System and method for testing dynamic permeability of hydrate rock core produced by pressure reduction or heat shock method

Abstract

The invention discloses a dynamic permeability testing system and method for hydrate core production by a pressure reduction or heat shock method, and the system comprises a dynamic permeability testing unit (1) which is used for the preparation of a natural gas hydrate core sample and the measurement of permeability; the gas and liquid injection unit (2) is used for injecting required gas and liquid into the dynamic permeability testing system; the hydraulic oil control unit (3) is used for applying axial pressure and confining pressure to the dynamic permeability testing system; the gas-liquid separation metering unit (4) is used for metering the gas-liquid flow at the outlet; and the data acquisition monitoring and control unit (5) is used for monitoring data of each unit and controlling each unit to work. According to the invention, the natural gas hydrate-containing rock core can be subjected to pressure drop under the triaxial stress condition or the production dynamic permeability test by a heat shock method.

Description

Technical Field

[0001] This invention relates to the field of natural gas hydrate extraction technology, and in particular to a dynamic permeability testing system and method for hydrate core depressurization or thermal shock production. Background Technology

[0002] Natural gas hydrates, a new type of energy source found in permafrost regions and deep-sea environments, are widely recognized as one of the most promising alternative energy sources of the 21st century due to their vast reserves, high energy density, and clean, pollution-free characteristics. In recent years, with the continuous growth of energy demand and increasing emphasis on environmental protection, the exploration and development of natural gas hydrates has gradually become a global focus. In 2017, my country achieved a complete success in the trial exploitation of hydrates in the Shenhu area of ​​the South China Sea. This breakthrough not only proved the technical feasibility of my country's marine hydrate exploitation but also laid a solid foundation for accelerating commercial exploitation.

[0003] In the development of natural gas hydrates, permeability is a crucial parameter, directly affecting the flow rate and efficiency of water and gas produced after hydrate decomposition within the formation. The level of permeability determines whether these fluids can be successfully extracted from the formation, thus influencing the natural gas recovery rate. Specifically, permeability reflects the ease of fluid flow in porous media and is one of the key indicators for assessing reservoir productivity. During hydrate extraction, with the implementation of extraction methods such as depressurization or thermal shock, hydrates decompose, generating water and gas. These products need to migrate through the reservoir's pore structure into the wellbore, and the magnitude of permeability directly determines the migration rate. Higher permeability allows water and gas to flow more rapidly, thereby improving extraction efficiency and recovery rate; conversely, lower permeability hinders fluid migration, impacting extraction efficiency and recovery rate. Furthermore, permeability is not a constant parameter; it dynamically changes with factors such as hydrate decomposition-secondary formation, pore structure evolution, stress field disturbances, and the migration of framework particles. Therefore, accurately measuring and assessing permeability and its variation patterns is of paramount importance for optimizing mining plans, predicting mining results, and ensuring the safety and economy of the mining process.

[0004] Traditional permeability measurements are mostly based on the assumption of steady-state seepage, obtaining static permeability data through one-dimensional linear or radial flow experiments. This fails to capture the real-time impact of transient pressure and temperature changes on permeability during mining. Furthermore, existing methods generally suffer from difficulties in controlling the stability of hydrate phases and insufficient accuracy in dynamic data acquisition, leading to significant deviations between test results and actual mining dynamics. In recent years, related patents have made some progress in permeability testing methods, such as the unidirectional flow measurement method proposed in [CN105547964A], the synchronous measurement device developed in [CN105572014B], and the permeability model optimized for radial flow conditions in [CN105675441A]. However, these technologies still have the following limitations: first, they rely on steady-state seepage conditions and do not consider the transient pressure-temperature coupling effect during pressure reduction or thermal shock processes; second, the devices are complex and the environmental control accuracy is limited, making it difficult to simulate dynamic phase changes under real mining conditions; and third, they lack the ability to track the evolution of permeability under multi-field coupling effects in real time. Furthermore, although [CN110132818B] and [CN111735751B] introduced a pore network model and a dual-measurement device, they still failed to solve the problem of a real-time feedback mechanism between permeability and extraction parameters during dynamic gas production. On the one hand, simulating the high-pressure, low-temperature environment required for the experiment is quite difficult, and accurately controlling and maintaining stable temperature and pressure conditions to simulate the state of natural reservoirs is not easy. On the other hand, obtaining and preserving natural gas hydrate samples is extremely difficult, as they are prone to decomposition at room temperature and pressure, making it difficult to guarantee the stability and representativeness of the samples, thus affecting the accuracy of the measurement results.

