Apparatus and method for monitoring formation of shear plane in hydrate deposits based on piv

Abstract

The present application relates to the field of marine natural gas hydrate resource exploration and development engineering technology, and particularly relates to a monitoring device and method for formation and evolution process of hydrate-bearing sediment shear surface based on PIV. The device comprises a high-pressure reaction kettle mechanism, which is a visual high-pressure reaction kettle mechanism and comprises a high-pressure kettle body; the device further comprises a sediment shearing simulation mechanism, which comprises a loading plate and a shearing plate, and the loading plate and the shearing plate are arranged in the high-pressure kettle body, the loading plate is used to apply horizontal stress to the hydrate-bearing sediment sample, and the shearing plate is used to shear the hydrate-bearing sediment sample; a non-contact strain observation mechanism is arranged above the visual high-pressure reaction kettle mechanism and is used to obtain a high-definition image of the shear surface of the hydrate-bearing sediment sample. The device can simulate the formation and evolution process of the hydrate-bearing sediment shear surface, realize non-contact direct continuous observation of the morphology and distribution of the shear surface, and obtain the deformation and failure characteristics of the hydrate-bearing sediment and the formation and evolution mechanism of the shear surface.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of exploration and development engineering of marine natural gas hydrate resources, and particularly to a device and method for monitoring the formation and evolution process of a shear plane of hydrate-bearing sediments based on PIV. BACKGROUND

[0002] It is estimated that about 10% of submarine landslides worldwide are caused or affected by hydrate decomposition. Studying the formation and deformation of shear planes is a prerequisite for understanding the occurrence and evolution of submarine landslides in hydrate areas. However, due to the limitations of testing techniques and experimental devices, it is difficult to directly observe the morphology and distribution of shear planes in hydrate-bearing sediments, leading to a focus on the study of the macroscopic mechanical behavior of hydrate-bearing sediments, while neglecting the exploration of the formation and evolution of shear planes. Therefore, developing observation techniques and methods suitable for the formation process of shear planes in hydrate-bearing sediments is the basis for further exploring the laws and control mechanisms of submarine landslides in marine hydrate areas, and is also one of the key problems to be solved at present.

[0003] In order to observe the formation of shear planes in hydrate-bearing sediments and their influence on macroscopic mechanical behavior, researchers at home and abroad have established special triaxial shear, direct shear and ring shear devices for hydrates, and combined with CT detection technology, analyzed the microstructure change law of hydrate-bearing sediments, and studied the influence of microstructure change on macroscopic mechanical behavior. However, the existing experimental methods cannot continuously observe the formation and evolution process of shear planes, and can only observe and explore at specific stages.

[0004] Overall, there is a lack of a method that can continuously and directly observe the formation, development and evolution process of shear planes in hydrate-bearing sediments, and there are few related devices and techniques for hydrates, which cannot meet the current testing needs.

[0005] The main problems currently faced are as follows: (1) how to accurately obtain the morphology and distribution characteristics of shear planes in hydrate-bearing sediments; (2) how to accurately simulate the large deformation and shear failure process of hydrate-bearing sediments. At present, conventional methods cannot directly and quantitatively characterize the formation process of shear planes in hydrate-bearing sediments, which limits the in-depth exploration of the initiation and evolution mechanism of submarine landslides in marine hydrate areas. SUMMARY

[0006] The present application aims to overcome the above-mentioned defects of the prior art and provides a device and method for monitoring the formation of shear planes in hydrate-bearing sediments based on PIV, which can simulate the formation and evolution process of shear planes in hydrate-bearing sediments, realize non-contact direct and continuous observation of the morphology and distribution of shear planes, and obtain the deformation and failure characteristics of hydrate-bearing sediments and the formation and evolution mechanism of shear planes.

[0007] The technical scheme of the present application is: a device for monitoring the formation of a hydrate deposit shear surface based on PIV, comprising a high-pressure reaction kettle mechanism, wherein the high-pressure reaction kettle mechanism is a visual high-pressure reaction kettle mechanism, comprising a high-pressure kettle body;

[0008] The device further comprises a deposit shear simulation mechanism, comprising a loading plate and a shear plate, which are arranged in the high-pressure kettle body, the loading plate is used to apply horizontal stress to the hydrate deposit sample, and the shear plate is used to shear the hydrate deposit sample;

[0009] The visual high-pressure reaction kettle mechanism is provided with a non-contact strain observation mechanism above the visual high-pressure reaction kettle mechanism, which is used to obtain a high-definition image of the shear surface of the hydrate deposit sample.

[0010] In the present application, the visual high-pressure reaction kettle mechanism comprises:

[0011] The high-pressure kettle body is internally provided with a cavity for containing the hydrate deposit sample, and is provided with an opening at the top, and the top end of the opening is fixedly connected with an upper end cover;

[0012] A window is arranged in the central hole of the upper end cover;

[0013] A visual plug is arranged in the central hole of the upper end cover and is fixed between the window and the hydrate deposit sample, and directly contacts the hydrate deposit sample.

