A device and method for experimental shear characteristics of hydrate sediment and structure interface

Abstract

The present invention discloses an experimental device and method for shear characteristics of hydrate sediment and structure interface, which is in the field of basic physical property measurement of geotechnical engineering. The device includes a triaxial shear pressure box, a torsion and axial loading host, a methane gas source, a host computer, a first pressure volume controller, a water bath device, a second pressure volume controller, an oil tank, a back pressure valve, a gas-water separator, a gas flow meter and a data acquisition system; the triaxial shear pressure box includes an upper pressure plate, an upper fixed plate, a loading rod, a pressure chamber upper cover, a high-pressure sealing cover, a lower rotating chassis, a heat insulation plate, a lower pressure plate, a top cap and a base. The present invention has a simple structure and is easy to operate, and can realize the in-situ generation of hydrates. The shearing method of multi-directional load control can realize interface shear experiments under complex stress paths, providing hardware support for exploring the mechanical properties between hydrate sediments and structural interfaces.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering basic physical property measurement, and specifically relates to a shear property experimental device and method for hydrate sediment and structure interface. Background Art

[0002] Natural gas hydrates have the characteristics of high energy density, wide distribution, and large reserves. They are a clean energy with good development prospects. Due to their low temperature and high pressure formation conditions, hydrates generally only exist in the bottom of the deep seabed and the frozen ground zone on land. The multi-process coupling (deformation process, chemical process, seepage process, heat conduction, etc.) during the hydrate mining process will cause the hydrate sediments at the interface between the sediments and the well structure to undergo phase change decomposition, and the mechanical properties of the interface between the hydrate sediments and the well structure will change, thereby affecting the stability of the well structure and causing safety problems such as wellbore collapse and gas leakage. Therefore, the study of the mechanical properties of the interface between hydrate sediments and structures is of great significance to hydrate mining.

[0003] Most of the existing interface shear devices are relatively simple and cannot meet the low temperature, high pressure and other conditions required for the formation of hydrate deposits. Prior to the present invention, Dalian University of Technology proposed a soil-structure interface interaction parameter determination device and test method in 2020 (application number 202010806837.0); this experimental device has some problems and shortcomings: 1. It is impossible to achieve the low temperature and high pressure conditions for the formation of hydrate sediments, and it is impossible to generate and maintain the stability of hydrate sediments in situ; 2. The sealing of the pressure chamber is insufficient, and the sealing between the force transfer rod and the pressure chamber is insufficient, and high-pressure sealing cannot be achieved; 3. During the interface shear experiment, the force transfer seat is not tightly connected, resulting in inaccurate experimental data; 4. The stress loading method is single, and it is impossible to realize the complex stress path shear experiment under the action of vertical load and circumferential torque coupling.

[0004] Therefore, based on the existing technical equipment, the present invention improves the measuring equipment and testing methods, and develops a new experimental device for the shear characteristics of the interface between hydrate sediments and structures, which simulates the complex stress state of the interface between hydrate sediments and well structures during hydrate exploitation, and further corrects the accuracy of measuring the mechanical parameters of the interface between sediments and structures. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a hydrate sediment and structure interface shear characteristics experimental device and method. The present invention can accurately measure the shear mechanical properties of the hydrate sediment and structure interface during hydrate mining, display them using a data acquisition system, and has simple operation and reliable structure.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In a first aspect, the present invention provides a hydrate sediment and structure interface shear characteristics experimental device, including a triaxial shear pressure box, a torsion and axial loading host, a methane gas source, a first pressure volume controller, a water bath device, a second pressure volume controller, an oil tank, a back pressure valve, a gas-water separator, a gas flow meter and a data acquisition system;

[0008] The triaxial shear pressure box comprises a pressure chamber upper cover, a high-pressure sealing cover and a lower rotating chassis which are arranged in sequence from top to bottom and form a sealed pressure chamber; the pressure chamber upper cover and the lower rotating chassis are detachably connected by a plurality of locking screws, a water bath jacket connected to a water bath device is provided on the outer periphery of the high-pressure sealing cover, and a heat insulation plate and a lower pressure plate are connected in sequence below the lower rotating chassis; a top cap, a sample assembly and a base are coaxially arranged from top to bottom in the pressure chamber, and the sample assembly is clamped between the top cap and the base by a plurality of fixing screws; the base is fixed to the bottom of the pressure chamber, and a through cylindrical hole is opened at the central axis; the loading rod is arranged vertically, the lower part passes through the top cap and the sample assembly, the bottom extends into the cylindrical hole of the base, the top extends out of the pressure chamber upper cover and is connected to the upper fixed plate The top of the upper fixed plate is connected to the upper pressure plate in a detachable manner; the lower rotating chassis is respectively provided with an exhaust channel, a confining pressure control channel, a temperature sensor channel, an air intake channel and a drainage channel connected to the pressure chamber; the exhaust channel is sequentially connected to the fourth valve, the back pressure valve, the gas-water separator and the gas flow meter through a pipeline; the confining pressure control channel is externally connected to a pipeline with a third valve, and the end of the pipeline is connected in parallel with a second pressure volume controller and an oil tank; the temperature sensor channel is used to place a temperature sensor that can measure the temperature inside the pressure chamber; the air intake channel is connected to the methane gas source through a pipeline with a second valve, and the pipeline is also connected to the first pressure volume controller through a branch with a first valve; the drainage channel can connect the cylindrical hole of the base with the outside world;

[0009] The axial actuator at the upper end of the torsion and axial loading main machine is fixedly connected to the top of the upper pressure plate, and the torsion actuator at the lower end is fixedly connected to the bottom of the lower pressure plate. The axial actuator, the three-axis shear pressure box and the torsion actuator are coaxially arranged; the data acquisition system is connected to the first pressure volume controller, the temperature sensor, the second pressure volume controller, the water bath device and the torsion and axial loading main machine.