[0005] Existing measurement methods often struggle to simultaneously monitor dynamic processes and perform comprehensive multi-parameter analysis, failing to fully reflect the permeability changes during hydrate depressurization or thermal shock decomposition. Some patented devices are complex in structure and cumbersome to operate, hindering efficient and stable dynamic testing. Other methods are inadequate in data acquisition and processing, failing to fully extract key information during testing and thus failing to meet the demands of scientific research and engineering practice for accurate, real-time permeability data. Furthermore, some devices struggle to maintain pressure stability and synchronicity when applying axial and confining pressures simultaneously, leading to discrepancies between experimental results and actual permeability data from hydrate-bearing formations. Therefore, to meet the needs of scientific research and engineering practice for accurate, real-time permeability data, there is an urgent need to develop a permeability testing method capable of adapting to natural gas hydrate depressurization or thermal shock production processes and possessing efficient dynamic testing capabilities. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a dynamic permeability testing system and method for producing hydrate core samples using depressurization or thermal shock methods.

[0007] This invention is achieved using the following technical solution: a dynamic permeability testing system for hydrate core depressurization or thermal shock methods, comprising: The dynamic permeability testing unit is used for the preparation of natural gas hydrate core samples and the measurement of permeability. The gas and liquid injection unit is used to inject the required gas and liquid into the dynamic permeability testing system. A hydraulic oil control unit is used to apply axial pressure and confining pressure to the dynamic permeability testing system; A gas-liquid separation metering unit is used to measure the gas-liquid flow rate at the outlet. The data acquisition, monitoring, and control unit is used to monitor data from various systems and control the operation of each system.

[0008] Furthermore, the dynamic permeability testing unit includes a triaxial chamber, a core base, and a movable pressure bar. The triaxial chamber includes a triaxial chamber base, a triaxial chamber lid, and a triaxial chamber body, which are used to provide an environment for the preparation of natural gas hydrate cores and the measurement of permeability. The core base is mounted on the triaxial chamber base, and an acoustic-electric receiving probe is installed on the top of the core base. The movable pressure rod passes through the middle of the triaxial chamber lid and can move up and down. A gas injection pipe protection head is installed on the upper part of the movable pressure rod, and an acoustic-electric transmitting probe is installed on the bottom of the movable pressure rod. The core base and the movable pressure rod are also equipped with clamps to stably wrap the core sample with the casing. The cavity formed between the triaxial chamber and the installed core sample is a confining pressure chamber filled with hydraulic oil.

[0009] Furthermore, the dynamic permeability testing unit also includes a lifting component and an axial pressure component, wherein, The lifting component includes a fixed bracket, a lifting frame, a lifting reduction motor, and lifting slide rails; lifting slide rails are provided on both sides of the lifting frame, the fixed bracket is installed on the lifting slide rails, and a three-axis chamber is installed on the fixed bracket; by controlling the lifting reduction motor to drive the lifting slide rails to move vertically, the lifting function of the three-axis chamber is realized. The axial pressure component includes a hydraulic motor, a hydraulic press, and a hydraulic rod; the hydraulic press is located above the triaxial chamber, and the hydraulic rod is located below the hydraulic press, with the hydraulic rod aligned with the air injection pipe protection head; the hydraulic motor controls the hydraulic press to control the hydraulic rod to move downwards to provide axial pressure to the triaxial chamber; High and low temperature control chambers are used to provide the temperature environment for the preparation of triaxial hydrate samples and the testing of permeability.

[0010] Furthermore, the gas injection and liquid injection unit includes a methane cylinder, a gas booster pump, a water storage tank, and a liquid booster pump; wherein, the methane cylinder is connected to the input end of the gas booster pump, and the output end of the gas booster pump is connected to the gas inlet and liquid outlet of the gas injection pipe protection head; the water storage tank is connected to the input end of the liquid booster pump, and the output end of the liquid booster pump is connected to the gas inlet and liquid outlet of the gas injection pipe protection head.

[0011] Furthermore, the hydraulic oil control unit includes a hydraulic oil storage tank, a pump, a booster cylinder, and a blower pump; wherein, a first liquid level sensor is installed at the hydraulic oil storage tank, the hydraulic oil storage tank is connected to the input end of the pump, and the output end of the pump is connected to the bottom inlet of the triaxial chamber; the booster cylinder is connected to the bottom inlet of the triaxial chamber, and the booster cylinder pressurizes the hydraulic oil in the triaxial chamber to the specified confining pressure of the core sample by boosting the pressure; the blower pump is connected to the top outlet of the triaxial chamber, and the top outlet of the triaxial chamber is connected to the inlet of the hydraulic oil storage tank.

[0012] Furthermore, the gas-liquid separation metering unit includes a gas-liquid cyclone separator, an electronic igniter, a torch, a measuring cylinder, and an electronic balance; wherein, the input end of the gas-liquid cyclone separator is connected to the outlet of the core base, the gas output end of the gas-liquid cyclone separator is connected to the electronic igniter, the electronic igniter is also connected to the torch, the liquid output end of the gas-liquid cyclone separator is connected to the measuring cylinder, and the measuring cylinder is placed on the electronic balance.

