Device and method for in-situ testing of dynamic permeability and mechanical parameters of hydrate rock core

Abstract

The invention discloses an in-situ test device and method for dynamic permeability and mechanical parameters of a hydrate rock core, the device comprises a triaxial chamber (83) for placing a rock core (82), the triaxial chamber (83) is respectively connected with an axial pressure system, a confining pressure system, a gas injection system, a water injection system and a liquid injection system, the axial pressure system and the confining pressure system are used for providing pressure for the triaxial chamber (83); the gas injection system is used for injecting methane gas into the triaxial chamber (83); the water injection system is used for injecting water into the triaxial chamber (83); the liquid injection system is used for injecting drilling fluid into the triaxial chamber (83); and the lifting system is used for controlling the three-axis chamber (83) to move up and down. The device is high in measurement precision, reliable in performance, simple to operate and high in practicability, can meet the requirements of in-situ accurate measurement of the dynamic permeability, mechanical parameters and change rules of the hydrate core sample, and can provide important data support for efficient development of hydrates.

Description

Technical Field

[0001] The present invention relates to the technical field of basic physical property testing of hydrates, and in particular to an in-situ testing device and method for dynamic permeability and mechanical parameters of hydrate cores. Background Art

[0002] Natural gas hydrates, commonly known as combustible ice, possess high gas storage density and high calorific value. Their vast reserves and promising development prospects make them an important new clean energy source for the 21st century. However, due to their significantly lower abundance than tight gas and shale gas, low production, difficulties in continuous extraction, and the difficulty in achieving large-scale production, hydrates have hindered long-term, efficient, and economic development. Currently, research remains at a critical stage, necessitating extensive research into basic physical properties and mechanical parameters, as well as their changing patterns, to guide on-site construction.

[0003] Therefore, it is necessary to accurately measure the dynamic permeability, mechanical parameters, and variation patterns of hydrate reservoirs, thereby providing an important theoretical basis for the efficient development of hydrates. Existing scholars have only used triaxial mechanical experimental equipment to test the mechanical properties of rocks under normal conditions. They have not involved relevant tests on the dynamic permeability, mechanical parameters, and variation patterns of hydrate core samples with different saturations generated in situ to simulate actual reservoir conditions, nor have they involved tests on the dynamic permeability, mechanical parameters, and variation patterns of hydrate core samples after being mined with different pressure reduction amplitudes and durations, and with different types of drilling fluids and different invasion durations. During the hydrate mining process, the pore permeability of the reservoir is in a dynamic state of change. The basic physical properties and rock mechanical parameters and variation patterns of hydrates with different saturations vary to varying degrees. If there is a lack of relevant theoretical guidance in this regard, it will lead to inaccurate production capacity predictions during hydrate mining. If the dynamic permeability, mechanical parameters, and their changing patterns of hydrate deposits with different saturations, mined with different depressurization amplitudes and durations, mined with different types of drilling fluids, and with different intrusion times, cannot be accurately understood, the risk of geological disasters will increase during the mining process, which can easily lead to well wall instability, drill stuck, drill buried, and other accidents, threatening personnel safety, delaying construction progress, increasing production costs, and causing resource waste. Therefore, there is an urgent need to develop an apparatus and method that integrates triaxial mechanical testing, in-situ hydrate synthesis, simulated drilling fluid intrusion into hydrates, and measurement of the dynamic permeability, mechanical parameters, and their changing patterns of cores. Systematic testing has determined the dynamic permeability, mechanical parameters, and their changing patterns of hydrate deposits with different saturations, mined with different depressurization amplitudes and durations, mined with different types of drilling fluids, and with different intrusion times. By combining the results of mechanical research with engineering feasibility, this approach can guide the precise design of mining plans, achieve proactive prevention and control of construction risks, and provide a substantial theoretical basis for on-site construction. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ testing device and method for the dynamic permeability and mechanical parameters of hydrate cores. Through this experimental device and experimental method, it is possible to accurately measure the dynamic permeability and mechanical parameters and change patterns of in-situ generated hydrate core samples with different saturations after being mined with different pressure reduction amplitudes and durations, and after different drilling fluid types and different drilling fluid invasion durations. It also reveals the hydrate generation pattern and real-time spatial distribution, providing important data support for hydrate mining.

[0005] The present invention is implemented by adopting the following technical solutions: an in-situ testing device for the dynamic permeability and mechanical parameters of a hydrate core, comprising a triaxial chamber for placing the core, the triaxial chamber being connected to an axial pressure system, a confining pressure system, a gas injection system, a water injection system and a liquid injection system, respectively. The axial pressure system and the confining pressure system are used to provide pressure to the triaxial chamber; the gas injection system is used to inject methane gas into the triaxial chamber; the water injection system is used to inject water into the triaxial chamber; the liquid injection system is used to inject drilling fluid into the triaxial chamber; and the device also includes a lifting system for controlling the up and down displacement of the triaxial chamber.

