Acoustic emission monitoring device and experimental method for deformation and failure of hydrate-bearing sediments

Abstract

The present application relates to natural gas hydrate reservoir property detection engineering technical field, disclose a kind of acoustic emission monitoring device and experimental method of hydrate deposit deformation damage, device includes triaxial test system, hydrate generation system and data acquisition control system, triaxial test system is equipped with triaxial base, and triaxial base is integrated with multiple sensor connection ports;Data acquisition control system respectively collects acoustic emission signal, acoustic signal and resistivity signal through sensor connection port.The present application starts from the characteristics of reservoir sediment, and carries out hydrate deposit deformation damage experiment by acoustic emission, ultrasonic, resistivity testing means, illustrates the deformation damage mechanism of hydrate deposit, reveals its regular change, and establishes the link between its multiple monitoring data and the mechanical properties of hydrate deposit, which has important significance for avoiding environmental problems in actual engineering.

Description

Technical Field

[0001] This invention relates to the field of engineering technology for detecting the physical properties of natural gas hydrate reservoirs, and more specifically to an acoustic emission monitoring device and experimental method for detecting deformation and damage of hydrate-bearing sediments. Background Technology

[0002] Natural gas hydrates, as a new type of clean energy with vast reserves, often exist in deep-sea high-pressure, low-temperature sedimentary layers in cemented or skeletal forms, and their physical properties are extremely sensitive to temperature and pressure conditions. The environmental impact of hydrate extraction mainly stems from the potential mechanical damage to seafloor strata during extraction, weakening their stability. This damage further alters the temperature and pressure conditions of the strata and hydrate reservoirs, triggering hydrate decomposition and methane gas escape. Reservoir instability and damage during extraction can also induce large-scale, sudden secondary decomposition of hydrates and methane leaks, completely disrupting the mechanical balance of the subsurface strata, leading to severe geological disasters such as seabed collapse, continental slope slumping, and landslides, threatening the safety of extraction operations and the marine ecological environment. Therefore, before extracting natural gas hydrates, it is crucial to conduct in-depth research on the mechanical properties of hydrate sediments and the impact of deformation and damage on reservoir stability, revealing the deformation and damage characteristics and evolution patterns of hydrate-bearing sediments, and providing a scientific basis for solving problems such as methane leaks and geological environmental damage during extraction.

[0003] Currently, numerous scholars have conducted extensive research on the basic physical properties of hydrate-bearing sediments using various methods such as acoustics, electricity, and mechanics, achieving a series of phased progress. However, a unified understanding of the dynamic evolution of deformation and failure characteristics in hydrate-bearing sediments has not yet been reached, and there is a lack of experiments capable of fully reproducing the actual working conditions of the reservoir to systematically reveal this process of change. Furthermore, research on deformation and failure of hydrate-bearing sediments generally suffers from the core problem of "single-dimensional data support," namely, an over-reliance on macroscopic mechanical parameters such as shear strength, elastic modulus, cohesion, and internal friction angle obtained from mechanical tests such as triaxial compression and direct shear, while severely lacking dynamic parameters such as acoustic emission, resistivity, and ultrasound that can reflect the entire process of microscopic damage initiation, propagation, and penetration within the sediment. This results in the explanation of deformation and failure mechanisms remaining only at the level of "macroscopic result description," making it difficult to establish a complete logical chain of "microscopic damage - macroscopic failure." In addition, existing multi-parameter monitoring experimental devices also suffer from defects such as low sensor integration and unreasonable layout. Most acoustic emission sensors are deployed outside the triaxial pressure chamber, and the signals are severely distorted after being attenuated multiple times by the confining pressure fluid and the cylinder. The acoustic wave and resistivity testing modules are also easily affected by the metal parts of the device and the external environment. At the same time, some devices cannot fully simulate the entire process from in-situ hydrate formation to triaxial shear failure, resulting in a large deviation between the experimental results and the actual deformation and failure characteristics of the reservoir in the field. Summary of the Invention

[0004] In view of this, the present invention provides an acoustic emission monitoring device and experimental method for the deformation and failure of hydrate-bearing sediments. Starting from the characteristics of reservoir sediments, the device conducts deformation and failure experiments on hydrate-bearing sediments through acoustic emission, ultrasound, and resistivity testing. This can elucidate the deformation and failure mechanism of hydrate-bearing sediments, reveal their regular changes, and establish the relationship between multiple monitoring data and the mechanical properties of hydrate-bearing sediments. This is of great significance for avoiding environmental problems in practical engineering.

