Natural gas hydrate sediment sample preparation system for microscopic observation

Abstract

The invention discloses a natural gas hydrate sediment sample preparation system for microscopic observation. The high-pressure reaction kettle, the gas injection module, the saturated solution injection module, the temperature control module, the sample saturation mold and the like can be carried on a centrifugal machine to work in a supergravity environment, and sample preparation devices with different functions can be carried in the high-pressure reaction kettle as required and comprise a multifunctional sample preparation seat, the sample saturation mold and an axial sample preparation mold. The sample preparation device is used for preparing a hydrate sediment sample, the gas injection module is used for providing gaseous methane for the saturated solution injection module and the reaction kettle, the saturated solution injection module can provide a methane saturated solution for the reaction kettle, and the temperature control module is used for controlling the temperature of the saturated solution and the reaction kettle. According to the device and the method, hydrate samples can be prepared under the conditions of different temperature and pressure environments, different effective stress and stress gradients and the like, and a way is provided for researching the generation process and mechanical properties of hydrates with different occurrence depths in practical engineering.

Description

Technical Field

[0001] The invention belongs to the fields of geotechnical engineering and energy engineering, and in particular relates to a natural gas hydrate sediment sample preparation system for microscopic observation. Background Art

[0002] Natural gas hydrate is a cage-shaped crystalline compound formed by water molecules and methane molecules under high pressure and low temperature conditions. Its reserves are twice the carbon content of the world's proven conventional fossil energy. It has the characteristics of large reserves, wide distribution, and low combustion pollution. It is considered to be one of the most promising substitutes for conventional fossil energy. As global energy demand continues to increase, the development of natural gas hydrates has received widespread attention from countries around the world, and scholars from various countries have carried out research on the characteristics of hydrate mining. The microscopic characteristics of hydrate sediments are the most important basis for clarifying their basic physical properties, which directly determines the choice of hydrate mining methods and disaster prevention and control technologies. With the advancement of microscopic testing technology, advanced technologies such as nuclear magnetic resonance, scanning electron microscopy, and Raman spectroscopy have been initially applied to the experiment and test analysis of natural gas hydrates, hoping to reveal the crystal structure, occurrence mode and dynamic evolution law of hydrates in sediment pores from a microscopic perspective, which is the core component of basic theoretical research on natural gas hydrates.

[0003] Natural gas hydrates are usually found in terrestrial permafrost and seabed sediments at a certain depth. It is technically difficult to obtain undisturbed samples, so hydrate sediment samples are usually prepared in the laboratory for related research. Indoor preparation uses a high-pressure reactor to synthesize hydrate samples under low temperature and high pressure conditions, then the samples are taken out of the reactor and frozen with liquid nitrogen for preservation, and finally the samples are transferred to a microscopic observation device for testing to obtain the microscopic characteristics of the samples. The formation environment such as temperature, water pressure, and sediment stress state has a significant impact on the hydrate occurrence mode, the combination morphology with the sediment, the stress state, the sediment pore characteristics, etc., which in turn affects the macroscopic mechanical properties of the hydrate.

[0004] Existing preparation technologies mostly use the method of injecting methane gas into sediments with a certain water content. During the hydrate formation process, there is a large amount of free gas in the sediment pores, that is, the sample is in a gas-saturated state, which is significantly different from the actual hydrate formation environment in the sea area; at the same time, the seabed sediments at a certain depth are subject to a significant self-weight stress field, and it is difficult for existing technologies to apply effective stress to the sample during the hydrate formation process. Therefore, it is urgent to develop a natural gas hydrate sediment sample preparation system for microscopic observation, which can simulate the hydrate formation process under different temperature and pressure formation environments, different effective stresses and stress gradients, and at the same time ensure that the sample removal operation is simple and fast so that it can be quickly transferred to the microscopic observation equipment. Summary of the invention

[0005] In view of the problems existing in the background technology, the purpose of the present invention is to provide a natural gas hydrate sediment sample preparation system for microscopic observation. The system can prepare natural gas hydrate samples in gas-saturated and water-saturated environments and under a certain effective stress through a replaceable sample preparation device inside the kettle body. At the same time, it can be carried in the basket of an ultragravity centrifuge to prepare samples with a certain self-weight stress gradient. The system also has the characteristics that the high-pressure reactor can be quickly disassembled and the samples are easy to take out and store.

[0006] The present invention is implemented by the following technical solutions:

[0007] The system includes a reactor, a gas injection module, a saturated solution injection module, a temperature control module, a sample preparation device and a data acquisition module; the sample preparation device is placed in the reactor and is used to prepare hydrate sediment samples; the gas injection module is connected to the reactor via the saturated solution injection module; the gas injection module is used to provide gaseous methane to the saturated solution injection module and the reactor; the saturated solution injection module is used to provide methane saturated solution to the reactor; the gas injection module and the reactor are both electrically connected to the data acquisition module; the mechanical properties of the hydrate sediment samples are collected through the data acquisition module; the saturated solution injection module and the reactor are both placed in the temperature control module; the temperature control module is used to control the temperature of the saturated solution and the reactor.