[0006] Furthermore, a rubber ring is provided in the triaxial chamber, and the core is placed in the rubber ring. The triaxial chamber is connected to an acoustic wave detector and an electric bridge instrument, and the acoustic wave detector and the electric bridge instrument are also connected to a data acquisition and control system; the triaxial chamber is also provided with a variety of sensors, including a temperature sensor and a pressure sensor.

[0007] Furthermore, the axial pressure system includes an oil tank, which is connected to the axial loading cylinder of the three-axis chamber through a No. 1 oil pump. The axial loading cylinder pushes the pressure rod to provide axial pressure for the three-axis chamber.

[0008] Furthermore, the confining pressure system includes a motor and a No. 2 oil pump, the motor is connected to the No. 2 oil pump, the No. 2 oil pump is connected to the booster cylinder through a pipeline, and the booster cylinder is connected to the three-axis chamber through the three-axis chamber oil inlet valve.

[0009] Furthermore, the gas injection system includes a No. 1 gas container and a No. 2 gas container, and the No. 1 gas container and the No. 2 gas container are connected to the triaxial chamber via a gas booster pump, and the gas booster pump is also connected to an air compressor.

[0010] Furthermore, the water injection system includes a water tank, which is connected to the triaxial chamber through a high-pressure injection pump.

[0011] Furthermore, the injection system includes a drilling fluid container, which is connected to the triaxial chamber via a high-pressure injection pump.

[0012] Furthermore, the lifting system includes a lifting frame, a lifting slide rail is provided on the lifting frame, a transmission screw is provided on the lifting slide rail, a lifting screw nut is provided on the transmission screw, a three-axis lifting fixed support is provided on the lifting screw nut, and the three-axis chamber is provided on the three-axis lifting fixed support. The transmission screw is driven to rotate by the lifting reduction motor on the lifting frame, thereby driving the three-axis chamber to rise or fall.

[0013] Furthermore, a movable three-axis chamber support is provided below the three-axis chamber, and the three-axis chamber support is transferred by a movable trolley.

[0014] The in-situ testing method for the dynamic permeability and mechanical parameters of hydrate cores is implemented based on the above-mentioned in-situ testing device for the dynamic permeability and mechanical parameters of hydrate cores, and includes the following steps: S1: core preparation and packing; S2: connect to data acquisition and control system; S3: Fill the booster cylinder with oil; S4: filling the triaxial chamber with water; S5: Fill the triaxial chamber with oil; S6: injecting gas into the triaxial chamber; S7: in situ hydrate generation in the core; S8: Triaxial indoor core dynamic permeability test; S9: core mechanical properties test; S10: Triaxial test of dynamic permeability and mechanical parameters and their changing patterns after hydrate decomposition under reduced pressure; S11: Testing of dynamic permeability and mechanical parameters and their changing patterns after drilling fluid invasion.

[0015] The beneficial effects of the present invention are: The present invention generates hydrate core samples in situ, which can avoid the decomposition and destruction of hydrates in the sample during movement and truly simulate actual reservoir conditions. During the in situ hydrate generation stage, the real-time measured acoustic wave and resistivity data can be compared and analyzed with the logging data of the actual field reservoir to prepare hydrate core samples that match the actual reservoir.

[0016] The present invention can simulate the dynamic permeability changes and mechanical parameter change laws of hydrate core samples under different types of drilling fluids and different drilling fluid invasion times; it can simulate the dynamic permeability changes and mechanical parameters and change laws of core samples during the mining process with different pressure reduction amplitudes and durations after the preparation of hydrate core samples.

[0017] The present invention is equipped with an acoustic wave detector, a CT scanner, and a bridge instrument, which can combine acoustic wave and resistivity data to reveal the distribution law and spatial distribution characteristics of hydrates during the in-situ generation stage and the decompression decomposition stage of hydrate reservoirs; based on the Darcy formula, the dynamic permeability and change law of hydrate-containing core samples can be calculated in real time according to the measured data.