[0005] On the one hand, the acoustic emission monitoring device for deformation and damage of hydrate-containing sediments provided by the present invention includes a triaxial testing system, a hydrate generation system, and a data acquisition and control system. The triaxial testing system is provided with a triaxial base, and a sample fixing module is installed on the triaxial base. The hydrate generation system is connected to the triaxial testing system, and the data acquisition and control system is electrically connected to the triaxial testing system and the sample fixing module respectively. The sample fixing module includes two electrode heads arranged opposite each other, with a sample clamped between the two electrode heads. The electrode heads have gas channels inside and cavities on the end face of the electrode heads facing the sample. The triaxial base integrates multiple sensor connection ports, which are respectively connected to an acoustic emission sensor, an acoustic probe, and a resistivity testing fixture. The acoustic emission sensor is disposed on the side wall of the sample, the acoustic probe is embedded in the cavity of the electrode indenter, and the resistivity testing fixture is electrically connected to the electrode indenter. The data acquisition and control system includes a triaxial device parameter acquisition system, an acoustic wave parameter acquisition system, a resistivity acquisition system, and an acoustic emission signal parameter acquisition and control system. The data acquisition and control system acquires acoustic emission signals, acoustic wave signals, and resistivity signals respectively through the sensor connection ports.

[0006] Preferably, the triaxial testing system includes an axial loading system, a triaxial pressure chamber, a confining pressure loading system, and a confining pressure fluid filling and discharging system. The axial loading system is located at the top of the triaxial pressure chamber, and the confining pressure loading system and the confining pressure fluid filling and discharging system are respectively connected to the triaxial pressure chamber.

[0007] Preferably, the axial loading system includes a balance chamber, an axial pressure chamber, and a return chamber. During the axial pressure loading test, the balance chamber adjusts the internal pressure state to achieve a balance between the axial loading system and the confining pressure loading system.

[0008] Preferably, the triaxial pressure chamber includes a cylinder disposed on a triaxial base, the triaxial base being connected to a pressure chamber lifting system, and the cylinder being provided with a spiral multi-turn cooling coil, the cooling coil being connected to a hydrate generation system.

[0009] Preferably, the acoustic emission sensor is fixed to the side wall of the sample by a latex sleeve, the contact surface between the acoustic emission sensor and the sample is coated with a coupling agent, and multiple acoustic emission sensors are symmetrically distributed along the circumference of the sample.

[0010] Preferably, a ceramic insulating pad is provided between the electrode pressure head, the axial pressure column, and the triaxial base. The side wall of the electrode pressure head is provided with a groove, and an insulating flange positioning ring is installed in the groove. The insulating flange positioning ring is used to fix the axial extensometer.

[0011] Preferably, the hydrate generation system includes a temperature control system and a gas control and pressurization system; the temperature control system is connected to the cooling coil in the triaxial test system, and the gas control and pressurization system is connected to the gas channel in the electrode indenter.

[0012] Preferably, the gas control and pressurization system includes a gas supply tank, a gas booster pump, a high-pressure gas storage tank, a gas pressure reducing valve, and an automatic back pressure control system connected in sequence, wherein the automatic back pressure control system is connected to the gas outlet end of the sample.

[0013] On the other hand, the acoustic emission monitoring method for deformation and damage of hydrate-bearing sediments provided by the present invention, applied to the acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments as described above, includes the following steps: S1: Preparation of sediment samples; S2: Install the sample between the two electrode indenters, set up the acoustic emission sensor, acoustic probe and resistivity test fixture, and connect each sensor to the data acquisition and control system through the sensor connection port of the triaxial base; S3: Start the hydrate formation system, construct the temperature and pressure environment for hydrate formation within the triaxial test system, and monitor resistivity and acoustic velocity in real time through the data acquisition and control system until hydrate formation is complete; S4: Start the axial loading system of the triaxial test system to conduct a triaxial shear failure test on the hydrate-containing sediment sample; S5: During the experiment, mechanical data, acoustic emission data, acoustic wave data and resistivity data were collected synchronously through the data acquisition and control system.

[0014] Preferably, in step S3, confining pressure fluid is first injected into the triaxial pressure chamber through the confining pressure fluid filling and discharging system, then the temperature control system is activated to reduce the temperature inside the chamber, and then the gas control and pressurization system is activated to introduce methane gas and control the inlet pressure and back pressure.

[0015] As can be seen from the above technical solution, compared with the prior art, the acoustic emission monitoring device and experimental method for deformation and failure of hydrate-bearing sediments provided by the present invention can simulate the hydrate-bearing sediment occurrence environment in the deep sea using a triaxial device in the laboratory. By designing various testing systems and experimental devices, the deformation and failure process of hydrate-bearing sediments can be simulated in the laboratory, and its dynamic evolution process can be monitored in real time, achieving the following beneficial effects: (1) By combining the triaxial test system and the hydrate formation system, the entire process of sediments from the formation of hydrates to their deformation and failure in the deep sea environment was simulated. Relying on the data acquisition and control system, the dynamic evolution of the deformation and failure of hydrate-bearing sediments was ingeniously monitored in real time. (2) The present invention has a clever design for the sample fixing module, and designs electrode indenters of different specifications and sizes, which not only meets the conditions for resistivity testing, but also does not affect the application of axial pressure to the sample. Secondly, the reserved acoustic probe mounting cavity at both ends of the electrode indenter solves the problem of inaccurate acoustic data acquisition, and does not affect the triaxial test. In addition, the acoustic emission sensor is different from the probe layout method of traditional acoustic emission monitoring technology. The present invention adopts the method of "latex sleeve + coupling agent", which solves the problem that the probe cannot effectively collect the acoustic emission parameters of the sample, and prevents the probe from falling off during the experiment. Finally, by integrating multiple physical field parameter test interfaces on the triaxial base and connecting them to the test instruments outside the device, the various types of data in the experiment can be collected and processed in an all-round, all-time, and all-process manner.

