CT-based hydrate deposit fracture propagation simulation experimental apparatus and method

Abstract

The present application relates to natural gas hydrate exploitation simulation technical field, especially be based on CT scan's hydrate deposit crack propagation simulation experimental device and method. Including high pressure reaction system, fracturing fluid injection system, fixed rotating system, gas supply system, confining pressure control system, CT scanning system and data collection processing system, fixed rotating system is located below high pressure reaction system, fracturing fluid injection system, gas supply system, confining pressure control system are connected with high pressure reaction system respectively, CT scanning system is located outside high pressure reaction system. Through the expansion method simulates the crack propagation process of hydrate deposit, and through the real-time observation of CT scanning device, can analyze the crack propagation law of hydrate deposit and the crack shape characteristics under different working conditions, so as to realize the compressibility evaluation of hydrate deposit, can provide theory and experimental reference for the realization of natural gas hydrate reservoir hydraulic fracturing reconstruction and yield increasing target.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas hydrate exploitation simulation, in particular to a hydrate deposit fracture propagation simulation experimental device and method based on CT scanning. BACKGROUND

[0002] With the progress of natural gas hydrate development technology and the success of test production, hydrate development gradually enters the exploration stage of commercial exploitation. Countries around the world are developing hydrate development technology to meet the demand for increased production, and China also regards the commercial development of natural gas hydrates as a goal of energy strategy. In the commercial exploitation stage of hydrates, how to greatly increase the single well production is the focus of research. Therefore, developing stimulation technology to achieve the target capacity of commercial test production has become the focus of current natural gas hydrate development research.

[0003] At present, the main methods of natural gas hydrate exploitation include depressurization method, heat injection method, gas displacement method, chemical agent method and solid state fluidization method. Natural gas hydrate test production is generally carried out by one or a combination of the above methods, which realizes the test production target of hydrates and proves the technical recoverability of marine natural gas hydrates. However, there is still a big gap between the production of the above traditional methods and the demand for commercial exploitation. In order to solve the above problems, domestic and foreign researchers have proposed reservoir reconstruction technologies represented by hydraulic fracturing and hydraulic slotting, in order to achieve the demand for large-scale production increase. Among them, the hydraulic fracturing technology can create a large number of fractures in the reservoir, increase the reservoir drainage area, and improve the reservoir flow conditions, thereby promoting the hydrate decomposition process and increasing the production capacity. This technology has been widely used in traditional oil and gas reservoirs and has achieved good results. However, due to the poor cementation and low strength of natural gas hydrate reservoirs, the fracture propagation process and fracture morphology during fracturing are obviously different from those of traditional oil and gas reservoirs, which causes the lack of corresponding theory and experimental basis for the implementation of hydrate reservoir hydraulic fracturing, especially in the aspects of fracture propagation law and fracture morphology characteristics affecting production. Therefore, in-depth study of the fracture propagation law and fracture morphology characteristics of hydrate reservoirs has become a key problem to be solved in the process of hydraulic fracturing stimulation. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned defects existing in the prior art, and a hydrate deposit fracture propagation simulation experimental device and method based on CT are proposed. The expansion method is used to simulate the hydrate deposit fracture propagation process, and the CT scanning device is used for real-time observation, which can analyze the hydrate deposit fracture propagation law and the fracture morphology characteristics under different working conditions, so as to realize the evaluation of the fracturing property of hydrate deposits and provide theoretical and experimental reference for the realization of the hydraulic fracturing reconstruction and stimulation target of natural gas hydrate reservoirs.

[0005] The technical scheme of the present application is: a CT-based hydrate deposit crack propagation simulation experiment device, comprising a high-pressure reaction system, a fracturing fluid injection system, a fixed rotating system, a gas supply system, a confining pressure control system, a CT scanning system and a data collection and processing system, the fixed rotating system is located below the high-pressure reaction system, the fracturing fluid injection system, the gas supply system and the confining pressure control system are connected with the high-pressure reaction system, and the CT scanning system is located outside the high-pressure reaction system.

[0006] The high-pressure reaction system comprises an autoclave body, an annular rubber sleeve is arranged in the middle of the cylindrical cavity of the autoclave body, a confining pressure liquid cavity is formed between the inner side of the autoclave body and the outer side of the rubber sleeve, the hydrate deposit is arranged in the rubber sleeve, an upper plug is sealingly fixed to the top of the autoclave body, and a lower plug is sealingly arranged at the bottom of the autoclave body; the rubber sleeve is sealingly connected with the upper plug and the lower plug.