[0010] Preferably, the sample assembly includes a sample, filter paper, a water-permeable plate and a rubber membrane, wherein filter paper and water-permeable plates are placed in sequence at the upper and lower ends of the sample from the inside to the outside, and ribs for transmitting torque are provided on one side of the two water-permeable plates adjacent to the sample, and the sample and the outer periphery of the filter paper and water-permeable plates at the upper and lower ends are wrapped by a rubber membrane, and the two ends of the rubber membrane are respectively fixed on the top cap and the base.

[0011] Furthermore, the two water-permeable plates are annular structures and are fixedly connected to the top of the base and the bottom of the top cap by bolts respectively.

[0012] Preferably, the bottom of the loading rod is sequentially sleeved with a second guide ring and a sealing ring from bottom to top to be sealed and connected with the cylindrical hole of the base.

[0013] Preferably, one end of the air inlet channel passes through the base and is connected to the water-permeable plate below the sample, and the other end is externally connected to a pipeline with a second valve; one end of the exhaust channel passes through the top cap and is connected to the water-permeable plate above the sample, and the other end is externally connected to a pipeline with a fourth valve; one end of the confining pressure control channel is connected to the pressure chamber, and the other end is externally connected to a pipeline with a third valve, and the pipeline is then divided into two branches, the first branch is sequentially connected to the sixth valve and the second pressure volume controller, and the second branch is sequentially connected to the fifth valve and the oil tank.

[0014] Preferably, the loading rod is a cylindrical structure as a whole, with a protrusion with a square cross-section on the top, and a groove with a square cross-section on the bottom of the upper fixed plate. The protrusion on the top of the loading rod can be embedded in the groove at the bottom of the upper fixed plate and the two are connected by screws.

[0015] Preferably, the upper pressure plate, upper fixed plate, loading rod, pressure chamber upper cover, high-pressure sealing cover, lower rotating chassis, heat insulation plate, lower pressure plate, top cap, sample assembly and base are all coaxially arranged; the pressure chamber upper cover, high-pressure sealing cover, lower rotating chassis, heat insulation plate, lower pressure plate, top cap, sample assembly and base can rotate synchronously and sealably with the loading rod as the central axis, and the loading rod can slide sealably in the vertical direction under the limitation of the pressure chamber upper cover, top cap, sample assembly and base.

[0016] Preferably, the pressure chamber upper cover and sealing cover are made of 7075 aviation aluminum alloy, the top cap, base and lower rotating chassis are made of 316L stainless steel, the insulation board is made of polyetheretherketone, and the locking screw is made of tungsten steel.

[0017] Preferably, the loading rod is sealed and connected to the upper cover of the pressure chamber via a first guide ring.

[0018] In a second aspect, the present invention provides a testing method using any of the hydrate sediment and structure interface shear characteristics experimental devices described in the first aspect, which is as follows:

[0019] S1: Open the triaxial shear pressure box, and inject water into the cylindrical hole of the base through the drainage channel. When the water surface completely submerges the sealing ring in the cylindrical hole, close the drainage channel, insert the loading rod into the cylindrical hole, open the drainage channel and adjust the depth of the loading rod into the cylindrical hole until the bottom of the loading rod is lower than the height of the second guide ring, and close the drainage channel so that the water remaining in the cylindrical hole can support the loading rod;

[0020] S2: Fix the permeable plate with ribs to the top of the base and the bottom of the top cap respectively, place filter paper on the permeable plate on the top of the base, and set the bottom of the rubber membrane on the base; use the sample preparation mold to prepare soil samples with corresponding moisture content according to the experimental working conditions, use the compaction block to compact the sample in layers along the axial direction of the loading rod, place filter paper and the top cap on the top of the sample, fix the top cap to the base with fixing screws to clamp the sample, set the top of the rubber membrane on the top cap, remove the sample preparation mold, and connect the exhaust channel; then install the compression screw, high-pressure sealing cover and pressure chamber upper cover in turn, use the nut to fix the compression screw to seal the pressure chamber, and finally fix the top of the loading rod on the upper fixed plate;

[0021] S3: Open the third valve and the fifth valve of the control oil tank, start the submersible pump in the oil tank, and inject silicone oil into the pressure chamber through the confining pressure control channel. When the pressure chamber is filled with silicone oil, close the fifth valve and the submersible pump, open the sixth valve of the second pressure volume controller, and control the second pressure volume controller to control the confining pressure inside the pressure chamber through the confining pressure control channel; when the pressure in the second pressure volume controller rises to 0.2MPa, adjust the second pressure volume controller to constant pressure mode, open the first valve, the second valve and the fourth valve, and adjust the back pressure valve opening to the maximum; open the methane gas source, and inject methane gas into the first pressure volume controller and the pressure chamber through the pipeline respectively. When the pressure of the first pressure volume controller rises to 0. 1MPa, turn off the methane gas source, adjust the back pressure valve to the minimum opening, and close the fourth valve; adjust the first pressure volume controller and the second pressure volume controller to control the increase rate of the confining pressure in the pressure chamber to be the same as the increase rate of the pore pressure, and always keep the confining pressure 0.1MPa higher than the pore pressure until the confining pressure and the pore pressure reach 10.1MPa and 10Mpa respectively; turn on the water bath device, adjust the silicone oil temperature in the pressure chamber to 15°C to prevent hydrate formation, adjust the first pressure volume controller and the second pressure volume controller to enter the constant pressure mode, when the methane gas volume in the first pressure volume controller is no longer consumed, it is considered that the sample has reached full gas saturation, and S4 is performed to generate hydrates in situ;

[0022] S4: adjusting the temperature of the silicone oil in the pressure chamber to 1°C through a water bath device, so that the sample temperature is lower than the hydrate phase equilibrium temperature; when the volume of the methane gas in the first pressure-volume controller does not change significantly again, it indicates that the water in the pores of the sample has completely reacted with the methane gas to form methane hydrate; according to the volume change of the methane gas in the first pressure-volume controller when it is stable in S3 and S4, the saturation of methane hydrate is calculated;

