fracture toughness of hydrate sediments. The direct shear test unit can be detachably replaced with the three-point bending test unit and connected to the sample synthesis unit to measure the Mode II fracture toughness of hydrate sediments. The sample synthesis unit is used to synthesize hydrate sediment samples and control their decomposition process.

[0036] The three-point bending test unit includes a fixed bracket 1, a first base 2, a three-point bending bracket 3, a pressure head 4, a first force sensor 5, a first hydraulic cylinder 6, a first data acquisition instrument 7, a first hydraulic system 8, a triangular base plate 9, a steel rod 10, a first top cover 11, a screw 12 and a ball pulley 13, wherein the fixed bracket 1 is a cylinder, the fixed bracket 1 is welded to the first base 2, and the first base 2 is detachably fixed to the bottom of the reactor 39 by screws, and the fixed bracket 1 is provided with two and corresponds to the position of the baffles provided on the sides of the two three-point bending brackets 3. The three-point bending bracket 3 is close to the fixed bracket 1, and a ball-and-socket connection groove is provided at the bottom of the three-point bending bracket 3, and a ball pulley 13 is provided in the ball-and-socket connection groove. The three-point bending bracket 3 reduces friction through the ball pulley 13 to ensure that the specimen is uniformly stressed when a horizontal load is applied. A bearing is provided on the top of the three-point bending bracket 3, and there are two three-point bending brackets 3. The two three-point bending brackets 3 are symmetrically arranged, and the two three-point bending brackets 3 form an integrated structure; such as Figure 4 and Figure 5As shown, in this embodiment, the side of the first top cover 11 is provided with a T-shaped baffle matching the concave structure formed on the side of the two three-point bending brackets 3. The T-shaped baffle on one side of the fixed bracket 1 is in contact with the pressure head 4 set in the horizontal direction. The pressure head 4 is connected to the first force sensor 5, and the first force sensor 5 is connected to the first hydraulic cylinder 6. The first force sensor 5 is connected to the first data acquisition instrument 7 through a data line. The first hydraulic cylinder 6 is the actuator of the first hydraulic system 8. The first hydraulic system 8 is connected to the first hydraulic cylinder 6. The first hydraulic system 8 is used to drive the first hydraulic cylinder 6 to move; the screw 12 sequentially passes through the end cover of the reactor top 39 with a through hole and the first top cover 11 with a threaded hole, and finally connects with the bearing set on the top of the three-point bending bracket 3. Connection; the triangular base plate 9 is arranged between the two three-point bending brackets 3, and the triangular base plate 9 can be matched with the bottom plate of the three-point bending bracket 3 to form a complete rectangular base plate. Threaded holes are provided at both ends of the triangular base plate 9, and the bottom plate of the three-point bending bracket 3 is provided with a circular hole at a position corresponding to the triangular base plate 9. The steel rod 10 first passes through the side wall of the reactor 39, and then is threadedly connected to the corresponding circular holes of the triangular base plate 9 and the bottom plate of the three-point bending bracket 3; the sample to be tested is placed on the three-point bending bracket 3, and the first hydraulic system 8 controls the first hydraulic cylinder 6 to slowly apply a horizontal load at a constant speed and pressure. The load is sequentially transmitted to the sample through the first force sensor 5 and the pressure head 4 until the sample is tensilely damaged. The first data acquisition instrument 7 records the load value when the sample is damaged, that is, the maximum load value, and the load is recorded by the first data acquisition instrument 7. The expression is used to calculate the mode I fracture toughness value of the sample.

[0037] The direct shear test unit includes a second top cover 14, a fixed base 15, a second base 16, a sliding base 17, a second force sensor 18, a second hydraulic cylinder 19, a second data acquisition instrument 20, a second hydraulic system 21 and a guide rail 22. The second top cover 14 is a split structure, divided into a first split and a second split. The first split and the second split are respectively fixed to the fixed base 15 and the sliding base 17 with screws. The fixed base 15 is fixed to the second base 16 and forms a cubic shear box with the sliding base 17. The fixed base 15 and the sliding base 17 are two symmetrical parts. When used, they are only pressed against each other without being connected. They are used to place the sample. The second base 16 is detachably fixed to the bottom of the reactor 39 by screws. One side of the sliding base 17 It contacts the second force sensor 18, the sliding base 17 slides with the guide rail 22, the guide rail 22 is welded to the second base 16, the second force sensor 18 is connected to the second data acquisition instrument 20 through a data line, the second force sensor 18 is connected to the second hydraulic cylinder 19, and the second hydraulic system 21 is connected to the second hydraulic cylinder 19; the test sample is placed on the cubic shear box composed of the fixed base 15 and the sliding base 17, and the second hydraulic system 21 controls the second hydraulic cylinder 19 on one side of the sliding base 17 to slowly apply a horizontal load at a constant pressure and speed. The fixed base 15 acts as a reaction force and is fixed, and the sliding base 17 slides along the guide rail 22. Finally, the sample is sheared and broken. The second data acquisition instrument 20 can record the maximum load value, that is, the shear failure load. According to The sliding base 17 cooperates with the guide rail 22 through a slideway to ensure that the friction force is minimized during the shearing process.

