Device and method for monitoring formation of hydrate sediment shear plane based on PIV (Particle Image Velocimetry)

Abstract

The invention relates to the technical field of marine natural gas hydrate resource exploration and development engineering, in particular to a PIV-based monitoring device and method for a hydrate-containing sediment shear plane formation evolution process. Comprising a high-pressure reaction kettle mechanism, and the high-pressure reaction kettle mechanism is a visual high-pressure reaction kettle mechanism and comprises a high-pressure kettle body; the sediment shear simulation mechanism comprises a loading plate and a shear plate, the loading plate and the shear plate are arranged in the autoclave body, horizontal stress is applied to the hydrate sediment sample through the loading plate, and the hydrate sediment sample is sheared through the shear plate; a non-contact strain observation mechanism is arranged above the visual high-pressure reaction kettle mechanism and is used for acquiring a shear surface high-definition image of the hydrate sediment sample. The device can simulate the formation and evolution process of the hydrate-containing sediment shear surface, realizes the non-contact direct continuous observation of the form and distribution of the shear surface, and obtains the deformation and failure characteristics of the hydrate-containing sediment and the formation and evolution mechanism of the shear surface.

Description

Technical Field

[0001] The present invention relates to the technical field of marine natural gas hydrate resource exploration and development engineering, and in particular to a device and method for monitoring the formation and evolution process of shear surfaces of hydrate-containing sediments based on PIV. Background Art

[0002] It is estimated that approximately 10% of submarine landslides worldwide are caused or influenced by hydrate decomposition. Studying shear surface formation and deformation failure is a prerequisite for a deeper understanding of the occurrence and evolution of submarine landslides in hydrate zones. However, due to limitations in testing technology and experimental equipment, direct observation of the morphology and distribution of shear surfaces in hydrate-bearing sediments is difficult. This has led to a focus on the macroscopic mechanical behavior of hydrate-bearing sediments, while neglecting the exploration of the mechanisms governing shear surface formation and evolution. Therefore, developing techniques and methods suitable for observing the shear surface formation process in hydrate-bearing sediments is fundamental to further exploring the mechanisms governing submarine landslides in marine hydrate zones and remains a key challenge that needs to be addressed.

[0003] In order to observe the formation of shear surfaces in hydrate-containing sediments and their impact on macroscopic mechanical behavior, researchers at home and abroad have established hydrate-specific triaxial shear, direct shear, and ring shear devices. Combined with CT detection technology, they have analyzed the changes in the microstructure of hydrate-containing sediments and studied the impact of microstructural changes on macroscopic mechanical behavior. However, existing experimental methods cannot continuously observe the formation and evolution process of shear surfaces and can only observe and explore specific stages.

[0004] Overall, there is a lack of a method that can continuously and intuitively observe the formation, development and evolution of shear surfaces in hydrate-containing sediments. There are few hydrate-specific devices and technologies, which make it difficult to meet current testing needs.

[0005] There are two main challenges currently faced: (1) how to accurately obtain the morphology and distribution characteristics of the shear surface of hydrate-bearing sediments; and (2) how to accurately simulate the large-scale deformation shear failure process of hydrate-bearing sediments. At present, conventional methods are difficult to achieve an intuitive and quantitative characterization of the shear surface formation process of hydrate-bearing sediments, which limits the in-depth exploration of the initiation and evolution mechanism of submarine landslides in marine hydrate areas. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and propose a device and method for monitoring the formation of shear surfaces in hydrate sediments based on PIV. The device and method can simulate the formation and evolution process of shear surfaces in hydrate-containing sediments, realize non-contact direct and continuous observation of shear surface morphology and distribution, and obtain the deformation and failure characteristics of hydrate-containing sediments and the shear surface formation and evolution mechanism.

[0007] The technical solution of the present invention is: a device for monitoring the formation of shear planes of hydrate sediments based on PIV, comprising a high-pressure reactor mechanism, wherein the high-pressure reactor mechanism is a visual high-pressure reactor mechanism, comprising a high-pressure reactor body;

[0008] The autoclave also includes a sediment shear simulation mechanism, including a loading plate and a shear plate, which are arranged in the autoclave body, and the loading plate is used to apply horizontal stress to the hydrate sediment sample, and the shear plate is used to shear the hydrate sediment sample;

[0009] A non-contact strain observation mechanism is provided above the visualization high-pressure reactor mechanism, which is used to obtain high-definition images of the shear surface of the hydrate sediment sample.