[0013] Furthermore, various sensors, flow meters, and valves are installed inside and / or between the dynamic permeability testing unit, the gas injection unit, the hydraulic oil control unit, and the gas-liquid separation metering unit. The sensors include pressure sensors, temperature sensors, and liquid level sensors; the flow meters include liquid flow meters and gas flow meters.

[0014] Furthermore, the data acquisition, monitoring, and control unit includes a computer, a data acquisition control cabinet, and an acoustic-electric detector; wherein, the data acquisition control cabinet is used to acquire data measured by various pressure sensors, temperature sensors, liquid flow meters, gas flow meters, and liquid level sensors, and send them to the computer; the acoustic-electric detector is used to acquire data on acoustic waves and resistivity of hydrate core samples collected by acoustic-electric transmitting probes and acoustic-electric receiving probes, and send them to the computer.

[0015] A method for testing dynamic permeability of hydrate cores produced by depressurization or thermal shock, based on the aforementioned system for testing dynamic permeability of hydrate cores produced by depressurization or thermal shock, includes the following steps: Check the airtightness of the device; Preparation of core samples; Install core samples; Measure the absolute permeability of the core sample; Generate hydrate-containing porous media; Gas phase permeability measurement of natural gas hydrate core samples; Dynamic permeability testing during depressurization gas production; Dynamic permeability test during thermal gas generation.

[0016] The beneficial effects of this invention are as follows: This invention enables dynamic permeability testing of triaxial stress conditions in natural gas hydrate core samples using depressurization or thermal shock methods.

[0017] This dynamic permeability measurement device and its corresponding testing methods can be used to conduct dynamic permeability testing experiments on triaxial stress conditions for depressurization or thermal shock production of hydrate cores containing natural gas hydrates. The results show the relationship between the cumulative gas production and permeability during the depressurization or thermal shock production process of hydrate cores under triaxial stress conditions. The dynamic permeability data is closer to the actual situation of hydrate field mining, thus providing an effective theoretical basis for the gas production law of the depressurization or thermal shock mining process of hydrates. Attached Figure Description

[0018] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of a triaxial chamber structure; In the picture, 1-Dynamic permeability testing unit, 101-Triaxial chamber base, 102-Core base, 103-Clamp, 104-Acoustic and electrical receiving probe, 105-Casing, 106-Triaxial chamber vessel body, 107-Acoustic and electrical emission probe, 108-Triaxial chamber vessel cover, 109-Modible pressure rod, 110-Gas injection pipe protection head, 111-Lifting slide rail, 112-Fixed bracket, 113-Lifting reduction motor, 114-Hydraulic motor, 115-Hydraulic press, 116-Hydraulic rod, 117-Insulating sponge, 118-High and low temperature control box movable door, 119-Pulley, 120-High and low temperature control box, 121-Lifting frame; 2-Gas and liquid injection unit, 21-Methane cylinder, 22-Gas booster pump, 23-Water storage tank, 24-Liquid booster pump; 3-Hydraulic oil control unit, 31-Hydraulic oil storage tank, 32-Oil pump, 33-Booster cylinder, 34-Oil blowing pump; 4-Gas-liquid separation metering unit, 41-Gas-liquid cyclone separator, 42-Electronic igniter, 43-Flame, 44-Grating cylinder, 45-Electronic balance; 5-Data acquisition, monitoring and control unit; 51-Computer; 52-Data acquisition control cabinet; 53-Acoustic and electrical detector; T-01~T-02 - First temperature sensor~Second temperature sensor; P-01~P-05 - First pressure sensor~Fifth pressure sensor; V-01~V-14 - First shut-off valve~Fourteenth shut-off valve; V-21 - First back pressure valve; F-01 - First gas flow meter; F-02 - First liquid flow meter; F-03 - Second gas flow meter; F-04 - Second liquid flow meter; H-01 - First liquid level sensor. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] See Figure 1 , Figure 2 A dynamic permeability testing system for natural gas hydrate core depressurization or thermal shock production includes a dynamic permeability testing unit 1, a gas injection and liquid injection unit 2, a hydraulic oil control unit 3, a gas-liquid separation and metering unit 4, and a data acquisition, monitoring and control unit 5.