[0008] The reactor comprises a cylinder, a reactor cover, a clamp, a welding handle, a pressure sensor and a hanging ring; the reactor cover is installed on the cylinder, and the cylinder and the reactor cover are connected by two semicircular clamps, a sealing ring is arranged at the contact position between the cylinder and the reactor cover, the reactor cover is provided with a liquid injection hole, a liquid outlet hole, a transmission through hole and two cover opening auxiliary holes, and a pressure sensor and a hanging ring are arranged on the surface of the reactor cover, and welding handles are installed on the two clamps; the interior of the reactor is used to place sample preparation devices with different functions, and the sample preparation devices are filled with sediments, and the sample preparation devices adopt one of a multifunctional sample preparation seat, a sample saturation mold and an axis pressing sample mold.

[0009] The multifunctional sample preparation seat is used to prepare gas-saturated samples. The multifunctional sample preparation seat is mainly composed of a placement ring, a support plate and a sampler. The placement ring is installed in the cylinder of the reactor. The inside of the placement ring is connected with three layers of support plates. The support plate is mainly composed of an upper and a lower sample preparation plate stacked in sequence. The upper sample preparation plate is provided with a plurality of rectangular through holes. The sampler is placed in the rectangular through holes of the upper sample preparation plate. The sampler is used to prepare gas-saturated samples.

[0010] The axial compression sampling mold comprises a portal frame, a tightening nut, a load sensor, a loading pressure rod, a sampler, and a sampler limit block; the portal frame is installed in the cylinder of the reactor, the sampler is placed at the bottom end of the portal frame, the sampler limit block is fixedly connected to the lower side of the portal frame for limiting the sampler, the tightening nut is fixed to the upper side of the portal frame, the loading pressure rod extends into the portal frame and is connected to the tightening nut to achieve up and down movement, a load sensor is provided at the lower end of the loading pressure rod, and the loading pressure rod is pressed on the axial compression sample in the sampler through the load sensor, and an axial pressure N is applied to the axial compression sample. Under the condition of ng supergravity, the effective stress σ′ at any position inside the axial compression sample n According to the following formula:

[0011]

[0012] Where r is the diameter of the axial compression specimen; N is the axial pressure applied to the axial compression specimen; f is the friction resistance of the loading rod; ρ s is the dry density of the axial compression specimen; ng is the gravitational acceleration under supergravity; H is the height of the axial compression specimen, π is the circumference of the circumference; P iz represents the pore water pressure of the axial compression specimen; h a is the distance from this arbitrary position to the bottom of the axial compression specimen.

[0013] The sample saturation mold comprises an upper end cover, a lower end cover, a cylinder, a liquid inlet pipe and a liquid outlet pipe. The upper end cover and the lower end cover are fixedly mounted on the top section and the bottom end of the cylinder respectively. The lower end cover is placed on the inner bottom surface of the cylinder of the reactor. Both the upper end cover and the lower end cover are provided with through holes. The through holes on the upper end cover are connected with the liquid outlet holes in the reactor through the liquid outlet pipe. The through holes on the lower end cover are connected with the liquid injection holes in the reactor through the liquid inlet pipe. The sample saturation mold is used to prepare water-saturated samples; therefore, the sample saturation mold generates normal gravity water-saturated samples and super gravity water-saturated samples in normal gravity environment and super gravity environment respectively.

[0014] Under normal gravity environment, the pore water pressure P at any position inside the normal gravity water-saturated sample is i According to the following formula:

[0015] P i =P-ρ w gh

[0016] In the formula, ρ w is the density of the methane saturated solution; g is the acceleration of gravity; h is the distance from the arbitrary position to the bottom of the water saturated sample; P is the injection pressure of the methane saturated solution.

[0017] Under the hypergravity environment, the pore water pressure P at any position inside the hypergravity water-saturated sample is iAccording to the following formula:

[0018] P i =P-ρ w ngh

[0019] In the formula, ρ w is the density of the methane saturated solution; ng is the supergravity acceleration, h′ is the distance from the arbitrary position to the bottom of the water-saturated sample, and P is the injection pressure of the methane saturated solution.