[0016] In summary, the formation process of hydrates in sediments realized in the laboratory of this invention is closer to the accumulation process of hydrates in real marine sedimentary environments. This experimental process can simulate the damage of hydrate-bearing sediments under real conditions, so as to make the indoor simulation experiment more in line with the actual situation on site. It has important reference and reference value for the development of the evaluation of the reservoir properties of hydrate-bearing sediments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the acoustic emission monitoring device for deformation and damage of hydrate-containing sediments according to the present invention. Figure 2 For the present invention Figure 1 Schematic diagram of the structure of the three-axis base; Figure 3 This is a schematic diagram of the structure of the triaxial base and sample installation of the present invention.

[0019] Explanation of reference numerals in the attached drawings: 1. Balance chamber; 2. Axial pressure chamber; 3. Return chamber; 4. Cylinder; 5. Triaxial base; 6. Balance piston assembly; 7. Plunger rod; 8. Sample fixing triaxial base; 9. Sensor connection port; 10. Gas inlet / outlet; 11. Cryogenic cooling circulation device; 12. Multi-layer sealing ring; 13. High-temperature gear pump; 14. Liquid storage tank; 15. High-pressure pipeline; 16. High-pressure manual needle valve; 17. Pneumatic needle valve; 18. Pump body; 19. Servo motor; 20. Pneumatic valve; 21. Liquid storage tank; 22. Electrode indenter; 23. Insulating flange positioning ring; 24. Axial extensometer; 25. Circumferential extensometer; 26. Acoustic probe; 27. Gas channel; 28. Ceramic insulating pad; 29. ​​Positioning pin; 30. Data acquisition and control system; 31. Temperature control system; 32. Gas supply. 33. Gas booster pump; 34. High-pressure gas storage tank; 35. Gas pressure reducing valve; 36. Automatic backpressure control system; 37. Confining pressure fluid pressurization port; 38. Confining pressure fluid filling and discharging port; 39. Cooling coil; 40. Pressure chamber lifting system; 41. Triaxial testing system; 42. Gas control and pressurization system; 43. Confining pressure fluid filling and discharging system; 44. Confining pressure loading system; 45. Fastening nut; 46. Inlet and outlet gas pipelines; 47. Pressure head sealing ring; 48. Circumferential extensometer sensor connection port; 49. Axial extensometer sensor connection port; 50. Acoustic wave sensor connection port; 51. Resistivity sensor connection port; 52. Acoustic emission sensor connection port; 53. Confining pressure fluid inlet and outlet of the cavity; 54. Acoustic wave probe pressure ring; 55. Resistivity testing fixture; 56. Acoustic emission sensor; 57. Fixed hinge. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of an exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Example 1: The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments provided by this invention includes a triaxial testing system, a sample fixing module, a data acquisition and control system, and a hydrate generation system. The triaxial testing system 41 is the main part of the testing system, providing a testing environment for hydrate-bearing sediments. The hydrate generation system includes a temperature control system 31 and a gas control and pressurization system 42. The hydrate generation system and the triaxial testing system 41 are used to simulate hydrate generation conditions and environment. Both the gas control and pressurization system 42 and the temperature control system 31 are connected to the interface provided on the triaxial base 5. The gas control and pressurization system 42 is used to provide a stable gas source with the required pressure for hydrate generation; the temperature control system 31 provides the required temperature conditions for the hydrate generation environment during the experiment. Each system is connected to the triaxial testing system 41 through a high-pressure pipeline 15. The data acquisition system 30 is connected to the axial loading system and the sensor interface 9 on the triaxial base 5 to realize the control of various parameters and experimental conditions during the experiment on hydrate-bearing sediments.