[0024] The dynamic permeability testing unit 1 includes a triaxial chamber, a core base 102, a movable pressure rod 109, a lifting component, an axial pressure component, and a high and low temperature control box 120. The triaxial chamber consists of a triaxial chamber base 101, a triaxial chamber vessel body 106, and a triaxial chamber vessel cover 108, and is used to provide an environment for the preparation of natural gas hydrate cores and the measurement of permeability. The core base 102 is fixed to the triaxial chamber base 101 by threads; the movable pressure rod 109 passes through the middle of the triaxial chamber vessel cover 108 and can move up and down; a gas injection pipe protection head 110 is installed on the upper part of the movable pressure rod 109 to provide a passage for the gas injection and liquid injection lines and the acoustic and electrical detection signal lines, and to prevent the hydraulic rod 116 from damaging the cables; an acoustic and electrical receiving probe 104 is installed on the top of the core base 102, and an acoustic and electrical transmitting probe 107 is installed on the bottom of the movable pressure rod 109; the core base 102 and the movable pressure rod 109 are also equipped with clamps 103, and after the core sample is placed between the core base 102 and the movable pressure rod 109, the clamps 103 are used to stably wrap the sleeve 105 around the core sample; the cavity formed between the triaxial chamber and the installed core sample is the confining pressure chamber filled with hydraulic oil; a second temperature sensor T-02 is installed on the top of the triaxial chamber vessel body 106 to monitor the temperature inside the confining pressure chamber.

[0025] The lifting component includes a fixed bracket 112, a lifting frame 121, a lifting reduction motor 113, and a lifting slide rail 111. The lifting component adopts a frame structure welded from profiles, with the lifting reduction motor 113 integrated at its upper end; lifting slide rails 111 are provided on both sides of the lifting frame 121; the fixed bracket 112 is precisely installed on the lifting slide rails 111, and a three-axis chamber is installed on the fixed bracket 112; by controlling the lifting reduction motor 113 to drive the lifting slide rails 111 to move vertically, the lifting function of the three-axis chamber is realized.

[0026] The axial pressure component includes a hydraulic motor 114, a hydraulic press 115, and a hydraulic rod 116. The hydraulic press 115 is located above the triaxial chamber, and the hydraulic rod 116 is located below the hydraulic press 115. The hydraulic rod 116 is aligned with the air injection pipe protection head 110. Controlling the hydraulic motor 114 can drive the hydraulic press 115 to control the hydraulic rod 116 to move downward to provide axial pressure to the triaxial chamber.

[0027] The high and low temperature control chamber 120 is used to provide a temperature environment for the preparation of triaxial hydrate samples and the testing of permeability.

[0028] The gas injection and liquid injection unit 2 includes a methane cylinder 21, a gas booster pump 22, a water storage tank 23, and a liquid booster pump 24. The methane cylinder 21 is connected to the input terminal of the gas booster pump 22 via a first shut-off valve V-01. The output terminal of the gas booster pump 22 is connected to the gas and liquid inlet of the gas injection pipe protection head 110 via a second shut-off valve V-02 and a fifth shut-off valve V-05. A first temperature sensor T-01, a first pressure sensor P-01, and a fifth pressure sensor P-05 are also installed between the gas booster pump 22 and the second shut-off valve V-02. A gas flow meter F-01 is provided; the water storage tank 23 is connected to the input end of the liquid booster pump 24 through the third shut-off valve V-03, and the output end of the liquid booster pump 24 is connected to the air and liquid inlet of the gas injection pipe protection head 110 through the fourth shut-off valve V-04 and the fifth shut-off valve V-05. A first liquid flow meter F-02 is also provided between the liquid booster pump 24 and the fourth shut-off valve V-04; a second pressure sensor P-02 is also provided between the fifth shut-off valve V-05 and the air and liquid inlet of the gas injection pipe protection head 110.