[0010] In the present invention, the visual high-pressure reactor mechanism includes:

[0011] The autoclave body has a cavity for containing the hydrate sediment sample, an opening at the top, and a top end fixedly connected to the upper end cover;

[0012] a viewing window disposed in the central hole of the upper end cover;

[0013] The visual plug is arranged in the central hole of the upper end cover and fixed between the viewing window and the hydrate sediment sample, and is in direct contact with the hydrate sediment sample.

[0014] The visual high-pressure reactor mechanism also includes a three-stage sealing part, which includes:

[0015] An outer cover plate is disposed in the center hole of the upper end cover and is fixedly connected to the upper end cover;

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

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

[0018] 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 outside the annular ring of the secondary sealing gasket, and the tertiary sealing gasket is located at the fixed connection between the outer cover plate and the upper end cover.

[0019] Sediment shear simulation mechanisms are respectively provided on two symmetrical outer sides of the hydrate sediment sample, and the shear plates are embedded in the grooves on the inner surface of the loading plate;

[0020] 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.

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

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

[0023] The hydraulic piston passes through the autoclave body, and the end portion of the hydraulic piston located outside the autoclave body is arranged in the hydraulic cylinder, and a hydraulic cavity is formed between the side of the hydraulic piston facing away from the hydrate sediment sample and the hydraulic cylinder;

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

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

[0026] The outer side surface of the shear plate is fixedly connected to a plurality of thrust rods, and the plurality of thrust rods are arranged at intervals along the vertical direction;

[0027] The thrust rod passes through the loading plate and the autoclave body, and its end located outside the autoclave body is fixedly connected to the screw, which is in transmission connection with the output end of the propulsion motor;

[0028] The propulsion motor is fixed on the fixing plate, and the screw rod and the fixing plate are connected via a sliding sleeve.

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

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

[0031] The loading piston is movably arranged in the loading cylinder, the top of the loading piston is provided with a top block, a rubber sleeve is provided between the top block and the hydrate sediment sample, and the rubber sleeve is fixedly connected to the bottom of the autoclave body;

[0032] A loading chamber is formed between the bottom of the loading piston and the loading cylinder. The loading liquid flows into or out of the loading chamber, and the loading piston drives the top block to reciprocate up and down.

[0033] The non-contact strain observation mechanism includes:

[0034] CCD camera, located just above the viewing window;

[0035] a laser, located above the hydrate sediment sample;

[0036] PIV control unit, connected to CC camera and laser;

[0037] The connecting rod, the CCD camera and the laser are all arranged on the connecting rod. The connecting rod is fixedly connected to the top of the supporting rod through a clamping sleeve, and the bottom of the supporting rod is fixedly connected to the base.

[0038] The present application also discloses a method for monitoring the formation and evolution of shear surfaces of hydrate-containing sediments using the above-mentioned device for monitoring the formation of shear surfaces of hydrate sediments based on PIV, which includes the following steps:

[0039] S1. Connect the device and perform an airtightness test on the device;

[0040] S2. Filling the fully mixed sediment and deionized water into the cavity of the autoclave to synthesize the hydrate;

[0041] S3. Install a non-contact strain observation mechanism to conduct shear simulation experiments on hydrate sediment samples to achieve 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, and the window and the visual plug are installed in the center hole of the upper end cover through the three-stage 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;

[0043] In step S3, during the sediment shear simulation experiment, the movement of the shear plate is adjusted to simulate the shear process of the hydrate-containing sediment sample, and the loading plate and the top block are controlled to maintain constant horizontal stress and vertical stress, and the displacement and shear stress values ​​are recorded;

[0044] Use a CCD camera to capture images of the top of the hydrate-containing sediment sample during the shearing process and record relevant data until the shearing process is completed;

[0045] In the initial unsheared stage, a CCD camera was used to capture a grayscale image of the surface of the hydrate-containing sediment sample as a reference surface. During the constant-rate shearing process, the CCD camera automatically captured an image every 1 second, maintaining uniform lighting and fixed instrument positions. The image of the top of the hydrate-containing sediment sample was observed and relevant data was recorded until the shearing process was completed.