[0007] The fracturing fluid injection system comprises a conduit, a high-pressure membrane, a joint and an injection pump, the conduit and the high-pressure membrane are arranged in the middle of the hydrate deposit, the conduit is arranged along the axial direction of the autoclave body, a plurality of through holes are arranged on the outer wall of the conduit at intervals, the conduit is arranged in the high-pressure membrane, a fracturing fluid cavity is formed between the conduit and the high-pressure membrane, the upper and lower ends of the conduit and the high-pressure membrane are fixedly connected with the autoclave body through the joint and the fixing block, the joint and the fixing block at the upper and lower ends are respectively provided with fracturing fluid channels, and the injection pump is communicated with the cavity in the conduit through the fracturing fluid channel in the joint and the fixing block at the upper end.

[0008] In the present application, the upper part of the autoclave body is provided with a confining pressure liquid inlet, the lower part of the autoclave body is provided with a confining pressure liquid outlet, the upper part of the upper plug is provided with a pressing block, the upper plug is provided with a fracturing fluid flow channel and a gas injection channel, the fracturing fluid injection system is communicated with the hydrate deposit through the fracturing fluid flow channel, and the gas supply system is communicated with the hydrate deposit through the gas injection channel.

[0009] The lower plug is connected with the fixed rotating system, and the top of the lower plug is provided with a temperature probe inserted into the hydrate deposit.

[0010] The fixed rotating system comprises a pressure-bearing block, an axial pressure loading mechanism, a fixed support frame and a rotating disc, the pressure-bearing block is located below the autoclave body, the top of the pressure-bearing block is fixedly connected with the lower plug above it, the lower part of the pressure-bearing block is connected with the axial pressure loading mechanism, the axial pressure loading mechanism is arranged on the fixed support frame, and the bottom of the fixed support frame is provided with the rotating disc.

[0011] The gas supply system comprises a gas cylinder, the gas cylinder and the gas injection channel of the upper plug are connected through a connecting pipeline, the connecting pipeline is provided with a second valve, a first flow meter and a second pressure sensor.

[0012] The confining pressure control system comprises a refrigeration circulation mechanism and a booster pump, the outlet of the refrigeration circulation mechanism is connected with the inlet of the booster pump, the outlet of the booster pump is communicated with the confining pressure liquid inlet on the autoclave body through a connecting pipeline, and a No.

[0013] The refrigeration circulation mechanism is communicated with the confining pressure liquid outlet of the autoclave body through a connecting pipeline, and a No.

[0014] The CT scanning system comprises a receiver and an X-ray generator, and the receiver and the X-ray generator are symmetrically arranged outside the autoclave body.

[0015] The data collection and processing system comprises a data processor and a computer, the data processor is connected with each flow meter, pressure sensor and temperature probe through a data line, and the data processor is connected with the computer.

[0016] The application also comprises a method for performing experiments by using the experimental device for simulating the crack propagation process of the hydrate deposit, and the method comprises the following steps:

[0017] S1. connecting the experimental device;

[0018] S2. synthesizing hydrates;

[0019] S3. simulating the crack propagation process:

[0020] The injection pump is started, the fracturing fluid is injected into the fracturing fluid cavity along the conduit, the high-pressure membrane is deformed and expanded, the fracturing fluid is extruded from the hydrate deposit through the high-pressure membrane, so that cracks are generated in the hydrate deposit; the injection of the fracturing fluid is continuously performed, the high-pressure membrane is continuously expanded and extruded from the hydrate deposit, and the cracks in the hydrate deposit are continuously expanded and developed;

[0021] The stress state of the hydrate deposit is kept unchanged by adjusting the refrigeration circulation mechanism and the axial pressure loading mechanism during the injection process;

[0022] S4. observing the crack characteristics:

[0023] During the crack propagation process, the injection pressure of the fracturing fluid is kept unchanged by controlling the injection pump, the X-ray emitter and the receiver are started, the rotating disc is started to rotate, the hydrate deposit is CT scanned by the X-ray emitter and the receiver, and the change of the internal structure of the hydrate deposit is observed;

[0024] S5. reconstruction and analysis of the crack morphology, and evaluation of the pressureability of the hydrate reservoir.