[0029] The hydraulic oil control unit 3 includes a hydraulic oil storage tank 31, an oil pump 32, a booster cylinder 33, and an oil blowing pump 34. A first level sensor H-01 is installed at the hydraulic oil storage tank 31. The hydraulic oil storage tank 31 is connected to the input end of the oil pump 32 through the sixth shut-off valve V-06. The output end of the oil pump 32 is connected to the bottom oil inlet of the triaxial chamber through the seventh shut-off valve V-07 and the ninth shut-off valve V-09. The booster cylinder 33 is connected to the bottom oil inlet of the triaxial chamber through the eighth shut-off valve V-08 and the ninth shut-off valve V-09. The booster cylinder 33 pressurizes the hydraulic oil in the triaxial chamber to the specified confining pressure of the core sample. A third pressure sensor P-03 is also installed between the ninth shut-off valve V-09 and the bottom oil inlet of the triaxial chamber. The oil blowing pump 34 is connected to the top oil outlet of the triaxial chamber body 106 through the eleventh shut-off valve V-11 and the tenth shut-off valve V-10. The top oil outlet of the triaxial chamber body 106 is connected to the oil inlet of the hydraulic oil storage tank 31 through the tenth shut-off valve V-10 and the twelfth shut-off valve V-12. The gas-liquid separation metering unit 4 includes a gas-liquid cyclone separator 41, an electronic igniter 42, a torch 43, a measuring cylinder 44, and an electronic balance 45. The input end of the gas-liquid cyclone separator 41 is connected to the outlet of the core base 102 through the first back pressure valve V-21. A fourth pressure sensor P-04 is installed between the input end of the gas-liquid cyclone separator 41 and the outlet of the core base 102. The gas output end of the gas-liquid cyclone separator 41 is connected to the electronic igniter 42 through the thirteenth shut-off valve V-13. The electronic igniter 42 is also connected to the torch 43. A second gas flow meter F-03 and a fifth pressure sensor P-05 are installed between the gas output end of the gas-liquid cyclone separator 41 and the thirteenth shut-off valve V-13. The liquid output end of the gas-liquid cyclone separator 41 is connected to the measuring cylinder 44 through the fourteenth shut-off valve V-14. The measuring cylinder 44 is placed on the electronic balance 45. A second liquid flow meter F-04 is installed between the liquid output end of the gas-liquid cyclone separator 41 and the fourteenth shut-off valve V-14. The data acquisition, monitoring, and control unit 5 includes a computer 51, a data acquisition control cabinet 52, and an acoustic-electric detector 53. The computer 51 contains a data receiving module, a parameter setting module, a lifting control module, a valve control module, and a data processing module. The data acquisition control cabinet 52 collects data measured by various pressure sensors, temperature sensors, liquid flow meters, gas flow meters, and liquid level sensors, and sends this data to the computer 51. The acoustic-electric detector 53 collects acoustic wave and resistivity data from the core sample collected by the acoustic-electric transmitting probe 107 and the acoustic-electric receiving probe 104, and sends this data to the computer 51. The data receiving module receives data sent by the data acquisition control cabinet 52. The parameter setting module is used to pre-set the required liquid flow rate for hydrate preparation, the required gas flow rate and pressure for gas injection, the required ventilation flow rate and pressure for permeability testing, and the triaxial chamber confining pressure and axial pressure. The lifting control module controls the operation of the lifting reduction motor 113 according to the needs of core sample installation and experimental testing, thereby controlling the rise and fall of the triaxial chamber. The valve control module controls the opening or closing of the corresponding shut-off valve and back pressure valve according to the preset vacuum degree required for vacuuming, liquid flow rate required for liquid injection, methane volume required for gas injection, hydraulic oil injection, and gas flow rate and pressure required for permeability measurement, so as to carry out airtightness operation, vacuuming operation, liquid injection operation, gas injection operation, hydraulic oil injection operation, permeability measurement operation, and termination operation. The data processing module calculates the porosity and absolute permeability of the hydrate core sample based on the gas flow rate and liquid flow rate measured by the temperature sensor, pressure sensor, gas flow meter, liquid flow meter, measuring cylinder 44, and electronic balance 45, and calculates the saturation and dynamic permeability during the hydrate decomposition process in real time.

[0030] A method for testing the dynamic permeability of natural gas hydrate core samples produced by depressurization or thermal shock includes the following steps: (1) Check the airtightness of the device The data acquisition, monitoring and control system 5 controls the lifting and reduction motor 113 to raise the triaxial chamber, open the triaxial chamber lid 108, install any core sample, install the triaxial chamber lid 108, control the first shut-off valve V-01, the second shut-off valve V-02 and the fifth shut-off valve V-05 to open, control the other valves to close, inject a certain pressure into the triaxial chamber to check for pressure leakage. The standard for good airtightness of the entire device is that the system pressure does not change for more than 1 hour.

[0031] (2) Preparation of core samples Wash 800-3000 mesh quartz sand and rinse it with distilled water 3-5 times. After drying, fill it into the core sample mold and compact it layer by layer to form a dense and uniform core sample.

[0032] (3) Install core samples Open the triaxial chamber vessel lid 108, install the core base 102 onto the triaxial chamber base 101, fix the acoustic-electric receiving probe 104 onto the core base 102, place the prepared core sample onto the core base 102, control the hydraulic rod 116 to descend until it is about to contact the top of the core sample and then stop, install the sleeve 105, fix the clamp 103, and close the triaxial chamber vessel lid 108; the data acquisition, monitoring and control system 5 controls the lifting reduction motor 113 to lower the triaxial chamber into the high and low temperature control box 120, and close the high and low temperature control box movable door 118 through the pulley 119, and insulate the remaining part with heat-insulating sponge 117; control the opening of the tenth stop valve V-10 and the eleventh stop valve V-11, start the oil blowing pump 34 to maintain a negative pressure of 0.1MPa to evacuate the core sample for 1-3 hours, and close the tenth stop valve V-10 and the eleventh stop valve V-11.

[0033] (4) Measure the porosity of the core sample. Open the third shut-off valve V-03, the fourth shut-off valve V-04, the fifth shut-off valve V-05, the fourteenth shut-off valve V-14, and the first back pressure valve V-21 to inject distilled water from the water storage tank 23 into the core sample in the triaxial chamber. After the measuring cylinder 44 sees water, continue injecting. When the values ​​of the first liquid flow meter F-02 and the second liquid flow meter F-04 are the same, record the cumulative injection volume V1 and the cumulative output volume V2 of the distilled water at this time. Calculate the porosity ϕ of the core sample using the following formula: ; In the formula, ϕ is the porosity of the core sample, a decimal; R is the radius of the core sample, cm; and L is the length of the core sample, cm.