[0023] S5: According to the specific experimental conditions, the pressure of the first pressure-volume controller and the second pressure-volume controller are adjusted and maintained to release the excess pore pressure inside the sample, thereby achieving consolidation of the sediment sample; when the volume of methane gas in the first pressure-volume controller no longer changes, it is considered that the sample consolidation is completed, and then S6 is performed to perform interface shear on the sample;

[0024] S6: Open the drainage channel, carry out different tests according to the actual working conditions, select the control mode of the first pressure-volume controller and the second pressure-volume controller, select the torsional shear test or the axial shear test through the torsion and axial loading host, and use different control loading methods to select the single shear or cyclic loading method; during the test, the stress sensor readings, torque sensor readings, torsion angle sensor readings, displacement sensor readings and pore pressure sensor readings are collected and recorded through the data acquisition system, and then the influence of the hydrate extraction process on the mechanical properties of the sediment-structure interface is analyzed.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention adds a shearing method for controlling loads in multiple directions. The upper pressure plate is connected to the axial actuator of the torsion and axial loading main machine, and the lower pressure plate is connected to the torsion actuator of the torsion and axial loading main machine, thereby realizing axial force and torque coupling loading, and can truly simulate the mechanical response characteristics of the interface between hydrate sediments and structures under complex stress states.

[0027] (2) The present invention innovatively overcomes the drawback that existing contact interface experimental devices cannot conduct experimental research on the interface between hydrate sediments and structures under high pressure and low temperature.

[0028] (3) The testing method of the present invention is simple in overall operation, the instrument is easy to operate, and the results are accurate. It has extremely strong promotion value and practical value in a series of experiments on contact surfaces, and has important reference significance for subsequent research on the constitutive relationship of contact surfaces and the calibration of related numerical simulation parameters.

[0029] (4) The split structural design of the present invention can ensure that the installation of the triaxial pressure chamber after sample preparation will not disturb or damage the sample containing the loading rod, and the sample can be three-dimensionally consolidated to ensure uniform density of the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural diagram of a triaxial shear pressure cell in an experimental device for shear characteristics of hydrate sediment and structure interface;

[0031] Figure 2 It is an overall system diagram of an experimental device for shear characteristics of hydrate sediment and structure interface;

[0032] In the figure: 1 triaxial shear pressure box; 2 torsion and axial loading host; 3 methane gas source; 4 host computer; 5 first pressure volume controller; 6 water bath device; 7 second pressure volume controller; 8 oil tank; 9 back pressure valve; 10 gas-water separator; 11 gas flow meter; 12 data acquisition system; 13a first valve; 13b second valve; 13c third valve; 13d fourth valve; 13e fifth valve; 13f sixth valve; 14 upper pressure plate; 15 upper solid Fixed plate; 16 loading rod; 17 first guide ring; 18 water bath jacket; 19 high pressure sealing cover; 20 locking screw; 21 top cap; 22 fixing screw; 23 rubber membrane; 24 water permeable plate; 25 ribs; 26 base; 27 second guide ring; 28 lower rotating chassis; 29 exhaust channel; 30 confining pressure control channel; 31 heat insulation board; 32 lower pressure plate; 33 temperature sensor channel; 34 air inlet channel; 35 drainage channel; 36 pressure chamber cover; 37 specimen. DETAILED DESCRIPTION

[0033] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0034] like Figure 2 As shown, an experimental device for shear characteristics of hydrate sediment and structure interface provided by the present invention is provided, and the device mainly includes a triaxial shear pressure box 1, a torsion and axial loading host 2, a methane gas source 3, a first pressure volume controller 5, a water bath device 6, a second pressure volume controller 7, an oil tank 8, a back pressure valve 9, a gas-water separator 10, a gas flow meter 11 and a data acquisition system 12.

[0035] The structure and connection method of each component will be described in detail below.

[0036] In the present invention, if Figure 1As shown, the triaxial shear pressure box 1 mainly includes an upper pressure plate 14, an upper fixed plate 15, a loading rod 16, a pressure chamber upper cover 36, a high-pressure sealing cover 19, a lower rotating chassis 28, a heat insulation plate 31, a lower pressure plate 32, a top cap 21 and a base 26. Among them, the pressure chamber upper cover 36, the high-pressure sealing cover 19 and the lower rotating chassis 28 are arranged in sequence from top to bottom and are detachably connected. The three together form a sealed pressure chamber, which is used to place a sample 37 and can realize the corresponding hydrate sediment and structure interface shear characteristic experiment. In other words, the two ends of the high-pressure sealing cover 19 are respectively fixed on the pressure chamber upper cover 36 and the lower rotating chassis 28, and a sealing ring is installed between the high-pressure sealing cover 19 and the pressure chamber upper cover 36, and a sealing ring is installed between the high-pressure sealing cover 19 and the lower rotating chassis 28. The pressure chamber upper cover 36 and the lower rotating chassis 28 are detachably connected via a plurality of locking screws 20. Specifically, the bottom of the locking screw 20 is threadedly connected to the lower rotating chassis 28, and the upper part is fixed to the pressure chamber upper cover 36 via a nut, thereby tightly sealing the pressure chamber.

[0037] That is to say, the triaxial shear pressure box 1 of the present invention adopts a split structural design, and sealing rings are used to seal between the pressure chamber upper cover 36 and the high-pressure sealing cover 19, and between the lower rotating chassis 28 and the high-pressure sealing cover 28 respectively. The pressure chamber upper cover 36 and the lower rotating chassis 28 are connected and fixed by a locking screw 20. By dividing the pressure chamber sealing cover 19 and the pressure chamber upper cover 36 into two parts, the subsequent connection between the pressure chamber upper cover 36 and the loading rod 16 is facilitated without damaging the sample 37.