[0046] The calculation formulas for stress σ and strain ε of hydrate-containing sediments are:

[0047] ,

[0048] ;

[0049] Among them, N s Indicates the load of the shear plate, N p Denotes the load on 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 horizontal length of the specimen;

[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 entire 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] Where M represents the length of the image block; N represents the width of the image block; f represents the coordinates of the center point of a certain image block at time t (x i (t), y i (t)) at the gray value distribution function; g represents the coordinates of the center point of the image block at time t+Δt (x i (t+Δt), y i Gray value distribution function of (t+Δt)); represents the displacement increment in the x direction; Indicates 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.

[0054] The velocity field is used to calculate the position of each particle at the next moment. The calculation formula for the position of the i-th particle is as follows:

[0055] ,

[0056] Among them, u(x,y) represents the lateral velocity of the particle, and v(x,y) represents the longitudinal velocity of the particle.

[0057] The beneficial effects of the present invention are:

[0058] (1) According to the requirements of PIV observation technology, this application adopts a sediment shear simulation mechanism dedicated to hydrate-containing loose sediments to achieve "overall loading-local shearing" on the lateral side of the hydrate-containing sediment sample, better presenting the formation and evolution characteristics of the shear surface. It has the advantages of miniaturization and high stability, can be efficiently adapted to the non-contact strain observation mechanism, can analyze the shear surface morphology and distribution characteristics under different stress states frame by frame, and obtain parameters such as the position and shape of the shear surface and microcracks at different times;

[0059] (2) A visual window structure and a three-stage sealing part are set on the top of the autoclave body, which has the characteristics of strong sealing, good demisting effect and stable structure, and is suitable for the high-pressure visualization requirements of hydrate synthesis and shearing processes. Through the visual window structure and non-contact strain observation mechanism, the formation and evolution characteristics of the shear surface can be accurately characterized, and the quantitative evaluation of the shear deformation characteristics of hydrate-containing sediments can be achieved, breaking through the limitations of the existing device functions.

[0060] (3) The non-contact strain observation mechanism is located outside the constant temperature section. The shear surface morphology is observed through a window and is not affected by the low temperature and high pressure environment. The reliability of the equipment and the accuracy of the results are more guaranteed. Combined with digital image analysis technology, the observation results are highly accurate.

[0061] (4) Combined with the stress and deformation data obtained during the shear process, it is possible to analyze the influence of the formation and development of the shear surface on the macroscopic shear deformation behavior, which is of great significance for the in-depth exploration of the initiation and evolution mechanism of seabed sliding in the hydrate area of ​​the sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0063] Figure 2 It is a structural diagram of the visualized high-pressure reactor mechanism, sediment shear simulation mechanism, and axial loading mechanism;

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

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

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

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

[0068] The following description sets forth specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art will be able to make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0069] like Figure 1 As shown, the PIV-based monitoring device for the formation and evolution of shear surfaces in hydrate-bearing sediments described in this application includes a visual autoclave mechanism, a sediment shear simulation mechanism, an axial loading mechanism, an air supply mechanism, a non-contact strain observation mechanism, a cryogenic maintenance mechanism, and a data processing mechanism. The visual autoclave mechanism is placed within the cryogenic maintenance mechanism and is connected to the sediment shear simulation mechanism, the axial loading mechanism, the air supply mechanism, and the data processing mechanism. The non-contact strain observation mechanism is located above the visual autoclave mechanism.

[0070] The visualized high-pressure reactor mechanism can simulate the shear surface and development process of hydrate-bearing sediments under different stress states, and assist the non-contact strain observation mechanism to realize direct observation of shear surfaces and microcracks.

[0071] like Figure 1 and Figure 2 As shown, the visualized high-pressure reactor structure includes a cylindrical high-pressure reactor body 11. The high-pressure reactor body 11 is provided with a cavity. The cavity contains a hydrate-containing sediment sample 12. The hydrate saturation can be controlled according to the initial water content.