[0034] (5) Measure the absolute permeability of the core sample: Continue injecting distilled water into the core sample. After the water flow velocity at the output end stabilizes, close the third shut-off valve V-03, the fourth shut-off valve V-04, the fifth shut-off valve V-05, the fourteenth shut-off valve V-14, and the first back pressure valve V-21. Based on the recorded readings q of the first liquid flow meter F-02 and the second liquid flow meter F-04, the pressure reading P1 of the second pressure sensor P-02 at the injection end, and the pressure reading P2 of the fourth pressure sensor P-04 at the output end, calculate the absolute permeability k of the core sample using the following formula. a : ; In the formula, k a The absolute permeability of the core sample is expressed in μm². w ρ is the viscosity of distilled water, mPa·s.

[0035] (6) Generate hydrate-containing porous media Control the opening of the sixth shut-off valve V-06, the seventh shut-off valve V-07, the ninth shut-off valve V-09, the tenth shut-off valve V-10, and the twelfth shut-off valve V-12, and control the oil pump 32 to pump the hydraulic oil from the hydraulic oil storage tank 31 into the triaxial chamber. When the hydraulic oil in the circulation pipeline flows back to the oil tank, turn off the oil pump 32 and close the sixth shut-off valve V-06, the seventh shut-off valve V-07, the tenth shut-off valve V-10, and the twelfth shut-off valve V-12; control the first shut-off valve V-01, the second shut-off valve V-02, the fifth shut-off valve V-05, and the eighth shut-off valve V-06. 08. Control the start of pressurization cylinder 33, hydraulic motor 114, and gas booster pump 22 to simultaneously pressurize the confining pressure, axial pressure, and pore pressure in the triaxial chamber to the preset pressure Ps. Close the first shut-off valve V-01, the second shut-off valve V-02, the fifth shut-off valve V-05, and the eighth shut-off valve V-08. Close pressurization cylinder 33, hydraulic motor 114, and gas booster pump 22. Set the temperature of the high and low temperature control box 120 to the preset temperature Ts. Start the hydrate formation process and record the temperature and pressure changes of the core sample. The hydrate formation process ends when the system pressure no longer changes.

[0036] (7) Measurement of gas phase permeability of natural gas hydrate core samples Open the first shut-off valve V-01 to start the gas booster pump 22 and pressurize the methane gas to Ps; open the second shut-off valve V-02, the fifth shut-off valve V-05, the thirteenth shut-off valve V-13, the fourteenth shut-off valve V-14, and the first back pressure valve V-21; record the gas flow rate q1 of the first gas flow meter F-01 at the input end and the flow rate q2 of the second gas flow meter F-03 at the output end; when q1=q2, record the pressure reading P1 of the second pressure sensor P-02 at the injection end and the pressure reading P3 of the fourth pressure sensor P-04 at the output end; calculate the permeability at this time using the following formula. ; ; In the formula, K g q0 is the gas phase permeability of the natural gas hydrate core sample, mD; q0 is the flow rate of the fluid at steady-state seepage under atmospheric pressure, cm3 / s; P0 is the standard atmospheric pressure, MPa; T0 is the indoor temperature, K; Z0 is the compressibility factor of methane gas at temperature T0 and pressure P0; Z s The temperature is T s The pressure is P s The compressibility factor of methane gas; μ g The temperature is T s The pressure is P s The viscosity of methane gas at that time, in mPa·s.

[0037] (8) Dynamic permeability test After the natural gas hydrate core sample is prepared, the pressure can be reduced by controlling the first back pressure valve V-21 at the bottom of the triaxial chamber or the temperature can be increased by controlling the high and low temperature control box to 120°C. Dynamic permeability testing during depressurization gas production and dynamic permeability testing during thermal shock gas production can then be continued. Specifically: Dynamic permeability testing during natural gas hydrate depressurization and gas production: Control the first back pressure valve V-21 at the bottom of the triaxial chamber to decrease by 0.5 MPa to Ps1, record the gas flow rate q1 of the first gas flow meter F-01 and the flow rate q3 of the second gas flow meter F-03 at the output end, the temperature Ts1 inside the triaxial chamber, record the pressure reading P1 of the second pressure sensor P-02 at the injection end and the pressure reading P4 of the fourth pressure sensor P-04 at the output end, and calculate the dynamic permeability K during the hydrate decomposition process using the following formula. p ; ; In the formula, K p The gas phase permeability, mD; q, during the depressurization production process of natural gas hydrate core samples. 01 The flow rate of the fluid under steady-state seepage at atmospheric pressure is expressed in cm. 3 / s;Z s1 μ is the compressibility factor of methane gas at temperature Ts1 and pressure (P1+P4) / 2. g1 The temperature is T s1 The viscosity of methane gas at a pressure of (P1+P4) / 2, in mPa·s; Since the decomposition of hydrates produces gas due to pressure reduction, q1 > q3. When q1 = q3, the hydrates have completely decomposed. Close the first shut-off valve V-01, the second shut-off valve V-02, the fifth shut-off valve V-05, the thirteenth shut-off valve V-13, the fourteenth shut-off valve V-14, and the first back pressure valve V-21. Turn off the gas booster pump 22 and the high and low temperature control box 120.