[0038] In the present invention, if Figure 1 As shown, a water bath jacket 18 is coaxially sleeved on the outer periphery of the high-pressure sealing cover 19, and a water inlet and a water outlet are respectively opened on the water bath jacket 18. The water inlet and the water outlet are respectively connected to the water outlet and the water inlet of the water bath device 6 through pipelines to form a circulation loop, and the temperature in the pressure chamber can be adjusted by the water bath device 6. In actual use, the water bath jacket 18 should be sealed and connected to the high-pressure sealing cover 19 with a sealing ring, and the water bath jacket 18 and the outer surface of the high-pressure sealing cover 19 are fixed by bolts; the water bath jacket 18 can be made of a material with good thermal insulation performance, and the interior is processed with spiral patterns to improve heat exchange efficiency and reduce heat loss.

[0039] In the present invention, if Figure 1As shown, the lower rotating chassis 28 is connected to the heat insulation board 31 at the bottom, and the heat insulation board 31 is connected to the lower pressure plate 32 at the bottom. A top cap 21, a sample assembly and a base 26 are coaxially arranged from top to bottom in the pressure chamber, and the sample assembly is clamped between the top cap 21 and the base 26 by a plurality of fixing screws 22. Specifically, the fixing screw 22 has threads processed at the bottom and unprocessed threads at the top, and the bottom of the fixing screw 22 is connected to the base 26 by threads. The top cap 21 is circumferentially fixed by the fixing screw 22, and then when the sample is consolidated, the top cap 21 can move up and down to achieve three-dimensional consolidation. In other words, in order to avoid torsional deformation of the sample 37 in the torsional shear test, the top cap 21 on the upper part of the sample 37 and the base 26 on the lower part are fixed by fixing screws 22, and the top cap 21 can move freely up and down to ensure that the sample 37 can be consolidated in three dimensions.

[0040] In the present invention, if Figure 1 As shown, the base 26 is fixed to the bottom of the pressure chamber, and a through cylindrical hole is opened at the central axis. The loading rod 16 is arranged vertically, and the lower part passes through the top cap 21 and the sample assembly in sequence, and the bottom extends into the cylindrical hole of the base 26. The bottom of the loading rod 16 is sealed and connected to the cylindrical hole of the base 26 through a sealing ring, and the connection between the loading rod 16 and the top cap 21 is sealed by a sealing ring to prevent the silicone oil used for confining pressure in subsequent experiments from leaking into the sample and causing the sample 37 to be contaminated. In actual use, a second guide ring 27 and a sealing ring can be sleeved from bottom to top on the bottom of the loading rod 16, and the inner wall of the cylindrical hole of the base 26 is sealed and connected through the sealing ring and the second guide ring 27. The top part of the loading rod 16 extends out of the pressure chamber cover 36 and is detachably connected to the upper fixed plate 15. The top of the upper fixed plate 15 is connected to the upper pressure plate 14, and the connection between the loading rod 16 and the pressure chamber cover 36 remains sealed. In actual use, the loading rod 16 as a whole can be set as a solid steel cylindrical structure with smooth ends and roughness in the middle, but a protrusion with a square cross section is provided on the top, and a groove with a square cross section is provided at the bottom of the upper fixed plate 15. The protrusion on the top of the loading rod 16 can be embedded in the groove at the bottom of the upper fixed plate 15, and the two are connected by screws to maintain the stability of the loading rod 16 during the experiment. The top of the loading rod 16 is processed into a square shape to ensure the maximum moment of inertia and avoid damage to the loading rod 16 during the torsion shear test. In actual use, the loading rod 16 and the pressure chamber cover 36 can be sealed and connected by the first guide ring 17. In other words, in order to reduce the friction between the loading rod 16 and the triaxial shear pressure box 1 during the experiment, the first guide ring 17 and the second guide ring 27 are respectively installed at the upper end and the bottom end of the loading rod 16.

[0041] As a preferred embodiment of the present invention, the sample assembly mainly includes a sample 37, filter paper, a water-permeable plate 24 and a rubber membrane 23. Filter paper and water-permeable plates 24 are placed in sequence from the inside to the outside at the upper and lower ends of the sample 37. Ribs 25 for transmitting torque are provided on one side of the two water-permeable plates 24 adjacent to the sample 37. The ribs 25 should be embedded in the sample 37 during the experiment. The outer periphery of the sample 37 and the filter paper and water-permeable plates 24 at the upper and lower ends are wrapped by the rubber membrane 23, and the two ends of the rubber membrane 23 are respectively fixed to the top cap 21 and the base 26. In actual use, the two water-permeable plates 24 can be set as an annular structure, and are respectively fixed to the top of the base 26 and the bottom of the top cap 21 by bolts.

[0042] In the present invention, if Figure 1 and 2 As shown, the lower rotating chassis 28 is provided with an exhaust channel 29, a confining pressure control channel 30, a temperature sensor channel 33, an air intake channel 34 and a drainage channel 35 which are connected to the pressure chamber. The exhaust channel 29 is connected to the fourth valve 13d, the back pressure valve 9, the gas-water separator 10 and the gas flow meter 11 in sequence through pipelines; the confining pressure control channel 30 is externally connected to a pipeline provided with a third valve 13c, and the end of the pipeline is connected in parallel with a second pressure volume controller 7 and an oil tank 8; the temperature sensor channel 33 is used to place a temperature sensor capable of measuring the internal temperature of the pressure chamber; the air intake channel 34 is connected to the methane gas source 3 through a pipeline provided with a second valve 13b, and the pipeline is also connected to the first pressure volume controller 5 through a branch provided with a first valve 11a; the drainage channel 35 can connect the cylindrical hole of the base 26 with the outside.