[0072] An upper end cap 13 is installed above the autoclave body 11 and is fixedly connected to the autoclave body 11 via fixing bolts 17. A central hole is provided in the center of the upper end cap 13, within which is a viewing window 14. This window 14 is coated with an anti-fog coating 16, which provides a fog-proofing effect. A visual plug 15 is installed between the viewing window 14 and the hydrate-containing sediment sample 12, which is in direct contact with the hydrate-containing sediment sample 12 within the autoclave body 11.

[0073] The viewing window 14 and the visual plug 15 are fixedly connected to the upper end cover 13 respectively, and sealing rings are provided at the connections between the viewing window 14, the visual plug 15 and the upper end cover 13 for sealing.

[0074] The upper end cover is provided with a three-level sealing part at the window 14. The three-level sealing part is mainly used to fix the window 14 under low temperature and high pressure conditions and to seal the gas in the kettle cavity. It has the characteristics of high sealing, high stability and suitability for hydrate systems.

[0075] The tertiary seal includes an outer cover plate 21, which is located in the center hole of the upper end cover 13 and above the viewing window 14. A hole is opened in the center of the outer cover plate 21, and the outer cover plate 21 is fixed to the upper end cover 13 via set bolts 23. A window pressure block 22 is provided between the bottom surface of the outer cover plate 21 and the viewing window 14. The outer cover plate 21 presses the window pressure block 22 against the viewing window 14, securing the window.

[0076] A primary sealing gasket 24 is installed at the interface between the window block 22 and the window 14. A secondary sealing gasket 25 and a tertiary sealing gasket 26 are installed at the interface between the outer cover 21 and the upper end cover 13. The secondary sealing gasket 25 is located inside the tertiary sealing gasket 26, which is located at the fixed connection of the set bolt 23. The primary sealing gasket 24, the secondary sealing gasket 25, and the tertiary sealing gasket 26 provide sealing and assist in observation.

[0077] An axial loading mechanism is installed below the autoclave body 11. The bottom of the autoclave body 11 is connected to the axial loading mechanism via a fixing block 19. A rubber sleeve 18 is installed at the intersection of the axial loading mechanism and the hydrate-containing sediment sample 12. The upper surface of the rubber sleeve 18 is in direct contact with the hydrate-containing sediment sample 12, while the lower surface of the rubber sleeve 18 is in contact with the axial loading mechanism.

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

[0079] Sediment shear simulation mechanisms are respectively provided on the two symmetrical outer sides of the hydrate-containing sediment sample 12. The sediment shear simulation mechanisms extend along the axial direction of the autoclave body. The sediment shear simulation mechanisms are in direct contact with the hydrate-containing sediment sample in the vertical direction. By applying the loading force and shear force to the hydrate-containing sediment sample, the direct shear process simulation of the hydrate-containing sediment sample is realized.

[0080] like Figure 2 and Figure 3As shown, sediment shear simulation mechanisms are provided on both axially outer sides of the hydrate-containing sediment sample 12. The sediment shear simulation mechanism includes a loading plate 38 and a shear plate 31. The cavity inside the autoclave body 11 is a rectangular cavity, so the hydrate-containing sediment sample inside the autoclave body 11 is a rectangular parallelepiped with four axial side surfaces. The loading plate 38 is located inside the autoclave body 11 and contacts one of the axial side surfaces of the hydrate-containing sediment sample. The shear plate 31 is embedded in the groove on the inner side surface of the loading plate 38, and the shear plate 31 only contacts a portion of the surface of the axial side surface of the hydrate-containing sediment sample. This achieves "overall loading-local shearing" on the lateral side of the hydrate-containing sediment sample, better presenting the formation and evolution characteristics of the shear surface.

[0081] The inner side of the loading plate 38 contacts the hydrate-containing sediment sample, while the outer side of the loading plate 38 is fixedly connected to a hydraulic piston 39. The hydraulic piston 39 is movably disposed within a hydraulic cylinder 310. One end of the hydraulic piston 39 passes through the side wall of the autoclave body 11 and is fixedly connected to the loading plate 38 disposed within the autoclave body. A hydraulic chamber 311 is formed between the side wall of the hydraulic piston 39 facing away from the loading plate and the hydraulic cylinder 310. The hydraulic chamber 311 is provided with liquid inlets and outlets, which are connected to a liquid collection tank 313 via connecting pipes. A high-pressure pump 312 is also provided on the connecting pipes.