[0022] Specifically, such as Figure 1 and Figure 2As shown, the triaxial testing system includes an axial loading system, a triaxial pressure chamber, a pressure chamber lifting system 40, a confining pressure fluid filling and discharging system 43, a confining pressure loading system 44, and a fastening nut 45. The axial loading system is located at the top of the triaxial pressure chamber and is responsible for providing axial pressure for the triaxial test. It consists of a balance chamber 1, an axial pressure chamber 2, and a return chamber 3. During the axial pressure loading test, the balance chamber 1 adjusts the internal pressure state to achieve a balance between the axial loading system and the confining pressure loading system 44, thereby ensuring that the axial pressure loading is basically unaffected by the confining pressure and effectively avoiding interference during the axial loading process. In this test, the ring pressure changes due to variations in the ring pressure volume. The axial pressure chamber 2 provides a stable pressure source, maintaining the stability of the axial pressure on the sample during the test. The return chamber 3, through its internal cavity, makes the application of axial pressure smoother and gentler, avoiding stress damage to the loading system itself when axial pressure is applied. Without axial pressure, it ensures that the pressure on the sediment sample is exactly the same in all directions. This optimization of the loading mechanism can also improve the loading accuracy and stability of the testing machine, reduce errors and fluctuations during the loading process, and ensure the reliability of the test results and the accuracy of the test data. The triaxial pressure chamber includes a cylinder 4, a triaxial base 5, a balance piston assembly 6, and a plunger rod 7. The balance piston assembly 6 and the plunger rod 7 are located inside the cylinder 4. The triaxial pressure chamber is used to simulate the required experimental environment conditions and to mount the sample. The sample is placed and fixed on the triaxial base 5, which is connected to the pressure chamber lifting system 40. The pressure chamber lifting system 40 lifts the sample and tightly connects it to the cylinder 4, and it is pressed and fixed with a fastening nut 45 to form a closed test environment. The pressure chamber lifting system 40 is installed at the bottom of the triaxial pressure chamber and is used to lift the triaxial base 5 and the cylinder 4 during the test, thereby completing the rapid installation of the test platform; the confining pressure liquid filling and discharging system 43 and the confining pressure loading system 44 are used to provide confining pressure conditions in the triaxial pressure chamber.

[0023] In this embodiment, the triaxial pressure chamber is made of 2205 duplex stainless steel with a nitrided surface, exhibiting high hardness, wear resistance, and fatigue strength. Its internal dimensions are φ160mm × 250mm, accommodating samples of different sizes. The cylinder 4 and the triaxial base 5 are tightly fitted together by multi-layer sealing rings 12. These multi-layer sealing rings provide a multi-level sealing effect, effectively preventing leakage of confining liquid and gas under high pressure and low temperature conditions. The chamber is secured with fastening nuts 45. The sample and other fixtures are placed on the triaxial base 5. The fixture structure for the hydrate-containing sediment sample includes the sample fixing triaxial base 5, sensor connection port 9, gas inlet / outlet 10, cryogenic coolant circulation inlet / outlet 11, multi-layer sealing ring 12, electrode indenter 22, insulating flange positioning ring 23, axial extensometer 24, circumferential extensometer 25, acoustic emission sensor 56, acoustic probe 26, resistivity testing fixture 55, ceramic insulating pad 28, positioning pin 29, confining pressure fluid pressurization port 37, confining pressure fluid filling / discharging port 38, cooling coil 39, and inlet / outlet gas lines. In this embodiment, the sample size used is a cylindrical specimen with a diameter of φ50mm × 100mm.

[0024] The triaxial base 5 uses positioning pins 29 to calibrate the sample fixing position, ensuring that the axial pressure head can fully contact the plugs at both ends of the sample, avoiding mechanical parameter testing errors caused by axial loading eccentricity. The triaxial base 5 integrates sensor connection ports 9 for axial and circumferential extensometers (LVTD), acoustic emission sensors 56, acoustic probes, and resistivity test leads, corresponding to one circumferential extensometer 25, two axial extensometers 24, six to eight acoustic emission sensors 56, resistivity test leads, and two acoustic probes 26, respectively. By connecting each sensor, the measured signal data is transmitted to the data acquisition and control system in real time. The extensometer plug is a 4-pin type, the acoustic and resistivity plugs are 5-pin type, and the acoustic emission sensor 56 is a single-pin type. The front end of the triaxial base 5 is equipped with a gas inlet / outlet connection port 10 for connecting the sample's inlet / outlet gas lines 46. Both the inlet and outlet gas lines are spirally wound around the sample to prevent damage due to the strength of the lines themselves during sample loading. To address the issue of inaccurate testing of sample mechanical parameters, the triaxial base 5 is equipped with two gas pipelines, one inlet and one outlet, for connecting the sample's inlet and outlet gas pipelines. In this embodiment, the lower end is used as the inlet end and the upper end as the outlet end, and both the inlet and outlet gas pipelines are spirally wrapped around the sample to prevent inaccurate testing of sample mechanical parameters due to the strength of the pipelines themselves during sample loading. The triaxial base 5 is equipped with a low-temperature coolant circulation inlet and outlet 11, which are sealed using a special metal cooling coil 39 to ensure the cooling effect of the sample in the cavity. The outer edge of the triaxial base 5 is equipped with multi-layer sealing rings 12 for contacting the triaxial pressure chamber cylinder to achieve a sealing effect. All lead wire connectors and valve pipeline inlets of the pressure chamber are integrated on the lower flange of the triaxial base 5, which is simple, neat, and easy to operate. The prepared sample is placed between the upper and lower electrode heads 22 and fixed by wrapping it with a latex film. A sealing ring 12 is installed at the contact position between the latex film and the electrode heads. There is a groove in the middle of each of the upper and lower electrode heads 22 for installing an insulating flange positioning ring 23. There is a cavity at the top of each of the upper and lower electrode heads 22 for embedding an acoustic probe 26. A zirconia ceramic insulating pad 28 of the same size is installed at the contact position between the upper and lower electrode heads 22 and the axial pressure column and triaxial base 5 to avoid the metal parts of the device from affecting the measurement of the sample resistivity and to ensure the accuracy of the resistivity measurement. There is a gas channel 27 inside the upper and lower electrode heads for connecting an external gas inlet / outlet pipeline 46. The pipeline is a φ3mm high-pressure pipeline.