[0020] The gas injection module includes a gas cylinder, a gas booster pump, an air compressor, a gas storage container, a pressure regulating valve, a gas flow controller, a one-way valve, a first gas injection valve and a second gas injection valve; gaseous methane is stored in the gas cylinder, the outlet of the gas cylinder is connected to the inlet of the gas storage container through the gas booster pump, the outlet of the gas storage container is connected to one end of the one-way valve through a pipeline, a pressure regulating valve and a gas flow controller are sequentially arranged on the pipeline from the gas storage container to the one-way valve, the other end of the one-way valve is respectively connected to one end of the first gas injection valve and one end of the second gas injection valve, the other end of the first gas injection valve and the other end of the second gas injection valve are respectively connected to the reactor and the dissolving tank in the saturated solution injection module, and the gas booster pump and the air compressor are connected.

[0021] The saturated solution injection module is mainly composed of a water storage tank, a double-cylinder pump, a liquid injection container, a recovery container, a dissolution tank and a control valve; the water storage tank is used to provide a deionized water source, the water storage tank, the liquid injection container and the recovery container are all connected to the double-cylinder pump, the double-cylinder pump alternately pumps deionized water into and out of the liquid injection container and the recovery container to provide power for solution circulation, the bottom ports of the liquid injection container and the recovery container are respectively connected to the ports on both sides of the control valve, the upper and lower ports of the control valve are respectively connected to the bottom of the dissolution tank and the reactor through pipelines, an agitator is arranged inside the dissolution tank, the agitator is used to stir the injected methane gas and deionized water to form a uniform methane saturated solution, the two ends of the dissolution tank are respectively connected to the gas injection module and the reactor through pipelines, and an inlet valve is arranged on the pipeline from the dissolution tank to the reactor.

[0022] The data acquisition module comprises a data acquisition device and an industrial computer. The industrial computer is connected to the data acquisition device, and the data acquisition device is connected to a pressure sensor in the reactor and a gas flow controller in the gas injection module through a data line.

[0023] The present invention can realize the preparation of hydrate samples under different temperature and pressure environments, different effective stresses and stress gradients, and at the same time ensure that the sample removal operation is simple and fast so that it can be quickly transferred to the microscopic observation equipment. In the same preparation system, hydrate samples at different depths and thicknesses of the reservoir are obtained through different stress gradients, and a model consistent with the hydrate reservoir with a certain self-weight stress gradient in the real stratum on site is prepared, which provides a way to study the hydrate formation process and mechanical properties at different storage depths in actual engineering.

[0024] The beneficial effects of the present invention are:

[0025] 1. This device is equipped with three replaceable high-pressure reactor built-in sample preparation devices. The same set of devices can be used to prepare hydrate samples under different environments. It can simulate the natural gas hydrate formation process under natural conditions such as temperature, pressure, effective stress at a specific depth, and self-weight stress. At the same time, it saves the time of disassembly and assembly of the device, reduces manufacturing costs, and improves experimental efficiency.

[0026] 2. This device solves the problem of loading effective stress on the sample during the formation of natural gas hydrates by setting an axial compression sample mold inside the high-pressure reactor. Natural gas hydrate sediment samples for microscopic observation can be prepared under a certain effective stress, providing a way to study the hydrate formation process and mechanical properties at different storage depths in actual engineering.

[0027] 3. This device can prepare hydrate sediment samples under supergravity conditions and water-saturated environments. In the same model, hydrate samples at different depths and thicknesses in the reservoir can be obtained through different stress gradients, and a model consistent with the hydrate reservoir with a certain self-weight stress gradient in the real formation on site can be prepared.

[0028] 4. Through the gas injection module and the saturated solution injection module, this device can prepare natural gas hydrate samples for microscopic observation in gas-saturated and water-saturated environments respectively, meeting the needs of preparing samples of different occurrence modes of hydrates in sediment pores for microscopic research.

[0029] 5. The lid of the high-pressure reactor of this device adopts a quick-release structure, so that liquid nitrogen can be used to achieve rapid freezing after sample preparation is completed, avoiding the decomposition of hydrates affecting the observation effect and meeting the needs of microscopic observation for rapid sampling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the device of the present invention;

[0031] Figure 2 It is a top view of the top cover of the high-pressure reactor and its connected auxiliary structures;

[0032] Figure 3It is a cross-sectional view of the high-pressure reactor and the multifunctional sample preparation seat inside when preparing gas-saturated samples;

[0033] Figure 4 It is a cross-sectional view of the high-pressure reactor and the internal axial compression specimen mold when preparing a certain effective stress specimen;

[0034] Figure 5 It is a cross-sectional view of the high-pressure reactor and the internal sample saturation mold when preparing water-saturated samples;

[0035] Figure 6 It is the methane hydrate phase equilibrium pressure curve.