[0014] The visual high-pressure reaction kettle mechanism further comprises a three-stage sealing part, which comprises:

[0015] An outer cover plate is arranged in the central hole of the upper end cover and is fixedly connected with the upper end cover;

[0016] A window pressing block is arranged between the outer cover plate and the window and is used to fix the window;

[0017] A primary sealing gasket is arranged on the contact surface between the window pressing block and the window;

[0018] Secondary sealing gaskets and tertiary sealing gaskets are respectively arranged on the contact surface between the outer cover plate and the upper end cover, the tertiary sealing gaskets are located on the annular outer side of the secondary sealing gaskets, and the tertiary sealing gaskets are located at the fixed connection between the outer cover plate and the upper end cover.

[0019] The two symmetrical outer sides of the hydrate deposit sample are respectively provided with deposit shear simulation mechanisms, and the shear plates are inlaidly arranged in the grooves on the inner surface of the loading plate;

[0020] The loading plates of the two deposit shear simulation mechanisms are symmetrically arranged, and the shear plates of the two deposit shear simulation mechanisms are staggered.

[0021] The inner side surface of the loading plate contacts the vertical side surface of the hydrate deposit sample;

[0022] The outer side of the loading plate is fixedly connected to the hydraulic piston;

[0023] The hydraulic piston passes through the autoclave body, and its end located on the outside of the autoclave body is set inside the hydraulic cylinder. The side of the hydraulic piston away from the hydrate deposit sample and the hydraulic cylinder form a hydraulic chamber.

[0024] The horizontal reciprocating motion of the loading plate and the horizontal loading force of the loading plate are controlled by the inflow or outflow of hydraulic oil into the hydraulic chamber.

[0025] The inner side of the shear plate is in contact with the hydrate deposit sample;

[0026] The outer side of the shear plate is fixedly connected to several thrust rods, which are spaced apart in the vertical direction.

[0027] The thrust rod passes through the loading plate and the autoclave body, and its end located on the outside of the autoclave body is fixedly connected to the screw. The screw is connected to the output end of the propulsion motor.

[0028] The propulsion motor is fixed on the fixed plate, and the screw is connected to the fixed plate by a sliding sleeve.

[0029] The device also includes an axial loading mechanism, which comprises:

[0030] The loading cylinder is fixedly connected to the bottom surface of the autoclave body;

[0031] The loading piston is movably installed inside the loading cylinder. A top block is provided on the top of the loading piston. A rubber sleeve is provided between the top block and the hydrate sediment sample. The rubber sleeve is fixedly connected to the bottom of the autoclave.

[0032] A loading chamber is formed between the bottom of the loading piston and the loading cylinder. The loading fluid flows in or out of the loading chamber, which drives the top block to move up and down reciprocally through the loading piston.

[0033] Non-contact strain monitoring mechanisms include:

[0034] The CCD camera is located directly above the viewport;

[0035] A laser is positioned above the hydrate deposit sample.

[0036] The PIV control unit connects to the CC camera and laser.

[0037] The connecting rod, CCD camera, and laser are all mounted on the connecting rod. The connecting rod is fixedly connected to the top of the support rod via a clamp, and the bottom of the support rod is fixedly connected to the base.

[0038] The application also discloses a method for monitoring the evolution process of the formation of a hydrate deposit shear surface by using the device.

[0039] S1, connecting the device and performing an air tightness test on the device;

[0040] S2, filling the mixed deposit and deionized water into the cavity of the autoclave body to synthesize hydrates;

[0041] S3, installing a non-contact strain observation mechanism to perform a shear simulation experiment on the hydrate deposit sample to realize observation and analysis of the shear surface.

[0042] In step S2, the sample in the cavity of the autoclave body is fully compacted, the upper end cover is installed and fixed, the viewing window and the visible plug are installed in the central hole of the upper end cover through the three-stage sealing part, and the horizontal stress of the sample is controlled by the loading plate and the vertical stress of the sample is controlled by the top plate during the generation of hydrates;

[0043] In step S3, the action of the shear plate is adjusted during the deposit shear simulation experiment to simulate the shear process of the hydrate deposit sample, the horizontal stress and the vertical stress are maintained constant by controlling the loading plate and the top block, and the displacement and shear stress values are recorded;

[0044] CCD cameras are used to shoot images of the top of the hydrate deposit sample during the shear process and record related data until the shear process is completed;

[0045] In the initial non-shear stage, a CCD camera is used to obtain a gray-scale image of the surface of the hydrate deposit sample as a reference surface, in the constant-rate shear process, the CCD camera automatically shoots a picture every 1s, the space light is uniform and the positions of related instruments are fixed, the top image of the hydrate deposit sample is observed and related data are recorded until the shear process is completed;

[0046] The calculation formula of the stress σ and the strain ε of the hydrate deposit is as follows:

[0047]

[0048]

[0049] wherein N s represents the load of the shear plate, N p represents the load of the loading plate, D s represents the displacement of the shear plate, D p represents the displacement of the loading plate, Ss represents the area of the shear plate, Sp represents the area of the loading plate, P represents the pore pressure, and L represents the length of the sample in the horizontal direction. ​​

[0050] The acquired image is divided into several small image blocks, the displacement of the small image blocks is calculated to obtain the displacement field of the whole image, and then the pixel coordinates and physical coordinates are converted to obtain the actual displacement field:

[0051] The standard correlation function required for image matching is:

[0052] ,

[0053] Wherein, M represents the length of the image block; N represents the width of the image block; f represents the gray value distribution function at the center point coordinate (x i (t), y i (t)) of the image block at t moment; g represents the gray value distribution function of the center point coordinate (x i (t+Δt), y i (t+Δt)) of the image block at t+Δt moment; The displacement increment in the x direction is represented by Δx; The displacement increment in the y direction is represented by Δy; x i (t) represents the horizontal position at t moment; y i (t) represents the vertical position at t moment; x i (t+Δt) represents the horizontal position at t+Δt moment; y i (t+Δt) represents the vertical position at t+Δt moment.