[0043] Specifically, one end of the exhaust channel 29 is connected to the water-permeable plate 24 located above the sample 37 through the top cap 21, and the other end is connected to the pipeline with the fourth valve 13d through the lower rotating chassis 28. In actual use, for the convenience of structural assembly, the exhaust channel 29 can be divided into three sections of pipelines, and the three sections of pipelines are respectively arranged on the top cap 21, inside the pressure chamber and on the lower rotating chassis 28 along the exhaust direction. Among them, the pipelines located on the top cap 21 and the lower rotating chassis 28 can be realized by opening holes, and the pipelines located inside the pressure chamber can be made of polytetrafluoroethylene hoses. One end of the confining pressure control channel 30 is connected to the pressure chamber, and the other end is connected to the pipeline with the third valve 13c. The pipeline is then divided into two branches. The first branch is connected to the sixth valve 13f and the second pressure volume controller 7 in sequence, and the second branch is connected to the fifth valve 13e and the oil tank 8 in sequence. One end of the temperature sensor channel 33 is connected to the pressure chamber, and the other end is connected to the outside world. The temperature sensor can be placed through the channel, and the probe of the temperature sensor is located inside the pressure chamber, so as to measure the temperature data inside the pressure chamber. One end of the air inlet channel 34 passes through the base 26 and is connected to the water-permeable plate 24 below the sample 37, and the other end is externally connected to a pipeline with a second valve 13b. One end of the drainage channel 35 is connected to the cylindrical hole of the base 26, and the other end is connected to the outside world, which is used to inject water into or drain water from the pressure chamber.

[0044] In the present invention, if Figure 2 As shown, the torsion and axial loading host 2 adopts the device structure in the prior art, which includes an axial actuator at the upper end, a torsion actuator at the lower end, a force and torque sensor (for recording stress sensor readings and torque sensor readings), a displacement sensor, a torsion angle sensor, etc. The specific structure is not repeated here. Among them, the axial actuator at the upper end of the torsion and axial loading host 2 is fixedly connected to the top of the upper pressing plate 14, and the torsion actuator at the lower end is fixedly connected to the bottom of the lower pressing plate 32. The axial actuator, the triaxial shear pressure box 1 and the torsion actuator are coaxially arranged. The data acquisition system 12 is connected to the first pressure volume controller 5, the temperature sensor, the second pressure volume controller 7, the water bath device 6 and the torsion and axial loading host 2. The data acquisition system 12 can be connected to the host computer 4 to display data in real time.

[0045] As a preferred embodiment of the present invention, in order to ensure a better transmission effect, the upper pressure plate 14, the upper fixed plate 15, the loading rod 16, the pressure chamber upper cover 36, the high pressure sealing cover 19, the lower rotating chassis 28, the heat insulation plate 31, the lower pressure plate 32, the top cap 21, the sample assembly and the base 26 should all be coaxially arranged. And the pressure chamber upper cover 36, the high pressure sealing cover 19, the lower rotating chassis 28, the heat insulation plate 31, the lower pressure plate 32, the top cap 21, the sample assembly and the base 26 can be synchronously sealed and rotated with the loading rod 16 as the central axis, and the loading rod 16 can be sealed and slid in the vertical direction under the limit of the pressure chamber upper cover 36, the top cap 21, the sample assembly and the base 26.

[0046] As a preferred embodiment of the present invention, the material of the pressure chamber upper cover 36 and the sealing cover 19 can be 7075 aviation aluminum alloy, and the corrosion resistance is treated by hard anodizing. The 7075 aviation aluminum alloy has high strength and high heat conductivity, can withstand high pressure and improve heat exchange efficiency. The top cap 21, the base 26 and the lower rotating chassis 28 can be made of 316L stainless steel. In order to reduce heat loss during the experiment, a heat insulation board 31 is installed at the bottom of the lower rotating chassis 28. The material of the heat insulation board 31 can be a rigid material with good thermal insulation performance, such as polyetheretherketone (peek material). The locking screw 20 can be made of tungsten steel, which has high strength and hardness, and can fix the sealing cover 19 and the pressure chamber upper cover 36 to ensure that the pressure chamber can withstand high pressure.

[0047] Using the above-mentioned hydrate sediment and structure interface shear characteristics experimental device, the present invention also provides a testing method, which is specifically as follows:

[0048] Before the experiment, Figure 2 Check whether the pipelines of the device are connected correctly, as shown below:

[0049] The water bath channel on the water bath jacket 18 is connected to the water bath device 6 using a flexible pipeline (such as a rubber tube) to achieve temperature control of the pressure chamber. The confining pressure control channel 30 is connected to the second pressure volume controller 7 and the oil tank 8 using a pressure-resistant pipeline (such as a steel pipe) through the third valve 13c, the fifth valve 13e, and the sixth valve 13f, respectively, to achieve confining pressure control of the sediment sample. The air inlet channel 34 is connected to the first pressure volume controller 5 and the methane gas source 3 using a pressure-resistant pipeline through the first valve 13a and the second valve 13b, respectively, to achieve pore pressure control of the sediment sample. Among them, the methane gas source provides the sediment sample with the gas supply required for the in-situ generation of hydrates. The exhaust channel 29 is connected to the back pressure valve 9, the gas-water separator 10 and the gas flowmeter 11 through the fourth valve 13d, respectively, using a pressure-resistant pipeline to achieve back pressure control of the sediment sample. Among them, the gas flowmeter 11 is used to calculate the hydrate saturation change of the sediment sample in the decomposition experiment. The temperature sensor in the temperature sensor channel 33, the first pressure-volume controller 5, the second pressure-volume controller 7, the torsion and axial loading host 2, the water bath device 6 and the data acquisition device 12 are connected to realize data acquisition of the shear characteristics experimental device of hydrate sediment and structure interface during the experiment.

[0050] After confirming that all pipelines in the device are connected correctly, perform the following operations in sequence:

[0051] S1: Installation of loading rod:

[0052] Open the triaxial shear pressure box 1, that is, keep the connection between the lower pressure plate 32, the heat insulation plate 31, the lower rotating chassis 28 and the base 26. Inject deionized water into the cylindrical hole of the base 26 through the drainage channel 35. When the water surface completely submerges the sealing ring in the cylindrical hole, close the drainage channel 35, extend the loading rod 16 into the cylindrical hole, open the drainage channel 35 and adjust the depth of the loading rod 16 extending into the cylindrical hole until the bottom of the loading rod 16 is lower than the height of the second guide ring 27, and close the drainage channel 35 so that the water remaining in the cylindrical hole can support the loading rod 16.