[0082] The hydraulic cylinder 310 is mounted on the outer side of the autoclave body by screws or other fixing means. A sealing ring is provided at the connection between the hydraulic cylinder 310 and the autoclave body to prevent leakage of hydraulic oil during loading, which would affect the loading process.

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

[0084] During operation, the hydraulic oil in the fluid collection tank 313 is pumped into the hydraulic chamber 311 via the high-pressure pump 312. Driven by the hydraulic oil, the hydraulic piston 39 is moved, pushing the loading plate 38 toward the hydrate sediment sample. The loading plates of the two sediment shear simulation mechanisms, located outside the hydrate sediment sample, are symmetrically arranged and move simultaneously toward the hydrate sediment sample, simulating the stress state of the hydrate sediment sample. After the simulation is complete, the hydraulic oil in the hydraulic chamber 311 is pumped into the fluid collection tank 313 via the high-pressure pump 312. The hydraulic piston 39 then pulls the loading plate 38 away from the hydrate sediment sample, removing the stress applied to the hydrate sediment sample.

[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 a plurality of thrust rods 32 , which are arranged at intervals along the vertical direction. The thrust rods 32 are connected to a propulsion motor 35 through a screw 33 .

[0086] The inner end of the thrust rod 32 passes through the autoclave body and is fixedly connected to the shear plate 31 disposed inside the loading plate. The outer end of the thrust rod 32 is fixedly connected to a screw 33. The screw 33 is in driving connection with the output end of a propulsion motor 35. In this embodiment, the propulsion motor 35 is mounted on a fixed plate 34, which 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, sealing rings are provided on the contact surfaces between the thrust rod 32 and the autoclave body 11. Sealing rings are also provided on the contact surfaces between the upper surface of the thrust rod 32 and the upper end cover 13, and on the contact surfaces 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 shear simulation mechanisms located outside the hydrate sediment sample are staggered, not symmetrically arranged. During operation, the propulsion motor 35 operates, driving the screw 33 to rotate while simultaneously generating axial movement, driving the thrust rod 32 toward the hydrate sediment sample. The shear plates 31 on either side simultaneously move toward the hydrate sediment sample, while the loading plates 38 also move toward the hydrate sediment sample. The loading plates 38 simulate the stress state of the hydrate sediment sample while cooperating with the shear plates 31 on either side to complete the shearing process. After the simulation is complete, the propulsion motor 35 rotates in the opposite direction, driving the thrust rod 32 away from the hydrate sediment sample via the screw 33, thereby removing the shear force applied to the hydrate sediment 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 in a loading cylinder 44. A loading chamber 43 is formed between the side of the loading piston 42 facing away from the hydrate-containing sediment sample and the sidewall of the loading cylinder 44. A loading liquid flow channel 46 is provided at the bottom of the loading cylinder 44. The loading liquid flow channel 46 is connected to the liquid collection tank 313 via a connecting pipeline. A loading pump 47 is provided in the connecting pipeline between the loading liquid flow channel 46 and the liquid collection tank 313. The loading pump 47 controls the injection or extraction of loading liquid into the loading chamber 43, thereby controlling the reciprocating motion of the loading piston 42.

[0090] When the loading pump 47 injects the loading liquid into the loading chamber 43 , the loading piston 42 pushes the top block 41 to move upward, thereby applying an axial load to the hydrate-containing sediment sample.

[0091] In this embodiment, the loading cylinder 44 is fixedly connected to the bottom surface of the autoclave body 11 via a fixing block 19. A sealing ring is also provided at the connection between the loading cylinder and the autoclave body. The fixing block 19 not only connects 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. Furthermore, a sealing ring is provided on the contact surface between the upper portion of the loading piston 42 and the opening of the loading cylinder 44 to prevent hydraulic oil leakage during axial loading and ensure stable axial load during testing.