[0038] The sample synthesis unit includes a high-pressure gas cylinder 23, a gas booster pump 24, a first gas flow meter 25, a first valve 26, a second valve 27, a third valve 28, a vacuum pump 29, a thermometer 30, a fourth valve 31, a pneumatic back pressure valve 32, a gas-water separator 33, a second gas flow meter 34, a gas collecting bottle 35, a constant temperature water bath 36, an intermediate storage tank 37, a pressure gauge 38 and a reactor 39. The high-pressure gas cylinder 23 is connected to the gas booster pump 24 through a pipeline, the gas booster pump 24 is connected to the first gas flow meter 25 through a pipeline, the first gas flow meter 25 is connected to the first valve 26 through a pipeline, the first valve 26 is connected to the intermediate storage tank 37 through a pipeline, and the intermediate storage tank 37 is connected to the intermediate storage tank 37 through a pipeline. The reactor 39 is connected to the third valve 28 through a pipeline, the third valve 28 is connected to the vacuum pump 29 through a pipeline, and the third valve 28 and the second valve 27 are connected to the reactor 39 through the same pipeline; the top of the reactor 39 is connected to a thermometer 30 and a pressure gauge 38; the reactor 39 is connected to the fourth valve 31 through a pipeline, the fourth valve 31 is connected to the pneumatic back pressure valve 32 through a pipeline, the pneumatic back pressure valve 32 is connected to the gas-water separator 33 through a pipeline, the gas-water separator 33 is connected to the second gas flow meter 34 through a pipeline, and the second gas flow meter 34 is connected to the gas collecting bottle 35 through a pipeline; a constant temperature water bath 36 is connected to the fourth valve 31 through a pipeline, the fourth valve 31 is connected to the pneumatic back pressure valve 32 through a pipeline, the pneumatic back pressure valve 32 is connected to the gas-water separator 33 through a pipeline, the gas-water separator 33 is connected to the second gas flow meter 34 through a pipeline, and the second gas flow meter 34 is connected to the gas collecting bottle 35 through a pipeline; The intermediate storage tank 37 and the reactor 39 are located in a constant temperature water bath 36. A mixture of water and muddy silt is added to the reactor 39. After the reactor 39 is sealed, the third valve 28 is opened, and the air in the reactor 39 is evacuated by the vacuum pump 29. The third valve 28 is closed, and the water bath temperature in the constant temperature water bath 36 is adjusted to the design temperature. The first valve 26 is opened, and the methane gas in the high-pressure gas cylinder 23 is pumped into the intermediate storage tank 37 by the gas booster pump 24. The methane gas is allowed to stand in the intermediate storage tank 37 for half an hour to avoid the influence of the gas temperature entering the reactor on the hydrate synthesis. The first valve 26 and the second valve 27 are closed, and the intermediate storage tank 3 The gas in 7 is steadily injected into the reactor 39 until the pressure in the reactor is higher than the design value. The second valve 27 is closed and the pressure value of the pressure gauge 38 is observed. When the pressure value finally drops to and maintains at the design pressure value, it indicates that the hydrate is completely formed. Then, the hydrate is decomposed by reducing the pressure. The water bath temperature in the constant temperature water bath 36 is maintained unchanged. A series of pressures lower than the design pressure value are set by the pneumatic back pressure valve 32. The fourth valve 31 is opened, and the pressure in the reactor 39 begins to drop. The hydrate begins to decompose. The hydrate decomposition products pass through the gas-water separator 33, and the gas finally reaches the gas collecting bottle 35. When the pressure value of the pressure gauge 38 is maintained at the back pressure value and the second gas flow meter 34 is 0, it indicates that the hydrate decomposition has stopped.