[0036] In the figure: 11, gas cylinder; 12, gas booster pump; 13, air compressor; 14, gas storage container; 15, pressure regulating valve; 16, gas flow controller; 17, one-way valve; 18, first gas injection valve; 19, second gas injection valve; 21, water storage tank; 22, double-cylinder pump; 23, liquid injection container; 24, recovery container; 25, dissolving tank; 26, control valve; 27, inlet valve; 28, outlet valve; 31, cylinder; 32, kettle cover; 33, sealing ring; 34, clamp; 35, buckle; 36, welding handle; 37, pressure sensor; 38, lifting ring; 321, liquid injection hole; 322, Liquid outlet hole; 323, transmission hole; 324, opening auxiliary hole; 41, constant temperature box; 42, constant temperature water bath; 51, data acquisition device; 52, industrial computer; 53, data line; 61, placement ring; 62, support plate; 63, sampler; 64, gas saturated sample; 71, portal frame; 72, tightening nut; 73, load sensor; 74, loading pressure rod; 75, sampler; 76, sampler limit block; 77, axial pressure sample; 81, upper end cover; 82, lower end cover; 83, cylinder; 84, cylinder sealing ring; 85, water saturated sample; 86, liquid inlet pipe; 87, liquid outlet pipe. DETAILED DESCRIPTION

[0037] The content of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] like Figure 1As shown, the system includes a high-pressure reactor, a gas injection module, a saturated solution injection module, a temperature control module, a sample preparation device and a data acquisition module; the sample preparation device is placed in the reactor and is used to prepare a hydrate sediment sample, the gas injection module is connected to the reactor via the saturated solution injection module, the gas injection module is used to provide gaseous methane to the saturated solution injection module and the reactor, the saturated solution injection module is connected to the reactor, the saturated solution injection module is used to provide a methane saturated solution to the reactor, the gas injection module and the reactor are both electrically connected to the data acquisition module, the mechanical properties of the hydrate sediment sample are collected through the data acquisition module, the saturated solution injection module and the reactor are both placed in the temperature control module, and the temperature control module is used to control the temperature of the saturated solution and the reactor.

[0039] Among them, the high-pressure reactor, gas injection module, saturated solution injection module, temperature control module and sample saturation mold can work under normal gravity on the ground, and can also be carried on a centrifuge to work in a supergravity environment. The inner cavity of the high-pressure reactor can withstand a certain pressure; the hydrate sediment samples include gas-saturated samples, axial pressure samples, and water-saturated samples. The sample preparation device includes a multifunctional sample preparation seat, a sample saturation mold, and an axial pressure sample mold. The multifunctional sample preparation seat is used to prepare gas-saturated samples of different sizes. The sample saturation mold is used to prepare conventional water-saturated samples under normal gravity and saturated samples with a certain stress gradient under supergravity. The axial pressure sample mold is used to prepare axial pressure samples under a certain effective stress. The data acquisition module is used to detect data such as temperature, pressure, and gas flow during the sample preparation process.

[0040] like Figure 2 As shown, the reactor comprises a cylinder 31, a reactor cover 32, a clamp 34, a welding handle 36, a pressure sensor 37 and a hanging ring 38; the reactor cover 32 is installed on the cylinder 31, and the cylinder 31 and the reactor cover 32 are connected by two semicircular clamps 34, and the two clamps 34 are fixedly connected by a buckle 35, thereby fixing the cylinder 31 and the reactor cover 32, and a sealing ring 33 is arranged at the contact position between the cylinder 31 and the reactor cover 32, and the reactor cover 32 of the reactor is provided with a liquid injection hole 321, a liquid outlet hole 322, a transmission through hole 323 and two cover opening auxiliary holes 324, and the surface of the reactor cover 32 is provided with a pressure sensor 37 and a hanging ring 38, and the two clamps 34 are both installed with welding handles 36; the interior of the reactor is used to place sample preparation devices with different functions, and the sample preparation devices are filled with sediments, and the sample preparation devices adopt one of a multifunctional sample preparation seat, a sample saturation mold and an axis pressing sample mold.

[0041] When preparing a gas-saturated sample, the liquid outlet hole 322 is used as a gas injection hole. The two cover-opening auxiliary holes 324 are provided with screws, by which the kettle cover 32 can be lifted up, so as to facilitate the rapid opening of the kettle for sampling after the sample preparation is completed. The interior of the high-pressure reactor can be equipped with sample preparation devices with different functions as needed, such as a multifunctional sample preparation seat, a sample saturation mold and an axial pressing sample mold. The inner cavity of the high-pressure reactor can withstand a certain pressure, and hydrate sample preparation devices with different functions can be placed inside. The sample preparation device is filled with sediments, and methane gas or gas-saturated solution is injected into the sediments under low temperature and high pressure conditions to generate natural gas hydrate samples.