[0092] The gas supply mechanism is used to inject gas for forming hydrate deposits into the autoclave. The gas supply mechanism includes a gas cylinder 51 connected to the gas inlet on the autoclave via a connecting pipe. A valve 52, a flow meter 53, and a pressure gauge 54 are sequentially provided on the connecting pipe between the gas cylinder 51 and the autoclave.

[0093] The non-contact strain observation mechanism includes a CCD camera 61 and a laser 62, both mounted on a connecting rod 64. Connecting rod 64 is secured to the top of a support rod 66 via a ferrule 65. A base 67 is located at the bottom of support rod 66. The CCD camera 61 is positioned directly above the viewing window 14, ensuring that the observation surface is within the camera's field of view and that image clarity requirements are met. The CCD camera 61 and laser 62 are each connected to a PIV control unit 63. These three components work together to capture high-definition images of the shear surface of the hydrate-bearing sediment sample 12 at different shear stages.

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

[0095] The data processing mechanism is electrically connected to the visual autoclave mechanism, the sediment shear simulation mechanism, the axial loading mechanism, the air supply mechanism, the non-contact strain observation mechanism, and the cryogenic maintenance mechanism. It includes a data processor 81 and a computer 82. The data processor 81 is equipped with a temperature interface 83, a pressure interface 84, and a flow interface 85 for real-time monitoring and control of temperature, pressure, and flow during the test.

[0096] The data processor can also be equipped with more interfaces, which can be directly connected to various sensors and measuring tools required for the experiment to assist in completing data collection and processing.

[0097] The skeleton of the hydrate-containing sediment sample can be made of quartz sand, clay, muddy silt, etc. Distilled water or deionized water is preferably used for synthesizing hydrates, and the synthesis time can be shortened by using additives. The gas used for synthesizing hydrates can be methane, ethane, carbon dioxide, tetrahydrofuran, etc., and the specific choice of gas can be made according to the specific experiment.

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

[0099] In the first step, the sediment and deionized water are mixed.

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

[0101] The second step is to connect the device and test the air tightness of the device.

[0102] according to Figure 1 Connect the visualized autoclave mechanism, sediment shear simulation mechanism, axial loading mechanism, and gas supply mechanism, clean the autoclave body, and inject nitrogen to test the airtightness of the entire device to ensure the normal operation of the experimental device.

[0103] The third step is hydrate synthesis.

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

[0105] Methane gas is slowly injected into the sample filling chamber of the autoclave body 11 through the gas supply mechanism to raise the pore pressure to the set value. Simultaneously, the sediment shear simulation mechanism controls the loading plate 38 to apply horizontal stress to the sample, while the axial loading mechanism controls the top block 41 to apply vertical stress to the sample.

[0106] Increase the pore pressure, horizontal stress and axial stress to the set values ​​again, while keeping the pore pressure slightly smaller than the horizontal stress and axial stress.

[0107] During the hydrate synthesis process, the temperature of the constant temperature portion 71 is set by the low temperature maintaining mechanism, and the sample temperature in the sample filling cavity is controlled to slowly drop to the set value and remain constant until the pore pressure stops decreasing, and the hydrate synthesis process ends.

[0108] The fourth step is the installation of the non-contact strain observation mechanism.

[0109] Connect the connecting rod 64, the ferrule 65, the support rod 66 and the base 67, and place them in appropriate positions. Install the CCD camera 61 and the laser 62 on the connecting rod 64, and the CCD camera 61 and the laser 62 are located above the autoclave body. The CCD camera 61 and the laser 62 are both connected to the PIV control unit 63. Turn on the laser 62 and align the laser 62 with the sample; adjust the position of the CCD high-speed camera 61 so that it is located directly above the window 14 and the visual plug 15. Operate the PIV control unit 63, calibrate the shooting scale, and calibrate the non-contact strain observation mechanism.

[0110] Step 5: Sediment shear simulation experiment.

[0111] The air supply mechanism is controlled to maintain the pore pressure constant, and the action of the shear plate 31 in the sediment shear simulation mechanism is adjusted to simulate the shear process of the hydrate-containing sediment sample 12. At the same time, 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 capture images of the top of the hydrate-containing sediment sample 12 during the shearing process and record relevant data until the shearing process is completed.