[0054] The position of each particle at the next moment is calculated by using the velocity field, and the calculation formula of the position of the i-th particle is as follows:

[0055] ,

[0056] Wherein, u(x,y) represents the horizontal velocity of the particle, and v(x,y) represents the vertical velocity of the particle.

[0057] The beneficial effects of the application are:

[0058] (1) According to the technical requirements of PIV observation, the sediment shear simulation mechanism special for hydrate-containing loose sediment is adopted in the application, the "overall loading-local shear" on the lateral side of the hydrate-containing sediment sample is realized, the formation and evolution characteristics of the shear surface are better presented, the miniaturization and high stability advantages are possessed, the non-contact strain observation mechanism can be efficiently adapted, the shear surface morphology and distribution characteristics under different stress states can be analyzed frame by frame, and the position and shape of the shear surface and micro-cracks at different moments and other parameters can be obtained;

[0059] (2) The visual window structure and the three-stage sealing part are arranged on the top of the autoclave body, have the characteristics of strong sealing, good demisting effect and stable structure, are suitable for the high-pressure visualization requirement of hydrate synthesis and shearing process, and can accurately depict the formation and evolution characteristics of the shear surface, realize quantitative evaluation of the shearing deformation characteristics of the hydrate-bearing sediment, and break through the limitation of the function of the existing device;

[0060] (3) The non-contact strain observation mechanism is located outside the constant temperature part, the shear surface morphology is observed through the window, is not affected by the low-temperature and high-pressure environment, the reliability of the equipment and the accuracy of the result are more guaranteed, and the observation result precision is high in cooperation with the digital image analysis technology;

[0061] (4) Combined with the stress and deformation data obtained in the shearing process, the influence law of the formation and development of the shear surface on the macroscopic shearing deformation behavior can be analyzed, and it is of great significance for in-depth exploration of the starting and evolution mechanism of the seabed sliding of the hydrate area in the sea. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 It is a structural schematic diagram of the device described in the application;

[0063] Figure 2 It is a structural schematic diagram of the visual high-pressure reaction kettle mechanism, the sediment shearing simulation mechanism and the axial loading mechanism;

[0064] Figure 3 It is a top view structural schematic diagram of the sediment shearing simulation mechanism;

[0065] Figure 4 It is a top view structural schematic diagram of the upper end cover.

[0066] In the figure: 11 is an autoclave body, 12 is a hydrate-bearing sediment sample, 13 is an upper end cover, 14 is a window, 15 is a visual plug, 16 is an anti-fog coating, 17 is a fixed bolt, 18 is a rubber sleeve, 19 is a fixed block, 21 is an outer cover plate, 22 is a window pressing block, 23 is a set screw, 24 is a first-stage sealing gasket, 25 is a second-stage sealing gasket, 26 is a third-stage sealing gasket, 31 is a shear plate, 32 is a thrust rod, 33 is a screw rod, 34 is a fixed plate, 35 is a pushing motor, 36 is a sliding sleeve, 37 is a fixed rod, 38 is a loading plate, 39 is a hydraulic piston, 310 is a hydraulic cylinder, 311 is a hydraulic cavity, 312 is a high-pressure pump, 313 is a liquid collecting tank, 41 is a top block, 42 is a loading piston, 43 is a loading cavity, 44 is a loading cylinder, 45 is a gasket, 46 is a loading liquid inflow channel, 47 is a loading pump, 51 is a gas cylinder, 52 is a valve, 53 is a flow meter, 54 is a pressure gauge, 61 is a CCD camera, 62 is a laser, 63 is a PIV control system, 64 is a connecting rod, 65 is a clamping sleeve, 66 is a supporting rod, 67 is a base, 71 is a constant temperature device, 72 is a low-temperature controller, 81 is a data processor, 82 is a computer, 83 is a temperature interface, 84 is a pressure interface, and 85 is a flow interface. DETAILED DESCRIPTION

[0067] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0068] In the following description, specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond those described herein without departing from the spirit of the present application, which would be understood by one skilled in the art. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0069] As shown in Figure 1 The PIV-based hydrate-bearing sediment shear plane formation evolution process monitoring device described in the present application includes a visual high-pressure reaction kettle mechanism, a sediment shear simulation mechanism, an axial loading mechanism, a gas supply mechanism, a non-contact strain observation mechanism, a low-temperature holding mechanism, and a data processing mechanism. The visual high-pressure reaction kettle mechanism is placed in the low-temperature holding mechanism, and the visual high-pressure reaction kettle mechanism is connected with the sediment shear simulation mechanism, the axial loading mechanism, the gas supply mechanism, and the data processing mechanism, respectively. The non-contact strain observation mechanism is located above the visual high-pressure reaction kettle mechanism.

[0070] The visual high-pressure reaction kettle mechanism can simulate the shear plane and development process of hydrate-bearing sediments under different stress states, and assist the non-contact strain observation mechanism to realize direct observation of the shear plane and micro-cracks.