[0042] like Figure 3 As shown, the multifunctional sample preparation seat is used to prepare gas-saturated samples. The multifunctional sample preparation seat is mainly composed of a placement ring 61, a support plate 62 and a sampler 63. The placement ring 61 is installed in the cylinder 31 of the reactor. The interior of the placement ring 61 is connected with upper, middle and lower three-layer support plates 62 of different sizes, so that multiple samples can be prepared at the same time. The support plate 62 is mainly composed of upper and lower sample preparation plates stacked in sequence. The upper sample preparation plate is provided with a plurality of rectangular through holes. The sampler 63 is placed in the rectangular through holes of the upper sample preparation plate. The rectangular through holes limit the sampler 63. The sampler 63 is used to prepare gas-saturated samples 64. The sampler 63 is filled with sediments with a certain water content to generate hydrate samples. The sampler 63 can prepare corresponding samples according to the requirements of experimental equipment such as scanning electron microscopes and Raman spectroscopy.

[0043] When preparing a hydrate sample under a gas-saturated environment, close the second gas injection valve 19, open the first gas injection valve 18, and connect the methane gas cylinder 11 to the inlet of the gas storage container 14 via the gas booster pump 12. The outlet of the gas storage container 14 is connected to the high-pressure reactor via the pressure regulating valve and the gas flow controller and the first gas injection valve 19. The methane gas is directly injected into the high-pressure reactor by the gas injection module. When the pressure sensor 27 reaches the set pressure, close the first gas injection valve 19, and maintain the temperature in the high-pressure reactor at the set value through the temperature control module. When the pressure of the pressure sensor 37 no longer changes, it is considered that the hydrate in the sample has been completely generated. Place the high-pressure reactor in a liquid nitrogen tank, wait until the pressure of the pressure sensor 27 drops to zero, open the buckle 35, remove the clamp 34, and lift the reactor cover 32 with the screws in the auxiliary hole 324 to quickly take out the hydrate sample (gas-saturated sample 64).

[0044] The axial pressing mold is used to prepare methane hydrate samples under a certain effective stress. Figure 4As shown, the axial compression sample mold includes a portal frame 71, a tightening nut 72, a load sensor 73, a loading pressure rod 74, a sampler 75, and a sampler limit block 76; the portal frame 71 is installed in the cylinder 31 of the reactor, the sampler 75 is placed at the bottom end of the portal frame 71, the sampler limit block 76 is fixedly connected to the lower side of the portal frame 71 by screws, and is used to limit the sampler 75, the tightening nut 72 is fixed to the upper side of the portal frame 71, the loading pressure rod 74 extends into the portal frame 71 and is connected to the tightening nut 72 to achieve up and down movement, the lower end of the loading pressure rod 74 is provided with a load sensor 73, and the loading pressure rod 74 is pressed on the axial compression sample 77 in the sampler 75 through the load sensor 73, and the axial pressure N is applied to the axial compression sample 77, and the load sensor 73 uploads the axial pressure N data to the data acquisition module through the data line 53. Under the condition of ng hypergravity, the effective stress σ′ at any position inside the axial compression sample 77 n According to the following formula:

[0045]

[0046] Where r is the diameter of the axial compression specimen 77; N is the axial pressure applied to the axial compression specimen 77; f is the friction resistance of the loading rod 74, which is obtained by calibration before the experiment; ρ s is the dry density of the axial compression sample 77; ng is the gravitational acceleration under the supergravity environment; H is the height of the axial compression sample 77, π is the circumference; P iz represents the pore water pressure of axial compression specimen 77; h a is the distance from the arbitrary position to the bottom of the axial compression specimen 77.

[0047] The sample saturation mold can prepare samples under normal gravity, and can also be loaded into a centrifuge to prepare samples under super gravity, respectively preparing conventional water-saturated samples under normal gravity or preparing saturated samples with a certain stress gradient under super gravity. Figure 5 As shown, the sample saturation mold includes an upper end cover 81, a lower end cover 82, a cylinder 83, a liquid inlet pipe 86 and a liquid outlet pipe 87. The cylinder 83 is a circular tube composed of two semi-circular ring columns. A cylinder sealing ring 84 is provided at the connection between the two semi-circular ring columns. The upper end cover 81 and the lower end cover 82 are respectively fixedly mounted on the top section and the bottom end of the cylinder 83. The lower end cover 82 is placed on the inner bottom surface of the cylinder 31 of the reactor. Through holes are opened on the upper end cover 81 and the lower end cover 82. The through hole on the upper end cover 81 is connected to the liquid outlet hole 322 in the reactor through the liquid outlet pipe 87, and the through hole on the lower end cover 82 is connected to the injection hole 321 in the reactor through the liquid inlet pipe 86. The sample saturation mold is used to prepare a water-saturated sample 85; so the sample saturation mold generates a normal gravity water-saturated sample and a super gravity water-saturated sample in a normal gravity environment and a super gravity environment respectively. The normal gravity water-saturated sample and the super gravity water-saturated sample are collectively referred to as a water-saturated sample 85.