[0113] In the initial unsheared stage, a CCD camera 61 is used to obtain a grayscale image of the surface of the hydrate-containing sediment sample 12 as a reference surface. During the constant rate shearing process, the CCD camera 61 automatically captures an image every 1 second, maintaining uniform lighting in the space and fixed positions of related instruments. The image of the top of the hydrate-containing sediment sample 12 is observed and relevant data is recorded until the shearing process is completed.

[0114] The calculation formulas for stress σ and strain ε of hydrate-containing sediments are:

[0115] ,

[0116] .

[0117] Among them, N s Indicates the load of the shear plate, N p Denotes the load on the loading plate, D s represents the displacement of the shear plate, D prepresents 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 horizontal length of the specimen.

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

[0119] Based on the shear surface formation and development images obtained in the fifth step, digital image analysis technology was used to study the morphology and distribution characteristics of the shear surface and microcracks. The displacement data of the shear surface at different stages were compared to obtain the displacement field at the top of the hydrate-bearing sediment sample 12. Based on the fitting and calculation of the displacement data, the strain field during the shear surface formation process was determined, and finally the formation and evolution laws of the shear surface were determined.

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

[0121] ,

[0122] Where M represents the length of the image block; N represents the width of the image block; f represents the coordinates of the center point of a certain image block at time t (x i (t), y i (t)) at the gray value distribution function; g represents the coordinates of the center point of the image block at time t+Δt (x i (t+Δt), y i Gray value distribution function of (t+Δt)); represents the displacement increment in the x direction; Indicates 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.

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

[0124] ,

[0125] Among them, u(x,y) represents the lateral velocity of the particle, and v(x,y) represents the longitudinal velocity of the particle.

[0126] The above is a detailed introduction to the device and method for monitoring the formation of shear surfaces of hydrate sediments based on PIV provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The above description of the disclosed embodiments enables professionals in this field to implement or use the present invention. Various modifications to these embodiments will be obvious to professionals in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments 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 formation of shear planes in hydrate sediments based on PIV, comprising a high-pressure reactor mechanism, characterized in that: The high-pressure reactor mechanism is a visual high-pressure reactor mechanism, including a high-pressure reactor body; The autoclave also includes a sediment shear simulation mechanism, including a loading plate and a shear plate, which are arranged in the autoclave body, and the loading plate is used to apply horizontal stress to the hydrate sediment sample, and the shear plate is used to shear the hydrate sediment sample; A non-contact strain observation mechanism is provided above the visualization high-pressure reactor mechanism, which is used to obtain high-definition images of the shear surface of the hydrate sediment sample.

2. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 1, characterized in that: Visual high-pressure reactor mechanism includes: The autoclave body has a cavity for containing the hydrate sediment sample, an opening at the top, and a top end fixedly connected to the upper end cover; a viewing window disposed in the central hole of the upper end cover; The visual plug is arranged in the central hole of the upper end cover and fixed between the viewing window and the hydrate sediment sample, and is in direct contact with the hydrate sediment sample.

3. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 2, characterized in that: The visual high-pressure reactor mechanism also includes a three-stage sealing part, which includes: An outer cover plate is disposed in the center hole of the upper end cover and is fixedly connected to the upper end cover; A window pressing block is provided between the outer cover plate and the window and is used to fix the window; A primary sealing gasket is provided on the contact surface between the window pressing 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 outside the annular ring of the secondary sealing gasket, and the tertiary sealing gasket is located at the fixed connection between the outer cover plate and the upper end cover.

4. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 1, characterized in that: Sediment shear simulation mechanisms are respectively provided on two symmetrical outer sides of the hydrate sediment sample, and the shear 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.

5. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 1, characterized in that: The inner side of the loading plate contacts the vertical side of the hydrate sediment sample; The outer side surface of the loading plate is fixedly connected to the hydraulic piston; The hydraulic piston passes through the autoclave body, and the end portion of the hydraulic piston located outside the autoclave body is arranged in the hydraulic cylinder, and a hydraulic cavity is formed between the side of the hydraulic piston facing away from the hydrate sediment sample and the hydraulic cylinder; The horizontal reciprocating motion of the loading plate and the horizontal loading force of the loading plate are controlled by the hydraulic oil flowing into or out of the hydraulic chamber.