[0018] The present invention has high measurement accuracy, reliable performance, simple operation, and strong practicality. It can meet the needs of in-situ precise measurement of the dynamic permeability and mechanical parameters of hydrate core samples and their changing patterns, and can provide important data support for the efficient development of hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0020] Figure 1 It is a schematic diagram of the structure of the present invention; Figure 2 It is a schematic diagram of the partial structure of the triaxial chamber; Figure 3 This is a diagram of the placement of core samples; In the figure, 1-vacuum pump; 2-valve No. 10; 3-pressure sensor No. 5; 4-valve No. 9; 5-gas flow meter No. 1; 6-valve No. 8; 7-temperature sensor No. 1; 8-pressure sensor No. 4; 9-gas booster pump; 10-pressure sensor No. 3; 11-stop valve; 12-pressure sensor No. 2; 13-valve No. 6; 14-valve No. 4; 15-gas container No. 1; 16-gas container No. 2; 17-valve No. 5; 18-air compressor; 19-valve No. 7; 20-safety valve; 21-valve No. 12; 22-check valve No. 13; 23-temperature sensor No. 2 Temperature sensor; 24-Sensor No. 6; 25-Liquid flow meter No. 1; 26-High-pressure injection pump; 27-Valve No. 11; 28-Water tank; 29-Drilling fluid container; 30-Pump No. 14; 31-High-pressure injection pump; 32-Liquid flow meter No. 2; 33-Data acquisition and control system; 34-Pressure sensor No. 7; 35-Valve No. 15; 36-Valve No. 16; 37-Pressure sensor No. 8; 38-CT scanner; 39-Bridge instrument; 40-Valve No. 17; 41-Pressure sensor No. 10; 42-Gas flow meter No. 2; 43-Acoustic tester No. 1 ;44-Ambient pressure sensor;45-No. 9 pressure sensor;46-No. 3 temperature sensor;47-Oil tank;48-No. 2 acoustic wave detector;49-No. 18 valve;50-No. 19 exhaust valve;51-Boost cylinder;52-Axial cylinder;53-No. 2 servo valve;54-No. 1 servo valve;55-Solenoid valve;56-No. 1 check valve;57-No. 1 filter;58-No. 20 valve;59-Level gauge;60-Overflow valve;61-Pressure gauge;62-No. 2 check valve;63-No. 2 filter;64-Cooler;65-No. 3 filter;66-No. No. 1 oil pump; 67-motor; 68-oil tank; 69-No. 1 oil pump; 70-No. 2 valve; 71-No. 1 pressure sensor; 72-No. 1 valve; 73-lifting and reducing motor; 74-lifting device; 75-lifting frame; 76-drive screw; 77-lifting screw nut; 78-slider; 79-high and low temperature control box; 80-moving trolley; 81-rubber sleeve; 82-core sample; 83-triaxial chamber; 84-axial loading cylinder; 85-pressure rod; 86-lifting support; 87-slide rail; 88-limit switch; 89-triaxial chamber support; 90-pressure relief valve. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0023] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0024] See also Figures 1 to 3 , an in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores. This device is used to accurately measure the dynamic permeability changes and mechanical parameters and change laws of hydrate core samples with different saturations generated in situ and the conditions of different pressure reduction amplitudes and durations of exploitation, different drilling fluid types, and different drilling fluid invasion durations of hydrate cores.

[0025] The apparatus includes a triaxial chamber 83 for holding a core sample 82, an axial pressure system for providing pressure to the triaxial chamber 83, a confining pressure system, a gas injection system for injecting methane gas into the triaxial chamber 83, a water injection system for injecting water into the triaxial chamber 83, a liquid injection system for injecting drilling fluid into the triaxial chamber 83, a lifting system for controlling the vertical displacement of the triaxial chamber 83, a data acquisition and control system 33, and a temperature control system. The triaxial chamber 83 has a titanium alloy housing with a CT scanner 38 mounted on its exterior. A rubber ring 81 is positioned within the triaxial chamber 83, and the core sample 82 is placed within the rubber ring 81. A first acoustic wave detector 43, a second acoustic wave detector 48, and a bridge meter 39 are connected externally above and below the triaxial chamber 83. These first and second acoustic wave detectors 43, 48, and the bridge meter 39 are all connected to a terminal connected to the data acquisition and control system 33. The triaxial chamber 83 is equipped with a No. 3 temperature sensor 46 and a No. 9 pressure sensor 45. A No. 10 pressure sensor 41 and a No. 2 gas flowmeter 42 are located at the top of the chamber. A No. 17 valve 40 is located at the upper left end of the chamber 83, facilitating both exhaust and air intake and oil removal from the chamber. The No. 8 pressure sensor 37 below the chamber 83 compares its readings with those of the No. 10 pressure sensor 41 and the No. 2 gas flowmeter 42 above the chamber 83. Using Darcy's equation, the dynamic permeability of the core sample 82 under different conditions within the chamber 83 can be calculated.

[0026] The axial pressure system that provides pressure to the three-axis chamber 83 is powered by the No. 1 oil pump 69 connected to the oil tank 68 and is loaded by oil pressure. A No. 2 valve 70 and a No. 1 pressure sensor 71 are provided behind the No. 1 oil pump 69, and then a No. 1 valve 72 is provided for control. An axial loading cylinder 84 is provided on the upper part of the three-axis chamber 83, which pushes the pressure rod 85 to provide axial pressure for the three-axis chamber 83.