[0025] The confining pressure fluid filling and discharging system 43 consists of a high-temperature gear pump 13, a storage tank 14, a high-pressure pipeline 15, a high-pressure manual needle valve 16, and a pneumatic needle valve 17. The high-pressure pipeline connects all components and stably transmits high-pressure oil, possessing excellent pressure resistance and capable of reliably connecting all components and stably transmitting high-pressure oil in various complex working environments. The high-pressure manual needle valve and pneumatic needle valve can precisely control the flow of oil, ensuring the accuracy and safety of operation. The 15L transparent storage tank's transparent material allows for visualization of the liquid level, making it convenient for operators to monitor the oil storage status at any time. The high-temperature gear pump, combined with a brushless motor, provides powerful power support for oil injection and extraction, ensuring high working efficiency.

[0026] The confining pressure loading system 44 comprises a pump body 18, a servo motor 19, a pneumatic valve 20, a liquid storage tank 21, etc. Driven by the servo motor and under precise speed control, the plunger moves up and down through a worm gear and ball screw transmission, thereby allowing liquid to enter and exit the pump body, achieving the function of quantitative constant speed or constant pressure loading.

[0027] The sample fixing module consists of two electrode heads 22, with the prepared sample placed in the middle. It is secured by a latex film, with a sealing ring 12 at the contact point between the latex film and the electrode head 22. Each of the upper and lower electrode heads 22 has a groove in the middle for installing an insulating flange positioning ring 23, ensuring the overall verticality and preventing interference when installing the radial circumferential extensometer 25. Each of the upper and lower electrode heads 22 has a cavity at its top for embedding an acoustic probe 26, placing the probe within the triaxial pressure cavity. The cavity dimensions match the probe 26, ensuring tight contact and effective capture of acoustic velocity data without affecting data acquisition. Gas channels are provided inside the upper and lower electrode heads 22 for connecting to external gas inlet and outlet pipes. To prevent the metal parts of the device from affecting the sample resistivity measurement, zirconia ceramic insulating pads of the same size are installed at the contact points between the upper and lower electrode heads 22 and the axial pressure column and triaxial base 5, ensuring the accuracy of the resistivity measurement.

[0028] like Figure 1As shown, the data acquisition and control system 30 includes a triaxial device parameter acquisition and control system, an acoustic wave parameter acquisition system, a resistivity acquisition system, and an acoustic emission signal parameter acquisition and control system. The triaxial device parameter acquisition system can acquire real-time values ​​from pressure sensors, temperature sensors, displacement sensors, gas flow meters, and outlet metering data. It can also acquire real-time injection speed, cumulative injection volume, and injection pressure from the constant flow pump. The software can automatically identify and protect the system in case of abnormal data program settings, axial deformation, radial deformation, time reaching limit or preset values, sample breakage, oil circuit blockage, or excessively high oil temperature. It provides real-time, intuitive text feedback of instrument fault information for easy retrieval and troubleshooting. The acoustic wave acquisition system has a transmitter and a receiver, enabling real-time acquisition of changes in transverse and longitudinal waves in the sample. The resistivity acquisition system… The alligator clips at both ends of the lead wire are respectively clamped to the connection points of the upper and lower electrode indenters and the inlet and outlet gas lines of the sample. The resistivity test fixture adopts a four-terminal Kelvin test system with a four-terminal test fixture and a shorting plate. One end is connected to the resistivity tester, and the other end is clamped to the inlet and outlet gas line connection ports on the upper and lower electrode indenters 22 of the sample, effectively eliminating the influence of lead wire resistance and contact resistance on the measurement results, so as to measure the change of sample resistivity between electrode indenters. The acoustic emission signal parameter acquisition and control system can effectively filter, process and analyze the signals generated during the shearing and destruction of the sample by adjusting the threshold value, sampling frequency, peak discrimination time, impact discrimination time, etc.