[0071] As shown in Figure 1 and Figure 2 The visual high-pressure reaction kettle mechanism includes a cylindrical high-pressure kettle body 11, a cavity is arranged in the high-pressure kettle body 11, and a hydrate-bearing sediment sample 12 is contained in the cavity. The hydrate saturation degree can be controlled according to the initial water content.

[0072] An upper end cover 13 is arranged above the high-pressure kettle body 11, and the upper end cover 13 is fixedly connected with the high-pressure kettle body 11 through fixing bolts 17. A central hole is arranged in the middle of the upper end cover 13, a viewing window 14 is arranged in the central hole, an anti-fog coating 16 is arranged on the viewing window 14, and the anti-fog coating can play an anti-fog role. A visible plug 15 is arranged between the viewing window 14 and the hydrate-bearing sediment sample 12, and the visible plug 15 is in direct contact with the hydrate-bearing sediment sample 12 in the high-pressure kettle body 11.

[0073] The viewing window 14 and the visible plug 15 are fixedly connected with the upper end cover 13, and sealing rings are arranged at the connection positions of the viewing window 14, the visible plug 15, and the upper end cover 13 for sealing treatment.

[0074] The upper end cover is provided with a three-stage sealing part at the window 14, which is mainly used to fix the window 14 and seal the gas in the cavity of the kettle body under low temperature and high pressure conditions, and has the characteristics of high sealing property, high stability and being suitable for hydrate system.

[0075] The three-stage sealing part includes an outer cover plate 21 located at the central hole of the upper end cover 13 and above the window 14. The outer cover plate 21 is provided with a hole in the middle, and is fixedly connected with the upper end cover 13 through a set screw 23. The bottom surface of the outer cover plate 21 is provided with a window pressing block 22 between the window 14, and the window pressing block 22 is pressed on the window 14 by the outer cover plate 21, thereby fixing the window.

[0076] A primary sealing gasket 24 is arranged at the contact surface between the window pressing block 22 and the window 14. The contact surface between the outer cover plate 21 and the upper end cover 13 is respectively provided with a secondary sealing gasket 25 and a tertiary sealing gasket 26, wherein the secondary sealing gasket 25 is located on the inner side of the tertiary sealing gasket 26, and the tertiary sealing gasket 26 is located at the fixed connection of the set screw 23. The primary sealing gasket 24, the secondary sealing gasket 25 and the tertiary sealing gasket 26 can play the role of sealing and auxiliary observation.

[0077] The lower part of the autoclave body 11 is provided with an axial loading mechanism. The bottom of the autoclave body 11 is connected with the axial loading mechanism through a fixing block 19. The intersection surface between the axial loading mechanism and the hydrate deposit sample 12 is provided with a rubber sleeve 18. The upper surface of the rubber sleeve 18 directly contacts with the hydrate deposit sample 12, and the lower surface of the rubber sleeve 18 contacts with the axial loading mechanism.

[0078] In this embodiment, the circumferential edge of the rubber sleeve 18 is fixedly connected with the bottom surface of the autoclave body 11 through the fixing block 19.

[0079] The two symmetrical outer sides of the hydrate deposit sample 12 are respectively provided with a deposit shear simulation mechanism, which extends along the axial direction of the autoclave body and directly contacts with the hydrate deposit sample in the vertical direction. Through the applied loading force and shear force on the hydrate deposit sample, the direct shear process simulation of the hydrate deposit sample is realized.

[0080] As Figure 2 and Figure 3As shown, the two outer sides of the hydrate-bearing sediment sample 12 along the axial direction are respectively provided with sediment shearing simulation mechanisms. The sediment shearing simulation mechanism comprises a loading plate 38 and a shearing plate 31. The cavity in the autoclave body 11 is a rectangular cavity, so the hydrate-bearing sediment sample in the autoclave body 11 is a cuboid, which has four axial sides. The loading plate 38 is located in the autoclave body 11 and is in contact with one of the axial sides of the hydrate-bearing sediment sample. The shearing plate 31 is embedded in the groove on the inner side of the loading plate 38, and the shearing plate 31 is only in contact with part of the surface of the axial side of the hydrate-bearing sediment sample. The "overall loading and local shearing" on the lateral side of the hydrate-bearing sediment sample is achieved, and the formation and evolution characteristics of the shear plane are better presented.

[0081] The inner side of the loading plate 38 is in contact with the hydrate-bearing sediment sample, and the outer side of the loading plate 38 is fixedly connected with the hydraulic piston 39. The hydraulic piston 39 is movably arranged in the hydraulic cylinder 310, one end of the hydraulic piston 39 penetrates through the side wall of the autoclave body 11 and is fixedly connected with the loading plate 38 arranged in the autoclave body, and the side wall of the hydraulic piston 39 away from the loading plate forms a hydraulic cavity 311 with the hydraulic cylinder 310. The hydraulic cavity 311 is provided with an inlet and outlet port, which is connected with the liquid collecting tank 313 through a connecting pipeline, and the connecting pipeline is provided with a high-pressure pump 312.

[0082] The hydraulic cylinder 310 is installed on the outer side of the autoclave body by screws or other fixing forms. A sealing ring is arranged at the connection between the hydraulic cylinder 310 and the autoclave body to prevent hydraulic oil from leaking during the loading process and affecting the loading process.