[0027] The confining pressure system is powered by a motor 67 connected to a No. 2 oil pump 66. Oil flows from the oil tank 47 through a filter 65, filtered by a No. 3 filter, and then enters the No. 2 oil pump 66. After the No. 2 oil pump 66, a No. 2 filter 63 and a No. 2 check valve 62 are installed. The pipeline then connects to the boost cylinder 51, equipped with a No. 19 exhaust valve 50, followed by a No. 1 filter 57 and a confining pressure sensor 44. The oil then flows through the No. 18 valve 49 into the triaxial chamber 83, and is discharged through the No. 17 valve 40 at the upper left end of the triaxial chamber 83. It then flows through a transparent pipeline into the oil tank 47, which is also equipped with a level gauge 59 to monitor the oil level. The confining pressure system's servo valve assembly, including the solenoid valve 55, the No. 1 servo valve 54, and the No. 2 servo valve 53, is the core component of the power control. It also includes an axial pressurization system, in which the oil enters the axial cylinder 52 after passing through the cooler 64 and the No. 2 service valve 53, converting the hydraulic energy into mechanical energy, and then enters the booster cylinder 51 through the No. 1 one-way valve 56. A pipeline is provided between the cooler 64 and the No. 2 service valve 53, to which an overflow valve 60 and a pressure gauge 61 are connected to detect and maintain the safety of the pipeline.

[0028] The gas injection system is supplied by gas container No. 1 15 and gas container No. 2 16. Each is equipped with valve No. 4 14 and valve No. 5 17 to control the gas volume. Valve No. 6 13 serves as the master control for both cylinders. Pressure sensor No. 2 12 monitors the gas volume in cylinders No. 15 and No. 2 17 in real time. A shutoff valve 10 is connected. An air compressor 18 and a gas booster pump 9 are used to pressurize the gas. Pressure sensor No. 3 10 is installed before pressurization, and pressure sensor No. 4 8 is installed after pressurization to achieve the desired pressure. Pressure relief valve No. 8 6 is installed after the gas booster pump 9 to ensure there is no pressure inside the gas booster pump 9 when not in operation. A temperature sensor No. 1 7 is installed before gas is injected into the triaxial chamber 83 for temperature monitoring. A gas flowmeter No. 1 5 is installed to monitor the specific flow rate entering the triaxial chamber 83. A safety valve 20 and a manual shutoff valve No. 12 21 are installed in the gas injection pipeline. The gas injection system is equipped with a vacuum system, which consists of a vacuum pump 1 connected to valve No. 10 2, followed by a pressure sensor No. 5 3 and then a valve No. 9 4.

[0029] The water injection system is provided with water from a water tank 28, which is then controlled by valve No. 11 27 and powered by a high-pressure injection pump 26. The water flows through liquid flow meter No. 1 25 , pressure sensor No. 6 24 , and temperature sensor No. 2 23 , and is controlled by check valve No. 13 22 . The water is injected into the triaxial chamber 83 through a pipeline to ensure that there is no backflow during the experiment.

[0030] In the injection system, the drilling fluid is controlled by valve No. 14 30, powered by the high-pressure injection pump 31, and injected into the triaxial chamber 83 through valve No. 15 33. The pipeline is equipped with a liquid flow meter No. 2 32 and a pressure sensor No. 7 34 in sequence. During the drilling fluid invasion process, the specific flow rate and pressure can be obtained in real time, which is used to explore the dynamic permeability and mechanical parameters of the core sample 82 and their changing laws when different types of drilling fluids and different drilling fluid invasion amounts and invasion times are used.

[0031] The lifting system for controlling the up and down displacement of the three-axis chamber 83 includes a lifting frame 75. The lifting frame 75 is a profile welded structure. A lifting reduction motor 73 is installed on the upper part. A transmission screw 76 is installed in the middle of the lifting frame 75. Lifting rails 87 are installed on both sides of the lifting frame 75. The three-axis lifting fixed support 86 is installed on the lifting rails 87. The three-axis lifting fixed support 86 is equipped with the three-axis chamber 83. The lifting screw nut 77 is installed in the middle of the lifting frame 75. When the lifting reduction motor 73 rotates and drives the transmission screw 76 rotates, the transmission screw 76 rotates to drive the lifting support 86, and the three-axis chamber 83 rises or falls; limit switches 88 are installed on the upper and lower sides of the lifting frame 75, which can limit the different rising and falling positions of the three-axis chamber 83 by controlling the position of the slider 78; the three-axis chamber 83 is lowered and placed on the mobile trolley 80 of the lower bracket, and the three-axis chamber support 89 can be moved out and pushed forward, and is used to install the core sample 82 on the triaxial chamber base, push it under the triaxial chamber 83, and carry out the loading test after it is installed with the triaxial chamber body.