[0029] The temperature control system 31 is equipped with a circulation pump, which is connected to the cooling coil 39 installed inside the triaxial base 5 through the coolant supply pipeline and the coolant recovery pipeline to form a coolant circulation loop. The coolant supply pipeline is connected to the low-temperature coolant circulation port 11, and the coolant outlet is connected to the coolant recovery pipeline. Ethylene glycol is used as the coolant. All coolant pipelines are wrapped with insulation cotton sleeves to ensure the cooling effect of the experimental equipment. The cooling coil 39 connected to the triaxial cavity is a multi-turn spiral, surrounding the sample to increase the contact area with the surrounding liquid in the cavity, improve the cooling rate, and ensure the overall temperature uniformity of the sample.

[0030] The gas control and pressurization system 42 includes a gas supply tank 32, a gas booster pump 33, a high-pressure gas storage tank 34, a gas pressure reducing valve 35, and an automatic backpressure control system 36. The gas supply tank 32 provides a continuous and stable gas source for the synthesis of natural gas hydrates in the sediments. The gas booster pump 33 compresses and pressurizes the methane gas supplied in the gas supply tank and then injects it into the high-pressure gas storage tank 34. The gas pressure reducing valve 35 controls the flow rate between the high-pressure gas storage tank 34 and the gas inlet pipeline of the test device to adjust the appropriate gas pressure required for the test. The gas pressure reducing valve 35 is connected to the high-pressure gas storage tank to adjust the appropriate gas pressure required for the test. The automatic backpressure control system 36 is connected to the gas outlet of the test equipment. By controlling the position of the backpressure valve in the built-in buffer container, the pressure in the gas outlet of the test equipment is adjusted, thereby achieving pressure control in the gas pipeline of the test equipment and ensuring constant pressure conditions during the hydrate formation process.

[0031] like Figure 2 , Figure 3 As shown, the acoustic emission sensor 56 uses a pressure-resistant probe, which can meet the requirements of normal operation in low temperature and high pressure test environments. Each probe is connected to the data acquisition and control system 30 outside the triaxial cavity through the connection port reserved on the triaxial base 5. In order to avoid the error of the acquired data caused by the acoustic emission sensor 56 being placed on the periphery of the device in traditional acoustic emission monitoring, the acoustic emission sensor 56 is directly contacted with the sample and fixed to the side wall of the sample through a latex sleeve. At the same time, coupling agent is applied to the contact position to enhance the capture of acoustic emission signals and reduce signal attenuation. In this embodiment, six acoustic emission sensors 56 are arranged in three groups, symmetrically distributed in pairs, and placed at angles of 0°, 60°, 120°, 180°, 240° and 300° on the cylindrical sample, respectively. The acoustic probe is placed in the cavity reserved at both ends of the upper and lower electrode pressure head 22 and a spring is installed to ensure that the acoustic probe is in close contact with the cavity and avoids the distortion of acoustic signal caused by poor contact. After installation, sealing pressure heads are installed at both ends of the probe to prevent the acoustic probe from falling off. It should be noted that this embodiment provides a detailed description of the materials and specific dimensions of certain components. Unless otherwise specified, these are merely illustrative examples. In actual implementation, the above material and parameter ranges are not used as a limitation, but rather should be based on meeting the actual experimental requirements.

[0032] In summary, this scheme utilizes the invented experimental apparatus to simulate the environment of hydrate-bearing sediments in the deep sea within the laboratory. Through the control systems for temperature, gas, and pressure, it can meet the experimental requirements under different working conditions. The prepared sediment samples are monitored under the shear failure action of the triaxial apparatus using multiple methods such as acoustic emission, sound waves, and resistivity. The placement of all sensor probes avoids interference from the external environment, truly reflecting the complete process of deformation and failure of the samples under specific environmental conditions. It cleverly avoids the limitations of experimental parameter acquisition conditions and enables comprehensive and continuous monitoring of the entire experimental process. Ultimately, it achieves the goal of simulating the deformation and failure process of hydrate-bearing sediments under special environments in the laboratory in a way that more closely resembles the real situation.

[0033] Example 2: Based on the acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments disclosed in Example 1, this example discloses an experimental method for acoustic emission monitoring of deformation and damage of hydrate-bearing sediments, specifically including: Step 1. Sediment Sample Preparation: Following the sample preparation method for natural gas hydrate tests, calculate the target sample volume based on the selected mold size, soil specific gravity, porosity, and initial water saturation. Determine the required soil mass and water mass for sample preparation. After thoroughly mixing the water and soil, fill the soil sample in layers until all the water-soil mixture is filled into the mold and the sample reaches the target height. Remove the sample from the mold, record the actual height of the sample with calipers, and calculate the actual porosity of the sample. Wrap the sample surface with plastic wrap and store it in a sealed bag.