[0025] In step S2, the sediment mixed with water is filled into the rubber sleeve, the conduit and the high-pressure membrane are installed in the middle of the hydrate sediment through the joint and the fixing block, the whole experimental device is sealed, then the methane gas is injected into the sediment through the gas supply system, then the fixed axial pressure and the confining pressure are applied through the refrigeration circulation mechanism and the axial loading mechanism, then the refrigeration circulation mechanism is adjusted to cool the autoclave body, and the hydrate is synthesized in the autoclave body.

[0026] The present application has the following beneficial effects:

[0027] (1) The present application can simulate the crack propagation process of the natural gas hydrate sediment under different stress states: the horizontal loading force is applied to the autoclave body through the confining pressure control system, the vertical loading force is applied to the autoclave body through the fixed rotating system, the triaxial simulation stress state of the whole device is realized, the crack initiation, propagation and gradual development of the middle part of the sediment are realized through the injection of the fracturing fluid based on the expansion method, and the crack propagation process simulation of the hydrate sediment under different stress states is realized.

[0028] (2) Real-time observation of the expanding crack and crack morphology analysis: the crack development state at different times can be observed in real time through the X-CT scanning system, and the crack morphology and position in the sediment can be accurately analyzed through reconstruction and modeling, and the crack characteristics and development degree under different stress states and expansion processes are evaluated.

[0029] (3) Analysis of the crushability of the hydrate sediment: by comparing the crack development degree of the hydrate sediment under different working conditions, the influence of hydrate saturation on the crack characteristics and development degree is analyzed, and the crushability of the hydrate sediment under different stress states is explored. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural schematic view of the hydrate sediment crack propagation process simulation experimental device.

[0031] In the figure: 11 hydrate sediment; 12 rubber sleeve; 13 temperature probe; 14 confining pressure liquid cavity; 15 confining pressure liquid inlet; 16 upper plug; 17 autoclave body; 18 pressure block; 19 lower plug; 21 conduit; 22 high-pressure membrane; 23 fracturing fluid cavity; 24 joint; 25 fixing block; 26 first pressure sensor; 27 first valve; 28 injection pump; 29 elastic sleeve; 31 pressure-bearing block; 32 axial pressure loading device; 33 fixing device; 34 turntable; 41 gas cylinder; 42 second valve; 43 first flowmeter; 44 second pressure sensor; 51 refrigeration circulation device; 52 booster pump; 53 third valve; 54 second flowmeter; 55 third pressure sensor; 56 fourth valve; 61 receiver; 62 X-ray emitter; 71 data processor; 72 computer. DETAILED DESCRIPTION

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0034] like Figure 1 As shown, the CT-based hydrate sediment fracture propagation simulation experimental device of the present invention includes a high-pressure reaction system, a fracturing fluid injection system, a fixed-rotation system, a gas supply system, a confining pressure control system, a CT scanning system, and a data collection and processing system. The fixed-rotation system is located below the high-pressure reaction system. The fracturing fluid injection system, the gas supply system, and the confining pressure control system are respectively connected to the high-pressure reaction system. The CT scanning system is located outside the high-pressure reaction system.

[0035] The high-pressure reaction system includes a high-pressure vessel 17. The high-pressure vessel in this application is made of high-strength steel and carbon fiber, capable of withstanding high pressure while meeting the penetration requirements of an X-ray-CT scanning device. An annular rubber sleeve 12 is provided in the middle of the cylindrical cavity of the high-pressure vessel 17. A gap exists between the inner surface of the high-pressure vessel 17 and the outer surface of the rubber sleeve 12, forming a confining pressure liquid chamber 14. A confining pressure liquid inlet 15 is provided at the upper part of the high-pressure vessel 17, and a confining pressure liquid outlet is provided at the lower part of the high-pressure vessel 17. The confining pressure liquid inlet 15 and the confining pressure liquid outlet are respectively connected to a confining pressure control system to realize the circulation of the low-temperature confining pressure liquid within the confining pressure liquid chamber. Hydrate deposits 11 are present inside the rubber sleeve 12. An upper plug 16 is sealed and fixed at the top of the high-pressure vessel 17, and a lower plug 19 is sealed at the bottom of the high-pressure vessel 17. Both the upper plug 16 and the lower plug 19 are in contact with the hydrate deposits 11. The upper and lower ends of the rubber sleeve 12 are equipped with sealing rings between them and the plug, thus achieving a sealed connection between the rubber sleeve 12 and the plug of the high-pressure vessel body.