[0032] The data acquisition and control system 33 primarily collects real-time data from the various pressure and temperature sensors used in this device and method, while also monitoring data from the gas and liquid flowmeters. Using data from different locations, Darcy's equation is used to perform calculations to determine the dynamic permeability of core sample 82 under different conditions (e.g., varying in-situ hydrate formation saturations, varying pressure reduction amplitudes and durations, varying drilling fluid invasion durations, and varying drilling fluid types). The data acquisition and control system 33 also precisely controls the axial force and confining pressure of the core sample under different conditions (e.g., varying in-situ hydrate formation saturations, varying pressure reduction amplitudes and durations, varying drilling fluid invasion durations, and varying drilling fluid types). It also measures longitudinal and lateral deformation to determine the mechanical parameters and their variations in these conditions. The experimental device utilizes stable, easy-to-use automated control software. The front-end equipment features remote upgrade and troubleshooting capabilities, simplifying maintenance and reducing system operation and management costs. It also automatically monitors the operating status of any instrument in the system and displays and stores detailed parameters, helping managers to promptly and accurately diagnose and resolve issues. The core digital high-definition encoding array, storage devices, important servers and background analysis and processing software in the device support automatic restoration of normal connections after power outages, network disconnections or network storms.

[0033] The temperature control system includes a high and low temperature insulation box 79, which is placed below the triaxial chamber 83. Water and methane gas that meet the conditions are injected into the core sample 82 in the triaxial chamber 83. Then, the mobile cart 80 is pushed out to lower the triaxial chamber 83 into the high and low temperature insulation box 79, and then the insulation box cover is pushed in. The high and low temperature control system is used to heat or cool it to meet the experimental requirements.

[0034] A method for accurately measuring the dynamic permeability changes and mechanical parameters and change patterns of hydrate cores generated in situ with different saturations and produced under different pressure reduction amplitudes and durations, and under different drilling fluid types and different drilling fluid invasion durations, comprises the following steps: S1: Core preparation and filling process Based on the experimental requirements and the reservoir characteristics of a particular region, a core sample is prepared according to the actual reservoir composition, particle size distribution, and shale content. This sample is then added to a beaker and mixed evenly to form a fine shale sand for later use. The sample is then placed in a triaxial chamber. The pressure in the data acquisition and control system is set to a preset value, subjecting the core sample 82 in the preparation kettle to axial pressure, compacting it into a standard cylinder (typically 25-50 mm in diameter and 2-3 times the diameter in height, e.g., Φ50 mm x 100 mm). This compression is repeated three times to stabilize the porosity of the experimental sample. The prepared core sample 82 is then placed in a triaxial holding device and encased in a rubber sleeve 81. Both ends are sealed with sealing rings to prevent infiltration of the confining pressure fluid. The triaxial chamber cover is then closed, and the sealing sleeve is secured to the triaxial chamber 83 with a single screw. This completes the assembly, ensuring no gaps.

[0035] S2: Connecting to data acquisition and control systems Open the data acquisition and control system 33, connect all peripheral pressure sensors, flow meters, and temperature sensors to the data acquisition and control system 33 terminal through a computer program, connect the bridge instrument 39 and the acoustic wave detector, and detect and control the various data required for the method (longitudinal variables, transverse variables, longitudinal stress, and confining pressure loading).

[0036] S3: Booster cylinder oil filling process Open valve No. 19 50 and valve No. 20 58 on the pipeline above the boost cylinder 51, select the confining pressure, click "Unload" to retract the boost cylinder piston to the bottom (observe the value displayed by the boost cylinder displacement sensor, when it displays 0, the piston is retracted to the bottom), press the "Fill Oil" button on the control cabinet, observe that there are no bubbles in the transparent hose at the oil tank 47, and when the oil continuously flows into the oil tank 47, the boost cylinder 51 is filled with oil. Press the "Fill Oil" button again to complete the filling of the boost cylinder 51.

[0037] S4: Water filling process in triaxial chamber Open valves 11 and 13 on the water injection system pipeline, close all valves on the gas and liquid injection system pipelines, and inject water from a water tank 28 into the pipelines using a high-pressure injection pump 26. After the water enters the pipeline, open the main control valve 16, which enters the triaxial chamber 83, and inject water into the triaxial chamber 83. The pressure, temperature, and specific flow rate of the water flowing through the pipeline are monitored in real time via the main control valve 16, the pressure sensor 24, the temperature sensor 23, and the liquid flow meter 1, 25. A pressure sensor 8 is installed behind the main control valve 16, the triaxial chamber, to detect the specific pressure of the water entering the triaxial chamber 83. The specific amount of water entering is numerically controlled by the liquid flow meter 1, 25. Once the required amount of water is met, the flow is stopped and all valves are closed.