[0048] At a certain pore water pressure P i When preparing samples under water-saturated environment, the temperature T in the autoclave needs to be controlled below the corresponding phase equilibrium temperature. When preparing hydrate samples under water-saturated environment, close the first gas injection valve 18, open the second gas injection valve 19, the inlet valve 27, and the outlet valve 28, and the methane gas cylinder 11 is connected to the dissolution tank 24 through the pressure regulating valve 15, the gas flow controller 16, the one-way valve 17, and the second gas injection valve 19, and the methane gas is injected into the dissolution tank by the gas injection module. The outlet of the piston container 23 is connected to both sides of the control valve 26, and the upper and lower ends of the control valve 26 are respectively connected to the dissolution tank 26 and the autoclave, and the double-cylinder pump 22 pumps deionized water alternately from the injection container 23 and the recovery container 24. When pumping in, deionized water is injected from the injection container 23 into the dissolution tank 25, and a motor and a stirrer are provided inside the dissolution tank 25 to stir the injected methane gas and deionized water to form a uniform methane saturated solution, which is injected into the injection mold 50 through the injection hole 321. When the solution is pumped out, it enters the recovery container 24 from the liquid outlet 322 through the dissolution tank 24 and the liquid injection mold. The temperature in the high-pressure reactor is maintained at the set value by the temperature control module. After a period of time, the double-cylinder pump 22, the inlet valve 27, and the outlet valve 28 are closed, the pipeline is removed, and the high-pressure reactor is placed in a liquid nitrogen tank. When the pressure of the pressure sensor 27 is basically reduced to zero, the upper end cover 81 and the lower end cover 82 are quickly removed, and the hydrate sediment sample (water-saturated sample 85) is taken out from the cylinder 83.

[0049] The inner cavity of the sample saturation mold can withstand a certain pressure and is used to generate water-saturated samples.

[0050] Under constant gravity environment, the pore water pressure P at any position inside the constant gravity water-saturated sample is i According to the following formula:

[0051] P i =P-ρ w gh

[0052] In the formula, ρ w is the density of the methane saturated solution; g is the acceleration of gravity; h is the distance from the arbitrary position to the bottom of the water saturated sample; P is the injection pressure of the methane saturated solution.

[0053] In a hypergravity environment, a certain stress gradient is generated inside the sample through high-speed rotation of the centrifuge. The pore water pressure P at any position inside the hypergravity water-saturated sample is i According to the following formula:

[0054] P i =P-ρ w ngh

[0055] In the formula, ρ wis the density of the methane saturated solution; ng is the supergravity acceleration, h′ is the distance from the arbitrary position to the bottom of the water-saturated sample, and P is the injection pressure of the methane saturated solution.

[0056] like Figure 6 As shown, the natural gas hydrate phase equilibrium curve equation can be expressed as:

[0057]

[0058] At a certain pore water pressure P i To prepare samples under these conditions, it is necessary to control the temperature T in the autoclave to be below the corresponding phase equilibrium temperature.

[0059] The gas injection module includes a gas cylinder 11, a gas booster pump 12, an air compressor 13, a gas storage container 14, a pressure regulating valve 15, a gas flow controller 16, a one-way valve 17, a first gas injection valve 18 and a second gas injection valve 19; gaseous methane is stored in the gas cylinder 11, the outlet of the gas cylinder 11 is connected to the inlet of the gas storage container 14 through the gas booster pump 12, the outlet of the gas storage container 14 is connected to one end of the one-way valve 17 through a pipeline, and the pressure regulating valve 15 and the gas flow controller 16 are sequentially arranged on the pipeline from the gas storage container 14 to the one-way valve 17, the other end of the one-way valve 17 is respectively connected to one end of the first gas injection valve 18 and one end of the second gas injection valve 19, the other end of the first gas injection valve 18 and the other end of the second gas injection valve 19 are respectively connected to the reactor and the dissolving tank 25 in the saturated solution injection module, and the gas booster pump 12 and the air compressor 13 are connected.

[0060] The gas injection module is used to provide gaseous methane to the high-pressure reactor and the saturated solution injection module, and realize constant pressure / constant flow injection of high-pressure gas through a pressure regulating valve and a gas flow controller.

[0061] The saturated solution injection module is mainly composed of a water storage tank 21, a double-cylinder pump 22, a liquid injection container 23, a recovery container 24, a dissolution tank 25 and a control valve 26; the water storage tank 21 is used to provide a deionized water source, the water storage tank 21, the liquid injection container 23 and the recovery container 24 are all connected to the double-cylinder pump 22, the double-cylinder pump 22 alternately pumps deionized water into and out of the liquid injection container 23 and the recovery container 24 to provide power for solution circulation, and the bottom ports of the liquid injection container 23 and the recovery container 24 are respectively connected to the ports on both sides of the control valve 26 The upper and lower ports of the control valve 26 are connected to the bottom of the dissolving tank 25 and the reactor through pipelines, respectively. An outlet valve 28 is provided on the pipeline from the control valve 26 to the reactor. An agitator is provided inside the dissolving tank 25. The agitator is externally connected to a motor. The agitator is used to stir the injected methane gas and deionized water to form a uniform methane saturated solution. The two ends of the upper part of the dissolving tank 25 are connected to the second gas injection valve 19 of the gas injection module and the reactor through pipelines, respectively. An inlet valve 27 is provided on the pipeline from the dissolving tank 25 to the reactor.