[0053] This is because the loading rod will be pressed down during the subsequent formal test, so there is a certain distance between the bottom of the loading rod and the base. However, in order to prevent the loading rod from moving downward under the action of gravity, water is used to support the loading rod. In addition, since the soil sample and the loading rod form a whole during the subsequent sample preparation, the weight increases. This operation can also prevent the loading rod from falling under the action of gravity and thus destroying the overall structure.

[0054] S2: Sample preparation and installation:

[0055] The permeable plate 24 with ribs 25 is fixed to the top of the base 26 and the bottom of the top cap 21 respectively, and filter paper is placed on the permeable plate 24 at the top of the base 26. The bottom of the rubber membrane 23 is fixed on the base 26. The sample preparation mold is placed on the base, and the other end of the rubber membrane is fixed on the upper end of the sample preparation mold. The rubber membrane is adsorbed on the sample preparation mold using a vacuum pump. According to the experimental working conditions, soil samples with corresponding moisture content are prepared, and compaction blocks are used to compact the soil samples 37 along the axial direction of the loading rod 16. After the sample preparation is completed, filter paper and a top cap 21 are placed on the top of the sample 37. The top cap 21 is fixed to the base 26 by fixing screws 22 to clamp the sample 37. The top of the rubber membrane 23 is fixed on the top cap 21, and the sample preparation mold is removed to connect the exhaust channel 29. Then, the compression screw 20, the high-pressure sealing cover 19 and the pressure chamber upper cover 36 are installed in sequence, and the compression screw 20 is fixed with a nut to seal the pressure chamber. Finally, the top of the loading rod 16 is fixed on the upper fixed plate 15.

[0056] S3: Sample saturation:

[0057] The third valve 13c and the fifth valve 13e of the control oil tank 8 are opened, the submersible pump in the oil tank 8 is started, and the silicone oil is injected into the pressure chamber through the confining pressure control channel 30. When the pressure chamber is filled with silicone oil, the fifth valve 13e and the submersible pump are closed, and the sixth valve 13f of the second pressure volume controller 7 is opened to control the second pressure volume controller 7 to control the confining pressure inside the pressure chamber through the confining pressure control channel 30. When the pressure in the second pressure volume controller 7 rises to 0.2MPa, the second pressure volume controller 7 is adjusted to the constant pressure mode, the first valve 13a, the second valve 13b and the fourth valve 13d are opened, and the back pressure valve 9 is adjusted to the maximum opening. The methane gas source 3 is opened, and the methane gas is injected into the first pressure volume controller 5 and the pressure chamber respectively through the pipeline. When the pressure of the first pressure volume controller 5 rises to 0.1MPa, the methane gas source 3 is closed, the back pressure valve 9 is adjusted to the minimum opening, and the fourth valve 13d is closed. Adjust the first pressure volume controller 5 and the second pressure volume controller 7 to control the rate of increase of the confining pressure in the pressure chamber to be the same as the rate of increase of the pore pressure, and always keep the confining pressure 0.1MPa higher than the pore pressure until the confining pressure and pore pressure reach 10.1MPa and 10Mpa respectively. Turn on the water bath 6 and adjust the temperature of the silicone oil in the pressure chamber to 15°C to prevent the formation of hydrates. Adjust the first pressure volume controller 5 and the second pressure volume controller 7 to enter the constant pressure mode. When the volume of methane gas in the first pressure volume controller 5 is no longer consumed, it is considered that the sample 37 has reached full gas saturation, and S4 is performed to generate hydrates in situ.

[0058] During this process, the temperature of the silicone oil in the pressure chamber is obtained by a temperature sensor.

[0059] S4: Hydrate in situ generation:

[0060] The temperature of the silicone oil in the pressure chamber is adjusted to 1°C by the water bath device 6, so that the temperature of the sample 37 is lower than the hydrate phase equilibrium temperature. When the volume of the methane gas in the first pressure volume controller 5 does not change significantly again, it indicates that the water in the pores of the sample 27 has completely reacted with the methane gas to form methane hydrate. According to the volume change of the methane gas in the first pressure volume controller 5 when it is stable in S3 and S4, the saturation of methane hydrate is calculated.

[0061] S5: Specimen consolidation:

[0062] According to the specific experimental conditions, the pressure of the first pressure volume controller 5 and the second pressure volume controller 7 is adjusted and maintained to release the excess pore pressure inside the sample 37, thereby achieving consolidation of the sediment sample. When the volume of the methane gas in the first pressure volume controller 5 no longer changes, it is considered that the consolidation of the sample 37 is completed, and then S6 is performed to shear the sample 37.

[0063] S6: Specimen shearing:

[0064] Open the drainage channel 35, carry out different tests according to the actual working conditions, select the control mode of the first pressure volume controller 5 and the second pressure volume controller 7, select the torsion shear test or the axial shear test through the torsion and axial loading host 2, and use different control loading methods to select the single shear or cyclic loading method. The control system of the instrument adopts two sets of control methods, which are divided into stress control and strain control. Stress control is a control method for controlling the rate of change of stress increment, and strain control is a control method for controlling the rate of change of displacement. Both sets of control methods can determine different loading rates according to needs. During the test, it can be stopped manually or automatically stopped by setting the failure criterion. During the test, the stress sensor readings, torque sensor readings, torsion angle sensor readings, displacement sensor readings and pore pressure sensor readings are collected and recorded by the data acquisition system 12, and then the influence of the hydrate mining process on the mechanical properties of the sediment-structure interface is analyzed.

[0065] Specifically, when the device carries out torsional shear and axial shear tests, the torsion chassis 28 drives the sealing cover 18, the base 26, the sample 37, the top cap 21, and the pressure chamber cover 36 to torsionally move together; the upper fixed plate 15 drives the loading rod 16 to move axially, and a shear test is carried out at the interface between the sample and the loading rod.

[0066] The invention has a simple structure and is easy to operate, and can realize the in-situ generation of hydrates. The shearing method of multi-directional controlled loads can realize interface shear experiments under complex stress paths, providing hardware support for exploring the mechanical properties between hydrate sediments and structural interfaces.