[0038] S5: Triaxial chamber oil filling process After the boost cylinder 51 is filled with oil, close the No. 20 valve 58 of the pipeline above the boost cylinder 51, keep the No. 19 valve 50 in the open state, then open the No. 17 valve 40 and No. 18 valve 49 above and below the three-axis chamber 83, press the "fill oil" button, the oil in the oil tank 47 passes through the No. 3 filter 65, and is driven by the motor 67 to drive the No. 2 oil pump 66 to provide power, through the No. 2 check valve 62 and the No. 1 service valve 55, enters the boost cylinder 51, and then passes through the No. 19 valve 50 on the pipeline again, and then passes through the No. 1 filter 57 and No. 18 valve 49 into the three-axis chamber 83. Observe that there is oil flowing out of the transparent hose connected to the No. 17 valve 40 above the three-axis chamber 83 and enters the oil tank 47. When the oil in the transparent tube does not flow out intermittently and there are no bubbles, the three-axis chamber 83 is filled with oil and the exhaust is completed. Press the fill oil button again to complete the oil filling. In order to prevent the pressure difference between the confining pressure chamber and the triaxial chamber 83 from being too large, which would cause the core sample 82 to break, the oil filling and gas injection processes in the triaxial chamber were actually performed alternately to maintain the internal and external pressure difference to reach the effective confining pressure required for the experiment (no more than 4 MPa).

[0039] S6: Triaxial chamber gas injection process Powered by vacuum pump 1, valves 9, 4, 2, and 36 are opened. Pressure sensor 45 is used to monitor the vacuum level. When the vacuum reaches -0.090 to -0.095 MPa, the operator issues a command to shut down the vacuum system, completing the evacuation process. Valve 4 and 2 are then closed. Pressure sensor 12, located in front of gas cylinders 15 and 16, detects the remaining gas in the cylinders. First, open the valves of the respective cylinders and monitor pressure sensor 12. If the gas level is insufficient, replace it immediately. If sufficient, open shutoff valve 10, valve 19, and valve 6 on the gas injection system pipeline. Methane gas now enters the pipeline, and the specific flow rate is measured by gas flowmeter 5. Air compressor 18 and gas booster pump 9 are then activated to provide pressure (the amount of methane injected can be used to control the hydrate saturation). The pressurized gas pressure and temperature are monitored in real time by pressure sensor No. 4 (8) and temperature sensor No. 1 (7) after the air compressor 18. Pressure sensor No. 8 (37) before the triaxial chamber 83 measures the gas pressure upon entering the chamber. After the gas enters the chamber 83, pressure sensor No. 9 (45) is located within the chamber. Once the injected gas has raised the pressure within the chamber to meet the requirements for in-situ hydrate formation, all valves in the gas injection system pipeline are closed.

[0040] S7: In-situ hydrate generation stage in the core After completing the water injection process in S5 triaxial chamber 83 and the gas injection process in S6 triaxial chamber 83, the mobile carriage 80 is pushed, and the triaxial chamber is lowered into the high-temperature and low-temperature control box 79 via the lifting system. The high-temperature and low-temperature insulation box lid is then closed, and the temperature inside the box is set using the high-temperature and low-temperature control system to the temperature required for in-situ hydrate formation. The temperature inside the high-temperature and low-temperature control box is monitored and adjusted in real time using the data acquisition and control system 33. Using the acoustic wave detectors 43 / 48 and bridge instrument 39 installed on the triaxial mechanical experimental apparatus, data such as P-waves, S-waves, and resistivity during the in-situ hydrate formation process are measured in real time. These acoustic wave and resistivity data are then compared and analyzed with actual field logging data such as P-waves, S-waves, and resistivity. If the P-wave, S-wave, and resistivity logging data agree well, it indicates that the core sample 82 prepared in the chamber is highly compatible with the actual reservoir (meeting the sample requirements for the experiment). The acoustic wave detectors 43 / 48 and the CT scanner 38 are set up to detect the hydrate formation and spatial distribution every 2 to 4 hours, and the bridge instrument 39 is used for real-time monitoring to reveal the hydrate formation pattern.