[0036] A pressure block 18 is provided above the upper plug 16, which secures the upper plug 16. The upper plug 16 contains a fracturing fluid flow channel and a gas injection channel. The fracturing fluid injection system is connected to the hydrate deposit 11 through the fracturing fluid flow channel, and the gas supply system is connected to the hydrate deposit 11 through the gas injection channel. The lower plug 19 is connected to the fixed-rotation system, thus achieving the connection between the high-pressure reaction system and the fixed-rotation system. A temperature probe 13 is provided at the top of the lower plug 19, which is inserted into the hydrate deposit 11 to monitor the temperature changes of the hydrate deposit 11 in real time.

[0037] The fracturing fluid injection system comprises a conduit 21, a high-pressure membrane 22, a joint 24 and an injection pump 28, wherein the conduit 21 and the high-pressure membrane 22 are located in the middle of the hydrate deposit 11, the conduit 21 is arranged along the axial direction of the autoclave body, the conduit 21 is arranged in the high-pressure membrane 22, a fracturing fluid cavity 23 is formed between the conduit 21 and the high-pressure membrane 22, and a plurality of through holes are uniformly and spacedly arranged on the outer wall of the conduit 21. The upper end and the lower end of the conduit 21 and the high-pressure membrane 22 are connected with fixing blocks 25 through the joints 24, respectively, the fixing block above the conduit is fixedly connected with the upper plug 16, the fixing block below the conduit is fixedly connected with the lower plug 19, and the conduit 21 and the high-pressure membrane 22 are fixed in the middle of the autoclave body through the joints 24 and the fixing blocks 25 on the upper side and the lower side. The joints 24 and the fixing blocks 25 on the upper side and the lower side are respectively provided with fracturing fluid channels, wherein the injection pump 28 is communicated with the cavity in the conduit 21 through the fracturing fluid channel of the joint and the fixing block above, a first valve 27 and a first pressure sensor 26 are arranged on the connecting pipeline of the injection pump 28 and the fracturing fluid channel, and the injection pressure of the fracturing fluid is controlled through the first valve 27 and the first pressure sensor 26. After the fracturing fluid is injected into the conduit 21 through the injection pump 28, the fracturing fluid in the conduit 21 enters the fracturing fluid cavity 23 between the high-pressure membrane 22 and the conduit 21 through the through holes on the side wall of the conduit, the high-pressure membrane 22 is deformed by expansion under the pushing of the fracturing fluid, and the hydrate deposit 11 outside the high-pressure membrane 22 is extruded to generate and promote the development of cracks. The conduit 21 in the application is mainly used to realize the inflow of the fracturing fluid into the fracturing fluid cavity 23 so as to make the high-pressure membrane 22 deformed by expansion, and the conduit 21 also plays a certain supporting role, so the conduit 21 in the embodiment can adopt a rigid conduit with hole distribution characteristics.

[0038] The fixed rotating system comprises a pressure block 31, an axial pressure loading mechanism 32, a fixed support frame 33 and a rotating disc 34. The pressure block 31 is located below the autoclave body 17, the top of the pressure block 31 is fixedly connected with the lower plug 19 above it, and the lower part of the pressure block 31 is connected with the axial pressure loading mechanism 32. The axial pressure loading mechanism 32 can be a hydraulic cylinder or a pneumatic cylinder, and thus the structure of the axial pressure loading mechanism is not described herein. The axial pressure loading mechanism 32 is arranged on the fixed support frame 33, the bottom of the fixed support frame 33 is provided with the rotating disc 34. The fixed support frame 33 supports the axial pressure loading mechanism 32 and the high-pressure reaction system, and the rotating disc 34 is arranged to realize the 360° rotation of the autoclave body 17 during CT scanning and the fixation of the autoclave body at any angle value after rotation. In this embodiment, a sleeve and a protective sleeve are arranged at the connection between the rotating disc 34 and the axial pressure loading mechanism 32, so as to realize the 360° rotation and start-stop at any position of the whole device, and the contact surface can also prevent large deformation. The fixed rotating system can not only drive the high-pressure reaction system to rotate, but also apply axial pressure to the high-pressure reaction system.