[0062] The temperature control module is composed of a constant temperature box 41 and a constant temperature water bath 42. The liquid injection container 23, the recovery container 24 and the dissolution tank 25 are placed in the constant temperature box 41 of the temperature control module, and the reactor is placed in the constant temperature water bath 42 of the temperature control module.

[0063] The data acquisition module includes a data acquisition device 51 and an industrial computer 52. The industrial computer 52 is connected to the data acquisition device 51. The data acquisition device 51 is connected to the pressure sensor 37 in the reactor and the gas flow controller 16 in the gas injection module through a data line 53. When preparing samples under ultra-gravity conditions on a centrifuge, the data acquisition module is connected to the control center through the centrifuge quick-connect aviation plug for remote servo control.

[0064] Personnel in the technical field can easily make various changes and modifications based on the text description, drawings and claims provided by the present invention without departing from the concept and scope of the present invention defined by the claims. Any modification, modification or equivalent change made to the above embodiments based on the technical concept and essence of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A natural gas hydrate sediment sample preparation system for microscopic observation, characterized in that: The method comprises a reactor, a gas injection module, a saturated solution injection module, a temperature control module, a sample preparation device and a data acquisition module; the sample preparation device is placed in the reactor and is used to prepare hydrate sediment samples; the gas injection module is connected to the reactor via the saturated solution injection module; the gas injection module is used to provide gaseous methane to the saturated solution injection module and the reactor; the saturated solution injection module is used to provide methane saturated solution to the reactor; the gas injection module and the reactor are both electrically connected to the data acquisition module; the mechanical properties of the hydrate sediment samples are collected through the data acquisition module; the saturated solution injection module and the reactor are both placed in the temperature control module; the temperature control module is used to control the temperature of the saturated solution and the reactor.

2. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 1, characterized in that: The reactor comprises a cylinder (31), a reactor cover (32), a clamp (34), a welding handle (36), a pressure sensor (37), and a hanging ring (38); the reactor cover (32) is mounted on the cylinder (31), and the cylinder (31) and the reactor cover (32) are connected by two semicircular clamps (34); a sealing ring (33) is arranged at the contact position between the cylinder (31) and the reactor cover (32); the reactor cover (32) is provided with a liquid injection hole (321), a liquid outlet hole (322), a transmission through hole (323), and two cover opening auxiliary holes (324); a pressure sensor (37) and a hanging ring (38) are arranged on the surface of the reactor cover (32); and welding handles (36) are installed on the two clamps (34); the interior of the reactor is used to place sample preparation devices with different functions, and sediment is filled in the sample preparation devices, and the sample preparation devices adopt one of a multifunctional sample preparation seat, a sample saturation mold, and an axial pressing sample mold.

3. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 2, characterized in that: The multifunctional sample preparation seat is used for preparing gas-saturated samples. The multifunctional sample preparation seat mainly consists of a placement ring (61), a support plate (62) and a sampler (63). The placement ring (61) is installed in the cylinder (31) of the reactor. The interior of the placement ring (61) is connected with three layers of support plates (62). The support plate (62) mainly consists of an upper and a lower sample preparation plate stacked in sequence. The upper sample preparation plate is provided with a plurality of rectangular through holes. The sampler (63) is placed in the rectangular through holes of the upper sample preparation plate. The sampler (63) is used for preparing gas-saturated samples (64).

4. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 2, characterized in that: The axial pressing sample mold comprises a door frame (71), a tightening nut (72), a load sensor (73), a loading pressure rod (74), a sampler (75), and a sampler stop block (76); the door frame (71) is installed in the cylinder (31) of the reactor, the sampler (75) is placed at the bottom end of the door frame (71), the sampler stop block (76) is fixedly connected to the lower side of the door frame (71) for limiting the sampler (75), and the tightening nut (72) is fixed to the On the upper side of the portal frame (71), a loading rod (74) extends into the portal frame (71) and is connected to a tightening nut (72) to achieve up and down movement. A load sensor (73) is provided at the lower end of the loading rod (74). The loading rod (74) is pressed on an axial pressure specimen (77) in a sampler (75) through the load sensor (73) to apply an axial pressure N to the axial pressure specimen (77). Under the condition of ng supergravity, the effective stress σ′ at any position inside the axial pressure specimen (77) is n According to the following formula: Where r is the diameter of the axial compression specimen (77); N is the axial pressure applied to the axial compression specimen (77); f is the friction resistance of the loading rod (74); ρ s is the dry density of the axial compression specimen (77); ng is the gravitational acceleration under the hypergravity environment; H is the height of the axial compression specimen (77); P iz represents the pore water pressure of the axial compression specimen (77); h a is the distance from the arbitrary position to the bottom of the axial compression specimen (77).

5. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 2, characterized in that: The sample saturation mold comprises an upper end cover (81), a lower end cover (82), a cylinder (83), a liquid inlet pipe (86) and a liquid outlet pipe (87). The upper end cover (81) and the lower end cover (82) are fixedly mounted on the top section and the bottom end of the cylinder (83) respectively. The lower end cover (82) is placed on the inner bottom surface of the cylinder (31) of the reactor. Through holes are provided on the upper end cover (81) and the lower end cover (82). The through holes on the upper end cover (81) are connected to the liquid outlet hole (322) in the reactor through the liquid outlet pipe (87), and the through holes on the lower end cover (82) are connected to the liquid injection hole (321) in the reactor through the liquid inlet pipe (86). The sample saturation mold is used to prepare a water-saturated sample (85); therefore, the sample saturation mold generates a normal gravity water-saturated sample and a super gravity water-saturated sample in a normal gravity environment and a super gravity environment respectively.

6. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 5, characterized in that: Under a constant gravity environment, the pore water pressure P1 at any position inside the constant gravity water-saturated sample is obtained by the following formula: P i =P-ρ w gh In the formula, ρ w is the density of the methane saturated solution; g is the acceleration of gravity; h is the distance from the arbitrary position to the bottom of the water saturated sample; P is the injection pressure of the methane saturated solution.

7. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 5, characterized in that: Under the hypergravity environment, the pore water pressure P at any position inside the hypergravity water-saturated sample is i According to the following formula: P1=P-ρ w ngh In the formula, ρ w is the density of the methane saturated solution; ng is the supergravity acceleration, h′ is the distance from the arbitrary position to the bottom of the water-saturated sample, and P is the injection pressure of the methane saturated solution.

8. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 1, characterized in that: The gas injection module comprises a gas cylinder (11), a gas booster pump (12), an air compressor (13), a gas storage container (14), a pressure regulating valve (15), a gas flow controller (16), a one-way valve (17), a first gas injection valve (18) and a second gas injection valve (19); gaseous methane is stored in the gas cylinder (11); the outlet of the gas cylinder (11) is connected to the inlet of the gas storage container (14) through the gas booster pump (12); the outlet of the gas storage container (14) is connected to one end of the one-way valve (17) through a pipeline. A pressure regulating valve (15) and a gas flow controller (16) are sequentially arranged on the pipeline from the gas storage container (14) to the one-way valve (17); the other end of the one-way valve (17) is respectively connected to one end of the first gas injection valve (18) and one end of the second gas injection valve (19); the other end of the first gas injection valve (18) and the other end of the second gas injection valve (19) are respectively connected to the reactor and the dissolving tank (25) in the saturated solution injection module; and the gas booster pump (12) and the air compressor (13) are connected.

9. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 1, characterized in that: The saturated solution injection module is mainly composed of a water storage tank (21), a double-cylinder pump (22), a liquid injection container (23), a recovery container (24), a dissolution tank (25) and a control valve (26); the water storage tank (21) is used to provide a deionized water source, the water storage tank (21), the liquid injection container (23) and the recovery container (24) are all connected to the double-cylinder pump (22), the double-cylinder pump (22) alternately pumps deionized water into and out of the liquid injection container (23) and the recovery container (24) to provide power for solution circulation, and the liquid injection container (2 3) and the bottom ports of the recovery container (24) are respectively connected to the ports on both sides of the control valve (26), and the upper and lower ports of the control valve (26) are respectively connected to the bottom end of the dissolving tank (25) and the reactor through pipelines. A stirrer is arranged inside the dissolving tank (25), and the stirrer is used to stir the injected methane gas and deionized water to form a uniform methane saturated solution. The two ends of the dissolving tank (25) are respectively connected to the gas injection module and the reactor through pipelines, and an inlet valve (27) is arranged on the pipeline from the dissolving tank (25) to the reactor.

10. A natural gas hydrate sediment sample preparation system for microscopic observation according to claim 1, characterized in that: The data acquisition module comprises a data acquisition device (51) and an industrial computer (52), the industrial computer (52) is connected to the data acquisition device (51), and the data acquisition device (51) is connected to a pressure sensor (37) in the reaction kettle and a gas flow controller (16) in the gas injection module via a data line (53).

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