[0067] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A hydrate sediment and structure interface shear characteristics experimental device, characterized in that: It comprises a triaxial shear pressure box (1), a torsion and axial loading main unit (2), a methane gas source (3), a first pressure volume controller (5), a water bath device (6), a second pressure volume controller (7), an oil tank (8), a back pressure valve (9), a gas-water separator (10), a gas flow meter (11) and a data acquisition system (12); The triaxial shear pressure box (1) comprises a pressure chamber upper cover (36), a high-pressure sealing cover (19) and a lower rotating chassis (28) which are arranged in sequence from top to bottom and enclose a sealed pressure chamber; the pressure chamber upper cover (36) and the lower rotating chassis (28) are detachably connected via a plurality of locking screws (20); a water bath jacket (18) which is connected to a water bath device (6) is provided on the outer periphery of the high-pressure sealing cover (19); a heat insulation plate (31) and a lower pressure plate (32) are connected in sequence below the lower rotating chassis (28); A top cap (21), a sample assembly and a base (26) are coaxially arranged from top to bottom in the pressure chamber, and the sample assembly is clamped between the top cap (21) and the base (26) by a plurality of fixing screws (22); the base (26) is fixed to the bottom of the pressure chamber, and a through cylindrical hole is opened at the center axis; the loading rod (16) is vertically arranged, the lower part penetrates the top cap (21) and the sample assembly, the bottom extends into the cylindrical hole of the base (26), and the top extends out of the pressure chamber upper cover (36) and is detachable from the upper fixing plate (15). The upper fixed plate (15) is connected to the upper pressure plate (14) at the top; the lower rotating chassis (28) is respectively provided with an exhaust passage (29) connected to the pressure chamber, a confining pressure control passage (30), a temperature sensor passage (33), an air intake passage (34) and a drainage passage (35); the exhaust passage (29) is connected to the fourth valve (13d), the back pressure valve (9), the gas-water separator (10) and the gas flow meter (11) in sequence through pipelines; the confining pressure control passage (30) is externally connected to the fourth valve (13d), the back pressure valve (9), the gas-water separator (10) and the gas flow meter (11); A pipeline with three valves (13c), with a second pressure-volume controller (7) and an oil tank (8) connected in parallel at the end of the pipeline; a temperature sensor channel (33) for placing a temperature sensor capable of measuring the temperature inside the pressure chamber; an air intake channel (34) connected to a methane gas source (3) via a pipeline provided with a second valve (13b), and the pipeline is also connected to a first pressure-volume controller (5) via a branch provided with a first valve (13a); a drainage channel (35) capable of connecting the cylindrical hole of the base (26) to the outside; The axial actuator at the upper end of the torsion and axial loading main machine (2) is fixedly connected to the top of the upper pressure plate (14), and the torsion actuator at the lower end is fixedly connected to the bottom of the lower pressure plate (32). The axial actuator, the triaxial shear pressure box (1) and the torsion actuator are coaxially arranged; the data acquisition system (12) is connected to the first pressure volume controller (5), the temperature sensor, the second pressure volume controller (7), the water bath device (6) and the torsion and axial loading main machine (2).

2. The hydrate sediment and structure interface shear characteristics experimental device according to claim 1, characterized in that: The sample assembly comprises a sample (37), filter paper, a water-permeable plate (24) and a rubber membrane (23). The filter paper and the water-permeable plate (24) are placed in sequence from the inside to the outside at the upper and lower ends of the sample (37). Ribs (25) for transmitting torque are provided on one side of the two water-permeable plates (24) adjacent to the sample (37). The outer periphery of the sample (37) and the filter paper and the water-permeable plate (24) at the upper and lower ends are wrapped by the rubber membrane (23), and the two ends of the rubber membrane (23) are respectively fixed to the top cap (21) and the base (26).

3. The hydrate sediment and structure interface shear characteristics experimental device according to claim 2, characterized in that: The two water-permeable plates (24) are annular structures and are respectively fixedly connected to the top of the base (26) and the bottom of the top cap (21) by bolts.

4. The hydrate sediment and structure interface shear characteristics experimental device according to claim 1, characterized in that: The bottom of the loading rod (16) is sleeved with a second guide ring (27) and a sealing ring in sequence from bottom to top, so as to be sealed and connected to the cylindrical hole of the base (26).

5. The hydrate sediment and structure interface shear characteristics experimental device according to claim 2, characterized in that: One end of the air inlet channel (34) passes through the base (26) and is connected to the water-permeable plate (24) below the sample (37), and the other end is externally connected to a pipeline with a second valve (13b); one end of the air outlet channel (29) passes through the top cap (21) and is connected to the water-permeable plate (24) above the sample (37), and the other end is externally connected to a pipeline with a fourth valve (13d); one end of the confining pressure control channel (30) is connected to the pressure chamber, and the other end is externally connected to a pipeline with a third valve (13c), and the pipeline is then divided into two branches, the first branch is connected in sequence to the sixth valve (13f) and the second pressure volume controller (7), and the second branch is connected in sequence to the fifth valve (13e) and the oil tank (8).

6. The hydrate sediment and structure interface shear characteristics experimental device according to claim 5, characterized in that: The loading rod (16) is a cylindrical structure as a whole, with a protrusion having a square cross section on the top, and a groove having a square cross section on the bottom of the upper fixing plate (15). The protrusion on the top of the loading rod (16) can be embedded in the groove on the bottom of the upper fixing plate (15), and the two are connected by screws.