[0039] The gas supply system comprises a gas cylinder 41, which is connected with the gas injection channel of the upper plug 16 through a connecting pipeline. The connecting pipeline is provided with a second valve 42, a first flow meter 43 and a second pressure sensor 43. The gas supply system realizes the injection and release of the hydrate synthesis gas, and the pressure of the injected gas is controlled through the first flow meter 43 and the second pressure sensor 43.

[0040] The confining pressure control system comprises a refrigeration circulation mechanism 51 and a booster pump 52. The outlet of the refrigeration circulation mechanism 51 is connected with the inlet of the booster pump 52. The outlet of the booster pump 52 is connected with the confining pressure liquid inlet 15 of the autoclave body 17 through a connecting pipeline. The confining pressure liquid pressurized by the booster pump 52 directly flows into the confining pressure liquid chamber 14 through the connecting pipeline. The connecting pipeline between the booster pump 52 and the confining pressure liquid inlet 15 is sequentially provided with a third valve 53, a second flow meter 54 and a third pressure sensor 55. The pressure of the low-temperature confining pressure liquid flowing into the confining pressure liquid chamber is controlled through the second flow meter 54 and the third pressure sensor 55. Meanwhile, the refrigeration circulation mechanism 51 is also connected with the confining pressure liquid outlet of the autoclave body through a connecting pipeline. The connecting pipeline between the refrigeration circulation mechanism and the confining pressure liquid outlet is provided with a fourth valve 56. Through the confining pressure control system, the temperature of the confining pressure liquid flowing into the confining pressure liquid chamber can be accurately controlled, and the temperature and confining pressure of the hydrate deposit can be accurately controlled.

[0041] The CT scanning system comprises a receiver 61 and an X-ray generator 62, the X-ray generated by the X-ray generator 62 passes through the hydrate deposit 11 in the autoclave body 17, and the passing X-ray is received by the receiver 61, so that the scanning process of the hydrate deposit 11 is realized, and the internal microstructure change of the hydrate deposit 11 can be observed through the reconstruction model.

[0042] The data collection processing system comprises a data processor 71 and a computer 72, the data processor 71 is provided with an interface connected with each flow meter, pressure sensor and temperature probe 13 through a data line, and the data processor 71 is connected with the computer 72, so that the real-time monitoring and control of the physical property parameters such as pressure, flow and temperature of each system in the whole device are realized, and the data collection and processing are completed.

[0043] Through the CT-based hydrate deposit crack propagation simulation experiment device described in the embodiment, the hydrate deposit crack propagation process can be observed in real time, and the crack propagation law and crack morphology characteristics under different working conditions can be analyzed.

[0044] The application also discloses a method for performing experiments based on the CT-based hydrate deposit crack propagation simulation experiment device.

[0045] Firstly, the connection of the experiment device is performed.

[0046] According to the device schematic diagram, the related components are connected, and then the air tightness of the whole experiment device is checked to ensure that the air tightness of the device meets the experimental requirements.

[0047] Secondly, the hydrate is synthesized.

[0048] A certain amount of sediment mixed with a proper amount of water, such as quartz sand and clay, is filled into the rubber sleeve 12, the conduit 21 and the high-pressure membrane 22 are installed at the predetermined position inside the hydrate deposit 11 through the joint 24 and the fixing block 25, the whole experiment device is sealed, then the methane gas is injected into the sediment through the gas supply system, then the fixed axial pressure and confining pressure are applied through the refrigeration circulation mechanism 51 and the axial loading mechanism 32, then the refrigeration circulation device mechanism is adjusted to reduce the temperature of the autoclave body 17, and the hydrate is synthesized in the autoclave body 17.

[0049] Thirdly, the crack propagation process is simulated.

[0050] The injection pump 28 is started to make the fracturing fluid enter the fracturing fluid cavity 23 along the conduit 21, so that the high-pressure membrane 22 is deformed and expanded, the fracturing fluid is extruded from the high-pressure membrane 22 to the hydrate deposit 11, so that the cracks are generated in the hydrate deposit 11; the fracturing fluid is continuously injected, the high-pressure membrane 22 is continuously expanded and extruded to the hydrate deposit 11, so that the cracks in the hydrate deposit 11 are continuously expanded and developed.