[0041] S8: Triaxial indoor core dynamic permeability test process After controlling the amount of injected methane gas, and after hydrates with different saturations are generated in situ, the S6 process is repeated. The dynamic permeability K (a real-time changing value) of hydrates with different saturations is calculated using the Darcy formula based on the specific values ​​of the No. 1 gas flow meter 5 on the gas injection pipeline and the No. 2 gas flow meter 42 above the triaxial chamber 83, as well as the values ​​of the No. 8 pressure sensor 37 and the No. 10 pressure sensor 41 before and after entering and exiting the triaxial chamber. The Darcy formula is as follows: ; K : permeability, unit m² or D (Darcy); : Volume flow rate, unit: m³ / s or cm³ / s; : cross-sectional area, in m² or cm²; : pressure difference, unit: Pa or atm; : Fluid viscosity, unit: Pa・s or mPa・s; : Seepage length, unit: m or cm.

[0042] S9: Core mechanical properties testing process After completing the dynamic permeability test of the core sample, the mechanical parameters and their changing patterns are tested. Confining pressure is applied to the triaxial chamber 83. The data acquisition and control system gradually applies confining pressure to the target value (simulating formation pressure of 10-50 MPa) at a set rate according to the settings, and the pressure is maintained stable. The axial loading system is then activated, and data such as axial force, axial displacement, circumferential displacement, and confining pressure are simultaneously recorded. The deformation trend of the core sample 82 is observed. When the axial stress reaches its peak and then begins to decline, or when the deformation increases significantly, the core is considered to have failed, and loading is stopped. The raw data is exported, and a stress-strain curve is plotted. The core is removed, and the failure mode (e.g., shear failure) is observed. The fracture surface features are photographed and recorded. The triaxial chamber 83 is then disassembled and the components cleaned.

[0043] S10: Triaxial test process of dynamic permeability and mechanical parameters and their changing patterns after hydrate decomposition under reduced pressure Repeat the experimental process from S1 to S7, and then depressurize and extract the hydrates generated in the triaxial chamber 83. Open the pressure relief valve 90 above the triaxial chamber 83, and control the opening time of the pressure relief valve 90. The pressure reduction amplitude is detected by the No. 9 pressure sensor 45, and the specific gas volume extracted is monitored by the No. 2 gas flowmeter 42. An external CT scanner 38 monitors the spatial distribution of the hydrates in the triaxial chamber 83 after depressurization. This allows the decomposition pattern of the hydrates during depressurization to be determined. Then, repeat S8 to test the dynamic permeability of the hydrate core sample 82 after depressurization. Repeat the process of testing the core mechanical parameters and their variation patterns in S9 to determine the mechanical parameters and variation patterns of the hydrate core sample 82 after extraction with different pressure reduction amplitudes and durations.

[0044] S11: Testing process of dynamic permeability and mechanical parameters and their changing rules after drilling fluid invasion Repeat steps S1 through S7. After hydrates of varying saturations are generated, open valves 30 and 35 on the injection system pipeline. Open master control valve 36 below triaxial chamber 83. Use oil pump 31 to inject drilling fluid into triaxial chamber 83. Pressure sensor 34 is installed in the pipeline to monitor pressure, and liquid flowmeter 32 is installed in the pipeline to monitor the flow rate of the injected drilling fluid in real time. Once the required flow rate is reached, stop injecting drilling fluid and close all valves. After stopping the injection of drilling fluid into triaxial chamber 83, repeat step S8 (calculating the dynamic permeability of the core in the triaxial chamber) every one or two hours. Changes in the dynamic permeability of the core with increasing drilling fluid invasion time are measured. Once the dynamic permeability changes are determined, repeat step S9 again to test the mechanical parameters and their changing patterns of the core sample. Then, the drilling fluid type is changed, and S11 is repeated again to record and compare the dynamic permeability changes and mechanical parameters and change rules of the core sample 82 under different drilling fluid types and different drilling fluid invasion times.

[0045] The present invention generates hydrate core samples in situ, which can avoid the decomposition and destruction of hydrates in the sample during movement and truly simulate actual reservoir conditions. During the in situ hydrate generation stage, real-time measured acoustic wave and resistivity data can be compared and analyzed with actual on-site reservoir logging data to prepare hydrate core samples that match the actual reservoir.

[0046] The present invention can simulate the dynamic permeability changes, mechanical parameters and change laws of hydrate core samples under different types of drilling fluids and different drilling fluid invasion times; it can simulate the dynamic permeability changes, mechanical parameters and change laws of core samples during the mining process with different pressure reduction amplitudes and durations after the preparation of hydrate core samples.

[0047] The present invention is equipped with an acoustic wave detector, a CT scanner, and a bridge instrument, which can combine acoustic wave and resistivity data to reveal the distribution law and spatial distribution characteristics of hydrates during the in-situ generation stage and the decompression decomposition stage of hydrate reservoirs; based on the Darcy formula, the dynamic permeability and change law of hydrate-containing core samples can be calculated in real time according to the measured data.