[0083] In this embodiment, a sealing ring is arranged on the contact surface between the hydraulic piston 39 and the autoclave body 11. Sealing rings are arranged on the contact surface between the upper surface of the loading plate 38 and the upper end cover 13 and the contact surface between the lower surface of the loading plate 38 and the bottom surface of the autoclave body.

[0084] In the working state, the hydraulic oil in the liquid collecting tank 313 is injected into the hydraulic cavity 311 through the high-pressure pump 312. Under the driving action of the hydraulic oil, the hydraulic piston 39 is pushed to move, and at this time the hydraulic piston 39 pushes the loading plate 38 to move towards the hydrate-bearing sediment sample. The loading plates of the two sediment shearing simulation mechanisms located on the outer side of the hydrate-bearing sediment sample are symmetrically arranged, and the two loading plates move towards the hydrate-bearing sediment sample at the same time to realize the stress state simulation of the hydrate-bearing sediment sample. After the simulation work is completed, the hydraulic oil in the hydraulic cavity 311 is pumped into the liquid collecting tank 313 through the high-pressure pump 312, at this time the hydraulic piston 39 pulls the loading plate 38 to move away from the hydrate-bearing sediment sample, and the stress applied to the hydrate-bearing sediment sample is removed.

[0085] The inner side of the shear plate 31 contacts the hydrate-containing sediment sample, and the outer side of the shear plate 31 is fixedly connected to several thrust rods 32, which are spaced apart in the vertical direction. The thrust rods 32 are connected to the propulsion motor 35 via screws 33.

[0086] One inner end of the thrust rod 32 passes through the autoclave body and is fixedly connected to the shear plate 31 located inside the loading plate. The outer end of the thrust rod 32 is fixedly connected to the screw 33. The screw 33 is drivenly connected to the output end of the propulsion motor 35. In this embodiment, the propulsion motor 35 is mounted on the fixed plate 34, and the fixed plate 34 is fixedly connected to the outer surface of the autoclave body 11 via a fixing rod 37. The screw 33 passes through the fixed plate 34, and a sliding sleeve 36 is provided between the screw 33 and the fixed plate 34.

[0087] In this embodiment, a sealing ring is provided on the contact surface between the thrust rod 32 and the autoclave body 11. Sealing rings are also provided on the contact surface between the upper surface of the thrust rod 32 and the upper end cover 13, and on the contact surface between the lower surface of the thrust rod 32 and the bottom surface of the autoclave body.

[0088] The loading plates of the two sediment shearing simulation mechanisms located outside the hydrate-bearing sediment sample are staggered and not symmetrically arranged. During operation, the propulsion motor 35 rotates, causing the screw 33 to rotate axially and move the thrust rod 32 towards the hydrate-bearing sediment sample. Simultaneously, the shear plates 31 on both sides move towards the hydrate-bearing sediment sample, and the loading plate 38 also moves towards the sample. The loading plate 38 simulates the stress state of the hydrate-bearing sediment sample while simultaneously cooperating with the shear plates 31 to complete the shearing process. After the simulation, the propulsion motor 35 rotates in the opposite direction, causing the screw 33 to move the thrust rod 32 away from the hydrate-bearing sediment sample, thus removing the shearing force applied to the sample.

[0089] like Figure 2 As shown, the axial loading mechanism includes a top block 41 and a loading piston 42. The top block 41 is located at the top of the loading piston 42 and is in direct contact with the bottom surface of the rubber sleeve 18. The loading piston 42 is located inside the loading cylinder 44. A loading cavity 43 is formed between the side of the loading piston 42 away from the hydrate-containing sediment sample and the side wall of the loading cylinder 44. The bottom of the loading cylinder 44 is provided with a loading liquid flow channel 46, which is connected to the collection tank 313 through a connecting pipe. A loading pump 47 is provided on the connecting pipe between the loading liquid flow channel 46 and the collection tank 313. The loading pump 47 controls the injection of loading liquid into the loading cavity 43 or the extraction of loading liquid from the loading cavity 43, thereby controlling the reciprocating motion of the loading piston 42.

[0090] When the loading pump 47 injects the loading liquid into the loading cavity 43, the loading piston 42 pushes the anvil 41 to move upward, thereby exerting an axial load on the hydrate deposit sample.

[0091] In this embodiment, the loading cylinder 44 is fixedly connected with the bottom surface of the autoclave body 11 through the fixed block 19, and a sealing ring is arranged at the connection between the loading cylinder and the autoclave body. The fixed block 19 not only serves as a connection between the loading cylinder and the autoclave body, but also cooperates with the sealing ring to seal the connection between the loading cylinder and the autoclave body. Meanwhile, a sealing ring is arranged on the contact surface between the upper part of the loading piston 42 and the opening of the loading cylinder 44 to prevent hydraulic oil from leaking during the axial loading process and ensure the stability of the axial load during the test.

[0092] The gas supply mechanism is used to inject the gas for generating the hydrate deposit into the autoclave body. The gas supply mechanism includes a gas cylinder 51, which is connected with the gas inlet of the autoclave body through a connecting pipeline, and a valve 52, a flow meter 53 and a pressure gauge 54 are arranged in sequence on the connecting pipeline between the gas cylinder 51 and the autoclave body.