[0039] The specific working process is as follows:

[0040] 1. Type I fracture toughness test of hydrate sediments

[0041] The test of Type I fracture toughness of hydrate sediments requires the joint use of a three-point bending test unit and a sample synthesis unit. Assemble the sample synthesis unit and the three-point bending test unit separately, push the steel rod 10 to drive the triangular bottom plate 9 to make close contact with the bottom plate of the three-point bending bracket 3, add a mixture of water and muddy silt to the three-point bending bracket 3, compact it, and adjust the crack width of the sample automatically. Open a through crack according to the test needs, rotate the screw 12, and drive the first top cover 11 to descend so that the first top cover 11 is tightly combined with the three-point bending bracket 3. After completing the sealing of the reactor 39, open the third valve 28, use the vacuum pump 29 to evacuate the air in the reactor 39, and close the third valve 28. Three valves 28 are used to adjust the water bath temperature in the constant-temperature water bath 36 to the designed temperature. The first valve 26 is opened, and methane gas from the high-pressure gas cylinder 23 is pumped into the intermediate storage tank 37 via the gas booster pump 24. The methane gas is allowed to rest in the intermediate storage tank 37 for half an hour. The first valve 26 is closed, and the second valve 27 is opened. The gas from the intermediate storage tank 37 is steadily injected into the reactor 39 until the pressure inside the reactor exceeds the designed value. The second valve 27 is closed, and the pressure on the pressure gauge 38 is observed. When the pressure finally drops to and remains at the designed value, it indicates that the hydrate has been completely formed. Subsequently, the temperature is lowered using the constant-temperature water bath 36, and the pressure is reduced using the pneumatic back-pressure valve 32 to ensure that the hydrate does not decompose under normal pressure. Rotate the screw 12 to make the first top cover 11 rise to the top of the sample, pull the steel rod 10 to drive the triangular bottom plate 9, so that the triangular bottom plate 9 is separated from the bottom plate of the three-point bending bracket 3. The first hydraulic system 8 controls the first hydraulic cylinder 6 to slowly load at a constant speed and pressure. Under the action of the force, the sample bends. The three-point bending bracket 3 takes the contact point between the vertex of the triangular bottom plate 9 and the bottom plate of the three-point bending bracket 3 as the center of the circle. Under the rolling of the ball pulley 13, the two ends of the three-point bending bracket 3 move in an arc until the sample is tensilely damaged. The first data acquisition instrument 7 can record the load when the sample is damaged, that is, the maximum load value, and substitute it into The Type I fracture toughness value is calculated from the expression. Hydrate decomposition is then performed by depressurizing the hydrate. The water bath temperature in the constant-temperature water bath 36 is maintained constant. A series of pressures below atmospheric pressure are set using the pneumatic backpressure valve 32. The fourth valve 31 is opened, and the pressure within the reactor 39 begins to drop, causing hydrate decomposition. The hydrate decomposition products pass through the gas-water separator 33, and the gas eventually reaches the gas collection bottle 35. When the pressure on the pressure gauge 38 remains at the backpressure value and the second gas flowmeter 34 reaches 0, hydrate decomposition has ceased. At this point, the reactor 39 can be opened, and the three-point bend test unit can be removed to complete the Type I fracture toughness test of the hydrate sediment.

[0042] ;

[0043] ;

[0044] in represents the mode I fracture toughness of hydrate sediments; Represents the correlation coefficient of mode I fracture toughness, which is related to the parameter and Related; represents the critical failure load; Indicates the specimen span; Indicates the thickness of the specimen; Indicates the width of the specimen; Indicates the initial crack depth; the specific measurement method of the corresponding letters in the formula is as follows Figure 10 Same as shown in .