[0038] The data acquisition, monitoring and control system 5 can plot the cumulative gas production Q and permeability Kp in the computer 51, thus obtaining the dynamic permeability change curve of the gas phase during the depressurization production process of the natural gas hydrate core sample.

[0039] Dynamic permeability testing during natural gas hydrate thermal shock gas production: Control the high and low temperature control box to raise the temperature by 1℃ to Ts2, record the gas flow rate q1 of the first gas flow meter F-01 and the flow rate q4 of the second gas flow meter F-03 at the output end, record the pressure reading P1 of the second pressure sensor P-02 at the injection end and the pressure reading P5 of the fourth pressure sensor P-04 at the output end, and calculate the dynamic permeability during the thermal shock decomposition of hydrate using the following formula: ; ; In the formula, K T The gas phase permeability (mD) during the thermal quenching process of natural gas hydrate core samples is given by q. 02 The flow rate of the fluid under steady-state seepage at atmospheric pressure is expressed in cm. 3 / s;Z s2 The temperature is T s2 The compressibility factor of methane gas at a pressure of (P1+P5) / 2; μ g2 The temperature is T s2 The viscosity of methane gas at a pressure of (P1+P5) / 2, in mPa·s; Due to the depressurization and thermal shock of the hydrate to produce gas, q1 > q4. When q1 = q4, the hydrate is completely decomposed. Close the first shut-off valve V-01, the second shut-off valve V-02, the fifth shut-off valve V-05, the thirteenth shut-off valve V-13, the fourteenth shut-off valve V-14, and the first back pressure valve V-21. Turn off the gas booster pump 22 and the high and low temperature control box 120.

[0040] The data acquisition, monitoring and control system 5 can plot the cumulative gas production Q against the permeability KT in the computer 51, thus obtaining the dynamic permeability change curve of the gas phase during the thermal quenching production process of the natural gas hydrate core sample.

[0041] This dynamic permeability measurement device and its corresponding testing methods can be used to conduct dynamic permeability testing experiments on triaxial stress conditions for depressurization or thermal shock production of hydrate cores containing natural gas hydrates. The results show the relationship between the cumulative gas production and permeability during the depressurization or thermal shock production process of hydrate cores under triaxial stress conditions. The dynamic permeability data is closer to the actual situation of hydrate field mining, thus providing an effective theoretical basis for the gas production law of the depressurization or thermal shock mining process of hydrates.

[0042] It should be noted that the terms "connection" and "setting" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "connection" or "setting" may explicitly or implicitly include one or more of that feature. Furthermore, the terms "connection" and "setting," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Moreover, for the foregoing embodiments, for the sake of simplicity, they are all described as a series of actions; however, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Secondly, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to this application.

[0043] 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 embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Modifications and variations made by those skilled in the art without departing from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. A dynamic permeability testing system for hydrate core depressurization or thermal shock methods, characterized in that, include: Dynamic permeability testing unit (1) is used for the preparation of natural gas hydrate core samples and the measurement of permeability; The gas and liquid injection unit (2) is used to inject the required gas and liquid into the dynamic permeability testing system; Hydraulic oil control unit (3) is used to apply axial pressure and confining pressure to the dynamic permeability testing system; Gas-liquid separation metering unit (4) is used to measure the gas-liquid flow rate at the outlet; The data acquisition, monitoring and control unit (5) is used to monitor the data of each unit and control the operation of each unit.

2. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 1, characterized in that, The dynamic permeability testing unit (1) includes a triaxial chamber, a core base (102), and a movable pressure bar (109). The triaxial chamber includes a triaxial chamber base (101), a triaxial chamber lid (108), and a triaxial chamber body (106), which are used to provide an environment for the preparation of natural gas hydrate cores and the measurement of permeability. The core base (102) is set on the triaxial chamber base (101), and an acoustic-electric receiving probe (104) is installed on the top of the core base (102); the movable pressure rod (109) passes through the middle of the triaxial chamber lid (108) and can move up and down. A gas injection pipe protection head (110) is installed on the upper part of the movable pressure rod (109), and an acoustic-electric emission probe (107) is installed on the bottom of the movable pressure rod (109); the core base (102) and the movable pressure rod (109) are also provided with clamps (103), which stably wrap the casing (105) around the core sample through the clamps (103); the cavity formed between the triaxial chamber and the installed core sample is a confining pressure chamber filled with hydraulic oil.

3. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 2, characterized in that, The dynamic permeability testing unit (1) also includes a lifting component and an axial pressure component, wherein, The lifting component includes a fixed bracket (112), a lifting frame (121), a lifting reduction motor (113), and a lifting slide rail (111); the lifting frame (121) is provided with lifting slide rails (111) on both sides, the fixed bracket (112) is installed on the lifting slide rails (111), and a three-axis chamber is installed on the fixed bracket (112); by controlling the lifting reduction motor (113) to drive the lifting slide rails (111) to move vertically, the lifting function of the three-axis chamber is realized; The axial pressure component includes a hydraulic motor (114), a hydraulic press (115), and a hydraulic rod (116); the hydraulic press (115) is located above the triaxial chamber, and the hydraulic rod (116) is located below the hydraulic press (115), with the hydraulic rod (116) aligned with the air injection pipe protection head (110); the hydraulic motor (114) controls the hydraulic press to control the hydraulic rod (116) to move downward to provide axial pressure to the triaxial chamber; The high and low temperature control chamber (120) is used to provide a temperature environment for the preparation of triaxial hydrate samples and the testing of permeability.

4. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 1, characterized in that, The gas injection and liquid injection unit (2) includes a methane cylinder (21), a gas booster pump (22), a water storage tank (23), and a liquid booster pump (24); wherein, the methane cylinder (21) is connected to the input end of the gas booster pump (22), and the output end of the gas booster pump (22) is connected to the gas inlet and liquid inlet of the gas injection pipe protection head (110); the water storage tank (23) is connected to the input end of the liquid booster pump (24), and the output end of the liquid booster pump (24) is connected to the gas inlet and liquid inlet of the gas injection pipe protection head (110).

5. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 1, characterized in that, The hydraulic oil control unit (3) includes a hydraulic oil storage tank (31), an oil pump (32), a booster cylinder (33), and a blower pump (34); wherein, the hydraulic oil storage tank (31) is connected to the input end of the oil pump (32), and the output end of the oil pump (32) is connected to the bottom oil inlet of the triaxial chamber; the booster cylinder (33) is connected to the bottom oil inlet of the triaxial chamber, and the booster cylinder (33) pressurizes the hydraulic oil in the triaxial chamber to the specified confining pressure of the core sample by boosting the pressure; the blower pump (34) is connected to the top oil outlet of the triaxial chamber, and the top oil outlet of the triaxial chamber is connected to the oil inlet of the hydraulic oil storage tank (31).

6. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 1, characterized in that, The gas-liquid separation metering unit (4) includes a gas-liquid cyclone separator (41), an electronic igniter (42), a torch (43), a measuring cylinder (44), and an electronic balance (45); wherein, the input end of the gas-liquid cyclone separator (41) is connected to the outlet of the core base, the gas output end of the gas-liquid cyclone separator (41) is connected to the electronic igniter (42), the electronic igniter (42) is also connected to the torch (43), the liquid output end of the gas-liquid cyclone separator (41) is connected to the measuring cylinder (44), and the measuring cylinder (44) is placed on the electronic balance (45).

7. The dynamic permeability testing system for hydrate core depressurization or thermal shock methods as described in any one of claims 1 to 6, characterized in that, Various sensors, flow meters, and valves are installed inside and / or between the dynamic permeability testing unit (1), the gas injection and liquid injection unit (2), the hydraulic oil control unit (3), and the gas-liquid separation metering unit (4). The sensors include pressure sensors, temperature sensors, and liquid level sensors; the flow meters include liquid flow meters and gas flow meters.

8. The dynamic permeability testing system for hydrate core depressurization or thermal shock as described in claim 7, characterized in that, The data acquisition, monitoring and control unit (5) includes a computer (51), a data acquisition control cabinet (52), and an acoustic-electric detector (53); wherein, the data acquisition control cabinet (52) is used to acquire data measured by various pressure sensors, temperature sensors, liquid flow meters, gas flow meters and liquid level sensors, and send them to the computer (51); the acoustic-electric detector (53) is used to acquire data on acoustic waves and resistivity of hydrate core samples acquired by acoustic-electric transmitting probes and acoustic-electric receiving probes, and send them to the computer (51).

9. A method for testing dynamic permeability of hydrate cores produced by depressurization or thermal shock, implemented based on the dynamic permeability testing system for hydrate cores produced by depressurization or thermal shock as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Check the airtightness of the device; Preparation of core samples; Install core samples; Measure the absolute permeability of the core sample; Generate hydrate-containing porous media; Gas phase permeability measurement of natural gas hydrate core samples; Dynamic permeability testing during depressurization gas production; Dynamic permeability test during thermal gas generation.

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