[0093] The non-contact strain observation mechanism includes a CCD camera 61 and a laser 62, both of which are installed on a connecting rod 64, which is fixed at the top end of a support rod 66 through a clamping sleeve 65, and the bottom end of the support rod 66 is provided with a base 67. The CCD camera 61 is located directly above the window 14, ensuring that the observation surface can be located within the camera field of view and meeting the image clarity requirement. The CCD camera 61 and the laser 62 are respectively connected with a PIV control part 63, and the CCD camera 61, the laser 62 and the PIV control part 63 cooperate with each other to obtain high-definition images of the shear surface of the hydrate deposit sample 12 at different shear stages.

[0094] The low-temperature maintaining mechanism can provide a suitable temperature for synthesizing hydrate and inhibiting hydrate decomposition, and includes a constant-temperature part 71 and a low-temperature controller 72. The autoclave body 11, the deposit shear simulation mechanism and the axial loading mechanism are all arranged in the constant-temperature part 71, and the temperature of the constant-temperature part 71 is controlled by the low-temperature controller 72, and the dimension of the constant-temperature part 71 is kept constant.

[0095] The data processing mechanism is electrically connected with the visual autoclave mechanism, the deposit shear simulation mechanism, the axial loading mechanism, the gas supply mechanism, the non-contact strain observation mechanism and the low-temperature maintaining mechanism. The data processing mechanism includes a data processor 81 and a computer 82, and a temperature interface 83, a pressure interface 84 and a flow interface 85 are arranged on the data processor 81, which are used to realize real-time monitoring and control of the temperature, the pressure and the flow during the test.

[0096] More interfaces can be provided on the data processor to connect with various sensors and measuring tools required by the experiment, to assist in data collection and processing.

[0097] The skeleton of the hydrate-bearing sediment sample can be quartz sand, clay, argillaceous silt, etc., and distilled water or deionized water is preferably used for synthesizing hydrates, and an additive can be added to shorten the synthesis time; methane, ethane, carbon dioxide, tetrahydrofuran, etc., can be used as the gas for synthesizing hydrates, and the specific gas can be selected according to the specific experiment.

[0098] The application also provides a method for monitoring the formation and evolution process of a hydrate-bearing sediment shear surface by using the above-mentioned PIV-based hydrate-bearing sediment shear surface formation and evolution process monitoring device, and the method comprises the following steps.

[0099] First step, mixing of the sediment and deionized water.

[0100] According to the target reservoir geological data and core test results, dry quartz sand with a certain particle size is mixed with deionized water, and the volume of the added deionized water can be calculated according to the target hydrate saturation and the quartz sand porosity.

[0101] Second step, connection of the device and air tightness test of the device.

[0102] According to the target reservoir geological data and core test results, dry quartz sand with a certain particle size is mixed with deionized water, and the volume of the added deionized water can be calculated according to the target hydrate saturation and the quartz sand porosity. Figure 1 The visualization high-pressure reaction kettle mechanism, the sediment shear simulation mechanism, the axial loading mechanism, and the gas supply mechanism are connected, and the high-pressure kettle body is cleaned. Nitrogen is injected to detect the air tightness of the entire device, to ensure the normal operation of the experimental device.

[0103] Third step, hydrate synthesis.

[0104] The mixed sample obtained in the first step is filled into the sample filling cavity of the high-pressure kettle body 11, and the sample is fully compacted. The upper end cover 13 is installed and fixed, and the viewing window 14 and the visual plug 15 are installed in the center hole of the upper end cover 13 through the three-stage sealing part.

[0105] Methane gas is slowly injected into the sample filling cavity of the high-pressure kettle body 11 through the gas supply mechanism, so that the pore pressure reaches the set value. At the same time, the sediment shear simulation mechanism is used to control the loading plate 38 to apply a horizontal stress to the sample, and the axial loading mechanism is used to control the top block 41 to apply a vertical stress to the sample.

[0106] The pore pressure, the horizontal stress, and the axial stress are increased to the set value again, and the pore pressure is kept slightly smaller than the horizontal stress and the axial stress during the period.

[0107] During the hydrate synthesis process, the temperature of the constant temperature part 71 is set by the low temperature holding mechanism, the temperature of the sample in the sample filling cavity is controlled to slowly decrease to the set value and remain unchanged until the pore pressure no longer decreases, and the hydrate synthesis process ends.

[0108] Fourth step, installation of the non-contact strain observation mechanism.

[0109] The connecting rod 64, the sleeve 65, the support rod 66 and the base 67 are connected and placed in a suitable position. The CCD camera 61 and the laser 62 are installed on the connecting rod 64 and located above the autoclave body. The CCD camera 61 and the laser 62 are connected with the PIV control part 63. The laser 62 is turned on and aligned with the sample, and the position of the CCD high-speed camera 61 is adjusted to be directly above the window 14 and the visual plug 15. The PIV control part 63 is operated to calibrate the shooting scale and calibrate the non-contact strain observation mechanism.

[0110] Fifth step, sediment shear simulation experiment.

[0111] The gas supply mechanism is controlled to maintain the constant pore pressure, the action of the shear plate 31 in the sediment shear simulation mechanism is adjusted to simulate the shearing process of the hydrate-bearing sediment sample 12, and the loading plate 38 and the top block 41 are controlled to maintain the horizontal stress and vertical stress constant, and the displacement and shear stress values are recorded.