[0048] The present invention has high measurement accuracy, reliable performance, simple operation, and strong practicality. It can meet the needs of in-situ precise measurement of the dynamic permeability and mechanical parameters of hydrate core samples and their changing patterns, and can provide important data support for the efficient development of hydrates.

[0049] It should be noted that the terms "connected" and "set" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "connected" and "set" may explicitly or implicitly include one or more of the features. Moreover, the terms "connected", "set", etc. are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. And for the aforementioned embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should know that this application is not limited to the order of the actions described, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily required by this application.

[0050] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, modifications and variations made by those skilled in the art without departing from the spirit and scope of the present invention should be within the scope of protection of the appended claims.

Claims

1. In-situ testing device for dynamic permeability and mechanical parameters of hydrate core, characterized by: The invention comprises a triaxial chamber (83) for placing a core (82), wherein the triaxial chamber (83) is connected to an axial pressure system, a confining pressure system, an air injection system, a water injection system and a liquid injection system, respectively. The axial pressure system and the confining pressure system are used to provide pressure to the triaxial chamber (83); the air injection system is used to inject methane gas into the triaxial chamber (83); the water injection system is used to inject water into the triaxial chamber (83); the liquid injection system is used to inject drilling fluid into the triaxial chamber (83); and the invention also comprises a lifting system for controlling the up and down displacement of the triaxial chamber (83).

2. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: A rubber ring (81) is provided in the triaxial chamber (83), and a rock core (82) is placed in the rubber ring (81). The triaxial chamber (83) is externally connected to an acoustic wave detector and an electric bridge instrument, and the acoustic wave detector and the electric bridge instrument are also connected to a data acquisition and control system (33). The triaxial chamber (83) is also provided with a variety of sensors, including a temperature sensor and a pressure sensor.

3. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate core according to claim 1, characterized in that: The axial pressure system includes an oil tank (68), which is connected to the axial loading cylinder (84) of the three-axis chamber (83) through a No. 1 oil pump (69), and the axial loading cylinder (84) pushes the pressure rod (85) to provide axial pressure for the three-axis chamber (83).

4. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: The confining pressure system includes a motor (67) and a No. 2 oil pump (66), wherein the motor (67) is connected to the No. 2 oil pump (66), and the No. 2 oil pump (66) is connected to the booster cylinder (51) through a pipeline, and the booster cylinder (51) is connected to the three-axis chamber (83) through the three-axis chamber oil inlet valve (49).

5. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate core according to claim 1, characterized in that: The gas injection system includes a No. 1 gas container (15) and a No. 2 gas container (16), wherein the No. 1 gas container (15) and the No. 2 gas container (16) are connected to the triaxial chamber (83) via a gas booster pump (9), and the gas booster pump (9) is also connected to an air compressor (18).

6. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: The water injection system includes a water tank (28), and the water tank (28) is connected to the triaxial chamber (83) via a high-pressure injection pump (26).

7. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: The injection system comprises a drilling fluid container (29), and the drilling fluid container (29) is connected to the triaxial chamber (83) via a high-pressure injection pump.

8. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: The lifting system includes a lifting frame (75), a lifting slide rail (87) is provided on the lifting frame (75), a transmission screw (76) is provided on the lifting slide rail (87), a lifting screw nut (77) is provided on the transmission screw (76), a three-axis lifting fixed support (86) is provided on the lifting screw nut (77), and the three-axis chamber (83) is provided on the three-axis lifting fixed support (86). The transmission screw (76) is driven to rotate by the lifting reduction motor (73) on the lifting frame (75), thereby driving the three-axis chamber (83) to rise or fall.

9. The in-situ testing device for dynamic permeability and mechanical parameters of hydrate cores according to claim 1, characterized in that: A movable three-axis chamber support (89) is provided below the three-axis chamber (83), and the three-axis chamber support (89) is transferred by a movable trolley (80).

10. A method for in-situ testing of dynamic permeability and mechanical parameters of a hydrate core, implemented based on the in-situ testing device for dynamic permeability and mechanical parameters of a hydrate core according to any one of claims 1 to 9, characterized in that: The steps include: S1: core preparation and packing; S2: Connect to data acquisition and control system; S3: Fill the boost cylinder with oil; S4: filling the triaxial chamber with water; S5: Fill the triaxial chamber with oil; S6: injecting gas into the triaxial chamber; S7: in situ hydrate generation in the core; S8: Triaxial indoor core dynamic permeability test; S9: core mechanical properties test; S10: Triaxial test of dynamic permeability and mechanical parameters and their changing patterns after hydrate decomposition under reduced pressure; S11: Testing of dynamic permeability and mechanical parameters and their changing patterns after drilling fluid invasion.

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