[0051] During the injection process, the stress state of the hydrate deposit 11 is kept unchanged by adjusting the refrigeration cycle mechanism 51 and the axial pressure loading mechanism 32.

[0052] In the fourth step, the crack characteristics are observed.

[0053] During the crack propagation process, the injection pressure of the fracturing fluid is kept unchanged by controlling the injection pump 28, and then the X-ray emitter 62 and the receiver 61 are started, and the rotating disc 34 is started to rotate, and the CT scanning of the hydrate deposit 11 is performed by the X-ray emitter 62 and the receiver 61, so as to observe the change of the internal structure of the hydrate deposit 11.

[0054] In the fifth step, the reconstruction and analysis of the crack morphology and the evaluation of the fracturability of the hydrate reservoir are performed.

[0055] The data obtained by the receiver 61 are processed and reconstructed to obtain the characteristics such as the morphology and the position of the cracks in the hydrate deposit 11.

[0056] Meanwhile, the crack development degree and the crack morphology characteristics of the hydrate deposit 11 under different conditions at different times are obtained, and the crack propagation law and the crack morphology of the existing oil and gas reservoirs are compared and analyzed, so as to further evaluate the fracturability of the hydrate reservoir.

[0057] During the process, the data that can be recorded include the gas inlet amount, the inlet and outlet amount of the confining pressure fluid, the injection amount of the fracturing fluid, the deposit weight, the pressure, the flow rate, the temperature and the like.

[0058] The CT-based hydrate deposit crack propagation simulation experiment device and method provided by the present application are described in detail above. The principles and implementation manners of the present application are described by using specific examples in the present text, and the above description of the examples is only used to help understand the method of the present application and the core idea thereof. 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 to the examples will be apparent to those skilled in the art, and the general principles defined in the present text 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 in the present text, but will conform to the widest scope consistent with the principles and novel features disclosed in the present text.

Claims

1. A CT-based experimental device for simulating crack propagation in hydrate deposits, characterized in that, It includes a high-pressure reaction system, a fracturing fluid injection system, a fixed-rotation system, a gas supply system, a confining pressure control system, a CT scanning system, and a data collection and processing system. The fixed-rotation system is located below the high-pressure reaction system. The fracturing fluid injection system, the gas supply system, and the confining pressure control system are connected to the high-pressure reaction system. The CT scanning system is located outside the high-pressure reaction system. The high-pressure reaction system includes a high-pressure vessel body (17), with an annular rubber sleeve (12) in the middle of the cylindrical cavity of the high-pressure vessel body (17). A confining pressure liquid cavity (14) is formed between the inner side of the high-pressure vessel body (17) and the outer side of the rubber sleeve (12). Hydrate deposits (11) are provided inside the rubber sleeve (12). An upper plug (16) is sealed and fixed at the top of the high-pressure vessel body (17), and a lower plug (19) is sealed at the bottom of the high-pressure vessel body (17). The rubber sleeve (12) is sealed to the upper plug (16) and the lower plug (19). The fracturing fluid injection system includes a conduit (21), a high-pressure membrane (22), a connector (24), and an injection pump (28). The conduit (21) and the high-pressure membrane (22) are located in the middle of the hydrate deposit (11). The conduit (21) is arranged along the axial direction of the high-pressure vessel. Several through holes are arranged at intervals on the outer wall of the conduit (21). The conduit (21) is placed inside the high-pressure membrane (22). A fracturing fluid cavity (23) is formed between the conduit (21) and the high-pressure membrane (22). The upper and lower ends of the conduit (21) and the high-pressure membrane (22) are fixedly connected to the high-pressure vessel through the connector (24) and the fixing block (25), respectively. Fracturing fluid channels are provided in the connector (24) and the fixing block (25) at the upper and lower ends, respectively. The injection pump (28) is connected to the cavity inside the conduit (21) through the fracturing fluid channels in the connector and the fixing block at the upper end. Fracturing fluid enters the fracturing fluid chamber along the conduit, causing the high-pressure membrane to expand and deform. The fracturing fluid then squeezes the hydrate deposit through the high-pressure membrane, thereby creating cracks within the hydrate deposit. With continuous injection of fracturing fluid, the high-pressure membrane continuously expands and squeezes the hydrate deposit, causing the internal cracks in the hydrate deposit to continuously expand and develop.

2. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 1, characterized in that, The upper part of the high pressure vessel body (17) is provided with a confining pressure fluid inlet (15), the lower part of the high pressure vessel body (17) is provided with a confining pressure fluid outlet, a pressure block (18) is provided above the upper plug (16), and a fracturing fluid flow channel and an injection channel are provided inside the upper plug (16). The fracturing fluid injection system is connected to the hydrate deposit (11) through the fracturing fluid flow channel, and the gas supply system is connected to the hydrate deposit (11) through the injection channel. The lower plug (19) is connected to the fixed rotation system. A temperature probe (13) is provided on the top of the lower plug (19). The temperature probe (13) is inserted into the hydrate deposit (11).

3. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 1, characterized in that, The fixed rotation system includes a pressure block (31), an axial pressure loading mechanism (32), a fixed support frame (33), and a turntable (34). The pressure block (31) is located below the autoclave body (17). The top of the pressure block (31) is fixedly connected to the lower plug (19) above it. The bottom of the pressure block (31) is connected to the axial pressure loading mechanism (32). The axial pressure loading mechanism (32) is set on the fixed support frame (33). The bottom of the fixed support frame (33) is provided with a turntable (34).

4. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 2, characterized in that, The gas supply system includes a gas cylinder (41), and the gas cylinder (41) is connected to the gas injection channel of the upper plug (16) through a connecting pipe. The connecting pipe is equipped with a second valve (42), a first flow meter (43), and a second pressure sensor (44).

5. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 2, characterized in that, The confining pressure control system includes a refrigeration cycle mechanism (51) and a booster pump (52). The outlet of the refrigeration cycle mechanism (51) is connected to the inlet of the booster pump (52). The outlet of the booster pump (52) is connected to the confining pressure liquid inlet (15) on the high pressure vessel body (17) through a connecting pipe. A third valve (53), a second flow meter (54), and a third pressure sensor (55) are sequentially installed on the connecting pipe between the booster pump (52) and the confining pressure liquid inlet (15). The refrigeration cycle mechanism (51) is connected to the confining pressure liquid outlet of the high pressure vessel through a connecting pipe. A fourth valve (56) is provided on the connecting pipe between the refrigeration cycle mechanism and the confining pressure liquid outlet.

6. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 1, characterized in that, The CT scanning system includes a receiver (61) and an X-ray generator (62), which are symmetrically arranged on the outside of the autoclave body (17).

7. The CT-based hydrate sediment crack propagation simulation experimental device according to claim 1, characterized in that, The data collection and processing system includes a data processor (71) and a computer (72). The data processor (71) is connected to each flow meter, pressure sensor and temperature probe (13) via data lines. The data processor (71) is connected to the computer (72).

8. A method for conducting experiments using the apparatus according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Connection of the experimental setup; S2. Synthetic hydrate; S3. Simulation of crack propagation process: Start the injection pump to allow fracturing fluid to enter the fracturing fluid chamber along the conduit, causing the high-pressure membrane to expand and deform. The fracturing fluid squeezes the hydrate deposit through the high-pressure membrane, thereby creating fractures within the hydrate deposit. Continue injecting fracturing fluid, and the high-pressure membrane will continuously expand and squeeze the hydrate deposit, causing the internal fractures of the hydrate deposit to continuously expand and develop. During the injection process, the stress state of the hydrate deposits is kept constant by adjusting the cooling cycle mechanism and the axial pressure loading mechanism; S4. Observe the characteristics of the cracks: During the fracture propagation process, the injection pump is controlled to maintain a constant fracturing fluid injection pressure. The X-ray emitter and receiver are activated, and the turntable is started to rotate. The X-ray emitter and receiver are used to perform CT scans on the hydrate deposits to observe the changes in the internal structure of the hydrate deposits. S5. Reconstruction and analysis of fracture morphology, and evaluation of the compressibility of hydrate reservoirs.

9. The method according to claim 8, characterized in that, In step S2 above, a sediment thoroughly mixed with water is filled into the rubber sleeve. The conduit and high-pressure membrane are installed in the middle of the hydrate sediment through the connector and fixing block. The entire experimental device is sealed. Then, methane gas is injected into the sediment through the gas supply system. Then, a fixed axial pressure and confining pressure are applied through the refrigeration cycle mechanism and the axial loading mechanism. Then, the refrigeration cycle mechanism is adjusted to cool the autoclave body and synthesize hydrates in the autoclave body.

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