[0045] 2. Type II fracture toughness test of hydrate sediments

[0046] The test of type II fracture toughness of hydrate sediments requires the combined use of a direct shear test unit and a sample synthesis unit. Assemble the components except the second top cover 14, add a mixture of water and muddy silt into the cubic shear box assembled by the fixed base 15 and the sliding base 17, and compact it. The crack width of the sample can be adjusted by itself, and a through crack is opened according to the test needs. The second top cover 14 is divided into two symmetrical parts, namely the first part and the second part. The first part and the second part are fixed to the fixed base 15 and the sliding base 17 with screws respectively. After the reactor 39 is sealed, open the third valve 28, and use the vacuum pump 29 to evacuate the air in the reactor 39, and close it. The third valve 28 is set. The water bath in the constant-temperature water bath 36 is adjusted to the designed temperature. The first valve 26 is opened, and the gas booster pump 24 pumps methane gas from the high-pressure gas cylinder 23 into the intermediate storage tank 37. The methane gas is allowed to rest in the intermediate storage tank 37 for half an hour. The first valve 26 is closed, and the second valve 27 is opened. The gas from the intermediate storage tank 37 is steadily injected into the reactor 39 until the pressure inside the reactor 39 exceeds the designed value. The second valve 27 is closed, and the pressure on the pressure gauge 38 is observed. When the pressure finally drops to and remains at the designed value, it indicates that the hydrate has been completely formed. Subsequently, the constant-temperature water bath 36 is used to cool the reaction, and the pneumatic back-pressure valve 32 is used to reduce the pressure to ensure that the hydrate does not decompose under normal pressure. The second hydraulic system 21 controls the second hydraulic cylinder 19 to slowly load at a constant pressure and speed. The sliding base 17 moves along the guide rail 22, while the fixed base 15 remains stationary, so that the sample eventually undergoes shear failure. The second data acquisition instrument 20 can record the load when the sample undergoes shear failure, that is, the maximum load, and substitute it into The expression can be used to calculate the Type II fracture toughness of the hydrate sediment. Hydrate decomposition is then performed by depressurizing the hydrate. The water bath temperature in the constant-temperature water bath 36 is maintained constant. A series of pressures below atmospheric pressure are set using the pneumatic backpressure valve 32. The fourth valve 31 is opened, and the pressure in the reactor 39 begins to drop, causing hydrate decomposition. The hydrate decomposition products pass through the gas-water separator 33, and the gas eventually reaches the gas collection bottle 35. When the pressure on the pressure gauge 38 remains at the backpressure value and the second gas flowmeter 34 reaches 0, hydrate decomposition has ceased. At this point, the reactor 39 can be opened, the direct shear test unit removed, and the Type II fracture toughness test of the hydrate sediment is complete.

[0047] ;

[0048] ;

[0049] ;

[0050] in represents the type II fracture toughness of hydrate sediments; Represents the correlation coefficient of mode II fracture toughness, which is related to the parameter and Related; represents the critical shear load; Indicates the thickness of the specimen; Indicates the width of the specimen; represents the initial crack depth; Indicates the width of the specimen; the specific measurement method of the corresponding letters in the formula is as follows Figure 11 Same as shown in .

[0051] In summary, the advantages of the hydrate sediment fracture toughness testing system proposed in the present invention are as follows:

[0052] 1. In the hydrate sediment fracture toughness testing system proposed by the present invention, the first hydraulic cylinder 6 and the second hydraulic cylinder 19 are placed horizontally, adopting a horizontal loading method to eliminate the influence of gravity on the fracture toughness of hydrate sediments. On the other hand, the system adopts a solution of a ball pulley 13, a sliding base 17 and a guide rail 22 to reduce the effect of friction and make the fracture toughness more accurate.

[0053] 2. The sample synthesis unit in the hydrate sediment fracture toughness testing system proposed in the present invention can realize the synthesis and decomposition of hydrates and ensure that the hydrates do not decompose during the testing process, thereby avoiding the problem of hydrate decomposition affecting the mechanical properties of hydrate sediments.

Claims

1. A hydrate sediment fracture toughness testing system, comprising a sample synthesis unit, wherein the sample synthesis unit comprises a reaction kettle (39), characterized in that: The system further comprises a three-point bending test unit and a direct shear test unit which are interchangeably connected to the sample synthesis unit; the three-point bending test unit comprises a three-point bending bracket (3), a triangular bottom plate (9), a steel rod (10), a first top cover (11), a first horizontal loading mechanism, a first data acquisition instrument (7) and a screw rod (12); a ball-and-socket type connection groove is provided at the bottom of the three-point bending bracket (3), and a ball pulley (13) is installed in the ball-and-socket type connection groove; the number of the three-point bending brackets (3) is two and they are symmetrically arranged, the two three-point bending brackets (3) form an integrated structure, and the side surfaces of the three-point bending brackets (3) correspond to the positions of the fixed bracket (1) to achieve positioning; the triangular bottom plate (9) is arranged between the two three-point bending brackets (3), and cooperates with the bottom plate of the three-point bending bracket (3) to form a rectangular bottom plate; the steel rod (10) passes through the side wall of the reactor (39) and locks the triangular bottom plate (9) and the three-point bending bracket (3); the screw rod (12) The first horizontal loading mechanism is arranged horizontally and abuts against the side baffle of the first top cover (11); the first data acquisition instrument (7) is in communication connection with the first horizontal loading mechanism; the direct shear test unit comprises a second base (16), a cubic shear box, a second top cover (14), a second horizontal loading mechanism and a second data acquisition instrument (20); the cubic shear box is formed by combining a fixed base (15) and a sliding base (17); the fixed base (15) is fixed to the second base (16), and the sliding base (17) is slidably connected to the second base (16) through a guide rail (22); the second top cover (14) is a split structure, which is respectively fixed above the fixed base (15) and the sliding base (17); the second horizontal loading mechanism is arranged horizontally and abuts against the sliding base (17); the second data acquisition instrument (20) is in communication connection with the second horizontal loading mechanism.

2. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The first horizontal loading mechanism comprises a first hydraulic cylinder (6), a first force sensor (5), and a pressure head (4) connected in sequence, wherein the pressure head (4) is arranged horizontally and abuts against a lateral baffle of the first top cover (11); the first force sensor (5) is communicatively connected to a first data acquisition instrument (7).

3. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The number of the fixed brackets (1) and the number of the three-point bending brackets (3) are the same and correspond one to one. The fixed brackets (1) and the first base (2) are welded to form a rigid support structure; the first base (2) is detachably fixed to the bottom of the reactor (39); the side baffles of the three-point bending brackets (3) and the fixed brackets (1) form a positioning matching surface; the triangular bottom plate (9) and the bottom plates of the three-point bending brackets (3) on both sides are spliced ​​to form a complete bearing surface; the first top cover (11) realizes vertical displacement control through a screw (12) with threaded matching.

4. The hydrate sediment fracture toughness testing system according to claim 1 or 3, characterized in that: The triangular bottom plate (9) is provided with threaded holes at both ends, and the bottom plate of the three-point bending bracket (3) is provided with corresponding circular holes. The steel rod (10) passes through the side wall of the reactor (39), the threaded holes of the triangular bottom plate (9), and the circular holes on the bottom plate of the three-point bending bracket (3) in sequence to achieve locking.

5. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The second horizontal loading mechanism comprises a second force sensor (18) and a second hydraulic cylinder (19) connected in sequence, the second force sensor (18) being arranged horizontally and abutting against the sliding base (17), and the second force sensor (18) being communicatively connected to a second data acquisition device (20).

6. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The top of the reactor (39) is connected to a thermometer (30) and a pressure gauge (38).

7. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The second base (16) is detachably fixed to the bottom of the reaction kettle (39).

8. The hydrate sediment fracture toughness testing system according to claim 1, characterized in that: The sample synthesis unit also includes a gas supply module, a vacuum module, a constant temperature control module and an exhaust metering module: The gas supply module includes a high-pressure gas cylinder (23), a gas booster pump (24), a first gas flow meter (25), a first valve (26), a second valve (27), and an intermediate storage tank (37); the high-pressure gas cylinder (23), the gas booster pump (24), the first gas flow meter (25), the first valve (26), and the intermediate storage tank (37) are connected in sequence through pipelines, and the intermediate storage tank (37) is connected to the reactor (39) through the second valve (27); The vacuum pump module includes a third valve (28) and a vacuum pump (29), and the third valve (28) is installed on the connecting pipeline between the reaction kettle (39) and the vacuum pump (29); The constant temperature control module includes a constant temperature water bath (36) covering the intermediate storage tank (37) and the reactor (39); The exhaust metering module comprises a fourth valve (31), a pneumatic back pressure valve (32), a gas-water separator (33), a second gas flow meter (34) and a gas collecting bottle (35), wherein the fourth valve (31) is arranged at the gas outlet end of the reaction kettle (39), and the fourth valve (31), the pneumatic back pressure valve (32), the gas-water separator (33), the second gas flow meter (34) and the gas collecting bottle (35) are connected in sequence through pipelines.

9. The hydrate sediment fracture toughness testing system according to claim 2, characterized in that: The first hydraulic cylinder (6) is connected to a first hydraulic system (8).

10. The hydrate sediment fracture toughness testing system according to claim 5, characterized in that: The second hydraulic cylinder (19) is connected to a second hydraulic system (21).

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