6. The device for monitoring the formation of shear plane 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 sediment sample; The outer side surface of the shear plate is fixedly connected to a plurality of thrust rods, and the plurality of thrust rods are arranged at intervals along the vertical direction; The thrust rod passes through the loading plate and the autoclave body, and its end located outside the autoclave body is fixedly connected to the screw, which is in transmission connection with the output end of the propulsion motor; The propulsion motor is fixed on the fixing plate, and the screw rod and the fixing plate are connected via a sliding sleeve.

7. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 1, characterized in that: The axial loading mechanism is also included, and the axial loading mechanism includes: a loading cylinder fixedly connected to the bottom surface of the autoclave body; The loading piston is movably arranged in the loading cylinder, the top of the loading piston is provided with a top block, a rubber sleeve is provided between the top block and the hydrate sediment sample, and the rubber sleeve is fixedly connected to the bottom of the autoclave body; A loading chamber is formed between the bottom of the loading piston and the loading cylinder. The loading liquid flows into or out of the loading chamber, and the loading piston drives the top block to reciprocate up and down.

8. The device for monitoring the formation of shear plane of hydrate sediments based on PIV according to claim 1, characterized in that: The non-contact strain observation mechanism includes: CCD camera, located just above the viewing window; a laser, located above the hydrate sediment sample; PIV control unit, connected to CC camera and laser; The connecting rod, the CCD camera and the laser are all arranged on the connecting rod. The connecting rod is fixedly connected to the top of the supporting rod through a clamping sleeve, and the bottom of the supporting rod is fixedly connected to the base.

9. A method for monitoring the formation of a shear surface of a hydrate sediment using the device for monitoring the formation of a shear surface of a hydrate sediment based on PIV according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Connect the device and perform an airtightness test on the device; S2. Filling the fully mixed sediment and deionized water into the cavity of the autoclave to synthesize the hydrate; S3. Install a non-contact strain observation mechanism to conduct shear simulation experiments on hydrate sediment samples to achieve observation and analysis of the shear surface.

10. The monitoring method according to claim 9, characterized in that: In step S2, the sample in the cavity of the autoclave body is fully compacted, the upper end cover is installed and fixed, and the window and the visual plug are installed in the center hole of the upper end cover through the three-stage 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 movement of the shear plate is adjusted to simulate the shear process of the hydrate-containing sediment sample, and the loading plate and the top block are controlled to maintain constant horizontal stress and vertical stress, and the displacement and shear stress values ​​are recorded; Use a CCD camera to capture images of the top of the hydrate-containing sediment sample during the shearing process and record relevant data until the shearing process is completed; In the initial unsheared stage, a CCD camera was used to capture a grayscale image of the surface of the hydrate-containing sediment sample as a reference surface. During the constant-rate shearing process, the CCD camera automatically captured an image every 1 second, maintaining uniform lighting and fixed instrument positions. The image of the top of the hydrate-containing sediment sample was observed and relevant data was recorded until the shearing process was completed. The calculation formulas for stress σ and strain ε of hydrate-containing sediments are: , ； Among them, N s Indicates the load of the shear plate, N p Denotes the load on 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 horizontal length of the specimen; 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 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: , Where M represents the length of the image block; N represents the width of the image block; f represents the grayscale value distribution function of the coordinates of the center point of an image block at time t (xi(t), yi(t)); g represents the grayscale value distribution function of the coordinates of the center point of the image block at time t+Δt (xi(t+Δt), yi(t+Δt)); represents the displacement increment in the x direction; represents the displacement increment in the y direction; xi(t) represents the horizontal position at time t; yi(t) represents the vertical position at time t; xi(t+Δt) represents the horizontal position at time t+Δt; yi(t+Δt) represents the vertical position at time t+Δt, The velocity is used to calculate the position of each particle at the next moment. The calculation formula for the position of the i-th particle is as follows: , Among them, u(x,y) represents the lateral velocity of the particle, and v(x,y) represents the longitudinal velocity of the particle.

Images