7. The hydrate sediment and structure interface shear characteristics experimental device according to claim 5, characterized in that: The upper pressure plate (14), the upper fixed plate (15), the loading rod (16), the pressure chamber upper cover (36), the high-pressure sealing cover (19), the lower rotating chassis (28), the heat insulation plate (31), the lower pressure plate (32), the top cap (21), the sample assembly and the base (26) are all coaxially arranged; the pressure chamber upper cover (36), the high-pressure sealing cover (19), the lower rotating chassis (28), the heat insulation plate (31), the lower pressure plate (32), the top cap (21), the sample assembly and the base (26) can be synchronously and sealedly rotated with the loading rod (16) as the central axis, and the loading rod (16) can be sealed and slid in a vertical direction under the limit of the pressure chamber upper cover (36), the top cap (21), the sample assembly and the base (26).

8. The hydrate sediment and structure interface shear characteristics experimental device according to claim 5, characterized in that: The pressure chamber upper cover (36) and the high-pressure sealing cover (19) are made of 7075 aviation aluminum alloy, the top cap (21), the base (26) and the lower rotating chassis (28) are made of 316L stainless steel, the heat insulation plate (31) is made of polyetheretherketone, and the locking screw (20) is made of tungsten steel.

9. The hydrate sediment and structure interface shear characteristics experimental device according to claim 5, characterized in that: The loading rod (16) and the pressure chamber upper cover (36) are sealed and connected via a first guide ring (17).

10. A testing method using the hydrate sediment and structure interface shear characteristics experimental device according to any one of claims 5 to 9, characterized in that: The details are as follows: S1: Open the triaxial shear pressure box (1), inject water into the cylindrical hole of the base (26) through the drainage channel (35), close the drainage channel (35) when the water surface completely submerges the sealing ring in the cylindrical hole, extend the loading rod (16) into the cylindrical hole, open the drainage channel (35) and adjust the depth of the loading rod (16) in the cylindrical hole until the bottom of the loading rod (16) is lower than the height of the second guide ring (27), close the drainage channel (35), and allow the water remaining in the cylindrical hole to support the loading rod (16); S2: A permeable plate (24) with ribs (25) is fixed to the top of the base (26) and the bottom of the top cap (21), filter paper is placed on the permeable plate (24) at the top of the base (26), and the bottom of the rubber membrane (23) is fixed on the base (26); a soil sample with a corresponding moisture content is prepared according to the experimental working conditions using a sample preparation mold, and a compaction block is used to compact the soil sample in layers along the axial direction of the loading rod (16) to prepare a sample (37), and a filter paper and a top cap (21) are placed on the top of the sample (37). 1), the top cap (21) is fixed to the base (26) by means of fixing screws (22) to clamp the sample (37), the top of the rubber membrane (23) is fixed on the top cap (21), the sample preparation mold is removed, and the exhaust passage (29) is connected; then, the compression screw (20), the high-pressure sealing cover (19) and the pressure chamber upper cover (36) are installed in sequence, the compression screw (20) is fixed with a nut to seal the pressure chamber, and finally, the top of the loading rod (16) is fixed on the upper fixing plate (15); S3: Open the third valve (13c) and the fifth valve (13e) of the control oil tank (8), start the submersible pump in the oil tank (8), and inject silicone oil into the pressure chamber through the confining pressure control channel (30). When the pressure chamber is filled with silicone oil, close the fifth valve (13e) and the submersible pump, open the sixth valve (13f) controlling the second pressure volume controller (7), and control the second pressure volume controller (7) to control the confining pressure in the pressure chamber through the confining pressure control channel (30); when the pressure in the second pressure volume controller (7) rises to 0.2 MPa, adjust the second pressure volume controller (7) to a constant pressure mode, open the first valve (13a), the second valve (13b) and the fourth valve (13d), and adjust the back pressure valve (9) to the maximum opening; open the methane gas source (3), and inject methane gas into the first pressure volume controller (5) and the pressure chamber through the pipeline, respectively. When the pressure of the first pressure volume controller (5) rises to 0.1 MPa, the methane gas source (3) is closed, the back pressure valve (9) is adjusted to the minimum opening, and the fourth valve (13d) is closed; the first pressure volume controller (5) and the second pressure volume controller (7) are adjusted to control the rate of increase of the confining pressure in the pressure chamber to be the same as the rate of increase of the pore pressure, and the confining pressure is always kept 0.1 MPa higher than the pore pressure until the confining pressure and the pore pressure reach 10.1 MPa and 10 MPa respectively; the water bath device (6) is turned on, and the temperature of the silicone oil in the pressure chamber is adjusted to rise to 15°C to prevent the formation of hydrates, and the first pressure volume controller (5) and the second pressure volume controller (7) are adjusted to enter the constant pressure mode. When the volume of methane gas in the first pressure volume controller (5) is no longer consumed, it is considered that the sample (37) has reached full gas saturation, and S4 is performed to generate hydrates in situ; S4: The temperature of the silicone oil in the pressure chamber is adjusted to 1°C by a water bath device (6) so that the temperature of the sample (37) is lower than the hydrate phase equilibrium temperature; when the volume of the methane gas in the first pressure-volume controller (5) does not change significantly again, it indicates that the water in the pores of the sample (37) has completely reacted with the methane gas to form methane hydrate; based on the volume change of the methane gas in the first pressure-volume controller (5) when it is stable in S3 and S4, the saturation of the methane hydrate is calculated; S5: According to specific experimental conditions, the pressure of the first pressure-volume controller (5) and the second pressure-volume controller (7) is adjusted and maintained to release the excess pore pressure inside the sample (37), thereby achieving consolidation of the sediment sample; when the volume of the methane gas in the first pressure-volume controller (5) no longer changes, it is considered that the consolidation of the sample (37) is completed, and then S6 is performed to perform interface shear on the sample (37); S6: Open the drainage channel (35), carry out different tests according to actual working conditions, select the control mode of the first pressure volume controller (5) and the second pressure volume controller (7), select the torsion shear test or the axial shear test through the torsion and axial loading host (2), and use different control loading methods to select the single shear or cyclic loading method; during the test, the stress sensor reading, torque sensor reading, torsion angle sensor reading, displacement sensor reading and pore pressure sensor reading are collected and recorded through the data acquisition system (12), so as to analyze the influence of the hydrate extraction process on the mechanical properties of the sediment-structure interface.

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