[0112] At the same time, the CCD camera 61 is used to shoot the image of the top of the hydrate-bearing sediment sample 12 during the shearing process and record the related data until the shearing process is completed.

[0113] In the initial un-sheared stage, the CCD camera 61 is used to obtain the gray-scale image of the surface of the hydrate-bearing sediment sample 12 as a reference surface, and in the constant rate shearing process, the CCD camera 61 automatically takes a picture every 1s, maintains uniform space light and fixes the position of the related instruments, observes the image of the top of the hydrate-bearing sediment sample 12 and records the related data until the shearing process is completed.

[0114] The calculation formula of the stress σ and strain ε of the hydrate-bearing sediment is:

[0115] ,

[0116] .

[0117] wherein N s represents the load of the shear plate, N p represents the load of the loading plate, D s represents the displacement of the shear plate, D pSs represents displacement of the loading plate, S p represents area of the loading plate, P represents pore pressure, and L represents length of the sample in the horizontal direction.

[0118] Step 6: Observation and analysis of the shear plane.

[0119] According to the shear plane formation and development images obtained in the fifth step, the digital image analysis technology is applied to study the morphology and distribution characteristics of the shear plane and microcracks; the displacement data of the shear plane at different stages are compared to obtain the displacement field of the top of the hydrate-bearing sediment sample 12, the strain field in the shear plane formation process is determined based on fitting and calculation of the displacement data, and finally the shear plane formation and evolution law is determined.

[0120] In the series of images obtained in the fifth step, the entire image can be divided into a plurality of small image blocks, then the displacement of the small image blocks is calculated to obtain the displacement field of the entire image, and then the pixel coordinates and physical coordinates are converted to obtain the actual displacement field. The standard correlation function required for image matching is as follows:

[0121] ,

[0122] Wherein, M represents the length of the image block; N represents the width of the image block; f represents the gray value distribution function at the center point coordinate (x i (t), y i (t)) of a certain image block at t moment; g represents the gray value distribution function of the center point coordinate (x i (t+Δt), y i (t+Δt)) of the image block at t+Δt moment; represents the displacement increment in the x direction; represents the displacement increment in the y direction; x i (t) represents the horizontal position at t moment; y i (t) represents the vertical position at t moment; x i (t+Δt) represents the horizontal position at t+Δt moment; y i (t+Δt) represents the vertical position at t+Δt moment.

[0123] The velocity field can be used to calculate the position of each particle at the next moment, so the calculation formula of the position of the i th particle is as follows:

[0124] ,

[0125] Wherein, u(x,y) represents the horizontal velocity of the particle, and v(x,y) represents the vertical velocity of the particle.

[0126] The above describes in detail the device and method for monitoring the formation of the shear plane of the hydrate deposit based on PIV provided by the present application. The principles and implementation manners of the present application are described by using specific examples in this paper, and the above description of the examples is only used to help understand the method of the present application and its core idea. It should be pointed out that, for those skilled in the art, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application. The above description of the disclosed examples enables those skilled in the art to implement or use the present application. Various modifications of the examples will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other examples without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the examples shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for monitoring the shear surface formation of hydrate deposits based on PIV, comprising a high-pressure reactor mechanism, characterized in that, The high-pressure reactor structure is a visualized high-pressure reactor structure, including the high-pressure reactor body; It also includes a sediment shearing simulation mechanism, which includes a loading plate and a shearing plate. The loading plate and the shearing plate are set inside the autoclave. The loading plate applies horizontal stress to the hydrate sediment sample, and the shearing plate shears the hydrate sediment sample. A non-contact strain observation mechanism is installed above the visualization high-pressure reactor mechanism to obtain high-resolution images of the shear surface of hydrate sediment samples; The visualized high-pressure reactor structure includes: The autoclave body has an internal cavity for holding hydrate sediment samples, and an opening at the top, with its top end fixedly connected to the upper end cap. A viewing window is located in the center hole of the upper end cover; The visible plug is set in the center hole of the upper end cap and fixed between the viewing window and the hydrate deposit sample, directly contacting the hydrate deposit sample; The visualized high-pressure reactor mechanism also includes a three-stage sealing section, which includes: The outer cover plate is set in the center hole of the upper cover and is fixedly connected to the upper cover. A window retainer block is installed between the outer cover plate and the window to fix the window in place. A primary sealing gasket is provided on the contact surface between the window pressure block and the window; A secondary sealing gasket and a tertiary sealing gasket are respectively provided on the contact surface between the outer cover plate and the upper end cover. The tertiary sealing gasket is located on the outer side of the annular ring of the secondary sealing gasket and is located at the fixed connection between the outer cover plate and the upper end cover. The hydrate sediment sample is provided with sediment shearing simulation mechanisms on its two symmetrical outer sides, and the shearing plates are embedded in the grooves on the inner surface of the loading plate. The loading plates of the two sediment shearing simulation mechanisms are symmetrically arranged, and the shearing plates of the two sediment shearing simulation mechanisms are staggered along the radial direction of the autoclave.