[0034] Step 2. Sample Fixing and Sensor Probe Setup: Place the prepared sample between the two electrode indenters 22, wrap the sample with a latex film of the same size, and connect the excess portion to the upper and lower indenter sealing rings 47. Wrap the entire sample with heat shrink tubing and heat it with a hot air gun until the sample is tightly connected to the upper and lower electrode indenters. Install insulating flange rings 23 in the grooves of the upper and lower electrode indenters. The upper flange ring is used to fix the axial extensometer 24, and the lower flange ring is used to install the displacement sensor. The upper and lower flange rings are adjusted by two positioning pins to ensure that the magnetic ring on the axial extensometer can be accurately inserted into the coil of the displacement sensor on the lower flange ring. The circumferential extensometer 25 is cleverly installed on the sample by a special high-precision roller chain. Each LVDT is mechanically adjusted to accurately set the output value to zero, thus providing an accurate starting state for measurement. Place the acoustic probe 26 at both ends of the upper and lower electrode indenters. A spring is installed inside the cavity. After installation, sealing pressure heads are installed at both ends of the probe to prevent the acoustic probe from falling off. The acoustic emission sensor 56 is directly contacted with the sample and fixed to the side wall of the sample through a latex sleeve. Coupling agent is applied to the contact position to enhance the capture of acoustic emission signals. The sensor is arranged with 6 probes, divided into 3 groups, symmetrically distributed in pairs, and placed at 0°, 60°, 120°, 180°, 240° and 300° positions on the cylindrical sample. The inlet and outlet gas pipes 46 are installed. The resistivity test fixture is clamped at both ends of the gas channel 27 connection on the upper and lower electrode pressure heads of the sample, and a zirconia ceramic insulating pad 28 is placed. After all sensors and probes are installed, they are connected one by one to the reserved sensor connection port 9 on the triaxial base 5, and connected to the data acquisition and control system 30 through the interface reserved on the lower flange of the triaxial base 5. The low temperature cooling coil 39 is installed and the sealing is checked.

[0035] Step 3. Simulation of hydrate formation process in sediment: Turn on the power, start the pressure chamber lifting system 40, and raise the triaxial base 5 until the cylinder 4 is close to the triaxial base 5, making the cylinder and the triaxial base 5 in close contact. After the lifting is completed, tighten the triaxial fastening nut 45; open the confining pressure liquid filling and discharging system 43, turn the valve to the filling position, turn on the filling pump, and start filling the confining pressure liquid through the confining pressure liquid inlet and outlet 53 of the cavity; after the confining pressure liquid is full, tighten the filling and discharging valve, turn on the temperature control system 31, and lower the cavity. Internal temperature; turn on the gas control and pressurization system 42, open the valve of the gas supply tank 32, turn on the gas booster pump 33, adjust the gas pressure reducing valve to control the inlet pressure, and set the pressure of the automatic back pressure control system 36; turn on the data acquisition and control system 30 to continuously measure the gas pressure, triaxial cavity temperature, resistivity value, and acoustic velocity data, and pay attention to the changes in acoustic velocity and resistivity over time. When the resistivity and acoustic velocity tend to stabilize and no longer change over time, it can be determined that the hydrate formation in the sediment is complete.

[0036] Step 4. Conduct shear failure test on hydrate-bearing sediments: After hydrates are formed in the sediments, start the axial loading system and preload the sediments to make the axial pressure head contact the electrode head at the top of the specimen and eliminate the loading gap; set the loading rate, axial load and other parameters, and conduct a triaxial shear test.

[0037] Step 5. Real-time Data Acquisition and Experiment Processing: During the experiment, mechanical data, acoustic emission data, acoustic wave data, and resistivity data are acquired in real time. The changes in the mechanical parameters of the sample are monitored to determine whether the experiment should be terminated. After the experiment, the temperature control system 31 is turned off; the triaxial pressure is removed; the gas supply tank valve and the gas pressure reducing valve 35 are closed to stop the gas supply. The automatic backpressure control system 36 is adjusted to discharge excess gas from the pipeline. The confining pressure loading system 44 is turned off, the applied confining pressure is removed, and the confining pressure liquid filling and discharging valve is switched to the drain valve. After the automatic draining of the pressure chamber is completed, the pressure chamber confining pressure valve is closed. The fastening nut 45 is removed, the cylinder 4 is removed, the sample is disassembled, and the hydrate-containing sediment sample is taken out for observation and photography. The experimental apparatus is cleaned.

[0038] It is evident that this invention can efficiently simulate the deformation and failure process of hydrate-bearing sediments under different working conditions, which is closer to the failure and deformation process of natural gas hydrate reservoirs in real marine sedimentary environments. This achieves the goal of making indoor simulation experiments more consistent with actual field conditions, and has important reference and learning value for the development of natural gas hydrate reservoir property evaluation.

[0039] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments, characterized in that, The system includes a triaxial testing system (41), a hydrate generation system, and a data acquisition and control system (30). The triaxial testing system (41) is equipped with a triaxial base (5), and a sample fixing module is installed on the triaxial base (5). The hydrate generation system is connected to the triaxial testing system (41), and the data acquisition and control system (30) is electrically connected to the triaxial testing system (41) and the sample fixing module, respectively. The sample fixing module includes two electrode heads (22) arranged opposite each other, with the sample clamped between the two electrode heads (22). The electrode heads (22) have gas channels (27) inside and a cavity on the end face of the electrode heads (22) facing the sample. The triaxial base (5) integrates multiple sensor connection ports (9), and the sensor connection ports (9) are respectively connected to an acoustic emission sensor (56), an acoustic probe (26) and a resistivity test fixture (55). The acoustic emission sensor (56) is set on the side wall of the sample, the acoustic probe (26) is embedded in the cavity of the electrode indenter (22), and the resistivity test fixture (55) is electrically connected to the electrode indenter (22). The data acquisition and control system (30) includes a triaxial device parameter acquisition system, an acoustic wave parameter acquisition system, a resistivity acquisition system, and an acoustic emission signal parameter acquisition and control system. The data acquisition and control system (30) acquires acoustic emission signals, acoustic wave signals, and resistivity signals through the sensor connection port (9).

2. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 1, characterized in that, The triaxial test system (41) includes an axial loading system, a triaxial pressure chamber, a confining pressure loading system (44) and a confining pressure liquid filling and discharging system (43). The axial loading system is located at the top of the triaxial pressure chamber, and the confining pressure loading system (44) and the confining pressure liquid filling and discharging system (43) are respectively connected to the triaxial pressure chamber.

3. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 2, characterized in that, The axial loading system includes a balance chamber (1), an axial pressure chamber (2), and a return chamber (3). During the axial pressure loading test, the balance chamber (1) adjusts the internal pressure state to achieve a balance between the axial loading system and the confining pressure loading system (44).

4. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 2, characterized in that, The triaxial pressure chamber includes a cylinder (4) mounted on a triaxial base (5). The triaxial base (5) is connected to a pressure boosting system. The cylinder (4) is provided with a spiral multi-turn cooling coil (39), which is connected to a hydrate generation system.

5. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 1, characterized in that, The acoustic emission sensor (56) is fixed to the side wall of the sample by a latex sleeve. The contact surface between the acoustic emission sensor (56) and the sample is coated with a coupling agent. Multiple acoustic emission sensors (56) are symmetrically distributed along the circumference of the sample.

6. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 1, characterized in that, A ceramic insulating pad (28) is provided between the electrode pressure head (22) and the axial pressure column and the triaxial base (5). The side wall of the electrode pressure head (22) is provided with a groove, and an insulating flange positioning ring (23) is installed in the groove. The insulating flange positioning ring (23) is used to fix the axial extensometer (24).

7. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 1, characterized in that, The hydrate generation system includes a temperature control system (31) and a gas control and pressurization system (42); the temperature control system (31) is connected to the cooling coil (39) in the triaxial test system (41), and the gas control and pressurization system (42) is connected to the gas channel (27) in the electrode indenter (22).

8. The acoustic emission monitoring device for deformation and damage of hydrate-bearing sediments according to claim 7, characterized in that, The gas control and pressurization system (42) includes a gas supply tank (32), a gas booster pump (33), a high-pressure gas storage tank (34), a gas pressure reducing valve (35), and an automatic back pressure control system (36) connected in sequence. The automatic back pressure control system (36) is connected to the gas outlet of the sample.

9. An acoustic emission monitoring method for deformation and damage of hydrate-bearing sediments, characterized in that, An acoustic emission monitoring device for monitoring the deformation and damage of hydrate-bearing sediments according to any one of claims 1-8 comprises the following steps: S1: Preparation of sediment samples; S2: Install the sample between two electrode indenters (22), set up acoustic emission sensors (56), acoustic probes (26) and resistivity test fixtures (55), and connect each sensor to the data acquisition and control system (30) through the sensor connection port (9) of the triaxial base (5). S3: Start the hydrate generation system, construct the temperature and pressure environment for hydrate generation in the triaxial test system (41), and monitor the resistivity and acoustic velocity in real time through the data acquisition and control system (30) until the hydrate generation is completed; S4: Start the axial loading system of the triaxial test system (41) to conduct a triaxial shear failure test on the hydrate-containing sediment sample; S5: During the experiment, mechanical data, acoustic emission data, acoustic wave data and resistivity data were collected synchronously through the data acquisition and control system (30).

10. The acoustic emission monitoring method for deformation and damage of hydrate-bearing sediments according to claim 9, characterized in that, In step S3, confining pressure liquid is first injected into the triaxial pressure chamber through the confining pressure liquid filling and discharging system (43), then the temperature control system (31) is started to reduce the temperature inside the chamber, and then the gas control and pressurization system (42) is started to introduce methane gas and control the inlet pressure and back pressure.

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