2. The device for monitoring the shear surface formation of hydrate sediments based on PIV according to claim 1, characterized in that, The inner side of the loading plate is in contact with the vertical side of the hydrate deposit sample; The outer side of the loading plate is fixedly connected to the hydraulic piston; The hydraulic piston passes through the autoclave body, and its end located on the outside of the autoclave body is set inside the hydraulic cylinder. The side of the hydraulic piston away from the hydrate deposit sample and the hydraulic cylinder form a hydraulic chamber. The horizontal reciprocating motion of the loading plate and the horizontal loading force of the loading plate are controlled by the inflow or outflow of hydraulic oil into the hydraulic chamber.

3. The device for monitoring the shear surface formation of hydrate sediments based on PIV according to claim 1, characterized in that, The inner side of the shear plate is in contact with the hydrate deposit sample; The outer side of the shear plate is fixedly connected to several thrust rods, which are spaced apart in the vertical direction; The thrust rod passes through the loading plate and the autoclave body, and its end located on the outside of the autoclave body is fixedly connected to the screw. The screw is driven by the output end of the propulsion motor. The propulsion motor is fixed on the fixed plate, and the screw is connected to the fixed plate by a sliding sleeve.

4. The device for monitoring the shear surface formation of hydrate sediments based on PIV according to claim 1, characterized in that, It also includes an axial loading mechanism, which includes: The loading cylinder is fixedly connected to the bottom surface of the autoclave body; The loading piston is movably installed inside the loading cylinder. A top block is provided on the top of the loading piston. A rubber sleeve is provided between the top block and the hydrate sediment sample. The rubber sleeve is fixedly connected to the bottom of the autoclave. A loading chamber is formed between the bottom of the loading piston and the loading cylinder. The loading fluid flows in or out of the loading chamber, which drives the top block to move up and down reciprocally through the loading piston.

5. The device for monitoring the shear surface formation of hydrate sediments based on PIV according to claim 1, characterized in that, Non-contact strain monitoring mechanisms include: The CCD camera is located directly above the viewport; A laser is positioned above the hydrate deposit sample. The PIV control unit connects to the CCD camera and laser. The connecting rod, CCD camera, and laser are all mounted on the connecting rod. The connecting rod is fixedly connected to the top of the support rod via a clamp, and the bottom of the support rod is fixedly connected to the base.

6. A method for monitoring the formation of shear surfaces in hydrate deposits using the apparatus for monitoring shear surface formation in hydrate deposits based on PIV as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Connect the device and perform an airtightness test on the device; S2. Fill the cavity of the autoclave with the thoroughly mixed sediment and deionized water to synthesize hydrates; S3. Install a non-contact strain observation mechanism to conduct shear simulation experiments on hydrate sediment samples, and realize the observation and analysis of the shear surface.

7. The method according to claim 6, characterized in that, In step S2, the sample inside the cavity of the autoclave is fully compacted, the upper end cover is installed and fixed, and the viewing window and the visible plug are installed in the center hole of the upper end cover through the three-level sealing part. During the hydrate formation process, the loading plate is controlled to apply horizontal stress to the sample, and the top plate is controlled to apply vertical stress to the sample. In step S3, during the sediment shear simulation experiment, the action of the shear plate is adjusted to simulate the shearing process of the hydrate-containing sediment sample. At the same time, the loading plate and the top block are controlled to maintain constant horizontal and vertical stresses, and the values ​​of displacement and shear stress are recorded. A CCD camera was used to capture images of the top of the hydrate-containing sediment sample during the shearing process and record relevant data until the shearing process ended. In the initial unsheared stage, a grayscale image of the surface of the hydrate-bearing sediment sample was acquired using a CCD camera as a reference surface. During the constant rate shearing process, the CCD camera automatically took one picture every 1 second, keeping the light in the space uniform and the positions of the relevant instruments fixed. The top image of the hydrate-bearing sediment sample was observed and relevant data were recorded until the shearing process ended. The formulas for calculating the stress σ and strain ε of hydrate-bearing sediments are as follows: , ， Where, N s The load on the shear plate is represented by N. p D represents the load on the loading plate. s D represents the displacement of the shear plate. p Ss represents the displacement of the loading plate, Sp represents the area of ​​the shear plate, P represents the pore pressure, and L represents the horizontal length of the sample. The acquired image is divided into several small image blocks. The displacement of each small image block is calculated to obtain the displacement field of the entire image. Then, the pixel coordinates and physical coordinates are transformed to obtain the actual displacement field. The standard association function required for image matching is: , Where M represents the length of the image patch; N represents the width of the image patch; and f represents the coordinates (x, y) of the center point of the image patch at time t. i (t), y i The gray value distribution function at (t) represents the coordinates of the center point (x, y) of the image patch at time t+Δt; g represents the coordinates of the center point (x, y) of the image patch at time t+Δt. i (t+Δt), y i The grayscale distribution function of (t+Δt)); ∆x represents the displacement increment in the x-direction; ∆y represents the displacement increment in the y-direction; x i (t) represents the horizontal position at time t; y i (t) represents the longitudinal position at time t; x i (t+Δt) represents the lateral position at time t+Δt; y i (t+Δt) represents the longitudinal position at time t+Δt; The position of each particle at the next moment is calculated using its velocity. The formula for calculating the position of the i-th particle is as follows: , Where u(x,y) represents the transverse velocity of the particle, and v(x,y) represents the longitudinal velocity of the particle.

Images